Cabin Cooling Systems PDF

CABIN-COOLING SYSTEMS AMT 2204 INTRODUCTION ⦿ Aircraft-cooling systems, also called air-conditioning systems, are used to reduce the temperature inside an aircraft for crew and passenger comfort. ⦿ The two basic methods of reducing the temperature of aircraft are the Freon Vapor - Cy...

CABIN-COOLING SYSTEMS AMT 2204 INTRODUCTION ⦿ Aircraft-cooling systems, also called air-conditioning systems, are used to reduce the temperature inside an aircraft for crew and passenger comfort. ⦿ The two basic methods of reducing the temperature of aircraft are the Freon Vapor - Cycle machine and the Air - Cycle Machine. ⦿ The Vapor - Cycle Machine is a closed system using the evaporation and condensation of Freon to remove heat from the cabin interior. ⦿ The Air - Cycle Machine uses the compression and expansion of air to lower the temperature of the cabin air. CABIN – COOLING SYSTEM CABIN COOLING SYSTEM PRIMARY HEAT EXCHANGER – Cools the engine/APU bleed air. SECONDARY HEAT EXCHANGER – Removes the heat of compression of the ACM. CABIN COOLING SYSTEM  AIR CYCLE MACHINE ⦿ An air cycle machine (ACM) is the refrigeration unit of the environmental control system (ECS) used in pressurized gas turbine- powered aircraft. Normally an aircraft has two or three of these ACM. ⦿ Each ACM and its components are often referred as an air conditioning pack. VAPOR CYCLE COOLING SYSTEM VAPOR CYCLE COOLING SYSTEM VAPOR CYCLE COOLING SYSTEM The vapor-cycle air-conditioning system is used in reciprocating-engine-powered aircraft and in smaller turboprop aircraft that do not make use of air-cycle machines to reduce the cabin interior temperature. The operation of vapor-cycle machines is controlled by the pilot and may incorporate automatic cutout or interrupt systems. VAPOR CYCLE COOLING SYSTEM These cutout and interrupt systems are used to disengage the refrigerant compressor during demand for high engine power output, such as during takeoff operations or when one engine of a multiengine aircraft has failed. This interruption in compressor operation allows all available power to be used to maintain controllable flight. VAPOR CYCLE COOLING SYSTEM In Aircraft Basic Science. where the nature of gases is discussed, it is shown that the temperature of a gas is directly proportional to its pressure and/or volume. In addition, as heat is added to a solid, it becomes liquid and then a gas. Conversely. as heat is extracted from a gas it becomes a liquid and then a solid. VAPOR CYCLE COOLING SYSTEM As liquids change to a gas (or are vaporized), they absorb heat. This heat is called the latent heat of vaporization. As a given quantity of gas is condensed to a liquid, it emits heat in the same amount that it absorbs when being changed from a liquid to a gas. When a gas is compressed, its temperature increases, and when the pressure on a gas is decreased, its temperature decreases. VAPOR CYCLE COOLING SYSTEM A vapor-cycle cooling system takes advantage of these laws of nature using two heat-exchangers to control the temperature of the cockpit and cabin. One heat exchanger works in a fashion similar to the one previously discussed, taking heat from the closed system, and is called an evaporator. The other heat exchanger draws heat from the air and adds it to the closed system. This heat exchanger is called a condenser. VAPOR CYCLE COOLING SYSTEM The cooling process starts at the compressor, where the refrigerant is in a gaseous form. The function of the compressor is to push the refrigerant, under pressure, through the entire system. As the gas enters the condenser, heat is drawn from the refrigerant and passed to the atmosphere. The cooling of the refrigerant causes it to condense into a liquid. Because of the compressor, the liquid is under pressure. The pressurized liquid is then metered into tiny droplets by an expansion valve. VAPOR CYCLE COOLING SYSTEM Because of the change in form, the pressure past the expansion valve is lowered. The droplets then enter the evaporator, where they draw heat from the air and then change into a gas. As a result of heat being drawn from the air, the temperature of the air is decreased. It is this cooler air that is introduced to the cabin REFRIGERANT 12 A system of this type usually employs Refrigerant 12, also known as Freon 12, as the refrigerant. It is a gas at standard pressure and temperature but becomes a liquid when its pressure is increased sufficiently or when the temperature is reduced to the required level.  The refrigeration cycle, beginning with the compressor, involves the compression of the refrigerant gas, which is comparatively cold and at a low pressure as it leaves the evaporator and flows to the compressor. The compressor is the source of energy required for the operation of the system.  From the compressor, the hot, high pressure gas (vapor) flows into the condenser, which is a heat radiator through which cool air is passed to remove heat from the vapor.  As the refrigerant vapor is cooled in the condenser, it becomes a liquid and flows to the receiver-dryer- filter. The receiver-dryer-filter is essentially a reservoir containing a filter and a desiccant. A sight glass is usually located on top of the receiver to allow observation of the fluid flow through the unit. If bubbles are seen in the fluid, the system refrigerant is known to be low and requires replenishment. VAPOR CYCLE COOLING SYSTEM AIR CYCLE COOLING SYSTEM AIR - CYCLE COOLING SYSTEM AIR – CYCLE COOLING SYSTEM Modern large turbine-powered aircraft make use of air cycle machines to adjust the temperature of the air directed into the passenger and crew compartments of these large aircraft. Although this portion of the discussion of air-cycle machines is directed to the ability to provide cabin- cooling air, it should be noted that the cabin can also be heated and pressurized by the use of an air-cycle machine. AIR – CYCLE COOLING SYSTEM These large aircraft utilize air -cycle cooling because of its simplicity, freedom from troubles, and economy. In these systems, the refrigerant is air. Air-cycle cooling systems utilize the same principles of thermodynamics and the same laws of gases involved in vapor-cycle systems. One principal difference is that the air is not reduced to a liquid, as is the refrigerant in a vapor-cycle system. AIR – CYCLE COOLING SYSTEM The principle of cooling by means of a gas is rather simple. When a gas (air) is compressed, it becomes heated, and when the pressure is reduced, the gas becomes cooled. If a pressure cylinder is connected to an air compressor and compressed air is forced into the cylinder, one can observe that the cylinder becomes warm or even hot, depending upon the level of compression and the rate at which the air is compressed.  AIR – CYCLE COOLING SYSTEM If the cylinder filled with highly compressed air is then allowed to cool to ambient temperature, the pressure in the cylinder will be reduced to a certain degree as the air temperature is reduced. If a valve is then opened and the air is allowed to escape from the cylinder, the temperature of the escaping air will be much lower than the ambient temperature due to the air expanding as its pressure returns to the ambient value. This cold air can then be used as a cooling agent. AIR CYCLE COOLING SYSTEM AIR CYCLE COOLING SYSTEM