Exhaust gases at 1 atm and 300°C are used to preheat water in an industrial facility by passing them over a bank of tubes through which water is flowing at a rate of 6 kg/s. The mean tube wall temperature is 80°C. Exhaust gases approach the tube bank in normal direction at 4.5 m/s. The outer diameter of the tubes is 0.035 m, and the tubes are arranged in-line with longitudinal and transverse pitches of SL = ST = 0.09 m. There are 16 rows in the flow direction with eight tubes in each row. Assume the air properties at 250°C and 1 atm. The air properties at the assumed mean temperature of 250°C and 1 atm are
Exhaust gases at 1 atm and 300°C are used to preheat water in an industrial facility by passing them over a bank of tubes through which water is flowing at a rate of 6 kg/s. The mean tube wall temperature is 80°C. Exhaust gases approach the tube bank in normal direction at 4.5 m/s. The outer diameter of the tubes is 0.035 m, and the tubes are arranged in-line with longitudinal and transverse pitches of SL = ST = 0.09 m. There are 16 rows in the flow direction with eight tubes in each row. Assume the air properties at 250°C and 1 atm. The air properties at the assumed mean temperature of 250°C and 1 atm are
k = 0.04104 W/m·K ρ = 0.6746 kg/m3
cp =1.033 kJ/kg·K Pr = 0.6946
μ = 2.76 × 10−5 kg/m·s Prs = Pr@Ts = 80°C = 0.7154
The density of air at the inlet temperature of 300°C (for use in the mass flow rate calculation at the inlet) is ρi = 0.6158 kg/m3. The specific heat of water at 80°C is 4.197 kJ/kg·°C.
Determine the rate of heat transfer per unit length of tubes.
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