Parts & Process involved: Evaporator – Refrigerant Vapourization Absorber – Refrigerant (Vapour) –Absorption by Absorbent Generator – Regeneration of Refrigerant& Absorbent Condenser – Liquefaction of Refrigerant Totally we have 2 Shells: Lower Shell – Evaporator and Absorber Upper Shell – Generator and CondenserVapour Compression Machine
The standard vapor compressionrefrigeration system is acondenser, evaporator, throttlingvalve, and a compressor.In the vapor-compression refrigeration cycle, refrigerantenters the evaporator in the form of a cool, low-pressuremixture of liquid and vapor. Heat is transferred from therelatively warm air or water to the refrigerant, causing theliquid refrigerant to boil. The resulting vapor is then pumpedfrom the evaporator by the compressor, which increases thepressure and temperature of the refrigerant vapor.
Absorption refrigerationsystems replace thecompressor with agenerator and an absorber.Refrigerant enters the evaporator in the form of a cool,low-pressure mixture of liquid and vapor. Heat is transferredfrom the relatively warm water to the refrigerant, causing theliquid refrigerant to boil.
Key Characteristics1. Ammonia is a refrigerant and water is an absorbent;2. Used for applications requiring temperatures in the range of -40ºC to Generally +5ºC. The preferred heat source temperatureis 95ºC to 180ºC;3. Available as very small pump-less systems to largerefrigeration capacities in applications ranging from domesticrefrigerators to large cold storages;4. Unlike lithium bromide system, these chillers operate atmoderate pressures and NO vacuum is required till -30ºC;5. Unlike lithium bromide system, these chillers do not suffer fromthe problem of crystallization.
Problem Power supply failure Reason EB supply failure Remedy Alarm acknowledgement Reset the alarm after 2 minutes. Problem Internal anti freeze trip Reason Brine inlet & outlet temperature too low. VAM refrigeration temperature is too low. Liquid refrigeration water temperature too low. Remedy Alarm acknowledgement, after 15 minutes, reset the alarm..
Problem Compressor discharge pressure too high. Reason Refrigerant maybe switched off.HTG temperature maybe too low Remedy Acknowledgement of alarm, wait for HTG temperature to reach above 100oC& then switch on refrigerant pump, after resting the alarm. Problem Brine DP switch trip. Reason Brine inlet and outlet pressure maybe below marked. Air maybe present in the circulation line. Remedy Check the pressure gages. (especially brine inlet and outlet pressure gages) check whether the above mentioned values are beyond marked values. Reset the alarm after acknowledging it..
Problem Oil flow switch trip. Reason Maybe due to high pressure. Remedy Acknowledge the alarm. Reset the alarm after 3 minutes. Problem Compression motor winding trip. Remedy Reset in the presence of an electrician.
Problem Compression suction pressure trip Reason Compression suction pressure may be too low This could be found by looking at the suction. Expansion valve maybe closed off. Remedy Acknowledge the alarm. Give the machine dilution after 15 minutes. Check whether suction and pressure gages are the same. While resting the machine, look into the expansion valve sight glass andformed see if there water is flowing. Bubbles will be in case water is flowing.
Problem Cooling water pump interlock. ReasonFailure of cooling water pump. Failure of cooling water fan. Remedy Acknowledge the alarm. Check the cooling water pressure gage valve.Reset after few minutes. Problem Compression motor protection trip. Remedy Reset.
Generator:The purpose of the generator is to deliver the refrigerant vapor to therest of the system. It accomplishes this by separating the water (refrigerant)from the lithium bromide-and-water solution. In the generator, a high-temperature energy source, typically steam or hot water, flows through tubesthat are immersed in a dilute solution of refrigerant and absorbent. The solutionabsorbs heat from the warmer steam or water, causing the refrigerant to boil(vaporize) and separate from the absorbent solution. As the refrigerant is boiledaway, the absorbent solution becomes more concentrated. The concentratedabsorbent solution returns to the absorber and the refrigerant vapor migrates tothe condenser.
Condenser:The purpose of condenser is to condense the refrigerant vapors.Inside the condenser, cooling water flows through tubes and the hot refrigerantvapor fills the surrounding space. As heat transfers from the refrigerant vapor tothe water, refrigerant condenses on the tube surfaces. The condensed liquidrefrigerant collects in the bottom of the condenser before traveling to theexpansion device. The cooling water system is typically connected to a coolingtower. Generally, the generator and condenser are contained inside of thesame shell.
Expansion Device:From the condenser, the liquid refrigerant flows through anexpansion device into the evaporator. The expansion device is used tomaintain the pressure difference between the high-pressure (condenser)and low-pressure (evaporator) sides of the refrigeration system by creating aliquid seal that separates the high-pressure and low pressure sides of thecycle. As the high-pressure liquid refrigerant flows through the expansiondevice, it causes a pressure drop that reduces the refrigerant pressure tothat of the evaporator. This pressure reduction causes a small portion of theliquid refrigerant to boil off, cooling the remaining refrigerant to the desiredevaporator temperature. The cooled mixture of liquid and vapor refrigerantthen flows into the evaporator.
Evaporator:The purpose of evaporator is to cool the circulating water. Theevaporator contains a bundle of tubes that carry the system water to becooled/chilled. High pressure liquid condensate (refrigerant) is throttled downto the evaporator pressure (typically around 6.5 mm Hg absolute).At this low pressure, the refrigerant absorbs heat from the circulatingwater and evaporates. The refrigerant vapors thus formed tend to increase thepressure in the vessel. This will in turn increase the boiling temperature andthe desired cooling effect will not be obtained. So, it is necessary to removethe refrigerant vapors from the vessel into the lower pressure absorber.Physically, the evaporator and absorber are contained inside the same shell,allowing refrigerant vapors generated in the evaporator to migrate continuouslyto the absorber.
Absorber:Inside the absorber, the refrigerant vapor is absorbed by the lithiumbromide solution. As the refrigerant vapor is absorbed, it condenses from a vaporto a liquid, releasing the heat it acquired in the evaporator.The absorption process creates a lower pressure within the absorber.This lower pressure, along with the absorbent’s affinity for water, induces acontinuous flow of refrigerant vapor from the evaporator. In addition, theabsorption process condenses the refrigerant vapors and releases the heatremoved from the evaporator by the refrigerant. The heat released from thecondensation of refrigerant vapors and their absorption in the solution isremoved to the cooling water that is circulated through the absorber tube bundle.