Chapter 8, Problem 8.60P

A hot fluid passes through a thin-walled tube of 10-mm diameter and 1-m length, and a coolant at $T_{\infty }=25°C$ is in cross flow over the tube. When the flow rate is $\stackrel{\dot{}}{m}=18kg/h$ and the inlet temperature is $T_{m,i}=85°C$ , the outlet temperature is $T_{m,o}=78°C$ .

Assuming fully developed flow and thermal conditions in the tube, determine the outlet temperature, $T_{m,o}$ . If the flow rate is increased by a factor of 2. That is, $\stackrel{\dot{}}{m}=36kg/h$ , with all other conditions the same. The thermophysical properties of the hot fluid are $\rho =1079kg/m^3,c_p=2637J/kg\cdot K,\mu =0.0034N\cdot s/m^2,\text{and}k=0.261W/m\cdot K$ .