A walk-in refrigerator at a restaurant gains 1.6 kW of heat on average from the

Question

A walk-in refrigerator at a restaurant gains 1.6 kW of heat on average from the door being opened and new food being added constantly. Three fans rated at 0.08 kW each inside the walk-in work to keep the interior air well mixed. The evaporator of the refrigeration system works to remove heat from the walk-in in order to maintain the temperature of 35 degree F. What type of system do you have in this example? Determine the rate at which heat must be removed from the walk-in to maintain the desired temperature. A 3000 lb car is travelling up at quarter mile long uphill road. The incline of the road is estimated to be 30 degree (from horizontal), taking the car 50 seconds in total to climb. What will be the power needed to: keep the car at a constant velocity; if the car starts at rest and reaches a final velocity of 40 m/s. Please note the trig function you are using to determine the height! A granting agency must decide between two renewable energy sources: wind or hydro. The proposed wind turbine being considered for construction is in a location where the wind blows at 11 m/s. The proposed turbine has blade diameters of 40 m and the air density at this location was measured to be 1.3 kg/m^3. The hydro turbine proposal plans to install a turbine-generator 200 meters below the free surface of a large reservoir. The density of the salt water is to be taken as 1020 kg/m^3 with a supply rate of 0.5 m^3/s. Which of these two proposals would provide a larger maximum power generation? Decide which you think is the best option for the funding agency to grant.

Explanation / Answer

2) sin(theta) = h/l

l is the length of the incline = 0.25*mile = 402.33 m

sin(30) = h/402.33

h = 201.165 m

a) power needed is P = (m*g*h)/t

3000 lb = 1360.7 kg

P = (1360.7*9.8*201.165)/50

P = 53650.14 W = 53.650 kW

b) P = [(m*g*h) + (0.5*m*v^2)]/t

P = ((1360.7*9.8*201.165)+(0.5*1360.7*40^2))/50

P = 75.421 kW

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