Investigation On Properties Of Metal Foam Based And Nanofluid Composite PCM

Phase change materials(PCM) have the disadvantages of low thermal conductivityand high supercooling degree, which reduce the energy storage efficiency. Generally,the problem is solved by fabricating metal foam based PCM and nanofluid PCM. Thisstudy investigated and analyzed the properties of metal foam based PCM and nanofluidsPCM deeply to gain a better understanding of PCM.For metal foam based PCM, this study investigated the melting and heat transferprocess of n-docosane in a squarecontainer by experimental and numerical method. Thetemperature and flow field in PCM was analyzed by CFD simulation. The melting andheat transfer process of pure n-docosane and metal foam based n-docosane wascompared and analyzed. The effect of Ste number, viscosity μ and the porosity of metalfoam εon heat transfer and phase change process were analyzed. The melting process ofpure PCM between experiment and numerical method agreed very well. Compared topure PCM, metal foam based PCM had a higher melting velocity. The temperaturefields of PCM and metal foam were similar but still with deferences. The result showedthe Ste number affected the propagation velocity of melting interface and the size ofmushy zone. The viscosity μ affected the incline extent of melting interface. Theporosity of metal foam ε also affected the propagation velocity of melting interface. Thecomposite phase change material hasbetterheat transfer performancewith smaller Ste,smaller μ and larger ε.For nanofluids PCM, stability, thermal conductivity, phase change propertiesandthe effect of surface modification on stability were invesitated. The result showed thatrepeated ultrasonication, solidification and melting and trace water deteriorated thestability. The stability was enhanced with increasing ultrasonication power. Anoptimum ultrasonication duration for stability existed. The temperature hadlittleinfluence on stability. For all the three dispersants, the optimum mass fractionswere thesame with the mass fraction of nanoparticle. Span80had a best effect to enhance thestability among three dispersants. For both SiO2-PDA-ODM and SiO2-hexadecyltrimethoxysilane, with the increasing of reactant,the number of decoratedstructure on particle surface increased,the corresponding stability was also enhanced. The nanofluid with surface modification had better stability than those with dispersants,which had much better stability than that without treatment. The stability ofnanofluidwith surface modification deteriorated a litte with increasing of temperature,but was still better than that of nanofluids with dispersants even in high temperature.The average molecule number per nm2decorated on SiO2particle surface ranged from0.7to7among the six samples. The MWCNT has the most significant effect to enhancethe thermal conductivity compared to otherthree nanoparticles. The thermalconductivity of nanofluids was enhanced with smaller nanoparticles and higher particleconcentration. The temperature hadno significance on thermal conductivityenhancement of nanofluids. Forming framework could be eliminated for interpretingthethermal conductivity enhancement for tetradecane based nanofluids.Cu and SiO2nanoparticles could decrease the supercooling degree with lower concentration (0.1%),but had no significant effect under higher concentration (0.3%). CuO and MWCNTincreased the supercooling degree. The latent heat of PCMs with nanoparticles waslower than that of pure PCM. When the heating or cooling rate increased, thesupercooling degree and the latent heat increased. The supercooling degree decreased atfirst and then tended to be constant with the increasing cycling number of melting andsolidification.