A Low-temperature Environment Test Method for a Liquid Cooling System Based on a Normal-temperature Flowmeter

Abstract

The present invention provides a low-temperature environment test method for a liquid cooling system based on a normal-temperature flowmeter, including: the first step: fitting the component flow characteristic curve; the second step: studying the operation of the system. The present invention is applied to the measurement of the system flow rate in the low-temperature environment test of the liquid cooling system: without changing the connection mode of the original aircraft system and maintaining the original appearance of the system, through fine experiments and a large amount of data, a highly reliable measurement result of the low-temperature environment system is obtained in the way of normal-temperature calibration and low-temperature conversion.

Description

Technical Field

[0001] The present invention relates to the field of aircraft environment control, and in particular to a low-temperature environment test method for a liquid cooling system based on a normal temperature flow meter. Background Art

[0002] When aircraft perform missions at high altitudes, the electronic equipment they carry generates significant heat, requiring either air or oil cooling to dissipate the excess heat. The medium used for heat transfer is coolant, and its ability to flow smoothly under extreme conditions determines the proper functioning of the liquid cooling system.

[0003] At low temperatures, the viscosity of the coolant in the system is high, which can hinder flow. To ensure that flow in the conduit is not affected by factors other than low temperatures, the system should have as few components as possible.

[0004] To restore the aircraft's system architecture during flight, the system should not be connected to separate measurement equipment to restore the system's original state as much as possible. Therefore, a highly reliable low-temperature environment test method for the liquid cooling system is required to ensure that the liquid cooling system can be monitored for normal operation with minimal impact on the system.

[0005] Most flowmeters on the market are rated for temperatures as low as -20°C, while aircraft systems can experience temperatures as low as -55°C during operation. Conventional calibration methods are no longer suitable, necessitating a novel circuit modification solution to calibrate the flow characteristic curves of these components. Summary of the Invention

[0006] The present invention provides a low-temperature environment test method for a liquid cooling system based on a normal temperature flow meter, which ensures that the operation of the liquid cooling system can be monitored under extreme conditions.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A low-temperature environment test method for a liquid cooling system based on a normal temperature flow meter, characterized by:

[0009] The first step is fitting the component flow characteristic curve:

[0010] (1) For components in a liquid system at the same temperature, the pressure difference between the inlet and outlet, i.e., the pressure loss, determines the liquid flow rate through the component. This is based on the characteristics of liquid flow: when liquid flows through a pipe or component, it loses some energy to overcome resistance. This energy loss can be represented by the pressure loss of the liquid. The pressure loss is related to the flow state and the Reynolds number. The flow characteristics (inherent characteristics) of a component refer to the relationship between the relative flow rate and the relative pressure loss of the fluid flowing through the component. There are two typical characteristics: linear characteristics and percentage characteristics.

[0011] Linear flow characteristics:

[0012]

[0013] Percentage flow characteristics:

[0014]

[0015] Where:

[0016] Q——flow rate, unit: kg / s;

[0017] Q max ——maximum flow rate, unit: kg / s;

[0018] h——hydraulic loss, unit: m;

[0019] h max ——maximum hydraulic loss, unit: m.

[0020] (2) For multiple sets of experimental data of a component, after defining the horizontal axis (pressure loss) and the vertical axis (flow rate), a best-fit curve can be found to quantify the flow characteristics of the component;

[0021] (3) In view of the limitation of the applicable temperature range of the flow meter, a heater and a cooler are added before and after the normal temperature flow meter. The working power of the heater and the cooler is calculated by the following formula:

[0022] W=Q m C p (t c -t)

[0023] Where:

[0024] Q m ——Mass flow rate, unit: kg / s;

[0025] C p ——Specific heat of coolant, unit: KJ / (kg·℃);

[0026] t c ——The lowest operating temperature of the flow meter, in °C;

[0027] t——coolant temperature in low temperature system, unit: °C.

[0028] (4) For a liquid cooling system with complex branches, the flow characteristic curve of the typical components of the branch (such as cold plate, heat exchanger, etc.) can be drawn as the flow monitoring window of this branch.

[0029] The second step is to study the system operation status:

[0030] (1) Connect the system pipelines and plan the positions and sequences of each component;

[0031] (2) After reducing the environment where the system is located to the specified temperature and pressure, run the system loop;

[0032] (3) Record the pressure loss of specific components, and the flow rate of the loop where the component is located can be obtained according to the flow rate characteristic curve at the corresponding temperature;

[0033] (4) According to the flow rates of the main pipeline and each branch pipeline, the operating conditions of the system under extreme environments can be judged.

[0034] In the first step, it is necessary to calibrate the relationship between the flow rate and the pressure loss of a component at the same temperature. Multiple groups of data can be measured by changing the environmental temperature according to actual needs, and the flow rate characteristic curves of the component at different temperatures can be obtained.

[0035] Step (2) of the first step is based on the least squares method, and various fitting methods such as the straight line fitting method, the polynomial fitting method, and the semi-logarithmic fitting regression can be adopted.

[0036] In step (3) of the first step, each typical component can be connected in series into a loop according to the actual situation, and the pressure loss of each component can be measured at the same temperature and the same flow rate. Change the flow rate and measure multiple groups of data, and the flow rate characteristic curves of each component at a specific temperature can be obtained.

[0037] Since the lowest applicable temperature range of most liquid flow meters on the market can only reach -20°C, for low-temperature systems (the lowest temperature can reach -55°C), the use effect is limited. Therefore, it is necessary to add a regulating component to ensure that the flow rate characteristic curves of typical components can be calibrated under low-temperature conditions.

[0038] For the same loop, different temperatures before and after the system will not affect the mass flow rate of the coolant. As shown in the following formula:

[0039] Q m =ρ·Q v

[0040] In the formula:

[0041] Q m —— The mass flow rate of the coolant, unit kg / s;

[0042] ρ —— The density of the coolant, unit kg / m 3 ;

[0043] Q v —— The volume flow rate of the coolant, unit m 3 / s;

[0044] Taking coolant No. 65 as an example, as the temperature rises, the viscosity decreases, the flow velocity increases, and the volume flow rate increases. As the temperature rises, the density of the coolant decreases. The combined effect of these two factors results in a constant mass flow rate of the coolant.

[0045] The second step is based on the continuity theorem, which states that for a fluid system, the mass flow rate through different components connected in series in the same pipeline is constant. Therefore, the flow rate of a specific component can be regarded as the flow rate of the pipeline it is in.

[0046] Beneficial effects:

[0047] The present invention is mainly applied to the measurement of the flow rate in the liquid cooling system test under low-temperature environments, solving the problem of accurately measuring the flow rate of the main pipeline and each branch pipeline of the system without changing the original appearance of the system (without flow measurement equipment). This method includes two steps: fitting the flow rate characteristic curve of the components and studying the operation of the system, and can calibrate the flow rate characteristics of each typical component of the low-temperature system using most conventional flow meters on the market. Description of the drawings

[0048] Figure 1 is a schematic diagram of the series connection for measuring the flow rate characteristic of components using a conventional flow meter;

[0049] Figure 2 is a schematic diagram of the construction of a low-temperature and low-pressure system; Detailed implementation manners

[0050] The present invention will be described in detail below in conjunction with the drawings and specific implementation manners, but the protection scope of the present invention is not limited thereto.

[0051] A method for testing a liquid cooling system in a low-temperature environment based on a normal-temperature flow meter according to the present invention includes two steps: fitting the flow rate characteristic curve of the components and studying the operation of the system, and can obtain the flow rate characteristic and operation of the system on the basis of restoring the original system construction of the aircraft as much as possible.

[0052] The first step:

[0053] (1) As shown in, connect the liquid cooling components, valves, heaters, conventional flow meters (minimum operating temperature of -20 °C), refrigerators, heat exchangers, cold plates, etc. in series in a loop according to requirements. Arrange pressure sensors and temperature sensors at both ends of the inlet and outlet of each component. As shown in, where P represents pressure, T represents temperature, and the subscript represents the number. Check the tightness of the system to ensure there are no leaks. Figure 1 shown, connect the liquid cooling components, valves, heaters, conventional flow meters (minimum operating temperature of -20 °C), refrigerators, heat exchangers, cold plates, etc. in series in a loop according to requirements. Arrange pressure sensors and temperature sensors at both ends of the inlet and outlet of each component. As shown in, where P represents pressure, T represents temperature, and the subscript represents the number. Check the tightness of the system to ensure there are no leaks. Figure 1 In, P represents pressure, T represents temperature, and the subscript represents the number. Check the tightness of the system to ensure there are no leaks.

[0054] (2) Reduce the ambient pressure of the system to the altitude of 8 Km and the temperature to -20 °C. Keep it warm for a period of time to allow the coolant to also reach the specified temperature.

[0055] (3) Operate the liquid cooling component to start the circulation of the coolant. Control the flow rate to be stable at 14, 16, 18, 20, and 22 L / min respectively, record the pressure and temperature at each measuring point, and the pressure difference between the inlet and outlet of the component is the pressure loss of the component. The same set of data can be measured multiple times and the average value can be taken to ensure the accuracy of the data.

[0056] (4) According to the operation in (3), the change curve of the pressure loss of each component with the flow rate (range 14 L / min to 22 L / min) at a specific temperature can be plotted. Fit the curve into a formula for convenient operation of the next step.

[0057] (5) To calibrate the flow characteristics of the components under lower temperature conditions, the coolant about to enter the normal temperature flowmeter needs to be heated. After measuring the flow rate, it is cooled by a refrigerator and then injected back into the original low-temperature circuit. Taking the required temperature of -25°C and the volume flow rate of 14 L / min of the 65th coolant as an example: The physical property parameters of the coolant are as follows: at -20°C, the density is 1115 kg / s, and the specific heat is 2695 KJ / (kg·°C); at -25°C, the density is 1119 kg / s, and the specific heat is 2657 KJ / (kg·°C). Calculate the heating (cooling) power:

[0058]

[0059] (6) Control the temperature to change from -20°C to -55°C. Every time the temperature is reduced by 5°C, repeat the operations in steps (3), (4), and (5). The flow characteristic curves of different components at different temperatures can be obtained.

[0060] The second step:

[0061] (1) As Figure 2 shown, build the system as required. There can be multiple branches and other devices can be connected in series, but it should be ensured that each branch has a typical component (cold plate or heat exchanger) with a flow characteristic curve. Pressure sensors and temperature sensors are arranged at both ends of the inlet and outlet of each typical component. Check the tightness of the system to ensure there are no leakage points.

[0062] (2) Reduce the ambient pressure of the system to the altitude of 8 Km and the temperature to the required temperature. Keep it insulated for a period of time to make the coolant drop to the specified temperature.

[0063] (3) Operate the system, record the pressure and temperature at the inlet and outlet of each typical component, and the pressure loss is the pressure difference between the inlet and outlet. The same set of data can be measured multiple times and the average value can be taken to ensure the accuracy of the data.

[0064] (4) According to the coolant temperature, find the flow characteristic curve of the typical component at the corresponding temperature. Substitute the pressure loss into the formula to inversely deduce the flow rate of the coolant flowing through the component. Thus, the flow characteristics of the main circuit and each branch in the original system and the operation of the system can be obtained.

Claims

1. A low-temperature environment test method for a liquid cooling system based on a normal-temperature flowmeter, characterized in that, It includes the following steps: The first step, fitting the component flow characteristic curve: (1) The component has a flow characteristic as its inherent characteristic, that is, the relationship between the relative flow rate of the fluid flowing through the component and the relative pressure loss. Two characteristics are adopted: linear characteristic and percentage characteristic; Linear flow characteristic: Percentage flow characteristic: In the formula: Q —— Flow rate, unit kg / s; Q max —— Maximum flow rate, unit: kg / s; h —— Hydraulic loss, unit m; h max —— Maximum hydraulic loss, unit: m; (2) For multiple groups of experimental data of a component, after defining the abscissa of the pressure loss and the ordinate of the flow rate, find an optimal fitting curve to quantify the flow characteristic of the component; (3) Regarding the limitation of the applicable temperature range of the flowmeter, add a heater and a cooler before and after the normal temperature flowmeter respectively; The working power of the heater and the cooler is calculated by the following formula: W = Q m C p (t c - t) In the formula: Q m —— Mass flow rate, unit: kg / s; C p ——Specific heat of coolant, unit: KJ / (kg·℃); t c ——The minimum temperature at which the flowmeter operates, unit: °C; t —— Coolant temperature in the low-temperature system, unit °C; (4) For a liquid cooling system with complex branches, draw the flow characteristic curves of the typical components in the branches as the flow monitoring window of this branch; The second step, analysis of the system operation situation: Connect the system pipeline and plan the position and sequence of each component; After reducing the environment where the system is located to the specified temperature and pressure, run the system loop; Record the pressure loss of a specific component, and the flow rate of the loop where the component is located can be obtained according to the flow characteristic curve corresponding to that temperature; According to the flow rates of the main pipeline and each branch, the operation situation of the system under extreme conditions can be judged.

2. The low-temperature environment test method of a liquid cooling system based on a normal temperature flowmeter according to claim 1, characterized in that: In the first step, calibrate the relationship between the flow rate and the pressure loss of a component at the same temperature, and change the environmental temperature according to actual needs to measure multiple groups of data to obtain the flow characteristic curves of the component at different temperatures.

3. A low-temperature environment test method for a liquid cooling system based on a normal-temperature flowmeter according to claim 1, characterized in that: Step (2) of the first step is based on the least squares method and adopts one of the fitting methods: linear fitting method, polynomial fitting method, semi-logarithmic fitting regression.

4. A low-temperature environment test method for a liquid cooling system based on a normal-temperature flowmeter according to claim 1, characterized in that: In step (3) of the first step, first connect the typical components in series into a loop according to the actual situation, measure the pressure loss of each component at the same temperature and the same flow rate; change the flow rate and measure multiple groups of data to obtain the flow characteristic curves of each component at a specific temperature.

5. A low-temperature environment test method for a liquid cooling system based on a normal-temperature flowmeter according to claim 1, characterized in that: Add an adjustment component to the liquid flowmeter to ensure that the flow characteristic curves of the typical components can be calibrated under low-temperature conditions.

6. A low-temperature environment test method for a liquid cooling system based on a normal-temperature flowmeter according to claim 1, characterized in that: In the second step, regard the flow rate of a specific component as the flow rate of the pipeline where it is located.

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