Design an air-conditioning system for a luxury car Engineering (Coursework Sample)
Your company is to design an air-conditioning system for a luxury car, which is to operate in the desert in temperatures of up to 40 °C. The car passenger compartment is approximately 3 m × 3 m × 1.5 m and ten changes per hour of air are required at the desired internal temperature of 20 °C.
The car is to be equipped with an HFA-134a based refrigeration unit, which operates with a 30 K temperature difference between the cooled air and the working fluid to keep the heat exchanger down to a modest size. The HFA-134a cycle peak pressure is 1200 kPa and there is no sub-cooling.
In order to select the appropriate components, your line-manager assign you to carry out the following tasks:
1. To calculate the heat extraction required from the refrigeration cycle. (You may assume the water vapor content is negligible)
2. Sketch the block diagram for the refrigeration cycle and plot the cycle on a T-s diagram.
3. Calculate the enthalpies at all points in the cycle and hence calculate the refrigerant flow rate required to cool the incoming air.
4. Determine the power input to the refrigeration cycle. Why might a higher pressure be desirable for the cycle?
5. What methods could be used to control the humidity inside the car. Why might they be needed?
Task 2
Designing Air-Conditioner
1 Calculating the heat extraction required from the refrigeration cycle
T0=400C
Ti=200C
Volume, v=3m×3m×1.5m
Air change per hour (ACH) = 10
∆T=30k=Tc-Tw
Cycle peak pressure = 1200 kPa
Heat extraction required infiltration rate
v0=ACH∙V3600=10×13.53600=0.0375m3s
Q0=v0×ρ0×CpmTc-Tw=0.0375m3s×1.095×1021.640-20=838.989W
Where ρ0 is density of air and Cpm is the specific heat capacity of air
2 The block diagram for the refrigeration cycle and plot the cycle on a T-s diagram
Figure SEQ Figure \* ARABIC 1: Block Diagram for the refrigeration cycle
Figure SEQ Figure \* ARABIC 2: T-S Diagram
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