A Review of Concentric Annular Heat Pipes

Nouri-Borujerdi, A.; Layeghi, Mohammad

doi:10.1080/01457630590950934

Cited by 28 publications

(6 citation statements)

References 42 publications

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“…As a large diameter pipe is located on the outside and the small diameter pipe is on the inside, the two ends are sealed. An annular heat pipe has the same shape as Figure 1 and, as the internal space and the external surface are exposed to the outside, the heat transfer area can be significantly increased to increase the heat transfer capacity [9]. In addition, as the area of the room can be expanded without significantly increasing the external diameter, a cooling system with a small and excellent thermal effect can be constructed, if used for the component cooling of an electric vehicle.…”

Section: Introductionmentioning

confidence: 99%

Thermal and Flow Simulation of Concentric Annular Heat Pipe with Symmetric or Asymmetric Condenser

2021

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The current research work describes the flow and thermal analysis inside the circular flow region of an annular heat pipe with a working fluid, using computational fluid dynamics (CFD) simulation. A two-phase flow involving simultaneous evaporation and condensation phenomena in a concentric annular heat pipe (CAHP) is modeled. To simulate the interaction between these phases, the volume of fluid (VOF) technique is used. The temperature profile predicted using computational fluid dynamics (CFD) in the CAHP was compared with previously obtained experimental results. Two-dimensional and three-dimensional simulations were carried out, in order to verify the usefulness of 3D modeling. Our goal was to compute the flow characteristics, temperature distribution, and velocity field inside the CAHP. Depending on the shape of the annular heat pipe, the thermal performance can be improved through the optimal design of components, such as the inner width of the annular heat pipe, the location of the condensation part, and the amount of working fluid. To evaluate the thermal performance of a CAHP, a numerical simulation of a 50 mm long stainless steel CAHP (1.1 and 1.3 in diameter ratio and fixed inner tube diameter (78 mm)) was done, which was identical to the experimental system. In the simulated analysis results, similar results to the experiment were obtained, and it was confirmed that the heat dissipation was higher than that of the existing conventional heat pipe, where the heat transfer performance was improved when the asymmetric area was cooled. Moreover, the simulation results were validated using the experimental results. The 3-D simulation shows good agreement with the experimental results to a reasonable degree.

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Section: Introductionmentioning

confidence: 99%

Thermal and Flow Simulation of Concentric Annular Heat Pipe with Symmetric or Asymmetric Condenser

2021

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“…Therefore, it is possible to customize the surface area of heat input and output to improve the thermal performance. Unfortunately, this type of heat pipe is uncommon in the literature as well as in industrial applications [8,9,[11][12][13]. Yan et al [12] reported an excellent temperature flattening ability using annular sodium heat pipes operating from 500 to 1200 • C. Their experimental results showed that the largest temperature difference within 150 mm at the bottom of the thermometer is better than 15 mK in the aluminum point cell installed in the sodium heat pipe furnace, which was controlled to about 657 • C. Choi et al [13] investigated a concentric annular heat pipe with almost half area heating.…”

Section: Introductionmentioning

confidence: 99%

“…In earlier studies, it was reported that the CAHP provides a larger surface area for radial heat flux compared to the conventional heat pipes. Larger possible heat transfer area can lead to increase in heat transport capacity [8,9,11]. Kim et al [16] reported the visualization study in the vertical upward annular thermosyphon.…”

Section: Introductionmentioning

confidence: 99%

Thermal and Flow Characteristics in a Concentric Annular Heat Pipe Heat Sink

et al. 2020

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A concentric annular heat pipe heat sink (AHPHS) was proposed and fabricated to investigate its thermal behavior. The present AHPHS consists of two concentric pipes of different diameters, which create vacuumed annular vapor space. The main advantage of the AHPHS as a heat sink is that it can largely increase the heat transfer area for cooling compared to conventional heat pipes. In the current AHPHS, condensation takes place along the whole annular space from the certain heating area as the evaporator section. Therefore, the whole inner space of the AHPHS except the heating area can be considered the condenser. In the present study, AHPHSs of different diameters were fabricated and studied experimentally. Basic studies were carried out with a 50 mm-long stainless steel AHPHS with diameter ratios of 1.1 and 1.3 and the same inner tube diameter of 76 mm. Several experimental parameters such as volume fractions of 10–70%, different air flow velocity, flow configurations, and 10–50 W heat inputs were investigated to find their effects on the thermal performance of an AHPHS. Experimental results show that a 10% filling ratio was found to be the optimum charged amount in terms of temperature profile with a low heater surface temperature and water as the working fluid. For the methanol, a 40% filling ratio shows better temperature behavior. Internal working behavior shows not only circular motion but also 3-D flow characteristics moving in axial and circular directions simultaneously.

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“…Most importantly, while various methods were developed to incorporate the effect of the momentum transport in the gas phase, the phase change and the associated heat and Figure 3: A schematic of a concentric annular heat pipe. [83] momentum flux are computed in a rather crude way. For instance, the relation between the (externally imposed) heat flux and phase change used in the studies of condensation is only valid in extremely simplified geometries (e.g., thin liquid films on essentially flat solid surfaces) and cannot be applied to quantitative modeling of two-phase evaporative cooling devices which usually have a more complicated geometry.…”

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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A Review of Concentric Annular Heat Pipes

Cited by 28 publications

References 42 publications

Thermal and Flow Simulation of Concentric Annular Heat Pipe with Symmetric or Asymmetric Condenser

Thermal and Flow Simulation of Concentric Annular Heat Pipe with Symmetric or Asymmetric Condenser

Thermal and Flow Characteristics in a Concentric Annular Heat Pipe Heat Sink

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

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