Upward and downward facing high mass flux spray cooling with additives: A novel technique to enhance the heat removal rate at high initial surface temperature

This paper reports the critical heat flux (CHF) enhancement that was observed experimentally when a porous metal was placed in a small flow channel (hereafter, this channel is called a “porous microchannel”). In the porous microchannel, the CHF value increased almost linearly with increased values of the mass flux and the inlet subcooling. In consequence, higher cooling performance was achieved under high mass flux and high inlet subcooling conditions. It was also found that considerable fluctuation of the pressure loss frequently encountered in a small heated channel disappears in the porous microchannel. It was considered that the stabilization of the pressure loss can mainly be attributed to inhibition of the formation of large bubbles. The effects of the material and the pore size of the porous metal were also investigated. Silver and nickel were selected as the porous metal material and the pore size tested was 0.2 and 0.6 mm. In the present experiments, the CHF value was not influenced significantly by the material in spite of the distinct difference of the thermal conductivity between silver and nickel, whilst it was dependent noticeably on the pore size. It was hence suggested that the CHF enhancement observed in this work was mainly caused by the complex thermal-hydraulic field formed in the porous microchannel. Preliminary results of the flow visualization performed to reveal the mechanisms of the CHF enhancement in the porous microchannel was also reported.

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Experimental Studies of Spray Cooling of High Temperature Metals Using High Mass Flux Industrial Nozzles

Heat Transfer, Volume 2 ◽

10.1115/imece2006-15632 ◽

2006 ◽

Author(s):

Hamed M. Al-Ahmadi ◽

S. C. Yao

Keyword(s):

Stainless Steel ◽

High Temperature ◽

Mass Flux ◽

Experimental Studies ◽

Spray Cooling ◽

Spray Angle ◽

High Mass ◽

Product Quality Control ◽

Wide Range ◽

Different Types

Systemic experiments were conducted for the spray cooling of high temperature stainless steel using three different types of industrial sprays, full cone and flat hydraulic nozzles and a flat air-mist nozzle. In the present study wide range of mass flux (1.5-30 kg/m2sec) is covered, which has never been thoroughly investigated before. Orientations with respect to gravity and spray angle were also explored. The data have been analyzed and correlated. The results of this study will be important to the product quality control in industries by providing a good estimate of heat flux at different mass flux, spray types and surface temperatures, especially for spray cooling of stainless steel and other metals with similar thermal properties.

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Aircraft Fuel Thermal Management System and Flight Thermal Endurance

Transactions of the Canadian Society for Mechanical Engineering ◽

10.1139/tcsme-2021-0146 ◽

2021 ◽

Author(s):

Rafiq Manna ◽

Natarajan Ravikumar ◽

Stephen Harrison ◽

Kiari Goni Boulama

Keyword(s):

Surface Temperature ◽

Thermal Management ◽

Management System ◽

Removal Rate ◽

Heat Removal ◽

Fuel Temperature ◽

Removal Capacity ◽

Thermal Management System ◽

Aircraft Fuel ◽

Over Time

An aircraft thermal management model was created in which fuel is circulated through the heat dissipating components for cooling purposes. A fraction of this fuel is then fed to the engine for combustion, while the excess is cooled by rejecting heat to the ambient and returned to the tank. The thermal management system was designed with the intent of controlling the heat dissipating surface temperature, ensuring a certain heat removal rate, while safeguarding the physical integrity of the fuel. The time variation of the fuel temperature and heat transfer rates was calculated. It was observed that for a constant heat dissipating surface temperature, the heated fuel temperature increased, and the heat removal capacity degraded over time. Conversely, for a specified heat removal rate, both the heat dissipating surface temperature and heated fuel temperature increased during the flight. Lastly, when the maximum fuel temperature was specified, both the heat dissipating surface temperature and heat removal rate decreased over time. In all cases, the time taken for these variables to hit the user-defined threshold values was recorded. A detailed sensitivity analysis was also presented highlighting the critical importance of the fuel recirculation rate on the performance of the thermal management system.

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