Evaluation of Heat Pipes in the Temperature Range of 450 to 700 K

Anderson, William G.

doi:10.1063/1.1867132

Cited by 7 publications

(4 citation statements)

References 5 publications

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“…Based on the above discussion, water heat pipes may be used in radiators operating between 350-500 K, while alkali metal heat pipes (with Cs, Rb or K) could be used in radiators operating at 650-800 K. It has long been a challenge for the heat pipe engineers to find a suitable working fluid in the range ~450-700 K; however, some promising ones, such as iodine and antimony tribromide, are currently being investigated (Anderson, 2005).…”

Section: Vapor Pressurementioning

confidence: 98%

Radiator Heat Pipes with Carbon-Carbon Fins and Armor for Space Nuclear Reactor Power Systems

Tournier¹,

El‐Genk²

2005

AIP Conference Proceedings

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Technologies for Space Reactor Power Systems are being developed to enable future NASA's missions early next decade to explore the farthest planets in the solar system. The choices of the energy conversion technology for these power systems require radiator temperatures that span a wide range, from 350 K to 800 K. Heat pipes with carbon-carbon fins and armor are the preferred choice for these radiators because of inherent redundancy and efficient spreading and rejection of waste heat into space at a relatively small mass penalty. The performance results and specific masses of radiator heat pipes with cesium, rubidium, and potassium working fluids are presented and compared in this paper. The heat pipes operate at 40% of the prevailing operation limit (a design margin of 60%), typically the sonic and/or capillary limit. The thickness of the carbon-carbon fins is 0.5 mm but the width is varied, and the evaporator and condenser sections are 0.15 and 1.35 m long, respectively. The 400-mesh wick and the heat pipe thin metal wall are titanium, and the carbon-carbon armor (~ 2 mm-thick) provides both structural strength and protection against meteoroids impacts. The cross-section area of the Dshaped radiator heat pipes is optimized for minimum mass. Because of the low vapor pressure of potassium and its very high Figure-Of-Merit (FOM), radiator potassium heat pipes are the best performers at temperatures above 800 K, where the sonic limit is no longer an issue. On the other hand, rubidium heat pipes are limited by the sonic limit below 762 K and by the capillary limit at higher temperature. The transition temperature between these two limits for the cesium heat pipes occurs at a lower temperature of 724 K, since cesium has lower FOM than rubidium. The present results show that with a design margin of 60%, the cesium heat pipes radiator is best at 680-720 K, the rubidium heat pipes radiator is best at 720-800 K, while the potassium heat pipes radiator is the best performer and lightest at higher temperatures > 800 K.

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Section: Vapor Pressurementioning

confidence: 98%

Radiator Heat Pipes with Carbon-Carbon Fins and Armor for Space Nuclear Reactor Power Systems

Tournier¹,

El‐Genk²

2005

AIP Conference Proceedings

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“…The merit number is used to compare the potential performance of different working fluids at different temperatures with higher numbers being better. Figure 8 shows the variation of the figure of merit with changes in temperature (Anderson, 2005). Despite being able to handle higher temperatures than water, the peak figure of merit of water is much higher than the peak figure of merit for naphthalene.…”

Section: Timementioning

confidence: 99%

Operating Characteristics of Naphthalene Heat Pipes

Orr¹,

Singh²,

Akbarzadeh³

et al. 2019

Frontiers in Heat and Mass Transfer

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Heat pipes that operate in the medium temperature range (550-700 K) are very rarely used in industry despite the potential demand of use. There is no consensus about suitable working fluids in this temperature range as research on possible working fluids is limited. One proposed working fluid is naphthalene. In this paper, a number of tests have been undertaken on both an individual naphthalene heat pipe and a naphthalene heat pipe heat exchanger. Unlike room temperature working fluids, medium temperature working fluids are solid at ambient temperature therefore they have unusual transient start up behaviour. Testing has indicated that these heat pipes start to operate when the temperature of the adiabatic section reaches approximately 200 °C. The tested heat pipes were 8 mm in diameter and 278 mm long. The container and mesh material were stainless steel. They were found to have a thermal resistance of approximately 1 °C/W and a maximum rate of heat transfer of 40 W. The orientation was found to have a large effect on the performance of the heat pipes. Compared to the bottom heat mode orientation, when in a horizontal orientation the heat exchanger effectiveness more than halved and when in the top heat mode orientation heat exchanger effectiveness was significantly further reduced.

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“…Unlike alkali-metals, the flow of water vapor in heat pipes is always in the continuum regime, even during the startup from a frozen state. However, for practical considerations, the operation of water heat pipes is limited to < 500 K. Thus, water heat pipes may be used in the heat rejection radiator panels of space reactor power systems with average radiator temperature from 350 to 500 K. On the other hand, alkali metal heat pipes (with Cs, Rb or K working fluids) could be used in radiators operating at 650 -800 K. It has long been a challenge to find a suitable heat pipes working fluid for the temperature range ~ 450 -700 K; however, some promising ones, such as iodine and antimony tri-bromide, have been investigated (Anderson, 2005).…”

Section: Operation Limits Of Heat Pipesmentioning

confidence: 99%

“…A number of space reactor power system concepts have been developed or proposed with liquidmetal heat pipes for the passive and redundant removal and transport of the fission power generated in the reactor to the energy conversion subsystem (Angelo and Buden, 1985;El-Genk, 1994 and2008b;Ranken, 1982 andDeterman and Hagelston, 1992;, Poston et al, 2002;Ring et al, 2003; These heat pipes have also been considered for transporting waste heat from the energy conversion subsystems, and redundant and enhanced performance of heat rejection radiators. Energy conversion options considered for uses in space reactor power systems include Free-Piston Stirling Engine, FPSE (e.g., Angelo and Buden, 1985;Moriarty and Determan, 1989;Schreiber, 2001;Thieme et al, 2002 and2004;Schmitz et al, 1994 and2005), Thermoelectric (e.g., Ranken, 1982;Moriarty and Determan, 1989;Josloff et al, 1994;Marriott and Fujita, 1994;Caillat et al, 2000;Saber, 2003 and2005;Tournier, 2006b, El-Genk, 2008), Closed Brayton Cycle (CBC) with rotating turbo-machines (e.g., Harty and Mason, 1993;Shepard et al, 1994;Barrett and Reid, 2004;Barrett and Johnson, 2005;Gallo and El-Genk, 2009;El-Genk et al 2010;El-Genk, 1994 and2008), Potassium Rankine cycle (Angelo and Buden, 1985;Yoder and Graves, 1985;Bevard and Yoder, 2003), Thermionic (e.g., El-Genk and Paramonov, 1999;Ranken, 1990;…”

Section: Introductionmentioning

confidence: 99%

Uses of Liquid-Metal and Water Heat Pipes in Space Reactor Power Systems

El‐Genk¹,

Tournier²

2011

Frontiers in Heat Pipes

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Water and liquid-metal heat pipes are considered for redundant and passive cooling of nuclear reactors and redundant operation of light-weight heat rejection radiators of space reactor power systems. The systems operate continuously for many years independent of the Sun, are enabling of deep space exploration and could provide 10's of kilowatts of electrical power for lunar and Martian outposts. Space reactors typically operate at 900 K -1400 K could be cooled using liquid-metal heat pipes with either sodium (900 -1100 K) or lithium (1100 K-1400 K) working fluids. The heat rejection temperatures dictate the working fluid of the radiator heat pipes; potassium for 600 -800 K, rubidium for 500 -700 K, and water for < 500 K. These working fluids would be frozen prior to starting up the power systems in orbit or at destination. The startup of water and liquid-metal heat pipes from a frozen state is complex, involving a number of non-linear mass and heat transport processes that require implementing appropriate procedures, depending on the type of working fluid. This paper reviews operation and design constraints pertinent to the uses of water and liquidmetal heat pipes in space reactor systems, and the modeling capabilities of the startup from a frozen state. In addition to models validation, results of design optimization of liquid-metal and water heat pipes in a number of space reactor power systems are presented and discussed.

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Evaluation of Heat Pipes in the Temperature Range of 450 to 700 K

Cited by 7 publications

References 5 publications

Radiator Heat Pipes with Carbon-Carbon Fins and Armor for Space Nuclear Reactor Power Systems

Radiator Heat Pipes with Carbon-Carbon Fins and Armor for Space Nuclear Reactor Power Systems

Operating Characteristics of Naphthalene Heat Pipes

Uses of Liquid-Metal and Water Heat Pipes in Space Reactor Power Systems

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