Temperature subcooled

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

Arsub difference between saturation temperature and temperature (subcooling), K... 

Stripping Tower Theoretical Trays Reboiler Temperature Subcooled Condenser 12 190 °C... 

Va.por Pressure. Vapor pressure is one of the most fundamental properties of steam. Eigure 1 shows the vapor pressure as a function of temperature for temperatures between the melting point of water and the critical point. This line is called the saturation line. Liquid at the saturation line is called saturated Hquid Hquid below the saturation line is called subcooled. Similarly, steam at the saturation line is saturated steam steam at higher temperature is superheated. Properties of the Hquid and vapor converge at the critical point, such that at temperatures above the critical point, there is only one fluid. Along the saturation line, the fraction of the fluid that is vapor is defined by its quaHty, which ranges from 0 to 100% steam. 

For subcooling, a liquid inventory may be maintained in the bottom end of the shell by means of a weir or a hquid-level-controUer. The subcoohng heat-transfer coefficient is given by the correlations for natural convection on a vertical surface [Eqs. (5-33 ), (5-33Z )], with the pool assumed to be well mixed (isothermal) at the subcooled condensate exit temperature. Pressure drop may be estimated by the shell-side procedure. 

Outlet Temperature and Pressure. It is important to have proper subcooling in the vent end of the unit to prevent large amounts of process vapors from going to the vacuum system along with the inerts. 

Calculate condensing pressure, with to as bubble point (if subcooling exists, and to is below bubble point, use bubble point temperature for pressure calculation only). 

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... 

The overhead condenser on a distillation column is to subcool the condensed vapors from the condensation temperature of 46.4°F down to 35°F. The specific heat of the liquid is 0.3 Btu/lb (°F), and the latent heat of vaporization at 46.4°F is 265 Btu/lb. The vapor rate to the condenser is 740.3 Ib/hr. What is the total heat load on the condenser ... 

Care should be used in determining the temperatures that prevail at tube inlet and oudet, as well as the shell side in and out for the subcooling portion. This becomes particularly tedious for multipass units. 

The usual range of film coefficient values is 40-50 for organic solvents and light petroleum fractions such as hexanes 25 for heavier materials such as aniline, straw oil, etc. and 0.5-3 for low temperature (10-40°F) subcooling of heavier organics and inorganics such as chlorine. 

The total unit size is the sum of the area requirements for condensation plus subcooling of the liquid to the desired oudet temperature. For the subcooling portion ... 

The mean temperature of condensate film before subcooling ... 

Note that the temperature at this hg is lower than when no subcooling exists. 

Note that the method described assumes that the high-pressure condensate has not been sub-cooled. If any subcooling has taken place, then the figure taken for the enthalpy of water at the higher pressure is reduced by the amount of sub-cooling. The chart or table can still be used if the upstream pressure is taken as that corresponding to saturated steam at the same temperature as the sub-cooled condensate. 

The boiling point is limited by the critical temperature at the upper end, beyond which it cannot exist as a liquid, and by the triple point at the lower end, which is at the freezing temperature. Between these two limits, if the liquid is at a pressure higher than its boiling pressure, it will remain a liquid and will be subcooled below the saturation condition, while if the temperature is higher than saturation, it will be a gas and superheated. If both liquid and vapour are at rest in the same enclosure, and no other volatile substance is present, the condition must lie on the saturation line. 

Fast burn-out, Fig. 4A, occurs when the temperature rise is very rapid, for example, less than one second elapsing between the initiation of burn-out and the time at which the metal temperature becomes dangerously high. Unless the channel power is quickly interrupted, a fast burn-out will usually result in physical burn-out. Lee and Obertelli (L4) report having examined a large number of instrument traces to see whether fast burn-out could be associated with any particular ranges of flow velocity, pressure, or quality at the burn-out point, but no generalization could be made. However, it does appear that in the case of water, fast burn-out is nearly always associated with subcooled or low-quality conditions at burn-out. 

Figure 8 shows that increasing the heat flux at constant mass velocity causes the peak in wall temperature to increase and to move towards lower enthalpy or steam quality values. The increase in peak temperature is thus due not only to a higher heat flux, which demands a higher temperature difference across the vapor film at the wall, but to a lower flow velocity in the tube as the peaks move into regions of reduced quality. The latter effect of lower flow velocity is probably the dominant factor in giving fast burn-out its characteristically rapid and often destructive temperature rise, for, as stated earlier, fast burn-out is usually observed at conditions of subcooled or low quality boiling. 

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