Refrigeration Components
• evaporator
• compressor
• condenser
• ref. metering device
The evaporator
• absorbs heat into the system when the refrigerant is boiled at a lower temp. than that of the substance to be cooled
• coil temp. is temp. of refrigerant in evaporator Coil
• coil uses conduction
• just before the end of the evaporator coil the liquid should be 100% saturated
• when a vapor is superheated, it no longer corresponds to a P/T relationship. Because no liquid remains to boil off to vapor, no more vapor pressure can be added. The vapor will now take on sensible heat when heated, and its temp. will rise, but the pressure will remain unchanged
• the 3. main functions
- absorb heat
- allow the heat to boil off the refrigerant to a vapor in its tubing bundle
- allow the heat to superheat the remaining refrigerant vapor in its tubing bundle
• evaporators have many design configurations
• remember absorbs heat into the system from the substance to be cooled
• the suction line simply connects the evaporator to the compressor
The Compressor or Vapor Pump
• heart of the refrigeration system
• pumps heat- laden refrigerant
• it lowers the pressure for the evaporator and increases pressure on the high-pressure side of the system
• this creates refrigerant flow from the low pressure side to the high pressure side
• all compressor in refrigerant systems perform this function by compressing the vapor refrigerant
• most common residential and light commercial air conditioning and refrigeration are
- reciprocating- uses piston and one-way valve
- rotary- used on small applications like window units, refrigerators and some residential. – use of a rotating drum-like piston pushes pressure from low side to high side. –these compressors are typically very small compared to the same capacity of reciprocating compressors.
- scroll – is one of the latest compressors to be developed and has a totally different working mechanism. – the scroll use a coil spring shape part that moves over a matching stationary piece and as the movable part orbits inside the stationary part it squeezes vapor from the low-pressure side to the high pressure side. (used in all types of systems)
- Centrifugal compressors are used on Commercial systems
The Condenser
• rejects both sensible heat and latent heat from ref. system
• heat comes from evaporator and heat of compression or mechanical friction generated in the compression stroke, motor winding heat and any heat absorbed by superheating the suction line
• receives hot gas after it leaves the compressor thru the hot gas line
• forced into top by compressor
• gas pushed at high speed and temp.
• the vapor pressure is often referred to as the head pressure, high-side pressure, discharge pressure or condensing pressure
• three important things may happen to the refrigerant in condensers
- the hot gas from the compressor is de-superheated from the hot discharge temperature to the condensing temperature. Remember, the condensing temp. determines the head pressure. This is sensible heat transfer
- the ref. is condensed from vapor to a liquid (this is latent heat transfer)
- the liquid refrigerant temp. may then be lowered below the condensing temp., or sub cooled. The refrigerant can usually be sub cooled to between 10 F and 20F below the condensing temperature, but is system dependent(this sensible heat transfer.
The Refrigerant Metering Devise
• the warm subcooled liquid is moving down the liquid line in the direction of the metering devise
• liquid lines may give up heat to the surroundings because it came from the system, this will help capacity
• an orifice is a small restriction of fixed size in the line
• this devise holds back the full flow of refrigerant and is one of the dividing points between the high side and the low side
• only pure liquid must enter
• after leaving the orifice it is a mixture of about 25% vapor and 75% liquid
• a pressure change is created by the metering devise and this pressure change changes the boiling point so that the refrigerant loses some of it capacity
• this is called flash gas |
