a. Use the guideline from Tables 11. 11 and \(\underline{11.18}\) to establish "normal" limits on the amount of heat that could be exchanged.

b. How do these limits explain the fouling of the heat exchanger observed in the operating unit?

c. Under the constraints identified in Part (a), what is the highest temperature allowed (flowrates limited to range of \(M\) values shown)?

Table 11.11

Table 11.18

Transcribed Image Text:

1. Fans are used to raise the pressure about 3% (12 in (30 cm) water), blowers to raise less than 2.75 barg (40 psig), and compressors to higher pressures, although the blower range is commonly included in the compressor range. 2. Theoretical reversible adiabatic power = mz, RT,[([P/P-1)]/a where T, is inlet temperature, R= gas constant, z = compressibility, mmolar flow rate, a = (k-1)/k and k=C/C Values of R: 8.314 J/mol K = 1.987 Btu/lbmol R = 0.7302 atm ft/lbmol R 3. Outlet temperature for reversible adiabatic process T = T, (P-/P)*. 4. Exit temperatures should not exceed 167-204C (350-400F); for diatomic gases (C/C 1.4). This corresponds to a compression ratio of about 4. = 5. Compression ratio should be about the same in each stage of a multistage unit, ratio = (P/P), with stages. 6. Efficiencies of reciprocating compressors: 65% at compression ratios of 1.5, 75% at 2.0, and 80-85% at 3-6. 7. Efficiencies of large centrifugal compressors, 2.83-47.2 m/s (6000-100,000 acfm) at suction, are 76-78%. 8. For vacuum pumps use the following: Reciprocating piston type Rotary piston type Two-lobe rotary type Steam jet ejectors Down to 1 Torr Down to 0.001 Torr Down to 0.0001 Torr 1-stage down to 100 Torr 3-stage down to 1 Torr 5-stage down to 0.05 Torr 9. A three-stage ejector needs 100 kg steam/kg air to maintain a pressure of 1 Torr. 10. In-leakage of air to evacuated equipment depends on the absolute pressure, Torr, and the volume of the equipment, V in m (ft) according to W=kV2 kg/h (lb/hr) with k = 0.98 (0.2) when P > 90 Torr, k=0.39 (0.08) between 3 and 20 Torr, and k=0.12 (0.025) at less than 1 Torr..