Question

(a) (iWhen is heat transfer through a fluid by conduction or by convection? For what case is the rate of heat transfer higher? How does the convection heat transfer coefficient differ from the thermal conductivity of a fluid? (ii) Explain the physical significance of Nusselt number (ii) By definition, discuss hydraulic diameter. Obtain an expression for hydraulic diameter of a circular tube of diameter, D (b) The local atmospheric pressure in Gboko, Benue State Nigeria (elevation 1610 m), is 834 kPa. Air at this pressure and 20°C flows with a velocity of 8 m/s over a 1.5 m by 6 m flat plate whose temperature is 140°C. Determine the rate of heat transfer from the plate if the air flows parallel to the (a) 6-m-long side and (b) the 1.5-m side The following correlations are valid: Nu=0.664 Re," Pri/J for RCL<5x10s and Nu-(0.037 Reas-871)Pr for 0.65 Pr 60 and 5 x 105 ReLS 10. The properties of air at 80°C and 1 atm pressure are: k = 0.02 953 W/m·°C. Pr = 0.7154, v@ 1 atm = 2.097 x 10'5 ㎡ls.

Answer 1

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