Evaporation:
The rate of heat transfer in the evaporator is calculated using equations 10 and 11
Q_in=(εC)_evap (T_(in,evap)-T_evap ) (10)
Where ε is the effectiveness of the evaporator, C is the capacitance rate for the air or chilled water passing through the evaporator. Tevap is the temperature of refrigerant in evaporator and Tin, evap is the temperature of the air or chilled water at the inlet of the evaporator.
Equation 11 express Qin in terms of enthalpy.
Q_in=m ̇_ref (h_4-h_1) (11) h4 is the enthalpy before the evaporator and h1 is the enthalpy after the evaporator.
Heat loss and gain from environment:
Due to the refrigerant flowing through, the piping from the evaporator to the compressor is at much lower temperature relative …show more content…
However, it is impractical to find the enthalpy at so many difference points as that would require more pressure gauges and thermometer at various points in the system. Good insulation and shorter piping through good design planning can reduce the heat loss and gain in the system.
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2.3.2 VA cycle
The thermodynamic calculations of the VA cycle is described by Shukla, et al. (2015) and Eastop and McConkey(2009). The designation of each character in the equations has been changed to reflect the naming of each state in figure 3. The following assumptions are also made: Only vapour refrigerant enter the condenser, i.e. only refrigerant boil in the generator Only absorber fluid leaves the generator to return to the absorber vessel. Pump work, pressure loss and heat loss are …show more content…
COPref is the ratio of cooling provided to the work required. This means that for the same amount of work, a VC refrigerator can provide more cooling than a VA refrigerator. This high COP is the reason VA refrigerator has gained widespread usage. However, it is not fair to compare the two systems based purely on the magnitude of its COP as the work required in a VA refrigerator is produced by heat, it is much cheaper than the work required in VC refrigerator which require electrical or mechanical energy.
Environmental issue
Conventional VC refrigerant such as CFC or HCFC can deplete the ozone layer and is already phased out based on the Montreal Protocol. Modern VC refrigerant like HFC - also known as f-gases (fluorinated greenhouse gases) - has no ozone depleting property but has high global warming potential (GWP) and its use is being reduced and phased down by the EU f-gases Regulation No 517/2014. VA refrigerant on the other hand mostly use organic refrigerant such as water or ammonia, however recent development began using HFC refrigerant such as R134a in VA refrigerator (Roy & Maiya, 2012).
Noise, size, and cooling
The rate of heat transfer in the evaporator is calculated using equations 10 and 11
Q_in=(εC)_evap (T_(in,evap)-T_evap ) (10)
Where ε is the effectiveness of the evaporator, C is the capacitance rate for the air or chilled water passing through the evaporator. Tevap is the temperature of refrigerant in evaporator and Tin, evap is the temperature of the air or chilled water at the inlet of the evaporator.
Equation 11 express Qin in terms of enthalpy.
Q_in=m ̇_ref (h_4-h_1) (11) h4 is the enthalpy before the evaporator and h1 is the enthalpy after the evaporator.
Heat loss and gain from environment:
Due to the refrigerant flowing through, the piping from the evaporator to the compressor is at much lower temperature relative …show more content…
However, it is impractical to find the enthalpy at so many difference points as that would require more pressure gauges and thermometer at various points in the system. Good insulation and shorter piping through good design planning can reduce the heat loss and gain in the system.
________________________________________
2.3.2 VA cycle
The thermodynamic calculations of the VA cycle is described by Shukla, et al. (2015) and Eastop and McConkey(2009). The designation of each character in the equations has been changed to reflect the naming of each state in figure 3. The following assumptions are also made: Only vapour refrigerant enter the condenser, i.e. only refrigerant boil in the generator Only absorber fluid leaves the generator to return to the absorber vessel. Pump work, pressure loss and heat loss are …show more content…
COPref is the ratio of cooling provided to the work required. This means that for the same amount of work, a VC refrigerator can provide more cooling than a VA refrigerator. This high COP is the reason VA refrigerator has gained widespread usage. However, it is not fair to compare the two systems based purely on the magnitude of its COP as the work required in a VA refrigerator is produced by heat, it is much cheaper than the work required in VC refrigerator which require electrical or mechanical energy.
Environmental issue
Conventional VC refrigerant such as CFC or HCFC can deplete the ozone layer and is already phased out based on the Montreal Protocol. Modern VC refrigerant like HFC - also known as f-gases (fluorinated greenhouse gases) - has no ozone depleting property but has high global warming potential (GWP) and its use is being reduced and phased down by the EU f-gases Regulation No 517/2014. VA refrigerant on the other hand mostly use organic refrigerant such as water or ammonia, however recent development began using HFC refrigerant such as R134a in VA refrigerator (Roy & Maiya, 2012).
Noise, size, and cooling