Views: 0 Author: Site Editor Publish Time: 2022-08-26 Origin: Site
Aircraft air conditioners come from the bleed air of the air source system. The bleed air temperature of the air source system is very high and cannot be directly applied. The air conditioner must be cooled by the cooling component. The cooling component is cooled by the bleed air of the air source system and the external punch. The heat exchange of air is realized.
The bleed air of the air source system first conducts preliminary cooling and depressurization through the heat exchange between the main radiator and the ram air, and then enters the compressor part of the ACM. After the secondary heat exchange of the ram air, it enters the ACM turbine part to impact the turbine to perform work and cool down again, and then enters the water separator and then enters the air conditioning system.
In the whole process, according to the law of conservation of energy, energy can neither be generated nor destroyed, but can only be converted from one form to another, so the cooling only has the internal energy of high temperature bleed air (expressed as temperature and pressure) and ram air Heat exchange can only be achieved.
The heat exchange can only be accomplished through primary and secondary heat exchange. Therefore, the cooling effect of the bleed air is determined by the flow and temperature of the heat exchanger and the ram air. The work done by the partial impact of the ACM turbine is only to convert the energy entering the bleed air into the turbine through the ACM compressor to increase the internal energy of the bleed air entering the secondary heat exchanger. The stage heat exchanger exchanges heat with the ram air to improve the exchange efficiency.
Working principle of air conditioner heat exchanger:
1. Heat exchange area A
2. Heat exchange temperature difference △t
3. Thermal conductivity η
For the molded heat exchanger, the heat exchange area is fixed, so in order to improve the effect, we can only start from the two aspects of temperature difference and heat conduction effect.
The temperature difference is the temperature difference between the air source bleed air and the ram air. The larger the Δt, the better the effect. Δt = t bleed air - t ram air, and the ram air on the ground is constant at a specific location. Therefore, in order to increase Δt, Raising t bleed air becomes the only key point, the bleed air for the main radiator is constant, so the main radiator Δt is constant, and the bleed air for the secondary radiator t is determined by the compression effect of ACM, and the ACM efficiency is high t lead The higher the gas, the higher the Δt.
From the working principle, we know that the air-conditioning bleed air is to make high-temperature hot air into low-temperature and low-pressure cold air, mainly through the heat exchange of the main and secondary radiators. The efficiency of the radiator depends on the amount of heat exchanged, and the amount of heat that affects the heat exchange is mainly due to the following aspects according to the heat exchange principle Q0=η *△t*A:
1. The ACM itself is dirty or damaged, affecting the blade geometry.
2. Thermal conductivity η: According to the principle of thermal conductivity, the internal and external dirt of the radiator causes the thermal conductivity of the thermal conductive material to be poor, and the heat transfer route is long. The amount of ram air on the ground is determined by the speed of the ACM, the fan efficiency and the sealing of the bypass valve. The fan efficiency is mainly caused by whether the geometry is damaged and dirty, and the bypass valve is not well sealed or lost. This will reduce the amount of ram air, so the loss of the bypass valve will also objectively cause poor cooling effect.
3. Whether the turbine blades are damaged or difficult to rotate, whether the turbine outlet temperature is low enough, the size of the outlet airflow, and the compression efficiency is mainly affected by the following aspects: ACM speed and ACM geometry. The high ACM outlet pressure is caused by the low ACM speed, and the high ACM outlet pressure is caused by the dirty filter of the water separator or the freezing of the lower limit control. Dirty or worn air shafts also affect RPM. Therefore, in order to increase Δt, it is necessary to increase t bleed air, and t bleed air is determined by the ACM compression effect, and the ACM itself is dirty or damaged, and the water separator filter is dirty, or caused by freezing, which affects the ACM compression effect. .
4. The inlet and outlet temperatures of the reheater and condenser can be compared with other aircraft, whether the condensed water has been significantly reduced, etc. Regarding the condenser, the 5157 aircraft managed by our company reacted to the air conditioning condenser crack on August 18, 2011, and then China Southern Airlines issued a non-card for checking the trachoma of the condenser crack. In 2013, China Southern Airlines found that the NG aircraft reacted for 5 times of condensation Cracks and trachoma appear in the device, and the inspection of this part should be strengthened during the regular inspection work.
5. Check that all components are installed correctly and there is no air leakage.
6. It can be checked whether the valve of the component is opened normally and whether the flow control is normal.
7. Whether the heat exchanger is blocked, leaks, and when has it been cleaned.
By analyzing the working principle of the heat exchanger, according to the law of energy conservation, we can judge whether the performance of the air conditioner is declining and whether the cooling effect is poor by measuring and analyzing the performance of the ram air system, the heat exchanger and the ACM, and the outlet temperature of the components.
1. For the performance of the stamping system, we mainly judge the performance of the stamping system by measuring the air flow of the stamping system. The exhaust fan of the stamping system is coaxial with the ACM, so the speed and performance of the ACM can also be indirectly judged.
2. For heat exchangers, the performance of the heat exchanger is mainly judged by measuring the temperature difference between the inlet and the outlet.
3. For ACM, mainly by measuring the temperature difference between the inlet and the outlet of the compressor part, the temperature difference between the inlet and the outlet of the turbine part, and the flow rate of the ram air, and checking the installation time of the ACM, to determine whether the ACM performance declines.
4. Judge the performance of the entire module by measuring the temperature at the outlet of the module.
