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Today Vapor-Compression Refrigeration Psychrometrics Tomorrow Team Project

Today Vapor-Compression Refrigeration Psychrometrics Tomorrow Team Project Wed – Test 3 (Entropy and Refrigeration). Refrigeration Terms Cooling Load, Cooling Capacity – Q in Compressor Load – W in Condenser Load – Q out Tons of Refrigeration – Rate of Heat Input

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Today Vapor-Compression Refrigeration Psychrometrics Tomorrow Team Project

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  1. Today Vapor-Compression Refrigeration Psychrometrics Tomorrow Team Project Wed – Test 3 (Entropy and Refrigeration)

  2. Refrigeration Terms • Cooling Load, Cooling Capacity – Qin • Compressor Load – Win • Condenser Load – Qout • Tons of Refrigeration – Rate of Heat Input • Refrigerant – The Fluid • Vapor-Compression Refrigeration • Heat Pump – Same Cycle, Use Qout

  3. Refrigeration Efficiency = desired output / required input Desired output = Heat removal from refrigerated space (Qin) Required input = Work input to compressor Conservation of Energy: Qin + Win = Qout COP can be > 1.0 = Cooling Capacity

  4. Refrigeration Applying Conservation of Energy…

  5. Refrigeration • Used when no other method of cooling is available • Very expensive (40-60% of a brewery’s utility bill) • Removal of heat from low T source to high T sink

  6. Primary Refrigerants • Ammonia (R-717), R-12, R-134a • Saturation temp < Desired application temp • 2 to 8C Maturation tanks • 0 to 1C Beer Chillers • -15 to -20C CO2 liquefaction • Typically confined to small region of brewery • Secondary Refrigerants • Water with alcohol or salt solutions • Methanol/glycol, potassium carbonate, NaCl • Lower freezing temperature of water • Low-toxicity (heat exchange with product) • Pumped long distances across brewery

  7. Refrigeration Qout Hop Storage Cooler Cond Air Conditioning Lagering Cellar Cooler Comp Win Yeast Tanks Flash Tank Fermenting Room Pasteurizer Beer Chiller Green Beer Chiller Fermenting Vessels Wort Cooler Secondary Refrigerant Storage Tank Evaporator

  8. Theory and the Cycle Qout 3 2 Condenser Compressor Win Evaporator 1 4 Qin

  9. Refrigeration 1-2: Constant entropy compression (s1 = s2) 2-3: Constant pressure heat rejection (3 = sat liq.) 3-4: Constant enthalpy throttling 4-1: Constant pressure heat addition (1 = sat vap.)

  10. Coefficient of Performance • Describes how well a refrigeration plant is running • Heat removed divided by energy input • COP increase with temperature difference between source and sink

  11. “Calculation of Performance using Mollier” • Find the COP of a refrigeration plant when the evaporation temperature is -15C and the condenser temperature is 30C. • hsatvap @ -15C = 1426 kJ/kg • hsatliq @ 30C = 323.1 kJ/kg • hafter comp = 1662.4 kJ/kg • hbefore comp = 1426 kJ/kg

  12. Refrigeration Example • An ideal vapor-compression refrigeration cycle using ammonia operates between the pressures of 14 and 2 bar. The system cools a secondary refrigerant at a rate of 25 kW. • Determine the mass flow rate of refrigerant. • Determine COP of the system. • Determine the power consumed by the compressor, in kW

  13. Typical Manufacturers Performance Curves

  14. Compressor Types • Reciprocating – similar to piston pump • Good for full and part-load • Good speed control and smaller apps • Screw – Single or Twin • Smooth operation, good for large apps • Good at full-load, poor at part-load

  15. Dry Air Fin Condensers • Fluid in condenser does not contact cooling fluid • High electricity costs for fans

  16. Wet Evaporative Condensers • Fluid in condenser does not contact cooling fluid • Water sprayed onto tubes to evaporate and cool

  17. Cooling Tower Condensers • A secondary fluid (water) sprayed • Air passes across water droplets, cools • Forced or induced draft, counter or cross • Cool water to heat exchange condenser

  18. Condenser Selection Considerations • Ambient temperature (Air-fin?) • Ambient humidity (evaporation?) • Space, accessibility, maintenance • Electricity costs (air-fin) • Chemical costs (evaporative, tower) • Legionellosis or L. pneumophila • Major source cooling towers and evaporative coolers • Name from 1976 meeting of American Legion – killed 36 people • Kill by heating to 60oC or chlorine

  19. Evaporators and Expansion Devices • Direct expansion with thermostat valve • Regulates flow of liquid being throttled into evaporator • Diaphragm to balance pressure between liquid in condenser and sum of evaporator and spring pressure

  20. Evaporators and Expansion Devices • Flooded with level control • Level of liquid in reservoir (typically shell and tube heat exchanger) controlled with variable throttle valve.

  21. For a 10 ton capacity refrigeration system, the pressure of the refrigerant in the evaporator is 210 kPa, whereas in the condenser it is 750 kPa, If ammonia (R-717) is used under saturated conditions, calculate the theoretical power required to operate the compressor.

  22. For a 10 ton capacity refrigeration system, the pressure of the refrigerant in the evaporator is 210 kPa, whereas in the condenser it is 750 kPa, If ammonia (R-717) is used under saturated conditions, calculate the theoretical power required to operate the compressor.

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