Suction ratio

This effect of mis-matched air velocities was shown by May for a nozzle of 1-2 cm diameter sampling at 5 m/s (see Figure 13.2). This diagram suggests there is a maximum loss of sampling efficiency at a wind suction ratio of 0.4. Below 0.4 the efficiency increases as the still air situation is... 

The measuring of temperature rise permits monitoring efficiency for a fixed pressure ratio and suction temperature. Efficiencies should always exceed 0.6, and 1.00 is approachable in reciprocating devices. Their better efficiency needs to be balanced against their greater cost, greater maintenance, and lower capacity. 

In some cases, blade-type rotary compressors are used in low temperature appHcations as high volume, low stage, or booster compressor (Fig. 9). These booster compressors are appHed at suction conditions varying from —87 to —20°C with compression ratios of 7 1 using CFC-12, HCFC-22, or ammonia. 

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). 

The performance of a centrifugal compressor (discharge to suction-pressure ratio vs. the flow rate) for different speeds is shown in Fig. 11-87. Lines of constant efficiencies show the maximum efficiency. Unstable operation sequence, called surging, occurs when compressors fails to operate in the range left of the surge envelope. It is characterized by noise and wide fluctuations of load on the compressor and the motor. The period of the cycle is usually 2 to 5 s, depending upon the size of the installation. 

Eor good control, design the pressure drop for the control valve between the fractionating system and the jet system for sonic velocity (approximately 2 1 pressure ratio). This means that the jets suction must be designed for half the absolute pressure of the evacuated system. 

It has played a dual role, one in Equation 2.18 on specific heat ratio and the other as an isentropic exponent in Equation 2.53. In the previous calculation of the speed of sound. Equation 2.32, the k assumes the singular specific heat ratio value, such as at compressor suction conditions. When a non-perfect gas is being compressed from point 1 to point 2, as in the head Equation 2.66, k at 2 will not necessarily be the same as k at 1. Fortunately, in many practical conditions, the k doesn t change very... 

The terms pressure ratio and volume ratio are used interchangeably in the literature on these machines. To prevent confusion, volume ratio t , is defined as the volume of the trapped gas at the start of the compression cycle divided by the volume of the gas just prior to the opening of the discharge port. Pressure ratio is defined, in Equation 2.64, as the discharge pressure divided by the suction pressure. Their relationship is given in the following equation. 

Ratio of hood suction to plume flow rate at the hood... 

An equation can be developed which expresses the ratio of spilled contaminant to total contaminant in terms of the ratio of hood suction to plume flow rate. This equation is as follows ... 

Pressure factor The test ratio between the suction effect and air velocity passing over a cowl or roof outlet, represented by... 

At a constant speed, a constant volume of gas (at suction conditions of pressure and temperature) will be drawn into the cylinder. As the flow rate to the compressor decreases, the suction pressure decreases until the gas available expands to satisfy the actual volume required by the cylinder. When the suction pressure decreases, the ratio per stage increases and therefore the discharge temperature increases. In order to keep from having too high a discharge temperature, the recycle valve opens to help fill the compressor cylinder volume and maintain a minimum suction pressure. 

C = cylinder clearance, percent of piston displacement Z5 = compressibility factor at suction, psia Z(j = compressibility factor at discharge, psia k = ratio of specific heats, Cp/C ... 

These relations do not hold exactly if the ratio of speed change is greater than 1.5 to 2.0, nor do they hold if suction conditions become limiting, such as NPSH. 

The minimum recommended saturated suction temperature on single-stage reciprocating applications, column (J), is based on a compression ratio of about 9 to 1. The refrigerants 114, 11 (soon to be replaced by R-123), and 113 are not included due to the large cfm/ton. 

Refrigerant Evapo- rator Pressure, psia Con- denser Pressure, psia Com- pression Ratio Net Refrig- erating Effect, Btu/lb , Refrigerant Circulated, 1b /min Specific Volume of Suction Gas, ftVlb Com- pressor Displace- ment, cfm Power Consump- tion, hp... 

The compression ratio is the ratio, R, of the absolute discharge pressure to the absolute suction pressure of the cylinder. 

Loss Factor. The loss factor is a correction fector for standard horsepower curves for high suction pressures at low ratios of compression. The bhp (brake horsepower) is obtained from the curves. Figures 12-21A-C. These curves are a plot of the n or k value of the gas versus the required brake horsepower (required to compress 1 million fti of gas at 14.4 psia and suction temperatures) for various ratios of compression. 

For suction drums, AV is evaluated using the suction volumetric efficiency, E . E = cfm at suction conditions/PD at the selected rpm, or E can he obtained from curves of volumetric efficiency versus the compression ratio for varying cylinder clearances. 

This loss of useful working stroke will increase with the ratio of the suction and discharge absolute pressures, and the compressor efficiency will fall off. This effect is termed the volumetric efficiency [11]. Typical figures are shown in Figure 2.8. 

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