Miniature Loop Heat Pipes for Electronic Cooling

2003 ◽  
Author(s):  
Triem T. Hoang ◽  
Tamara A. O’Connell ◽  
Jentung Ku ◽  
C. Dan Butler ◽  
Theodore D. Swanson
Keyword(s):  
Heat Transport ◽  
Electrical Power ◽  
Heat Pipes ◽  
Thermal Control ◽  
Electronic Cooling ◽  
Working Fluid ◽  
Cooling Systems ◽  
Loop Heat Pipes ◽  
Steel Tubing ◽  
Operational Issues

Thermal management of modern electronics has become a problem of significant interest due to the demand for power and reduction in packaging size. Requirements of next-generation microprocessors in terms of power dissipation and heat flux will certainly outgrow the capability of today’s thermal control technology. LHPs, like conventional heat pipes, are capillary pumped heat transport devices. They contain no mechanical moving part to wear out or require electrical power to operate. But unlike heat pipes, LHPs possess much higher heat transport capabilities enabling them to transport large amounts of heat over long distances in small flexible lines for heat rejection. In fact, a miniature ammonia LHP developed for a NASA space program is capable of transporting 60W over a distance of 1 meter in 1/16”O.D. stainless steel tubing. Therefore, miniature LHPs using water as the working fluid are excellent candidates to replace heat pipes as heat transports in electronic cooling systems. However, a number of operational issues regarding system performance, cost, and integration/packaging must be resolved before water LHPs can become a viable option for commercial electronics.

The Performance of Methanol and Water Heat Pipes for Electronics Cooling Applications in Spacecraft Instrumentation

2005 ◽  
Author(s):  
John D. Bernardin
Keyword(s):  
Heat Pipe ◽  
Heat Transport ◽  
Thermal Performance ◽  
Electronics Cooling ◽  
Heat Pipes ◽  
Electronic Cooling ◽  
Working Fluid ◽  
Cooling Systems ◽  
Experimental Apparatus ◽  
Moving Parts

Increases in the power density of electronics and the corresponding decreases in packaging space have driven the development and enhancement of numerous electronics cooling strategies. The design of cooling systems for electronics are particularly challenging in spacecraft environments where there exists the additional requirements of minimal mass and volume, high reliability, reduced complexity and number of moving parts, and ability to operate in a reduced or gravity-free environment. One cooling technique that has proven to satisfy these demanding and integrated requirements for spacecraft electronics cooling applications, involves the use of heat pipes. The heat pipe is a passive heat transport device that requires no moving parts, is highly compact and reliable, and is an efficient mover of thermal energy in reduced gravity environments. Despite all of these positive features, heat pipes do have limitations and functional characteristics that designers must be keenly aware of when incorporating them into the development of electronic cooling systems. These include, in part, limits on the heat transport capacity and operational temperature, as well as performance variations between seemingly identical heat pipes due to contamination or manufacturing flaws. This paper discusses thermal analyses and performance testing of commercial copper heat pipes that utilize a sintered copper wick with either methanol or water as the working fluid. First, the electronic cooling application, thermal operating requirements, and commercial heat pipe designs are introduced. Next, the models and analyses used to predict the heat transport limits for the heat pipes are discussed. Following this, the experimental apparatus and procedures used to characterize the thermal performance of the heat pipes are presented. Finally, with the aid of empirical data, assessments of the thermal performance of each heat pipe, the range of performance variation between heat pipes, as well as the applicability and accuracy of the analytical performance models are provided.

A High Performance Semi-Passive Cooling System: The Pulse Thermal Loop

Volume 3 ◽  
2004 ◽  
Author(s):  
Mark M. Weislogel ◽  
Michael A. Bacich
Keyword(s):  
Heat Transport ◽  
High Performance ◽  
Driving Forces ◽  
Cooling System ◽  
Heat Pipes ◽  
Thermal Control ◽  
High Heat ◽  
Transport Systems ◽  
Passive Cooling ◽  
Cooling Systems

Over the past decade, the search for and development of high performance thermal transport systems for a variety of cooling and thermal control applications have intensified. One approach employs a new semi-passive oscillatory heat transport system called the Pulse Thermal Loop (PTL). The PTL, which has only recently begun to be characterized, exploits large pressure differentials from coupled evaporators to force (pulse) fluid through the system. Driving pressures of over 1.8MPa (260psid) have been demonstrated. Other passive cooling systems, such as heat pipes and Loop Heat Pipes, are limited by capillary driving forces, typically less than 70kPa (10psid). Large driving forces can be achieved by a mechanically pumped loop, however, at the expense of increased power consumption, increased total mass, and increased system cost and complexity. The PTL can be configured in either active or semi-passive modes, it can be readily designed for large ∼ O(100kW) or small ∼ O(10W) heat loads, and it has a variety of unique performance characteristics. For low surface tension dielectric fluids such as R-134a, the PTL system has over a 10-fold heat carrying capacity in comparison to high performance heat pipes. Data accumulated thus far demonstrate that the PTL can meet many of the requirements of advanced terrestrial and spacecraft cooling systems: a system that is robust, ‘semi-passive,’ high flux, and offers high heat transport thermal control while remaining flexible in design, potentially lightweight, and cost competitive.

scholarly journals ADVANCED TWO-PHASE PASSIVE THERMAL CONTROL DEVICES: LOOP HEAT PIPES AND PULSATING HEAT PIPES

2006 ◽  
Vol 5 (1) ◽  
pp. 54
Author(s):  
Roger R. Riehl
Keyword(s):  
Heat Pipes ◽  
Experimental Tests ◽  
Thermal Control ◽  
Working Fluid ◽  
Pulsating Heat Pipe ◽  
Two Phase ◽  
Space Applications ◽  
Source Temperature ◽  
Loop Heat Pipes ◽  
Control Devices

This paper presents the development of two-phase passive thermal control devices that can be used at both ground and space applications. These devices operate by acquiring heat through their evaporation section and rejecting through their condensation section, keeping a tight control on the heat source temperature without the presence of moving parts. Recent researches with loop heat pipes (LHPs) have showed the great capability of such a device in managing high levels of heat while keeping the source temperature within certain levels. For this case, experimental tests of a LHP are presented, where the behavior related to its operation with power cycles can be evaluated and its performance can be verified. This paper also presents an investigation of a two-phase thermal control device called pulsating heat pipe (PHP) configured as an open loop. Experimental tests with different working fluids are presented, which shows the great capability of the PHP in operating at both horizontal and vertical orientations and promoting the thermal control, which is highly affected by the working fluid and geometric parameters. The experimental results presented for both devices are intended to contribute for the continuous development of these two passive thermal control devices.

scholarly journals Experimental Study on Thermal Performance of a Loop Heat Pipe with Different Working Wick Materials

Energies ◽  
2021 ◽  
Vol 14 (9) ◽  
pp. 2453
Author(s):  
Kyaw Zin Htoo ◽  
Phuoc Hien Huynh ◽  
Keishi Kariya ◽  
Akio Miyara
Keyword(s):  
Stainless Steel ◽  
Heat Pipes ◽  
Working Fluid ◽  
Stable Operation ◽  
Loop Heat Pipe ◽  
Heater Surface ◽  
Loop Heat Pipes ◽  
Limited Temperature ◽  
Sintered Stainless Steel ◽  
Continuous Heat

In loop heat pipes (LHPs), wick materials and their structures are important in achieving continuous heat transfer with a favorable distribution of the working fluid. This article introduces the characteristics of loop heat pipes with different wicks: (i) sintered stainless steel and (ii) ceramic. The evaporator has a flat-rectangular assembly under gravity-assisted conditions. Water was used as a working fluid, and the performance of the LHP was analyzed in terms of temperatures at different locations of the LHP and thermal resistance. As to the results, a stable operation can be maintained in the range of 50 to 520 W for the LHP with the stainless-steel wick, matching the desired limited temperature for electronics of 85 °C at the heater surface at 350 W (129.6 kW·m−2). Results using the ceramic wick showed that a heater surface temperature of below 85 °C could be obtained when operating at 54 W (20 kW·m−2).

Thermal Control with Low Power, Miniature Loop Heat Pipes

1999 ◽  
Author(s):  
Walter B. Bienert ◽  
William J. Krotiuk ◽  
Michael N. Nikitkin
Keyword(s):  
Low Power ◽  
Heat Pipes ◽  
Thermal Control ◽  
Loop Heat Pipes

Experimental Study of Linear and Radial Two-Phase Heat Transport Devices Driven by Electrohydrodynamic Conduction Pumping

2015 ◽  
Vol 137 (2) ◽  
Author(s):  
Matthew R. Pearson ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Source ◽  
Capillary Pressure ◽  
Heat Transport ◽  
Radial Direction ◽  
Heat Pipes ◽  
Working Fluid ◽  
Phase Flow ◽  
Transport Capacity ◽  
Two Phase ◽  
Capillary Phenomenon

Heat pipes are well known as simple and effective heat transport devices, utilizing two-phase flow and the capillary phenomenon to remove heat. However, the generation of capillary pressure requires a wicking structure and the overall heat transport capacity of the heat pipe is generally limited by the amount of capillary pressure generation that the wicking structure can achieve. Therefore, to increase the heat transport capacity, the capillary phenomenon must be either augmented or replaced by some other pumping technique. Electrohydrodynamic (EHD) conduction pumping can be readily used to pump a thin film of a dielectric liquid along a surface, using electrodes that are embedded into the surface. In this study, two two-phase heat transport devices are created. The first device transports the heat in a linear direction. The second device transports the heat in a radial direction from a central heat source. The radial pumping configuration provides several advantages. Most notably, the heat source is wetted with fresh liquid from all directions, thereby reducing the amount of distance that must be travelled by the working fluid. The power required to operate the EHD conduction pumps is a trivial amount relative to the heat that is transported.

Experimental Investigation of the Maximum Heat Transport in Triangular Grooves

1996 ◽  
Vol 118 (3) ◽  
pp. 740-746 ◽  
Author(s):  
H. B. Ma ◽  
G. P. Peterson
Keyword(s):  
Experimental Investigation ◽  
Heat Transport ◽  
Heat Pipes ◽  
Effective Area ◽  
Experimental Results ◽  
Test Facility ◽  
Working Fluid ◽  
Maximum Heat ◽  
Pressure Losses ◽  
Micro Heat Pipes

An experimental investigation was conducted and a test facility constructed to measure the capillary heat transport limit in small triangular grooves, similar to those used in micro heat pipes. Using methanol as the working fluid, the maximum heat transport and unit effective area heat transport were experimentally determined for ten grooved plates with varying groove widths, but identical apex angles. The experimental results indicate that there exists an optimum groove configuration, which maximizes the capillary pumping capacity while minimizing the combined effects of the capillary pumping pressure and the liquid viscous pressure losses. When compared with a previously developed analytical model, the experimental results indicate that the model can be used accurately to predict the heat transport capacity and maximum unit area heat transport when given the physical characteristics of the working fluid and the groove geometry, provided the proper heat flux distribution is known. The results of this investigation will assist in the development of micro heat pipes capable of operating at increased power levels with greater reliability.

Effect of Fluid Loading on the Performance of Wicked Heat Pipes

Volume 3 ◽  
2004 ◽  
Author(s):  
R. Kempers ◽  
A. Robinson ◽  
C. Ching ◽  
D. Ewing
Keyword(s):  
Heat Flux ◽  
Heat Pipe ◽  
Heat Transport ◽  
Heat Pipes ◽  
Working Fluid ◽  
Fluid Loading ◽  
Maximum Heat ◽  
Horizontal Orientation ◽  
Maximum Heat Flux ◽  
Dry Out

A study was performed to experimentally characterize the effect of fluid loading on the heat transport performance of wicked heat pipes. In particular, experiments were performed to characterize the performance of heat pipes with insufficient fluid to saturate the wick and excess fluid for a variety of orientations. It was found that excess working fluid in the heat pipe increased the thermal resistance of the heat pipe, but increased maximum heat flux through the pipe in a horizontal orientation. The thermal performance of the heat pipe was reduced when the amount of working fluid was less than required to saturate the wick, but the maximum heat flux through the heat pipe was significantly reduced at all orientations. It was also found in this case the performance of this heat pipe deteriorated once dry-out occurred.

Experimental Study on Applied Thin Vapor Chamber and Embedded Heat Pipe Heat Sinks

2009 ◽  
Author(s):  
Garrett A. Glover ◽  
Yongguo Chen ◽  
Annie Luo ◽  
Herman Chu
Keyword(s):  
Heat Pipe ◽  
Heat Sink ◽  
High Performance ◽  
Structural Integrity ◽  
Heat Pipes ◽  
Electronic Cooling ◽  
Working Fluid ◽  
Vapor Chamber ◽  
Trade Offs ◽  
Pipe Heat

The current work is a survey of applied applications of passive 2-phase technologies, such as heat pipe and vapor chamber, in heat sink designs with thin base for electronic cooling. The latest improvements of the technologies and manufacturing processes allow achievable heat sink base thickness of 3 mm as compared to around 5 mm previously. The key technical challenge has been on maintaining structural integrity for adequate hollow space for the working fluid vapor in order to retain high performance while reducing the thickness of the overall vapor chamber or flattened heat pipe. Several designs of thin vapor chamber base heat sink and embedded heat pipe heat sink from different vendors are presented for a moderate power density application of a 60 W, 13.2 mm square heat source. Numerous works have been published by both academia and commercial applications in studying the fundamental science of passive 2-phase flow technologies; their performance has been compared to solid materials, like aluminum and copper. These works have established the merits of using heat pipes and vapor chambers in electronic cooling. The intent of this paper is to provide a methodical approach to help to accelerate the process in evaluating the arrays of different commercial designs of these devices in our product design cycle. In this paper, the trade-offs between the different types of technologies are discussed for parameters such as performance advantages, physical attributes, and some cost considerations. This is a bake-off evaluation of the complete heat sink solutions from the various vendors and not a fundamental research of vapor chambers and heat pipes — for that, it is best left to the vendors and universities.

Effect of Thin Film Condensation on Thermal Performance of Oscillating Heat Pipes

2006 ◽  
Author(s):  
S. B. Liang ◽  
G. P. Xu
Keyword(s):  
Thin Film ◽  
Liquid Film ◽  
Heat Pipe ◽  
Heat Transport ◽  
Slug Flow ◽  
Thin Liquid Film ◽  
Experimental Studies ◽  
Heat Pipes ◽  
Film Condensation ◽  
Working Fluid

Self-sustainable motions of the slug flow in oscillating heat pipes have been investigated in the paper. Thin film condensation in the capillary channels of the condenser of the oscillating heat pipes was studied. Instability of the thin liquid film on the characteristics of heat pipes was analysed. The extra thermal resistance caused by the thickness of the thin liquid film was taken into account for the numerical simulation of the oscillatory motions of the slug flow in the heat pipes. Saturated temperatures and pressures of the working fluid in the condenser were obtained. Thermoacoustic theory was applied to calculate heat transport through the adiabatic section of the heat pipes. Experimental studies were carried out to understand the heat transfer behaviours of heat pipes. One heat pipe with the working fluid of HFC-134a was evaluated. The heat pipe is made of aluminium plate and has the width of 50 mm and thickness of 1.9 mm. Numerical and experimental results relevant to the heat transport capability of the heat pipe were analysed and compared.

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