answer quickly Question 6: Air is to be cooled in the evaporator section of arefrigerator by passing it over a bank of 0.8-cm-outer-diameterand 0.8-m-long tubes inside which the refrigerant isevaporating at -20°C. Air approaches the tube bank in thenormal direction at 0°C and 1 atm with a mean velocity of 5m/s. The tubes are arranged in-line with longitudinal andtransverse pitches ofSL = ST = 1.5 cm. There are 25 rows in the flow direction with15 tubes in each row. Determine the refrigeration capacity ofthis system. Evaluate the air properties at an assumed meantemperature of -5°C and 1 atm. Is this a good assumption?0.8 mAirO°CI atm5 m/sS = 1.5 cm0.8 cmS = 1.5 cmRefrigerant, -20°CHint: The refrigeration capacity isT;=-20°CQ = hA,ATm = (179.5 W/m? .°C)(7.540 m²(11.85°C) = 16,040 WSLV=5Answers: 16,040W; The arithmetic mean fluid temperature is (T;+m/sTe)/2 = (0-13.7)/2 = -6.9°C, which is fairly close to the assumed valueSTof -5°C. Therefore, there is no need to repeat calculations.Properties The exit temperature of air, and thus the meantemperature, is not known. We evaluate the air properties at theassumed mean temperature of -5°C (will be checked later) and 1 atm(Table A-15):k = 0.02326 W/m-Kp = 1.317 kg/m3C, =1.006 kJ/kg-Kµ = 1.705x105 kg/m-sPr = 0.7375Pr; = Pre Ts- -20°c = 0.7408Also, the density of air at the inlet temperature of 0°C (for use in the mass flow rate calculation at theinlet) is p, = 1.292 kg/m.

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Answered: Question 6: Air is to be cooled in the…

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter7: Forced Convection Inside Tubes And Ducts

Section: Chapter Questions

Problem 7.4P

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