A dairy plant requires a refrigeration system that provides 7150 kW of cooling capacity at -4.00C...

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A dairy plant requires a refrigeration system that provides 7150 kW of cooling capacity at -4.00C to cool milk and 9150 kW of cooling capacity at -35.0C to fast chill milk. The system condenser pressure is 1.60 MPa and the system utilises an air-cooled condenser. A multi-pressure system is proposed with two compressors and two evaporators, utilising flash gas removal and inter-cooling as per Fig. 1. Assuming all compressors have an isentropic efficiency of 84.5%, there is no heat transfer in connecting components/pipework, the flashtank intercooler issues saturated vapour and saturated liquid in the respective streams, there is no pressure drop in the pipework, 5.00C of subcooling in the condenser, and 4.00C of superheating in both evaporators and R134a* is the refrigerant for the initial analysis, determine using a basic hand calculation: i) ii) iii) iv) v) The mass flow rates of the refrigerant through the evaporators and condenser. (5 marks) The power requirements for the compressors. (5 marks) It is proposed that the capital cost of the system could be reduced by $32,000 if two separate single-stage systems with air-cooled condensers rather than a single multi-pressure system were utilised. Assuming the lifetime of the system to be 6.0 years, the system runs 22 hrs a day with 95.0% uptime and electricity costs are $0.45/kW.hr, which is the better approach: the multi-pressure system or two independent systems? Why? (5 marks) The cooling requirement for the high-temperature (-4.00C) evaporator has the potential to vary through the day. Construct a model of the multi-pressure system in Matlab using the NISTref prop library and create a figure of total electrical power input vs. the high-temperature (-4.00C) evaporator cooling heat absorption rates from 4000 to 10000 kW. Note at a heat absorption rate of 7150 kW the total power input should be close to the value obtained in part ii). The idea is to use part iv) to check your hand calculation results so do not use part iv) as a replacement for the hand calculation answer in part ii) of the question. You must include a well-documented copy of the code you develop and utilise. (25 marks) If the refrigerant were changed to ammonia (NH3), and all other parameters equal to the system as modelled in part iv), determine and report a plot of the energy usage for high-temperature (-4.00C) evaporator cooling heat absorption rates from 4000 to 10000 kW, explicitly reporting the value at 7150 kW. Would ammonia as a refrigerant be a better option? (10 marks) A dairy plant requires a refrigeration system that provides 7150 kW of cooling capacity at -4.00C to cool milk and 9150 kW of cooling capacity at -35.0C to fast chill milk. The system condenser pressure is 1.60 MPa and the system utilises an air-cooled condenser. A multi-pressure system is proposed with two compressors and two evaporators, utilising flash gas removal and inter-cooling as per Fig. 1. Assuming all compressors have an isentropic efficiency of 84.5%, there is no heat transfer in connecting components/pipework, the flashtank intercooler issues saturated vapour and saturated liquid in the respective streams, there is no pressure drop in the pipework, 5.00C of subcooling in the condenser, and 4.00C of superheating in both evaporators and R134a* is the refrigerant for the initial analysis, determine using a basic hand calculation: i) ii) iii) iv) v) The mass flow rates of the refrigerant through the evaporators and condenser. (5 marks) The power requirements for the compressors. (5 marks) It is proposed that the capital cost of the system could be reduced by $32,000 if two separate single-stage systems with air-cooled condensers rather than a single multi-pressure system were utilised. Assuming the lifetime of the system to be 6.0 years, the system runs 22 hrs a day with 95.0% uptime and electricity costs are $0.45/kW.hr, which is the better approach: the multi-pressure system or two independent systems? Why? (5 marks) The cooling requirement for the high-temperature (-4.00C) evaporator has the potential to vary through the day. Construct a model of the multi-pressure system in Matlab using the NISTref prop library and create a figure of total electrical power input vs. the high-temperature (-4.00C) evaporator cooling heat absorption rates from 4000 to 10000 kW. Note at a heat absorption rate of 7150 kW the total power input should be close to the value obtained in part ii). The idea is to use part iv) to check your hand calculation results so do not use part iv) as a replacement for the hand calculation answer in part ii) of the question. You must include a well-documented copy of the code you develop and utilise. (25 marks) If the refrigerant were changed to ammonia (NH3), and all other parameters equal to the system as modelled in part iv), determine and report a plot of the energy usage for high-temperature (-4.00C) evaporator cooling heat absorption rates from 4000 to 10000 kW, explicitly reporting the value at 7150 kW. Would ammonia as a refrigerant be a better option? (10 marks)