Temperature compression discharge

The dischai e temperature of a compressor can be calculated by Eq, (4) or Eq. (9), it is a fimetion of inl gas temperature, compression ratio, isentioplc exponent, and compressor efficiency. Compressor discharge temperature is sensitive to the value of isentroptc or polytropic exponent. This is true for all types of compressors. 

Equation (6-128) does not require fric tionless (isentropic) flow. The sonic mass flux through the throat is given by Eq. (6-122). With A set equal to the nozzle exit area, the exit Mach number, pressure, and temperature may be calculated. Only if the exit pressure equals the ambient discharge pressure is the ultimate expansion velocity reached in the nozzle. Expansion will be incomplete if the exit pressure exceeds the ambient discharge pressure shocks will occur outside the nozzle. If the calculated exit pressure is less than the ambient discharge pressure, the nozzle is overexpanded and compression shocks within the expanding portion will result. 

Ejector Performance The performance of any ejec tor is a function of the area of the motive-gas nozzle and venturi throat, pressure of the motive gas, suction and discharge pressures, and ratios of specific heats, molecular weights, and temperatures. Figure 10-102, based on the assumption of constant-area mixing, is useful in evaluating single-stage-ejector performance for compression ratios up to 10 and area ratios up to 100 (see Fig. 10-103 for notation). 

Z= Average compressibility factor using 1.0 will yield conservative results R = 1,544/mol. wt T = Suction temperature, °R P, Pi = Suction, discharge pressures, psia K = Adiabatic exponent. Cp/C,. 

Step 2. At this point the discharge temperature must be calculated to arrive at a value for the discharge compressibility. 

Non-lubricated screw compressors have very close clearances and thus they are designed for limited ranges of discharge temperature, temperature rise, compression ratio, etc., all of which can cause changes in thesc clearances. Lubricated compressors have a somewhat broader tolerance to changes in operating conditions, but they are still more limited than reciprocating compressors. 

The discharge temperature for any single stage of compression can be calcuhiled from ... 

The discharge temperature can be lowered by cooling the suction gas and reducing the value of P[Pg.274]

Compute discharge temperature, volumetric efficiency, required clearance, rod load, and required horsepower for the given conditions. Also calculate the lowest suction pressure at which this unit can compress lOOMMscfd. 

Condition 1 Figure 12-12. Start of the compression stroke. The cylinder is full of gas at suction pressure and essentially suction temperature (neglecting valve loss). The piston moves during compression toward condition (2) with suction and discharge valves closed. 

The relation between the suction and discharge temperatures of a gas during any single compression step is... 

Tj = discharge temperature from cylinder, Rankine R = ratio of cylinder compression... 

The polytropic process is mathematically easier to handle than the adiabatic approach for the following (1) determination of the discharge temperature (see later discussion under Temperature Rise During Compression ) and (2) advantage of the polytropic efficiency ... 

Adiabatic Head. The height in ft of gas supported at the compressor discharge as the gas discharges into a system at the desired pressure level is the adiabatic head. The compression of the gas column is adiabatic. The temperature and pressure of the compression column will be related by the adiabatic expression. 

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