High efficency, high qaulity air conditioning units designed for easy installation and years of trouble free operation to save you money.
Evaporator Units for Limousines, Buses, Mini Buses, Shuttle Buses, Transit Vehicles, Heavy Duty Off Road Vehicles.
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AC EVAPORATOR DESCRIPTION |
AC EVAPORATOR PART NO. |
| IN DASH AC EVAPORATOR UNIT (12V) | AC EVAPORATOR 400P |
| IN DASH EVAPORATOR UNIT (24V) | EVAPORATOR 400-24VP |
| UNDER DASH EVAPORATOR UNIT (12V) | EVAPORATOR 410P |
| UNDER DASH EVAPORATOR UNIT (24V) | EVAPORATOR 410-24VP |
| UNDER DASH EVAPORATOR UNIT (RIGHT-HAND CONNECTED COIL) | EVAPORATOR 0550R |
| IN DASH HEATER | Heater 600 |
| HEATER WITH LARGE LOUVER OPTION | Heater 600L |
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Eskimo Air, Automotive Air Conditioning. Tel:
714-654-4582
|
Description of the vapor-compression refrigeration system
Figure 1: Vapor compression refrigerationThe vapor-compression refrigeration system uses a circulating liquid refrigerant as the medium which absorbs and removes heat from the space to be cooled and subsequently rejects that heat elsewhere. Figure 1 depicts a typical, single-stage vapor-compression system. All such systems have four components: a compressor, a condenser, an expansion valve (also called a throttle valve), and an evaporator. Circulating refrigerant enters the compressor in the thermodynamic state known as a saturated vapor[3] and is compressed to a higher pressure, resulting in a higher temperature as well. The hot, compressed vapor is then in the thermodynamic state known as a superheated vapor and it is at a temperature and pressure at which it can be condensed with typically available cooling water or cooling air. That hot vapor is routed through a condenser where it is cooled and condensed into a liquid by flowing through a coil or tubes with cool water or cool air flowing across the coil or tubes. This is where the circulating refrigerant rejects heat from the system and the rejected heat is carried away by either the water or the air (whichever may be the case).
The condensed liquid refrigerant, in the thermodynamic state known as a saturated liquid, is next routed through an expansion valve where it undergoes an abrupt reduction in pressure. That pressure reduction results in the adiabatic flash evaporation of a part of the liquid refrigerant. The auto-refrigeration effect of the adiabatic flash evaporation lowers the temperature of the liquid and vapor refrigerant mixture to where it is colder than the temperature of the enclosed space to be refrigerated.
The cold mixture is then routed through the coil or tubes in the evaporator. A fan circulates the warm air in the enclosed space across the coil or tubes carrying the cold refrigerant liquid and vapor mixture. That warm air evaporates the liquid part of the cold refrigerant mixture. At the same time, the circulating air is cooled and thus lowers the temperature of the enclosed space to the desired temperature. The evaporator is where the circulating refrigerant absorbs and removes heat which is subsequently rejected in the condenser and transferred elsewhere by the water or air used in the condenser.
To complete the refrigeration cycle, the refrigerant vapor from the evaporator is again a saturated vapor and is routed back into the compressor.
[edit] Refrigerants
"Freon" is a trade name for a family of haloalkane refrigerants
manufactured by DuPont and other companies. These refrigerants were commonly
used due to their superior stability and safety properties: they were
not flammable nor obviously toxic as were the fluids they replaced. Unfortunately,
these chlorine-bearing refrigerants reach the upper atmosphere when they
escape. In the stratosphere, CFCs break up due to UV-radiation, releasing
their chlorine atoms. These chlorine atoms act as catalysts in the breakdown
of ozone, which does severe damage to the ozone layer that shields the
Earth's surface from the Sun's strong UV radiation. The chlorine will
remain active as a catalyst until and unless it binds with another particle,
forming a stable molecule. CFC refrigerants in common but receding usage
include R-11 and R-12. Newer and more environmentally-safe refrigerants
include HCFCs (R-22, used in most homes today) and HFCs (R-134a, used
in most cars) have replaced most CFC use. HCFCs in turn are being phased
out under the Montreal Protocol and replaced by hydrofluorocarbons (HFCs),
such as R-410A, which lack chlorine.
Newer refrigerants are currently the subject of research, such as supercritical carbon dioxide, known as R-744.[4] These have similar efficiencies compared to existing CFC and HFC based compounds.
[edit] Thermodynamic analysis of the system
Figure 2: Temperature–Entropy diagramThe thermodynamics of the vapor
compression cycle can be analyzed on a temperature versus entropy diagram
as depicted in Figure 2. At point 1 in the diagram, the circulating refrigerant
enters the compressor as a saturated vapor. From point 1 to point 2, the
vapor is isentropically compressed (i.e., compressed at constant entropy)
and exits the compressor as a superheated vapor.
From point 2 to point 3, the superheated vapor travels through part of the condenser which removes the superheat by cooling the vapor. Between point 3 and point 4, the vapor travels through the remainder of the condenser and is condensed into a saturated liquid. The condensation process occurs at essentially constant pressure.
Between points 4 and 5, the saturated liquid refrigerant passes through the expansion valve and undergoes an abrupt decrease of pressure. That process results in the adiabatic flash evaporation and auto-refrigeration of a portion of the liquid (typically, less than half of the liquid flashes). The adiabatic flash evaporation process is isenthalpic (i.e., occurs at constant enthalpy).
Between points 5 and 1, the cold and partially vaporized refrigerant travels through the coil or tubes in the evaporator where it is totally vaporized by the warm air (from the space being refrigerated) that a fan circulates across the coil or tubes in the evaporator. The evaporator operates at essentially constant pressure. The resulting saturated refrigerant vapor returns to the compressor inlet at point 1 to complete the thermodynamic cycle.
It should be noted that the above discussion is based on the ideal vapor-compression refrigeration cycle which does not take into account real world items like frictional pressure drop in the system, slight internal irreversibility during the compression of the refrigerant vapor, or non-ideal gas behavior (if any).
[edit] Types of gas compressors
Main article: Gas compressor
The most common compressors used in chillers are reciprocating, rotary
screw, centrifugal, and scroll compressors. Each application prefers one
or another due to size, noise, efficiency and pressure issues.
[edit] Reciprocating compressors
Main article: Reciprocating compressor
Reciprocating compressors are piston-style, positive displacement compressors.
[edit] Rotary screw compressors
Main article: Rotary screw compressor
Rotary screw compressors are also positive displacement compressors. Two
meshing screw-rotors rotate in opposite directions, trapping refrigerant
vapor, and reducing the volume of the refrigerant along the rotors to
the discharge point.
[edit] Centrifugal compressors
Main article: Centrifugal compressor
Centrifugal compressors are dynamic compressors. These compressors raise
the pressure of the refrigerant by imparting velocity or dynamic energy,
using a rotating impeller, and converting it to pressure energy.
[edit] Scroll compressors
Main article: Scroll compressor
Scroll compressors are also positive displacement compressors. The refrigerant
is compressed when one spiral orbits around a second stationary spiral,
creating smaller and smaller pockets and higher pressures. By the time
the refrigerant is discharged, it is fully pressurized.
[edit] Others
Main article: Diaphragm compressor
Main article: Axial-flow compressor
Main article: Diagonal or mixed-flow compressor
Main article: Liquid ring compressor
Main article: Roots blower
[edit] Other features and facts of interest
The schematic diagram of a single-stage refrigeration system shown in
Figure 1 does not include other equipment items that would be provided
in a large commercial or industrial vapor compression refrigeration system,
such as:
A horizontal or vertical pressure vessel, equipped
internally with a demister, between the evaporator and the compressor
inlet to capture and remove any residual, entrained liquid in the refrigerant
vapor because liquid may damage the compressor. Such vapor-liquid separators
are most often referred to as "suction line accumulators". (In
other industrial processes, they are called "compressor suction drums"
or "knockout drums".)
Large commercial or industrial refrigeration systems may have multiple
expansion valves and multiple evaporators in order to refrigerate multiple
enclosed spaces or rooms. In such systems, the condensed liquid refrigerant
may be routed into a pressure vessel, called a receiver, from which liquid
refrigerant is withdrawn and routed through multiple pipelines to the
multiple expansion valves and evaporators.
Some refrigeration units may have multiple stages which requires the use
of multiple compressors in various arrangements.[5]
The cooling capacity of refrigeration systems is often defined in units
called "tons of refrigeration". The most common definition of
that unit is: 1 ton of refrigeration is the rate of heat removal required
to freeze a short ton (i.e., 2000 pounds) of water at 32 °F in 24
hours. Based on the heat of fusion for water being 144 Btu per pound,
1 ton of refrigeration = 12,000 Btu/h = 12,660 kJ/h = 3.517 kW. Most residential
air conditioning units range in capacity from about 1 to 5 tons of refrigeration.
A much less common definition is: 1 tonne of refrigeration
is the rate of heat removal required to freeze a metric ton (i.e., 1000
kg) of water at 0 °C in 24 hours. Based on the heat of fusion being
334.9 kJ/kg, 1 tonne of refrigeration = 13,954 kJ/h = 3.876 kW. As can
be seen, 1 tonne of refrigeration is 10 percent larger than 1 ton of refrigeration