Thermal Control Of Electronic Equipment Research Articles

Ultrasounds Used as Promoters of Heat-Transfer Enhancement of Natural Convection in Dielectric Fluids for the Thermal Control of Electronic Equipment

We present an experimental investigation of the effect of ultrasound application to increase the heat-transfer coefficient for natural convection of a dielectric fluid. An experimental analysis is carried out to estimate the increase of the convective heat-transfer coefficient between an electronic board and a refrigerant fluid, the Fluorinert Electronic Fluid FC-72. For this purpose, an experimental apparatus composed of an electronic board, its electronic control circuit, and data acquisition systems have been designed and implemented. The data collected appear to confirm in some situations of practical interest the enhancement effect of the convective heat-transfer coefficient in connection with the use of ultrasound. The most favorable condition was observed with the fluid in quite low subcooled conditions.

THERMAL PERFORMANCE OF THERMOSYPHON FOR DIFFERENT WORKING FLUIDS

In this paper, an experimental investigation was performed of the thermal performance of different working fluids in thermosyphons that can be used in thermal control of electronic equipment. The working fluids were considered acetone, water, ethanol, and methanol. The thermosyphon are manufactured of copper with an outer diameter of 9.45 mm, an inner diameter of 7.75 mm, a total length of 200 mm, whereas an evaporator of 80 mm length, an adiabatic region of 20 mm in length and a condenser of 100 mm in length. They were loaded with 1.39 ml of the working fluid, corresponding to a filling ratio of 40% of the evaporator volume. Experimental tests were performed in a vertical position considering thermal loads between 5W and 25W. The thermosyphons operated satisfactorily in all the tests. The operating temperature distribution as a function of time and the heat resistance behavior as a function of power dissipation have been presented for each analyzed working fluid. These results indicated that acetone is the working fluid that has the best thermal performance.

ЕКСПЕРИМЕНТАЛЬНІ ДОСЛІДЖЕННЯ МОЖЛИВОСТЕЙ ІНТЕНСИФІКАЦІЇ ТЕПЛООБМІНУ ПРИ ПАРОУТВОРЕННІ НА МІКРОКАНАЛЬНИХ ПОВЕРХНЯХ

The use of grooves, as the structure of flat plate heat pipe is widespread and is a popular and effective technical solution in the practical implementation of various design systems for thermal control of electronic equipment. Advanced thermal control system must meet two criteria: 1) have a high heat transfer coefficient; 2) remove heat of high density. However, the last criterion leads to the fact that the high density heat flux may lead to a boiling limit, which leads to a drastic decrease in heat transfer coefficient, and conducts to a rapid increase of surface temperature. The paper presents an experimental investigation of the heat transfer characteristics of the microgrooved structures at vaporization of water and ethanol. The structures are represented in the form of axial grooves with a square section dimensions of 0.3, 0.5 and 0.7 mm, and a rectangular cross section with the same width and pitch parameters of the channel but with double depth of channels. Studies showed that in the grooved structures three modes of vaporization occur as follows: evaporation, evaporation-pulsation and boiling. The experiment revealed the area having constancy of the heat transfer coefficient at varying specific heat flux that is typical for evaporation. At certain heat flux value the nucleate boiling in the grooves is initiated, and heat transfer coefficient is growing at increasing heat flux. Boiling in the channels of micro-grooved surface is accompanied by a slug boiling regime, and formation of a thin liquid film on the surface of the channel. It is essentially increasing the heat transfer characteristics of the micro-grooved structures. Double of the channel depth leads to increase in heat transfer coefficient up to 30 - 40% for both water and ethanol. Increase of the heat transfer coefficient could be explained by the enlargement of the heat transfer surface of the channels. Increasing of the effective pore radius by the increasing of the channels depth leads to reduction in the hydraulic resistance of the channels that accompanies increase of the critical heat flux up to 50 - 60%.

Применение тепловых труб в системах обеспечения тепловых режимов РЭА: современное состояние и перспективы

Today, the widespread application of cooling systems based on heat pipes makes significant contribution to the solution of the thermal control of electronic equipment. The use of heat pipes as heat transfer devices and heat exchanging equipment allows creating an efficient new-generation heat sinks. Nowadays, heat pipes are widely used in the following areas: electronic equipment, special application computer equipment (from small computers to large data centres), high power electronics. The article provides an analysis of the current state and prospects of heat pipes application in thermal control systems for ground-based electronic equipment.

Miniature Loop Heat Pipe With Flat Evaporator for Cooling Computer CPU

This paper presents an experimental investigation on a copper miniature loop heat pipe (mLHP) with a flat disk shaped evaporator, 30mm in diameter and 10-mm thick, designed for thermal control of computer microprocessors. Tests were conducted with water as the heat transfer fluid. The device was capable of transferring a heat load of 70W through a distance up to 150mm using 2-mm diameter transport lines. For a range of power applied to the evaporator, the system demonstrated very reliable startup and was able to achieve steady state without any symptoms of wick dry-out. Unlike cylindrical evaporators, flat evaporators are easy to attach to the heat source without need of any cylinder-to-plane reducer material at the interface and thus offer very low thermal resistance to the heat acquisition process. In the horizontal configuration, under air cooling, the minimum value for the mLHP thermal resistance is 0.17degC/W with the corresponding evaporator thermal resistance of 0.06degC/W. It is concluded from the outcomes of the current study that a mLHP with flat evaporator geometry can be effectively used for the thermal control of electronic equipment including notebooks with limited space and high heat flux chipsets. The results also confirm the superior heat transfer characteristics of the copper-water configuration in mLHPs

Experimental and numerical analysis of the transient response of a miniature heat pipe

The aim of this research is to analyse the behaviour of a miniature heat pipe during transient events. This type of heat pipe is used for thermal control of electronic equipment in space applications. A one-dimensional model has been developed. It allows to calculate the transient evolution of a series of profiles along the heat pipe: liquid and vapour fluxes; liquid and vapour pressures; and wall, liquid and vapour temperatures. It is based on the numerical solution of the differential equations for mass, momentum and energy conservation in the two phases, the equation of thermodynamic equilibrium at the interface, and the energy equation of the wall. This model uses three hydraulic parameters (wick porosity, pore radius and permeability) and three thermal parameters (condenser and evaporator thermal conductances, saturated wick capacitance) which have to be determined from experiments. The model was validated with tests on a 2.1 × 10 mm 2 rectangular cross section flat copper-water heat pipe (length = 200 mm, wick: metallic mesh). Steady-state tests have first been performed to determine the performance characteristics—temperature difference as a function of the heat rate—up to the capillary limit, for different inclination angles. These tests allow to determine the values of the hydraulic parameters and the thermal conductances of the heat pipe. As a first approximation, constant values of the parameters can be used to cover the whole range of the experimental conditions. The transient behaviour has then been investigated, resulting from a step variation of the evaporator heat rate.

Thermal control of electronic equipment by heat pipes

In the frame of the BRITE-EURAM european programme (KHIEPCOOL project), a literature survey on the main heat pipe and micro heat pipe technologies developed for thermal control of electronic equipment has been carried out. The conventional heat pipes are cylindrical, flat or bellow tubes, using wicks or axial grooves as capillary structures. In the field of micro heat pipes, three and four corner tubes have been developed. The pipes are mounted on single chips, in-line chip arrays or integrated into the component interconnection substrate. The best performances were achieved with Plesch's axially grooved flat miniature heat pipe [1], which is able to transfer a heat flux of about 60 W·cm −2. Theoretical models have shown that the performance of micro heat pipe arrays increase with increasing tube diameter, decreasing tube length and increasing heat pipe density. The heat pipe technologies are classified and compared according to their geometry and location in the system. A list of about 150 references, classified according to their subjects, is presented.

The effect of tip convection on the performance and optimum dimensions of cooling fins

Cooling fins are the most used thermal devices. They are used mostly in thermal control of electronic equipment as well as in compact heat exchangers. In this paper, three types of fins are analyzed: longitudinal, spine and annular; each of them has three possible shapes: constant thickness, triangular and parabolic. The paper considers effect of the tip condition and fins with convective tips are compared to insulated tip fins. The comparison is important mostly because usually the solutions for insulated tip fins are easier and available for more cases.

Heat pipe research and development in the Americas

The purpose of this paper is to present a review of the recent heat pipe research and development efforts in the Americas. After discussing the research and development of high performance monogroove, tapered artery, trapezoidally grooved, dual-slot, double wall artery, ceramic and other specially designed heat pipes, the transient modeling and testing efforts are reviewed for a variety of heat pipes that also includes variable conductance heat pipes and thermosyphons. The application of heat pipes to terrestrial systems is discussed for the heat recovery systems, Rankine and solar systems, fusion reactor core cooling and the thermal control of electronic equipment. The application of heat pipes to space systems includes the thermal control of space station and satellites, and the radiator design of large space power systems. Although many advances have been made in the past few years in the development of high heat transfer performance heat pipes, the heat pipe modeling efforts are not in step with the technological requirements.