scholarly journals Buoyancy Driven Turbulent Heat Transfer Characteristics in Enclosure Filled with Phase Change Materials

2020 ◽  
Vol 9 (1) ◽  
pp. 717-721
Keyword(s):  
Heat Source ◽  
Phase Change ◽  
Phase Change Materials ◽  
Transient Flow ◽  
Turbulent Heat Transfer ◽  
Convection Flow ◽  
Turbulent Heat ◽  
Navier Stokes Equation ◽  
Flow Physics ◽  
Turbulent Characteristics

The exponentially growing computing capabilities of electronic circuits require effective and efficient heat sink designs to control the temperature inside the system. To achieve the desired temperature for efficient working of electronic devices, phase change materials are widely used. In the present study we discuss the complex flow physics of a phase change material filled in a cubical enclosure in the turbulent flow regime with a local heater mounted on the enclosure bottom wall. The thermal properties of local heat source are that of silicon at a working temperature of 330 K. The walls of the enclosure other than the heat source are considered as adiabatic. The turbulent natural convection flow is modeled by the computational fluid dynamics (CFD) approach using Reynolds averaged Navier-stokes equation (RANS) with Lambremhorst k-ε turbulence model. A finite difference method is used to discretize the governing equations and an in-house CFD code is developed for simulating the turbulent characteristics. The flow physics of three different phase change materials (n-Octadecane, PEG900, Paraffin (RT60)) has been analyzed with Groshof number being fixed for all three phase change materials. The transient flow characteristics are investigated by plotting the stream function, velocity and temperature contours of the phase change materials..

Effect of Turbulent Heat Transfer on Continuous Ingot Solidification

1993 ◽  
Vol 115 (1) ◽  
pp. 8-16 ◽  
Author(s):  
W. Shyy ◽  
Y. Pang ◽  
G. B. Hunter ◽  
D. Y. Wei ◽  
M.-H. Chen
Keyword(s):  
Heat Transfer ◽  
Mushy Zone ◽  
Phase Change ◽  
Critical Role ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Ingot Casting ◽  
Zone Formation ◽  
Continuous Ingot ◽  
The Impact

For many continuous ingot casting processes, turbulent heat transfer in the molten pool plays a critical role which, along with buoyancy and surface tension, is responsible for the quality of the end products. Based on a modified low Reynolds number k-ε two-equation closure, accounting for the phase change and mushy zone formation, the effect of turbulent heat transfer on the solidification characteristics during titanium alloy ingot casting in an electron beam melting process is investigated. The overall heat transfer rate is enhanced by turbulent transport via two sources, one through the correlated velocity and temperature fluctuations present for both single- and multi-phase flows, and the other through the correlated velocity and release of latent heat fluctuations which are unique to the flows with phase change. The roles played by both mechanisms are identified and assessed. The present turbulence model predicts that although the mushy zone defined by the mean temperature field is generally of substantial thickness as a result of the convection effect, the actual instantaneous zone thickness varies substantially due to turbulence effect. This finding is in contrast to the traditionally held viewpoint, based on the conduction analysis, of a generally thin mushy zone. The impact of turbulent heat transfer on local dendrite formation and remelting is illustrated and the issues involved in model development highlighted.

Numerical Evaluation of Multiple Phase Change Materials for Pulsed Electronics Applications

2016 ◽  
Author(s):  
David Gonzalez-Nino ◽  
Lauren M. Boteler ◽  
Dimeji Ibitayo ◽  
Nicholas R. Jankowski ◽  
Pedro O. Quintero
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Source ◽  
Phase Change ◽  
Phase Change Materials ◽  
High Energy ◽  
Heat Of Fusion ◽  
Maximum Temperature ◽  
Conductivity Enhancement ◽  
Fast Transient

A simple and easy to implement 1-D heat transfer modeling approach is presented in order to investigate the performance of various phase change materials (PCMs) under fast transient thermal loads. Three metallic (gallium, indium, and Bi/Pb/Sn/In alloy) and two organic (erythritol and n-octadecane) PCMs were used for comparison. A finite-difference method was used to model the transient heat transfer through the system while a heat integration or post-iterative method was used to model the phase change. To improve accuracy, the material properties were adjusted at each iteration depending on the state of matter of the PCM. The model assumed that the PCM was in direct contact with the heat source, located on the top of the chip, without the presence of a thermal conductivity enhancement. Results show that the three metallic PCMs outperform organic PCMs during fast transient pulses in spite of the fact that two of the metallic PCMs (i.e. indium and Bi/Pb/Sn/In) have considerably lower volumetric heats of fusion than erythritol. This is due to the significantly higher thermal conductivity values of metals which allow faster absorption of the heat energy by the PCM, a critical need in high-energy short pulses. The most outstanding case studied in this paper, Bi/Pb/Sn/In having only 52% of erythritol’s heat of fusion, showed a maximum temperature 20°C lower than erythritol during a 32 J and 0.02 second pulse. This study has shown thermal buffering benefits by using a metallic PCM directly in contact with the heat source during short transient heat loads.

scholarly journals Impact of Fusion Temperature on Hydrothermal Features of Flow within an Annulus Loaded with Nanoencapsulated Phase Change Materials (NEPCMs) during Natural Convection Process

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Seyyed Masoud Seyyedi ◽  
M. Hashemi-Tilehnoee ◽  
M. Sharifpur
Keyword(s):  
Phase Change ◽  
Entropy Generation ◽  
Phase Change Materials ◽  
Control Volume ◽  
Convection Flow ◽  
Entropy Generation Number ◽  
Decision Variables ◽  
Study Characteristics ◽  
New Type ◽  
Energy And Momentum

A new type of nanofluids is nanoencapsulated phase change materials (NEPCMs), where nanoparticles are made of a shell and a core. In the current study, characteristics of free convection flow, entropy generation, and heat transfer of NEPCMs in an enclosure are investigated. The enclosure is an annulus between concentric horizontal circular and square cylinders with a porous medium. The governing equations (i.e., continuity, energy, and momentum) are written in the nondimensional form and then numerically solved by the control volume finite element method (CVFEM). The results of the validation are in good agreement with those of the literature. The effects of decision variables on the entropy generation number and the average Nusselt number are investigated. The outcomes discovered that there is a maximum for Nu ave and a minimum for N gen at θ f = 0.4 for each value of the Stefan number. Also, Nu ave and ECOP increase by 8.8% and 24.8%, respectively, while N gen decreases by 12.8% when ϕ increases from 0 (pure fluid) to 0.05 at θ f = 0.4 .

Voiding Effects on the Thermal Response of Metallic Phase Change Materials Under Pulsed Power Loading

2017 ◽  
Author(s):  
David Gonzalez-Nino ◽  
Lauren M. Boteler ◽  
Nicholas R. Jankowski ◽  
Dimeji Ibitayo ◽  
Pedro O. Quintero
Keyword(s):  
Silicon Nitride ◽  
Heat Source ◽  
Phase Change ◽  
Phase Change Materials ◽  
Cooling System ◽  
Thermal Response ◽  
Metallic Phase ◽  
Maximum Temperature ◽  
Before And After ◽  
Power Loading

Metallic phase change materials (PCMs) have been demonstrated as an excellent alternative to act as a passive cooling system for pulse power applications. The possibility of integrating metallic PCMs, directly on top of a heat source, reducing the thermal resistance between the device and the cooling solution, could result in a significant improvement in thermal management for transient applications. However, the effectiveness of this method of implementation will depend on the quality of the interface between the metallic PCM and the heat source. For this work, a metallic PCM (49Bi/18Pb/12Sn/21In-Bi/Pb/Sn/In for simplicity) was placed directly on top of a device that has a layer of silicon nitride on the top. The device was pulsed with powers of 40W – 160W (84W/cm2 – 338W/cm2) with a 20 ms duration. After reaching the maximum power, the device was pulsed for a second cycle, and the temperature profiles were compared. Micrographical inspections, at the interlayer between the silicon nitride and metallic PCM, were performed before and after the pulses and compared. A maximum temperature of ≈20–25% higher was observed in the performance (at 80W) after pulse cycling. A visual inspection at the mating surfaces, between the metallic PCM and device, showed a clear difference between the contact surfaces before and after pulses. Significant voiding at the PCM interfacial layer was observed after cyclic loading which is believed to be the cause of the recorded increment in maximum temperature.

Effect of Surface Emissivity on Conjugate Turbulent Natural Convection in an Air-Filled Cavity with a Heat Source

2016 ◽  
Vol 685 ◽  
pp. 315-319 ◽  
Author(s):  
Igor V. Miroshnichenko ◽  
Mikhail A. Sheremet
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Surface Radiation ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Heat Conducting ◽  
Surface Emissivity ◽  
Turbulent Natural Convection ◽  
Effect Of Surface

The interaction of conjugate turbulent natural convection and surface thermal radiation in an air-filled square enclosure having heat-conducting solid walls of finite thickness and a heat source has been numerically studied. The primary focus was on the influence of surface emissivity on complex heat transfer. The mathematical model has been formulated in dimensionless variables such as stream function, vorticity and temperature using k-ε turbulent model. The effect of surface emissivity on the average total Nusselt number has been defined. The distributions of streamlines and temperature fields, describing characteristics of the analyzed fluid flow and heat transfer have been obtained. The results clearly show an essential effect of surface radiation on unsteady turbulent heat transfer.

scholarly journals Effect of phase change materials on heat dissipation of a multiple heat source system

Open Physics ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 797-807
Author(s):  
Kai Yu ◽  
Yao Wang ◽  
Yanxin Li ◽  
Jakov Baleta ◽  
Jin Wang ◽  
...  
Keyword(s):  
Heat Source ◽  
Phase Change ◽  
Heat Pipe ◽  
Phase Change Materials ◽  
Heat Dissipation ◽  
Experimental Tests ◽  
Equilibrium Temperature ◽  
System Structure ◽  
Heat Sources ◽  
Lower Temperature

AbstractThis paper experimentally investigates heat dissipation of a heat pipe with phase change materials (PCMs) cooling in a multiple heat source system. Two heat sources are fixed at one end of the heat pipe. Considering that a heat sink cannot dissipate all the heat generated by two heat sources, various PCMs are used due to a large latent heat. Different materials in a container are wrapped outside of the middle heat pipe to take away the heat from the evaporation section. The experimental tests obtain temperature data of heat source, evaporation section, and energy storage characteristics of PCMs are also determined under constant and dynamic values of the heat source powers. It is found that under this multiple heat source system structure, the phase change material RT35 maintains temperature variations of the evaporation section at a lower temperature and shortens the required time to reach the equilibrium temperature under a heating power of 20 W.

scholarly journals Liquid Crystals as Phase Change Materials for Thermal Stabilization

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Eva Klemenčič ◽  
Mitja Slavinec
Keyword(s):  
Liquid Crystals ◽  
Heat Source ◽  
Electric Field ◽  
Phase Change ◽  
Phase Change Materials ◽  
Thermal Stabilization ◽  
Phase Change Temperature ◽  
Thermotropic Liquid Crystals ◽  
Key Factor ◽  
Change Temperature

Thermal stabilization exploiting phase change materials (PCMs) is studied theoretically and numerically. Using the heat source approach in numerical simulations, we focus on phase change temperature as a key factor in improving thermal stabilization. Our focus is to analyze possible mechanisms to tune the phase change temperature. We use thermotropic liquid crystals (LCs) as PCMs in a demonstrative system. Using the Landau-de Gennes mesoscopic approach, we show that an external electric field or appropriate nanoparticles (NPs) dispersed in LCs can be exploited to manipulate the phase change temperature.

The Characteristics of Turbulent Heat Transfer in a Curved Rectangular Duct With Various Aspect Ratios

2010 ◽  
Author(s):  
Hang Seok Choi ◽  
Tae Seon Park
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Rectangular Duct ◽  
Flow And Heat Transfer ◽  
Aspect Ratios ◽  
Turbulent Characteristics

The turbulent flow fields of a parallel plate or channel with spatially periodic condition have been widely investigated by many researchers. However the rectangular or square curved duct flow has not been fundamentally scrutinized in spite of its engineering significance, especially for cooling device. Hence, in the present study large eddy simulation is applied to the turbulent flow and heat transfer in a rectangular duct with 180° curved angle varying its aspect ratio. The turbulent flow and the thermal fields are calculated and the representative vortical motions generated by the secondary flow are investigated. From the results, the secondary flow has a great effect on the heat and momentum transport in the flow. With changing the aspect ratio, the effect of the geometrical variation to the secondary flow and its influence on the turbulent characteristics of the flow and heat transfer are studied.

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