# Experimental Method for Flow Calibration of the Aircraft Liquid Cooling System
## 3 Establishment of Experimental Platform  
For the aircraft liquid cooling system, the flow measurement is really difficult. Firstly, the pipeline of the aircraft liquid cooling system cannot meet the length requirements of the straight pipe before and after the throttle; Secondly, the installation of the throttle device on the pipe can affect the flow resistance characteristics of the whole system, which can also increase the possibility of the leakage of the coolant. In the technical index of a certain type of the aircraft liquid cooling system, the imported pressure of the radar components is 930 kPa, and the configuration of a throttle device may cause 50 kPa or even greater pressure loss. The pressure loss has a great impact on the performance of the whole system, and may even make the liquid cooling system work abnormally. Therefore, for the aircraft liquid cooling system, the flow calibration needs to learn from the flow measurement principle of differential pressure flowmeter, and carried out the ground experiments of flow calibration. Based on the principle of the differential pressure method, design and establish the experimental platform to conduct the flow calibration of the aircraft liquid cooling system, and the corresponding flow rate curve can be obtained through the ground calibration experiments. According to the flow calibration plan proposed above, the flow calibration experimental platform of the aircraft liquid cooling system is established in Figure 2.  
As shown in Figure 2, the cooling duct of the radar exit is a tube with variable diameters of 16 mm, 18 mm and 20 mm, and there is an elbow bend. Similar to the throttle, the pressure drop will also be caused at the inlet and outlet of the variable diameter pipe and the elbow bend. Therefore, the flow rate coefficient \(a\) can be obtained at the variable diameter pipe and the elbow bend by the ground calibration experiments, so as not to destroy the original cooling system layout or increase the additional pressure drop. The experimental system consists of 7 parts: a pump, a filter, a heater, an imported valve, a flowmeter, an exported valve and an experimental sample. The connection of the flow calibration experimental system is shown in Figure 3.  
Figure 2: Schematic diagram of the aircraft liquid cooling system. As shown in Figure 3, the pump is used to provide continuous fluid; the heater is mainly used to regulate the temperature of the coolant and heat the coolant in the experimental system; the temperature sensor is used to measure the temperature of the coolant; the flowmeter is used to measure the flow of the coolant in the experiment sample; the function of the inlet valve is to adjust the liquid pressure into the entrance of the experiment sample by adjusting the opening degree of the inlet valve; pressure sensors are used to measure the pressure before and after the experiment sample. The pipe, which needs to be detected, is first connected to the experiment platform. Under different pressures and temperatures, the flow of the ethylene glycol through the pipe is adjusted by the pump in the experimental platform, and the pressure drop at the import and export of the experimental sample is measured by the pressure sensors, which are set before and after the experimental sample. On the ground experimental platform of the standard flow device, the temperature, pressure and flow of the liquid cooling system are changed according to the experimental requirements, and the relation curve of the pressure drop and flow can be obtained, and the correction curve of the temperature and pressure can be obtained at the same time. The coolant is pressurized in the liquid pump, and filters into the electric heater through the filter. When the coolant is heated to the experimental required temperature, the coolant is flowing into the experimental tube through the regulating value. Then, the coolant flows back to the liquid pump through the flow control valve, and the circulation process is completed.