1.
Vapor Compression Refrigeration System:
Components:
1- Compressor.
2- Condenser.
3- Expansion valve.
4- Evaporator.
Process Table for Ideal Vapor-Compression Cycle
Process Component Key Rel'n Energy Balance
1->2 Compressor s2 = s1 wCV,IN,COMP = h 2 - h1
2->3 Condenser P3= P 2 qCV,OUT,COND = h 2 - h3
Throttling
3->4 h4= h 3 h4 = h3
Device
4->1 Evaporator P1= P 4 qCV,IN,EVAP = h1 - h 4
State Table for Ideal Vapor-Compression Cycle
State T P h s x Phase
Saturated
1 T MIN PMIN s1 1
Vapor
Superheated
2 TMAX PMAX = s2 -
Vapor
Saturated
3 = P2 h3 0
Liquid
Saturated
4 = T1 = P1 = h3 0<x<1 Liquid-Vapor
Mixture
Working Fluid:
1- R-12
2- R-22
3- R-602
4- Ammonia
Coefficient of Performance:
QEvap
C .O .P 0.1
WComp
Advantages:
1- High Coefficient of performance.
2- High Cooling Capacity.
Disadvantages:
1- Complex Component.
2- Difficult Maintenance.
2- Steam Jet Refrigeration System:
Components:
1- Expansion Valve.
2- Evaporator.
3- Nozzle.
4- Boiler.
5- Condenser.
6- Feed Pump.
Working Fluid:
Water (H2O)
Coefficient of Performance:
C .O. P 0. 5
Advantages:
1- Negligible maintenance required.
2- There are no moving parts.
3- Simple Construction, Compact Design.
4- Cheap Steam at low conditions is used as refrigerant.
Disadvantages:
1- Low Coefficient of performance.
2- Vacuum Pressure.
Idea of the Cycle:
Steam forming as saturated water expands in expansion valve 1
from pressure P1 to P2 flows into evaporator 2 arranged inside
the chilled volume. From the evaporator steam with a high
dryness factor and at the pressure P2 is directed into the
combining chamber of the ejector 3. Operating steam is
delivered to the ejector nozzle from boiler 4 at a pressure Pboil.
The rates of steam flow into the ejector combining chamber
from the evaporator and into the ejector nozzle from the boiler
and selected such that steam leave the ejector diffuser at a
pressure P1. From the ejector the dry saturated steam flows to
condenser 5 where it condensate at a pressure P1 splits into two
streams a greater portion of the water flows into the refrigerating
circuit to the inlet of expansion valve 1 while a smaller portion
flows to feed pump 6 in which water pressure is raised to Pboil
the pump delivers the water to boiler 4.
3-Absorption Refrigeration System:
With the application of heat at the generator, ammonia vapor is
driven from the solution. This hot vapor rises into the separator
and a portion of the water condenses and flows by gravity into
the absorber. The hot ammonia vapor continues to rise into the
condenser where it gives up its heat to the surrounding air and
condenses into a liquid. The liquid ammonia enters by gravity
into the evaporator, where it is mixed with hydrogen gas.
Circulation of hydrogen gas causes a reduction in pressure
within the evaporator. The low pressure causes the ammonia
liquid to boil into a gas (evaporating) and absorbing heat in the
process (refrigerating effect). The mixture of
hydrogen/ammonia vapor that’s carrying the absorbed heat is
now drawn by gravity into-the absorber. Because the water
from the separator has a greater affinity for ammonia, it
separates from the hydrogen gas. The hydrogen gas being very
light rises and returns to the generator to start the cycle again.
Components:
1- Evaporator.
2- Condenser.
3- Absorber.
4- Generator.
5- Pump.
Working Fluid:
Ammonia or lithium + (H2O)
Coefficient of Performance:
Q
C .O .P Evap 0.4 0 .7
QGen
Advantages:
1. No moving parts.
2. No vibration or noise on small systems.
3. Can make use of waste heat.
4. Small systems can operate without electricity using only
heat; large systems require power for chemical pumps.
Disadvantages:
1. Potential refrigerant leaks.
2. Operates under limited vibration and orientations.
3. Complicated and difficult to service and repair.
4. Stalls in hot ambient.
5. Very bulky.
6. Poor efficiency.
4- Air Refrigeration System:
Components:
1- Air Cooler.
2- Compressor.
3- Turbine.
4- Space to be cooled.
T-S Chart:
Working Fluid:
Air.
Coefficient of Performance:
Q Space
C .O.P 1
WWater
Advantages:
1- Low Weight.
2- Available.
Disadvantages:
1- Low Coefficient of performance.
2- Used in the near factories to the high energies source.
5- Thermo-Electrical Refrigeration Systems:
Sebeck-Effect:
The seebeck effect occurs when you take any two members of
the thermoelectric series and connect wires made of them to
form a circuit with two junctions. In the presence of a
temperature difference between the junctions a small current
flows around the circuit.
Peltier-Effect:
The peltier effect occurs when you take any two members of the
thermoelectric series and connect wires made of them to form a
circuit with two junctions. In the presence of a current a
temperature difference between the junctions is produced.
Seebeck-Effect Peltier-Effect
Advantages:
1. Light weight and compact for very small heat loads.
2. No moving parts, eliminating vibration, noise, and
problems of wear.
3. Operates in any orientation. Not affected by gravity or
vibration.
4. Very low cost device for cooling in small appliances.
Disadvantages:
1. Limited to very small refrigeration loads due to cost.
2. Not suitable for solar due to poor efficiency.
