A hot fluid passes through a thin-walled tube of 10-mm diameter and 1-m length and a coolant at T∞ = 25°C is in cross flow over the tube. When the flow rate is m = 18 kg/h and the inlet temperature is Tm,j = 85°C, the outlet temperature is Tm,o = 78°C. Assuming fully developed flow and thermal conditions in the tube, determine the outlet temperature, Tm,o, if the flow rate is increased by a factor of 2. That is, m = 36 kg/h, with all other conditions the same. The thermo physical properties of the hot fluid are p = 1079 kg/m3, cp = 2637 J/kg ∙ K, μ = 0.0034 N ∙ s/m2, and k = 0.261 W/m ∙ K.

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Tube, D= 10 mm, L=1m Coolant T= 25°C Tme=78°C Hot fluid T= 85°C n = 18 kg/h