Multiple quasi-steady states in a closed loop pulsating heat pipe

Khandekar, Sameer; Gautam, Anant Prasad; Sharma, Pradip Kumar

doi:10.1016/j.ijthermalsci.2008.04.004

Cited by 137 publications

(41 citation statements)

References 24 publications

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“…One should first recall that the number of turns N is different for these PHPs. The number of turns is known to influence the performance of PHPs: especially, increasing the number of turns reduces the effect of gravity on their behaviour [8,15]. Several explanations were proposed for this observation.…”

Section: Resultsmentioning

confidence: 99%

“…This short numerical example demonstrates that the dynamic contact angle difference between receding and advancing menisci should definitely be taken into account when trying to model the oscillating process of a PHP, as the capillary pressure difference will be as important as the other main term in the momentum equation for liquid, namely the frictional pressure drop. 15 Another aspect of hydrodynamics lies in the existence of wavelets that can be observed at the advancing meniscus (Fig. 8).…”

Section: Adiabatic Experiments: Hydrodynamic Aspectsmentioning

confidence: 99%

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Experimental evidences of distinct heat transfer regimes in pulsating heat pipes (PHP)

Lips¹,

Bensalem²,

Bertin³

et al. 2010

Applied Thermal Engineering

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Various experiments were conducted on two full-size Pulsating Heat Pipes (PHP) which differed from their diameter, number of turns, and working fluid. The analysis of the experimental results showed two kind of operating curves (overall thermal resistance vs. heat rate): for low heat fluxes, the curve is irregular and the PHP performance is sensitive to the orientation. For high heat fluxes, the operating curve is smooth and independent from the orientation. To contribute to the analysis of these results, experiments were conducted at the ACCEPTED MANUSCRIPT 2 scale of a single branch of a PHP. An oscillating motion was imposed to a single liquid plug surrounded by two vapour slugs in a capillary tube and high speed visualisations were performed. The test section was either adiabatic or heated. The adiabatic experiments brought to the fore the importance of dynamic contact angles in the flow and the dissymmetry between the advancing and receding contact angle. The non-adiabatic experiments showed that at low flux, the flow is disturbed by bubble nucleation, while at high heat flux, the main heat transfer mechanism is thin film evaporation, with a completely different thermal and hydrodynamic behaviour.

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Section: Resultsmentioning

confidence: 99%

Section: Adiabatic Experiments: Hydrodynamic Aspectsmentioning

confidence: 99%

Experimental evidences of distinct heat transfer regimes in pulsating heat pipes (PHP)

Lips¹,

Bensalem²,

Bertin³

et al. 2010

Applied Thermal Engineering

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show abstract

“…It is worth noting that several researchers (e.g., Tong et al [38], Xu et al [39], Khandekar et al [40][41][42], and Borgmeyer et al [43,44]) have proven that high-speed visualization of the operating OHP is an effective way for understanding the fluid flow in it. In addition, this previous research also pointed out that the detailed fluid flow behaviors inside are closely correlated with the thermal performance of the OHP, which are critical for clarifying the heat transfer mechanisms of the OHP.…”

Section: Introductionmentioning

confidence: 99%

High-Speed Visual Analysis of Fluid Flow and Heat Transfer in Oscillating Heat Pipes with Different Diameters

Liu¹,

Sun²,

Zhang

et al. 2016

Preprint

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Abstract:The oscillating heat pipe (OHP) is a new member in the family of heat pipes, and it has great potential applications in energy conservation. However, the fluid flow and heat transfer in the OHP as well as the fundamental effects of inner diameter on them have not been fully understood, which are essential to the design and optimization of the OHP in real applications. Therefore, by combining the high-speed visualization method and infrared thermal imaging technique, the fluid flow and thermal performance in the OHPs with inner diameters of 1, 2 and 3 mm are presented and analyzed. The results indicate that three fluid flow motions, including small oscillation, bulk oscillation and circulation, coexist or, respectively, exist alone with the increasing heating load under different inner diameters, with three flow patterns occurring in the OHPs, viz. bubbly flow, slug flow and annular flow. These fluid flow motions are closely correlated with the heat and mass transfer performance in the OHPs, which can be reflected by the characteristics of infrared thermal images of condensers. The decrease in the inner diameter increases the frictional flow resistance and capillary instability while restricting the nucleate boiling in OHPs, which leads to a smaller proportion of bubbly flow, a larger proportion of short slug flow, a poorer thermal performance, and easier dry-out of working fluid. In addition, when compared with the 2 mm OHP, the increasing role of gravity induces the thermosyphon effect and weakens the 'bubble pumping' action, which results in a little smaller and bigger thermal resistances of 3 mm OHP under small and bulk oscillation of working fluid, respectively.

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“…The oscillations are due to heat and mass transfer between the liquid and vapor slugs. Several studies [9][10][11][12][13] have been conducted of the working of this technology and some general remarks can be given.…”

Section: Introductionmentioning

confidence: 99%

“…Khandekar et al [13] demonstrated that with a simple set-up consisting of a single closed loop of capillary dimensions it was possible to obtain an oscillating behavior. The authors established that the oscillation of different frequencies in the range 0.1 to 3Hz could be achieved with such a device.…”

Section: Introductionmentioning

confidence: 99%

An experimental device designed to obtain repeatable condensation peaks in a closed system

Soupremanien¹,

Ollier²,

Salamon³

et al. 2014

Energy and Sustainability V

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The results of an experimental study related to repeatable condensation peaks in a closed system are presented and a discussion to describe their incipiencies is detailed. The test sections (D1: filling capacity = 15.14 x 1e ) were divided into three parts: an evaporator, an insulator and a conductive top cover where a pressure sensor was inserted. The impacts of several parameters have been studied: devices' filling ratio (α); hot temperature of the evaporator; cooling of the condensation chamber and; the devices' dimension. For all the obtained results the frequencies were low (< 0.15 Hz) but the peak pressure amplitudes were significant (up to 987 mbar). The influence of α had been studied and its increase led to an augmentation of the pressure amplitude (exponential-like function) but to a decrease in the oscillation frequencies. The hot temperature's increase enhanced the oscillation frequency but the pressure amplitude variations were slightly decreased. The cooling level diminution led to a frequency decrease, but to a slight variation of the pressure peak amplitude. Reducing the devices' dimensions from D1 to D2 for the same α and cooling level allowed the increasing of the oscillation frequency without significantly modifying the pressure peaks' amplitude. In a strategy for energy harvesting these oscillation peaks could be converted into electricity using piezo-electrics.

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Multiple quasi-steady states in a closed loop pulsating heat pipe

Cited by 137 publications

References 24 publications

Experimental evidences of distinct heat transfer regimes in pulsating heat pipes (PHP)

Experimental evidences of distinct heat transfer regimes in pulsating heat pipes (PHP)

High-Speed Visual Analysis of Fluid Flow and Heat Transfer in Oscillating Heat Pipes with Different Diameters

An experimental device designed to obtain repeatable condensation peaks in a closed system

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