Improving Performance of Cold-Chain Insulated Container with Phase Change Material: an Experimental Investigation

applied sciences

Article Improving Performance of Cold-Chain Insulated Container with Phase Change Material: An Experimental Investigation

Li Huang 1,* and Udo Piontek 2

1 Faculty of Architecture, Civil Engineering College, Ningbo University, Fenghua Street 818, Ningbo 315211, China 2 Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT, Osterfelder Strasse 3, Oberhausen 46047, Germany; [email protected] * Correspondence: [email protected]; Tel.: +86-574-8760-9510; Fax: +86-571-8760-9510

Received: 26 October 2017; Accepted: 27 November 2017; Published: 11 December 2017

Abstract: The cold-chain transportation is an important means to ensure the drug and food safety. An cold-chain insulated container incorporating with Phase Change Material (PCM) has been developed for a temperature-controlled transportation in the range of 2~8 ◦C. The container conﬁguration and different preconditioning methods have been determined to realize a 72-h transportation under extremely high, extremely low, and alternating temperature conditions. The experimental results showed that the temperature-controlled time was extended from 1 h to more than 80 h and the internal temperature maintained at 4~5 ◦C by using a PCM with a melting/freezing point of 5 ◦C, while the container presented a subcooling effect in a range of −1~2 ◦C when using water as PCM. The experimental values of the temperature-controlled time agreed well with the theoretical values.

Keywords: phase change materials (PCMs); insulated container; cold chain; temperature-controlled time; thermal performance; preconditioning; drugs and food safety

1. Introduction Drug and food safety have become more important issues with a growing population and demand in recent years. In order to extend and ensure the shelf-life of pharmaceutical drugs or food, it is very important to keep their temperature at a given range through the storage and transportation processes. Such a temperature-controlled supply chain is called cold chain. Large quantities of drugs or food are normally transported by refrigerated trucks, while small quantities are delivered by containers. There are at least 1 million refrigerated road vehicles and 400,000 refrigerated containers worldwide [1]. They run on a vapor compressor that is driven by electric or fuel energy, and release amounts of greenhouse gas. It was reported that the cold chain is responsible for approximately 2.5% of global greenhouse gas emissions when considering both direct and indirect effects [2]. Thermal energy storage based on phase change materials (PCMs) is an advanced energy technology that has recently attracted increasing interest in cold-chain systems. PCMs are able to absorb or release amounts of thermal energy during the phase transition process, maintaining the internal temperature in an acceptable range. Many studies have indicated that the energy savings can be achieved by utilizing PCMs in cold-chain systems. For example, Ahmed et al. added PCM into the insulation layer of a refrigerated truck trailer. The inclusion of the parafﬁn-based PCM in the standard trailer walls was studied as a heat transfer reduction technology. An average reduction of 16.3% in total heat transfer from the exterior to the refrigerated truck was achieved by adding PCM to the insulation foam of the trailer walls [3].

Appl. Sci. 2017, 7, 1288; doi:10.3390/app7121288 www.mdpi.com/journal/applsci Appl. Sci. 2017, 7, 1288 2 of 12

Liu et al. developed an innovative refrigeration system incorporating PCM to maintain refrigerated trucks at the desired thermal conditions. The PCM storage tank was charged by a refrigeration unit when stationary and provides cooling when in service. An analysis showed that delivery of refrigerated products can be made with a PCM system having a weight that is comparable to that of an on board conventional refrigeration system, with less than half of the energy cost [4]. Fioretti et al. integrated an external PCM layer with a refrigerated container envelop to reduce and displace the heat flux phase caused by the external climatic conditions. It was found that a PCM-added layer helps to store the incoming heat load at a constant temperature during the melting phase. A reduction on peak heat transfer rate of 5.55% and 8.57% during two experimental days was observed in comparison with the reference [5]. Copertaro et al. presented the first numerical investigation of the energy behavior of a refrigerated container envelope that was fitted with PCMs. An organic PCM named RT35HC manufactured by Rubitherm® Technologies GmbH in Berlin in Germany, which has a melting peak temperature of 35 ◦C, was found to perform best on a typical summer day in Milan, Ancona, and Palemo. It was observed that the heat load peak was reduced by 20% and the peak was delayed for 2~3 h [6]. The above-mentioned studies focus on the trucks or containers having a refrigeration system. However, insulated containers integrated with PCMs are also an attractive alternative for cold-chain systems. Such containers do not use any conventional refrigerators, but a thermal energy storage of PCMs to control the internal temperature. The PCMs are normally preconditioned when stationary and provide cooling or heating when in service. The temperature-controlled time is mostly within 48 h due to the limited thermal capacity of PCMs and the poor insulation of the containers. For example, the company EMBALL’ISO in Saint-Georges-de-Reneins in France provides a packaging comprising a cardboard box, six vacuum insulation panels, and six PCM briquettes [7]. This packaging is normally used for an isothermal transportation up to 48 h at extreme temperatures. In China, it usually takes two to three days for the drugs or food transportation between cities and the weather conditions could be very different in destination and departure sites. In order to meet this challenge, an insulated container with PCM panels has been developed for a 72-h transportation in the range of 2~8 ◦C, which is the most common temperature range for cold-chain systems. Different preconditioning methods have been determined for the application under various temperature conditions. The thermal performance of the container without PCM and with different PCMs have been experimentally investigated and compared with the results being theoretically calculated.

2. Materials and Methods

2.1. Conﬁguration of Cold-Chain Insulated Container As shown in Figure1, the cold-chain insulated container is comprised of an insulator base, an insulator lid, and double-layer panels ﬁlled with PCM. The seamless and leak-proof insulator base was made with all-in-one foaming technology and has a high insulation performance. The external dimension of the base is 540 × 420 × 480 mm and the internal 420 × 300 × 360 mm. The insulation material has a sandwich structure, which consists of 10 mm polyurethane (PU), 10 mm vacuum insulation panel (VIP), and 10 mm polyurethane (PU), namely the VIP layer is enclosed by PU material. The thermal conductivity of the PU and VIP are 0.022 W/(m·K) and 0.005 W/(m·K), respectively. Two layers of the PCM panels are inserted into the insulator base. The panels are made of high-density polyethylene (HDPE) and have an external dimension of 350 × 290 × 15 mm. Different preconditioning methods have been determined with the construction of the double-layer PCM panels, which contributes to a temperature-controlled transportation more than 72 h both at extreme temperatures and at alternating temperature. Water and an alkane mixture named OP5E manufactured by Ruhr New Material Technology Co., Ltd. in Hangzhou in China have been used as PCM in this paper. Their phase change temperature and enthalpy were analyzed with a three-layer calorimeter. Figures2 and3 present the stored heat of water Appl. Sci. 2017, 7, 1288 3 of 13

Water and an alkane mixture named OP5E manufactured by Ruhr New Material Technology Appl.Co., Sci. Ltd.2017, 7in, 1288 Hangzhou in China have been used as PCM in this paper. Their phase change3 of 12 temperature and enthalpy were analyzed with a three-layer calorimeter. Figures 2 and 3 present the andstored of OP5E heat as of a functionwater and of of temperature OP5E as a in function the case of of temperature heating/cooling in the respectively. case of heating/cooling The bars in the respectively. The bars in the figures display the partial enthalpy of the material in a temperature ﬁgures display the partial enthalpy of the material in a temperature interval of 1 K. The temperature, interval of 1 K. The temperature, at which the maximal partial enthalpy appears, corresponds to the at which the maximal partial enthalpy appears, corresponds to the melting/freezing point of the melting/freezing point of the material. From Figure 2 it can be seen that water has a material. From Figure2 it can be seen that water has a melting/freezing peak at 0 ◦C and the total melting/freezing peak at 0 °C and the total enthalpy is 340 kJ/kg between −2 °C and 4 °C, while enthalpy is 340 kJ/kg between −2 ◦C and 4 ◦C, while OP5E has a melting/freezing temperature at OP5E◦ has a melting/freezing temperature at 5~6 °C, and ◦the total enthalpy◦ is 235 kJ/kg between 2 °C 5~6andC, 8 and°C (see the Figure total enthalpy 3). Their is technical 235 kJ/kg paramete betweenrs and 2 C the and total 8 Cmass (see used Figure in 3the). Theircontainer technical are parametersgiven in Table and the1. The total enthalpy mass used and the in the total container mass of water are given and inOP5E Table were1. The used enthalpy for the heat and transfer the total masscalculation of water in and Section OP5E 2.2. were used for the heat transfer calculation in Section 2.2.

Figure 1. Configuration of the cold-chain insulated container with Phase Change Material (PCM). Figure 1. Conﬁguration of the cold-chain insulated container with Phase Change Material (PCM). Appl. Sci. 2017, 7, 1288 4 of 13

300 heat

cool 249 250 219

200

150

100

53 51 50 Partial Partial enthalpy distribution J/g / 20 15 9 9 13 2 7 2 6 2 7 2 6 3 7 3 3 3 4 5 6 4 4 4 3 4 4 4 0 -8-7-6-5-4-3-2-101234567 Temperature / °C

FigureFigure 2.2. Partial enthalpy enthalpy dist distributionribution of of water. water.

140 heat 122 120 cool 95 100

80 70

40 30 29 18 21 20 8 8 13 22 22 34 34 5 2 51 32 11 23 32 24 Partial enthalpyPartial distribution kJ/kg / 0 -2-1012345678910111213 Temperature / ℃

Figure 3. Partial enthalpy distribution of OP5E. OP5E: an alkane mixture manufactured by Ruhr New Material Technology Co.,Ltd. in Hangzhou in China.

Table 1. Technical parameters of water and OP5E. OP5E: an alkane mixture manufactured by Ruhr New Material Technology Co., Ltd. in Hangzhou in China.

Parameter Water OP5E Specific heat capacity/kJ/(kg·K) 4.2 2.0 Solid density (−15 °C)/kg/L 0.996 0.88 Liquid density (20 °C)/kg/L 0.998 0.76 Thermal conductivity liquid/W/(m·K) 0.56 0.2 Volume expansion/% 0.3 13 Total mass used in the container (kg) 10.87 8.28

2.2. Heat Transfer Calculation The following assumptions were made for the heat transfer calculations: (1) the ambient temperature and the air temperature inside the container distribute homogeneously; and, (2) the PCM’s temperature keeps constant and distributes homogeneously during the phase transition process. Figure 4 shows the heat transfer schema of the container at a high ambient temperature as an example. Appl. Sci. 2017, 7, 1288 4 of 13

300 heat

cool 249 250 219

200

150

100

53 51 50 Partial Partial enthalpy distribution J/g / 20 15 9 9 13 2 7 2 6 2 7 2 6 3 7 3 3 3 4 5 6 4 4 4 3 4 4 4 0 -8-7-6-5-4-3-2-101234567 Temperature / °C

Appl. Sci. 2017, 7, 1288 4 of 12 Figure 2. Partial enthalpy distribution of water.

140 heat 122 120 cool 95 100

80 70

40 30 29 18 21 20 8 8 13 22 22 34 34 5 2 51 32 11 23 32 24 Partial enthalpyPartial distribution kJ/kg / 0 -2-1012345678910111213 Temperature / ℃

FigureFigure 3. 3.Partial Partial enthalpy enthalpy distribution distribution of of OP5E. OP5E. OP5E: OP5E an: an alkane alkane mixture mixture manufactured manufactured by by Ruhr Ruhr New MaterialNew Material Technology Technology Co.,Ltd. Co.,Ltd. in Hangzhou in Hangzhou in China. in China.

TableTable 1. 1.Technical Technical parameters parameters ofof waterwater and OP5E. OP5E OP5E:: an an alkane alkane mixture mixture manufactured manufactured by byRuhr Ruhr NewNew Material Material Technology Technology Co.,Co., Ltd.Ltd. in Hangzhou in in China. China. Parameter Water OP5E Parameter Water OP5E Specific heat capacity/kJ/(kg·K) 4.2 2.0 · Speciﬁc heatSolid capacity/kJ/(kg density (−15 °C)/kg/LK) 0.996 4.2 0.88 2.0 Solid density (−15 ◦C)/kg/L 0.996 0.88 Liquid density (20 °C)/kg/L 0.998 0.76 Liquid density (20 ◦C)/kg/L 0.998 0.76 ThermalThermal conductivity conductivity liquid/W/(m liquid/W/(m·K)·K) 0.56 0.2 0.2 VolumeVolume expansion/% expansion/% 0.3 13 13 TotalTotal mass usedmass inused the containerin the container (kg) (kg) 10.87 8.28 8.28

2.2.2.2. Heat Heat Transfer Transfer Calculation Calculation TheThe following following assumptions assumptions werewere made for for the the heat heat transfer transfer calculations: calculations: (1) the ambient temperature and the air temperature inside the container distribute (1) the ambient temperature and the air temperature inside the container distribute homogeneously; and, (2) homogeneously;the PCM’s temperature and, keeps constant and distributes homogeneously during the phase (2) thetransition PCM’s process. temperature keeps constant and distributes homogeneously during the phase transition process. Figure 4 shows the heat transfer schema of the container at a high ambient temperature as an example.Figure 4 shows the heat transfer schema of the container at a high ambient temperature as anAppl. example. Sci. 2017, 7, 1288 5 of 13

Ta T1

Tb T2

VIP PCM PU Figure 4. Heat transfer schema of the cold-chain insulated container at a high ambient temperature. Figure 4. Heat transfer schema of the cold-chain insulated container at a high ambient temperature. VIP: vacuum insulation panel; PU: polyurethane. VIP: vacuum insulation panel; PU: polyurethane. The average heat transfer area F of the container can be calculated according to Equation (1) as follows: = × F Fa Fb (1) where Fa and Fb are the external and internal area of the container respectively. It was obtained that F = 0.856 m2 by substituting data into Equation (1). The overall heat transfer coefficient K of the container is obtained as follows:

= 1 K δ δ δ 1 + 1 + 2 + 3 + 1 (2) α λ λ λ α 1 1 2 3 2 where α1 and α2 are the heat transfer coefficient of air outside and inside the container. The air flows outside and inside the container can be considered as natural convection since the containers are normally transported in a closed cabin of refrigerated trucks or vans. The coefficient is 7.0~9.3 W/(m2K) for natural convection [8], here α1 = α2 = 8.0 W/(m2K). λ1, λ2 and λ3 are the thermal conductivity of PU, VIP, and PCM, respectively, here λ1 = 0.022 W/(m·K), λ2 = 0.005 W/(m·K), λ3 = 0.2 W/(m·K). δ1, δ2 and δ3 are the thickness of PU, VIP, and PCM, respectively. Heat is transferred from the ambient into the container or conversely by conduction and convection. The heat flow q1 can be estimated with the overall heat transfer coefficient K, the average heat transfer area F, the ambient temperature Ta and the air temperature Tb inside the container as follows: = × × − q1 K F (Ta Tb ) (3)

Tb is taken as the maximum temperature allowed in the container under extremely high temperature condition (Tb,max = 8 °C) or the minimum temperature allowed under extremely low temperature condition (Tb,min = 2 °C). The heat flow q2 caused by air leakage is obtained according to Equation (4): = β × q2 q1 (4) where β is the additional thermal load factor, here β = 0.2 .

The total heat flow q is the sum of the heat flow q1 and q2:

q = q1 + q2 (5) The heat capacity ΔH of PCM can be determined as follows: ΔH = m × Δh (6) Appl. Sci. 2017, 7, 1288 5 of 12

The average heat transfer area F of the container can be calculated according to Equation (1) as follows: p F = Fa × Fb (1) where Fa and Fb are the external and internal area of the container respectively. It was obtained that F = 0.856 m2 by substituting data into Equation (1). The overall heat transfer coefficient K of the container is obtained as follows: 1 K = (2) 1 + δ1 + δ2 + δ3 + 1 α1 λ1 λ2 λ3 α2 where α1 and α2 are the heat transfer coefficient of air outside and inside the container. The air flows outside and inside the container can be considered as natural convection since the containers are normally transported in a closed cabin of refrigerated trucks or vans. The coefficient is 7.0~9.3 W/(m2K) 2 for natural convection [8], here α1 = α2 = 8.0 W/(m K). λ1, λ2 and λ3 are the thermal conductivity of PU, VIP, and PCM, respectively, here λ1 = 0.022 W/(m·K), λ2 = 0.005 W/(m·K), λ3 = 0.2 W/(m·K). δ1, δ2 and δ3 are the thickness of PU, VIP, and PCM, respectively. Heat is transferred from the ambient into the container or conversely by conduction and convection. The heat flow q1 can be estimated with the overall heat transfer coefficient K, the average heat transfer area F, the ambient temperature Ta and the air temperature Tb inside the container as follows: q1 = K × F × (Ta − Tb) (3)

Tb is taken as the maximum temperature allowed in the container under extremely high ◦ temperature condition (Tb,max = 8 C) or the minimum temperature allowed under extremely low ◦ temperature condition (Tb,min = 2 C). The heat ﬂow q2 caused by air leakage is obtained according to Equation (4):

q2 = β × q1 (4) where β is the additional thermal load factor, here β = 0.2. The total heat ﬂow q is the sum of the heat ﬂow q1 and q2:

q = q1 + q2 (5)

The heat capacity ∆H of PCM can be determined as follows:

∆H = m × ∆h (6) where m is the total mass of PCM and ∆h is the melting/freezing enthalpy of PCM in a given temperature interval. The heat loads that are transferred from the ambient into the container are primarily absorbed by PCM. The air temperature inside the container maintains steady before the PCM are completely melted or frozen. Therefore, the temperature-controlled time t can be estimated with the heat capacity ∆H of PCM and the total heat ﬂow q: ∆H t = (7) q It can be seen that the temperature-controlled time depends on the phase transition temperature range, the melting/freezing enthalpy, and the mass of PCM that is used for the same container.

2.3. Experimental Method and Procedure According to Chinese National Standard “Temperature control facilities of pharmaceutical products cold chain logistics—Speciﬁcation for performance qualiﬁcation”, the container performance Appl. Sci. 2017, 7, 1288 6 of 13 where m is the total mass of PCM and Δh is the melting/freezing enthalpy of PCM in a given temperature interval. The heat loads that are transferred from the ambient into the container are primarily absorbed by PCM. The air temperature inside the container maintains steady before the PCM are completely melted or frozen. Therefore, the temperature-controlled time t can be estimated with the heat capacity ΔH of PCM and the total heat flow q: ΔH t = (7) q

It can be seen that the temperature-controlled time depends on the phase transition temperature range, the melting/freezing enthalpy, and the mass of PCM that is used for the same container.

2.3. Experimental Method and Procedure According to Chinese National Standard “Temperature control facilities of pharmaceutical products cold chain logistics—Specification for performance qualification”, the container performanceAppl. Sci. 2017should, 7, 1288 be determined for a temperature-controlled range between 2 °C and6 of 128 °C under the following conditions: ◦ ◦ (1) undershould extremely be determined high for temperature a temperature-controlled condition, th rangee ambient between temperature 2 C and 8 isC set under at 35 the ± following2 °C; conditions: (2) under extremely low temperature condition, the ambient temperature is set at −20 ± 2 °C; and, ◦ (3) under(1) under alternating extremely temperature high temperature condition, condition, the ambient the ambient temperature temperature is is set set at 3535± ±2 2 C;°C for the ◦ first(2) halfunder of the extremely time and low − temperature20 ± 2 °C for condition, the second the half ambient of the temperature time. is set at −20 ± 2 C; and, (3) under alternating temperature condition, the ambient temperature is set at 35 ± 2 ◦C for the first A temperature-controlledhalf of the time and −20 chamber± 2 ◦C for was the secondused to half simulate of the time. the above-mentioned temperature conditions. Eight temperature sensors were put inside the container and one for the ambient, as A temperature-controlled chamber was used to simulate the above-mentioned temperature shownconditions. in Figure Eight 5. The temperature time period, sensors in were which put inside one theof containerthe measuring and one forpoints the ambient,firstly reaches as shown the maximumin Figure or minimum5. The time temperature period, in which allowed, one of was the measuring taken as the points temperature-controlled firstly reaches the maximum time of or the container.minimum All of temperature the tests were allowed, repeated was taken three as to the five temperature-controlled times, and the typical time ofresults the container. were presented All of in thisthe paper. tests were repeated three to five times, and the typical results were presented in this paper.

Figure 5. Arrangement of the temperature measuring points. Figure 5. Arrangement of the temperature measuring points. The PCM could be either solid or liquid at the initial state according to the service temperature Thecondition PCM could to take be full either advantage solid ofor the liquid phase at transition the initial of state the PCM. according Therefore, to the the service PCM panels temperature were conditionpreconditioned to take full to adaptadvantage to the threeof the temperature phase transition conditions. of the PCM. Therefore, the PCM panels were preconditioned to adapt to the three temperature conditions. 2.3.1. Preconditioning for the Use at Extremely High Temperature The PCM should be fully frozen at the initial state for the application under extremely high temperature condition. Furthermore, the temperature of the PCM panels should not be too low to subcool or freeze drugs or foods. The preconditioning was carried out as follows: (1) place twelve PCM panels in a −20 ◦C freezer or below for a minimum of 48 h to ensure PCM was fully frozen; (2) place all frozen water panels in a 4~5 ◦C cooler for 60 h until the surface temperature reaches 0 ◦C, or place all frozen OP5E panels in a 4~5 ◦C cooler for 60 h until the surface temperature reaches 5 ◦C; (3) insert the PCM panels and temperature sensors into the container; (4) place the container and a temperature sensor into the temperature-controlled chamber; and, (5) set the chamber temperature at 35 ◦C and start the test.

2.3.2. Preconditioning for the Use at Extremely Low Temperature The PCM should be fully melted at the initial state for the application under a extremely low temperature condition. Furthermore, the temperature of the PCM panels should not be too high to overheat drugs or foods. The preconditioning was carried out as follows: Appl. Sci. 2017, 7, 1288 7 of 12

(1) place twelve PCM panels and the container in a 5~6 ◦C cooler for 8 h; (2) insert the PCM panels and temperature sensors into the container; and, (3) place the container and a temperature sensor into the temperature-controlled chamber. (4) set the chamber temperature at −20 ◦C and start the test.

2.3.3. Preconditioning for the Use at Alternating Temperature The PCM should be half melted and half frozen at the initial state for the utilization under alternating temperature condition. It takes advantage of the construction of the double-layer panels in this case. Therefore, one layer of PCM panels was fully frozen and the other was kept in the liquid state. The preconditioning was carried out as follows:

(1) place six PCM panels in a −20 ◦C freezer or below for 30 h; (2) place six PCM panels in a 5~6 ◦C cooler for 8 h; (3) insert the six frozen PCM panels into the container near to the drug or food packing and the other six cooled panels near to the insulator base. (4) insert the temperature sensors into the container; and, (5) place the container and a temperature sensor into the temperature-controlled chamber. (6) set the chamber temperature at 35 ◦C for the ﬁrst half of the time and then −20 ◦C for the next half of the time and start the test.

3. Results and Discussion

3.1. Performance under Extremely High Temperature Condition Figures6–8 present the ambient temperature and air temperature inside the container without PCM, with water as PCM and with OP5E as PCM under extremely high temperature condition, respectively. It can be seen that the temperature-controlled time was less than 1 h (about 54 min) by using the container without PCM. The performance was distinctly improved when incorporating a PCM into the container. However, the most measuring points inside the container showed a temperature at 1~2 ◦C for the first 70 h by applying water as PCM. This would cause a subcooling of drugs or food during the transportation. On the other hand, the air temperature inside the container was controlled in the range of 2~8 ◦C for 81 h by using OP5E as PCM. It kept at 4~5 ◦C for most of the time, which corresponds to the melting/freezing peak temperature of OP5E. In all three cases, the measuring point, which firstly exceeded the maximum temperature of 8 ◦C, was one of the points in the corner of the container, namely T1, T2, T3, or T4. The reason was that the tightness between the insulator base and lid is normally worse in the corner than elsewhere. Consequently, the heat transfer was intensified in the corner by the air leakage. Furthermore, it was observed that the air temperature in the container decreased firstly and then went up. The reason was that the container was not pre-cooled before the test because of the limited operation condition. The air in the container had the room temperature at the beginning and was firstly cooled when inserting the frozen PCM panels into the container. The air temperature began to rise when heat was transferred from the ambient to the inside of the container. Appl.Appl. Sci.Sci. 20172017,, 77,, 12881288 88 ofof 1313 pointspoints inin thethe cornercorner ofof thethe contcontainer,ainer, namelynamely T1,T1, T2,T2, T3,T3, oror T4.T4. TheThe reasonreason waswas thatthat thethe tightnesstightness betweenbetween thethe insulatorinsulator basebase andand lidlid isis normallynormally woworserse inin thethe cornercorner thanthan elsewhere.elsewhere. Consequently,Consequently, thethe heatheat transfertransfer waswas intensifiedintensified inin thethe cornercorner byby thethe airair leakage.leakage. Furthermore,Furthermore, itit waswas observedobserved thatthat thethe airair temperaturetemperature inin thethe contaicontainerner decreaseddecreased firstlyfirstly andand thenthen wewentnt up.up. TheThe reasonreason waswas thatthat thethe containercontainer waswas notnot pre-cooledpre-cooled beforebefore thethe testtest becausbecausee ofof thethe limitedlimited operationoperation condition.condition. TheThe airair inin thethe containercontainer hadhad thethe roomroom temperaturetemperature atat thethe begibeginningnning andand waswas firstlyfirstly cooledcooled whenwhen insertinginserting thethe Appl.frozenfrozen Sci. PCMPCM2017, 7 panels,panels 1288 intointo thethe container.container. TheThe airair temptemperatureerature beganbegan toto riserise whenwhen heatheat waswas transferredtransferred8 of 12 fromfrom thethe ambientambient toto thethe insideinside ofof thethe container.container.

4040 T1T1 3636 T2T2 T3T3 3232 T4T4 28 T5

C 28 T5 ° C ° T6T6 2424 T7T7 20 T8

20 T8 ambientambient 1616 12

Temperature / / Temperature 12 Temperature / / Temperature 88 44 00 00 6 6 12 12 18 18 24 24 30 30 36 36 42 42 48 48 54 54 60 60 66 66 72 72 TimeTime // minmin tt == 54min54min

FigureFigureFigure 6.6.6. TheTheThe ambientambientambient temperaturetemperaturetemperature andandand airairair temperaturetemperaturtemperaturee insideinsideinside thethethe containercontainercontainer withoutwithoutwithout PCMPCMPCM underunderunder extremelyextremelyextremely high highhigh temperature temperaturetemperature condition. conditcondition.ion. The TheThe shaded shadedshaded part partpart means meansmeans the thethe controlled controlledcontrolled temperature temperaturetemperature range rangerange of ofof 2 ◦ to22 toto 8 88C. °C.°C.

3636 T1T1 3232 T2T2 T3T3 2828 T4T4 24 T5 C 24 T5 ° C ° T6T6 2020 T7T7 16 T8

16 T8 ambientambient 1212 8

Temperature / 8 Temperature / 44 00 -4-4 00 6 6 12 12 18 18 24 24 30 30 36 36 42 42 48 48 54 54 60 60 66 66 72 72 78 78 Time / h Time / h Figure 7. The ambient temperature and air temperature inside the container with water as PCM FigureFigure 7.7.The The ambient ambient temperature temperature and and air air temperature temperatur insidee inside the containerthe container with waterwith water as PCM as under PCM under extremely high temperature condition. extremelyunder extremely high temperature high temperature condition. condition. Appl. Sci. 2017, 7, 1288 9 of 13

40 T1 36 T2 T3 32 T4 28 T5 C ° T6 24 T7 20 T8 ambient 16 12 Temperature / 8 4 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 Time / h t = 81h

FigureFigure 8. 8.The The ambient ambient temperature temperature and and air temperatureair temperatur insidee inside the container the container with OP5E with asOP5E PCM as under PCM extremelyunder extremely high temperature high temperature condition. condition.

3.2. Performance under Extremely Low Temperature Condition Figures 9–11 present the ambient temperature and air temperature is inside the container without PCM, with water as PCM, and with OP5E as PCM under extremely low temperature conditions, respectively. It was observed that the temperature-controlled time was about 1 h (62 min) by using the container without PCM. This time was extended to 10 h when using water as PCM and to 102 h when using OP5E as PCM. The air temperature in the container dropped swiftly to −6 °C and rose to −1~−2 °C by applying water. This phenomenon could be caused by the subcooling of water. The nucleation of water did not occur until the air temperature in the container decreased to −6 °C. The air temperature increased when water began to freeze and amounts of heat were released during the liquid-solid phase transition. The temperature inside the container kept constant at −1~−2 °C until the nucleation process ended. On the other hand, the air temperature in the container maintained at 4~5 °C for the first 60 h and then decreased slowly to 2 °C after 102 h when using OP5E as PCM. In all three cases, the measuring point, which firstly exceeded the minimum temperature of 2 °C, was also one of the points in the corner as in the case under extremely high temperature condition.

8 T1 T2 4 T3 T4 0 T5 C ° T6 -4 T7 T8

-8 ambient -12

Temperature / Temperature -16

-20

-24 0 6 12 18 24 30 36 42 48 54 60 66 72 Time / min t = 62min

Figure 9. The ambient temperature and air temperature inside the container without PCM under extremely low temperature condition. Appl. Sci. 2017, 7, 1288 9 of 13

40 T1 36 T2 T3 32 T4 28 T5 C ° T6 24 T7 20 T8 ambient 16 12 Temperature / 8 4 0 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 Time / h t = 81h

Figure 8. The ambient temperature and air temperature inside the container with OP5E as PCM under extremely high temperature condition. Appl. Sci. 2017, 7, 1288 9 of 12 3.2. Performance under Extremely Low Temperature Condition 3.2. PerformanceFigures 9–11 under present Extremely the Lowambient Temperature temperature Condition and air temperature is inside the container withoutFigures PCM,9–11 withpresent water the ambientas PCM, temperature and with OP5E and air as temperature PCM under is insideextremely the container low temperature without PCM,conditions, with waterrespectively. as PCM, It andwas withobserved OP5E that asPCM the temperature-controlled under extremely low temperaturetime was about conditions, 1 h (62 respectively.min) by using It wasthe observedcontainer thatwithout the temperature-controlled PCM. This time was extended time was to about 10 h 1when h (62 using min)by water using as thePCM container and to 102 without h when PCM. using This OP5E time as was PCM. extended The air to temperature 10 h when using in the water container as PCM dropped and to swiftly 102 h whento −6 using°C and OP5E rose as to PCM. −1~ The−2 °C air by temperature applying inwater. the containerThis phenomenon dropped swiftly could tobe− caused6 ◦C and by rose the tosubcooling−1~−2 ◦C of by water. applying The nu water.cleation This of phenomenon water did not could occur be until caused the byair thetemperature subcooling in of the water. container The nucleationdecreased ofto water−6 °C. didThe not air occurtemperature until the increased air temperature when water in the began container to freeze decreased and amounts to −6 ◦C. of Theheat airwere temperature released during increased the when liquid-solid water began phase to tran freezesition. and The amounts temperature of heat wereinside released the container during kept the liquid-solidconstant at phase−1~−2 transition.°C until the The nucleation temperature process inside ended. the container On the other kept hand, constant the atair− 1~temperature−2 ◦C until in thethe nucleation container processmaintained ended. at 4~5 On °C the for other the hand, first 60 the h airand temperature then decreased in the slowly container to 2 maintained°C after 102 at h 4~5when◦C forusing the OP5E ﬁrst 60 as h andPCM. then In decreased all three slowlycases, tothe 2 ◦measuringC after 102 hpoint, when whic usingh OP5Efirstly asexceeded PCM. In allthe threeminimum cases, thetemperature measuring of point, 2 °C, which was also ﬁrstly one exceeded of the thepoints minimum in the temperaturecorner as in of the 2 ◦ C,case was under also oneextremely of the points high temperature in the corner condition. as in the case under extremely high temperature condition.

8 T1 T2 4 T3 T4 0 T5 C ° T6 -4 T7 T8

-8 ambient -12

Temperature / Temperature -16

-20

-24 0 6 12 18 24 30 36 42 48 54 60 66 72 Time / min t = 62min

FigureFigure 9. 9. TheThe ambientambient temperaturetemperature andand airairtemperature temperature insideinside thethe containercontainer withoutwithout PCMPCMunder under Appl. extremelySci.extremely 2017, 7, low1288 low temperature temperature condition. condition. 10 of 13

12 T1 8 T2 T3 4 T4 T5 C

° 0 T6 -4 T7 T8 -8 ambient -12 Temperature / Temperature -16

-20

-24 0 6 12 18 24 30 36 42 48 54 60 66 72 t = 10h Time / h

FigureFigure 10.10.The The ambient ambient temperature temperature and and air air temperature temperatur insidee inside the containerthe container with waterwith water as PCM as under PCM extremelyunder extremely low temperature low temperature condition. condition.

12 T1 8 T2 T3 4 T4 T5

C 0 ° T6 -4 T7 T8 -8 ambient -12

Temperature / Temperature -16

-20

-24 0 102030405060708090100 t = 102h Time / h

Figure 11. The ambient temperature and air temperature inside the container with OP5E as PCM under extremely low temperature condition.

3.3. Performance under Alternating Temperature Condition Figures 12–13 show the ambient temperature and air temperature inside the container with water and with OP5E as PCM under alternating temperature conditions, respectively. The container without PCM was not tested under this condition since the holding time was just one hour at both of the extreme temperatures. The most measuring points in the container indicated a temperature below 2 °C when using water as PCM. The air temperature kept at 0 °C for the first 36 h and at −1 °C for the second 36 h. It may pose a subcooling risk to drugs or food. However, the container incorporated with OP5E maintained a stable internal temperature at 4~5 °C for the first 72 h and dropped to 2 °C after 100 h. Appl. Sci. 2017, 7, 1288 10 of 13

12 T1 8 T2 T3 4 T4 T5 C

° 0 T6 -4 T7 T8 -8 ambient -12 Temperature / Temperature -16

-20

-24 0 6 12 18 24 30 36 42 48 54 60 66 72 t = 10h Time / h

Appl. Sci.Figure2017, 710., 1288 The ambient temperature and air temperature inside the container with water as PCM10 of 12 under extremely low temperature condition.

12 T1 8 T2 T3 4 T4 T5

C 0 ° T6 -4 T7 T8 -8 ambient -12

Temperature / Temperature -16

-20

-24 0 102030405060708090100 t = 102h Time / h

FigureFigure 11. 11.The The ambient ambient temperature temperature and and air temperatureair temperatur insidee inside the container the container with OP5Ewith asOP5E PCM as under PCM extremelyunder extremely low temperature low temperature condition. condition.

3.3.3.3. PerformancePerformance under under Alternating Alternating Temperature Temperature Condition Condition FiguresFigures 12 12–13 and 13show show the the ambient ambient temperature temperature an andd air air temperature temperature inside thethe containercontainer withwith waterwater and and with with OP5E OP5E as as PCM PCM under under alternating alternating temperature temperature conditions, conditions, respectively. respectively. The The container container withoutwithout PCM PCM was was not not tested tested under under this this condition condition since since the the holding holding time time was was just just one one hour hour at bothat both of theof the extreme extreme temperatures. temperatures. The mostThe most measuring measuring points points in the in container the container indicated indicated a temperature a temperature below 2below◦C when 2 °C using when water using as water PCM. as The PCM. air temperature The air temperature kept at 0 ◦keptC for at the 0 °C ﬁrst for 36 the h andfirst at 36− 1h ◦andC for at the−1 second°C for the 36 h.second It may 36 pose h. It a may subcooling pose a risksubcooling to drugs risk or food. to drugs However, or food. the However, container incorporatedthe container withincorporated OP5E maintained with OP5E a stable maintained internal a temperaturestable internal at 4~5temperature◦C for the at ﬁrst 4~5 72 °C h andfor the dropped first 72 to h 2 and◦C afterdroppedAppl. 100Sci. 2017 h. to ,2 7 ,°C 1288 after 100 h. 11 of 13

36 T1 32 T2 28 T3 24 T4 20 T5 C 16 ° T6 12 T7 8 T8

4 ambient 0 -4

Temperature / -8 -12 -16 -20 -24 0 6 12 18 24 30 36 42 48 54 60 66 72 Time / h FigureFigure 12. 12.The The ambient ambient temperature temperature and and air temperatureair temperatur insidee inside the container the container withwater with aswater PCM as under PCM alternatingunder alternating temperature temperature condition. condition.

40 The experimental temperature-controlled36 time of the container with OP5E T1 was compared with that theoretically calculated32 according to the equations in Section 2.2. FromTable T2 2 it can be seen that 28 T3 the deviation was within24 an acceptable range of ±10%. The experiment error T4 mainly resulted from 20 T5 C

the inhomogeneous temperature° 16 distribution inside the container. In most cases, the temperature in 12 T6 the corner ﬁrstly exceeded8 the maximum or minimum temperature that was T8 allowed because of the 4 T9 air leakage. 0 ambient -4 -8

Temperature / Temperature -12 -16 -20 -24 -28 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96102 Time / h t = 100h Figure 13. The ambient temperature and air temperature inside the container with OP5E as PCM under alternating temperature condition.

The experimental temperature-controlled time of the container with OP5E was compared with that theoretically calculated according to the equations in Section 2.2. From Table 2 it can be seen that the deviation was within an acceptable range of ±10%. The experiment error mainly resulted from the inhomogeneous temperature distribution inside the container. In most cases, the temperature in the corner firstly exceeded the maximum or minimum temperature that was allowed because of the air leakage.

Table 2. The experimental and theoretical values of the temperature-controlled time of the container with OP5E as PCM under different temperature conditions.

Maximum or Minimum Temperature-Controlled Time (h) Deviation Ambient Temperature (°C) Temperature Allowed in Experimental Theoretical (%) the Container (°C) 35 8 81 88 −7.95 −20 2 102 108 −5.56 35 °C for the first 48 h and 8 °C for the first 48 h and 100 98 +2.04 −20 °C for rest time 2 °C for the rest time

4. Conclusions A cold-chain insulated container integrated with PCM has been developed for a temperature-controlled transportation in a range of 2~8 °C. A 72-h transportation under various Appl. Sci. 2017, 7, 1288 11 of 13

36 T1 32 T2 28 T3 24 T4 20 T5 C 16 ° T6 12 T7 8 T8

4 ambient 0 -4

Temperature / -8 -12 -16 -20 -24 0 6 12 18 24 30 36 42 48 54 60 66 72 Time / h Figure 12. The ambient temperature and air temperature inside the container with water as PCM Appl. Sci. 2017, 7, 1288 11 of 12 under alternating temperature condition.

40 36 T1 32 T2 28 T3 24 T4 20 T5 C

° 16 12 T6 8 T8 4 T9

0 ambient -4 -8

Temperature / Temperature -12 -16 -20 -24 -28 0 6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96102 Time / h t = 100h

Figure 13.13. TheThe ambientambient temperature temperature and and air air temperature temperatur insidee inside the containerthe container with with OP5E OP5E as PCM as underPCM underalternating alternating temperature temperature condition. condition.

TableThe experimental 2. The experimental temperature-controlled and theoretical values time of theof the temperature-controlled container with OP5E time was of the compared container with that theoreticallywith OP5E as PCMcalculated under differentaccording temperature to the equati conditions.ons in Section 2.2. From Table 2 it can be seen that the deviation was within an acceptable range of ±10%. The experiment error mainly resulted Maximum or Minimum from the inhomogeneous◦ temperature distributionTemperature-Controlled inside the container. Time (h)In most cases, the Ambient Temperature ( C) Temperature Allowed in Deviation (%) temperature in the corner firstly exceeded the maximumExperimental or minimum Theoretical temperature that was the Container (◦C) allowed because35 of the air leakage. 8 81 88 −7.95 −20 2 102 108 −5.56 35 ◦C for the ﬁrst 48 h and 8 ◦C for the ﬁrst 48 h and Table 2. The experimental and theoretical values of the temperature-controlled100 98 time of the container +2.04 −20 ◦C for rest time 2 ◦C for the rest time with OP5E as PCM under different temperature conditions.

Maximum or Minimum Temperature-Controlled Time (h) 4. Conclusions Deviation Ambient Temperature (°C) Temperature Allowed in Experimental Theoretical (%) A cold-chain insulated containerthe Container integrated (°C) with PCM has been developed for a ◦ temperature-controlled35 transportation in8 a range of 2~8 C. A81 72-h transportation88 under−7.95 various temperature conditions−20 has been achieved2 with the high insulation102 performance108 of the container−5.56 and 35 °C for the first 48 h and 8 °C for the first 48 h and the double-layer PCM panels. Different preconditioning methods100 have been determined98 to+2.04 take full advantage−20 °C of for the rest phase time transition 2 °C of for the the PCM. rest time The container performance depends largely on the phase transition temperature range, the 4.melting/freezing Conclusions enthalpy, and the mass of that is PCM used. The container presented a subcooling ◦ effectA in acold-chain range of −1~2insulatedC for 72container h under extremelyintegrated highwith temperature PCM has and been alternating developed temperature for a temperature-controlledconditions by applying watertransportation as PCM. Forin a the range utilization of 2~8 at°C. extremely A 72-h transportation low temperature, under the holdingvarious time was only 10 h. However, the temperature-controlled time was extended from 1 h to more than 80 h by using a PCM with a melting/freezing point at 5 ◦C. Furthermore, the air temperature in the container was maintained at a steady at 4~5 ◦C for most of the time under extremely high, extremely low, and alternating temperature conditions, which would contribute to extending the shelf-life of drugs or food. The experimental values of the temperature-controlled time agreed well with the theoretical values. The results showed that the insulated containers with PCM could be an attractive alternative to refrigerated trucks or containers having a compressor for cold-chain systems.

Acknowledgments: This work was developed within the framework of the research project 2017C34002 “Development of isothermal packaging technology based on phase change materials (PCMs) and intelligent monitoring system” funded by Science Technology Department of Zhejiang Province of China. Author Contributions: Li Huang conceived and designed the experiments; Udo Piontek performed the experiments and analyzed the data; Li Huang contributed materials and wrote the paper. Conﬂicts of Interest: There are no conﬂicts of interest. Appl. Sci. 2017, 7, 1288 12 of 12

Nomenclature

F average heat transfer area of the container, m2 2 Fa external heat transfer area of the container, m 2 Fb internal heat transfer area of the container, m ∆h melting/freezing enthalpy of PCM, kJ/kg ∆H heat capacity of PCM, kJ K overall heat transfer coefficient, W/(m2·K) m total mass of PCM, kg q total heat flow, W q1 heat flow rate, conduction and convection, W q2 heat flow rate, air leakage, W t temperature-controlled time, h ◦ Ta ambient temperature, C ◦ Tb air temperature inside the container, C 2 α1 air heat transfer coefficient outside, W/(m ·K) 2 α2 air heat transfer coefficient inside the container, W/(m ·K) β additional thermal load factor λ1 thermal conductivity of PU, W/(m·K) λ2 thermal conductivity of VIP, W/(m·K) λ3 thermal conductivity of PCM, W/(m·K) δ1 thickness of PU, m δ2 thickness of VIP, m δ3 thickness of PCM, m

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