Subcooling

About: Subcooling is a research topic. Over the lifetime, 6150 publications have been published within this topic receiving 99125 citations.

Two-phase heat exchange for new refrigerants and their mixtures

Abstract: Most of the studies on boiling and condensation heat transfer of new refrigerants have been done with pure substances. They show that existing correlations, for instance those presented in the VDI-Warmeatlas , adequately describe the nucleate boiling and condensation heat transfer of pure refrigerants. Boiling and condensation heat transfer coefficients of mixtures are often considerably lower than those of the pure components. The reduction depends mainly on the difference between dew- and bubble-point temperature for a given concentration. It compensates often to a great extent the advantage of a gliding temperature difference. In forced convection boiling these effects are well described by a model recently presented by Steiner and Taborek, tested with over 13 000 data points. As shown in this paper it applies also for refrigerant mixtures. When vapours are condensed the usual assumption of film condensation often does not hold for mixtures, particularly at condensation rates that are not too large. Measured heat transfer coefficients are then larger by up to a factor of 4 than those of film condensation. In the case of larger condensation rates, subcooling of the vapour phase with subsequent fog formation can occur.

CFD modelling of subcooled flow boiling for nuclear engineering applications

Abstract: In this work a general-purpose CFD code CFX-5 was used for simulations of subcooled flow boiling. The subcooled boiling model, available in a custom version of CFX-5, uses a special treatment of the wall boiling boundary, which assures the grid invariant solution. The simulation results have been validated against the published experimental data [1] of high-pressure flow boiling in a vertical pipe covering a wide range of conditions (relevant to the pressurized water reactor). In general, a good agreement with the experimental data has been achieved. To adequately predict the lateral distribution of two-phase flow parameters, the modelling of two-phase flow turbulence and non-drag forces under wall boiling conditions have been also investigated in the paper. (author)

Visualization Study on Boiling of Nitrogen During Quench for Fault Current Limiter Applications

Abstract: For the development of a 13.2 kV/630 A bifilar winding type high-Tc superconducting fault current limiter (SFCL), a visualization study has been conducted to clarify boiling characteristics during the quench of the high-Tc SFCL. A series of experiments was carried out using a stainless steel strip on a G10 plate as a heating element to simulate the quench state of the high-Tc SFCL. A pulse of DC power input was applied to the strip in saturated and subcooled liquid nitrogen. The magnitude of the heat generation was varied from 10 W/cm2 to 170 W/cm2 and the period of the heat impulse was fixed at approximately 100 ms. Bubble behavior was observed by a high-speed camera through view ports of a cryostat. The boiling phenomena, the temperature rising of the strip and the recovery time were compared for different power densities and liquid nitrogen operating conditions. The bubble suppression was clearly observed with respect to the degree of subcooling