scholarly journals NUMERICAL ANALYSES ON VAPOR TEMPERATURE DROP IN AN ULTRA-THIN HEAT PIPE WITH A THIN WICK SHEET

2021 ◽  
Vol 16 ◽  
Author(s):  
Yasushi Koito
Keyword(s):  
Heat Pipe ◽  
Temperature Drop ◽  
Numerical Analyses ◽  
Vapor Temperature

scholarly journals Numerical Analysis of Liquid–Liquid Heat Pipe Heat Exchanger Based on a Novel Model

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 589
Author(s):  
Qilu Chen ◽  
Yutao Shi ◽  
Zhi Zhuang ◽  
Li Weng ◽  
Chengjun Xu ◽  
...  
Keyword(s):  
Experimental Data ◽  
Heat Exchanger ◽  
Heat Pipe ◽  
Temperature Change ◽  
Current Model ◽  
Change Trend ◽  
Liquid Heat ◽  
Novel Model ◽  
Pipe Heat ◽  
Vapor Temperature

Heat pipe heat exchangers (HPHEXs) are widely used in various industries. In this paper, a novel model of a liquid–liquid heat pipe heat exchanger in a countercurrent manner is established by considering the evaporation and condensation thermal resistances inside the heat pipes (HPs). The discrete method is added to the HPHEX model to determine the thermal resistances of the HPs and the temperature change trend of the heat transfer fluid in the HPHEX. The established model is verified by the HPHEX structure and experimental data in the existing literature and demonstrates numerical results that agree with the experimental data to within a 5% error. With the current model, the investigation compares the effectiveness and minimum vapor temperature of the HPHEX with three types of HP diameters, different mass flow rates, and different H* values. For HPs with a diameter of 36 mm, the effectiveness of each is improved by about 0.018 to 0.029 compared to HPs with a diameter of 28 mm. The results show that the current model can predict the temperature change trend of the HPHEX well; in addition, the effects of different structures on the effectiveness and minimum vapor temperature are obtained, which improve the performance of the HPHEX.

Remote Heat Pipe Based Heat Exchanger Performance in Notebook Cooling

2005 ◽  
Author(s):  
Seyyed Khandani ◽  
Himanshu Pokharna ◽  
Sridhar Machiroutu ◽  
Eric DiStefano
Keyword(s):  
Heat Exchanger ◽  
Thermal Resistance ◽  
Heat Pipe ◽  
Cooling System ◽  
Temperature Drop ◽  
Operating Conditions ◽  
Cooling Systems ◽  
Temperature Variations ◽  
Non Linear ◽  
Condenser Temperature

Remote heat pipe based heat exchanger cooling systems are becoming increasingly popular in cooling of notebook computers. In such cooling systems, one or more heat pipes transfer the heat from the more populated area to a location with sufficient space allowing the use of a heat exchanger for removal of the heat from the system. In analsysis of such systems, the temperature drop in the condenser section of the heat pipe is assumed negligible due to the nature of the condensation process. However, in testing of various systems, non linear longitudinal temperature drops in the heat pipe in the range of 2 to 15 °C, for different processor power and heat exchanger airflow, have been measured. Such temperature drops could cause higher condenser thermal resistance and result in lower overall heat exchanger performance. In fact the application of the conventional method of estimating the thermal performance, which does not consider such a nonlinear temperature variations, results in inaccurate design of the cooling system and requires unnecessarily higher safety factors to compensate for this inaccuracy. To address the problem, this paper offers a new analytical approach for modeling the heat pipe based heat exchanger performance under various operating conditions. The method can be used with any arbitrary condenser temperature variations. The results of the model show significant increase in heat exchanger thermal resistance when considering a non linear condenser temperature drop. The experimental data also verifies the result of the model with sufficient accuracy and therefore validates the application of this model in estimating the performance of these systems.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.

A Simplified Conduction Based Modeling Scheme for Design Sensitivity Study of Thermal Solution Utilizing Heat Pipe and Vapor Chamber Technology

2003 ◽  
Vol 125 (3) ◽  
pp. 378-385 ◽  
Author(s):  
Ravi S. Prasher
Keyword(s):  
Heat Pipe ◽  
Temperature Drop ◽  
Heat Pipes ◽  
Sensitivity Study ◽  
Design Sensitivity ◽  
Thermal Design ◽  
Vapor Chamber ◽  
Modeling Tools ◽  
Heating Source ◽  
Thermal Solution

This paper introduces a simplified modeling scheme for the prediction of heat transport capability of heat pipes and vapor chambers. The modeling scheme introduced in this paper enables thermal designers to model heat pipes and vapor chambers in commercially available conduction modeling tools such as Ansys™ and IcePak™. This modeling scheme allows thermal designers to perform design sensitivity studies in terms of power dissipation of heat pipes and vapor chambers for different scenarios such as configurations, heat sink resistance for a given temperature drop between the heating source and the ambient. This paper also discusses how thermal designers can specify requirements to heat pipe/vapor chamber suppliers for their thermal design, without delving into the complete thermo-fluidic modeling of this technology.

Comparison of Boiling and Condensation Characteristics in the Porous Wick of a Flat Heat Pipe in Vertical and Horizontal Orientation

2014 ◽  
Vol 592-594 ◽  
pp. 1461-1465
Author(s):  
Rakesh Hari ◽  
Tom Jolly ◽  
C. Muraleedharan
Keyword(s):  
Phase Change ◽  
Heat Pipe ◽  
Temperature Drop ◽  
Similarity Solutions ◽  
Phase Zone ◽  
Two Phase ◽  
Water Steam ◽  
Pipe System ◽  
Porous Wick ◽  
Flat Heat Pipe

The two-phase flow through porous media is an important topic which spans a broad spectrum of engineering disciplines especially in porous heat pipes. Heat pipe is a thermodynamic device that transports heat energy from one location to another with a negligible temperature drop. The aim of the present work is to investigate the phase change mechanisms, namely boiling and condensation, in the flat heat pipe system with different orientation. Governing equations used for the formulation are continuity, mixture momentum, liquid conservation and energy equations. These equations are converted into three ordinary differential equations using similarity transformation and two-phase similarity solutions are obtained for both boiling and condensing flows. In each case, a two phase zone where the liquid and vapour can coexist appears adjacent to the wall. As the heat transfer at the wall gradually enhances, the liquid saturation at the wall approaches to the limiting value, zero, for boiling and unity for condensation. The present work is an attempt to predict numerically the liquid wall saturation, non-dimensional temperature, non-dimensional temperature gradient and effect of Sherwood number during the phase change of water-steam system in the heat pipe for horizontal and vertical cases. Nomenclature

Characterization of the Performance of Flat Heat Pipes for Electronics Cooling

2000 ◽  
Author(s):  
Unnikrishnan Vadakkan ◽  
Suresh V. Garimella ◽  
Choondal B. Sobhan
Keyword(s):  
Heat Pipe ◽  
Heat Input ◽  
Energy Transport ◽  
Temperature Drop ◽  
Thermal Conductance ◽  
Electronics Cooling ◽  
Heat Pipes ◽  
Flow And Heat Transfer ◽  
Parametric Studies ◽  
Axial Heat

Abstract A computational model has been developed to analyze the transient and steady-state performance of flat heat pipes and assess their performance under different operating and geometric parameters, in order to arrive at optimal designs. The model assumes two-dimensional fields for flow and heat transfer and solves the governing differential equations using a finite-difference approach. The wick region of the heat pipe is analyzed using transport equations for a porous medium. The influence of axial heat conduction along the wall, as well as the energy transport in the wick, on the velocity and temperature distributions is examined. The overall performance of the heat pipe is quantified by calculating an effective thermal conductance from the heat input and the temperature drop along the heat pipe wall. Parametric studies are conducted using the model to investigate the dependence of the heat pipe performance on the heat input at the evaporator, the containing wall thickness, and the porosity of the wick.

Temperature Response of Heat Transport in a Micro Heat Pipe

1999 ◽  
Vol 121 (2) ◽  
pp. 438-445 ◽  
Author(s):  
G. P. Peterson ◽  
H. B. Ma
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transport ◽  
Capillary Flow ◽  
Temperature Drop ◽  
Temperature Response ◽  
Axial Direction ◽  
Vapor Flow ◽  
Micro Heat Pipe

A detailed mathematical model for predicting the heat transport capability and temperature gradients that contribute to the overall axial temperature drop as a function of heat transfer in a micro heat pipe has been developed. The model utilizes a third-order ordinary differential equation, which governs the fluid flow and heat transfer in the evaporating thin film region; an analytical solution for the two-dimension heat conduction equation, which governs the macro evaporating film region in the triangular corners; the effects of the vapor flow on the liquid flow in the micro heat pipe; the flow and condensation of the thin film caused by the surface tension in the condenser; and the capillary flow along the axial direction of the micro heat pipe. With this model, the temperature distribution along the axial direction of the heat pipe and the effect on the heat transfer can be predicted. In order to verify the model presented here, an experimental investigation was also conducted and a comparison with experimental data made. This comparison indicated excellent correlation between the analytical model and experimental results, and as a result, the analysis provides a better understanding of the heat transfer capability and temperature variations occurring in micro heat pipes.

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.

Analysis of Heat Pipe Filled with Several Oxide Nanofluids on the Start-Up Process

2014 ◽  
Vol 490-491 ◽  
pp. 251-255 ◽  
Author(s):  
Yu Ying Gong ◽  
Zong Ming Liu ◽  
Wei Lin Zhao
Keyword(s):  
Temperature Distribution ◽  
Heat Pipe ◽  
Temperature Drop ◽  
Heat Pipes ◽  
Condenser Section ◽  
Evaporator Section ◽  
Heating Section ◽  
Start Up

Three heat pipes with nanofluids of Al2O3-water, CuO-water and SiO2-water were tested experimentally. The temperature distribution of their start-up process was analysed, and compared the heat pipe with water. The results showed that the start-up way of heat pipe filled with nanofluids was coincident, the heat pipe filled with nanofluids showed a lower start-up temperature and a shorter start-up time in evaporator section compared with heat pipe filled with water, the temperature drop between evaporator section and condenser section for the heat pipe filled with nanofluids were reduced by 2-5°C than that of the heat pipe filled with water. The effect of the length of the heating section of heat pipe filled with nanofluids on the start-up process was little.

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