Experimental Evaluation Of Cascade Refrigeration Plant

NIKHIL PANJWANIMECHANICAL ENGINEERING

KID- K10854

Experimental Evaluation of A cascade refrigeration system prototype with CO2 and NH3 for freezing process applications

AimTo obtain the optimum value of CO2

condensing temperature

Advantages and Disadvantages Of Ammonia RefrigerantAdvantages: naturally available excellent thermodynamic and transport properties as

refrigerant Ozone friendly• Disadvantages: toxicity Flammability Applications at temperatures lower than 35 degree C, the

volumetric displacement requirements of the NH3compressor works out relatively higher.

Evaporating pressure ˂ ambient pressure, could lead to leakage into the system.

Advantages and Disadvantages Of CO2Advantages: CO2 is environmentally friendly non-toxic non-explosive easily available can be used in refrigeration processes within a wide range of

temperatures. it is compatible with the oils commonly used in actual

refrigeration systems It offers low pressure ratios and low specific volume values which

when coupled with high pressure levels allows for reduction in size of refrigeration components

Disadvantage: high work pressures (7.2 MPa at 30 C)

Characteristics of prototypeDesigned to supply a horizontal plate freezerRefrigeration capacity of the plate freezer is 9 kW, at 50deg C of

evaporating temperature.The operating controller- PLC (Programmable Logic Controller).The controlled variables are: the condensing pressures of NH3, the

evaporating pressure of NH3 and the evaporating pressure of CO2.The condensing pressure of NH3 is controlled by modifying the

velocity of the fans of the air condenser. To control the evaporating pressure ofCO2, a flow line which connects

the CO2 compressor discharge line to its suction line was installed, thus allowing the recirculation of a small portion of the mass flow of compressed CO2. The recirculation of the mass flow of CO2 is controlled using a valve installed in the flow line previously mentioned.

The evaporating pressure of NH3 is controlled by varying the capacity of the high temperature system.

Observation

Observations...For CO2 refrigerant:

For NH3 refrigerant:

Condensing temperature

increase

Pressure ratio

increase

Electric power

increase

COP decrease

Condensing temperature

increase

COP increase

Electric power

decrease

Pressure ratio

decrease

Observations...The optimum CO2 condensing temperatures

experimentally measured were compared to the values of the optimum CO2 condensing temperatures given by several correlations published by different authors. The resulting maximum difference was 2.4%.

Experimental Evaluation Of Cascade Refrigeration Plant using R134a and CO2 couple

AimEnergy performance analysis of the plant.Focusing on: compressors’ performance, temperature difference in the cascade heat

exchanger,Cooling capacity,COP, andCompressors’ discharge temperatures

Cascade Refrigeration Prototype

CO2 compressor

R134a compressor

Characteristics Of ExperimentLT evaporating temperatures -40 to -30 ºC HT condensing temperatures from 30 to 50

ºCOperation of the cascade was registered at

five LT condensing temperatures regulating the HT compressor speed.

Degree of superheat in the valves of the R134a cascade condensers and of the CO2 evaporator at 10 ºC.

Observations And Conclusions..Energy Balance Of The Cascade Plant-COP of cascade plant-1.42COP of LT cycle- 3.10COP of HT cycle- 2.84

• Compressor’s Performance:Compressor’s speed varied under fixed compression

ratiosR134a Compressor Speed increased

efficiency improvedCO2 compressor Below nominal speed or at high

compression ratio efficiency degraded

Energy Performance Of The Cascade Refrigeration Plant

Cooling CapacityCooling capacity is negatively linear

dependent with the condensing temperature of the LT cycle.

Changes in cooling capacity is significant when subjected to modification of low evaporating temperature.

Discharge Temperature of CO2 Compressorhigher than the environment temperature,

which brings the possibility of using a gas-cooler to reject heat, which improves COP of the plant.

EXPERIMENTAL EVALUATION OF A CASCADE REFRIGERATION SYSTEM FOR LOW TEMPERATURE APPLICATIONS USING THE PAIR R22/R404A

AimTo obtain the condensing temperature of the

LT that provides an optimal value for the coefficient of performance (COP) of the cycle.

Schematic Diagram of the Experimental Plant

COP Of Cascade Refrigeration

Experimental Results For The HT, LT and Global COPs

•The increase in intermediate temperature causes intersection of the two curves, as provided by the simulation process.

• The COPG had a maximum value at the intersection of the COPcurves of each circuit.

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