Incompressible Laminar Vapor Flow in Cylindrical Heat Pipes.

Bankston, C.A.; Smith, Hugh

doi:10.2172/4691028

Cited by 14 publications

(7 citation statements)

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“…If the heat pipe input and output rates are then equal, the heat pipe will be functioning in the steady-state condition. If an imbalance between the heat input and output rates, take place, then the temperature of the fully operational heat pipe will continue to change with time to a level at which the balance between heat input and output rates is restored [9].…”

Section: Heat Pipe Operational Limitsmentioning

confidence: 99%

“…The sonic limit, also dominant at low temperatures, should be avoided. The vapor pressure of the working fluid is a good indicator of reaching this limit [9]. The vapor pressure and physical state of the heat pipe liquid at ambient temperature, as well as the thermal resistance between the condenser and the adjacent heat sink has significant influence of the startup behavior of a heat pipe.…”

Section: Sonic Limitmentioning

confidence: 99%

“…If this shear force exceeds the surface tension of the liquid, liquid droplets are entrained into the vapor flow and are carried towards the condenser section as it is illustrated in Figure 8. The magnitude of this shear force depends on the thermo-physical properties of the vapor and its velocity and if it becomes large enough, it causes dry out of the evaporator [9].…”

Section: Sonic Limitmentioning

confidence: 99%

“…The drag force on the heat pipe liquid is proportional to the liquid surface area in the wick pores, whereas the resisting surface tension force is proportional to the pore width normal to the drag force. Consequently, the ratio of the drag force to the surface tension force is proportional to the pore size and decreases as the pore size diminishes [9].…”

Section: Entrainment Limitmentioning

confidence: 99%

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Heat Pipe as a Passive Cooling System Driving New Generation of Nuclear Power Plants

Nezam

Zohuri

2021

ECS

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The technology of the Heat Pipe (HP) system is very well known for scientists and engineers working in the field of thermal-hydraulic since its invention at Las Alamos Nation Laboratory around the 1960s time frame. It is a passive heat transfer/heat exchanger system that comes in the form of either a constant or variable system without any mechanical built-in moving part. This passive heat transfer system and its augmentation within the core of nuclear power reactors have been proposed in the past few decades. The sodium, potassium, or mercury type heat pipe system using any of these three elements for the cooling system has been considered by many manufacturers of fission reactors and recently fusion reactors particularly Magnetic Confinement Fusion (MCF). Integration of the heat pipes as passive cooling can be seen in a new generation of a nuclear power reactor system that is designed for unconventional application field such as a space-based vehicle for deep space or galaxy exploration, planetary surface-based power plants as well as operation in remote areas on Earth. With the new generation of Small Modular Reactor (SMR) in form of Nuclear Micro Reactors (NMR), this type of fission reactor has integrated Alkali metal heat pipes to a series of Stirling convertors or thermoelectric converters for power generation that would generate anywhere from 13kwt to 3Mwt thermal of power for the energy conversion system.

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Section: Heat Pipe Operational Limitsmentioning

confidence: 99%

Section: Sonic Limitmentioning

confidence: 99%

Section: Sonic Limitmentioning

confidence: 99%

Section: Entrainment Limitmentioning

confidence: 99%

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Heat Pipe as a Passive Cooling System Driving New Generation of Nuclear Power Plants

Nezam

Zohuri

2021

ECS

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“…The effect of the gas phase was considered for the most part only in terms of the shear stress that it exerts on the liquid layer [66][67][68][69][70][71][72][73][74]. The latter was typically incorporated by modifying the friction factor or the Poiseuille number (the product of the friction factor and the Reynolds number for the liquid flow), which was typically obtained from the solutions of a fully developed duct flow of the vapor [75] or from relevant correlations [76,77].…”

Section: One-sided Transport Modelsmentioning

confidence: 99%

Buoyancy-Thermocapillary Convection of Volatile Fluids in Confined and Sealed Geometries

Qin

2017

Springer Theses

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Convection in a layer of fluid with a free surface due to a combination of thermocapillary stresses and buoyancy is a classic problem of fluid mechanics. It has attracted increasing attentions recently due to its relevance for two-phase cooling. Many of the modern thermal management technologies exploit the large latent heats associated with phase change at the interface of volatile liquids, allowing compact devices to handle very high heat fluxes. To enhance phase change, such cooling devices usually employ a sealed cavity from which almost all noncondensable gases, such as air, have been evacuated. Heating one end of the cavity, and cooling the other, establishes a horizontal temperature gradient that drives the flow of the coolant. Although such flows have been studied extensively at atmospheric conditions, our fundamental understanding of the heat and mass transport for volatile fluids at reduced pressures remains limited. A comprehensive and quantitative numerical model of two-phase buoyancy-thermocapillary convection of confined volatile fluids subject to a horizontal temperature gradient has been developed, implemented, and validated against experiments as a part of this thesis research. Unlike previous simplified models used in the field, this new model incorporates a complete description of the momentum, mass, and heat transport in both the liquid and the gas phase, as well as phase change across the entire liquid-gas interface.Numerical simulations were used to improve our fundamental understanding of the importance of various physical effects (buoyancy, thermocapillary stresses, wetting properties of the liquid, etc.) on confined two-phase flows. In particular, the effect of noncondensables (air) was investigated by varying their average concentration from that corresponding to ambient conditions to zero, in which case the gas phase becomes a pure vapor. It was found that the composition of the gas phase has a crucial impact on heat and mass transport as well as on the flow stability.A simplified theoretical description of the flow and its stability was developed and used xvi to explain many features of the numerical solutions and experimental observations that were not well understood previously. In particular, an analytical solution for the base return flow in the liquid layer was extended to the gas phase, justifying the previous ad-hoc assumption of the linear interfacial temperature profile. Linear stability analysis of this two-layer solution was also performed. It was found that as the concentration of noncondensables decreases, the instability responsible for the emergence of a convective pattern is delayed, which is mainly due to the enhancement of phase change.Finally, a simplified transport model was developed for heat pipes with wicks or microchannels that gives a closed-form analytical prediction for the heat transfer coefficient and the optimal size of the pores of the wick (or the width of the microchannels).

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Introduction

Qin¹

2017

Springer Theses

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Incompressible Laminar Vapor Flow in Cylindrical Heat Pipes.

Cited by 14 publications

References 0 publications

Heat Pipe as a Passive Cooling System Driving New Generation of Nuclear Power Plants

Heat Pipe as a Passive Cooling System Driving New Generation of Nuclear Power Plants

Buoyancy-Thermocapillary Convection of Volatile Fluids in Confined and Sealed Geometries

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