Experimental study on a cryogenic loop heat pipe with high heat capacity

In this investigation, a Loop Heat Pipe (LHP) evaporator has been studied using a borescope inserted through the compensation chamber into the liquid core. This minimally intrusive technique allows liquid/vapor interactions to be observed throughout the liquid core and compensation chamber. A low conductivity ceramic was used for the wick and ammonia as the working fluid. Results indicate that buoyancy driven flows, both two-phase and single-phase, play essential roles in evacuating excess heat from the core, which explains the several differences in performance between horizontal and vertical orientations of the evaporator. This study also found no discernable effect of the pre-start fill level of the compensation chamber on thermal performance during startup at moderate and high heat loads.

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Sector Rotating Heat Pipe With Interconnected Branches and Reservoir for Turbomachinery Cooling

Journal of Heat Transfer ◽

10.1115/1.4034487 ◽

2016 ◽

Vol 139 (1) ◽

Cited By ~ 1

Author(s):

Brian Reding ◽

Yiding Cao

Keyword(s):

Experimental Study ◽

Heat Pipe ◽

Heat Pipes ◽

High Heat ◽

Heat Fluxes ◽

Practical Solution ◽

Pipe System ◽

Current Configuration ◽

Cooling Technique

Heat pipe technology offers a possible cooling technique for structures exposed to high heat fluxes, as in turbomachinery such as compressors and turbines. However, in its current configuration as single heat pipes, implementation of the technology is limited due to the difficulties in manufacturability and costs. Hence, a study to develop a new radially rotating (RR) heat pipe system was undertaken, which integrates multiple RR heat pipes with a common reservoir and interconnected braches for a more effective and practical solution to turbomachinery cooling. Experimental study has shown that the integration of multiple heat pipe branches with a reservoir at the top is feasible.

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Effects of sleep on a high-heat capacity mattress on sleep stages, EEG power spectra, cardiac interbeat intervals and body temperatures in healthy middle-aged men‡

SLEEP ◽

10.1093/sleep/zsz271 ◽

2019 ◽

Vol 43 (5) ◽

Cited By ~ 1

Author(s):

Sebastian Herberger ◽

Kurt Kräuchi ◽

Martin Glos ◽

Katharina Lederer ◽

Lisa Assmus ◽

...

Keyword(s):

Heart Rate ◽

Heat Capacity ◽

Body Temperature ◽

Wave Energy ◽

Sleep Stage ◽

High Heat ◽

Body Temperatures ◽

High Heat Capacity ◽

Eeg Power ◽

Core Body

Abstract Study Objectives This study deals with the question whether a slow (non-disturbing) reduction of core body temperature (CBT) during sleep increases sleep stage N3 and EEG slow wave energy (SWE) and leads to a slowing of heart rate in humans. Participants Thirty-two healthy male subjects with a mean ± SD age 46 ± 4 years and body mass index 25.2 ± 1.8 kg/m2. Methods A high-heat capacity mattress (HM) was used to lower body temperatures in sleep and was compared to a conventional low-heat capacity mattress (LM) in a double-blinded fashion. Polysomnography was performed accompanied by measurements of skin-, core body- and mattress surface-temperatures, and heart rate. EEG power spectral analyses were carried out using Fast Fourier Transform. Interbeat intervals were derived from the electrocardiogram. Results The HM led to a larger decline in CBT, mediated through higher heat conduction from the core via the proximal back skin onto the mattress together with reduced heart rate. These effects occurred together with a significant increase in sleep stage N3 and standardized slow wave energy (sSWE, 0.791–4.297 Hz) accumulated in NREM sleep. In the 2nd half of the night sSWE increase was significantly correlated with body temperature changes, for example with CBT decline in the same phase. Conclusions A HM subtly decreases CBT, leading to an increased amount of sleep stage N3 and of sSWE, as well as a slowing of heart rate.

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Experimental Investigation of the Miniature Loop Heat Pipe With Flat Evaporator

Advances in Electronic Packaging, Parts A, B, and C ◽

10.1115/ipack2005-73498 ◽

2005 ◽

Cited By ~ 7

Author(s):

Randeep Singh ◽

Aliakbar Akbarzadeh ◽

Masataka Mochizuki ◽

Thang Nguyen ◽

Vijit Wuttijumnong

Keyword(s):

Thermal Resistance ◽

Heat Pipe ◽

Thermal Control ◽

Capillary Forces ◽

High Heat ◽

Working Fluid ◽

Loop Heat Pipe ◽

Wick Structure ◽

Flat Evaporator ◽

Heat Loads

Loop heat pipe (LHP) is a very versatile heat transfer device that uses capillary forces developed in the wick structure and latent heat of evaporation of the working fluid to carry high heat loads over considerable distances. Robust behaviour and temperature control capabilities of this device has enable it to score an edge over the traditional heat pipes. In the past, LHPs has been invariably assessed for electronic cooling at large scale. As the size of the thermal footprint and available space is going down drastically, miniature size of the LHP has to be developed. In this paper, results of the investigation on the miniature LHP (mLHP) for thermal control of electronic devices with heat dissipation capacity of up to 70 W have been discussed. Copper mLHP with disk-shaped flat evaporator 30 mm in diameter and 10 mm thickness was developed. Flat evaporators are easy to attach to the heat source without any need of cylinder-plane-reducer saddle that creates additional thermal resistance in the case of cylindrical evaporators. Wick structure made from sintered nickel powder with pore size of 3–5 μm was able to provide adequate capillary forces for the continuos circulation of the working fluid, and successfully transport heat load at the required distance of 60 mm. Heat was transferred using 3 mm ID copper tube with vapour and liquid lines of 60 mm and 200 mm length respectively. mLHP showed very reliable start up at different heat loads and was able to achieve steady state without any symptoms of wick dry-out. Tests were conducted on the mLHP with evaporator and condenser at the same level. Total thermal resistance, R total of the mLHP came out to be in the range of 1–4°C/W. It is concluded from the outcomes of the investigation that mLHP with flat evaporator can be effectively used for the thermal control of the electronic equipments with restricted space and high heat flux chipsets.

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