Accelerated Cryogenic Cooling Caused by the Temporary Frost Layer Enhancer

The possibility of using a frost layer, created on the surface of a sample that undergoes cryogenic treatment, as a heat transfer enhancer was recently studied. This layer grows on the preliminary cooled sample surface as a result of its contact with moist air flow prior to its immersion into liquid nitrogen. A significant increase in the outflow heat flux (up to 12.8 times), or, alternatively, a cooling time shortening, in comparison with the bare sample was found. A detailed description of the frost layer development along with the influence of the thickness of the layer on the efficiency of the cooling process, as well as environmental parameters that affect the thickness itself is presented in the paper.

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Wetting layer evolution and interfacial heat transfer in water-air spray cooling process of hot metallic surface

Thermal Science ◽

10.2298/tsci210615318n ◽

2021 ◽

pp. 318-318

Author(s):

Lidan Ning ◽

Liping Zou ◽

Zhichao Li ◽

Huiping Li

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Nucleate Boiling ◽

Spray Cooling ◽

Film Boiling ◽

Metallic Surface ◽

Interfacial Heat Transfer Coefficient ◽

Interfacial Heat Transfer ◽

Cooling Process ◽

Inverse Heat Transfer

Spray cooling experiments on the hot metallic surfaces with different initial temperatures were performed. This paper adopts a self-developing program which is based on the inverse heat transfer algorithm to solve the interfacial heat transfer coefficient and heat flux. The temperature-dependent interfacial heat transfer mechanism of water-air spray cooling is explored according to the wetting layer evolution taken by a high-speed camera and the surface cooling curves attained by the inverse heat transfer algorithm. Film boiling, transition boiling, and nucleate boiling stages can be noticed during spray cooling process of hot metallic surface. When the cooled surface?s temperature drops to approximately 369?C - 424?C; the cooling process transfers into the transition boiling stage from the film boiling stage. The wetting regime begins to appear on the cooled surface, the interfacial heat transfer coefficient and heat flux begin to increase significantly. When the cooled surface?s temperature drops to approximately 217?C - 280?C, the cooling process transfers into the nucleate boiling stage. The cooled surface was covered by a liquid film, and the heat flux begins to decrease significantly.

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Experimental Research of Boiling Heat Transfer Phenomena on Metal Surface in State of Low Gravitational Acceleration Field Between 0g and 1g

ASME/JSME 2011 8th Thermal Engineering Joint Conference ◽

10.1115/ajtec2011-44065 ◽

2011 ◽

Author(s):

Eiji Nemoto ◽

Tomohiro Saitoh

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Stainless Steel ◽

Liquid Nitrogen ◽

Metal Surface ◽

Boiling Heat Transfer ◽

Sample Surface ◽

Gravitational Acceleration ◽

Maximum Heat ◽

Acceleration Field

The paper deals with the characteristics of boiling heat transfer phenomena on the metal surfaces where gravitational acceleration between 0g and 1g acts. To conduct the experiment in the field where the gravitational acceleration between 1g and 0g acted accurately, we produced the Atwood machine that was able to obtain the fixed gravitational acceleration field known by physics well. The metallic materials used by the experiment were brass, stainless steel, aluminum, copper and these materials were processed to 10mm in the diameter, and we put these samples in liquid nitrogen and experimented on the boiling phenomenon. As a result, it has been understood that there is the feature shown next in boiling heat transfer phenomena on the metal surface in gravitational acceleration field between 0g and 1g. (1) When brass, copper, stainless steel, and aluminum of the sample were put in the liquid nitrogen, the temperature differentiation coefficient on the sample surface showed the tendency to decrease in proportion to gravitational acceleration changed from 1g into 0g. (2) In boiling heat flux curve in these metals (brass, stainless steel, aluminum and copper), it was clarified for gravitational acceleration 1g to indicate maximum heat flux value qmax.

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Influence of the Refrigerant Charge on the Heat Transfer Performance for a Closed-Loop Spray Cooling System

Energies ◽

10.3390/en14227588 ◽

2021 ◽

Vol 14 (22) ◽

pp. 7588

Author(s):

Nianyong Zhou ◽

Hao Feng ◽

Yixing Guo ◽

Wenbo Liu ◽

Haoping Peng ◽

...

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Heat Transfer Performance ◽

Cooling System ◽

Temperature Drop ◽

Nucleate Boiling ◽

Spray Cooling ◽

Cooling Process

With the rapid increase of heat flux and demand for miniaturization of electronic equipment, the traditional heat conduction and convective heat transfer methods could not meet the needs. Therefore, the spray cooling experiment was carried out to obtain the basic heat transfer and cooling process. In this experiment, the spray cooling system was set up to investigate the influence of refrigerant charge on heat transfer performance in steady-state, dynamic heating, and dissipating processes. In a steady-state, the heat transfer coefficient increased with the rise of the refrigerant charge. In the dynamic dissipating process, both heat flux and heat transfer coefficient decreased rapidly after the critical heat flux, and the surface temperature drop point of each refrigerant charge was presented. The optimum refrigerant charge was provided considering the cooling parameters and the system operating performance. When the refrigerant operating pressure was 0.5 MPa, the spray cooling process presented with the higher heat flux, heat transfer coefficient, and cooling efficiency in this experiment. Meanwhile, the suitable surface temperature drop point and more gentle heat flux curves in the nucleate boiling region were obtained. The research results will contribute to the spray cooling system design, which should be operated before departure from the nucleate boiling point for avoiding cooling failure.

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Surface Heat Transfer Coefficient’s Calculation of W9Mo3Cr4V during Cryogenic Treatment

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.43.424 ◽

2010 ◽

Vol 43 ◽

pp. 424-429

Author(s):

Zi Ran Liu ◽

Cai Xia Ren ◽

Xian Guo Yan

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Flux Density ◽

Heat Flux Density ◽

Cryogenic Treatment ◽

Surface Heat ◽

Surface Heat Transfer ◽

Surface Heat Transfer Coefficient

In the process of the finite element analogy of the Cryogenic Treatment of the high speed steel cutter with respect to the material of W9Mo3Cr4V, the surface heat transfer coefficient is a crucial parameter. In order to get this parameter, this paper employed the method of inverse heat conduction to process the temperature curve generated through the cryogenic treatment of the tested work piece with the material of W9Mo0Cr4V, thereby obtaining the surface heat transfer coefficient of the tested work piece. This coefficient can be considered the surface heat transfer coefficient of cryogenic treatment of the cutter with the same material. The principle of the inverse heat conduction is as follows: firstly, according to the boundary condition and the initial value in the tri-dimensional space, the equation of the sensitivity coefficient and the temperature field can be deduced. Second, the coupling of two equations is carried out, and the heat flux density is calculated based on above result. The heat flux density will be revise to get the reasonable value . Lastly, the surface heat transfer coefficient can be obtained by the heat flux density. In this paper, all the work is automatically accomplished with the aid of FEPG soft ware and Visual C++ programmable language.

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THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

Energy Technologies & Resource Saving ◽

10.33070/etars.3.2017.03 ◽

2017 ◽

pp. 25-34

Author(s):

V.N. Moraru

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Capacity ◽

Specific Heat ◽

Chemical Properties ◽

Heating Surface ◽

Physical Models ◽

Superheated Liquid ◽

Two Phase ◽

Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

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