Problem 1. Boundary layer external flow convection A store building has five show rooms on one side each with a large glass window of 5 m long and 3.5 m high. The glass is 10 mm thick and has an effective thermal conductivity of 1.4 W/m-K. Consider conditions for which the ambient air is in parallel flow over the outer surface of the glass window with u: = 5 m/s and Tair = -20C. The outside wall temperature Tw may be assumed to be the same as the air temperature since the wall is well insulated. The room air temperature is maintained at Troom = 25C, and the inside convection coefficient is h; = 5 W/m.K. The thermophysical properties of air may be assumed to be constant within the temperature range of interest (Air: v= 12.6 x 10 m/s, k=0.023 W/m-K, Pr=0.71). 4. - 5 m/s Tair: -20C TW 10 m T. - ? 25 m's 10 m ir 5 m **1 B ol D E Troom= 25c, hq- 5 W/m_ok a) Determine if you may assume turbulent boundary layer conditions for the ambient airflow over the entire wall and windows. b) Which room has the smallest heat loss from the glass window if the wind blows to the right? c) If the wind sometimes blow to the right and sometimes blows to the left (with about equal frequency), determine which room has the smallest heat loss from the glass window by estimating the convection coefficient for each room. d) Estimate the rate at which heat is lost from Room C through the glass window. (Ans. q = 2611.3 W) e) Determine the outer surface temperature at the midpoint of the glass window. (Ans. T. =-5.9C) Problem 1. Boundary layer external flow convection A store building has five show rooms on one side each with a large glass window of 5 m long and 3.5 m high. The glass is 10 mm thick and has an effective thermal conductivity of 1.4 W/m-K. Consider conditions for which the ambient air is in parallel flow over the outer surface of the glass window with u: = 5 m/s and Tair = -20C. The outside wall temperature Tw may be assumed to be the same as the air temperature since the wall is well insulated. The room air temperature is maintained at Troom = 25C, and the inside convection coefficient is h; = 5 W/m.K. The thermophysical properties of air may be assumed to be constant within the temperature range of interest (Air: v= 12.6 x 10 m/s, k=0.023 W/m-K, Pr=0.71). 4. - 5 m/s Tair: -20C TW 10 m T. - ? 25 m's 10 m ir 5 m **1 B ol D E Troom= 25c, hq- 5 W/m_ok a) Determine if you may assume turbulent boundary layer conditions for the ambient airflow over the entire wall and windows. b) Which room has the smallest heat loss from the glass window if the wind blows to the right? c) If the wind sometimes blow to the right and sometimes blows to the left (with about equal frequency), determine which room has the smallest heat loss from the glass window by estimating the convection coefficient for each room. d) Estimate the rate at which heat is lost from Room C through the glass window. (Ans. q = 2611.3 W) e) Determine the outer surface temperature at the midpoint of the glass window. (Ans. T. =-5.9C)