Diesel Engine Waste Heat Recovery System Comprehensive Optimization Based on System and Heat Exchanger Simulation

Open Physics 2021; 19: 331–340

Research Article

Da Li, Qiang Sun, Ke Sun*, Guodong Zhang, Shuzhan Bai*, and Guoxiang Li* Diesel engine waste heat recovery system comprehensive optimization based on system and heat exchanger simulation

https://doi.org/10.1515/phys-2021-0039 received February 04, 2021; accepted May 11, 2021 Nomenclature

Abstract: To further improve the thermal efficiency of E power output, kW diesel engines, a waste heat recovery system model uti- m mass flow rate, kg/s lizing organic Rankine cycle (ORC) is constructed and Q heat flux, kW verified through system bench test and heat exchanger h enthalpy, kJ/kg bench test. To recover waste heat from diesel engine η efficiency exhaust, ethanol, cyclopentane, cyclohexane, R1233zd out outlet (E), and R245fa were selected for comparison. The quality s heat source of heat source, the quality of evaporator, the system r working fluid output, and the system complicity were taken as vari- re recuperated ables for comparison. Analysis shows that for ORC systems without recuperator, ethanol system has the best system output of the five in a wide operation temper range, with the highest exergy efficiency of 24.1%, yet the exergy Subscripts and superscripts efficiency increase after the application of recuperator, 9.0%, is limited. For low temperature exhaust, cyclopen- eva evaporator tane system has the best performance with or without exp expander recuperator, and the cyclopentane system with recup- in inlet erator has the best performance in terms of exergy efficiency, 27.6%, though complex heat exchangers are also required for high power output. The system output of the R1233zd system is better than the R245fa system, yet the Acronyms advantage of low evaporate temperature can be better utilized for low quality waste heat recovery. ORC organic Rankine cycle EGR exhaust gas recirculation Keywords: organic Rankine cycle, exhaust, working fluid, PTD pinch point temperature difference recuperator CO2 carbon dioxide

 * Corresponding author: Ke Sun, School of Energy and Power Engineering, Shandong University, Jinan, 250061, China, 1 Introduction e-mail: [email protected] * Corresponding author: Shuzhan Bai, School of Energy and Power As the most favorable power source for heavy-duty road Engineering, Shandong University, Jinan, 250061, China, vehicles, the thermal efficiency of diesel engines has e-mail: [email protected] increased significantly in recent decades. However, other * Corresponding author: Guoxiang Li, School of Energy and Power methods of waste heat recovery also need to be applied, Engineering, Shandong University, Jinan, 250061, China, ffi e-mail: [email protected] to further increase system exergy e ciency and meet new - Da Li, Qiang Sun, Guodong Zhang: School of Energy and Power or upcoming regulations of CO2 emission. A large propor Engineering, Shandong University, Jinan, 250061, China tion of combustion energy would inevitably be lost

through engine cooling system and exhaust emissions. aCO2 transcritical power cycle using single working fluid The waste heat recovery system using organic Rankine with low evaporate temperature; the system has utilized cycle (ORC) can effectively recover waste heat from low 48.9% of the exhaust and 72.8% of the coolant energy. quantity heat sources [1]. The ORC system structure is Heat exchangers are essential components of ORC shown in Figure 1. High pressure working fluid recovers systems. Preheater, evaporator, superheater, and recup- waste heat in the evaporation process, exchanging heat erator determined the total waste heat recovery, and effi- within the evaporator, with or without separate preheater ciencies of heat exchangers are important for ORC system and superheater. Then the high pressure gas expands in structure design. For simple and compact ORC system the expander and generates kinetic power output through structure, Holik et al. [10] implemented a two-objective the expansion process. After expansion, working fluid optimization based on the maximization of power output condenses in the condenser and flows back to the fluid and minimization of the total heat exchanger surface area tank, ready for another cycle. and suggested that recuperator is not advisable for com- Conditions of heat sources are essential for ORC system pact ethanol ORC system. Amicabile et al. [5] considered working fluid selection. Studies of stationary ORC sys- layout with and without recuperator and also suggested tems [2,3], though valuable for system analysis and simu- that the ethanol system lay out without recuperator has lation, still have much difference with ORC systems for the minimum capital cost. The complicate systems of Shu road vehicles. To recover waste heat from heavy-duty et al. [11] and Li et al. [9] both take recuperator into diesel engines, Preißinger et al. [4] examined 3,000 pro- consideration. mising working fluid candidates and rank ethanol as the Turbine expander [12], though promising for ORC best ORC working fluid for heavy-duty trucks, as well as system, is less advisable for wet fluid expansion. Song passenger cars. Amicabile et al. [5] propose a comprehen- et al. [13] studied and summarized the application of a sive design methodology to optimize the ORC system, and scroll expander in ORC system with higher efficiency separate evaporator and superheater were applied to in single working condition and droplet tolerance. recover waste heat from engine exhaust and Exhaust When using ethanol and other wet working fluids with Gas Recirculation (EGR) cooler. Among ethanol, pentane, relatively large expansion, the piston expander has the and R245fa, Amicabile suggests ethanol has both the advantage of sufficient energy recovery. Li et al. [14] ana- best performance and the minimum capital cost. Other lyzed the output of the free single-piston expander used researches focused on dry fluids with low evaporate tem- in the compact ORC system and optimized the control perature, to recover waste heat from low quality heat strategy. Han et al. [15] conducted an experimental study sources. Yang et al. [6] suggested R1233zd (E) and other on the application of the rotary piston expander in the fluids as better replacement, while Talluri et al. [7] inves- ORC system. Piston expander can achieve large expan- tigated an ORC Tesla turbine through experiment using sion ratio without significant efficiency loss, and the R1233zd (E) as working fluid. Chen et al. [8] proposed scroll expander can achieve higher isentropic efficiency a confluent cascade expansion ORC system for engine at lower expansion ratio. As suggested by Chen et al. [8], waste heat recovery, using single fluid for both high-tem- large expansion ratio and high expander efficiency can be perature and low temperature recovery, and cyclopen- both achieved by using multiple high efficiency expan- tane is analyzed to be regarded as the most suitable ders, yet the cost of the system will increase significantly. working fluid for this novel system. Li et al. [9] created The paper chose piston expander with wide expansion ratio. Study on plate heat exchangers has progressed greatly in recent years; magnetic field [16], nanoparticles [16–18], and heat transfer within pipes [17–19] have been much considered. However, due to high evaporate pressure and limits in experiments, tube-fin heat exchangers are utilized in this paper. Though recover heat from low temperature heat sources has certain methods for stationary waste recovery systems [20], much practical difficulties restrain them for road vehicles. Former researches either exclude recuperater due to using wet fluids, or include recuperator in a complex Figure 1: ORC system structure. system. To further increase the thermal and exergy Diesel engine waste heat recovery system comprehensive optimization  333 efficiency of ORC system, other typical working fluids, especially dry fluid with similar evaporate temperature of ethanol, need comprehensive examination. This paper used a certain type of hybrid diesel engine for heavy-duty trucksastheheatsourceandselectedtheexhaust at typical operating points as the heat input of the ORC system. Beside ethanol, cyclopentane, cyclohexane, R1233zd (E), and R245fa were also selected for comparison. In order to achieve efficient waste heat recovery, working fluids of the ORC system need to evaporate at proper temperature. The selection of high-temperature heat exchangers and expanders also needs to be adjusted accordingly. Comprehensively optimizing the recuperator and evaporator can provide reference for future vehicle ORC system working fluid selection. Figure 2: T–s diagram of the ethanol ORC system.

fluids is shown in Figure 2, and related properties are 2 Methods given in Table 1. R245fa and R1233zd have much lower evaporating temperatures, thus the temperature differ- The ORC system model, a simple system with or without ence within the evaporator will remain large at wide recuperator, has been constructed for analysis, with the heat source temperature range; yet the condensing tem- system structure shown in Figure 1. The objective of the peratures of the two fluids are also low, resulting in optimization process is to achieve high power output relatively low condensing pressure and expansion ratio. with limited system complexity and cost. Ethanol, cyclopentane, and cyclohexane have higher evaporating temperatures, with the evaporating temperature of cyclohexane slightly higher than the other two; the thermal efficiency of the three fluids will be larger. 2.1 System construction The major disadvantage of the three systems will be the evaporation process, as high evaporation temperature The T–s diagram of an ethanol ORC system is shown in may reduce the proportion of waste heat recovery within Figure 2. With fixed evaporation temperature and the the evaporator, thus decreases exergy efficiency. The T–s condensing temperature, the thermal efficiency of the diagram of selected working fluids and related working system is largely determined by the expansion process fluid properties (include latent heat) are given in Figure 3 (4–5). Therefore, the optimal working fluid shall have a and Table 1. large expansion ratio, which means high evaporate pres- In order to focus on the simulation analysis of the sure and low condense pressure within the operation heat exchanger part, it is necessary to simplify the heat temperature range, since larger proportion of energy source and other parts of the system to reduce secondary will be recovered. However, the exergy efficiency of the variables and reduce the complexity of the model. To this system is also affected by the amount of energy recovery end, the following assumptions are made for the system: in waste heat exchanging of preheating, evaporation, and (1) The operating conditions in the ORC system model superheating (1–2–3–4). The working fluid largely deter- are all steady state, and the heat source inlet tempera- mines both the expansion ratio and the heat exchanging ture and flow rate at each operating point are constant. within the evaporator, thus the selection of the working (2) The condenser of the system is parallel to the engine fluid is essential to both the thermal efficiency and exergy cooling system. The superheat degree and the under- efficiency of the ORC system. cooling degree are both constant. To recover waste heat from diesel engine exhaust, the (3) The pressure drop and heat transfer loss of the eva- working fluid of the ORC system shall properly operate porator and recuperator are determined with refer- within the heat source temperature range. Ethanol, cyclo- ence to experimental data, and the pressure drop pentane, cyclohexane, R245fa, and R1233zd (E) were and heat transfer loss of pipelines and other compo- selected for comparison, and the T–s diagram of these nents are ignored. 334  Da Li et al.

Table 1: Working ﬂuid properties

Ethanol Cyclopentane R245fa Cyclohexane R1233zd

Evaporate temperature (°C) 200.4 208.5 143.3 256.3 155.4 Condense pressure (MPa) 0.10 0.17 0.53 0.10 0.45 Latent heat (kJ/kg) 505.5 185.1 73.8 157.6 71.36

With recuperator applied, the working fluid after expansion will preheat the working fluid after pump. The modified power output can be defined as equation (2):

EQηWre=⋅− eva pump ̇ hh45− =⋅⋅(−)⋅ηmhheva sinout ⋅ ηexp hh41re− (2)

hh19− −⋅mr ηpump

The power output gain can be deﬁned as equation (3):

ηmhḣ hh45− η E eva ⋅⋅(−)⋅⋅sinouthh exp η̇ =≈re 41re− E hh45− ηmhheva ⋅⋅(−)⋅·sinout ηexp hh41− (3) Figure 3: T–s Diagram of selected working fluids. (−hḣ )⋅(−) hh = in out 4 1 (−hhin out )⋅(− hh 4 1re ) (4) The working fluid can be fully expanded in the Therefore, the exhaust outlet temperature of the eva- expander, and the efficiency of the expander and porator and the recuperate rate are the critical factors of working fluid pump is constant. the power output gain. The largely simplified ORC system model is used to calculate system output and thermal or exergy efficiency. For system complicity analysis, an additional heat exchanger - 2.2 System modeling modelisappliedfordetailedevaporatorandrecuperatorcal culation. Equations of heat exchanger model are given in Table 2. The power output of the ORC system without recuperator As both the evaporator and the recuperator are com- can be defined as equation (1): pact tube-fin heat exchangers, the single phase turbulent EQηW=⋅−eva pump flow within the tube, namely in the recuperator and in the hh− preheating section and superheating section of the eva- ηmhh 45η =⋅⋅(−)⋅eva s in out ⋅ exp ( ) ( ) hh41− (1) porator, is calculated with equations 5 and 6 ; the two hh− phase turbulent flow of the evaporator is calculated with −⋅m 19 r equation (7). The exhaust side of the evaporator is calcu- ηpump lated with equation (4). The condenser is simplified. where ηeva stands for the thermal efficiency of the eva- The heat exchanger model is verified by the heat porator, ηexp stands for the expander isentropic effi- exchanger experiment. Parameters of the evaporator ciency, ηpump stands for the pump efficiency, ms stands and the recuperator are also mainly taken from the heat for heat source (exhaust) mass flow, mr stands for working exchanger bench test. The system model is verified by the fluid mass flow, hin and hout stand for the enthalpy of the ORC system experiment, and other parameters of the ORC heat source at the inlet and the outlet, h1, h4,andh5 stand system are determined through the ORC system bench for the enthalpy of the working fluid at each point in test with the recuperator. The relevant boundary condi- Figure 2, the same below. tions are shown in Table 3. Diesel engine waste heat recovery system comprehensive optimization  335

Table 2: Equations of heat exchanger model

Heat exchanger Equations [21–24]

Exhaust side −0.0887 −0.159 0.424  s   Ns· 2  Nu0.982Re=⋅ ⋅  ⋅  () 4  d3   d3  Cold side (Single 0.5  ff    23  phase) Nu =⋅()⋅/·  Re − 1000 Pr 12.7   ⋅()+()Pr/ − 1 1.07 5  8    8   f =(1.82 ⋅ lg Re−1.5 )−2 ( 6 ) Two phase zone 0.857 0.714 −0.143 kl hxtp=⋅30 Re lo ⋅ Bo ·() 1 − ·() 7 d

Heat source conditions are taken from the bench test 3 Result and analysis of a certain diesel engine, namely, the exhaust conditions at the minimum fuel consumption point. The parameters 3.1 Preliminary analysis of expanders are taken from The test bench (Figure 4) and use electric heated or water cooled exhaust to simulate Thermal efficiencies of simple ORC systems without (light actual engine exhaust at each working point, with a grey) and with recuperator (dark grey) are shown in water cooling condenser. The evaporator test used 95% Figure 6. The thermal efficiency of R245fa system is the ethanol as working fluid, while the recuperator test used lowest, which is 7.7% without recuperator and 10.0% R245fa. The heat exchanger model is also verified by the with recuperator. R1233zd shows a slightly better perfor- heat exchanger experiment. mance of 8.9 and 11.1%, yet still no better than the other The ORC system optimization process is shown in three fluids. Ethanol system without recuperator has the Figure 5. In the preliminary analysis, a largely simplified highest thermal efficiency of 13.2%, while cyclohexane model is utilized to perform simplified calculations. Para- system has the best performance of 16.6% among recup- meters are entirely preset to acquire a qualitative analysis erated systems. As for dry fluids, waste heat after expan- result of the ORC system, namely, the thermal efficiency sion process is proportionally larger than wet fluids; of systems with different working fluids. The coupled with proportionally larger temperature difference within analysis utilized the detailed heat exchanger model related the recuperator, the thermal efficiency increase will be in Table 2, to optimize the simplified heat exchanger cal- more significant. Ethanol is the only wet fluid of the culation data in the system model and to achieve a com- five, and the latent heat at 3 MPa is also proportionally prehensive optimization of the system complicity and power output, in terms of both heat exchanging area and exergy efficiency.

Table 3: Boundary conditions

Boundary conditions Parameters

Exhaust temperature (°C) 391 Exhaust mass flow (kg/s) 0.23 Evaporate pressure (MPa) 3 Heat exchanger efficiency 0.9 Expander efficiency 0.65 Pump efficiency 0.8 Superheat degree (K) 40 Undercooling degree (K) 20 Evaporator PTD (K) 20 Condenser PTD (K) 20 Environment temperature (°C) 25 Recuperate rate 0.5 Figure 4: Heat exchanger test bench. 336  Da Li et al.

though, has only slight direct influence on system exergy loss, yet in Figure 7, has shown much influence on system output, as it increased system thermal efficiency. There- fore, these two components need specific analysis during the ORC system working fluid selection.

3.2 Eﬀect of heat source

The system exergy efficiency without recuperator at different exhaust temperature is shown in Figure 8. With evaporate pressure fixed at 3 MPa, the exergy efficiency of all systems increases as exhaust temperature increases. At middle or high conditions, exhaust temperature of conventional diesel engines is above 350°C. In this temperature range, ORC system with ethanol, cyclopentane, and cyclohexane all benefit from the large expansion ratio, and ethanol system has the highest ORC system exergy efficiency of 24.5% at 350°C. However, at lower exhaust temperature, temperature difference within the evaporator will inevitably be smaller; the three systems with high evaporate temperature, though retained the higher thermal efficiencies, cannot achieve complete heat exchanging within the evaporator, due to design limita- Figure 5: System optimization process. tion. For cyclohexane, with the highest evaporate temperature of the five working fluids, the decrease at low temperature is most significant; the exergy efficiency at 300°C (8.6%) is only 37.8% of the exergy efficiency at 360°C (22.9%).R245fasystemandR1233zd system are less affected by evaporator design limitation at low exhaust temperature. However, both systems have significantly smaller exergy efficiency at high temperature, mainly due to the high condensing pressure hindering the expansion process. The exergy efficiency of ORC system with recuperator at different exhaust temperature is shown in Figure 9. The recuperate rate is fixed at 0.5. With exhaust temperature above 350°C, the application of recuperator increased the exergy efficiency of all five systems, yet to ethanol, the only wet fluid of the five, the benefit is rather limited. The exergy efficiency of cyclopentane system surpassed Figure 6: Thermal efficiencies of ORC systems with different working ethanol system after the application of recuperator, and fluids. the maximum exergy efficiency, 27.8%, occurred at 350°C. As the recuperator increased the working fluid inlet tem- the largest; recuperator will be less effective in the ethanol perature of the evaporator, the temperature difference system. will inevitably decrease; the exergy efficiency decrease The energy flow and mass balances of the cyclopen- of systems with the three high evaporate temperature tane ORC system are given in Figure 7. The configuration fluid is more drastic. At 300°C, the exergy efficiency of system units is given in Table 4. As shown in Table 4, of the recuperated cyclopentane ORC system (21.9%) the exergy loss of the evaporator, 45.4%, is much higher reduced to only 79.0% of the maximum efficiency, and than other system components. While the recuperator, the exergy efficiency increase compared to system without Diesel engine waste heat recovery system comprehensive optimization  337

Figure 7: Energy ﬂow of the cyclopentane ORC system.

Table 4: Conﬁguration of system units

System unit (%) Evaporator Expander Condenser Pump Recuperator

Thermal eﬃciency 90 65 — 80 90 Heat loss 10 —— —1.2 Exergy loss 45.4 8.6 14.5 1.3 2.5

Figure 8: ORC system (without recuperator) efficiency at different Figure 9: ORC system (with recuperator) efficiency at different exhaust temperature. exhaust temperature. recuperator is below 0.1%. The output of R245fa system requires explanation. The application of recuperator will fl and R1233zd system also significantly benefited from the increase the working uid temperature at the evaporator recuperator, while the low evaporate temperature of the inlet, thus the evaporator, especially the preheating section, two is advantageous at both low exhaust temperature and needs comprehensive analysis along with the recuperator. increased recuperate rate, though the exergy efficiency at A certain heat exchanging core is used in both the high exhaust temperature is still rather low. preheating section of the evaporator and the recuperator, to evaluate the effect of the recuperator and the evaporator on the ORC system exergy efficiency. The preheating section and the recuperator of the cyclopentane 3.3 System complicity analysis ORC system both have fixed heat exchanging cores, rather than achieving a preset pinch point temperature Before the detailed analysis of ORC system efficiency and difference or recuperate rate. The simulation result is complicity, the arrangement of heat exchangers also shown in Figure 10, with the amount of heat exchanging 338  Da Li et al.

priority from the recuperator to the preheating section is switched, the optimized scheme with seven heat exchanging cores in the preheating section of the evaporator and three heat exchanging cores in the recuperator increased the system exergy efficiency by 14.59%, which is 2.06 times of the comparison scheme. Therefore, to optimize the heat exchangers of ORC system with recuperator, achieve higher exergy efficiency and power output with same or similar system complicity and cost; the priority of the preheating section of the evaporator should be higher than the recuperator. The system exergy efficiency (light grey) and the total heat exchanging area of the evaporator and the recuperator (dark grey) are shown in Figure 11. For ORC systems without recuperator, the ethanol system has the Figure 10: Effect of heat exchanger optimization priority on ORC ffi - system efficiency. highest exergy e ciency of 24.1%, while the cyclopen tane system achieved 96.4% efficiency of the ethanol cores (E) in the preheating section of the evaporator and system, with only 85.2% of the heat exchanging area. the amount of heat exchanging cores (R) of the recup- The R1233zd system also achieved 67.1% efficiency of erator varies in each points. Of the simple cyclopentane the ethanol system with only 58.5% of the heat exchan- ORC system without recuperator, the amount of heat ging area, which is again better than the R245fa system, exchanging cores in the preheating section of the eva- yet the power output will be rather small. After the appli- porator is 3. On this basis, simply increase the core cation of recuperator, cyclopentane system still requires amount of the recuperator, although the exergy efficiency only 98.7% heat exchanging area of the ethanol system, indeed increased accordingly, yet as the temperature while the exergy efficiency increased by 18.9%; therefore difference within the recuperator gradually decreases, the exergy efficiency, 27.6%, is also the highest of the five. the thermal efficiency increase brought by additional The exergy efficiency increase of recuperated ethanol cores gradually decreases, and as the temperature of system, 9.0%, is the lowest of the five. In terms of both the working fluid at the evaporator inlet increases, the complicity and efficiency, cyclohexane has no advantage temperature difference in the preheating section decreases, to either ethanol or cyclopentane. hindering the waste heat recovery of the evaporator, thus With recuperate rate at 0.5, complicity of all systems the total increase of exergy efficiency is relatively limited. increased significantly as the heat exchanging area When the total number of cores is 10, the exergy effi- increased, which is more significant for the R1233zd ciency is only increased by 7.09%. If the optimization system (574.7%) and the R245fa system (562.6%). The

Figure 11: Comparison of simple ORC system with and without recuperator. Diesel engine waste heat recovery system comprehensive optimization  339 increase of the cyclopentane system (197.7%), though compared to complicity increase. The recuperate rate of much smaller, is still rather large, compared to the exergy ORC system requires further investigation. eﬃciency increase of only 18.9%. The recuperate rate can be further investigated and optimized, to achieve higher system output without the need of complex heat Acknowledgement: I appreciate the reviewers for their exchangers. constructive and detailed critique contributed to the quality of this paper. And I am also thankful to the editors for their kind and helpful supports.

4 Conclusion Funding information: This work was supported by the National Key Research and Development Project of China This paper constructed an ORC system simulation model, [grant numbers 2017YFB0103504]. and five working fluids were selected for comparison as the working fluid of a simple diesel engine ORC system. Conflicts of interest: The authors declare that they have The quality of heat source, the quality of evaporator, the no conflicts of interest to report regarding the present system output, and the system complicity were taken as study. variables for comparison. Of the five working fluids: (1) For systems without recuperator, ethanol system has Data availability statement: The datasets generated and the best system output of the five in a wide operation analyzed during the current study are available from the temper range. However, at low heat source tempera- corresponding authors on reasonable request. ture, the output of cyclopentane system is higher than the ethanol system. Also, as wet fluid, the recuperator is less effective for ethanol system. Cyclopentane and cyclohexane have similar parameters, yet at most References conditions considered in this paper, the performance - of the cyclopentane system is better than the cyclo [1] Shu G, Yu G, Tian H, Wei H, Liang X, Huang Z. Multi-approach hexane system. The cyclopentane system has the best evaluations of a cascade-Organic Rankine Cycle (C-ORC) exergy efficiency after the application of recuperator. system driven by diesel engine waste heat: Part The system output of the R1233zd system is better A – Thermodynamic evaluations. Energy Convers Manag. – than the R245fa system, and both systems have better 2016;108:579 95. doi: 10.1016/j.enconman.2015.10.084. [ ] ffi- 2 Mehrdad S, Dadsetani R, Amiriyoon A, Leon A, Safaei M, performance at low temperature. Yet the exergy e Goodarzi M. Exergo-economic optimization of organic rankine ciency is still limited compared to either the simple cycle for saving of thermal energy in a sample power plant by ethanol system or the recuperate cyclopentane system, using of strength pareto evolutionary algorithm II. Processes. and both systems have the disadvantage of high com- 2020;8(3). doi: 10.3390/pr8030264. [ ] plicity after the application of recuperator. The advan- 3 Sheikh R, Gholampour S, Fallahsohi H, Goodarzi M, Taheri M, Bagheri M. Improving the efficiency of an exhaust thermo- tage of low evaporate temperature can be better utilized electric generator based on changes in the baffle distribution for low quality waste heat recovery. of the heat exchanger. J Therm Anal Calorim. (2) In the exhaust temperature range of 300–500°C, 2020;143:523–33. doi: 10.1007/s10973-019-09253-x. ethanol and cyclopentane have better performance [4] Preißinger M, Schwöbel JAH, Klamt A, Brüggemann D. Multi- than the other three. Without recuperator, the ethanol criteria evaluation of several million working fluids for waste system has the highest exergy efficiency of 24.1%, heat recovery by means of Organic Rankine Cycle in passenger - – ffi- cars and heavy duty trucks. Appl Energy. 2017;206:887 99. while the cyclopentane system achieved 96.4% e doi: 10.1016/j.apenergy.2017.08.212. ciency of the ethanol system, with only 85.2% of the [5] Amicabile S, Lee Jl, Kum D. A comprehensive design metho- heat exchanging area. After the application of recup- dology of organic Rankine cycles for the waste heat recovery of erator, cyclopentane system has the highest exergy automotive heavy-duty diesel engines. Appl Therm Eng. – efficiency of 27.6%, while requires only 98.7% heat 2015;87:574 85. doi: 10.1016/j.applthermaleng.2015.04.034. [6] Yang J, Ye Z, Yu B, Ouyang H, Chen J. Simultaneous experi- exchanging area of the ethanol system. mental comparison of low-GWP refrigerants as drop-in repla- ( ) 3 At recuperate rate of 0.5, the system complicity in terms cements to R245fa for Organic Rankine cycle application: of heat exchanging area of all five system increased R1234ze(Z), R1233zd(E), and R1336mzz(E). Energy. significantly, while the power output increase is limited 2019;173:721–31. doi: 10.1016/j.energy.2019.02.054. 340  Da Li et al.

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