a 1m x 2m sheet of plywood is attached to the roof of your vehicle after being purchased at the hardware store. at what speed in kilometers per hour in 20 c air will the boundary layer first start becoming turbulent

Consider two concentric spheres forming an enclosure with diameters of 12 cm and 18 cm the spheres are maintained at uniform temperatures ti-50°c and t2 = 250°c and have emissivities .45 and .8, respectively. determine the net rate of radiation heat transfer between the two spheres per unit surface area.

Aheat pump using refrigerant-134a heats a house by using underground water at 8°c as the heat source. the house is losing heat at a rate of 60,000 kj/h. the refrigerant enters the compressor at 280 kpa and 0°c, and it leaves at 1 mpa and 60°c. the refrigerant exits the condenser at 30°c. determine: (a) the power input to the heat pump, (b) the rate of heat absorption from the water, and (c) the increase in electric power input if an electric resistance heater is used instead of a heat pump

An ideal vapor-compression refrigeration cycle is employed to maintain a building temperature of 23°c when the outside temperature is 37°c. the cycle operates at steady state using ammonia as the working fluid. the mass flow rate of the refrigerant is 15 kg/min. the refrigerant enters the compressor at 1.5 bar and 10 °c. the condenser pressure is 20 bar and the temperature at the condenser exit is 45 °c. determine (a) the compressor power in kw. (b) the refrigeration capacity in tons. (c) the coefficient of performance. d) the maximum theoretical coefficient of performance.