scholarly journals NUMERICAL ANALYSES ON VAPOR PRESSURE DROP IN A CENTERED-WICK ULTRA-THIN HEAT PIPE

2019 ◽  
Vol 13 ◽  
Author(s):  
Yasushi Koito
Keyword(s):  
Pressure Drop ◽  
Vapor Pressure ◽  
Heat Pipe ◽  
Numerical Analyses

scholarly journals Numerical Investigation on the Dielectric Working Fluid Effect on the Flow and Thermal Parameters of an Electrohydrodynamic Flat Heat Pipe

2020 ◽  
Vol 79 (1) ◽  
pp. 128-152
Author(s):  
Imène Saad ◽  
Samah Maalej ◽  
Mohamed Chaker Zaghdoudi
Keyword(s):  
Pressure Drop ◽  
Vapor Pressure ◽  
Electric Field ◽  
Heat Pipe ◽  
Liquid Velocity ◽  
Thermal Parameters ◽  
Working Fluid ◽  
Liquid Pressure ◽  
Pressure Drops ◽  
Capillary Limit

The present work highlights the impact of the working dielectric fluid on the flow and the thermal parameters of an axially grooved flat mini heat pipe (FMHP) submitted to Electrohydrodynamic (EHD) effects. Three dielectric working fluids are considered: pentane, R123, and R141b. A model is developed by considering the Laplace-Young, mass, momentum, and energy balance equations. The numerical results show that the electric field affects the liquid distribution along the heat pipe and helps the condensate to flow back to the evaporator section. Moreover, under the electric field conditions, the vapor pressure drop increases, however, the liquid pressure drop decreases. The effect of the electric field on the liquid velocity depends on the FMHP zone, and the vapor velocity is hardly affected by the EHD effects. Furthermore, lower capillary driving pressures are required to provide the necessary capillary pumping under EHD conditions. Besides, pentane allows for higher vapor pressure drops compared to those obtained with R123 and R141b, while the liquid pressure drops are highest for R123. It is found that with R123, the liquid velocity is higher than that reached with R141b and pentane. It is also demonstrated that the capillary limit increases under EHD conditions, and for R141b, the capillary limit is the highest either in zero-field and EHD conditions. Best heat pipe thermal performances are observed for wide and deep grooves with R141b. Finally, the optimum fill charge allowing the maximum heat transfer capacity is determined for each working fluid and different groove dimensions. It is shown that the optimum fill charge is hardly affected by the electric field whatever the working fluid. R123 requires the highest optimum fill charge, however, the heat transport capacity of the FMHP is the lowest when using this working fluid.

An advanced conduction based heat pipe model accounting for vapor pressure drop

2021 ◽  
Vol 175 ◽  
pp. 121014
Author(s):  
Sascha Zimmermann ◽  
Robert Dreiling ◽  
Thinh Nguyen-Xuan ◽  
Michael Pfitzner
Keyword(s):  
Pressure Drop ◽  
Vapor Pressure ◽  
Heat Pipe ◽  
Pipe Model

Transient Performance of Heat Pipes Using Nanofluids

2020 ◽  
Author(s):  
Mahboobe Mahdavi ◽  
Amir Faghri
Keyword(s):  
Numerical Model ◽  
Pressure Drop ◽  
Response Time ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Volume Concentration ◽  
Heat Pipes ◽  
Operating Conditions ◽  
Vapor Flow ◽  
Transient Performance

Abstract In the present works, a comprehensive transient numerical model was developed to evaluate the effect of nanofluid on the transient performance of heat pipes. The numerical model solves for compressible vapor flow, the liquid flow in the wick region, and the energy equations in the vapor, wick and wall. The distinctive feature of the model is that it can uniquely determine the heat pipe operating pressure based on the physical and operating conditions of the system. Three nanoparticle types were considered: Al2O3, CuO, and TiO2. The effects of the concentration of nanoparticles (5%, 10%, 20% and 40%) were investigated on the heat pipe response time, thermal resistance, and pressure drop under various operating conditions. The results showed that the use of nanofluid decreased the response time of the heat pipe by the maximum of 27%. It was also discovered that the thermal resistance decreased significantly with an increase in the volume concentration. A maximum reduction of 84%, 82% and 78% in thermal resistance was obtained for Al2O3, CuO, and TiO2, respectively. In addition, the effect of nanoparticles on the liquid pressure drop highly depends on the nanoparticle type and volume concentration.

Competitive Designs of Evaporator Top Cap of the Micro Loop Heat Pipe

2004 ◽  
Author(s):  
Praveen Kumar Arragattu ◽  
Frank M. Gerner ◽  
Priyanka Ponugoti ◽  
H. T. Henderson
Keyword(s):  
Finite Element ◽  
Pressure Drop ◽  
Finite Element Modeling ◽  
Heat Pipe ◽  
Temperature Drop ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Maximum Heat ◽  
Element Modeling

The Micro Loop Heat Pipe (LHP) is a two phase device that may be used to cool electronics, solar collectors and other devices in space applications. A LHP is a two-phase device with extremely high effective thermal conductivity that utilizes the thermodynamic pressure difference developed between the evaporator and condenser and capillary forces developed inside its wicked evaporator to circulate a working fluid through a closed loop. While previous experiments have shown reduction in chip temperature, maximum heat flux was less than theoretically predicted. This paper addresses the main problem with the past designs of top cap which has been the conduction of heat from the heat source to the primary wick. The new top cap design provides conduction pathways which enables the uniform distribution of heat to the wick. The provision of conduction pathways in the top cap increases the pressure losses and decreases the temperature drop. The feasible competitive designs of the top cap with conduction pathways from the fabrication point of view were discussed in detail. Calculation of pressure drop and temperature drop is essential for the determination of optimal solutions of the top cap. Approximate pressure drop was calculated for the top cap designs using simple 2-D microchannel principles. Finite element modeling was performed to determine the temperature drop in the conduction pathways. The conditions used for arriving at the optimal design solutions are discussed. A trapezoidal slot top cap design was chosen for fabrication as it was relatively easy to fabricate with available MEMS fabrication technologies. The exact pressure drop calculation was performed on the fabricated top cap using commercial flow solver FLUENT 6.1 with appropriate boundary conditions. The temperature drop calculation was performed by finite element modeling in ANSYS 6.1. Obtained values of pressure drop and temperature drop for fabricated trapezoidal slot top cap was found to be within the optimal limits.

Entropy Analysis and Optimization of Phase Transition Heat Exchangers

2012 ◽  
Vol 516-517 ◽  
pp. 276-283
Author(s):  
Jian Wang ◽  
Hu Chen ◽  
Hong Biao Huang ◽  
Han Zhong Tao
Keyword(s):  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Pipe ◽  
Entropy Production ◽  
Heat Exchangers ◽  
Entropy Analysis ◽  
Pipe Length ◽  
Analysis Process ◽  
Total Temperature ◽  
Working Media

Entropy analysis method was adopted to analyze and optimize a jacketed pipes-type heat pipe steam generator. In the entropy analysis process, the entropy production resulted from the total temperature difference across the heat exchanger, the entropy production from main heat transfer element – heat pipes and the entropy production caused by the pressure drop due to working media flow on cold and hot sides were taken into consideration. In the calculation, the entropy production in all parts of the heat exchanger was analyzed row by row in a discrete pattern, except for the entropy production due to pressure drop on flue gas side. Analysis results show that for the heat exchanger in this case, the proportions of entropy production in the above-mentioned three parts are respectively 74.79%, 21.75% and 3.46%. On this basis, the article also made optimizing analysis with the cold and hot source temperature, heat pipe length and No. of heat pipe rows as parameters, to provide theoretical basis for further improving the energy efficiency of heat exchangers.

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