Compression ratio calculating

First, calculate the overall compression ratio (R = Pa/Pj). If the compressor ratio is under 5, consider using one stage. If it is not, select an initial number of stages so that R < 5. For initial calculations it can be assumed that ratio per stage is equal for each stage. 

Note that the first approximation for R was obtained from Equation 12-41. This figure is not the exact compression ratio as it is difficult to calculate an exact ratio over such a wide range. The final R values calculated are close enough for process design calculation. 

Calculate the compression ratio, Pd/Ps = P2/P1 = Pc-From Table 12-9B for the compressor frame selected, select polytropic efficiency, Cp, and using Figure 12-65A, determine adiabatic efficiency, e d. 

Some situations bring into question the necessity of a surge drum in the system. This hecomes more evident in the low flow rate, high compression ratio units in which the drum is calculated to he only slighdy larger than the usual pipe size. In some of these cases, it has heen found satisfactory to enlarge the pipe size and eliminate the drum. Each system must he carefully evaluated as generalities cannot solve the variety of situations. 

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 ... 

Whilst compression ratios for staged compression of 7 or greater can be used, the maximum per stage is normally taken to be around 4. If the maximum temperature is known, then the maximum pressure ratio can be calculated. 

The smallest average compression ratio of all the branches in the transmission system is calculated by adding all the compression ratios in each branch and dividing by the number of compressors in the branch. The number of compressors in the branch that has smallest ratio becomes the partition variable. 

Conventional transition sections are constructed by simply decreasing the depth of the channel in the down-channel direction. The amount and rate of the depth change sets the performance of the melting process and the removal of entrained air that resides between the feedstock pellets or powders. The compression ratio sets the amount of compression while the compression rate sets the rate of the compression. The compression ratio and compression rate are calculated as follows for conventional-flighted transition sections ... 

The iead iength was 124 mm for the main flight of the barrier section and 88.9 mm for all other sections of the screw. The main flight width and clearance were 9 and 0.09 mm, respectively, in all sections of the screw. The first 2.5 diameters of the screw were inside a water-cooled feed casing. The compression ratio was 2.7 and the compression rate was 0.0050. The specific rotational rate was calculated at 2.51 kg/(h-rpm). ... 

The injection-molding press was producing a part and runner system that had a mass of 2.15 kg. The mass was plasticated using a 120 mm diameter, 8L/D screw. The screw used for the process had a barrier melting section that extended to the end of the screw, as shown by the specifications in Table 11.9. That is, the screw did not have a metering channel. Instead, the last sections of the barrier section were required to produce the pressure that was needed to flow the resin through the nonreturn valve and into the front of the screw. The specific rotational flow rate for the screw for the IRPS resin was calculated at 9.3 kg/(h-rpm) based on the depth of the channel at the end of the transition section. The screw was built with an extremely low compression ratio and compression rate of 1.5 and 0.0013, respectively. For IRPS resins and other PS resins, screws with low compression ratios and compression rates tend to operate partially filled. The compression ratio and compression rate for the screw are preferred to be around 3.0 and 0.0035, respectively. The flight radii on the screw were extremely small at about 0.2 times the channel depth. For IRPS resin, the ratio of the radii to the channel depth should be about 1. 

Flight width and flight clearance were 13.5 and 0.12 mm, respectively, in all sections of the screw. The extruder had a smooth-bore feed section. Three rings of pin mixers were evenly positioned in the middle portion of the metering section of the screw. All pins in a single ring had the same axial position as the type shown by Fig. 8.25. The specific rotational flow rate for the metering section was calculated at 5.0 kg/(h rpm). The compression ratio was 2.7. 

The compression ratio in an Otto cycle is 8. If the air before compression (state 1) is at 60°F and 14.7 psia, and 800Btu/lbm is added to the cycle and the mass of air contained in the cylinder is 0.025 Ibm, calculate (1) temperature and pressure at each point of the cycle, (2) the heat that must be removed, (3) the thermal efficiency, and (4) the MEP of the cycle. To solve this problem by CyclePad, we take the following steps ... 

A Diesel cycle has a compression ratio of 18. Air-intake conditions (prior to compression) are 72°F and 14.7 psia, and the highest temperature in the cycle is limited to 2500° F to avoid damaging the engine block. Calculate (a) thermal efficiency, (b) net work, and (c) mean effective pressure (d) compare engine efficiency with that of a Carnot cycle engine operating between the same temperatures. 

Permissible cut-in pressure will depend on the reduction ratios of the roots pump as against the roughing pump and is calculated by dividing the permissible pressure differential Ap, g by the compression ratio, reduced by the value of 1 ... 

Compaction properties of each material were determined with a standardized test performed on a custom-built hydraulic compaction simulator using 8 mm (0.3150 in.) round flat-faced punches. A linear saw-tooth upper punch position profile was selected with a punch velocity of 300 mm/sec for both punch extension and retraction. The lower punch position was at a fixed position within the die during the compaction event. The powder weight loaded into the die for each compression was calculated from the equation below so as to form a cylindrical tablet having a thickness-to-diameter ratio of 0.30 at a theoretical SF of 1.0. These dimensions are typical of commercially elegant tablets. 

We will need to use this table to calculate a jet s compression ratio, when we measure vacuum pressures with an American-type (in Hg) gauge. 

When considering the performance of a vacuum jet, we must first consider the jet s overall compression ratio. To calculate a jet s compression ratio ... 

Figure 16.2 shows a three-stage steam jet system. Let s first calculate the overall compression ratio for the combined effect of all three jets. 

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