Subcooling

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

Single-Bubble Dynamics During Pool Boiling Under Low Gravity Conditions

Abstract: Results of an experimental study on growth and detachment mechanisms of a single bubble on a heated surface conducted during the parabola e ights of the KC-135 aircraft are described. An artie cial cylindrical cavity 10 πm in diameter was etched in the center of a silicon wafer. The wafer was heated on the back side, and the wall superheat was controlled. Degassed distilled water was used as the test liquid. Bubble growth time, bubble size and shape from nucleation to liftoff were measured under subcooled and saturation conditions at system pressures varying from 0.101 to 0.115 MPa. The wall superheats were varied from 2.5 to 8.0 ±C. Signie cantly larger bubble diametersand longerbubble growth periods than thoseat Earth normal gravity were measured. Bubblediameters as large as 20 mm at liftoff were observed as opposed to about 2.5 mm at Earth normal gravity. Consistent with results of numerical simulations, it is found that for the same wall superheat and liquid subcooling the bubble liftoff diameter can be approximately related to the gravity level through the relation Dd / g i 0:5 and the growth period as tg / g i 1:05 . The effect of wall superheat and liquid subcooling on bubble liftoff diameter is found to be small. However, the growth periods are found to be very sensitive to liquid subcooling at a given wall superheat. Small accelerations along the heater surface can lead to sliding motion of the bubble prior to liftoff. At the same gravitational acceleration the liftoff diameter of sliding bubbles is smaller than that of nonsliding bubbles.

Performance optimization of transcritical CO2 refrigeration cycle with thermoelectric subcooler

Abstract: SUMMARY Use of thermoelectric subcooler is one of the techniques to improve the performance of transcritical CO2 cycle Thermodynamic analyses and optimizations of transcritical CO2 refrigeration cycle with thermoelectric subcooler are presented in this paper Further, the effects of various operating parameters on cycle performances are studied It is possible to optimize current supply, discharge pressure, and CO2 subcooling simultaneously based on maximum cooling COP for thermoelectrically enhanced transcritical CO2 refrigeration cycle to get best performance Results show that thermoelectric current supply, COP improvement, and discharge pressure reduction increase with increase in cycle temperature lift, with maximum values of 11 A, 256%, and 154%, respectively, for studied ranges Use of thermoelectric subcooler in CO2 refrigeration system not only improves the cooling COP, also reduces the system high-side pressure, compressor pressure ratio, and compressor discharge temperature, and enhances the volumetric cooling capacity Component-wise irreversibility distribution shows similar trend with basic CO2 cycle, although values are lower leading to higher second law efficiency Cooling capacity may be enhanced by increasing the current supply for the same thermoelectric configuration with penalty of COP Study reveals that thermoelectrically enhanced CO2 refrigeration cycle yields significant performance improvement especially for higher-cycle temperature lift Copyright © 2011 John Wiley & Sons, Ltd

Fundamental Study on Thermo-Hydraulics during Start-Up in Natural Circulation Boiling Water Reactors, (II)

Abstract: The authors have been investigating the fundamentals of thermo-hydraulic instabilities which may appear during the start-up in natural circulation BWRs in order to understand their driving mechanisms and to examine the methods preventing their occurrence with an aim of establishing a rational start-up procedure and reactor configuration In this paper, ‘Natural Circulation Oscillation’ was investigated experimentally under various conditions of heat input, inlet subcooling and non-heated riser length to reveal the driving mechanism and its feature As a result, it was made clear that the in-phase natural circulation oscillation was induced in parallel channels by hydrostatic head fluctuation in a long vertical non-heated channel such as steam separators and a divided chimney in natural circulation BWRs due to alternate flow of vapor and liquid therein while the vapor generation rate is insufficient

Critical flow of saturated and subcooled water at high pressure. [PWR; BWR]

Abstract: Critical flow rate measurements have been made with saturated and subcooled water to determine the effect of fluid enthalpy, flow geometry and size, and flow length. These tests were conducted by blowing down vessels from an initial fluid pressure of 1000 psia (6895 kN/m/sup 2/) with the discharging fluid temperature between 450 and 550 F (232 and 288 C). The results clearly demonstrate the influence of metastable and/or nonequilibrium, thermodynamic states for flow lengths less than about 5 in. (127 mm). Data for different diameter nozzles, from 0.5 to 3.0-in. (12.7 to 76.2 mm), are presented which suggest that the critical mass flux decreases with increasing diameter.

A highly stable microchannel heat sink for convective boiling

Abstract: To develop a highly stable two-phase microchannel heat sink, we experimented with convective boiling in diverging, parallel microchannels with different distributions of laser-etched artificial nucleation sites. Each microchannel had a mean hydraulic diameter of 120 µm. The two-phase flow visualization and the magnitudes of pressure drop and inlet temperature oscillations under boiling conditions demonstrated clearly the merits of using artificial nucleation sites to further stabilize the flow boiling in diverging, parallel microchannels. The stability map showed the plane of subcooling number versus phase change number. It illustrated that diverging, parallel microchannels with artificial nucleation cavities have a much wider stable region than parallel microchannels with uniform cross-sections or diverging, parallel microchannels without artificial nucleation cavities. In addition, the results revealed that the design with cavities distributed uniformly along the downstream half of the channel presented the best stability performance among the three distributions of nucleation sites. This particular design can be regarded as a highly stable microchannel heat sink for convective boiling.