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.

scholarly journals Modeling of Loop Heat Pipe Thermal Performance

2021 ◽  
Vol 81 (1) ◽  
pp. 41-72
Author(s):  
Inès Gabsi ◽  
Samah Maalej ◽  
Mohamed Chaker Zaghdoudi
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Conductive Heat ◽  
Steady State Operation ◽  
Evaporation Heat ◽  
Compensation Chamber ◽  
Heat Loads ◽  
Good Agreement

The present work deals with the heat transfer performance of a copper-water loop heat pipe (LHP) with a flat oval evaporator in steady-state operation. Modeling the heat transfer in the evaporator was particularly studied, and the evaporation heat transfer coefficient was determined from a dimensionless correlation developed based on experimental data from the literature. The model was based on steady-state energy balance equations for each LHP component. The model results were compared to the experimental ones for various heat loads, cooling temperatures, and elevations, and a good agreement was obtained. Finally, a parametric study was conducted to show the effects of different key parameters, such as the axial conductive heat leaks between the evaporator and the compensation chamber cases, the capillary structure porosity and material, and the groove dimensions.

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.

scholarly journals A Novel Analytical Modeling of a Loop Heat Pipe Employing Thin-Film Theory: Part II—Experimental Validation

Energies ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 2403 ◽  
Author(s):  
Eui Guk Jung ◽  
Joon Hong Boo
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Film Theory ◽  
Design Parameters ◽  
Working Fluid ◽  
Coolant Temperature ◽  
Loop Heat Pipe ◽  
Analysis Model ◽  
Proposed Model ◽  
Flat Evaporator

Part I of this study introduced a mathematical model capable of predicting the steady-state performance of a loop heat pipe (LHP) with enhanced rationality and accuracy. Additionally, investigation of the effect of design parameters on the LHP thermal performance was also reported in Part I. The objective of Part II is to experimentally verify the utility of the steady-state analytical model proposed in Part I. To this end, an experimental device comprising a flat-evaporator LHP (FLHP) was designed and fabricated. Methanol was used as the working fluid, and stainless steel as the wall and tubing-system material. The capillary structure in the evaporator was made of polypropylene wick of porosity 47%. To provide vapor removal passages, axial grooves with inverted trapezoidal cross-section were machined at the inner wall of the flat evaporator. Both the evaporator and condenser components measure 40 × 50 mm (W × L). The inner diameters of the tubes constituting the liquid- and vapor-transport lines measure 2 mm and 4 mm, respectively, and the lengths of these lines are 0.5 m. The maximum input thermal load was 90 W in the horizontal alignment with a coolant temperature of 10 °C. Validity of the said steady-state analysis model was verified for both the flat and cylindrical evaporator LHP (CLHP) models in the light of experimental results. The observed difference in temperature values between the proposed model and experiment was less than 4% based on the absolute temperature. Correspondingly, a maximum error of 6% was observed with regard to thermal resistance. The proposed model is considered capable of providing more accurate performance prediction of an LHP.

scholarly journals One-dimensional steady-state mathematical model of a novel loop heat pipe with liquid line capillary wick

2019 ◽  
Vol 38 (1) ◽  
pp. 253-273 ◽  
Author(s):  
Meng Fanxi ◽  
Quan Zhang ◽  
Sheng Du ◽  
Chang Yue ◽  
Xiaowei Ma
Keyword(s):  
Mathematical Model ◽  
Steady State ◽  
Heat Pipe ◽  
Characteristic Point ◽  
Loop Heat Pipe ◽  
One Dimensional ◽  
Liquid Line ◽  
Working Medium ◽  
Compensation Chamber ◽  
Relative Errors

A novel loop heat pipe used for data center with a liquid line wick is designed, and its one-dimensional steady-state mathematical model is developed based on the energy and thermodynamic equilibrium of each component and the simulation results were validated by comparing with the experimental data in this work. The compensation chamber of the loop heat pipe was removed, and a section of capillary wick was added in the end of liquid line in order to reduce heat leakage and vapor backflow and increase working medium circulation power. The mathematical model of the novel loop heat pipe can be used to predict the operating temperature of each characteristic point with small relative errors of <13%. A parametric study of the steady-state performance characteristics including the effects of material, diameter, length, and porosity of liquid line wick are conducted, which provides a powerful basis for the design of novel loop heat pipe experiment.

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.

Mathematical modeling of steady-state operation of a loop heat pipe

2009 ◽  
Vol 29 (13) ◽  
pp. 2643-2654 ◽  
Author(s):  
Lizhan Bai ◽  
Guiping Lin ◽  
Hongxing Zhang ◽  
Dongsheng Wen
Keyword(s):  
Mathematical Modeling ◽  
Steady State ◽  
Heat Pipe ◽  
Loop Heat Pipe ◽  
Steady State Operation

Steady-State Operation of a Loop Heat Pipe With Analytical Prediction

2000 ◽  
Author(s):  
Heather Watson ◽  
Charlotte Gerhart ◽  
George Mulholland ◽  
Donald Gluck
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Air Force ◽  
Nickel Powder ◽  
Loop Heat Pipe ◽  
Analytical Prediction ◽  
Excellent Correlation ◽  
Horizontal Orientation ◽  
Steady State Operation ◽  
Air Force Research Laboratory

Abstract The steady-state performance of an 800W, sintered nickel powder wick, loop heat pipe (LHP) has been analyzed using a modified Dynatherm LHP Thermal Model. Results from characterization tests of this LHP performed at the Air Force Research Laboratory in Albuquerque, NM are used as the basis for comparison and discussion of results for the analytical model. The analytical predictions gave excellent correlation to the measured data for power levels ranging from 50 to 1500W at condenser chiller settings between −40°C and 20°C, with the LHP in a horizontal orientation.

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.

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.

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