Heat Flow Characteristics of a Newly-Designed Cooling System with Multi-Fans and Thermal Bafﬂe in the Wheel Loader

applied sciences

Article Heat Flow Characteristics of a Newly-Designed Cooling System with Multi-Fans and Thermal Bafﬂe in the Wheel Loader

Yidai Liao 1, Jiwen Zhuo 2, Yinliang Zhang 1, Honger Guan 2, Heting Huang 2 and Huikun Cai 1,* 1 Department of Mechanical and Electrical Engineering of Xiamen University, No. 422 Siming South Road, Xiamen 361005, Fujian, China; [email protected] (Y.L.); [email protected] (Y.Z.) 2 Xiamen XGMA Machinery Co. Ltd., No. 668 Xiagong Machinery Industrial Park, Guankou Town, Xiamen 361023, Fujian, China; [email protected] (J.Z.); [email protected] (H.G.); [email protected] (H.H.) * Correspondence: [email protected]; Tel.: +86-156-5926-9026

Academic Editors: Xianchang Li and Luisa F. Cabeza Received: 19 December 2016; Accepted: 15 February 2017; Published: 1 March 2017

Abstract: In the traditional cooling case, there is usually one fan in charge of heat transfer and airflow for all radiators. However, this seems to be inappropriate, or even insufficient, for modern construction machinery, as its overall heat flow density is increasing but thermal distribution is becoming uneven. In order to ensure that the machine works in a better condition, this paper employs a new cooling system with multiple fans and an independent cooling region. Based on the thermal flow and performance requirements, seven fans are divided into three groups. The independent cooling region is segregated from the engine region by a thermal baffle to avoid heat flowing into the engine region and inducing an overheat phenomenon. The experiment validates the efficiency of the new cooling system and accuracy of simulation. After validation, the simulation then analyzes heat transfer and flow characteristics of the cooling system, changing with different cross-sections in different axis directions, as well as different distances of the fan central axes. Finally, thermal baffles are set among the fan groups and provided a better cooling effect. The research realizes a multi-fan scheme with an independent cooling region in a wheel loader, which is a new, but high-efficiency, cooling system and will lead to a new change of various configurations and project designs in future construction machinery.

Keywords: multi fans; independent cooling region; cooling system; construction machinery; heat transfer

1. Introduction In construction machinery, the heat-dissipating components always include an engine radiator, intercooler, hydraulic oil radiator, and torque converter radiator, and these share about 30 percent of the total engine power [1]. Take an ordinary loading machine for instance; total heat dissipating capacity is about 100 kW, which may even be up to 200 kW in some very large loaders [2,3]. The stricter fuel consumption and emission regulations put the worldwide carmakers and suppliers under pressure to develop more efﬁcient thermal management systems. Mahmound built up simulation-based vehicle thermal management system concept and methodology [4], whereas Li designed a high-precision performance test bench to study the automotive cooling system [5]. Torregrosa focused on the warm-up period performance of the cooling system [6], but Tong focused on the radiator of system key component [7]. All researches are aiming at the strong, but efﬁcient, cooling project to ensure all radiators operate in good conditions, so that a key issue for a construction machinery plant is matching a suitable and reliable cooling system in the machine design program.

Appl. Sci. 2017, 7, 231; doi:10.3390/app7030231 www.mdpi.com/journal/applsci Appl. Sci. 2017, 7, 231 2 of 13

In the traditional cooling case, there is usually one fan responsible for heat transfer and airflow for all radiators [8]. However, this seems to be inappropriate, or even insufficient, for modern construction machinery [9,10]. Due to energy savings and emission reduction, the machine tends to be lightweight and small in size, with the same power. Consequently, its overall heat flow density is increasing but its thermal distribution is becoming uneven [11]. If just one fan is still adopted, the fan should be of a large size and high rotating speed for supporting a large amount of cool air across the radiators for heat dissipation. This will lead to two new problems. One is that a large fan goes against the demand of light weight for modern machines. Another is that a high rotating-speed fan will greatly increase noise emission, while many national decrees are promulgated to restrict equipment noise for environment and operator health protection [12]. Therefore, in the requirements of increased power density, uneven thermal problems, engine compartment constraints, and working demands, the challenge now is how to ensure sufficient air flow, but maintain low noise emission for a cooling system. There are different ways, such as using electric coolant pump [13], or using integrated configuration [14], and one of the ways is adopting multiple fans. The cooling system with multiple fans has some advantages. First, it can enhance heat dissipation, since it benefits from the independent design of each radiator, such as its power, rotating speed, cross-section, size, and so on. Second, as each fan can be different in size and working parameters, it can improve thermal unevenness problem. Third, as not all radiators are arranged together anymore, they can be flexible configurations to satisfy various engine compartments. Stephens studied heat exchanger flow interactions of multiple fans and found that it, indeed, performed well [15]. Zhang used two fans in a tracked vehicle and each fan can be controlled independently. The fan speed reached a maximum 5200 rpm on a hot summer day, while the fan usually worked at a speed of 3000 rpm [16]. Fu used multiple fans with an auto temperature-controlled system in a large bus and decreased fuel consumption by 8% per hundred kilometers, both in null and full loads [17]. Sun imported a multiple fan scheme into a meter-rail motor train and found it was useful in a limited engine compartment situation [18]. Zhang found that adopting multiple fans could not achieve a good heat transfer effect in the old cooling system with all of the radiators together and, thus, it should alter its original configuration and separate the fans into different parts as well as radiators [19]. As described above, multi-fan designs have been used in many fields, and proved to be a good strategy for system cooling. However, there are few articles or reports about construction machinery with multi-fans, especially in wheel loaders. Therefore, this paper employs a new design cooling system with seven fans for a wheel loader, which is validated to be efficient by simulations and experimental tests. Meanwhile, in our previous research [20], it was found that there was energy stacking on the top of the engine and radiator due to heat air backflow, which caused a partial overheat phenomenon and increased the thermal damage to components in this area. At that time, as the components in engine compartment were kept in their positions, and they were forbidden to move, setting choke plates and adding an exhausting air outlet to optimize the airflow were suggested. The improvement decreased the system temperature by about 3 ◦C in practical experiment. However, this method was a partial correction and cannot radically eliminate heat stacking in the engine compartment. Therefore, this paper will arrange all radiators and fans into an independent cooling region segregated from the engine region by a thermal baffle in the system.

2. New-Design Engine Compartment The heat dissipating components of a wheel loader demonstrated in this paper consist of an engine radiator, intercooler, hydraulic oil radiator, and torque converter radiator, and the respective heat loadsare 75 kW, 26 kW, 26 kW, 50 kW, where total heat dissipating capacity is 177 kW. The thermal load of each radiator is of primary consideration when matching the fans and their rotating speeds. Appl. Sci. 2017, 7, 231 3 of 13

2.1. FanAppl. Design Sci. 2017 and, 7, 231 Matching 3 of 13 Appl. Sci. 2017, 7, 231 3 of 13 According2.1. Fan Design to and the Matching system thermal flow, as well as radiator configuration and performance 2.1. Fan Design and Matching requirement,According seven to fans the are system adopted thermal in thisflow, loader as well and as radiator they are configuration divided into and three performance groups. Two of themrequirement, areAccording used forseven to the thefans torque system are converteradopted thermal inoil thisflow, radiator loader as well inand upper as they radiator are area divided of configuration independent into three and coolinggroups. performance region,Two of four of themrequirement,them for are the used intercooler seven for thefans torque andare adopted engine converter radiatorin this oil radiatorloader down and in from they upper the are area torque divided of independent converter into three oil groups. cooling radiator, Tworegion andof, the last onethemfour for of are thethem used hydraulic for for the the intercooler oil torque radiator converter and on engine the oil sideradiator radiator of independent indown upper from area coolingthe of torqueindependent region, converter which cooling oil areradiator, region shown, in Figuresfourand1 andtheof them last2. The one for distributed forthe the intercooler hydraulic arrangement and oil engineradiator of radiator theon the fans sidedown benefits of fromindependent from the thetorque independentcooling converter region oil design, which radiator, ofare each radiator,andshown the such inlast Figure as one its for power,s 1 theand hydraulic 2. rotating The distribut oil speed, radiatored cross-section, arrangement on the side ofof size, theindependent andfans sobenefits on. cooling Here, from region wethe chooseindependent, which the are same showndesign inof Figureeach radiator,s 1 and 2.such The as distribut its power,ed arrangementrotating speed, of crossthe fans-section, benefits size, from and theso on.independent Here, we size and dimension, but different rotating fan speeds to form our cooling groups due to the limitation designchoose ofthe each same radiator, size and such dimension, as its power, but different rotating rotating speed, fan cross speeds-section, to form size, our and cooling so on. groups Here, duewe of power request, space restriction, and noise emission, which is shown in Table1. chooseto the limitation the same of size power and request,dimension, space but restriction, different rotatingand noise fan emission, speeds whichto form is our shown cooling in Table groups 1. due to the limitation of power request, space restriction, and noise emission, which is shown in Table 1.

Air cooling Engine region Airregion cooling Engine region region

Figure 1. 3-D model of engine compartment: (left) external view; (right) internal view. Figure 1. 3-D model of engine compartment: (left) external view; (right) internal view. Figure 1. 3-D model of engine compartment: (left) external view; (right) internal view. Torque converter Top air inlet Side fan Side outlet Hydraulic oil Torqueoil radiator converter Top gridair inlet Sidegroup fan Sidegrid outlet Hydraulicradiator oil oil radiator grid group grid radiator

Upper fan Uppergroup fan group

Front air outletFront gridair outlet grid

Lower fan Lowergroup fan group

Engine Bottom air Isolation Intercooler radiatorEngine Bottominlet grid air Isolationplate Intercooler radiator inlet grid plate Figure 2. Schematic diagram of the cooling system. FigureFigure 2. 2.Schematic Schematic diagramdiagram of of the the cooling cooling system. system. Table 1. Characteristic diameters of different radiators. Table 1. Characteristic diameters of different radiators. Table 1. Torque Converter Hydraulic Oil CharacteristicEngine Radiator diameters Intercooler of different radiators. TorqueRadiator Converter HydraulicRadiator Oil Engine Radiator Intercooler Heat dissipating capacity (kW) 75 26 TorqueRadiator Converter50 HydraulicRadiator26 Oil Engine Radiator Intercooler Heat dissipatingCooling medium capacity (kW) Engine75 coolant cooling26 air Radiator50oil HydraulicRadiator26 oil Coolingsize medium Engine coolant320 m m diameter,cooling 400 air m axis distance,oil 300 W powerHydraulic oil Heat dissipating capacity (kW) 75 26 50 26 3 CoolingVolume mediumsize (m ) Engine coolant0.0430320 mm coolingdiameter,0.0278 air 400 m axis distance,0.0296 oil 300 W power Hydraulic0.00905 oil 3 3 HeatVolumesize source (m(kW/m) ) 1745.160.0430 320 mm diameter,0.0278897.98 400 m axis distance,1688.620.0296300 W power0.009052874.52 HeatVolume sourceporosity (m3 )(kW/m 3) 0.04301745.160.7 0.0278897.980.7 1688.62 0.02960.7 2874.52 0.009050.7 HeatResistance sourceporosity (kW/m coefficient 3) KQ 1745.160.735 897.980.730 1688.620.730 2874.520.725 5 5 5 5 ResistanceporosityRe number coefficient KQ 0.71.3835 × 10 0.71.3830 × 10 1.38 0.730 × 10 1.8425 × 0.7 10 ResistanceRe coefﬁcient numberK Q 351.38 × 105 1.38 30 × 105 1.38 30 × 105 1.84 × 25 105 Re number 1.38 × 105 1.38 × 105 1.38 × 105 1.84 × 105 Appl. Sci. 2017, 7, 231 4 of 13

2.2. Flowing Channel Design Since there was heat stacking on some regions in the engine compartment due to air backflow, a thermal baffle is set to segregate the cooling area into an independent region and prevent heat flow into the other region. Thus, the engine compartment is divided into two regions: cooling system area with all radiators and fans and engine area with the other components, which, at the extreme, avoids hot air blowing into the engine region and causes an overheat phenomenon. Then the flowing channel is also rearranged. There is not only one inlet and one outlet. As described above, an additional outlet will produce extra hot air flowing away from engine compartment, so that two outlets are set here and one is on the front of engine compartment whereas the other is on the side. Meanwhile, there are also two inlets in order to ensure enough airflow from the environment and one is on the top of the engine compartment whereas the other is on the bottom. The whole configuration is shown in Figure2. More inlets and outlets are not suggested because they will induce greater air interaction and turbulent flow, which is bad to heat dissipation.

3. Simulation of the Engine Compartment In heat coupled with ﬂow simulation, it is based on the continuity equation ﬁrst.

∂ρ ∂(ρu) ∂(ρv) ∂(ρw) + + + = 0 (1) ∂t ∂x ∂y ∂z

Then comes with kinematic equations (N–S equations).

∂(ρu) ∂p + div(ρuu) = div(µgardu) − + S (2) ∂t ∂x u

∂(ρv) ∂p + div(ρvu) = div(µgardv) − + S (3) ∂t ∂y v ∂(ρw) ∂p + div(ρwu) = div(µgardw) − + S (4) ∂t ∂z w Finally, energy conservation equation is used.

∂(ρT) k ∂p + div(ρuT) = div gardT − + ST (5) ∂t Cp ∂x where: ρ is density; t is time; u, v and w are the velocities in x, y and z coordinate axis respectively; µ is dynamic viscosity; p is pressure; Su, Sv and Sw are generalized sources; Cp is heat capacity; T is temperature; k is heat transfer coefﬁcient; ST is thermal energy induced by ﬂuid inner heat and heat power due to viscidity action.

3.1. Model Building The model building and mesh generation should balance simulation reliability against computer calculation process. The more particular the model is and the more grid number is, the more reliable the simulation is but the longer calculating time needs. Hence, keep the details of radiators, cooling fans and engine cover as many as possible, and simplify the other components as much as possible. The 3-D model of the engine compartment in Figure1 is built in SolidWorks based on the real engine system. Then, we import the model into the ANSYS Workbench for simulation. Before meshing, the model is simpliﬁed by the following procedures: erasing all chamfers and circular beads except those of fans; replacing bolts and gaskets by solid blocks; redrawing engine compartment into a shell with a speciﬁc thickness and using air envelope region instead of cooling fans. Appl. Sci. 2017, 7, 231 5 of 13

After model simplification, we use the Enclosure Tool to set up a rotating air domain enveloping cooling fan and its neighborhood to replace fan entity, which benefits calculation process but also maintains computational accuracy. As the cooling system is arranged in an isolated region, the focus is put on this area. We use EnclosureAppl. Sci. 2017 Tool, 7, 231 to undertake Boolean Calculation for the entities in this area, and build the finite5 of 13 element analysis model as shown in Figure2, including four radiators, seven fans, two inlets and element analysis model as shown in Figure 2, including four radiators, seven fans, two inlets and two outlets. two outlets. Finally, we build up an air domain enclosing the engine compartment as the simulated outside Finally, we build up an air domain enclosing the engine compartment as the simulated outside working environment. The bottom surface of air domain is about 0.5 m far away from the bottom of working environment. The bottom surface of air domain is about 0.5 m far away from the bottom of engine compartment according to the real construction machinery. Taking the computational accuracy engine compartment according to the real construction machinery. Taking the computational and efficiency into consideration, the other surfaces are about 1 m far away from the corresponding accuracy and efficiency into consideration, the other surfaces are about 1 m far away from the surfaces of engine compartment referring to Paper 21. corresponding surfaces of engine compartment referring to Paper 21. 3.2. Mesh Generation 3.2. Mesh Generation For rotating air domains, tetrahedral mesh is used here as the surfaces of fan blades are irregular For rotating air domains, tetrahedral mesh is used here as the surfaces of fan blades are irregular and need special mesh density. For radiators, the structural grid is used as the structures of radiators and need special mesh density. For radiators, the structural grid is used as the structures of radiators are regular. Here we use porous medium to simulate the four radiators [21,22] because the computer are regular. Here we use porous medium to simulate the four radiators [21,22] because the computer cannot suffer such large meshes if the real structures of radiators are used. For the porous model, its cannot suffer such large meshes if the real structures of radiators are used. For the porous model, porosity and resistance coefficient are two important diameters. The porosity can be gained by plane its porosity and resistance coefficient are two important diameters. The porosity can be gained by map calculation according to CAD drawing of radiator manufacturers. The resistance coefficient can plane map calculation according to CAD drawing of radiator manufacturers. The resistance be calculated by the following formula: coefficient can be calculated by the following formula: = ( ) 22 KKQQ = (∆∆p/p/∆x)//cc (6(6)) wherewhere ∆∆pp isis thethe staticstatic pressurepressure differencedifference of the radiator, ∆∆x isis thethe radiator wall thickness, c isis thethe average speedspeed ofof coolingcooling air.air. AllAll radiatorradiator diametersdiameters areare shownshown inin TableTable1 .1. The structuralstructural gridgrid isis alsoalso usedused for for inlets, inlets, outlets outlets and and other other regions. regions. Finally, Finally the, the meshed meshed model model is shownis shown in in Figure Figure3. 3.

Figure 3. Meshed layout of engine compartment and whole air enclosing area.area.

3.3.3.3. Boundary Conditions Settlement For the rotating airair domain,domain, thethe rotatingrotating airair isis setset toto bebe a fluidfluid modelmodel andand sevenseven fansfans are setset toto be different domainsdomains rotatingrotating with with different different axes. axes. In In addition, addition the, the boundary boundary of theof the interfaces interfaces between between air andair and fan fan surfaces surfaces are are set toset be to wallbe w conditions.all conditions. As the the power power of of heat heat conduction conduction in in the the engine engine cover cover wall wall is small is small compared compared with with radiators radiators and systemand system maximum maximum temperature temperature is only is only up up to aboutto about 100 100◦C, °C the, the system system heat heat conduction conduction isis ignoredignored as well as as its its thermal thermal radiation. radiation. Hence, Hence, for for another another air airdomain, domain, the boundary the boundary of surfaces of surfaces is set isto setbe the adiabatic wall condition, with an opening boundary in air inlet and outlet, as well as a computational domain. The turbulence model adopts K-ε one, as a high Re number condition K-ε flow model can take a rotating effect into consideration and shows a higher computational accuracy in strong rotate flow [23]. The simulation employs the Thermal Energy model. The solver uses Segregated/Implicit type, and adopts the SIMPLE algorithm to solve the coupled analyses of speed and pressure. The type of discrete equation adopts the second order upwind scheme. Appl. Sci. 2017, 7, 231 6 of 13 to be the adiabatic wall condition, with an opening boundary in air inlet and outlet, as well as a computational domain. The turbulence model adopts K-ε one, as a high Re number condition K-ε flow model can take a rotating effect into consideration and shows a higher computational accuracy in strong rotate flow [23]. The simulation employs the Thermal Energy model. The solver uses Segregated/Implicit type, and adoptsAppl. Sci. the 2017 SIMPLE, 7, 231 algorithm to solve the coupled analyses of speed and pressure. The type of discrete6 of 13 equation adopts the second order upwind scheme. The cooling air is set with pressure of 101 kPa, and density of 1.293 kg/m3. As the speed of cooling The cooling air is set with pressure of 101 kPa, and density of 1.293 kg/m3. As the speed of air is much lower than sound speed and it is a small-Ma fluid situation, the cooling air is assumed to cooling air is much lower than sound speed and it is a small-Ma fluid situation, the cooling air is be incompressible and ideal gas. assumed to be incompressible and ideal gas. The grid independence is also studied to ensure the accuracy of simulation. As shown in Figure 4, The grid independence is also studied to ensure the accuracy of simulation. As shown in Figure4, with the growth of grid number, the temperatures of inlet and outlet in the engine radiator are with the growth of grid number, the temperatures of inlet and outlet in the engine radiator are changing. changing. Until the number of grids increases to 7 million, the curves of supervised temperatures Until the number of grids increases to 7 million, the curves of supervised temperatures become smooth become smooth and steady. This is the same as that of the torque convertor radiator. In overall and steady. This is the same as that of the torque convertor radiator. In overall consideration of consideration of hardware equipment, calculating time and simulation error, the total number of hardware equipment, calculating time and simulation error, the total number of grids is set to be about grids is set to be about 8.86 million in the following simulations. 8.86 million in the following simulations.

torque converter radiator inlet torque converter radiator outlet 100 engine radiator inlet engine radiator inlet 90

℃

/ 70

Temperature 60

4 6 8 10 12 Grid number / Million

Figure 4. The study of grid independence. Figure 4. The study of grid independence.

4.4. ExperimentalExperimental Comparison ◦ TheThe outdoor outdoor experiments experiments were carried out in surroundings surroundings of 35 °CC temperature and 67% humidityhumidity withwith aa good sunshine, and lasted for hours after temperature balance.balance. The temperature was measuredmeasured byby thethe k-typek-type sheathed sheathed thermocouples thermocouples with with an an accuracy accuracy of of 1.5 1. K.5 K The. The coolant coolant flow flow volume volume is measuredis measured by the by turbine the turbine flowmeters flowmeters with an with accuracy an accuracy of 1%. The of 1%. cooling The air cooling flow volume air flow is volume measured is bymeasured the industrial by the air industrial velocity air transmitter velocity oftransmitter Omega FMA1003A-MA of Omega FMA1003A with an- accuracyMA with ofan 1.5%. accuracy All the of experimental1.5%. All the experimental data are collected data byare the collected testing by modules the testing of Yanhua modules Company. of Yanhua Company. AsAs shownshown inin FigureFigure5 5,, the the working working conditions conditions were were the the same same as as those those of of the the simulation. simulation. The The air air temperaturetemperature ofof thethe torquetorque converterconverter radiatorradiator inletinlet waswas almostalmost thethe samesame asas thatthat ofof thethe engineengine radiatorradiator soso thatthat thethe twotwo curvescurves overlapped,overlapped, and it was seen in the figurefigure thatthat the green lineline isis coveredcovered byby thethe ◦ redred line.line. The cooling airair temperature ofof thethe engineengine radiatorradiator outletoutlet waswas keptkept atat aboutabout 7575 °CC,, lower than ◦ thethe temperaturetemperature ofof 80–9080–90 °CC usingusing oneone fanfan inin previousprevious systems.systems. Table2 2 shows shows the the comparisons comparisons ofof simulationsimulation andand experimentalexperimental results. results. The The relative relative errors errors can can be be induced induced by by measuring measuring the the accuracy accuracy of theof the experimental experimental apparatus, apparatus, computation computation accuracy accuracy of of the the simulation simulation model, model, environment environment situationsituation inconsistentinconsistent withwith simulationsimulation assumptionassumption moremore oror less,less, andand soso on.on. However, itit isis stillstill clearlyclearly seenseen thatthat the two results agree well, which indicates that our model and simulation are reliable and effective. Hence, the next part of the article will demonstrate more simulation details regarding the heat transfer and flow characteristics of this new cooling system. Appl. Sci. 2017, 7, 231 7 of 13 the two results agree well, which indicates that our model and simulation are reliable and effective. Hence, the next part of the article will demonstrate more simulation details regarding the heat transfer andAppl. flow Sci. 2017 characteristics, 7, 231 of this new cooling system. 7 of 13

torque converter radiator outlet ℃

/ / engine radiator outlet engine radiator inlet (red line)

Cooling air temperature air Cooling torque converter radiator inlet (green line)

Experimental time

FigureFigure 5. 5.Cooling Cooling airair temperaturetemperature curve curve of of different different radiators radiators by by experiments. experiments.

TableTable 2. 2.Experiment Experiment and and simulation simulation comparison comparison on on radiator radiator temperature. temperature. Experimental Value Simulation Value Relative Error Temperature of torque inlet Experimental321 Value Simulation Value330 Relative Error2.8% converterTemperature radiator of torque (K) outletinlet 321356 330360 2.8% 1.1% Temperatureconverter radiator of engine (K) outletinlet 356323 360318 1.1%−1.5% Temperatureradiator (K) of engine outletinlet 323348 318 349 −1.5%0.28% radiator (K) outletRelative error = 348(simulation value − experimental 349 value)/experimental 0.28% value Relative error = (simulation value − experimental value)/experimental value 5. Discussions of Simulation Analyses 5. DiscussionsThis part of Simulationthe article focuses Analyses on numerical simulations on the flow and temperature fields of the new cooling system in the engine compartment for a thorough understanding, in the hope of This part of the article focuses on numerical simulations on the flow and temperature fields of providing results that are helpful in future structure improvements and system designs. the new cooling system in the engine compartment for a thorough understanding, in the hope of providing results that are helpful in future structure improvements and system designs. 5.1. Temperature and Flow Distributions of the Cooling Regions 5.1. TemperatureFigure 6 shows and Flow the temperature Distributions distribution of the Coolings in Regions the inlet and outlet sections of the four radiators. In theFigure air inlet6 shows section, the the temperature averaged distributionsair temperature in the is almost inlet and uniform outlet at sections about 323 of the K. fourIn the radiators. air outlet Insection, the air the inlet temperature section, the in averaged the regions air temperature covered by is cooling almost fans uniform is obviously at about 323lower K. Inthan the that air outletout of section,the fan theacti temperatureon regions (red in the area). regions The coveredaverage bytemperature cooling fans of isthe obviously torque converter lower than radiator that out is oflower the fanthan action that regionsof the engine (red area). radiat Theor, because average in temperature the lower part of the the torque thermal converter load of radiator101 kW is lowerabout thantwice thatas large of the as engine that of radiator, the torque because converter in the radiator, lower part although the thermal there loadare four of 101 fans kW directly is about working twice as for large the asengine that of radiator. the torque The converter hydraulic radiator, oil radiator although achieves there are a four good fans cooling directly mark working as it for is the relatively engine radiator.independent The hydraulicand not greatly oil radiator influenced achieves by the a good other cooling fan groups. mark as it is relatively independent and not greatly influenced by the other fan groups. Figure7 shows the flow field of the whole air region. The velocity of most cooling air is about 5 m/s, except that on the edge of the fans, which could be up to 40 m/s. There are two positions needing additional attentions, circled by red lines in the figure. One is the top air inlet. Since the top air inlet is opened near to where the front outlet grids are, the air backflow problem is still occurring in this region and it will increase the intake air temperature. The same phenomenon also appears in the bottom air inlet, and this is even more serious because of the ground effect. Therefore, one suggestion in future modifications is that the location of the top air inlet can be slightly farther away from the front outlet grids to reduce air mixing and backflow in this area. Another suggestion is that the section

Figure 6. Temperature distributions of the outlet (left one) and inlet (right one) in the air cooling region.

Figure 7 shows the flow field of the whole air region. The velocity of most cooling air is about 5 m/s, except that on the edge of the fans, which could be up to 40 m/s. There are two positions Appl. Sci. 2017, 7, 231 7 of 13

torque converter radiator outlet ℃

/ / engine radiator outlet engine radiator inlet (red line)

Cooling air temperature air Cooling torque converter radiator inlet (green line)

Experimental time Figure 5. Cooling air temperature curve of different radiators by experiments.

Table 2. Experiment and simulation comparison on radiator temperature.

Experimental Value Simulation Value Relative Error Temperature of torque inlet 321 330 2.8% converter radiator (K) outlet 356 360 1.1% Temperature of engine inlet 323 318 −1.5% radiator (K) outlet 348 349 0.28% Relative error = (simulation value − experimental value)/experimental value

5. Discussions of Simulation Analyses This part of the article focuses on numerical simulations on the flow and temperature fields of the new cooling system in the engine compartment for a thorough understanding, in the hope of providing results that are helpful in future structure improvements and system designs.

5.1. Temperature and Flow Distributions of the Cooling Regions Figure 6 shows the temperature distributions in the inlet and outlet sections of the four radiators. In the air inlet section, the averaged air temperature is almost uniform at about 323 K. In the air outlet section, the temperature in the regions covered by cooling fans is obviously lower than that out of

Appl.the fan Sci. acti2017on, 7, 231regions (red area). The average temperature of the torque converter radiator is lower8 of 13 than that of the engine radiator, because in the lower part the thermal load of 101 kW is about twice as large as that of the torque converter radiator, although there are four fans directly working for the engineof the bottom radiator. air inlet The can hydraulic be made oil smaller radiator so that achieves the cooling a good air can cooling be sucked mark into as the it is region relatively from independentthe upper air and inlet not as muchgreatly as influenced possible for by better the other heat fan dissipation. groups.

Appl. Sci. 2017, 7, 231 8 of 13 needing additional attentions, circled by red lines in the figure. One is the top air inlet. Since the top air inlet is opened near to where the front outlet grids are, the air backflow problem is still occurring in this region and it will increase the intake air temperature. The same phenomenon also appears in the bottom air inlet, and this is even more serious because of the ground effect. Therefore, one suggestion in future modifications is that the location of the top air inlet can be slightly farther away from the front outlet grids to reduce air mixing and backflow in this area. Another suggestion is that the sectionFigure 6. of TemperatureTemperature the bottom distribution distributions air inlet cans of bethe made outlet (smaller left one) soand that inlet the ( right cooling one) in air the can air becooling sucked region. into the region from the upper air inlet as much as possible for better heat dissipation. Figure 7 shows the flow field of the whole air region. The velocity of most cooling air is about 5 m/s, except that on the edge of the fans, which could be up to 40 m/s. There are two positions

FigureFigure 7.7. The entire ﬂowflow ﬁeldfield ofof airair coolingcooling region.region.

5.2. Thermal Analyses of Six Cross-Sections 5.2. Thermal Analyses of Six Cross-Sections In order to obtain more details of heat transfer characteristics in the fan groups, temperature In order to obtain more details of heat transfer characteristics in the fan groups, temperature distributions of six cross-sections are added into the simulation analyses, as shown in Figure 8. distributions of six cross-sections are added into the simulation analyses, as shown in Figure8. Cross-sections Z − 236.5, Z − 651.5, and Z − 991.5 are parallel to the ceiling of the engine compartment Cross-sections Z − 236.5, Z − 651.5, and Z − 991.5 are parallel to the ceiling of the engine compartment and through the central axes of upper, middle and lower fans, named as Planes 1–3, respectively. and through the central axes of upper, middle and lower fans, named as Planes 1–3, respectively. Cross-sections Y − 273.26, Y + 126.74 are parallel to the side plane of the engine compartment and also Cross-sections Y − 273.26, Y + 126.74 are parallel to the side plane of the engine compartment and through the central axes, named as Planes 4–5, respectively. Cross-section X + 506.5 is parallel to the also through the central axes, named as Planes 4–5, respectively. Cross-section X + 506.5 is parallel front plane of the engine compartment and through the front outlet grids, named as Plane 6. The six to the front plane of the engine compartment and through the front outlet grids, named as Plane 6. cross-sections are used to study the local temperature distributions of different positions and the The six cross-sections are used to study the local temperature distributions of different positions and changing trends of the temperature field in different directions. the changing trends of the temperature field in different directions. Figure9 shows the temperature field of Plane 1 (Cross-section Z − 236.5). The red region Y-273.26 Y+126.74 represents the high temperature area in the torque converter radiator, corresponding to the fan hub areas without flowingX+506.5 air and the places not covered by the fans. However, the temperatures immediately become lower after air leaves the radiator, as is clearly seen in the figure. From Figure9 it can also be seen that, withZ- an236.5 isolation board, hot air is prevented from flowing into the engine region and the temperature in this region is almost kept at about 30 ◦C.

Z-651.5

Z-991.5

Figure 8. Six cross-sections set in the cooling region.

Figure 9 shows the temperature field of Plane 1 (Cross-section Z − 236.5). The red region represents the high temperature area in the torque converter radiator, corresponding to the fan hub areas without flowing air and the places not covered by the fans. However, the temperatures immediately become lower after air leaves the radiator, as is clearly seen in the figure. From Figure 9 Appl. Sci. 2017, 7, 231 8 of 13

needing additional attentions, circled by red lines in the figure. One is the top air inlet. Since the top air inlet is opened near to where the front outlet grids are, the air backflow problem is still occurring in this region and it will increase the intake air temperature. The same phenomenon also appears in the bottom air inlet, and this is even more serious because of the ground effect. Therefore, one suggestion in future modifications is that the location of the top air inlet can be slightly farther away from the front outlet grids to reduce air mixing and backflow in this area. Another suggestion is that the section of the bottom air inlet can be made smaller so that the cooling air can be sucked into the region from the upper air inlet as much as possible for better heat dissipation.

Figure 7. The entire flow field of air cooling region.

5.2. Thermal Analyses of Six Cross-Sections In order to obtain more details of heat transfer characteristics in the fan groups, temperature distributions of six cross-sections are added into the simulation analyses, as shown in Figure 8. Cross-sections Z − 236.5, Z − 651.5, and Z − 991.5 are parallel to the ceiling of the engine compartment and through the central axes of upper, middle and lower fans, named as Planes 1–3, respectively. Cross-sections Y − 273.26, Y + 126.74 are parallel to the side plane of the engine compartment and also through the central axes, named as Planes 4–5, respectively. Cross-section X + 506.5 is parallel to the front plane of the engine compartment and through the front outlet grids, named as Plane 6. The six Appl.cross Sci.-section2017, 7s, 231are used to study the local temperature distributions of different positions and9 ofthe 13 changing trends of the temperature field in different directions.

Y-273.26 Y+126.74 X+506.5

Z-236.5

Z-651.5

Z-991.5

Appl. Sci. 2017, 7, 231 9 of 13 it can also be seen that, withFigure an isolation 8. Six cross-sections board, hot set air in theis prevented cooling region. from flowing into the engine region and the temperatureFigure in this 8. region Six cross is- sectionsalmost keptset in atthe about cooling 30 region. °C. Appl. Sci. 2017, 7, 231 9 of 13 Figure 9 shows the temperature field of Plane 1 (Cross-section Z − 236.5). The red region representsit can alsothe behigh seen temperature that, with an area isolation in the board, torque hot converter air is prevented radiator, from cor flrespondingowing into the to theengine fan hub areasregion without and the flowi temperatureng air and in this the region places is almost not covered kept at about by the 30 fans.°C. However, the temperatures immediately become lower after air leaves the radiator, as is clearly seen in the figure. From Figure 9

FigureFigure 9. 9. TemperatureTemperature distribution ( left) and velocity distributiondistribution (right) of Plane 1.

Figure 10 shows the temperature field of Plane 2 (Cross-section Z − 651.5). The average Figure 10 showsFigure 9. theTemperature temperature distribution field (left of) and Plane velocity 2 (Cross-section distribution (right Z) of− Plane651.5). 1. The average temperature of this region is higher than that of Plane 1 because cooling air arrives here last and there temperature of this region is higher than that of Plane 1 because cooling air arrives here last and are two heatFigure sources, 10 shows the theintercooler temperature and fieldthe engine of Plane radiator. 2 (Cross In-s ectionthe fan Z hub− 651.5). area s The, heat average is stacked there are two heat sources, the intercooler and the engine radiator. In the fan hub areas, heat is stacked here,temperature whereas in ofthe this other region ar eais shigher heat isthan blown that of away Plane by 1 becausethe strong cooling wind. air Meanwhile,arrives here last the and two there fans are here, whereas in the other areas heat is blown away by the strong wind. Meanwhile, the two fans are interactingare two and heat coupling sources, inthe their intercooler edges andso that the temperatureengine radiator. distribution In the fan ishub like area a wave.s, heat Ais nstacked interesting interacting and coupling in their edges so that temperature distribution is like a wave. An interesting phenomenonhere, whereas of energy in the otherconvolution areas heat appears is blown in away each byedge the of strong the fan wind. group Meanwhile, because the of twothe airfans backflow are phenomenon of energy convolution appears in each edge of the fan group because of the air backflow explainedinteracting above and in coupling Figure in6. theirThe edgestemperature so that temperature field of Plane distribution 3 (Cross is- likesection a wave. Z − A 991.5),n interesting shown in explainedphenomenon above of in energy Figure convolution6. The temperature appears in each field edge of Plane of the 3fan (Cross-section group because Zof the− 991.5), air backflow shown in Figure 11, is almost the same as that of Plane 2, but the average temperature of Plane 3 is lower than Figureexplained 11, is almost above thein Figure same as6. The that temperature of Plane 2, butfield the of Plane average 3 (Cross temperature-section Z of − Plane991.5), 3 s ishown lower in than that of Plane 2. This is because the air inlet grids are opened at the bottom of the engine compartment that ofFigure Plane 11, 2. is This almost is becausethe same theas that air inletof Plane grids 2, but are the opened average at thetemperature bottom ofof thePlane engine 3 is lower compartment than and air is sucked into the lower fan groups in priority, so that the bottom fans enjoy more and cooler and airthat is of sucked Plane 2. into This the is because lower fanthe air groups inlet grids in priority, are open soed that at the the bottom bottom of the fans engine enjoy compartment more and cooler intakeand air air used is sucked in heat into dissipation. the lower fan groups in priority, so that the bottom fans enjoy more and cooler intake air used in heat dissipation. intake air used in heat dissipation.

FigureFigure 10. Temperature10. Temperature distribution distribution ((leftleft) and velocityvelocity distribution distribution (right (right) of )Plane of Plane 2. 2. Figure 10. Temperature distribution (left) and velocity distribution (right) of Plane 2.

Figure 11. Temperature distribution (left) and velocity distribution (right) of Plane 3. Figure 11. Temperature distribution (left) and velocity distribution (right) of Plane 3. The temperature distributions of Plane 4 (Cross-section Y − 273.26), Plane 5 (Cross-section Y + 126.74), Theand temperaturePlane 6 (Cross distributions-section X + 506.5) of Plane are, 4 respectively, (Cross-section shown Y − 273.26),in Figures Plane 12– 14.5 (Cross As the-s ectiondistributions Y + 126.74), are similar to each other, and quite close to those in Planes 1–3, they will no longer be explained in and Plane 6 (Cross-section X + 506.5) are, respectively, shown in Figures 12–14. As the distributions detail here. The differences of the side fan group shown in Figure 14 are: (i) that there is no fan are similar to each other, and quite close to those in Planes 1–3, they will no longer be explained in coupling activities due to only one fan set here; and (ii) its rotating speed is 3200 rpm in order to detailensure here. enough The differences air flow volume of the for side the hydraulicfan group oil shownradiator. in Figure 14 are: (i) that there is no fan coupling activities due to only one fan set here; and (ii) its rotating speed is 3200 rpm in order to ensure enough air flow volume for the hydraulic oil radiator. Appl. Sci. 2017, 7, 231 9 of 13

it can also be seen that, with an isolation board, hot air is prevented from flowing into the engine region and the temperature in this region is almost kept at about 30 °C.

Figure 9. Temperature distribution (left) and velocity distribution (right) of Plane 1.

Figure 10 shows the temperature field of Plane 2 (Cross-section Z − 651.5). The average temperature of this region is higher than that of Plane 1 because cooling air arrives here last and there are two heat sources, the intercooler and the engine radiator. In the fan hub areas, heat is stacked here, whereas in the other areas heat is blown away by the strong wind. Meanwhile, the two fans are interacting and coupling in their edges so that temperature distribution is like a wave. An interesting phenomenon of energy convolution appears in each edge of the fan group because of the air backflow explained above in Figure 6. The temperature field of Plane 3 (Cross-section Z − 991.5), shown in Figure 11, is almost the same as that of Plane 2, but the average temperature of Plane 3 is lower than that of Plane 2. This is because the air inlet grids are opened at the bottom of the engine compartment and air is sucked into the lower fan groups in priority, so that the bottom fans enjoy more and cooler intake air used in heat dissipation.

Appl. Sci. 2017, 7, 231 10 of 13 Figure 10. Temperature distribution (left) and velocity distribution (right) of Plane 2.

Figure 11. Temperature distribution (left) and velocity distribution (right) of Plane 3. Figure 11. Temperature distribution (left) and velocity distribution (right) of Plane 3. The temperature distributions of Plane 4 (Cross-section Y − 273.26), Plane 5 (Cross-section Y + 126.74), Theand Plane temperature 6 (Cross-s distributionsection X + 506.5) of are, Plane respectively, 4 (Cross-section shown in YFigures− 273.26), 12–14. As Plane the distributions 5 (Cross-section Y + 126.74),are similar and toPlane each other, 6 (Cross-section and quite close X +to 506.5)those in are, Planes respectively, 1–3, they will shown no longer in Figures be explained 12–14. in As the distributionsdetail here. are The similar differences to each of other,the side and fan quite group close shown to those in Figure in Planes 14 are: 1–3, (i) that they there will is no no longer fan be explainedcoupling in detailactivit here.ies due The to only differences one fan ofset the here side; and fan (ii) group its rotating shown speed in Figure is 3200 14 r are:pm in (i) order that thereto is ensure enough air flow volume for the hydraulic oil radiator. no fan coupling activities due to only one fan set here; and (ii) its rotating speed is 3200 rpm in order to ensureAppl. Sci. enough 2017, 7, 231 air ﬂow volume for the hydraulic oil radiator. 10 of 13 Appl.Appl. Sci. Sci. 2017 2017, 7,, 2317, 231 10 of10 13of 13

Figure 12. Temperature distribution (left) and velocity distribution (right) of Plane 4. Figure 12. Temperature distribution (left) and velocity distribution (right) of Plane 4. Figure 12. Temperature distribution (left) and velocity distribution (right) of Plane 4. Figure 12. Temperature distribution (left) and velocity distribution (right) of Plane 4.

Figure 13. Temperature distribution (left) and velocity distribution (right) of Plane 5. Figure 13. Temperature distribution (left) and velocity distribution (right) of Plane 5. Figure 13. Temperature distribution (left) and velocity distribution (right) of Plane 5. Figure 13. Temperature distribution (left) and velocity distribution (right) of Plane 5.

Figure 14. Temperature distribution (left) and velocity distribution (right) of Plane 6. Figure 14. Temperature distribution (left) and velocity distribution (right) of Plane 6. 5.3. The Effect of Different Axes Distances on Temperature Distribution 5.3. The EffectFigure of Different14. Temperature Axes Distances distribution on Temperature (left) and velocity Distribution distribution (right) of Plane 6. As Figureshown 14.in FiguresTemperature 6 and 10, distribution airflow interaction (left) and exists velocity in the distribution spaces between (right) the of Plane two fans 6. when the present axes distance is 400 mm. This phenomenon will aggravate flow turbulence and energy 5.3. TheAs Effect shown of Different in Figures Ax 6e sand Distances 10, airflow on Temperature interaction exists Distribution in the spaces between the two fans when wastethe present and is axes detrimental distance foris 400 syste mmm. cooling. This phenomenon In order to willdecrease aggravate mixing flow air flowturbulence at the junctionsand energy of fanwasteAss, shown theand central is indetrimental Figures axes distance 6 forand syste 10, of airflowm two cooling. fans interaction In will order be existsto changed decrease in the to mixingspaces study itsairbetween flow effect at the onthe two temperaturejunctions fans when of thedistribution,fan presents, the axes central which distance ax ise sshown distance is 400 in m Figure ofm. twoThis 15. fans phenomenonTaking will the be upper changed will fan aggravate group, to study for flow its instance, effect turbulence onthe temperaturecurve and of energy the wastedifferencesdistribution, and is detrimentalof which average is shown temperature for syste in Figurem betweencooling. 15. Taking outletIn order the and upperto inlet decrease fansection group, mixings versus for instance,air distanceflow at thes theof curve fan junctions ax ofe sthe is of fanshowndifferencess, the in central Figure of average ax16.e sWith distance temperature the ax e ofs distance two between fans changing outlet will beand from changed inlet 340 section to 500 to studysm versusm, the its distancetemperature effect s on of fantemperaturedifference axes is distribution,firstlyshown stays in Figure which at about 16. is Withshown 22 K the, thenin ax Figuree sincreases distance 15. Taking tochanging a maximum the from upper 340value fan to 500ofgroup, 30 m m,K forat the the instance, temperature distance the of differencecurve 440 m ofm the. differencesAfterwardsfirstly stays of, averageatthe about temperature temperature22 K, then difference increases between begins to outlet a tomaximum decrease and inlet valuewith section increasing of 30s Kversus at distance the distance distance ands drops of 440fan down maxmes. is showntoAfterwards 17. in45 Figure K at, the 16. temperaturedistance With the of 500ax differencee sm distancem. The begins reason changing to for decrease this from is that340with toif increasing the500 distance mm, distancethe of temperature two and fans drops is too difference down long, the radiators will not be covered fully by the fans, especially in the spaces between the two fans; but firstlyto 17. stays45 K at theabout distance 22 K ,of then 500 increasesmm. The reason to a maximum for this is thatvalue if theof 30distance K at theof tw distanceo fans is of too 440 long, mm . if they are too close, the airflow interaction will strengthen at the edges of fans. As a result, both Afterwardsthe radiators, the will temperature not be covered difference fully by begins the fans, to decrease especially with in the increasing spaces between distance the and two drops fans; downbut situations will lead to poor cooling effects and temperature increases. Hence, there is a best distance to 17.if they45 K are at thetoo distance close, the of airflow 500 mm. interaction The reason will for strengthen this is that at ifthe the edges distance of fans. of tw Aso fansa result, is too both long, ofsituations the fan axwilles. leadIn this to coolingpoor cooling system, effect its soptimal and temperature distance is increase 440 mms and. Hence, the interval there is ofa best the twodistance fans the radiators will not be covered fully by the fans, especially in the spaces between the two fans; but isof 120the mfanm. ax es. In this cooling system, its optimal distance is 440 mm and the interval of the two fans if they are too close, the airflow interaction will strengthen at the edges of fans. As a result, both is 120 mm. situations will lead to poor cooling effects and temperature increases. Hence, there is a best distance of the fan axes. In this cooling system, its optimal distance is 440 mm and the interval of the two fans is 120 mm. Appl. Sci. 2017, 7, 231 11 of 13

5.3. The Effect of Different Axes Distances on Temperature Distribution As shown in Figures6 and 10, airflow interaction exists in the spaces between the two fans when the present axes distance is 400 mm. This phenomenon will aggravate flow turbulence and energy waste and is detrimental for system cooling. In order to decrease mixing airflow at the junctions of fans, the central axes distance of two fans will be changed to study its effect on temperature distribution, which is shown in Figure 15. Taking the upper fan group, for instance, the curve of the differences of average temperature between outlet and inlet sections versus distances of fan axes is shown in Figure 16. With the axes distance changing from 340 to 500 mm, the temperature difference firstly stays at about 22 K, then increases to a maximum value of 30 K at the distance of 440 mm. Afterwards, the temperature difference begins to decrease with increasing distance and drops down to 17.45 K at the distance of 500 mm. The reason for this is that if the distance of two fans is too long, the radiators will not be covered fully by the fans, especially in the spaces between the two fans; but if they are too close, the airflow interaction will strengthen at the edges of fans. As a result, both situations will lead to poor cooling effects and temperature increases. Hence, there is a best distance of the fan axes. In this cooling Appl.system, Sci. 2017 its, optimal7, 231 distance is 440 mm and the interval of the two fans is 120 mm. 11 of 13 Appl. Sci. 2017, 7, 231 11 of 13

Interval of fan axis Interval of fan axis

Thermal bafflesThermal baffles

Figure 15. Schematic diagram of the cooling system with different intervals of the fan axis and Figure 15. SchematicSchematic diagram diagram of of the the cooling cooling system system with with differedifferentnt intervals of the fan axis and thermal baffles. thermal bafﬂes.baffles.

Figure 16. Temperature difference of the outlet and inlet in the torque converter radiator versus the Figure 16. Temperature difference of the outlet and inlet in the torque converter radiator versus the axisFigure distance 16. Temperature of two fans. difference of the outlet and inlet in the torque converter radiator versus the axis distance of two fans. 5.4. The Effect of Thermal Baffles on Temperature Distribution 5.4. The Effect of Thermal Baffles on Temperature Distribution Although there is an optimal distance of the fan axes, it is limited to the engine compartment Although there is an optimal distance of the fan axes, it is limited to the engine compartment space. In this case, the best distance is 440 mm, but it will enlarge the cooling cabin size. Therefore, space. In this case, the best distance is 440 mm, but it will enlarge the cooling cabin size. Therefore, thermal baffles are adopted according to the previous research. There are three baffles set to separate thermal baffles are adopted according to the previous research. There are three baffles set to separate the upper and lower fan groups into six individuals, which is shown in Figure 15. This can decrease the upper and lower fan groups into six individuals, which is shown in Figure 15. This can decrease air interaction and flow turbulence to a significant extent. As shown in Table 3, with baffle changes, air interaction and flow turbulence to a significant extent. As shown in Table 3, with baffle changes, the average temperature differences of the outlet and inlet sections in all radiators increase, especially the average temperature differences of the outlet and inlet sections in all radiators increase, especially for the engine radiator, which is up to 14 K. It can be seen that the effect of the thermal baffle is for the engine radiator, which is up to 14 K. It can be seen that the effect of the thermal baffle is obvious and this will be the main improvement in our new machinery. obvious and this will be the main improvement in our new machinery. Table 3. Temperature difference of outlet and inlet of all radiators versus thermal baffles. Table 3. Temperature difference of outlet and inlet of all radiators versus thermal baffles. Temperature Difference of Outlet and Inlet (K) Performance Improvement Temperature Difference of Outlet and Inlet (K) Performance Improvement Without baffle (A) With baffle (B) Without baffle (A) With baffle (B) Torque converter radiator 21.12 31.83 50.71% Torque converter radiator 21.12 31.83 50.71% Engine radiator 37.59 51.02 35.73% Engine radiator 37.59 51.02 35.73% Hydraulic oil radiator 18.71 22.5 20.26% Hydraulic oil radiator 18.71 22.5 20.26% Performance improvement = (B − A)/A Performance improvement = (B − A)/A

Appl. Sci. 2017, 7, 231 12 of 13

5.4. The Effect of Thermal Baffles on Temperature Distribution Although there is an optimal distance of the fan axes, it is limited to the engine compartment space. In this case, the best distance is 440 mm, but it will enlarge the cooling cabin size. Therefore, thermal baffles are adopted according to the previous research. There are three baffles set to separate the upper and lower fan groups into six individuals, which is shown in Figure 15. This can decrease air interaction and flow turbulence to a significant extent. As shown in Table3, with baffle changes, the average temperature differences of the outlet and inlet sections in all radiators increase, especially for the engine radiator, which is up to 14 K. It can be seen that the effect of the thermal baffle is obvious and this will be the main improvement in our new machinery.

Table 3. Temperature difference of outlet and inlet of all radiators versus thermal bafﬂes.

Performance Temperature Difference of Outlet and Inlet (K) Improvement Without bafﬂe (A) With bafﬂe (B) Torque converter radiator 21.12 31.83 50.71% Engine radiator 37.59 51.02 35.73% Hydraulic oil radiator 18.71 22.5 20.26% Performance improvement = (B − A)/A

6. Conclusions This paper employs a new cooling system with multiple fans and an independent cooling region. According to power flow and performance requirements, seven fans are divided into four groups: two of them in the upper part for cooling the torque converter radiator, four in the lower part for the engine radiator and intercooler, and the last one for the hydraulic oil radiator in the side. The independent cooling region is segregated from the engine region by a thermal baffle in order to avoid heat flowing into the engine region. The cooling air temperature of the engine radiator outlet was kept at about 75 ◦C, lower than that of previous systems, which were always about 80–90 ◦C. The experiment also validates the accuracy of the simulation. After validation, the simulation then analyzes heat transfer and flow characteristics of the cooling system changing with different cross-sections in different axis directions, as well as different distances of the fan central axis. It is found that there is a best distance of the fan axis and in this cooling system this best distance is 440 mm. Finally, thermal baffles are set between fan groups and it is found that this benefits the cooling effect greatly: the average temperature differences of outlet and inlet sections in all radiators increased, especially in the engine radiator, up to 14 K. The research realizes a multi-fan scheme with an independent cooling region in a wheel loader, which is a new, but high-efficiency, cooling system and will lead to a change of various configurations and system designs in future engine compartments.

Acknowledgments: The presented work was supported by the President Foundation, Great Scientific and Technological Foundation of Fujian Province of China (Grant No. 2016HZ0001-9). Author Contributions: The authors contributed equally to this work. Conflicts of Interest: The authors declare no conflict of interest.

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