Discussion AirCond Juwe

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2014885172

DISCUSSION a) Answer all the problems in the experimental, and discuss the results obtained by explaining the factors that contributes to the air property changes for each process problems. 1. Process A (NO PROCESS)

No process occur, so we can assume that there are no changes in temperature. There is no factors that contribute to the air property changes for this process A. 2. Process B (Sensible Heating)

Temperature rise for dry buld and wet buld are affected by heat exchanged by a body or thermodynamic system that changes the temperature. The amount of moisture for simple heating and cooling remains constant because no moisture is added or removed into the air stream. Therefore, the specific humidity at the inlet and the exit remains equal ( i =  e ). 3. Process C (Steam Humidification) Simple heating processes produced low relative humidity (air is dry), because the moisture amount is constant (mv and  constant) but the maximum moisture absorption capacity (mg) increases with temperature rise

3. Process D (Cooling and Dehumidification) Specific humidity of air remains constant during a simple cooling, but its relative humidity increases due to lower amount of maximum moisture (mg) that can be absorbed as the air temperature decreases. Air is allowed to cool at a longer period until it reaches its dew point (saturation state).

b) Find the schematic of a modem air-conditioning system with advanced air treatment processes and explain the function of the main devices.

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Air Filter Air filtration is essentially the insurance of a higher quality of air in indoor spaces. It is the procedure in which the harmful aspects of the atmosphere, such as bacteria, are withheld and the non-harmful aspects are released. Bacteria and viruses are not easy to remove from the air, due to their miniscule size and the fact that they reproduce so quickly. The usual size of bacteria is smaller than that of a pin head so filtration is difficult through normal methods. The speed at which they reproduce creates danger. And as so much of our lives is in an indoor atmosphere it is obvious that the air has to be filtered. Air filtration is important for indoor atmospheres because the work place is becoming increasingly dangerous due to either smoking or illnesses. As many illnesses are passed through air, it is sensible to filter air to sustain a healthy workforce. Filtration reduces allergies and the threat of asthma attacks to sufferers.

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Compressor Compresses the refrigerant from low pressure (low temperature) to high pressure (high temperature). This conversion raises the boiling point to higher temperature levels, facilitating elimination of the heat brought by the outdoor air.

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Condenser This component receives gas at high pressure and high temperature from the compressor. In air-cooled condensers, the metallic surfaces cool the gas which changes status and turns to liquid. In the case of water-cooled condensers, it is the circulation of the water that produces the same cooling effect.

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Evaporator Evaporator is an important component together with other major components in a refrigeration system such as compressor, condenser and expansion device. The reason for refrigeration is to remove heat from air, water or other substance. It is here that the liquid refrigerant is expanded and evaporated. It acts as a heat exchanger that transfers heat from the substance being cooled to a boiling temperature.

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Receiver Drier Act as a temporary storage containers for oil and refrigerant when neither are needed for system operation (such as during periods of low cooling demand). This is the “receiver” function of the receiver/drier. Most receiver/driers contain a filter that can trap debris that may be inside the A/C system. Receiver/driers contain a material called desiccant. The desiccant is used to absorb moisture (water) that may have gotten inside the A/C system during manufacture, assembly or service. Moisture can get into the A/C components from humidity in the air. This is the “drier” function of the receiver/drier.

c) Explain with suitable diagrams the operation and arrangements in an automotive airconditioning unit.

A vehicle’s air conditioning system does not create cold air. It actually takes the heat and moisture out of the air that is already in your car, leaving behind cooler air. Having a good understanding of how the components work can help to explain the methods of repairs in the air conditioning system. The refrigerant resides in the a/c system. The a/c compressor initiates the high-side of the system where it is compresses the refrigerant into a high-pressure state causing it to liquefy. It travels through the high-pressure lines to the condenser. The condenser which is similar to a small radiator, puts the liquid in contact with fresh air on the outside of the vehicle, which absorbs the heat from the liquid. It then flows into the expansion valve or orifice tube where it is restricted and becomes gaseous into the low-pressure side of the a/c system. Then it flows into the receiver dryer/accumulator that contains a desiccant bag to remove and collect unwanted moisture/water and impurities. The clean gaseous refrigerant then travels through the tubing into the evaporator (that is usually located in the passenger compartment of the dash). Refrigerant in its gaseous state is now able to absorb heat from the air passing through the evaporator fins, leaving behind the cooler air. Fans blow this cooler dry air into the car’s cabin. The refrigerant travels back to the compressor in the suction hose of the a/c system to get compressed back into the high-pressure gas and begin the process again.

The refrigerant also carries dispersed oil that helps to keep the air-conditioning compressor lubricated while operating. Refrigerant staying charged or in a full state is crucial to the proper operation and lubrication of the a/c compressor. R-12 used to be the commonly used refrigerant up to 1993. All vehicles that were produced in 1994 and later were required by the Environmental Protection Agency to be equipped with R-134 refrigerant, which was determined to be better for the environment. There were also stricter regulations enforced against the leakage and handling of refrigerant and the repairing of a vehicles a/c system. If the refrigerant level gets low, the a/c system can still operate, even though it may lose some of its cooling effect, or it can shorten the cycle of operation, and it can cause damage due to the compressor not being properly lubricated while operating. Checking pressures of the a/c system while in operation can give an indication of low refrigerant, but it cannot tell you how low the refrigerant is. If the refrigerant level is low, it is due to a leak that has developed in the system.

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2014885172

CONCLUSION As a conclusion, the Recirculating Air conditioning unit may use to demonstrate and evaluate most of the processes found in practical air conditioning plant, such as heating, cooling, humidification, dehumidification air stream. Sometime two or more of these process are needed to bring air to desired temperature and humidity level. Various air conditioning processes in psychrometric chart. Notice that simple heating and cooling processes appear as horizontal line on this chart since moisture content of the air remains constant (ω = constant) during this processes. Air is commonly heated and humidified in winter and cooled and dehumidified in summer. Notice how these processes appear on the psychrometric. The objective to observe

and understand the changes in air properties as it is treated in a basic air-conditioning unit is achieved.