Liquid Film Evaporation in the Presence of Micro Encapsulated Phase Change Materials: A Numerical Study

2013 ◽  
Author(s):  
Yasmin Khakpour ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Phase Change ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Finite Thickness ◽  
Operating Conditions ◽  
Evaporation Process ◽  
Constant Wall Temperature ◽  
Film Evaporation

This paper numerically investigates the flow and heat transfer characteristics of a slurry of micro encapsulated phase change materials (MEPCM) and R134a in the presence of film evaporation. The numerical domain is comprised of a minichannel in contact with a finite thickness solid zone with constant wall temperature. During the evaporation process, the concentration of MEPCM in the slurry increases, resulting in a continuous variation of effective thermal properties of the slurry. The effect of PCM concentration on the evolution of the liquid film thickness under different operating conditions along with the variation of the local heat transfer coefficients has been studied. A user defined function has been developed to incorporate the evaporation process by introducing the mass and energy source terms for the evaporation process as well as the variation of the MEPCM concentration along the channel.

Natural Convection in an Enclosure With Blend of Micro Encapsulated Phase Change Materials

2013 ◽  
Author(s):  
Yasmin Khakpour ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Thermal Expansion ◽  
Natural Convection ◽  
Phase Change ◽  
Latent Heat ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Pure Water ◽  
Operating Conditions ◽  
Effective Density

This numerical study investigates the effect of using a blend of micro-encapsulated phase change materials (MEPCMs) on the heat transfer characteristics of a liquid in a rectangular enclosure driven by natural convection. A comparison has been made between the cases of using single component MEPCM slurry and a blend of two-component MEPCM slurry. The natural convection is generated by the temperature difference between two vertical walls of the enclosure maintained at constant temperatures. Each of the two phase change materials store latent heat at a specific range of temperatures. During phase change of the PCM, the effective density of the slurry varies. This results in thermal expansion and hence a buoyancy driven flow. The effects of MEPCM concentration in the slurry and changes in the operating conditions such as the wall temperatures compared to that of pure water have been studied. The MEPCM latent heat and the increased volumetric thermal expansion coefficient during phase change of the MEPCM play a major role in this heat transfer augmentation.

Numerical Study of Heat Transfer Characteristics of Liquid Flow in a Microtube With Blend of Micro Phase Change Materials

2012 ◽  
Author(s):  
Yasmin Khakpour ◽  
Jamal Seyed Yagoobi
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Liquid Flow ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Finite Thickness ◽  
Local Heat Transfer ◽  
Outer Wall ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

This numerical investigation explores the heat transfer characteristics of liquid flow with two-component (blend) micro phase change materials (MPCM) and compares them with those of a single component MPCM slurry. The numerical domain is comprised of an axisymmetric micro-tube in contact with a finite-thickness solid zone and a constant heat flux applied on the solid outer wall. The ultimate objective is to demonstrate the tunability of PCM fluid’s thermal energy properties when the phase transition temperatures of the PCMs are chosen within a range required for a specific application. This is because different pure PCM materials store latent heat at a specific range of temperatures. The MPCM slurry flow does not reach a fully developed condition as long as the MPCM particles experience phase change in the developing region. The local heat transfer coefficient strongly depends on the corresponding location of the melting zone interface.

Phase Change Process Inside a Small-radii Cylinder Subjected to Cyclic Convective Boundary Conditions: a Numerical Study

2021 ◽  
Author(s):  
Yousef Kanani ◽  
Avijit Karmakar ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Surface Temperature ◽  
Phase Change ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Convective Boundary Condition ◽  
Freezing Process ◽  
Fourier Number ◽  
Two Phase ◽  
Convective Boundary

Abstract We numerically investigate the melting and solidi?cation behavior of phase change materials encapsulated in a small-radii cylinder subjected to a cyclic convective boundary condition (square wave). Initially, we explore the effect of the Stefan and Biot numbers on the non-dimensionalized time required (i.e. reference Fourier number Tref ) for a PCM initially held at Tcold to melt and reach the cross?ow temperature Thot. The increase in either Stefan or Biot number decreases Tref and can be predicted accurately using a correlation developed in this work. The variations of the PCM melt fraction, surface temperature, and heat transfer rate as a function of Fourier number are reported and analyzed for the above process. We further study the effect of the cyclic Fourier number on the periodic melting and freezing process. The melting or freezing front initiates at the outer periphery of the PCM and propagates towards the center. At higher frequencies, multiple two-phase interfaces are generated (propagating inward), and higher overall heat transfer is achieved as the surface temperature oscillates in the vicinity of the melting temperature, which increases the effective temperature difference driving the convective heat transfer.

Numerical Investigation of EHD Conduction Pumping of Liquid Film With Phase-Change

2007 ◽  
Author(s):  
Miad Yazdani ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Phase Change ◽  
Flow System ◽  
Thin Liquid Film ◽  
Finite Thickness ◽  
Constant Heat Flux ◽  
Two Dimensional ◽  
Enhanced Heat Transfer ◽  
Constant Heat

Electrohydrodynamic (EHD) conduction pumping is associated with the heterocharge layers of finite thickness in the vicinity of the electrodes, generated by the process of dissociation of the neutral electrolytic species and recombination of the generated ions. This paper numerically investigates the EHD conduction pumping of a thin liquid film in the presence of phase change. The flow system comprises a liquid film flowing over a two-dimensional flat plate while the vapor phase extended far beyond the interface to result in almost motionless vapor. The channel is separated into four different sections: the entrance, electrode, evaporation, and downstream sections. The entrance, electrode and downstream regions are adiabatic while a constant heat flux is applied in the evaporation side. The concept of EHD conduction pumping of liquid film in the presence of phase change is demonstrated in this paper. The enhanced heat transfer due to conduction pumping is evaluated.

Numerical study on the effect of phase change materials on heat transfer in asphalt concrete

2018 ◽  
Vol 133 ◽  
pp. 140-150 ◽  
Author(s):  
Zakariaa Refaa ◽  
Muhammad Rafiq Kakar ◽  
Anastasia Stamatiou ◽  
Jörg Worlitschek ◽  
Manfred N. Partl ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Asphalt Concrete ◽  
Phase Change Materials ◽  
Numerical Study

scholarly journals HEAT STORAGE SYSTEM WITH PHASE CHANGE MATERIALS IN COGENERATION UNITS: STUDY OF PRELIMINARY MODEL

2008 ◽  
Vol 39 (4) ◽  
pp. 9
Author(s):  
Claudio Caprara ◽  
Giovanni Stoppiello
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Phase Change ◽  
Thermal Energy ◽  
Phase Change Materials ◽  
Heat Storage ◽  
High Energy ◽  
Operating Conditions ◽  
Thermal Source ◽  
Continuous Increase

The continuous increase in the mechanization of farm activities, the rise in fuel prices and the environmental aspects concerning gas emissions are the main driving forces behind efforts toward more effective use of renewable energy sources and cogeneration systems even in agricultural and cattle farms. Nevertheless these systems are still not very suitable for this purpose because of their little flexibility in following the changing energy demand as opposed to the extremely various farm load curves, both in daytime and during the year. In heat recovery systems, the available thermal energy supply is always linked to power production, thus it does not usually coincide in time with the heat demand. Hence some form of thermal energy storage (TES) is necessary in order to reach the most effective utilization of the energy source. This study deals with the modelling of a packed bed latent heat TES unit, integrating a cogeneration system made up of a reciprocating engine. The TES unit contains phase change materials (PCMs) filled in spherical capsules, which are packed in an insulated cylindrical storage tank. Water is used as heat transfer fluid (HTF) to transfer heat from the tank to the final uses, and exhausts from the engine are used as thermal source. PCMs are considered especially for their large heat storage capacity and their isothermal behaviour during the phase change processes. Despite their high energy storage density, most of them have an unacceptably low thermal conductivity, hence PCMs encapsulation technique is adopted in order to improve heat transfer. The special modular configuration of heat exchange tubes and the possibility of changing water flow through them allow to obtain the right amount of thermal energy from the tank, according to the hourly demand of the day. The model permits to choose the electrical load of the engine, the dimensions of the tank and the spheres, thickness and diameter of heat exchanger and the nature of PCMs. According to the energy loads of the farm, a daily thermal energy balance is obtained and charging and discharging cycles during the day are showed as solid/ liquid percentages of the PCM. As an example, load curves of a milk cattle farm (100 heads of cattle), were considered in two different conditions, such as in summer and winter seasons, and model functioning was detected in both of the cases. Different PCMs were investigated for this application and TES unit dimensions were consequently changed in order to achieve optimal operating conditions. Results are presented and technical and economical issues are discussed.

Three-Dimensional Numerical Study on Freezing Phase Change Heat Transfer in Biological Tissue Embedded With Two Cryoprobes

2011 ◽  
Author(s):  
Fang Zhao ◽  
Zhenqian Chen ◽  
Mingheng Shi
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Biological Tissue ◽  
Numerical Study ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Freezing Process ◽  
Ice Crystal ◽  
Obvious Effect ◽  
Phase Change Heat Transfer

A mathematical model for phase change heat transfer in cryosurgery was established. In this model, a fractal tree-like branched network was used to describe the complicated geometrical frame of blood vessel. The temperature distribution and ice crystal growth process in biological tissue including normal tissue and tumor embedded with two cryoprobes were numerically simulated. The effects of cooling rate, initial temperature and distance of two cryoprobes on freezing process of tissue were also studied. The results show that the ice crystal grows more rapidly in the initial freezing stage and then slows down in the following process, and the pre-cooling of cryoprobes has no obvious effect on freezing rate of tissue. It also can be seen that the distance of 10 mm between two cryoprobes is the most appropriate choice for operation effect in the range of operating conditions presented in this study.

Melting Process Expedition of Phase Change Materials via Silicone Oil

2018 ◽  
Author(s):  
Sarvenaz Sobhansarbandi ◽  
Fatemeh Hassanipour
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Heat Transfer Enhancement ◽  
Phase Change Materials ◽  
Silicone Oil ◽  
Storage Systems ◽  
Ccd Camera ◽  
Melting Process ◽  
Operating Conditions ◽  
Transfer Enhancement

This paper presents a novel method of heat transfer enhancement and melting process expedition of phase change materials (PCMs) via silicone oil for the application in thermal energy storage systems. Sudden spot heating/cooling of the PCM causes a non-uniform melting process and in some cases the volume expansion/contraction. To avoid this malfunction, silicone oil can be applied in these systems to increase convective heat transfer (stirring effect). The feasibility of this method is investigated by two experimental analysis, one by having the mixture in a cylindrical container and one in a cubic container. The results from the images taken by Charge-Coupled Device (CCD) camera in the first analysis show a uniform melting process of the PCM. In the second analysis, the comparison is made for the two parallel setups with and without the silicone oil with the same operating conditions. The results show that in the system that lacks silicone oil, the paraffin starts melting after around 11 minutes from the heater start-up, while this time is around 6 minutes in the system with silicone oil. The effectiveness of silicone oil in enhancing the heat transfer rate is shown by a temperature rise of around 10 °C in the container. Applying PCMs in conjunction with silicone oil in various thermal storage systems for heating/cooling applications specifically in solar thermal collectors, enables heat transfer enhancement and consequently heat storage directly on the system.

Numerical Study of Phase Change of PCM in Spherical Cavities

2017 ◽  
Vol 372 ◽  
pp. 21-30 ◽  
Author(s):  
Fábio Faistauer ◽  
Petros Rodrigues ◽  
Rejane de Césaro Oliveski
Keyword(s):  
Phase Change ◽  
Melting Temperature ◽  
Wall Temperature ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Liquid Fraction ◽  
Fluid Dynamic ◽  
Melting Process ◽  
Constant Wall Temperature ◽  
Spherical Cavities

This work presents a numerical study of the phase change process of PCM (Phase Change Materials) stored in spherical cavities. The numerical model is two-dimensional and it is composed by the equations of conservation of mass, momentum, energy and volumetric fraction, which are modeled using the enthalpy-porosity technique. The computational mesh is tetrahedral, with refinements on regions that have large thermic and fluid dynamic gradients. The numeric model was validated with result from literature. It was studied the melting process of PCM RT35, RT 55 and RT 82 in spherical cavity with constant wall temperature. Four diameters of spheres D were used (40, 60, 80 and 100 mm) and three temperature differences ΔT (10, 20 and 30 oC) between the wall temperature and the melting temperature of the PCM. Liquid fraction results from the 36 cases studied are presented. It was observed that the time required to reach a certain liquid fraction increases with the diameter and reduces with the increment of ΔT, being possible to predict the fusion time by knowing the characteristic length of the sphere. The largest percentage reduction of the fusion time was obtained with ΔT = 10 oC – 20 oC for all the D considered. The shortest fusion time was obtained with the largest ΔT combined with the smallest D. It is possible to see the dependence of the liquid fraction results in relation with the PCM properties and the its independence in relation its melting temperature, since all the PCM studied presented equal fusion time for the same ΔT and D.

Numerical Model for Storage Systems Based on Phase-Change Materials

2011 ◽  
Author(s):  
Adriano Sciacovelli ◽  
Vittorio Verda ◽  
Francesco Colella
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Phase Change Materials ◽  
Storage Systems ◽  
Numerical Procedure ◽  
Thermal Storage ◽  
Operating Conditions ◽  
Heat Transfer Fluid ◽  
Inlet Temperature ◽  
Technical Problems

Phase-change materials (PCM) are particularly promising for thermal storage in various energy plants as solar plants, district heating, heat pumps, etc. mainly because of the possibility to reduce the volume of storage tanks, but also because the problems related with thermal stratification are considerably reduced. On the other hand, research is necessary in order to address technical problems, mainly related to the heat transfer in the medium, which needs to be enhanced in order to achieve reasonable charging and discharging processes. The present paper describes the application of computational fluid-dynamics (CFD) for the analysis of PCM thermal storage systems. The numerical analysis is directed at understanding the role of buoyancy-driven convection during constrained solidification and melting inside a shell-and-tube geometry. The 2D model is based on a finite-volume numerical procedure that adopts the enthalpy method to take in account the phase change phenomenon. The time-dependent simulations show the melting phase front and melting fraction of the PCM and incorporate the fluid flow in the liquid phase. The obtained temperature profiles are compared to a set of experimental data available in the literature. The results show that during the melting process natural convection within the PCM has non negligible effects on the behavior of the system. The numerical simulations of the solidification process show that the increasing solid fraction of the PCM inhibits the buoyancy in the remaining liquid portion of the phase-change-material. Furthermore, the paper discusses the effects on the phase-change processes of the main operating conditions, including inlet temperature and mass flow rate of the heat transfer fluid.

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