Effect of natural convection on conjugate heat transfer characteristics in liquid minichannel during phase change material melting

2013 ◽  
Vol 228 (3) ◽  
pp. 491-513 ◽  
Author(s):  
M Khamis Mansour
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Phase Change ◽  
Phase Change Material ◽  
Conjugate Heat Transfer ◽  
Thermal Characteristics ◽  
Melting Process ◽  
Heat Transfer Fluid ◽  
Local Surface Temperature ◽  
Change Material

This article presents numerical and experimental simulation of three-dimensional conjugate heat transfer problem in mini-scaled thermal storage system. The conjugate problem includes melting process of phase change material in the presence of natural convection during laminar flow of heat transfer fluid through circular minichannel. The paraffin wax is used as a phase change material while the water is used as a heat transfer fluid. The main objective of this study is to investigate the effect of the phase change material natural convection during the melting process on the heat transfer fluid thermal characteristics as well as the impact of the natural convection on the melting performance itself. The thermal characteristics are represented by local Nusselt number ( Nu) and local surface temperature. The melting performance is evaluated by fusion time and liquid fraction profile. Two inlet temperatures and velocities of the heat transfer fluid are adopted to highlight the effect of the natural convection. Combination of the inlet temperatures and velocities of the heat transfer fluid forms four cases: case_1 (at [Formula: see text] = 353 °K, [Formula: see text] = 1 m/s), case_2 (at [Formula: see text] = 453 °K, [Formula: see text] = 1 m/s), case_3 (at [Formula: see text] = 353 °K, [Formula: see text] = 0.1 m/s), and case_4 (at [Formula: see text] = 453 °K, [Formula: see text] = 0.1 m/s). Experimental test rig was constructed to verify the computational results and good agreement between both results was achieved. The study shows that the heat transfer fluid encounters an erratic thermal behavior during the phase change material melting process. For example, the local surface temperature experiences dramatic increase and decrease at certain sections of the channel length. The magnitude of this temperature inconsistency interrelates closely to the strength of natural convection impact, and this can expose the minichannel (which has short length) to severe wall thermal stress. The local Nu experiences improvement in some section of the channel and at the same time it suffers from drastic deterioration in its value particularly at the channel end at which the convection current accommodates. The case with the lowest inlet velocity and the highest inlet temperature has the smallest fusion time at expense of the largest heat transfer fluid bulk temperature gradient before reaching the fusion time. The study is considered as a benchmark and helpful guidelines in the design of small-scaled thermal storage systems of phase change material.

Experimental Study on Thermal Characteristics of Finned Coil LHSU Using Paraffin as Phase Change Material

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Guansheng Chen ◽  
Nanshuo Li ◽  
Huanhuan Xiang ◽  
Fan Li
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Phase Change ◽  
Phase Change Material ◽  
Water Flow ◽  
Water Flow Rate ◽  
Thermal Characteristics ◽  
Heat Transfer Fluid ◽  
Latent Heat Storage ◽  
Change Material

It is well known that attaching fins on the tubes surfaces can enhance the heat transfer into and out from the phase change materials (PCMs). This paper presents the results of an experimental study on the thermal characteristics of finned coil latent heat storage unit (LHSU) using paraffin as the phase change material (PCM). The paraffin LHSU is a rectangular cube consists of continuous horizontal multibended tubes attached vertical fins at the pitches of 2.5, 5.0, and 7.5 mm that creates the heat transfer surface. The shell side along with the space around the tubes and fins is filled with the material RT54 allocated to store energy of water, which flows inside the tubes as heat transfer fluid (HTF). The measurement is carried out under four different water flow rates: 1.01, 1.30, 1.50, and 1.70 L/min in the charging and discharging process, respectively. The temperature of paraffin and water, charging and discharging wattage, and heat transfer coefficient are plotted in relation to the working time and water flow rate.

scholarly journals Study of Thermal Behavior of a Horizontal Two Fins Annular Tube Heat Exchanger with Melting Phase Change Material: Fins Orientation Effects

2021 ◽  
Vol 45 (2) ◽  
pp. 141-151
Author(s):  
Nesrine Boulaktout ◽  
El Hacene Mezaache ◽  
Abdelghani Laouer
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Phase Change ◽  
Phase Change Material ◽  
Melting Process ◽  
Initial Time ◽  
Tube Heat Exchanger ◽  
Change Material ◽  
Annular Tube

This paper investigates the effect of fins orientations of a horizontal two fins annular tube heat exchanger on enhancing the heat transfer during the melting process of n-eicosane, as phase change material (PCM) used in thermal storage systems. Based on the enthalpy-porosity method, two-dimensional model is performed and solved by Ansys Fluent. The impact of the fins orientation on melting rate, thermal conduction and natural convection, as the angle of the system varied from 0º (vertical fins) to 90º (horizontal fins) are discussed. Numerical predictions are validated by comparison with experimental data and numerical results reported in the literature. Good agreements are achieved. The results show that at initial time of the melting process, the conduction heat transfer is dominant. During the melting process, the heat transfer in the horizontal fins is more effective while the upper half of PCM melts and less effective as the lower half of PCM melts because fin arrangement resists natural convection occurs. However, the effectiveness of heat transfer and convection in the vertical fins is almost constant during the entire melting process. From comparison, better heat transfer performance is achieved with vertical fins system; complete melting was reduced 250% compared to horizontal fins case.

scholarly journals Numerical Simulation of the Impact of the Heat Source Position on Melting of a Nano-Enhanced Phase Change Material

Nanomaterials ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1425
Author(s):  
Tarek Bouzennada ◽  
Farid Mechighel ◽  
Kaouther Ghachem ◽  
Lioua Kolsi
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Phase Change Material ◽  
Numerical Study ◽  
Melting Rate ◽  
Heat Transfer Fluid ◽  
Commercial Code ◽  
Tube Position ◽  
The Impact ◽  
Change Material

A 2D-symmetric numerical study of a new design of Nano-Enhanced Phase change material (NEPCM)-filled enclosure is presented in this paper. The enclosure is equipped with an inner tube allowing the circulation of the heat transfer fluid (HTF); n-Octadecane is chosen as phase change material (PCM). Comsol-Multiphysics commercial code was used to solve the governing equations. This study has been performed to examine the heat distribution and melting rate under the influence of the inner-tube position and the concentration of the nanoparticles dispersed in the PCM. The inner tube was located at three different vertical positions and the nanoparticle concentration was varied from 0 to 0.06. The results revealed that both heat transfer/melting rates are improved when the inner tube is located at the bottom region of the enclosure and by increasing the concentration of the nanoparticles. The addition of the nanoparticles enhances the heat transfer due to the considerable increase in conductivity. On the other hand, by placing the tube in the bottom area of the enclosure, the liquid PCM gets a wider space, allowing the intensification of the natural convection.

scholarly journals Analysis of the Thermal Characteristics of a Composite Ceramic Product Filled with Phase Change Material

Buildings ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 217 ◽  
Author(s):  
Joanna Krasoń ◽  
Przemysław Miąsik ◽  
Lech Lichołai ◽  
Bernardeta Dębska ◽  
Aleksander Starakiewicz
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Heat Transfer Coefficient ◽  
Phase Change ◽  
Transfer Coefficient ◽  
Phase Change Material ◽  
Thermal Characteristics ◽  
Ceramic Product ◽  
Change Material ◽  
The Heat Transfer Coefficient

The article presents a comparative analysis carried out using three methods, determining the heat transfer coefficient U for a ceramic product modified with a phase change material (PCM). The purpose of the article is to determine the convergence of the resulting thermal characteristics, obtained using the experimental method, numerical simulation, and standard calculation method according to the requirements of PN-EN ISO 6946. The heat transfer coefficient is one of the basic parameters characterizing the thermal insulation of a building partition. Most often, for the thermal characteristics of the partition, we obtain from the manufacturer the value of the thermal conductivity coefficient λ for individual homogeneous materials or the heat transfer coefficient U for the finished (prefabricated) partition. In the case of a designed composite element modified with a phase change material or other material, it is not possible to obtain direct information on the above parameter. In such a case, one of the methods presented in this article should be used to determine the U factor. The U factor in all analyses was determined in stationary conditions. Research has shown a significant convergence of the resulting value of the heat transfer coefficient obtained by the assumed methods. Thanks to obtaining similar values, it is possible to continue tests of thermal characteristics of partitions by means of numerical simulation, limiting the number of experimental tests (due to the longer test time required) in assumed different partition configurations, in stationary and dynamic conditions.

Numerical Survey of the Melting Driven Natural Convection Using Generation Heat Source: Application to the Passive Cooling of Electronics Using Nano-Enhanced Phase Change Material

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Hamza Faraji ◽  
Mustapha Faraji ◽  
Mustapha El Alami
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Phase Change ◽  
Phase Change Material ◽  
Metallic Nanoparticles ◽  
Simple Algorithm ◽  
Bottom Side ◽  
Volume Method ◽  
Change Material

Abstract The present paper reports numerical results of the melting driven natural convection in an inclined rectangular enclosure filled with nano-enhanced phase change material (NePCM). The enclosure is heated from the bottom side by a flush-mounted heat source (microprocessor) that generates heat at a constant and uniform volumetric rate and mounted on a substrate (motherboard). All the walls are considered adiabatic. The purpose of the investigation is analyzing the effect of nanoparticles insertion by quantifying their contribution to the overall heat transfer. Combined effects of the PCM type, the inclination angle and the nanoparticles fraction on the structure of the fluid flow and heat transfer are investigated. A 2D mathematical model based on the conservation equations of mass, momentum, and energy was developed. The governing equations were integrated and discretized using the finite volume method. The SIMPLE algorithm was adopted for velocity–pressure coupling. The obtained results show that the nanoparticles insertion has an important quantitative effect on the overall heat transfer. The insertion of metallic nanoparticles with different concentrations affects the thermal behavior of the heat sink. They contribute to an efficient cooling of the heat source. The effect of nanoparticles insertion is also shown at the temperature distribution along the substrate.

scholarly journals Testing the performance of a prototype thermal energy storage tank working with organic phase change material for space heating application conditions

2019 ◽  
Vol 116 ◽  
pp. 00038 ◽  
Author(s):  
Maria K. Koukou ◽  
Michail Gr. Vrachopoulos ◽  
George Dogkas ◽  
Christos Pagkalos ◽  
Kostas Lymperis ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Phase Change ◽  
Phase Change Material ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Finned Tube ◽  
Heat Transfer Fluid ◽  
Outlet Temperature ◽  
Change Material

A prototype Latent Heat Thermal Energy Storage (LHTES) unit has been designed, constructed, and experimentally analysed for its thermal storage performance under different operational conditions considering heating application and exploiting solar and geothermal energy. The system consists of a rectangular tank filled with Phase Change Material (PCM) and a finned tube staggered Heat Exchanger (HE) while water is used as Heat Transfer Fluid (HTF). Different HTF inlet temperatures and flow rates were tested to find out their effects on LHTES performance. Thermal quantities such as HTF outlet temperature, heat transfer rate, stored energy, were evaluated as a function of the conditions studied. Two commercial organic PCMs were tested A44 and A46. Results indicate that A44 is more efficient during the charging period, taking into account the two energy sources, solar and heat pump. During the discharging process, it exhibits higher storage capacity than A46. Concluding, the developed methodology can be applied to study different PCMs and building applications.

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