Background:
This assignment aims to provide an opportunity to design a refrigeration system to provide low temperature cooling --30°C for a specialized cold room warehouse facility.
The location in which the warehouse is located has an average temperature of 28°C. Due to the relatively low refrigeration temperature required, it is of interest to evaluate the benefits of adopting a cascade refrigeration system when compared to a conventional single loop refrigeration system. The required cooling load for the facility is 3.5 kW.
Tasks and further instructions
This is a very open ended assignment and there is no one fixed or correct answer. The assignment will be marked in terms of the approach and in arriving at reasonably realistic calculations and discussions. The group will have to undertake their own research to obtain additional information to complete this assignment, not provided in this document. The deliverable of this assignment is a group report. Please ensure consistent IEEE referencing and citation in this report.
Part A:
Design a conventional IDEAL single stage refrigeration cycle to achieve the cooling requirement above. Evaluate the use of (1) ammonia as the refrigerant versus (2) HCFC-- 123 as the refrigerant. Complete the following tasks and compile them in the final report:
1. With the aid of two P--h diagrams, illustrate the MOST efficient way to operate the single stage cycle for both refrigerants.
2. Complete Table 1 and provide a brief description (tentative ~1/2 or 1 page) on why the operating conditions in Table 1 were selected.
3. Provide a brief discussion comparing the efficiency of the two refrigerants for a single stage cycle (tentative ~1/2 - 1 page or can be more).
Table 1 - Design parameters for the single stage refrigeration cycle
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Evaporator:
Operating temperature (°C) Operating pressure (MPa) Inlet quality (-)
Condenser:
Inlet temperature (°C) Operating pressure (Mpa) Outlet temperature (°C) Rate of heat released (kJ/s)
Compressor:
Mass flow of the refrigerant (kg/s) Compression load (kJ/s)
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Ammonia
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HCFC-123
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Part B:
Design a conventional IDEAL two--stage refrigeration cycle to achieve the cooling requirement above. Evaluate the use of (1) ammonia as the refrigerant versus (2) HCFC-- 123 as the refrigerant. Complete the following tasks and compile them in the final report:
1. With the aid of two P--h diagrams, illustrate a possible way to operate the two--stage cycle for both refrigerants.
2. Complete Table 2 and provide a brief description (tentative ~1/2 or 1 page) on why the operating conditions in Table 1 were selected.
3. Provide a brief discussion comparing the efficiency of the two refrigerants for a two--stage cascade cycle (tentative ~1/2 - 1 page or can be more).
Table 2 - Design parameters for the two--stage cascade refrigeration cycle
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STAGE 1
Evaporator:
Operating temperature (°C) Operating pressure (MPa) Inlet quality (-)
Condenser:
Inlet temperature (°C) Operating pressure (MPa) Outlet temperature (°C) Rate of heat released (kJ/s)
Compressor:
Mass flow of the refrigerant (kg/s) Compression load (kJ/s)
STAGE 2
Evaporator:
Operating temperature (°C) Operating pressure (MPa) Inlet quality (-)
Condenser:
Inlet temperature (°C) Operating pressure (MPa) Outlet temperature (°C) Rate of heat released (kJ/s)
Compressor:
Mass flow of the refrigerant (kg/s) Compression load (kJ/s)
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Ammonia
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HCFC-123
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Part C:
Complete the following tasks and compile them in the final report:
1. Based on the calculations in Part A and B, provide a brief discussion comparing the efficiency of single stage and two--stage cascade refrigeration cycles (tentative
~1/2 or 1 page).
2. Provide a detailed discussion on the pros and cons of using ammonia versus HCFC--123 as refrigerants (~2 page or more).