Nucleate Boiling Inside the Evaporator of the Planar Loop Heat Pipe

2004 ◽  
Author(s):  
Junwoo Suh ◽  
Ahmed Shuja ◽  
Frank M. Gerner ◽  
H. Thurman Henderson
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Input Energy ◽  
Cooling Devices ◽  
Compensation Chamber ◽  
Dry Out ◽  
Transfer Device

The Loop Heat Pipe (LHP) under development is a next generation micro heat transfer device that utilizes the latent heat of a working fluid and has excellent transfer capacity compared with that of standard metallic cooling devices. A typical LHP consists of an evaporator, a reservoir (also called the compensation chamber), vapor and liquid lines, a subcooler, and a condenser. As heat is applied to the evaporator, all of the input energy goes into the evaporation of the liquid in the pores of the primary CPS wick or leak to the bottom. The nucleate boiling, which occurs beneath the primary wick in the evaporator, is a very significant phenomena. It affects critical operating issues, such as dry out of the primary wick. Using a clear evaporator machined from Pyrex glass, the nucleation, which occurred in the evaporator, was studied. De-ionized water was utilized as the working fluid.

scholarly journals Development of a Compensation Chamber for Use in a Multiple Condenser Loop Heat Pipe

2013 ◽  
Author(s):  
Nicholas A. Roche ◽  
Martin Cleary ◽  
Teresa B. Peters ◽  
Evelyn N. Wang ◽  
John G. Brisson
Keyword(s):  
Heat Pipe ◽  
Heat Sink ◽  
High Performance ◽  
Computational Simulation ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Operating Characteristics ◽  
Side Pressure ◽  
Compensation Chamber ◽  
Dry Out

We report the design and analysis of a novel compensation chamber for use in PHUMP, a multiple condenser loop heat pipe (LHP) capable of dissipating 1000 W. The LHP is designed for integration into a high performance air-cooled heat sink to address thermal management challenges in advanced electronic systems. The compensation chamber is integrated into the evaporator of the device and provides a region for volumetric expansion of the working fluid over a range of operating temperatures. Additionally, the compensation chamber serves to set the liquid side pressure of the device, preventing both flooding of the condensers and dry out of the evaporator. The compensation chamber design was achieved through a combination of computational simulation using COMSOL Multiphysics and models developed based on experimental work of previous designs. The compensation chamber was fabricated as part of the evaporator using Copper and Monel sintered wicks with various particle sizes to achieve the desired operating characteristics. Currently, the compensation chamber is being incorporated into a multiple condenser LHP for a high performance air-cooled heat sink.

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.

Study on Heat Transfer Characteristics of Loop Heat Pipe for Solar Collector

2012 ◽  
Author(s):  
Shota Sato ◽  
Shigeki Hirasawa ◽  
Tsuyoshi Kawanami ◽  
Katsuaki Shirai
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Heat Transfer Rate ◽  
Solar Collector ◽  
Transfer Rate ◽  
Thermal Conductance ◽  
Filling Ratio ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Single Tube

We experimentally study the thermal conductance of single-tube and loop heat pipes for a solar collector. The evaporator of the heat pipe is 1 m long, 6 mm in diameter and has 30° inclination. The thermal conductance is defined as the heat transfer rate divided by the temperature difference between the evaporator-wall and the condenser-wall. Effects of heat transfer rate, saturation temperature of the working fluid, liquid filling ratio, inclination angle, and position of the evaporator on the thermal conductance are examined. We found that the thermal conductance of the 30°-inclined loop heat pipe with an upper-evaporator is 40–50 (W/K), which is 1.8 times higher than that of the vertical loop type and 3 times higher than that of the single-tube type. Thus, the inclined loop heat pipe is preferable for a solar collector. There is an optimum liquid filling ratio. When the liquid filling ratio is too small, a dry-out portion appears in the evaporator. When the liquid filling ratio is too large, the liquid flows in the condenser to decrease heat transfer area. Also we numerically analyze the thermal conductance of a vertical loop heat pipe.

Design and Simulation of Visual Miniature Loop Heat Pipe

2012 ◽  
Vol 605-607 ◽  
pp. 346-351
Author(s):  
Yan Chen ◽  
Yan Qu ◽  
Shu Sheng Zhang
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Pipe ◽  
Flow Characteristics ◽  
System Level ◽  
Loop Heat Pipe ◽  
Design Requirements ◽  
Compensation Chamber ◽  
Fluid Flow Characteristics ◽  
Level Performance

A miniature loop heat pipe (MLHP) with a glass condenser was designed and manufactured. Stress analysis on compensation chamber/evaporator and glass condenser is made to confirm strength of loop heat pipe using the software MSC NASTRAN. Results indicate this new structure loop heat pipe can meet the design requirements and secure to work well. A system level performance analysis was made about heat transfer and fluid flow characteristics inside loop heat pipe using the software of SINDA/FLUINT. This miniature loop heat pipe realized visualization research of phase change phenomenon to some extent.

scholarly journals Heat-Transfer Characteristics of a Cryogenic Loop Heat Pipe for Space Applications

Energies ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1616
Author(s):  
Jaehwan Lee ◽  
Dongmin Kim ◽  
Jeongmin Mun ◽  
Seokho Kim
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Infrared Detectors ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Zero Gravity ◽  
Heat Transfer Characteristics ◽  
Space Applications ◽  
Transfer Characteristics ◽  
Start Up

Infrared detectors on satellites and spacecraft require cooling to increase their measurement sensitivity. To efficiently cool infrared detectors in a zero gravity environment and in limited spaces, a cryogenic loop heat pipe (CLHP) can be used to transfer heat over a certain distance by the capillary forces generated from porous wicks without a mechanical power source. The CLHP presented in this study transfers the heat load to a condenser 0.5 m away from an evaporator at temperatures below −150 °C. The CLHP with two evaporators includes a subloop for initial start-up, and uses a pressure reduction reservoir (PRR) for the supercritical start-up from room to cryogenic temperature. Nitrogen is used as the working fluid to verify the thermal behavior of the CLHP, and the heat-transfer capacity according to the nitrogen charging pressure of the PRR is investigated. To simulate a cryogenic environment, the CLHP is installed inside a space environment simulator, including a single-stage GM (Gifford McMahon) cryocooler to cool the condenser. The CLHP is horizontally installed to simulate zero gravity. The heat-transfer characteristics are experimentally evaluated through the loop circulation of the CLHP.

Effect of Nanoparticle Coating on the Performance of a Miniature Loop Heat Pipe for Electronics Cooling Applications

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Trijo Tharayil ◽  
Lazarus Godson Asirvatham ◽  
S. Rajesh ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Physical Vapor Deposition ◽  
Low Voltage ◽  
Circuit Breaker ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Transfer Coefficients ◽  
Nanoparticle Coating

The effect of nanoparticle coating on the performance of a miniature loop heat pipe (mLHP) is experimentally investigated for heat inputs of 20–380 W using distilled water as the working fluid. Applications include the cooling of electronic devices such as circuit breaker in low voltage switch board and insulated gate bipolar transistor. Physical vapor deposition method is used to coat the nanoparticles on the evaporator surface for different coating thicknesses of 100 nm, 200 nm, 300 nm, 400 nm, and 500 nm, respectively. An optimum filling ratio (FR) of 30% is chosen for the analysis. Experimental findings show that the nanoparticle coating gives a remarkable improvement in heat transfer of the heat pipe. An average reduction of 6.7%, 11.9%, 17.2%, and 22.6% in thermal resistance is observed with coating thicknesses of 100 nm, 200 nm, 300 nm, and 400 nm, respectively. Similarly, enhancements in evaporator heat transfer coefficients of 47%, 63.5%, 73.5%, and 86% are noted for the same coating thicknesses, respectively. Evaporator wall temperature decreased by 15.4 °C for 380 W with a coating thickness of 400 nm. The repeatability test ensures the repeatability of experiments and the stability of coatings in the long run.

Steady-State Operation of a Loop Heat Pipe: Network Thermofluid Model and Results

2003 ◽  
Author(s):  
Nima Atabaki ◽  
B. Rabi Baliga
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Horizontal Tube ◽  
Operating Conditions ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
Sintered Metal ◽  
Steady State Operation ◽  
Transport Line ◽  
Compensation Chamber

A network thermofluid model of a loop heat pipe (LHP) operating under steady-state conditions is presented. Attention is focused on a simple LHP, with one evaporator, a vapor transport line, a single condenser, a liquid transport line, and a compensation chamber. The evaporator is an internally grooved circular pipe, with a cylindrical wick installed on its inner surface. The wick is made of a sintered metal. The condenser is a horizontal tube covered with a high-thermal-conductivity sleeve, and the outer temperature of the sleeve is maintained at a constant sink temperature. Quasi one-dimensional mathematical models of the fluid flow and heat transfer in each of the elements of the LHP, and collectively of the entire LHP, are proposed and discussed. The working fluid considered in this work is ammonia, but the proposed model can work with any suitable fluid. Results pertaining to the LHP performance for a range of operating conditions are presented, compared (qualitatively) to corresponding results of an earlier experimental investigation in the literature, and discussed.

Experimental Study on a Flat Loop Heat Pipe Coupling the Compensation Chamber and the Condenser

2010 ◽  
Author(s):  
Dong-chuan Mo ◽  
Guan-sheng Zou ◽  
Shu-shen Lu
Keyword(s):  
Heat Transfer ◽  
Heat Pipe ◽  
Temperature Oscillation ◽  
Large Temperature ◽  
Loop Heat Pipe ◽  
Normal Type ◽  
Operation Temperature ◽  
High Efficient ◽  
New Type ◽  
Compensation Chamber

Loop heat pipes are high efficient heat transfer loops/devices. Compared to the typical loop heat pipe with cylinder evaporator, loop heat pipe with flat evaporator (flat loop heat pipe, FLHP) can reduce the thermal resistance between the evaporator and the heat loads. In order to remove the heat leak from the evaporator to the compensation chamber to reduce the operation temperature, a new type of FLHP coupling the compensation chamber and the condenser has been developed. Experiments have been conducted to compare the heat transfer characteristics between the normal type and the new type of FLHP. Part of the heat lead from the evaporator to the compensation chamber can be removed in the new type of FLHP, so it gives better heat transfer performance than the normal one. Results show that, the temperatures in the loop of the new type of FLHP are much more stable than the normal one. The evaporator temperatures and the total thermal resistances of the new type are much lower than those of the normal type. For the normal type of FLHP, it may be failed to start up under low power, and usually the larger temperature oscillation will happen. With the power increasing, the frequency of the oscillation is increasing. When the applied power is large enough, the loop can keep running in the design way, and the large temperature oscillation will disappear.

Effect of Wick Characteristics on the Thermal Performance of the Miniature Loop Heat Pipe

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Randeep Singh ◽  
Aliakbar Akbarzadeh ◽  
Masataka Mochizuki
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Working Fluid ◽  
Vapor Flow ◽  
Loop Heat Pipe ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Two phase heat transfer devices based on the miniature version of loop heat pipe (LHP) can provide very promising cooling solutions for the compact electronic devices due to their high heat flux management capability and long distance heat transfer with minimal temperature losses. This paper discusses the effect of the wick properties on the heat transfer characteristics of the miniature LHP. The miniature model of the LHP with disk-shaped evaporator, 10 mm thick and 30 mm disk diameter, was designed using copper containment vessel and water as the working fluid, which is the most acceptable combination in electronic cooling applications. In the investigation, wick structures with different physical properties including thermal conductivity, pore radius, porosity, and permeability and with different structural topology including monoporous or biporous evaporating face were used. It was experimentally observed that copper wicks are able to provide superior thermal performance than nickel wicks, particularly for low to moderate heat loads due to their low heat conducting resistance. With monoporous copper wick, maximum evaporator heat transfer coefficient (hev) of 26,270 W/m2 K and evaporator thermal resistance (Rev) of 0.06–0.10°C/W were achieved. For monoporous nickel wick, the corresponding values were 20,700 W/m2 K for hev and 0.08–0.21°C/W for Rev. Capillary structure with smaller pore size, high porosity, and high permeability showed better heat transfer characteristics due to sufficient capillary pumping capability, low heat leaks from evaporator to compensation chamber and larger surface area to volume ratio for heat exchange. In addition to this, biporous copper wick structure showed much higher heat transfer coefficient of 83,787 W/m2 K than monoporous copper wick due to improved evaporative heat transfer at wick wall interface and separated liquid and vapor flow pores. The present work was able to classify the importance of the wick properties in the improvement of the thermal characteristics for miniature loop heat pipes.

scholarly journals Investigation of Loop Heat Pipe Survival and Restart After Extreme Cold Environment Exposure

2009 ◽  
Author(s):  
Eric Golliher ◽  
Jentung Ku ◽  
Anthony Licari ◽  
James Sanzi
Keyword(s):  
Heat Pipe ◽  
Freezing Point ◽  
Thermal Control ◽  
Working Fluid ◽  
Loop Heat Pipe ◽  
The Moon ◽  
Novel Approach ◽  
Condenser Temperature ◽  
Extreme Cold ◽  
Compensation Chamber

NASA plans human exploration near the South Pole of the Moon, and other locations where the environment is extremely cold. This paper reports on the heat transfer performance of a loop heat pipe exposed to extreme cold under the simulated reduced gravitational environment of the Moon. A common method of spacecraft thermal control is to use a loop heat pipe with ammonia working fluid. Typically, a small amount of heat is provided either by electrical heaters or by environmental design, such that the loop heat pipe condenser temperature never drops below the freezing point of ammonia. The concern is that a liquid-filled, frozen condenser would not re-start, or that a thawing condenser would damage the tubing due to the expansion of ammonia upon thawing. This paper reports the results of an experimental investigation of a novel approach to avoid these problems. The loop heat pipe compensation chamber is conditioned such that all the ammonia liquid is removed from the condenser and the loop heat pipe is non-operating. The condenser temperature is then reduced to below that of the ammonia freezing point. The loop heat pipe is then successfully re-started.

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