Thermal calculations of the electronic device Cooling REA

In electronic equipment, only a few percent of the energy supplied from the power source is spent on useful signal processing. The rest of the energy is released in the form of thermal energy. The temperature regime of the elements of electronic equipment (computers, radio stations, cellular devices) is one of the main factors limiting the decrease in the dimensions of the body of electronic equipment. A number of electronic components require the removal of additional heat (cooling), which leads to an increase in weight and dimensions of the product.

The transfer of thermal energy from one part of the electronic equipment to another or to the environment is called heat transfer. The temperature state (spatio-temporal distribution of temperature inside the apparatus) is called the thermal regime.

The transfer of thermal energy can occur due to the phenomenon of heat conduction (conduction), convection and radiation. In real equipment, all three methods of heat transfer work simultaneously and the thermal mode of CEA is determined by all three phenomena at once. The exact calculation of cooling is possible only for bodies of simple geometric shape, so the calculation of cooling equipment can only be carried out approximately to determine the initial parameters of the structure. This is followed by the manufacture of a prototype product and the experimental verification of its temperature regime.

The complex of design solutions aimed at reducing the temperature of radio elements requires significant material costs. In the process of developing the design of electronic equipment, attention should be paid to reducing the cost of the cooling design of radioelectronic elements and units. From this point of view, it is best to achieve cooling with the help of natural convection, taking measures to increase heat transfer due to thermal conductivity and radiation. Forced cooling leads to additional energy consumption, increased noise and reduced reliability of the equipment.

With natural REA cooling under normal climatic conditions, about 80% of heat is removed from the external surfaces of its hull due to convection, 10% is given off by heat conduction and approximately 10% is radiated into the surrounding space. Thermal mode blocks and components of electronic equipment can be divided into heat loaded and heat loaded. Assessment of the heat load of the body is made by the heat flux passing through the surface unit. It is usually considered that the heat flux up to 0.05 W / cm determines a small heat load, in excess of 0.05 W / cm - a large one.

Before embarking on the development of electronic equipment, it is necessary to establish the degree of heat load of all radio electronic elements. After that, it is necessary to disperse the heat-sensitive elements from the maximum heated to the maximum distance and ensure their thermal insulation from each other. If this does not contradict the conditions of electromagnetic compatibility or other important parameters of the equipment, the heat loaded and heat sensitive electronic elements should be separated into separate blocks or subunits.

In blocks with low heat load during natural cooling, the ambient temperature of the internal space of the housing does not exceed the ambient temperature by more than Δt = 30 ° C. The thermally loaded blocks may require the use of forced cooling, the design of forced cooling depends on the heat flux density (q, W / cm).

Cooling systems are classified as:

• natural-air ....... q≤0.2 W / cm 2 ;
• forced-air ..... q≤1 W / cm 2 ;
• liquid ................... q≤20 W / cm 2 ;
• evaporative ............... q≤200 W / cm 2