# An Initial Design Calculation Is To Be Undertaken For A Large Refrigeration Plant: Thermal Engineering Assignment, SU, Australia

 University Sydney University Subject Thermal Engineering

Question 1

An initial design calculation is to be undertaken for a large refrigeration plant that will service a frozen goods warehouse. The warehouse is to be kept at a temperature of -20.0°C and the total refrigeration heat load is 1.50 MW. The refrigeration system is to reject heat to the ambient air at 30.0°C and operate with a discharge pressure of 1.60 MPa and a suction pressure of 60.0 kPa.
Model the refrigeration system as an ideal vapor compression cycle.

(i) Draw an equipment diagram, labeling all heat transfer and work interactions.

(ii) Draw the refrigeration cycle on T-s (temperature-entropy) and P-h (pressure-enthalpy) diagrams. The diagrams show the cycle with respect to the saturation lines, indicate the direction of the cycle progress and label all heat transfer and work interactions.

(iii) Determine the mass flow rate of the refrigerant flowing through the cycle (in kg/s).

(iv) Determine the power required to drive the compressor (in kW).

(v) Determine the coefficient of performance of the refrigeration system.

(vi) If the refrigeration system were modified by replacing the throttling valve with an isentropic turbine, what would the required net power input into the modified refrigeration cycle be (in kW)?

(vii) Show the modified refrigeration cycle in part vi) on a T-s (temperature-entropy) with respect to the saturation lines, indicating the direction of the cycle progress and labeling all heat transfer and work interactions.

(viii) If an ideal reversed Carnot cycle refrigeration system were used to cool the warehouse, what would the net input power requirement be (in kW)?

(ix) Show the reversed Carnot refrigeration cycle in part viii) on a T-s (temperature-entropy) with respect to the saturation lines, indicating the direction of the cycle progress and labelling all heat transfer and work interactions.

Question 2

The performance of a single-cylinder four-stroke engine is to be accurately modeled using a Diesel cycle with air-standard assumptions (accounting for variations in specific heats). The engine operates at 1200 rpm with a peak exhaust temperature of 620 K. At the start of the compression process the air in the cylinder is at 310 K and 95.0 kPa. The engine has a bore of 10.0 cm, a stroke of 15.0 cm, and a clearance volume of 84.0 mL. The heat delivered by the combustion of the fuel is 25.0 MJ/kg fuel.

(i) Plot the engine cycle on P-V (pressure-volume) and T-s (temperature entropy) diagrams showing each stage in the cycle, the direction of the cycle progress, and all heat transfer and work interactions.

(ii) Determine the compression ratio, r.

(iii) Determine the mass of air in the cylinder (in kg).

(iv) Determine the temperature (in K) and pressure (in kPa) at the end of the isentropic compression process.

(v) Determine the temperature at the end of the heat addition portion of the cycle (in K).

(vi) Determine the amount of heat rejected per cycle (in kJ).

(vii) Determine the total heat addition from combustion per cycle (in kJ).

(viii) Determine the total power output from the engine (in kW).

(ix) Determine the thermal efficiency of the cycle.

(x) Determine the mass of fuel required to run the engine for 8 hours (in kg).

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