Experimental Development and Computational Optimization of Flat Heat Pipes for CubeSat Applications

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Steven A. Isaacs ◽  
Diego A. Arias ◽  
Derek Hengeveld ◽  
Peter E. Hamlington
Keyword(s):  
Thermal Conductivity ◽  
Pure Copper ◽  
Working Fluid ◽  
Vapor Pressures ◽  
Two Phase ◽  
Experimental Development ◽  
Maximum Heat ◽  
Computational Optimization ◽  
Major Bottleneck ◽  
And Performance

Due to the compact and modular nature of CubeSats, thermal management has become a major bottleneck in system design and performance. In this study, we outline the development, initial testing, and modeling of a flat, conformable, lightweight, and efficient two-phase heat strap called FlexCool, currently being developed at Roccor. Using acetone as the working fluid, the heat strap has an average effective thermal conductivity of 2149 W/m K, which is approximately five times greater than the thermal conductivity of pure copper. Moreover, the heat strap has a total thickness of only 0.86 mm and is able to withstand internal vapor pressures as high as 930 kPa, demonstrating the suitability of the heat strap for orbital environments where pressure differences can be large. A reduced-order, closed-form theoretical model has been developed in order to predict the maximum heat load achieved by the heat strap for different design and operating parameters. The model is validated using experimental measurements and is used here in combination with a genetic algorithm to optimize the design of the heat strap with respect to maximizing heat transport capability.

Experimental Development and Computational Optimization of Flat Heat Pipes for CubeSat Applications

2016 ◽  
Author(s):  
Steven A. Isaacs ◽  
Diego A. Arias ◽  
Peter E. Hamlington ◽  
Derek Hengeveld
Keyword(s):  
Thermal Conductivity ◽  
Pure Copper ◽  
Working Fluid ◽  
Vapor Pressures ◽  
Two Phase ◽  
Experimental Development ◽  
Maximum Heat ◽  
Computational Optimization ◽  
Major Bottleneck ◽  
And Performance

Due to the compact and modular nature of CubeSats, thermal management has become a major bottleneck in system design and performance. In this study, we outline the development, initial testing, and modeling of a flat, conformable, lightweight, and efficient two-phase heat strap called FlexCool, currently being developed at Roccor1. Using acetone as the working fluid, the heat strap has an average effective thermal conductivity of 2,149 W/m-K, which is approximately four times greater than the thermal conductivity of pure copper. Moreover, the heat strap has a total thickness of only 0.86 mm and is able to withstand internal vapor pressures as high as 930 kPa, demonstrating the suitability of the heat strap for orbital environments where pressure differences can be large. A reduced-order, closed-form theoretical model has been developed in order to predict the maximum heat load achieved by the heat strap for different design and operating parameters. The model is validated using experimental measurements and is used here in combination with a genetic algorithm to optimize the design of the heat strap with respect to maximizing heat transport capability.

Pool Boiling Heat Transfer With Binary Mixture on Open Microchannel Surface

2013 ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Binary Mixture ◽  
Heat Dissipation ◽  
Surface Effect ◽  
Pure Water ◽  
Pool Boiling ◽  
Electronics Cooling ◽  
Working Fluid ◽  
Two Phase ◽  
Maximum Heat ◽  
Fluid Medium

Two-phase cooling is considered an attractive option for electronics cooling due to its ability to dissipate large quantities of heat. In recent years, pool boiling has shown tremendous ability in high heat dissipation applications. Researchers have used various fluid medium for pool boiling including water, alcohol, refrigerants, nanofluids and binary mixture. In the current work, binary mixture of water with ethanol was chosen as the working fluid. Plain copper chip was used as the boiling surface. Effect of various concentrations of binary mixture was investigated. A maximum heat flux of 1720 kW/m2 at a wall superheat of 28°C was recorded for 15% ethanol in water. It showed a 1.5 fold increase in CHF over pure water.

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.

Performance Evaluation of a Pump-Assisted, Capillary Two-Phase Cooling Loop

2009 ◽  
Vol 1 (2) ◽  
Author(s):  
Chanwoo Park ◽  
Aparna Vallury ◽  
Jon Zuo
Keyword(s):  
Heat Input ◽  
Heat Load ◽  
Fluid Transport ◽  
Active Flow Control ◽  
Working Fluid ◽  
Heat Sources ◽  
Two Phase ◽  
Relative Level ◽  
Maximum Heat ◽  
Two Phase Cooling

A hybrid (pump-assisted and capillary) two-phase loop (HTPL) is experimentally investigated to characterize its thermal performance under stepwise heat input conditions. An integration of mechanical pumping with capillary pumping is achieved by using planar evaporator(s) and a two-loop design separating liquid and vapor flows. The evaporator(s) use a sintered copper grooved wick bonded with a liquid screen artery. No active flow control of the mechanical pumping is required because of the autonomous capillary pumping due to the self-adjusting liquid menisci to variable heat inputs of the evaporators. Unlike other active two-phase cooling systems using liquid spray and microchannels, the HTPL facilitates a passive phase separation of liquid from vapor in the evaporator using capillary action, which results in a lower flow resistance of the single-phase flows than two-phase mixed flows in fluid transport lines. In this work, a newly developed planar form-factor evaporator with a boiling heat transfer area of 135.3 cm2 is used aiming for the power electronics with large rectangular-shaped heat sources. This paper presents the experimental results of the HTPLs with a single evaporator handling a single heat source and dual evaporators handling two separate heat sources, while using distilled water as the working fluid for both cases. For the single evaporator system, the temperature results show that the HTPL does not create a big temperature upset under a stepwise heat load with sudden power increases and decreases. The evaporator thermal resistance is measured to be as low as 0.5 K cm2/W for the maximum heat load of 4.0 kW. A cold-start behavior characterized by a big temperature fluctuation was observed at the low heat inputs around 500 W. The HTPL with dual evaporators shows a strong interaction between the evaporators under an asymmetric heat load of the total maximum heat input of 6.5 kW, where each evaporator follows a different heat input schedule. The temperatures of the dual-evaporator system follow the profile of the total heat input, while the individual heat inputs determine the relative level of the temperatures of the evaporators.

scholarly journals Working-fluid selection and performance investigation of a two-phase single-reciprocating-piston heat-conversion engine

2017 ◽  
Vol 186 ◽  
pp. 376-395 ◽  
Author(s):  
Oyeniyi A. Oyewunmi ◽  
Christoph J.W. Kirmse ◽  
Andrew J. Haslam ◽  
Erich A. Müller ◽  
Christos N. Markides
Keyword(s):  
Working Fluid ◽  
Two Phase ◽  
Working Fluid Selection ◽  
And Performance

A Review on Nanofluid Heat Pipe

2014 ◽  
Author(s):  
Maryam Shafahi ◽  
Kevin Anderson ◽  
Ali Borna ◽  
Michael Lee ◽  
Alex Kim ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Pipe ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Working Fluid ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Medical Instruments ◽  
Thermo Physical Properties

This paper reviews the improvement in the heat pipe’s performance using nanofluid as the working fluid. The use of nanofluid enhances heat transfer in the heat pipe due to its improved thermo-physical properties, such as a higher thermal conductivity. Nanofluids proved to be the innovative approach to a variety of applications, such as electronics, medical instruments, and heat exchangers. The influence of different nanoparticles on heat pipe’s performance has been studied. Utilizing nanofluid as the working fluid leads to a significant reduction in heat pipe thermal resistance, an increase in maximum heat transfer, and an improvement of heat pipe thermal performance.

Heat Recovery With Oscillating Heat Pipes

2013 ◽  
Author(s):  
Charles R. McCullough ◽  
Scott M. Thompson ◽  
Heejin Cho
Keyword(s):  
Thermal Conductivity ◽  
Temperature Difference ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Heat Pipes ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Two Phase ◽  
Maximum Temperature Difference

Waste-heat recovery applied in HVAC air systems is of interest to increase the energy efficiency of residential, commercial and industrial buildings. In this study, the feasibility of using tubular-shaped oscillating heat pipes (OHPs), which are two-phase heat transfer devices with ultra-high thermal conductivity, for heat exchange between counter-flowing air streams (i.e., outdoor and exhaust air flows) was investigated. For a prescribed volumetric flow rate of air and duct geometry, four different OHP Heat Exchangers (OHP-HEs) were sized via the ε-NTU method for the task of sub-cooling intake air 5.5 °C (10 °F). The OHP-HE tubes were assumed to have a static thermal conductivity of 50,000 W/m·K and only operate upon a minimum temperature difference in order to simulate their inherent heat transport capability and start-up behavior. Using acetone as the working fluid, it was found that for a maximum temperature difference of 7°C or more, the OHP-HE can operate and provide for an effectiveness of 0.36. Pressure drop analysis indicates the presented OHP-HE design configurations provide for a minimum of 5 kPa. The current work provides a necessary step for quantifying and designing the OHP for waste heat recovery in AC systems.

Choosing Working Fluid for Two-Phase Thermosyphon Systems for Cooling of Electronics

2003 ◽  
Vol 125 (2) ◽  
pp. 276-281 ◽  
Author(s):  
Bjo¨rn Palm ◽  
Rahmatollah Khodabandeh
Keyword(s):  
Heat Transfer ◽  
High Pressure ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients ◽  
And Performance ◽  
Cooling Of Electronics

The heat fluxes from electronic components are steadily increasing and have now, in some applications, reached levels where air-cooling is no longer sufficient. One alternative solution, which has received much attention during the last decade, is to use heat pipes or thermosyphons for transferring or spreading the dissipated heat. In this paper two-phase thermosyphon loops are discussed. Especially, the choice of fluid and its influence on the design and performance is treated. The discussion is supported by results from simulations concerning heat transfer and pressure drop. In general it is found that high-pressure fluids will give better performance and more compact designs as high-pressure results in higher boiling heat transfer coefficients and smaller necessary tube diameter.

scholarly journals The calculation of the heat control accumulator volume of two-phase heat transfer loop of a spacecraft thermal control system

2021 ◽  
pp. 15-23
Author(s):  
Artem Hodunov ◽  
Gennady Gorbenko ◽  
Pavel Gakal
Keyword(s):  
Control Systems ◽  
Single Phase ◽  
Operation Mode ◽  
Heat Removal ◽  
Thermal Control ◽  
Working Fluid ◽  
Phase Slip ◽  
Two Phase ◽  
Maximum Heat ◽  
Spacecraft Thermal Control

Spacecraft thermal control systems based on two-phase mechanically pumped loops have advantages in terms of mass and power consumption for auxiliary needs compared to single-phase thermal control systems. However, the disadvantage of two-phase mechanically pumped loops is that when changing the heat load and heat removal conditions, when switching from single-phase to two-phase operation mode and vice versa, the amount of working fluid in the loop changes significantly, which requires the use of a large volume heat-controlled accumulator.  Therefore, determining the minimum required volume of the heat-controlled accumulator for the loop operation is an urgent task due to the need to maintain the performance of the l loop at a minimum and maximum heat loads and minimize the mass of the structure and the working fluid charged. When determining the volume of the heat-controlled accumulator, it is necessary to correctly calculate the mass of the fluid in the loop during the two-phase operation mode. The mass of the fluid depends on the void fraction, which depends significantly on the phase slip. Many models and correlations have been proposed to calculate the phase slip factor. However, they all require justification for the parameters characteristic of spacecraft thermal control systems and weightlessness conditions.   The paper presents the results of ground-based experiments, based on which the verification of different models and correlations for phase slip was performed. The validation of models and correlations for the conditions of weightlessness was performed by comparing the results with the horizontal and vertical orientation of the elements of the experimental setup. The working fluid is ammonia. The experiments showed that the best coincidence of calculation and experience is provided by Chisholm correlation. The discrepancy between the calculated and experimental values did not exceed +/-7% in the entire range of study parameters both for horizontal and vertical orientations, which allow us to recommend the Chisholm correlation for determining the coolant mass in the two-phase mechanically pumped loops for parameters characteristic of spacecraft thermal control systems, including zero-gravity conditions.

Experimental Investigation of an Evaporator Enhanced With a Micro-Porous Structure in a Two-Phase Thermosyphon Loop

2008 ◽  
Author(s):  
Richard Furberg ◽  
Rahmatollah Khodabandeh ◽  
Bjo¨rn Palm ◽  
Shanghua Li ◽  
Muhammet Toprak ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Rectangular Channel ◽  
Large Diameter ◽  
Nucleate Boiling ◽  
Nano Particles ◽  
Working Fluid ◽  
Two Phase ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Following is an experimental study of six different evaporators in a closed two-phase thermosyphon loop system, where the influence of various evaporator dimensions and surfaces was investigated. The evaporators featured a 30 mm long rectangular channel with hydraulic diameters ranging from 1.2–2.7 mm. The heat transfer surface of one of the tested evaporators was enhanced with copper nano-particles, dendritically connected into an ordered micro-porous three dimensional network structure. To facilitate high speed video visualization of the two-phase flow in the evaporator channel, a transparent polycarbonate window was attached to the front of the evaporators. Refrigerant 134A was used as a working fluid and the tests were conducted at 6.5 bar. The tests showed that increasing channel diameters generally performed better. The three largest evaporator channels exhibited comparable performance, with a maximum heat transfer coefficient of about 2.2 W/(cm2K) at a heat flux of 30–35 W/cm2 and a critical heat flux of around 50 W/cm2. Isolated bubbles characterized the flow regime at peak performance for the large diameter channels, while confined bubbles and chaotic churn flow typified the evaporators with small diameters. In line with previous pool boiling experiments, the nucleate boiling mechanism was significantly enhanced, up to 4 times, by the nano- and micro-porous enhancement structure.

Sign in / Sign up

Export Citation Format

Share Document