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.

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.

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

2011 ◽  
Vol 3 (3) ◽  
Author(s):  
Fang Zhao ◽  
Zhenqian Chen
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Biological Tissue ◽  
Clinical Medicine ◽  
Numerical Study ◽  
Biological Tissues ◽  
Freezing Process ◽  
Ice Crystal ◽  
Obvious Effect ◽  
Phase Change Heat Transfer

Biological tissues undergo complex phase change heat transfer processes during cryosurgery, and a theoretical model is preferable to forecast this heat experience. A mathematical model for phase change heat transfer in cryosurgery was established. In this model, a fractal treelike branched network was used to describe the complicated geometrical frame of blood vessels. 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 (<600 s) and then slows down in the following process, and the precooling 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 produces an optimal freezing effect for the tumor size (20 mm × 10 mm) in the present study compared with the distances of 6 mm and 14 mm. The numerical results are significant in providing technical reference for application of cryosurgery in clinical medicine.

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.

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.

scholarly journals Oblique stagnation point flow of a non-Newtonian nanofluid over stretching surface with radiation: A numerical study

2017 ◽  
Vol 21 (5) ◽  
pp. 2139-2153 ◽  
Author(s):  
Abuzar Ghaffari ◽  
Tariq Javed ◽  
Fotini Labropulu
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Differential Equations ◽  
Layer Thickness ◽  
Stagnation Point ◽  
Boundary Layer Thickness ◽  
Numerical Study ◽  
Convective Boundary Condition ◽  
Stretching Surface ◽  
Convective Boundary

In this study, we discussed the enhancement of thermal conductivity of elasticoviscous fluid filled with nanoparticles, due to the implementation of radiation and convective boundary condition. The flow is considered impinging obliquely in the region of oblique stagnation point on the stretching surface. The obtained governing partial differential equations are transformed into a system of ordinary differential equations by employing a suitable transformation. The solution of the resulting equations is computed numerically using Chebyshev spectral newton iterative scheme. An excellent agreement with the results available in literature is obtained and shown through tables. The effects of involving parameters on the fluid flow and heat transfer are observed and shown through graphs. It is importantly noted that the larger values of Biot number imply the enhancement in heat transfer, thermal boundary layer thickness, and concentration boundary layer thickness.

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

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.

scholarly journals Numerical Study of the Thermal Behavior of a Composite Phase Change Material (PCM) Room

2018 ◽  
Vol 8 (2) ◽  
pp. 2663-2667 ◽  
Author(s):  
N. Ben Khedher
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Thermal Performance ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Indoor Temperature ◽  
Three Phase ◽  
Chloride Hexahydrate ◽  
Hot Weather ◽  
Building Walls

In this study, thermal performance of building walls integrated with phase change materials (PCM) was evaluated in terms of indoor temperature reduction and heat transfer time delay. PCM was incorporated as thin layer placed longitudinally within walls. The thermal performance of a room with and without PCM was evaluated numerically. The developed model is based on the enthalpy formulation for PCM melting and solidification, which is solved by an implicit finite difference method. The effect of PCM type on heat gain indoors was studied. Three phase change materials (n-octadecane, n-eicosane and calcium chloride hexahydrate) were tested in hot weather. Results showed that octadecane is the best in ensuring an indoor temperature close to 27 °C for the test room. Moreover, optimal thickness of the PCM layer within the walls is critical for heat transfer reduction and management and should be carefully chosen.

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