Loop Heat Pipe Design, Manufacturing, and Testing: An Industrial Perspective

2009 ◽  
Author(s):  
W. G. Anderson ◽  
P. M. Dussinger ◽  
S. D. Garner ◽  
J. R. Hartenstine ◽  
D. B. Saraff
Keyword(s):  
Heat Pipes ◽  
Two Phase ◽  
Temperature Changes ◽  
Loop Heat Pipes ◽  
Flow Balance ◽  
Power Cycling ◽  
Condenser Temperature ◽  
Phase Systems ◽  
Compensation Chamber ◽  
Design And Testing

Loop Heat Pipes (LHPs) are two-phase devices that can passively transport heat over long distances relative to other passive two phase systems such as heat pipes. Most of the art of LHP fabrication is in the primary and secondary wick. The manufacturing steps for an LHP are described, including the tests to validate the LHP during manufacture. The tests include wick property testing (pore size, permeability, and thermal conductivity), secondary wick testing, and parallel flow balance design and testing. The required tests after the LHP is fabricated include low power starts, shutdown through compensation chamber heating, unbalanced condenser temperature tests, transient testing — both power cycling and condenser temperature changes, and maximum power tests.

Minimizing the Wick Thickness in a Planar Microscale Loop Heat Pipe Using Efficient Thermodynamic Design

2011 ◽  
Author(s):  
Navdeep S. Dhillon ◽  
Jim C. Cheng ◽  
Albert P. Pisano
Keyword(s):  
Heat Flow ◽  
Heat Pipe ◽  
Thermal Characteristics ◽  
Heat Pipes ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Loop Heat Pipes ◽  
Evaporator Section ◽  
Compensation Chamber

Theoretical and numerical thermodynamic analysis of the evaporator section of a planar microscale loop heat pipe is presented, to minimize the permissible wick thickness in such a device. In conventional cylindrical loop heat pipes, a minimum wick thickness is required in order to reduce parasitic heat flow, and prevent vapor leakage, into the compensation chamber. By taking advantage of the possibilities allowed by microfabrication techniques, a planar evaporator/compensation chamber design topology is proposed to overcome this limitation, which will enable wafer-based loop heat pipes with device thicknesses on the order of a millimeter or less. Thermodynamic principles governing two-phase flow of the working fluid in a loop heat pipe are analyzed to elucidate the fundamental requirements that would characterize the startup and steady state operation of a planar phase-change device. A three dimensional finite element thermal-fluid solver is implemented to study the thermal characteristics of the evaporator section and compensation chamber regions of a planar vertically wicking micro-columnated loop heat pipe. The use of in-plane thermal conduction barriers to reduce parasitic heat flow into the compensation chamber is demonstrated.

scholarly journals Recent Advances in Loop Heat Pipes with Flat Evaporator

Entropy ◽  
2021 ◽  
Vol 23 (11) ◽  
pp. 1374
Author(s):  
Pawel Szymanski
Keyword(s):  
Reverse Flow ◽  
Construction Materials ◽  
Poor Performance ◽  
Heat Pipes ◽  
Manufacturing Cost ◽  
Heating Zone ◽  
Loop Heat Pipes ◽  
Start Up ◽  
Flat Evaporator ◽  
Compensation Chamber

The focus of this review is to present the current advances in Loop Heat Pipes (LHP) with flat evaporators, which address the current challenges to the wide implementation of the technology. A recent advance in LHP is the design of flat-shaped evaporators, which is better suited to the geometry of discretely mounted electronics components (microprocessors) and therefore negate the need for an additional transfer surface (saddle) between component and evaporator. However, various challenges exist in the implementation of flat-evaporator, including (1) deformation of the evaporator due to high internal pressure and uneven stress distribution in the non-circular casing; (2) heat leak from evaporator heating zone and sidewall into the compensation chamber; (3) poor performance at start-up; (4) reverse flow through the wick; or (5) difficulties in sealing, and hence frequent leakage. This paper presents and reviews state-of-the-art LHP technologies; this includes an (a) review of novel manufacturing methods; (b) LHP evaporator designs; (c) working fluids; and (d) construction materials. The work presents solutions that are used to develop or improve the LHP construction, overall thermal performance, heat transfer distance, start-up time (especially at low heat loads), manufacturing cost, weight, possibilities of miniaturization and how they affect the solution on the above-presented problems and challenges in flat shape LHP development to take advantage in the passive cooling systems for electronic devices in multiple applications.

Derivation and Validation of a Figure of Merit for Loop Heat Pipes With Medium Temperature Working Fluids

2016 ◽  
Vol 138 (5) ◽  
Author(s):  
Wukchul Joung ◽  
Jinho Lee ◽  
Sanghyun Lee ◽  
Joohyun Lee
Keyword(s):  
Steady State ◽  
Thermal Performance ◽  
Figure Of Merit ◽  
Saturation Pressure ◽  
Heat Pipes ◽  
Working Fluid ◽  
Medium Temperature ◽  
Working Fluids ◽  
Loop Heat Pipes ◽  
Compensation Chamber

The working fluids of loop heat pipes (LHPs) play an important role in the operation of the LHPs by influencing the operating temperatures and the heat transfer limits. Therefore, the proper selection of a working fluid is a key practice in LHP fabrication, and there has been a high demand for an appropriate index that enables the quantitative comparison of the steady-state thermal performance of the working fluids. In this work, a figure of merit for LHPs was theoretically derived and experimentally verified. In particular, the pressure losses in the LHP operation were balanced with the saturation pressure difference between the evaporator and the compensation chamber to derive the figure of merit. This derived figure of merit for LHPs successfully predicted the steady-state thermal performance of the tested working fluids within the variable conductance regime. In the constant conductance regime, the differences in the condenser cooling capacity and in the liquid subcooling for different working fluids determined the thermal performance of each working fluid. The limitations and prospects of the proposed figure of merit were discussed in detail.

scholarly journals Hysteresis phenomena in flat-type loop heat pipe

2020 ◽  
pp. 166-166
Author(s):  
Gai Dongxing ◽  
Sun Jingyu ◽  
Chen Chen ◽  
Chen Ting
Keyword(s):  
Previous History ◽  
Heat Pipes ◽  
Temperature Hysteresis ◽  
Liquid Distribution ◽  
Loop Heat Pipes ◽  
Load Dependence ◽  
Flat Type ◽  
History Of ◽  
Compensation Chamber ◽  
Hysteresis Phenomena

Testing of loop heat pipes (LHPs) showed that the heat-load dependence of the operating temperature was not always unambiguous. It may have hysteresis phenomena. The temperature hysteresis had a certain relationship with previous history of the power variation, and also related to the initial parameters of the LHP. It has been found that the temperature hysteresis of the LHP was related to the gas-liquid distribution in the compensation chamber (CC) which depended on the interaction between heat leak of evaporator and the reflux liquid from condenser. The temperature of the LHP evaporator rose with the gas phase in the compensation chamber increased.

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.

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