Liquid subcooling

SCI Propane liquid subcooler. Cooled by returning propane vapor. 

Often, a reasonable and convenient way to understand the heat transfer process in a heat exchanger unit is to break down the types of heat transfer that must occur such as, vapor subcooling to dew point, condensation, and liquid subcooling. Each of these demands heat transfer of a different type, using different AT values, film coefficients, and fouling factors. This is illustrated in Figure 10-36. It is possible to properly determine a weighted overall temperature... 

Example 10-6. Heat Duty of a Condenser with Liquid Subcooling... 

The variable orifice of the expansion valve can be replaced, in small systems, by a long thin tube. This is a non-modulating device and has certain limitations, but will give reasonably effective control over a wide range of conditions if correctly selected and applied. Mass flow is a function of pressure difference and the degree of liquid subcooling on entry. 

For most regimes, they found a linear rise in CHF with increasing liquid subcooling. Accordingly, subcooling was taken into account in the following equation ... 

The data of liquid subcooling at ONB point presented in Table 6.4 indicate that the value of ATsub.oNB = 7s - Tb.onb changes in the wide range of ATsub,ONB =... 

Figure 2.38 Effect of liquid subcooling on peak heat flux, for heaters of various sizes in isopropanol. (From Elkssabgi and Lienhard, 1988. Copyright 1988 by American Society of Mechanical Engineers, New York. Reprinted with permission.)... 

For a total condenser, the vapor composition used in the equilibrium relations is that determined during a bubble point calculation based on the actual pressure and liquid compositions found in the condenser. These vapor mole fractions are not used in the component mass balances since there is no vapor stream from a total condenser. It often happens that the temperature of the reflux stream is below the bubble point temperature of the condensed liquid (subcooled condenser). In such cases it is necessary to specify either the actual temperature of the reflux stream or the difference in temperature between the reflux stream and the bubble point of the condensate. 

In these numerical simulations, the independent variables are (i) wall superheat, (ii) liquid subcooling, (iii) system pressure, (iv) thermophysical properties of test fluid, (v) contact angle, (vi) gravity level, (vii) thermophysical properties of the solid and surface quality (conjugate problem), and (viii) heater geometry. 

Figure 4 Comparison of numerical simulations with experimental data (a) Effect of wall superheat, (b) elfect of liquid subcooling (fluid water, (fc = 54 , g = l.Oge).

Effects of wall superheat, liquid subcooling, contact angle and level of gravity on bubble growth process, bubble diameter at departure and growth period have been quantified. 

The heat flux transferred through mHP depends on the distance between the condenser and evaporator zone, the wall superheat and the liquid subcooling, the thermal contact between the heater and wick and the superficial boundary conditions of the wick. 

I - heat pipe evaporator, II - he condenser. III - liquid subcooler, sorption canister. 

The correlation is for saturated fluids the effect of liquid subcooling can be taken into account using Eq. 15.122. 

The heat transfer mode for subcooling liquid is that of sensible heat exchange. Subcooling heat transfer rates are much lower than condensation heat transfer rates for two reasons. First, sensible heat transfer coeflicients are much lower than condensation coeflicients and second, as the liquid subcools, the temperature difference between the... 

Consider a rise in liquid subcooling. Initially, this will lower the vapor pressure of the condensed liquid and, therefore, the pressure in the liquid compartment. The pressure difference between the top of the column and the liquid compartment will rise. This will enhance overhead vapor flow while retarding reflux flow. 

Still other examples of observable metastabilities include subcooled phases, such as subcooled vapors to make liquids, subcooled liquids to make solids, and subcooled solids to make other solids. The lifetimes of such metastable phases can be substantial, because the nucleation of new phases may require particular kinds of fluctuations that occur only rarely. Lastly we mention the huge number of observable conformational metastabilities that can be exhibited by large molecules such as proteins. 

Recycle ratio, 48-49 Reducing liquid subcooling (reflux problems), 279... 

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