today vapor-compression refrigeration psychrometrics tomorrow team project
DESCRIPTION
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 - PowerPoint PPT PresentationTRANSCRIPT
TodayVapor-Compression RefrigerationPsychrometrics
TomorrowTeam Project
Wed – Test 3 (Entropy and Refrigeration)
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
RefrigerationEfficiency = desired output / required inputDesired output = Heat removal from refrigerated
space (Qin)
Required input = Work input to compressorConservation of Energy: Qin + Win = Qout
COP can be > 1.0 = Cooling Capacity
in
in
WQ
COP
inQ
RefrigerationApplying Conservation of Energy…
12
41
21
32
14
0)(
0)(
0)(
hhhh
COP
hhmW
hhmQ
hhmQ
in
out
in
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
Primary RefrigerantsAmmonia (R-717), R-12, R-134aSaturation temp < Desired application temp
2 to 8C Maturation tanks0 to 1C Beer Chillers-15 to -20C CO2 liquefaction
Typically confined to small region of brewery
Secondary RefrigerantsWater with alcohol or salt solutionsMethanol/glycol, potassium carbonate, NaClLower freezing temperature of waterLow-toxicity (heat exchange with product)Pumped long distances across brewery
Refrigeration
Cond
Comp
Qout
Win
Fermenting Room
Lagering Cellar Cooler
Hop Storage Cooler
Flash Tank
EvaporatorSecondary Refrigerant
Storage Tank
Wort Cooler
Fermenting Vessels
Green Beer Chiller
Beer Chiller
Pasteurizer
Yeast Tanks
Air Conditioning
Theory and the Cycle
Condenser
Evaporator
Compressor
Qout
Qin
Win
1
23
4
Refrigeration1-2: Constant entropy compression (s1 = s2)2-3: Constant pressure heat rejection (3 = sat liq.)3-4: Constant enthalpy throttling4-1: Constant pressure heat addition (1 = sat vap.)
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
€
COP = QeWc
= h1 − h4
h2 − h1
“Calculation of Performance using Mollier”
• Find the COP of a refrigeration plant when the evaporation temperature is -15C and the condenser temperature is 30C.– hsatvap @ -15C = 1426 kJ/kg– hsatliq @ 30C = 323.1 kJ/kg– hafter comp = 1662.4 kJ/kg– hbefore comp = 1426 kJ/kg
Refrigeration ExampleAn 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.
(a) Determine the mass flow rate of refrigerant.
(b) Determine COP of the system.(c) Determine the power consumed by the
compressor, in kW
Typical Manufacturers Performance Curves
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
Dry Air Fin Condensers• Fluid in condenser does not contact cooling
fluid• High electricity costs for fans
Wet Evaporative Condensers• Fluid in condenser does not contact cooling
fluid• Water sprayed onto tubes to evaporate and
cool
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
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
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
Evaporators and Expansion Devices• Flooded with level control• Level of liquid in reservoir (typically shell and
tube heat exchanger) controlled with variable throttle valve.
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.
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.