Volume compression ratio

Four-stroke cycle. TDC and BDC = top dead center and bottom dead center positions of the piston, respectively. Vj = displacement. V, = clearance volume. Compression ratio = (Vj -I-... 

Fig. 2.14. Pressure developed in a liquid surrounding a collapse Rayleigh cavity Z = volume compression ratio.

VCR volume compression ratio VRP Vehicle Recycling Partnership... 

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. 

Low specific volume of vapor Low compression ratio Low viscosity... 

Various types of rapid, adiabatic compressions have caused explosions. With propane at an initial temperature of 25°C, To = 432°K (I59°C) for compression and specific heat ratios of 25 and I.I3, respectively. Assume that now air enters a compressor to bring propane into the flammable range at 5 percent by volume. The mixture then will be mostly air with k = 1.47. The same compression ratio of 25 will elevate the final temperature T2 to 834°K (56I°C), i.e., above the published autoignition temperature of 450°C for propane and perhaps high enough to cause an explosion. 

It follows that the efficiency of the Carnot engine is entirely determined by the temperatures of the two isothermal processes. The Otto cycle, being a real process, does not have ideal isothermal or adiabatic expansion and contraction of the gas phase due to the finite thermal losses of the combustion chamber and resistance to the movement of the piston, and because the product gases are not at tlrermodynamic equilibrium. Furthermore the heat of combustion is mainly evolved during a short time, after the gas has been compressed by the piston. This gives rise to an additional increase in temperature which is not accompanied by a large change in volume due to the constraint applied by tire piston. The efficiency, QE, expressed as a function of the compression ratio (r) can only be assumed therefore to be an approximation to the ideal gas Carnot cycle. 

Molding and injection Compression ratio Compression molding pressure (lbf/in. ) Compression molding temperature (°C) Injection molding pressure (Ibf/in. ) Injection molding temperature (°C) Molding qualities Mold (linear) shrinkage (in./in.) Specific volume (Ib )... 

The compressor manufacturer can control items a-c, e, f, and h however, the control of clearance volume at high compression ratios for gases/vapors with low specific heat ratios is of great concern. Compression efficiency is controlled by the clearance volume, valves, and valve pocket design. A decrease in compression efficiency leads to increased power requirements. ... 

The nominal compression ratio (which is usually specified) is the displacement volume plus the clearance volume divided by the clearance volume. Because of the mechanics of intake value closing, the actual compression ratio r is less than the nominal. Thus, the compression pressure p (psia) may be estimated by... 

The most important characteristic of this type of compressors is that all have a fixed built-in pressure compression ratio for each stage of compression (as well as a fixed built-in volume displacement) [25]. Thus, at a given rate of rotational speed provided by the prime mover, there will be a predetermined volumetric flowrate through the compressor, and the pressure exiting the machine at the outlet will be equal to the design pressure ratio times the inlet pressure. 

This type of compressor is classified as a constant volume, variable-pressure machine that is quite similar to the vane-type rotary in general characteristics. Both have a built-in compression ratio. 

Screw compressors have no clearance volume, and may work at high compression ratios without loss of volumetric efficiency . In all screw compressors, the gas volume will have been reduced to a pre-set proportion of the inlet volume by the time the outlet port is uncovered, and this is termed the built-in pressure ratio. At this point, the gas within the screws is opened to condenser pressure and gas will flow inwards or outwards through the discharge port if the pressures are not equal. 

The Debye temperature, can be calculated from the elastic properties of the solid. Required are the molecular weight, molar volume, compressibility, and Poisson s ratio.11 More commonly, do is obtained from a fit of experimental heat capacity results to the Debye equation as shown above. Representative values for 9o are as follows ... 

A chart which correlates experimental P - V - T data for all gases is included as Figure 2.1 and this is known as the generalised compressibility-factor chart.(1) Use is made of reduced coordinates where the reduced temperature Tr, the reduced pressure Pr, and the reduced volume Vr are defined as the ratio of the actual temperature, pressure, and volume of the gas to the corresponding values of these properties at the critical state. It is found that, at a given value of Tr and Pr, nearly all gases have the same molar volume, compressibility factor, and other thermodynamic properties. This empirical relationship applies to within about 2 per cent for most gases the most important exception to the rule is ammonia. 

Thus, theoretically, the clearance volume does not affect the work done per unit mass of gas, since Vi — V4 is the volume admitted per cycle. It does, however, influence the quantity of gas admitted and therefore the work done per cycle. In practice, however, compression and expansion are not reversible, and losses arise from the compression and expansion of the clearance gases. This effect is particularly serious at high compression ratios. 

Air at 290 K is compressed from 101.3 kN/m2 to 2065 kN/m2 in a two-stage compressor operating with a mechanical efficiency of 85 per cent. The relation between pressure and volume during the compression stroke and expansion of the clearance gas is PV1-25 = constant. The compression ratio in each of the two cylinders is the same, and the interstage cooler may be assumed 100 per cent efficient. If the clearances in the two cylinders are 4 per cent and 5 per cent respectively, calculate ... 

The compression ratio is the ratio of the cylinder volume at the beginning of the compression process (BDC) to the cylinder volume at the end of the compression process (TDC). 

Determine the heat supplied, work output, MEP, and thermal efficiency of an ideal Otto cycle with a compression ratio of 10. The highest temperature of the cycle is 3000°F. The volume of the cylinder before compression is 0.1 ft. What is the mass of air in the cylinder The atmosphere conditions are 14.7 psia and 70°F. 

An engine operates on an Otto cycle with a compression ratio of 8. At the beginning of the isentropic compression process, the volume, pressure, and temperature of the air are 0.01 m, llOkPa, and 50°C. At the end of the combustion process, the temperature is 900°C. Find (a) the temperature at the remaining two states of the Otto cycle, (b) the pressure of the gas at the end of the combustion process, (c) the heat added per unit mass to the engine in the combustion chamber, (d) the heat removed per unit mass from the engine to the environment, (e) the compression work per unit mass added, (f) the expansion work per unit mass done, (g) MEP, and (h) thermal cycle efficiency. 

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