Thermal subcooling

If the liquid state (P,T) lies above the saturation curve ABC and to the left hand side of the To isotherm, then the liquid is said to be subcooled , or strictly, thermally subcooled . The term subcooled also applies if the hquid temperature remains at To while the pressure is raised above Po i.e. the hquid is pressure subcooled. 

A thermal subcooled liquid state is generated when heat is removed from the liquid, initially at To, and the degree of subcooling can be specified by the enthalpy removed (Ho-H). 

Custody Management Filling with Thermally Subcooled Liquid Creating Thermal... 91... 

If a tank is topped up with thermally subcooled liquid—a dangerous practice—then auto-stratification will take place immediately (see Fig. 6.2). 

Thermally subcooled liquid, i.e. liquid cooled to below its boiling point at tank pressure, will be more dense than the heel of old liquid. If mixing is incomplete, the old liquid will rise above the in-coming subcooled liquid and collect as a stratified upper layer. 

FilUng an empty tank with thermally subcooled liquid will also lead to autostratification. Some of the subcooled liquid will absorb heat from the tank walls, piping, etc. to produce significant quantities of saturated Uquid at the tank operating pressure, which partially evaporates as cooldown vapour. This saturated Uquid will form a warmer, less dense stratified layer on top of the thermally subcooled liquid. 

FilUng a partly filled tank with thermally subcooled Uquid may result in possibly three layers, wifli a top saturated layer, a middle layer of heel Uquid, and a bottom layer of subcooled Uquid. 

The diagram in Fig. 11-101 presents enthalpy data for LiBr-water solutions. It is needed for the thermal calculation of the cycle. Enthalpies for water and water vapor can be determined from the table or properties of water. The data in Fig. 11-101 are apphcable to saturated or subcooled solutions and are based on a zero enthalpy of liquid water at 0°C and a zero enthalpy of solid LiBr at 25°C. Since... 

The thermal quality of the solvent feed has no effect on the value of (S/F)mjn, but does affect the minimum reflux to some extent, especially as the (S/F) ratio increases. R nax occurs at higher values of the reflux ratio as the upper-feed quality decreases a subcooled upper feed provides additional refluxing capacity and less external reflux is required for the same separation. It is also sometimes advantageous to introduce the primary feed to the extractive distillation column as a vapor to help maintain a higher solvent concentration on the feed tray and the trays immediately below... 

Air vents are most effective when they are fitted at the end of a length of 300 mm or 450 mm of uninsulated pipe that can act as a collecting/cooling leg. Air is an excellent insulating material, having a thermal conductivity about 2200 times less than that of iron. The last place where it can be allowed to collect is in the steam space of heat exchangers. Further, as it contains oxygen or carbon dioxide, which dissolve readily in any subcooled condensate that may be present, the presence of air initiates corrosion of the plant and the condensate return system. 

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... 

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. 

W-3 CHF correlation. The insight into CHF mechanism obtained from visual observations and from macroscopic analyses of the individual effect of p, G, and X revealed that the local p-G-X effects are coupled in affecting the flow pattern and thence the CHF. The system pressure determines the saturation temperature and its associated thermal properties. Coupled with local enthalpy, it provides the local subcooling for bubble condensation or the latent heat (Hfg) for bubble formation. The saturation properties (viscosity and surface tension) affect the bubble size, bubble buoyancy, and the local void fraction distribution in a flow pattern. The local enthalpy couples with mass flux at a certain pressure determines the void slip ratio and coolant mixing. They, in turn, affect the bubble-layer thickness in a low-enthalpy bubbly flow or the liquid droplet entrainment in a high-enthalpy annular flow. 

Enhancement of CHF subcooled water flow boiling was sought to improve the thermal hydraulic design of thermonuclear fusion reactor components. Experimental study was carried out by Celata et al. (1994b), who used two SS-304 test sections of inside diameters 0.6 and 0.8 cm (0.24 and 0.31 in.). Compared with smooth channels, an increase of the CHF up to 50% was reported. Weisman et al. (1994) suggested a phenomenological model for CHF in tubes containing twisted tapes. 

Celata, G. P, and A. Mariani, 1993, A Data Set of CHF in Water Subcooled Flow Boiling, Specialists Workshop on the Thermal-Hydraulics of Hight Heat Flux Components in Fusion Reactors, Coordinated by G. P. Celata/A. Mariani, ENEA-C.R.E. Casaccia, Italy. (5)... 

Westendorf, W. H., and W. F. Brown, 1966, Stability of Intermixing of High-Velocity Vapor with Its Subcooled Liquid in Cocurrent Streams, NASA TN D-3553, Lewis Res. Ctr., Cleveland, OH. (6) Westinghouse Electric Corp., 1969, Thermal Conductivity of Crud, Rep. WAPD-TM-918, Pittsburgh, PA. (14)... 

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