scholarly journals THERMAL TESTS AND TWO-PHASE PHENOMENA OBSERVATIONS IN A TRANSPARENT EXPERIMENTAL LOOP HEAT PIPE

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Frédéric Lefevre ◽  
Benjamin Siedel ◽  
Nathanaël Rivière ◽  
Valérie Sartre
Keyword(s):  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Thermal Tests

Investigation of Loop Heat Pipe Startup Using Liquid Core Visualization

2008 ◽  
Author(s):  
B. P. d’Entremont ◽  
J. M. Ochterbeck
Keyword(s):  
Heat Pipe ◽  
Liquid Core ◽  
High Heat ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Buoyancy Driven Flows ◽  
Compensation Chamber ◽  
Fill Level ◽  
Heat Loads

In this investigation, a Loop Heat Pipe (LHP) evaporator has been studied using a borescope inserted through the compensation chamber into the liquid core. This minimally intrusive technique allows liquid/vapor interactions to be observed throughout the liquid core and compensation chamber. A low conductivity ceramic was used for the wick and ammonia as the working fluid. Results indicate that buoyancy driven flows, both two-phase and single-phase, play essential roles in evacuating excess heat from the core, which explains the several differences in performance between horizontal and vertical orientations of the evaporator. This study also found no discernable effect of the pre-start fill level of the compensation chamber on thermal performance during startup at moderate and high heat loads.

Effect of Vibrations on Thermal Performance of Miniature Loop Heat Pipe for Avionics Cooling: An Experimental Analysis

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Prem Kumar ◽  
Sameer Khandekar ◽  
Yuri F. Maydanik ◽  
Bishakh Bhattacharya
Keyword(s):  
Heat Pipe ◽  
Thermal Performance ◽  
Longitudinal Vibration ◽  
Decisive Role ◽  
Fluid Distribution ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Horizontal Orientation ◽  
Acceleration Rate ◽  
Compensation Chamber

Abstract A loop heat pipe (LHP) is an efficient passive, two-phase heat transfer device which can transport heat up to large distances (over ∼ 5 m) even in the anti-gravity mode. It is necessary to miniaturize the LHPs to make them suitable for space-constrained avionics applications. However, before incorporating these devices under high-vibrational environmental conditions such as those encountered in avionics applications, it is imperative to study their thermal performance under such loads. With the aim of understanding the effect of acceleration and frequency of imposed vibration on thermal performance of miniature LHP (mLHP), a contextual experimental study has been reported here using an ammonia charged mLHP (8 mm evaporator diameter; titanium wick) in the horizontal orientation for two cases: (a) without vibration and (b) with the transverse and longitudinal harmonic vibrations (1–4g, frequencies 15–45 Hz, and sine sweep 15–45 Hz in 1 s). With start-up loads between 5 W and 8 W, the LHP can transfer heat load of about 120 W at safe evaporation temperature of 70 °C. Results show that for the transverse vibration, acceleration rate and frequency of imposed vibrations do not affect the thermal performance of mLHP. For the longitudinal vibration, the device performance gets noticeably enhanced with increased acceleration. The decisive role of heat leak (from evaporator to the compensation chamber (CC)) with imposed vibrations is clearly observed, and its link to the internal fluid distribution can be discerned from data trends.

Optimizing the design for a two-phase cooling loop heat pipe

2016 ◽  
Vol 99 ◽  
pp. 892-904 ◽  
Author(s):  
J. Esarte ◽  
A. Bernardini ◽  
J.M. Blanco ◽  
R. Sancibrian
Keyword(s):  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Cooling Loop ◽  
Two Phase Cooling

Competitive Designs of Evaporator Top Cap of the Micro Loop Heat Pipe

2004 ◽  
Author(s):  
Praveen Kumar Arragattu ◽  
Frank M. Gerner ◽  
Priyanka Ponugoti ◽  
H. T. Henderson
Keyword(s):  
Finite Element ◽  
Pressure Drop ◽  
Finite Element Modeling ◽  
Heat Pipe ◽  
Temperature Drop ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Maximum Heat ◽  
Element Modeling

The Micro Loop Heat Pipe (LHP) is a two phase device that may be used to cool electronics, solar collectors and other devices in space applications. A LHP is a two-phase device with extremely high effective thermal conductivity that utilizes the thermodynamic pressure difference developed between the evaporator and condenser and capillary forces developed inside its wicked evaporator to circulate a working fluid through a closed loop. While previous experiments have shown reduction in chip temperature, maximum heat flux was less than theoretically predicted. This paper addresses the main problem with the past designs of top cap which has been the conduction of heat from the heat source to the primary wick. The new top cap design provides conduction pathways which enables the uniform distribution of heat to the wick. The provision of conduction pathways in the top cap increases the pressure losses and decreases the temperature drop. The feasible competitive designs of the top cap with conduction pathways from the fabrication point of view were discussed in detail. Calculation of pressure drop and temperature drop is essential for the determination of optimal solutions of the top cap. Approximate pressure drop was calculated for the top cap designs using simple 2-D microchannel principles. Finite element modeling was performed to determine the temperature drop in the conduction pathways. The conditions used for arriving at the optimal design solutions are discussed. A trapezoidal slot top cap design was chosen for fabrication as it was relatively easy to fabricate with available MEMS fabrication technologies. The exact pressure drop calculation was performed on the fabricated top cap using commercial flow solver FLUENT 6.1 with appropriate boundary conditions. The temperature drop calculation was performed by finite element modeling in ANSYS 6.1. Obtained values of pressure drop and temperature drop for fabricated trapezoidal slot top cap was found to be within the optimal limits.

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.

Multilayer Wick Structure of Loop Heat Pipe

2007 ◽  
Author(s):  
Qingjun Cai ◽  
Chung-Lung Chen ◽  
Julie F. Asfia
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Two Phase ◽  
Transfer Resistance ◽  
Heat Leakage ◽  
Wick Structure ◽  
Operating Temperatures ◽  
Compensation Chamber ◽  
Two Phase Heat Transfer

Loop heat pipe (LHP) is known as a two-phase heat transfer device that utilizes the evaporation and condensation of an operating fluid to transfer heat. At the LHP low operating temperatures, heat leakage induced by saturated temperature differences between the evaporator and compensation chamber is more serious than at high operating temperatures, due to inherent thermophysical properties of the operating liquid. The serious heat leakage at the low operating temperature not only causes high liquid subcooling requirement but also leads to high total temperature difference and degraded heat transfer performance. In this paper, research efforts are placed on reducing the heat leakage by introducing a multilayer wick structure into the LHP. Based on the previous research results of LHP non-metallic wick structures, the multilayer wick LHP combines advantages of both metallic and non-metallic wick structures, retains good heat conduction from the evaporator case to the liquid/vapor interface and inhibits the reverse heat transfer from the interface to compensation chamber. By demonstrating the concept on a methanol LHP, experimental results exhibit a significant enhancement in reducing heat leakage and the total heat transfer resistance.

Ceramic Flat Plate Evaporator for Loop Heat Pipe Cooling of Electronics

2005 ◽  
Author(s):  
Walter Zimbeck ◽  
Jared Chaney ◽  
Patricio Espinoza ◽  
Edward Kroliczek ◽  
David C. Bugby ◽  
...  
Keyword(s):  
Flat Plate ◽  
Heat Pipe ◽  
Temperature Drop ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Heat Sources ◽  
Two Phase ◽  
Low Thermal Expansion ◽  
Phase Loop ◽  
Cooling Of Electronics

Two-phase loops are extremely efficient devices for passively transporting heat over long distances with low temperature drop. The heat acquisition component of a two-phase loop, the evaporator, is commonly made from conventional metal materials (aluminum, copper, etc.) and has cylindrical geometry. Neither characteristic is optimally suited for close integration to common electronic or photonic heat sources, which generally have flat interfaces and are constructed from low thermal expansion coefficient (CTE) semiconductor materials. This paper describes the development of a ceramic flat plate evaporator for cooling processor chips in network computers used onboard Navy submarines. The unique requirements of submarines give added motivation for the advantages offered by two-phase loops. The ceramic flat plate evaporator is constructed of low CTE, high thermal conductivity material and thus enables a low thermal resistance interface between the heat source and the working fluid of the loop heat pipe. Alumina and aluminum nitride flat plate evaporators were integrated into a water-based two-phase loop and thermally tested to a heat flux of 30 W/cm2.

Sign in / Sign up

Export Citation Format

Share Document