Some standard content:
Standard SJ3224--89 of the Ministry of Machinery and Electronics Industry of the People's Republic of China
Thermal Design Specifications for Airborne Radar
Published on February 10, 1989
Implemented on March 1, 1989
Approved by the Ministry of Machinery and Electronics Industry of the People's Republic of China Standard of the Ministry of Machinery and Electronics Industry of the People's Republic of China Thermal Design Specifications for Airborne Radar
1 Subject Content and Scope of Application
1.1 Subject Content
This specification specifies the basic requirements for thermal design of airborne radar. 1.2 Scope of Application
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This specification applies to thermal design requirements, thermal design procedures, thermal design tests and thermal design appraisals for airborne radars. 2 Reference standards
GB1920
GB2903
GB4993
GJB267
3 Terms and symbols
3.1 TermswwW.bzxz.Net
Standard atmosphere (part below 30 km)
Copper-Constantan thermocouple wire and scale
Nickel-chromium-steel nickel (Constantan) thermocouple wire and scale General specifications for airborne radar design
3.1.1 Temperature critical components
Components whose temperature may approach the maximum allowable operating temperature when the radar is working. 3.1.2 Ambient air temperature
The air temperature value within 75mm from the geometric center of each major surface of the radar chassis. 3.1.3 Average ambient temperature
is used to describe the combined effect of the ambient air temperature of the radar and the radiation surface temperature of the equipment compartment surrounding the radar chassis, and the average temperature value with area as the weighting factor, see formula (1) 3.1.4 Average temperature of components inside the aircraft
is used as the characteristic temperature of the reference thermal potential when conducting radar trend analysis, and is the average temperature of the components with power as the weighting factor, see formula (26).
3.1.5 Ram air
The relative movement between the aircraft and the oncoming air during flight makes the air introduced into the aircraft by the pipeline have a certain speed and pressure. This air is called ram air.
3.1.6 Cabin exhaust
The air of the aircraft environmental control system (abbreviated as the environmental control system) is the air discharged through the valve after completing the cabin environment control.
Approved by the Ministry of Machinery and Electronics Industry of the People's Republic of China on February 10, 1989 and implemented on March 1, 1989
3.1.7 Radar power consumption
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In thermal design, radar power consumption refers to all the electrical power converted into heat in the radar. Radar power consumption is equal to the input electrical power (the output power should be deducted from the transmitting extension). 3.1.8 Heat flux density
The heat dissipated per unit surface area of radar or electronic components is called surface heat flux density (W/m); the heat dissipated per unit volume is called volume heat flux density (W/m) 3.2 Symbols
The symbols used in this specification shall be as specified in Table 1
Cross-sectional area of pipe
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Convection heat transfer surface area
Surface area of the outer surface of the radar chassis at the nth direction Total area of the outer surface of the chassis
Specific heat of coolant, or specific heat of cooling air at constant pressure Inner diameter of pipe or equivalent diameter
Aircraft resistance
Equivalent resistance caused by air drawn out by compressor Moving disk resistance caused by ram air
Equivalent resistance caused by aircraft shaft power consumed by radar cooling system Equivalent aircraft resistance increment caused by cooling system Surface effective coefficient
MOODY ) Friction coefficient
Altitude
Total drag loss of coolant (air) flow channel Friction drag loss
Local drag loss
Aircraft lift
Characteristic dimensions of surfaces with different characteristics and spots Pipeline length
Flight Mach number
Mean time between failures
Atmospheric pressure at flight altitude
Power consumption of component numbered n
Ram air pressure
Consumption of aircraft shaft power
Coolant mass disk flow
Coolant volume flow
Contact thermal resistance between chassis and mounting bracket Compressor compression ratio
Pa;mmHg
Thrust fuel consumption
Ambient air temperature
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Continued Table 1
Average ambient temperature|| tt||Ambient air temperature refers to the temperature within 75mm from the geometric center of the surface at the nth position of the chassis
Atmospheric overflow at flight altitude
The wall temperature of the equipment compartment corresponding to the nth position of the chassis Temperature of the equipment compartment mounting bracket
Critical component temperature
Average component temperature
Surface temperature of component numbered n
Cooling air (cold air) temperature
Cooling air temperature at the inlet of the duct
Cooling air temperature at the outlet of the duct
Ram air temperature
Turbine inlet air temperature
Convection heat transfer surface temperature
Surface temperature of the nth surface of the radar chassis
Surface temperature at the connection between the radar chassis and the mounting bracket Average cooling air flow rate
Exit air flow disk
Ram Air flow rate
Mass of radar cooling system itself
Total mass of aircraft takeoff
Ratio of takeoff fuel loading tray to takeoff total massConvective heat transfer coefficient
Radiation coefficient
Radiation coefficient of equipment cabin wall
Radiation coefficient of radar chassis surface
Local resistance coefficient
kg/N·h
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Continued Table 1
Correction factor for altitude
Cooling air density
Radiation heat transfer
Convective heat transfer
Conduction heat transfer
4 Thermal design environment and cold source of equipment cabin
4.1 Thermal design environment
The thermal design environment of radar equipment cabin (referred to as equipment cabin) refers to the parameters such as temperature, humidity and air pressure in the cabin. The main factors affecting temperature
8. Atmospheric temperature at flight altitude;
b. Aerodynamic heating effect;
Solar radiation;
Heat generated by radar and other electronic equipment in the equipment cabin; coolant entering the equipment cabin,
Structure and materials of the equipment cabin.
Main factors affecting air pressure
Flight altitude;
b. Whether the equipment cabin has sealing and pressurization facilities. 4.1.3 Determination of equipment cabin ambient temperature
During the flight of the aircraft, the temperature of the equipment cabin wall is not necessarily the same as the air temperature in the cabin, and there are also differences relative to the various surfaces of the radar chassis. The average ambient temperature uses area as a weighting factor to reflect the comprehensive influence. When used in various calculations and when a numerical value is used to represent the ambient temperature, it is calculated by the following formula: Tbavg
Wherein: Travg - average ambient temperature, K; ZA.(Tha +Tm)
A. Surface area of the nth orientation of the outer surface of the radar chassis, m; A - total area of the outer surface of the radar chassis, m2; Tn ambient air temperature, refers to the temperature value within 75mm from the surface geometric center of the nth orientation of the radar chassis, K;
The wall temperature value corresponding to the nth orientation of the equipment compartment surrounding the radar chassis, K. Thn
In principle, the ambient temperature of the equipment compartment is provided by the aircraft design according to the aircraft ambient temperature technical conditions. When it is difficult to provide T according to formula (1)-5-
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, T, value (arithmetic mean of T in each orientation) can be provided. The radar developer may also use the environmental stress specified in the classification category of the radar as the basis for thermal design in accordance with the provisions of Article 1.2 of GJB267.
4.1.4 Equipment cabin pressure
The air pressure of an unsealed equipment cabin changes with the flight altitude. The relationship between altitude and air pressure should comply with the provisions of GB1920.
The pressure of the pressurized equipment cabin is specified by the general technical conditions of the aircraft. The air pressure data of the equipment cabin environment is provided to the radar developer by the aircraft designer based on the flight mission, together with the ambient temperature value.
4.1.5 Equipment cabin humidity
The main point of considering the humidity of the equipment cabin is to avoid the hazards caused by condensation and icing, which is specified by the general technical conditions of the aircraft.
4.2 Cold Source
The heat dissipated by the radar is absorbed and taken away by the cold source. The cleanliness requirements of the cold source should be fully paid attention to. The following cold sources can be used on the aircraft.
4.2.1 Natural (surrounding) environment
The temperature of the equipment cabin of a low-speed flying aircraft is relatively low. The heat dissipated by the radar can be directly dissipated into the space or aircraft components, and then transferred to the outside of the aircraft.
4.2.2 Ram air
When ram air is used to cool the radar, the temperature and pressure of the ram air are related to the flight Mach number, and the calculation formula is:
T,=(1+0.2M2)Tbo
Where: T ram air temperature, K;
- atmospheric temperature at flight altitude, K;
M--flight Mach number,
The actual temperature value obtained is slightly lower than the result calculated by the above formula. P,=Pbo(1+0.2M*)3.5...
Where: P-ram air pressure, Pa; Pbo-atmospheric pressure at flight altitude, Pa. (2)
The above formula is for the adiabatic compression process, which is actually a variable process. The ram pressure increase value (P-Pbo) is only 50%~70% of the calculated value.
4.2.3 Aircraft environmental control cooling air
This cooling air comes from the compressed air of the engine (i.e. the air drawn out of the compressor). After it passes through the heat exchanger and is initially cooled by the ram air, it is further expanded and cooled in the turbine cooler. It is then sent to the equipment cabin as a cooling source through accessories such as the water separator temperature control valve, as shown in Figure 1. The pressure, temperature and flow rate of the air after the turbine expansion change with the aircraft flight parameters. Therefore, when using it as a radar cooling air, the pressure, temperature and flow rate of the air after the turbine expansion change with the aircraft flight parameters. When designing, several typical design conditions should be specified, such as low-altitude flight, cruising flight, maximum flight altitude, maximum flight speed, slow flight or taxiing. At present, the cooling air parameters that can be provided by the turbine coolers commonly used in military single- and double-seat aircraft are as follows: flow rate: 80~600kg/h;
pressure: less than 40×10°Pa
temperature: -18~+20℃
4.2.4 Cabin exhaust
When the cabin exhaust is used as a cooling source, it can provide a temperature of less than 40℃, which is not too high. The pressure of 1200Pa and the wind source with large flow rate can be used as a cooling source to save a set of environmental control systems dedicated to the equipment compartment, thereby improving the overall performance of the aircraft. 4.2.5 Fuel
The fuel of the jet engine is generally aviation kerosene. The fuel consumption during the flight of the aircraft is very large. It is a cooling source with a large heat capacity. The fuel consumption of a single or double-seat military aircraft can reach 3000kg/h. When its temperature rises by 1℃, it can absorb 1700W of heat. The usable temperature of the fuel is 7~49℃. Ram air
Force regulator
Outside the room
Heat exchanger
Compressor
Load throttle orifice loader
Limiting valve
Figure 1 Block diagram of aircraft environmental control system
Temperature control valve
To electronic equipment
When using fuel as a cold source, the radar adopts a liquid cooling system, and the heat is taken out by the liquid cooling system and transferred to the fuel by the "fuel-coolant" heat exchanger in the fuel pipeline of Shenlian, or to the fuel of the fuel circulation system connected to the fuel tank.
4.2.6 Other cold sources
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When the radar adopts the consumable evaporative cooling method, water, Freon, liquid nitrogen and other cooling media are often used as cold sources. 5 Thermal design technical requirements
5.1 Thermal design environmental conditions
The thermal design environmental conditions of the radar on the aircraft refer to: a. b. Maximum and minimum ambient temperature, see Article 4.1.1; b. Ambient air pressure; c. Ambient humidity; d. Typical radar working environment state formed by the combination of air pressure and temperature e. Radar continuous working time; f. Combination of ambient temperature and time, temperature requirements for certain short-term harsh environments. For example, short-term high temperature during supersonic flight; short-term working point with minimum (or zero) cooling air flow during low-speed flight or taxiing: tolerance requirements when the environmental control system loses control, etc. 5.2 Lingyuan See Article 4.2. 5.3 Radar power consumption See Article 3.1.7, 5.4 Operating temperature of components in the radar The maximum allowable operating temperature of components in the radar should be determined according to the mean time between failures (MTBF) required by the radar.
5.5 Noise
When necessary, the limit index of the noise caused by the radar cooling system can be specified. 5.6 Volume and weight
The volume and weight of the radar's own cooling system should be included in the radar's volume and weight index, and can be specified separately when necessary.
5.7 Cooling system control and safety protection
The cooling system working procedure should be guaranteed by a control device, and it can automatically protect when the system fails or other factors cannot meet the cooling requirements.
5.8 Others
Whether insulation, constant temperature, etc. are required,
6 Common cooling methods and selection principles 6.1 Selection principles of cooling methods
The selection of cooling methods should not only be based on the heat flux density of the radar, but also on the conditions for the aircraft to provide a cold source. The heat transfer coefficient and corresponding surface heat flux density of common cooling methods are shown in Table 26.1.1 Radars with low heat density or extensions should preferably adopt natural cooling solutions, and use self-contained fan solutions to improve heat excitation capabilities when necessary.
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6.1.2 When using the aircraft cooling source to dissipate heat, cabin exhaust is preferred. When the cabin exhaust cannot meet the cooling requirements, a dedicated aircraft environmental control system can be used to provide cold air. 6.1.3 When the radar has a higher power consumption or the radar has components cooled by liquid, a cooling solution using fuel as the cooling source is generally used.
6.1.4 Evaporative cooling is suitable for cooling of heating components with high surface heat flux density, or when the heating components and their auxiliary components have constant temperature requirements, cold air or fuel should be used for secondary cooling. Table 2
Cooling method
Natural heat exchange with air
Natural convection with water
Forced convection with air Flow (air cooling)
Oil forced convection (cooling)
Water forced convection (water cooling)
Water boiling (evaporative cooling)
Water vapor film condensation
Organic liquid vapor film condensation
Heat transfer coefficient
230~580
25~150
60~5000
3500~11000
Maximum 54000
26000~11000
3800~1800
Note: 1) When the temperature difference between the heat exchange surface and the medium is 25K; 2) When the temperature difference between the heat exchange surface and the medium is 1~10K. Surface heat flux density W/cm
(When the temperature difference between the heat exchange surface and the medium is 40K) 0.024~0.064
Maximum 135)
0.38~1.82)
6.1.5 Equipment outside the equipment cabin should adopt independent cooling methods, such as natural cooling, built-in fan, ram air cooling, consumable evaporative cooling, etc. 6.1.6 Equipment using ram air as the cooling source should be prevented from the low temperature during high-altitude and low-speed flight, and the condensation and icing problems that may occur when the equipment is "cooled through" at low temperatures enters a high-temperature and high-evacuation environment. 6.2 Natural cooling
Natural cooling is mainly achieved through conduction, convection and radiation heat exchange. The natural heat dissipation of the radar chassis to the outside is the sum of the three. 6.2.1 The convective heat transfer capacity decreases as the air density decreases. The calculation formula for the convective heat exchange plate is: D = Z4.54Ancbn(Twn - Tba)125.. In the formula:
is the convective heat transfer capacity, W;
is the surface temperature of the nth surface of the chassis. The temperature of the geometric center point of the surface is expressed as Tw
, K;
ambient air temperature refers to the temperature value within 75mm from the geometric center of the surface at the nth orientation of the radar chassis, K;
wherein L
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A. Surface area of the nth orientation of the outer surface of the radar chassis, m; surface effective coefficient;
.—Altitude correction coefficient.
e=0.302L-0.26
—Characteristic dimensions of surfaces with different characteristics and positions, m. The characteristic dimensions of several typical surfaces are calculated as shown in formulas (6) to (11). When surfaces with different characteristics and positions are subjected to natural convection heat transfer, the characteristic dimensions are calculated as follows: a. Vertical plate, h (height) × b (width), height h is less than 0.6 m: Lmh.
b. Horizontal plate, length) × b (width), heat release surface upward: L-1. b / (+b)
c. Horizontal plate, heat release surface downward:
L=1.b/2(1+b)
d. Sphere, diameter D:
e. Vertical cylinder, diameter D greater than 0.005 m, height h less than 0.6 mL,-h..
t horizontal cylinder. True diameter D
5,1-0.0538h+0.00079h2
Where: h--altitude above sea level, km.
（10)
6.2.2 In order to maximize the radiation heat dissipation effect, the radar cabinet and equipment bulkheads should have high radiation coefficients. However, when part of the bulkhead may exceed the surface temperature of the radar cabinet under aerodynamic heating, radiation shielding measures should be considered. The calculation formula for radiation heat transfer is: @,Z5.7eAn [(Fw) -(
(T)4）
Where: ?Radiation heat transfer, W;
Twa——Surface temperature of the nth surface of the radar chassis, expressed by the temperature of the geometric center point of the surface (thermodynamic temperature), K;
The wall temperature value (thermodynamic temperature) corresponding to the nth direction of the equipment cabin surrounding the radar chassis, K;
A, —Surface area of the nth direction of the outer surface of the radar chassis, m2; Radiation coefficient,
Where: ew——Radiation coefficient of the radar chassis surface; &bRadiation coefficient of the equipment cabin wall.
6.2.3 Since the radar chassis is generally connected through seismic isolators when installed on the aircraft, the isolators actually also isolate the heat conduction channel. However, for radar extensions with excellent anti-thunder performance, or when high-damping materials are used to improve lightning resistance, they can be directly "hard-installed" on the aircraft frame without seismic isolators. In this case, conduction heat dissipation should be fully utilized, and the calculation formula for conduction heat transfer is:
, = (Twa-Tb) / R.
Where: conduction heat transfer, W;
Twa - surface temperature of the connection between the radar chassis and the mounting bracket, K; T - temperature of the equipment compartment mounting bracket, K;
R - contact thermal resistance between the chassis and the mounting bracket, K/W, which depends on the surface roughness of the mounting surface, the contact area and the clamping force of the contact surface. The contact surface can be filled with thermal conductive fillers, which can effectively reduce the contact thermal resistance.
6.2.4 The design of the naturally cooled unsealed chassis should allow ambient air to pass through the interior of the chassis, directly taking the heat out of the chassis and improving the heat dissipation capacity. However, the effect decreases with the increase of flight altitude. On the other hand, dust and moisture will also enter the chassis, causing hazards such as condensation and electrical breakdown, which should be given full attention. The naturally cooled sealed chassis can only dissipate heat through the outer surface of the chassis. In the interior, full use should be made of heat conduction to transfer the heat of the heating components to the chassis with the smallest possible thermal resistance. -1-
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