3. A concentric tube heat exchanger with UA = 10 4 W/Kis used to heat m c...
Question:
3. A concentric tube heat exchanger with UA = 104 W/Kis used to heat mc?=5kg/s of water at Tci =20°C from mh?=5kg/s of pressurized water atThi = 300°C.
(a) If it has a parallel - flow arrangement, find the heattransfer rate.
(b) If it has a counterflow arrangement, find the heat transferrate.
(c) If it has a cross-flow arrangement (both fluid unmixed),find the heat transfer rate.
properties
1. air - ?=1.2kg/m3, k = 0.026 W/mK, ? = 1.85 x10-5 kg/ms, C = 1000J/kgK, ? = 2x 10-3(1/K)
2. water: ? = 1000kg/m3, k= 0.6 W/mK, ? = 1x10-3 kg/ms, cp= 4200J/kgK
3. Steel: ? = 7800 kg/m3, k = 50 W/mK, S =700J/kgK
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4. Water at a flow rate of m?=0.2kg/s is heated from 10°C to30°C by passing it through a thin-walled tube of diameter D=20mmand maintaining an air at 200°C in cross flow over the tube.
(a) What is the required tube length if the air velocity isV=20m/s ?
(b) What is the required tube length if the air velocity isV=0.1m/s ?
properties
1. air - ?=1.2kg/m3, k = 0.026 W/mK, ? = 1.85 x10-5 kg/ms, cp= 1000J/kgK
2. water: ? = 1000kg/m3, k= 0.6 W/mK, ? = 1x10-3 kg/ms, cp= 4200J/kgK , , ? = 2.28x10--4 (1/K)
3. Steel: ? = 7800 kg/m3, k = 50 W/mK, cp= 700J/kgK
Fundamentals of Heat and Mass Transfer
ISBN: 978-0471457282
6th Edition
Authors: Incropera, Dewitt, Bergman, Lavine