Measurements and simulations of transient characteristics of heat pipes

Measurements and simulations of transient characteristics

of heat pipes

Jarosław Legierski a ,Bogusław Wie ßcek

a,*

,Gilbert de Mey

b

a

Technical University of Ło ´dz ´,Institute of Electronics,ul.Wo ´lczanska 223,90-924Ło ´dz ´,Poland

b

University of Ghent,Department of Electronics and Information Systems,Sint Pieternieuwstraat 41,9000Ghent,Belgium

Received 1April 2004;received in revised form 13May 2005

Available online 5August 2005

Abstract

The rejection of heat generated by components and circuits is a very important aspect in design of electronics sys-tems.Heat pipes are very effective,low cost elements,which can be used in cooling systems.This paper presents the modelling and measurements of the heat and mass transfer in heat pipes.The physical model includes the effects of liquid evaporation and condensation inside the heat pipe.The internal vapour flow was fully simulated using compu-tational fluid dynamics.The theory has been compared with experimental measurements using thermographic camera and contact thermometers.The main purpose of this study is to determine the effective heat pipe thermal conductivity in transient state during start up the pipe operation and temperature increase.Ó2005Elsevier Ltd.All rights reserved.

1.Introduction

The investigations of heat pipes and their applica-tions into thermal management are known for years,but lately they have become more attractive to transport and dissipate heat in electronics [2,3,6,7].It is mainly due to the high effectiveness,small size and compact con-struction.Most of the previous research was made for static thermal conditions,and it resulted in getting the effective thermal resistance [6,7,9–11].

Heat pipe is a passive heat transfer device with a high effective thermal conductivity.The device is built up as hermetic container that is partially filled with a fluid (typically water for electronic cooling design).The inner surfaces of the heat pipe have a capillary wicking mate-

rial.The liquid in the pipe saturates the capillary wick.When one heats up the end of the pipe,the liquid at this place evaporates.Because evaporated medium in the heated section has a higher pressure than in the other part of the pipe,the vapour moves to the colder section,where it is cooled down and condensed.The condensed liquid is then transported back to the hot area thought the capillary wicks.This process causes a transport of heat and mass along the pipe [7,12].

In such a heat sink one can define three sections:–evaporator,–condenser,

–adiabatic region in the middle of the pipe.

Usually,the heat pipe is modelled as a very high ther-mal conductivity

element (k =50000W/m K)[5].The purpose of the measurements and simulations presented in this paper is to determine the effective thermal

0026-2714/$-see front matter Ó2005Elsevier Ltd.All rights reserved.doi:10.1016/j.microrel.2005.06.003

*

Corresponding author.

E-mail address:wiecek@p.lodz.pl (B.Wie ßcek).

Microelectronics Reliability 46(2006)109–115

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