Measurements and simulations of transient characteristics of heat pipes
The rejection of heat generated by components and circuits is a very important aspect in design of electronics systems. 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 computational 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.
Heat pipes: the silent way to manage desktop thermal problems
The continuous increase in system power and decrease in available volume present challenges in desktop computer thermal management. Traditional desktop computer design has relied on natural convection from a heat sink placed directly on the processor. With increasing processor power, it has been necessary to add a processor fan to these local heat sinks. Components with moving parts are the most unreliable desktop computer components. The use of heat pipes may eliminate the use of processor fans and their inherent reliability concerns. A heat pipe heat sink is a passive cooling device that requires no moving parts, and operates silently and reliably. Heat pipe technology is emerging as a cost-effective thermal solution for the desktop industry. This paper explains the basic operation of heat pipes and provides a method to assess heat pipe heat sink design feasibility. Issues of heat pipe heat sink manufacturability and reliability are addressed. Fan sinks placed directly over the processor occupy the most valuable real estate in a computer and can interfere with the placement of add-on boards and other system components. Heat pipe sinks transport heat away from the obstructions and constraints of neighbouring boards to where it can be conveniently dissipated. The ability of the heat pipe to be formed to meet location and space availability and its characteristic low /spl Delta/T as a function of length permit the heat pipe heat sink system to provide the maximum effective heat sink surface area with minimum volume demand. The heat load can be conducted to open areas within the system.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.