Subcooling parameter

Latent heat High, depth Subcooling parameter Thermal conductivity Surface roughness Channel length Mass flow rate Power, number of sample Number of channels Pressure, precession limit Heat rate Heat flux... 

Figure 7 shows the variation of the two-phase heat transfer coeffient (htp) as a function of the local subcooling parameter (Sc), for subcooled flow boiling. The subcooling parameter is defined as. 

Sc, local subcooling parameter OSV, onset of significant void ... 

During the subcooled nucleate flow boiling of a liquid in a channel the bulk temperature of the liquid at ONB, 7b, is less than the saturation temperature, and at a given value of heat flux the difference ATsub.oNB = 7s - 7b depends on L/d. The experimental parameters are presented in Table 6.2. 

Inlet Inlet temperature Subcooling Heat Wall su- Parameter ... 

Parameters 7c,onb, s.onb, and 74,onb change in the range of 0 < 7 < 1. They account for a specific temperature field in heated micro-channels and are criteria for the relative micro-channel length. Note, if 7 < 1 the value of parameter 7 is significantly less than unity. The paper by Celata et al. (1997) reports the results of experimental research of the onset of subcooled water boiling in the circular... 

Available data sets for flow boiling critical heat flux (CHF) of water in small-diameter tubes are shown in Table 6.9. There are 13 collected data sets in all. Only taking data for tube diameters less than 6.22 mm, and then eliminating duplicate data and those not meeting the heat balance calculation, the collected database included a total of 3,837 data points (2,539 points for saturated CHF, and 1,298 points for subcooled CHF), covering a wide range of parameters, such as outlet pressures from 0.101 to 19.0 MPa, mass fluxes from 5.33 to 1.34 x lO kg/m s, critical heat fluxes from 0.094 to 276 MW/m, hydraulic diameters of channels from 0.330 to 6.22 mm, length-to-diameter ratios from 1.00 to 975, inlet qualities from —2.35 to 0, and outlet thermal equilibrium qualities from -1.75 to 1.00. 

Hall and Mudawar (2000) provided a comprehensive review of the current state of the knowledge of subcooled CHF for water flow boiling in channels, and designed a statistical correlation with five parameters based on almost all available subcooled CHF databases in the literature ... 

Axial heat flux parameter Y The parameter Y, which replaces the heat flux shape factor in the CHF correlation, is not only a measure of the nonuniformity of the axial heat flux profile but also a means of converting from the inlet subcooling (AHin) to the local quality, X, form of the correlation via the heat balance equation. It is defined as... 

Several parameters have been seen to influence the crystallization of ice crystals in subcooled aqueous solutions. The primary factor is the extent of subcooling of the solution. Other factors include the agitation rate, the types and levels of solutes in solution. Huige (6) has summarized past work on conditions under which dusk-shaped and spherical crystals can be found in suspension crystallizers. The effects of heat and mass transfer phenomena on the morphology of an ice crystal growing in a suspension have not been fully understood. 

Two parameters are necessary to fully describe nucleation kinetics the induction time and the rate of nucleation. The moment a driving force is created, whether a supersaturation in solution systems or a subcooling in melt systems, the molecules begin to organize into crystallite clusters. The time at any given driving force required for the first nuclei to form is called the induction time. Unfortunately, the true induction time is difficult to measure since the exact point when nuclei are first formed is nearly impossible to measure. Nuclei are probably only nanometers in size, too small to be detected with any methods developed to date. Thus, measurement of... 

Parameters that affect crystallization may influence either the thermodynamic behavior or the crystallization kinetics (or both). Parameters that influence lipid crystallization include chemical composition, subcooling, cooling rate, agitation, minor components of fats (mono- and diacylglycerols, polar lipids, etc.), and scale of operation. The effects of these parameters on lipid crystallization will be reviewed briefly in this section. More detailed information about the effects of these parameters on lipid nucleation and crystal growth may be found elsewhere (4, 24, 28, 54). 

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