Thermodynamics HW Solutions 603

Thermodynamics HW Solutions 603 - Chapter 7 External Forced...

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Chapter 7 External Forced Convection 7-69 Water is heated by a bundle of resistance heater rods. The number of tube rows is to be determined. Assumptions 1 Steady operating conditions exist. 2 The surface temperature of the rods is constant. Properties The properties of water at the mean temperature of (15 ° C +65 ° C)/2=40 ° C are (Table A-9): k = 0.631 W/m-K ρ = 992.1 kg/m 3 C p =4.179 kJ/kg-K Pr = 4.32 μ = 0.653 × 10 -3 kg/m-s Pr s = Pr @ Ts = 1.96 Also, the density of water at the inlet temperature of 15 ° C (for use in the mass flow rate calculation at the inlet) is ρ i =999.1 kg/m 3 . Analysis It is given that D = 0.01 m, S L = 0.04 m and S T = 0.03 m, and V = 0.8 m/s. Then the maximum velocity and the Reynolds number S L S T V=0.8 m/s T i =15 ° C T s =90 ° C D based on the maximum velocity become m/s 20 . 1 m/s) 8 . 0 ( 01 . 0 03 . 0 03 . 0 max = = = V V D S S T T 232 , 18 s kg/m 10 653 . 0 m)
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