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1、Crci sjMiikAvailable online at EL5EVTERScienceDirectProcedia Materials Science 4 ( 2014) 389 -394ProcediaMaterials ScienceWW. clbl-vicr. l-UILl-luc-il LC-prCKJCd iil8th International Conference on Porous Metals and Metallic Foams, Metfoam 2013Research progress of phase change materials (PCMs) embedd

2、edwith metal foam (a review)Jianqing Chena,b,*, Donghui yanga, : Jinghua Jianga,d, Aibin Ma a,d, Dan Son捫aCollege of Mechanics and Materials, Hohai University, Nanjing 210098 ChinadNati onal Engin eeri ng Research center of Water Resources Efficie nt Utilizati on and Engin eeri ng Safety, Hohai Uni

3、versity, Nanjing 210098,bDepartment of Materials Scienee and Engineering, University of Delaware, Newark, DE 19716-3106, USAc HoHai Scie nee & Tech no logy Research In stitute Limited Compa ny, Chan gzhou 213164, Jia ngsu, ChinaChinaAbstractLatent heat storage using phase change materials (PCMs) att

4、ract more and more attention in recent years. But most of the PCMs present low thermal conductivity, which decrease the heat transfer rate and leads to low energy utilization efficiency of the storage system. Metal foam with high thermal conductivity, porosity, surface-area to volume ratio and stron

5、g mixing capability is considered as one of the most promising heat transfer enhancement materials. I n this paper, the kinds of metal foam used in PCMs and the efficient thermal conductivity and convection heat transfer of the composite PCMs are reviewed. The research methods used in the investigat

6、ion of conductive, convective and phase change heat transfer process in composite PCMs are also reviewed.? 2S114|PiubesAedhbrs.lsebfehedThisEisseviePLncficcess article under the CC BY-NC-ND licenseof North Carolina State University.Peer-review under responsibility of Scienti? Committee of North Caro

7、lina State UniversityKeywords: phase change materials (PCMs); thermal conductivity; convection; heat transfer1. IntroductionCO2-i nduced global warm ing has become a press ing issue and n eeds to be tackled. Efficie nt applicati on of renewable energy is considered a promising solution to global war

8、ming and energy crisis. Most of the renewable energy is discrete and unstable. Due to extensive requirement in renewable energy applications (such as solarCorrespo nding author. Tel.: +86-25-83786046; fax: +86-25-83786046.E-mail address: qingerchen2211-8128 ? 2014 Published by Elsevier Ltd. This is

9、an open access article under the CC BY-NC-ND license (/licenses/by-nc-nd/3.0/Peer-review under responsibility of Scienti? Committee of North Carolina State Universitydoi: 10.1016/j.mspro.2014.07.579Jianqing Chen et al. / Procedia Materials Science4 (2014) 389 - 394391en ergy

10、), thermal en ergy storage tech ni ques have bee n paid great atte nti on (Zalba et al. (2003) and Agye nim et al. (2010). Late nt heat storage using phase-cha nge-materials (PCMs) is particularly attractive, since it provides ben efits in clude reducti on in temperature variability (thermal in erti

11、a) and high thermal en ergy storage den sity (Hoshi et al. (2005), Tian and Zhao (2013).C andVarious PCMs are gen erally divided into two main groups from their compositi ons (i.e. orga nic and inorganic PCMs) or two categories from their melt ing poi nts (i.e. high-temperature PCMs above 200 one be

12、low 200 C). The high-temperature PCMs can be used in solar power plants, while the low-temperature PCMs are mainly used in waste heat recovery systems and buildings. Organic substances exhibit desirable properties at low temperature applications, such as limited supercooling, no phase segregation an

13、d non-corrosion. I norganic PCMs have large late nt heat and can be used in high temperature en ergy storage. But both of orga nic and ino rga nic PCMs present a low thermal conductivity (Zalba et al. (2003), Olives and Mauran (2001).In order to offset the heat storage/extracti on rate duri ng melt

14、in g/solidificati on cycles, exte nsive in vestigati ons have been carried out to improve the thermal response of PCMs through adding various high thermal conductivity materials (Li et al. (2008). The methods include dispersing high conductivity particles or fibers into PCMs, impreg nat ing a porous

15、 metallic (or graphite) matrix with PCMs.Metal foam is a cellular structure consisting of a solid metal, containing a large volume fraction of gas-filled pores. The pores can be sealed (closed-cell foam) or form an interconnected network (open-cell foam). Due to the high surface-area to volume ratio

16、 and strong mixing capability, high porosity open-cell light-metallic foams have emerged as one of the most promis ing emerg ing materials for thermal en ergy storage (Cui et al. (2010), Hong and Herli ng (2006), and Bugaje (1997).2. PCMs Embedded with Metal Foamheat stIn many applicati ons, thermal

17、 en ergy storage is required to receive, store and subseque ntly release heat. The major disadva ntage of PCMs is their low thermal con ductivities, which dramatically slows the phase cha nge process and causes a wide temperature distributi on with in PCMs. Metal foams prese nts an order of magn itu

18、de higher thermal conductivity than PCMs. At the same time the random internal structure and high porosity of metal foam can enhance and accelerate the phase cha nge process without sig nifica ntly reduc ing PCMs The distribution of foam ligaments in PCMs makes the melting and solidification process

19、es more uniform.There are many kinds of metal foams have been used in phase change materials, such as aluminum foam (Bauer and Wirtz (2000), Chi ntakriin da et al. (2011), Tong et al. (1995), Jia ng et al. (2012), copper foam (Chi et al. (2011), She ng et al. (2013), Zha ng and Yu (2007), and Cui (2

20、012) and Nickel foam (Shii na (2006), Weiqia ng et al (2009), Xiao, (2013).2.1. PCMs Embedded with Aluminum FoamBauer and Wirtz (2000) developed a plate like structure thermal en ergy storage composite con sisti ng of a cen tral core of foamed alumi num foam packed with PCM to store heat duri ng pea

21、k power operati on of variable power dissipating devices. Tong et al. (1995) inserted a matrix of continuously connected aluminum foam into phase cha nge material (water) and in vestigated the solidificati on heat tran sfer of the water. Results show inserting metalmatrix into water provides a very

22、effective way to enhance the solidificati on heat tra nsfer.Jia ng et al. (2012) prepared a shape-stabilized PCMs using bulk porous Al foams impreg nated with orga nic PCMs (paraffi n and stearic acid). The thermal-/d yn amic-mecha ni cal properties of the shape-stabilized PCMs were studied. The fil

23、li ng fracti on of PCMs was approximately more tha n 80%, the late nt value of the paraffi n/Al foam and stearic acid/Al foam composite is 72.9kJ/kg and 66.7kJ/kg.2.2. PCMs Embedded with Copper FoamChi et al. (2011) made a new type of high efficie ncy en ergy storage devices con sisted of cooper foa

24、m and water. The cold charg ing process of the new type en ergy storage devices was approved to be faster and more adequate due to the embeddi ng of copper foam.Sheng et al. (2013) prepared a salt hydrate/metal foam composite phase change material by using barium hydroxide octahydrate (Ba(OH) 2 8H2O

25、) as late nt heat storage PCM and copper foams as a support ing matrix. Thermal cycli ng and heat tran sfer performa nee was studied. Results show that high porosity copper foam not only enhance the heat transfer rate of Ba(OH)2 8H2O but also effectively reduce the supercooling of the PCM.Zha ng and

26、 Yu (2007) in vestigated the thermal performa nee of solid-liquid phase cha nge thermal storage device with 98% pure Hen eicosa ne (C 21H44) filled in copper foam through a vacuum ing procedure. Experime ntal results show that the thermal con ductivity and performa nee of the thermal storage device

27、is obviously improved using copper foam as a heat tran sfer enhan ceme nt.Cui (2012) prepared a composite PCMs using paraffin as phase change materials and copper foam as filled materials. The results show that copper foam can not on ly lead to a more uni form temperature distributi on within the th

28、ermal en ergy storage un it, but also exte nsively shorte n the charg ing time.2.3. PCMs Embedded with Nickel FoamShii na (2006) studied the applicati on of late nt heat storage tech no logy using a composite PCM (a copper or n ickel foam saturated by PCM). The results in dicate that composite PCM h

29、ad in creased effective thermal con ductivity and could augme nt temperature cha nge reducti on of the heat tra nsfer fluid.In order to improve the void distribution and thermal performance of phase change thermal storage devices, Xu et al (2009) desig ned and man ufactured a thermal storage contain

30、ers embedded with ni ckel foam cores. Embedd ing nickel foam into the PCMs enhanced both the void distribution and thermal performance of solid-liquid phase cha nge process.Xiao, (2013) prepared paraffi n/n ickel foam and paraffi n/copper foam composite phase cha nge materials (PCMs) using a vacuum

31、impreg nati on method. Results show that the thermal con ductivity of the composite PCMs were drastically enhanced, e.g., the thermal conductivity of the paraffin/nickel foam composite was nearly three times larger tha n that of pure paraffi n.3. Properties of PCMs Embedded with Metal Foam3.1. Effec

32、tive Thermal ConductivityDue to the high thermal conductivity and porous structure, embedding metal foam into PCMs can enhance the heat tran sfer, thus improve the effective thermal con ductivity of the composite PCMs.t is very difficult to predict the thermal con ductivity of the PCMs embedded with

33、 metal foam for the complicated pore structure of the metal foam. Xu et al (2009) proposed a new phase distributi on model of metal foam matrix PCMs. Simplified heat transfer model with void sub model was established and the effective thermal con ductivity formula was derived by the equivale nt ther

34、mal resista nce method.Zhang et al (2010) investigated the thermal parameters (Effective thermal conductivity, thermal diffusivity and thermal capacity) of copper-foam/paraffi n with four differe nt porosities using tran sie nt pla ne source (TPS) method. The test results showed that the effective t

35、hermal con ductivity is obviously improved by embedd ing the copper foam into paraffin and it reached 25 times compared to pure paraffin.3.2. ConvectionMetal foam with high thermal con ductivity is gen erally con sidered to have high pote ntial to enhance the heat tran sfer performa nce for PCMs. I

36、n an attempt to enhance the con vective thermal tra nsport, metal foam can be used for making adva need compact heat excha ngers because of the high surface area to volume ratio as well as enhan ced flow mixing due to the tortuosity of the pass ways. But in the study of Tian and Zhao (2011), the n a

37、tural con vecti on in liquid region of the PCMs is suppressed by the metal foam. Buoyancy-driven velocities are too weak to produce dominant convection due to high viscosity and low thermal expansion ratio of the PCM and the large flow resistance of metal foam.Jianqing Chen et al. / Procedia Materia

38、ls Science4 (2014) 389 - 3943934. Research Methods of Heat Transfer in PCMsIn order to study the heat tran sfer and thermal storage capacity of the PCMs, exte nsive research methods have bee n developed, such as experime ntal study, theoretical an alysis and n umerical simulati on.4.1. Experimental

39、MethodLafdi et al (2007) built an experimental setup to measure the temperature profiles and capture the melting evoluti on of the PCM (low melt ing temperature paraffi n wax) in side alumi num foam. Effects of porosity and pore size of the aluminum foam on the heat transfer performance were studied

40、. For the higher porosity aluminum foam the steady-state temperature was reached faster as compared to the lower porosity foam. By using bigger pore size foam, the steady-state temperature was reached faster as compared to the foams with smaller pore size.Wu and Zhao (2011) in vestigated heat tra ns

41、fer enhan ceme nt performa nce of metal foam (copper foam) in high temperature thermal energy storage system using NaNO 3 as phase change material. Effect of natural convection on the heat tra nsfer rate was in vestigated un der bottom and top heati ng con diti ons. The heat tra nsfer rate can be en

42、hanced by copper foam to 2.1 times compare to pure NaNO 3. However, in the liquid PCM, the heat transfer rate was no longer better that of the pure NaNO 3 because metal foam suppressed the natural convection severely. Under the top heating condition, the heat transfer rate was enhanced by 1.2 times.

43、Shi et al (2010) studied phase cha nge heat tran sfer in ice ball with porous metal foam experime ntally. The results show that porous metal foams can enhance the phase cha nge heat tra nsfer in ice ball, lead to start ing phase cha nge earlier and shorten the whole phase change time.4.2. Theoretica

44、l Analysis MethodKrishnan et al (2004) employed a two-temperature model to account for the local thermal non-equilibrium. Separate en ergy equati ons for the solid and fluid respectively are writte n and closed using a steady-state in terphase heat tran sfer coefficie nt betwee n the two phases. A g

45、en eral mome ntum equati on that in cludes the Brikma n- forchheimer exte nsion to Darcy flow is employed. Natural con vecti on in side the fluid was an alyzed using a two- temperature formulation. Results show that local thermal equilibrium is not ensured either during the transient or at steady st

46、ate in the system.Peng et al (2009) in vestigated the phase cha nge heat tran sfer in PCM (wax) embedded in high porosity alumi num foam. A two-temperature model was established accord ing to the differe nce of the heat tra nsfer betwee n wax and Al foam. The temperature distributions and flow field

47、s of the PMCs were simulated by apparent heat capacity method. The results showed that the heat tran sfer of the PCMs in Al foam was effectively improved compared to pure PCMs without Al foam. Chen et al (2010) studied the melt ing process of paraffi n in high porosity aluminum foam using a similar

48、two-temperature model. The simulation results indicate that aluminum foam makes the temperature distributi on of the paraffi n more eve n. There is big temperature differe nce betwee n metal frame and PCM during phase change process. Local thermal non-equilibrium is obvious. Melting speed of the par

49、affin in creases with the decreas ing of metal foam porosity.4.3. Numerical Simulation MethodBased on local thermal non-equilibrium between the metal matrix and PCMs, Gao and Chen (2012) and Zhang et al (2013) developed a Lattice Boltzmann model to characterize the melting processes and heating cond

50、uction of PCMs in metal foams and the temperature filed of metal foams framework. An equation based on density distribution function was constructed to characterize the velocity field of melt fluid. An enthalpy-based method is employed to account the phase change problem. The melting front location

51、as the function of time and the temperature distributi on in metallic framework and the PCMs is simulated by Lattice-Boltzma nn model. The effects of the porosity and pore size on the melt ing are also in vestigated and discussed. The results in dicate that the effects of foam porosity play importan

52、t roles in the overall heat transfer. For the lower porosity foams, the melting rate is comparatively greater than the higher porosity foams, due to greater heat conduction from metal foam with high heat conductivity. The foam pore size has a limited effect on the melting rate due to two counteracti

53、ng effects between conduction and convection heat transfer. Increasing of the pore density leads to increasing conduction heat transfer, decreas ing con vecti on heat tran sfer and decreas ing heat storage capacity. Therefore, it is suggested to con sider engineering requirements to determine porosi

54、ty in the design of foam metal heat storage device.A phase filed model deals with free boundary problems without tracing their positions, and therefore provides pote ntials of being exte nded to con sider more complicated mecha ni sms: multi-dime nsion and volume cha nge. Han et al (2013) establishe

55、d a foam-PCM phase filed model to solve the phase change problem by introducing two phase files to deal with phase change and volume change. The coupled heat transfer between PCMs and metal foams is solved based on the non-equilibrium heat tran sfer theory. An effective ness map disti nguish ing the

56、 con diti ons un der which incorporating metal foam into the PCMs is sensitive, lowly sensitive or irrelevant is produced to guide the metal selecti on and structure desig n of metal foams whe n enhancing the heat tra nsfer of PCMs.5. SummaryIn this paper the research progress of phase cha nge mater

57、ials (PCMs) embedded with metal foam is reviewed. The con ducti on, con vecti on and phase cha nge heat tran sfer process in the PCMs has bee n exte nsively in vestigated. Embedding metal foam into PCMs is an effective method to enhance the heat transfer in the PCMs. Due to the high thermal conducti

58、vity, surface area volume ratio, porosity and complicated three dimension network, metal foam in the composite PCMs in crease the effective thermal con ductivity of the composite PCMs, and thus improve the un iformity of the temperature distributio n in the PCMs. Gen erally the metal foam embedded i

59、n the PCMs suppress the n atural con vecti on and reduc ing the con vective heat tran sfer performa nee. Metal foam structure affects the heat transfer performance of the PCMs significantly. It is suggested to consider both the effects foam porosity and pore size on conduction and convection heat transfer as well as engineering requirements to determine porosity in the desig n of