Vapor superheated

Air is compressed to modest pressures, typically 100 to 200 kPa ( 15-30 psig) with either a centrifugal or radial compressor, and mixed with superheated vaporized butane. Static mixers are normally employed to ensure good mixing. Butane concentrations are often limited to less than 1.7 mol 1 to stay below the lower flammable limit of butane (144). Operation of the reactor at butane concentrations below the flammable limit does not eliminate the requirement for combustion venting, and consequendy most processes use mpture disks on both the inlet and exit reactor heads. A dow diagram of the Huntsman fixed-bed maleic anhydride process is shown in Figure 1. 

If the vapor is superheated at the inlet, the vapor may first be desuperheated by sensible heat transfer from the vapor. This occurs if the surface temperature is above the saturation temperature, and a single-phase heat-transfer correlation is used. If the surface is below the saturation temperature, condensation will occur directly from the superheated vapor, and the effective coefficient is determined from the appropriate condensation correlation, using the saturation temperature in the LMTD. To determine whether or not condensation will occur directly from the superheated vapor, calculate the surface temperature by assuming single-phase heat transfer. 

When dry, or superheated, vapor is used to subcool the liquid, the COP in R12 systems will increase, and decrease the COP in NH3 sys-... 

The system shown in Fig. 11-75 is direct expansion where diy or slightly superheated vapor leaves the evaporator. Such systems are predominantly used in small applications because of their simplicity and light weight. For the systems where efficiency is crucial (large industrial systems), recirculating systems (Fig. 11-77) are more appropriate. 

Subcooled-hquid feed 9 > 1 Saturated-liquid feed 9 = 1 Partially flashed feed 1 > 9 > 0 Saturated-vapor feed 9 = 6 Superheated-vapor feed 9 < 0 The 9 value for a particular feed can be estimated from... 

FIG. 13-32 AU five cases of q lines (1) superheated-vapor feed, (2) saturated-vapor feed, (3) partially vaporized feed, (4) saturated-liquid feed, and (5) siih-cooled-liqiiid feed. Slope of q line = q/(q — 1). 

The condition of the feed as it enters the column has an effect on the number of trays, reflux requirements and heat duties for a given separation. Figure 8-15 illustrates the possible situations, i.e., sub-cooled liquid feed, feed at the boiling point of the column feed tray, part vapor and part liquid, all vapor but not superheated, and superheated vapor. The thermal condition is designated as q, and... 

This represents feed as a superheated vapor, and there is a decrease in liquid overflow from feed plate. 

Cool 7,936 Ib/hr ammonia from 292°F to 105°F and condense at this point. Pressure is 228.9 psia. Reading ammonia superheated vapor tables (or chart) ... 

All gases can be liquefied under suitable pressure and temperature conditions and therefore could be called vapors. The term gas is most generally used when conditions are such that a return to the liquid state, i.e. condensation, would be difficult within the scope of the operations being conducted. However, a gas under such conditions is actually a superheated vapor. 

Becker R, Doring W (1935) The kinetic treatment of nuclear formation in superheated vapors. Ann Phys 24 719-752... 

Farkas L (1927) The velocity of nucleus formation in superheated vapors. Z Phys Chem 125 236-240... 

What happens at the feed stage depends on the condition of the feed, whether it is subcooled, saturated liquid, partially vaporized, saturated vapor or superheated vapor. To define the condition of the feed, the variable q is introduced, defined as ... 

To solve Equation 9.50, start by assuming a feed condition such that q can be fixed. Saturated liquid feed (i.e. q = 1) is normally assumed in an initial design as it tends to decrease the minimum reflux ratio relative to a vaporized feed. Liquid feeds are also preferred because the pressure at which the column operates can easily be increased if required by pumping the liquid to a higher pressure. Increasing the pressure of a vapor feed is much more expensive as it requires a compressor rather than a pump. Feeding a subcooled liquid or a superheated vapor brings inefficiency to the separation as the feed material must first return to saturated conditions before it can participate in the distillation process. 

Mist flow, one component In a one-component system with finely dispersed drops in the mist flow, the mass transfer between phases over a large interfacial area has to be considered. For the compression wave the frozen state can be assumed to be subcooled liquid, superheated vapor conditions generated by the wave are fairly stable, and the expressions for the two-component system are valid (Henry, 1971) ... 

It is possible, however, to simplify the calculation of the energy transfer by assuming that the vapor phase is always a saturated vapor. O Connor (Ol) has shown that the rate of approach of a superheated vapor to saturated conditions is extremely rapid when the superheated vapor is in direct contact with its liquid phase. If the vapor phase is assumed to be saturated, the temperature of the phase can be calculated from an integrated form of the Clausius-Clapeyron equation instead of from the vapor-phase energy-transfer equation. 

ANNULAR MIST FLOW TRANSITION REGION MIST FLOW SUPERHEATED VAPOR... 

Water enters the pump at state 1 as a low-pressure saturated liquid to avoid the cavitation problem and exits at state 2 as a high-pressure compressed liquid. The heat supplied in the boiler raises the water from the compressed liquid at state 2 to saturated liquid to saturated vapor and to a much higher temperature superheated vapor at state 3. The superheated vapor at state 3 enters the turbine where it expands to state 4. The superheating moves the isentropic expansion process to the right on the T-s diagram as shown in Fig. 2.5, thus preventing a high moisture content of the steam as it exits the turbine at state 4 as a saturated mixture. The exhaust steam from the turbine enters the condenser at state 4 and is condensed at constant pressure to state 1 as saturated liquid. 

Draw an isobaric heating process on a T s diagram for a nonazeotropic mixture from a compressed liquid state to a superheated vapor state. Does the temperature remain the same in the boiling region ... 

An actual vapor compression refrigeration cycle operates at steady state with R-134a as the working fluid. Saturated vapor enters the compressor at 263 K. Superheated vapor enters the condenser at 311K. Saturated liquid leaves the condenser at 301 K. The mass flow rate of refrigerant is 0.1 kg/sec. Determine... 

R-134a enters the compressor of a steady-flow vapor compression refrigeration cycle as superheated vapor at 0.14 MPa and — 10°C at a rate of 0.04 kg/sec, and it leaves at 0.7 MPa and 50°C. The refrigerant is cooled in the condenser to 24°C and saturated liquid. Determine (a) the compressor power required, (b) the rate of heat absorbed from the refrigerated space, (c) the compressor efficiency, and (d) the COP. 

Why is the inlet state of the compressor of the actual vapor refrigeration cycle in the superheated vapor region ... 

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