Reconsider Prob. 8–80. The mass flow rate of the hot water can be varied between 0.05 and 0.5 kg/s. Using the EES (or other) software, evaluate the effect of the hot water mass flow rate on the pipe’s outer surface temperature. Plot the pipe’s outer surface temperature as a function of the hot water mass flow rate for the water exit temperature of

(a) 60°C

(b) 70°C. To prevent thermal burn on individuals working in the vicinity of the pipe, determine the condition of the hot water mass flow rate such that the pipe’s outer surface temperature is below 45°C.

Data from problem 80

In a food processing plant, hot liquid water is being transported in a pipe (k = 15 W/m ∙ K, D_i = 2.5 cm, D_o = 3 cm, and L = 10 m). The hot water flowing with a mass flow rate of 0.15 kg/s enters the pipe at 100°C and exits at 60°C. The plant supervisor thinks that since the hot water exits the pipe at 60°C, the pipe’s outer surface temperature should be safe from thermal burn hazards. In order to prevent thermal burn upon accidental contact with skin tissue for individuals working in the vicinity of the pipe, the pipe’s outer surface temperature should be kept below 45°C. Determine whether or not there is a risk of thermal burn on the pipe’s outer surface. Assume the pipe outer surface temperature remains constant.