High heat flux sensor for infrared thermography determination of heat transfer coefficient of liquid metal cooled target's wall

Detailed heat transfer characteristics of particle-sintered porous media and metal foams are evaluated to specify the important structural parameters suitable for high heat removal. The porous media used in this experiment are particle-sintered porous media made of bronze and SUS316L, and metal foams made of copper and nickel. Cooling water flows into the porous medium opposite to heat flux input loaded by a plasma arcjet. The result indicates that the bronze-particle porous medium of 100μm in pore size shows the highest performance and achieves heat transfer coefficient of 0.035MW/m2K at inlet heat flux 4.6MW/m2. Compared with the heat transfer performance of copper fiber-sintered porous media, the bronze particlesintered ones give lower heat transfer coefficient. However, the stable cooling conditions that the heat transfer coefficient does not depend on the flow velocity, were confirmed even at heat flux of 4.6MW/m2 in case of the bronze particle-sintered media, while not in the case of the copper-fiber sintered media. This signifies the possibility that the bronze-particle sintered media enable much higher heat flux removal of over 10MW/m2, which could be caused by higher permeability of the particle-sintered pore structures. Porous media with high permeability provide high performance of vapor evacuation, which leads to more stable heat removal even under extremely high heat flux. On the other hand, the heat transfer coefficient of the metal foams becomes lower because of the lower capillary and fin effects caused by too high porosity and low effective thermal conductivity. It is concluded that the pore structure having high performance of vapor evacuation as well as the high capillary and high fin effects is appropriate for extremely high heat flux removal of over 10MW/m2.

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Influence of Overweight Acceleration on Heat Transfer of Hydrocarbon Fuel in a Vertical Tube at Supercritical Pressures

ASME 2019 Heat Transfer Summer Conference ◽

10.1115/ht2019-3552 ◽

2019 ◽

Author(s):

Lulu Lv ◽

Yanchen Fu ◽

Bensi Dong ◽

Jie Wen ◽

Guoqiang Xu

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Buoyancy Force ◽

Hydrocarbon Fuel ◽

High Heat ◽

Vertical Tube ◽

High Heat Flux ◽

Gravitational Acceleration

Abstract The presented study numerically investigated the heat transfer characteristics of supercritical hydrocarbon fuel RP-3 in a vertical tube under overweight conditions with gravitational accelerations from 1g to 5g. The model was simplified as a vertical tube with the diameter of 1.8mm and the length of 250mm. Constant heat flux was applied to the wall, varying from 200kW/m2 to 700kW/m2. Variations of wall temperature and heat transfer coefficient under overweight conditions were obtained by simulation. The dimensionless buoyancy and thermal acceleration under different conditions were analyzed. The results show that the heat transfer is normal at low heat flux, while two types of heat transfer deterioration were observed in both upward and downward supercritical flow at high heat flux. The heat transfer coefficient of downward flow is generally higher than upward flow, and the difference between them becomes larger with the increase of gravitational acceleration. At high heat flux, when bulk temperature reaches the pseudo-critical temperature, the thermal acceleration will increase by 50% leading to the deterioration of heat transfer. However, after the pseudo-critical point, both buoyancy force and thermal acceleration decrease to negligible. The rise in gravitational acceleration enhances buoyancy force, but has no impact on the thermal acceleration. Based on the numerical analysis, two different criterion, Bo* and Kv, for supercritical RP-3 are obtained to present the influence of buoyancy and thermal acceleration.

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Effect of Pressure on the Performance of Passive Two-Phase Closed Thermosyphon System Using R-134a

Journal of Engineering Research and Technology ◽

10.33976/jert.7.1/2020/1 ◽

2020 ◽

Vol 7 (1) ◽

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

High Heat ◽

High Heat Flux ◽

Two Phase ◽

Heating Load ◽

R 134A ◽

The Heat Transfer Coefficient

Two-phase closed thermosiphon system for cooling high heat flux electronic devices was constructed and tested on a lab scale. The performance of the thermosyphon system was investigated using R-134a as a working fluid. The effect of heat flux and the refrigerant pressure on the evaporator side heat transfer coefficient were investigated. It was found that the heat transfer coefficient increases by increasing the heat flux on the evaporator or by reducing the inside pressure. The effect of heat transfer mode of the condenser (natural or forced) also affected the overall heat transfer coefficient in the cycle. At the 200W heating load, the values of the heat transfer coefficients were 32 and 1.5 kW/m². ˚C, for natural and forced convection modes, respectively. The temperature difference between the evaporator and the refrigerant saturation pressure was found to be dependent on heat flux and the pressure inside the system. At 40 W heating load, the heat transfer coefficient was calculated to be 500, 3000 and 7300 W/oC.m2 at 0.152, .135 and 0.117 reduced pressure, respectively. It can be concluded that such a thermosyphon system can be used to cool high heat flux devices. This can be done using an environmentally friendly refrigerant and without any need for power to force the convection at the condenser.

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Experimental Characterization of the Heat Transfer in Multi-Microchannel Heat Sinks for Two-Phase Cooling of Power Electronics

Fluids ◽

10.3390/fluids6020055 ◽

2021 ◽

Vol 6 (2) ◽

pp. 55

Author(s):

Gennaro Criscuolo ◽

Wiebke Brix Markussen ◽

Knud Erik Meyer ◽

Björn Palm ◽

Martin Ryhl Kærn

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Power Electronics ◽

Flow Boiling ◽

High Heat ◽

Heat Sinks ◽

High Heat Flux ◽

Average Heat

This study aims to characterize experimentally the heat transfer in micro-milled multi-microchannels copper heat sinks operating with flow boiling, in the attempt to contribute to the development of novel and high heat flux thermal management systems for power electronics. The working fluid was R-134a and the investigation was conducted for a nominal outlet saturation temperature of 30 ∘C. The microchannels were 1 cm long and covered a square footprint area of 1 cm2. Boiling curves starting at low vapor quality and average heat transfer coefficients were obtained for nominal channel mass fluxes from 250 kg/m2s to 1100 kg/m2s. The measurements were conducted by gradually increasing the power dissipation over a serpentine heater soldered at the bottom of the multi-microchannels, until a maximum heater temperature of 150 ∘C was reached. Infrared thermography was used for the heater temperature measurements, while high-speed imaging through a transparent top cover provided visual access over the entire length of the channels. The average heat transfer coefficient increased with the dissipated heat flux until a decrease dependent on hydrodynamic effects occurred, possibly due to incomplete wall wetting. Depending on the channel geometry, a peak value of 200 kW/m2K for the footprint heat transfer coefficient and a maximum dissipation of 620 W/cm2 at the footprint with a limit temperature of 150 ∘C could be obtained, showing the suitability of the investigated geometries in high heat flux cooling of power electronics. The experimental dataset was used to assess the prediction capability of selected literature correlations. The prediction method by Bertsch et al. gave the best agreement with a mean absolute percent error of 24.5%, resulting to be a good design tool for flow boiling in high aspect ratio multi-microchannels as considered in this study.

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Analysis of measurement errors of convective heat-transfer coefficient using a thin-walled heat-flux sensor

Journal of Engineering Physics ◽

10.1007/bf00860209 ◽

1978 ◽

Vol 35 (2) ◽

pp. 917-921

Author(s):

Yu. I. Yunkerov

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Convective Heat Transfer ◽

Measurement Errors ◽

Convective Heat Transfer Coefficient ◽

Heat Flux Sensor ◽

Thin Walled ◽

Flux Sensor

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Design and Calibration of a Novel High Temperature Heat Flux Gage

Heat Transfer: Volume 4 ◽

10.1115/ht2005-72761 ◽

2005 ◽

Cited By ~ 4

Author(s):

Sujay Raphael-Mabel ◽

Scott Huxtable ◽

Andrew Gifford ◽

Thomas E. Diller

Keyword(s):

Heat Flux ◽

High Temperature ◽

High Heat ◽

Heat Flux Sensor ◽

High Heat Flux ◽

Average Value ◽

Metal Plates ◽

New Type ◽

Flux Sensor ◽

Calibration Apparatus

A new type of heat flux sensor (HTHFS) has been designed and constructed for applications at high temperature and high heat flux. It is constructed by connecting solid metal plates to form brass/steel thermocouple junctions in a series circuit. The thermal resistance layer of the HTHFS consists of the thermocouple materials themselves, thus improving temperature limits and lowering the temperature disruption of the sensor. The sensor can even withstand considerable erosion of the surface with little effect on the operation. A new type of convection calibration apparatus was designed and built specifically to supply a large convection heat flux. The heat flux was supplied simultaneously to both a test and standard gage by using two heated jets of air that impinged perpendicularly on the surface of each gage. The sensitivity for the HTHFS was measured to have an average value of 20 μV/(W/cm2). The uncertainty in this result was determined to be ±10% over the entire range tested. The sensitivity agrees with the theoretically calculated sensitivity for the materials and geometry used. Recommendations for future improvements in the construction and use of the sensors are discussed.

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Micromachined Thermopile Based High Heat Flux Sensor

Journal of Microelectromechanical Systems ◽

10.1109/jmems.2019.2948645 ◽

2020 ◽

Vol 29 (1) ◽

pp. 36-42 ◽

Cited By ~ 2

Author(s):

Wei Tian ◽

Yi Wang ◽

Hong Zhou ◽

Yuelin Wang ◽

Tie Li

Keyword(s):

Heat Flux ◽

High Heat ◽

Heat Flux Sensor ◽

High Heat Flux ◽

Flux Sensor

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On the Scalability of Liquid Microjet Array Impingement Cooling for Large Area Systems

Journal of Heat Transfer ◽

10.1115/1.4003532 ◽

2011 ◽

Vol 133 (6) ◽

Cited By ~ 12

Author(s):

Avijit Bhunia ◽

C. L. Chen

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Heat Source ◽

Transfer Coefficient ◽

High Heat Flux ◽

Average Heat Transfer Coefficient ◽

Large Area ◽

Impingement Cooling ◽

Average Heat

The necessity for an efficient thermal management system covering large areas is growing rapidly with the push toward more electric systems. A significant amount of research over the past 2 decades has conclusively proved the suitability of jet, droplet, or spray impingement for high heat flux cooling. However, all these research consider small heat source areas, typically about a few cm2. Can a large array of impingement pattern, covering a much wider area, achieve similar heat flux levels? This article presents liquid microjet array impingement cooling of a heat source that is about two orders of magnitude larger than studied in the previous works. Experiments are carried out with 441 jets of de-ionized water and a dielectric liquid HFE7200, each 200 μm diameter. The jets impinge on a 189 cm2 area surface, in free surface and confined jet configurations. The average heat transfer coefficient values of the present experiment are compared with correlations from the literature. While some correlations show excellent agreement, others deviate significantly. The ensuing discussion suggests that the post-impingement liquid dynamics, particularly the collision between the liquid fronts on the surface created from surrounding jets, is the most important criterion dictating the average heat transfer coefficient. Thus, similar thermal performance can be achieved, irrespective of the length scale, as long as the flow dynamics are similar. These results prove the scalability of the liquid microjet array impingement technique for cooling a few cm2 area to a few hundred cm2 area.

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Deterioration in Heat Transfer to Fluids at Supercritical Pressure and High Heat Fluxes

Journal of Heat Transfer ◽

10.1115/1.3580115 ◽

1969 ◽

Vol 91 (1) ◽

pp. 27-36 ◽

Cited By ~ 86

Author(s):

B. S. Shiralkar ◽

Peter Griffith

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

High Heat ◽

Supercritical Pressure ◽

Heat Fluxes ◽

Bulk Temperature ◽

Operating Pressure ◽

The Heat Transfer Coefficient

At slightly supercritical pressure and in the neighborhood of the pseudocritical temperature (which corresponds to the peak in the specific heat at the operating pressure), the heat transfer coefficient between fluid and tube wall is strongly dependent on the heat flux. For large heat fluxes, a marked deterioration takes place in the heat transfer coefficient in the region where the bulk temperature is below the pseudocritical temperature and the wall temperature above the pseudocritical temperature. Equations have been developed to predict the deterioration in heat transfer at high heat fluxes and the results compared with previously available results for steam. Experiments have been performed with carbon dioxide for additional comparison. Limits of safe operation for a supercritical pressure heat exchanger in terms of the allowable heat flux for a particular flow rate have been determined theoretically and experimentally.

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