Mechanical losses

The actual steam rate is obtained by dividing the theoretical steam rate by the turbine efficiency, which includes thermodynamic and mechanical losses. Alternatively, internal efficiency can be used, and mechanical losses applied in a second step. 

Usually two or three extractions of the ammonium chloride residues after the addition of the last portion of the crude mixture are necessary in order to obtain all of the mandelic acid. On concentrating the benzene used for the extraction, about 5 g. of impure mandelic acid may be obtained. To diminish mechanical losses it is recommended that the same container be used to collect and crystallize the several filtrates. 

Compare the temperature rises which are proportional to the losses at the two outputs and the losses are proportional to the square of the load. Ignoring the mechanical losses then... 

Further purification of azulene may be achieved by sublimation at reduced pressure, mp 99 C. The checkers found that mechanical losses, particularly as mentioned in Note 9, lead to reduction in yield with reduction in scale (0.1 mol, 39% yield 0.5 mol, 43% yield 0.8 mol, 79% yield). 

Mechanical losses - Bearings, lip seals, mechanical seals, packings, etc., all consume energy and reduce the pump s efficiency. Small pumps (less than 15 HP) are particularly susceptible. 

Calculate the power using Equation 2.77 and setting 1)3 = mechanical losses = 0. 

Power requirements and discharge temperatures are calculated using the same relationships as used with the other rotary compressors already discussed. The efficiency is. 80 for air service and pressure in the 30 psig range. The mechanical losses are higher than the other rotaries. The mechanical loss is variable and dependent on gas, lubrication, and other factors. For an estimate, use. 15 of the gas horsepower. This approxuna tion should be close enough for an estimate. 

At this point, after a first pass through the calculation, a new polytropic exponent should be calculated. All values calculated to this point should be rechecked to see if original estimates were reasonable. If the deviation appears significant, a second pass should be made to improve the accuracy. Equation 2.78 can be used to calculate the power for the uncooled section. For an estimate, use a value of 1% for the mechanical losses. 

Step 13. Calculate the power required using Equation 2.78, allowing % for the mechanical losses. Use the conversion 33,000 ft-lb/min/hp. 

Calculate the shaft horsepower, using Equation 4.7 from Chapter 4. Read the mechanical losses from Figure 6-9. 

Mechanical losses shall not exceed 10% of the total shaft power input at test conditions. 

Good wetting is of course not a sufficient criterion for good contact adhesion because it takes no account of the factors that influence the mechanical loss factor, C, in Eq. 8, nor does it account for residual stress development during cure. But aside from these factors, one might inquire into the validity of the correlation between practical contact adhesion and VEa beyond 0° contact angle , i.e. can any distinction be made based on VEa between different adhesives, all of which perfectly wet the adherend ... 

The driver horsepower must be greater than the calculated (or value read from curves) input BHP to the shaft of the pump. The mechanical losses in the coupling, V-belt, gear-box, or other drive plus the losses in the driver must be accounted for in order that the driver rated power output will be sufficient to handle the pump. 

Note that this is horsepower available to the cylinders. It includes a 95% mechanical efficiency incorporated into the bhp/MMCFD curves. The rating of a gas engine must be such that its delivered horsepower is at least 420 hp, or if an electric motor drive is used, the mechanical losses of the intermediate frame (about 5%) must be added to arrive at the required motor shaft horsepower. 

This is approximately correct because the mechanical losses in the compressor are only about 1-3%. The head determined from Figure 12-67 can be used for the polytropic gas horsepower relation given previously. 

Figure 12-70B. Typical mechanical losses for seals on shafts of centrifugal compressors. (Used by permission Bui. P-26. Elliotl Co.)...

The overall compression and mechanical loss efficiency of these units averages between 70-75%. Peak values will reach 78%, and on the extremes of the performance curves, the values reach 60-65%. The efficiency increases with the larger units and at higher speed operations. 

The drive losses are generally based on the use of the V-helt drives, because the use of these types of drives is quite popular see losses from Figure 12-139. The mechanical losses in the drive train, must be considered separately, because they cannot be predicted by Fan Laws. 

Pj = fan input power, sum of power to impeller and mechanical losses also = Pjj,... 

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