BASIC REFRIGERATION - BASIC REFRIGERATION BASIC...

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Unformatted text preview: BASIC REFRIGERATION BASIC REFRIGERATION WHAT IS REFRIGERATION? The Process of Reducing Heat Energy WHAT IS REFRIGERATION? The Process of Reducing Heat Energy • One example is by the removal of sensible heat, chilled water from 10 C to 5 C. WHAT IS REFRIGERATION? The Process of Reducing Heat Energy • One example is by the removal of sensible heat, chilled water from 10 C to 5 C. • Another example is removing latent heat from water at 0 C to change it to ice at 0 C. SENSIBLE HEAT Heat which causes a change in temperature of a substance LATENT HEAT Heat absorbed in the process of changing the state of a substance. o o PRESSURE/TEMPERATURE RELATIONSHIPS WATER 0 psig 100 C • Water at atmospheric pressure (0psig) will boil at 100 C. • This is known as the saturation temperature. • At this temperature and pressure the water will be a mix of liquid and vapour (saturated). PRESSURE/TEMPERATURE RELATIONSHIPS WATER 0 psig 100 C • If at this temperature we continue to add heat the water will change from a saturated liquid into a saturated vapour. • This happens as the water absorbs latent heat. PRESSURE/TEMPERATURE RELATIONSHIPS 20 C Superheat 0 psig 120 C • If the vapour is then further heated above its saturation temperature, the vapour will become superheated. • Superheat is measured as a degree of temperature and is the difference between the saturation temperature and the actual temperature. • When a substance is superheated, it is 100% vapour. PRESSURE/TEMPERATURE RELATIONSHIPS 20 C Sub-cooling 0 psig 80 C • If at the same pressure, (0psig), the actual temperature is below the saturation temperature, the water is sub-cooled. • Sub-cooling is measured as a degree of temperature. • In this example there is 20 C of sub-cooling. • When a substance is sub-cooled it is 100% liquid. PRESSURE/TEMPERATURE RELATIONSHIPS R 134a 0 psig-25 C Water 0 psig 80 C R 22 0 psig-29 C TERMINOLOGY Saturation Point:- The boiling temperature of a substance at a given pressure. Saturation:- A mixture of liquid and vapour at its saturation temperature and pressure. Superheat:- Vapour at a temperature above its saturation temperature, measured in degrees of superheat. Subcooled:- Liquid below its saturation temperature, measured in degrees of subcooling. BASIC REFRIGERATION CYCLE COMPRESSOR EXPANSION VALVE CONDENSER EVAPORATOR BASIC REFRIGERATION CYCLE HIGH PRESSURE, HIGH TEMPERATURE, SUPERHEATED VAPOUR BASIC REFRIGERATION CYCLE HIGH PRESSURE, HIGH TEMPERATURE, SUPERHEATED VAPOUR STAGE 1 THE HIGH TEMPERATURE GAS IS DE-SUPERHEATED AS SENSIBLE HEAT IS TRANSFERED FROM THE REFIGERANT TO THE AMBIENT AIR. AMBIENT AIR THE CONDENSER WORKS IN 3 STAGES BASIC REFRIGERATION CYCLE HIGH PRESSURE, HIGH TEMPERATURE, SUPERHEATED VAPOUR STAGE 2 LATENT HEAT IS TRANSFERED FROM THE SATURATED REFRIGERANT TO THE AMBIENT AIR. THIS CAUSES THE REFRIGERANT TO CONDENSE INTO A LIQUID....
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This note was uploaded on 02/13/2012 for the course MECHANICAL 1234 taught by Professor Zfp during the Spring '11 term at Alexandria University.

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BASIC REFRIGERATION - BASIC REFRIGERATION BASIC...

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