The cooling design for switching power supply

The basic method of cooling and its calculation method

There are three kinds of heat transfer: heat transfer, heat exchange and heat radiation.

For transmission or direct heat conduction by physical contact with the hair of heat transfer heat transfer. The machine is not the same temperature of body or the body temperature of each part, divided into sub mutual transfer. Heat conduction and electrical flow concept is very similar, the heat is always from the temperature of high temperature and low heat conduction process in the thermal resistance of the as current flow process in electrical resistance. The thermal flow in RT is the thermal resistance and tau temperature difference. And heat resistance and Delta for conductor thickness, lambda is the thermal conductivity, a conductor cross-sectional area. This kind of, in switching power supply design, to the heating source of dissipation power rate, temperature rise of tau = Phi RT. by in actual application, the heat flow from the heat source out to of the heat radiator to to the several different material of the heat conductor, the deposit in the same thermal resistance on, in the calculation, total heat resistance for a plurality of heat resistance and.

2) of converter heat quantity to and it close in a fluid layer through the heat conduction and the fluid by heat, volume expansion, density becomes smaller, on the flow to the, surrounding a high density of fluid over-current to fill, fill fluid filled to the ceiling thermal expansion to the on flow, such as the cycle, from heat element is a surface take away heat quantity, the process called on flow and heat transfer. 1 – product flow, and a 1 – flow on heat transfer calculation generally uses Newton proposed the formula: Phi alpha = a (theta theta 2) [w], [the fluid contact surface area [m2] alpha heat line number, theta 1 for wall temperature [k] and theta 2 fluid average temperature. The visible and thermal flow diameter and the flow heat transfer coefficient alpha, Section A and solid surface and flow of the temperature difference (theta theta 2) multiplication positive ratio. The flow heat exchanger is a kind of complex heat transfer process, it not only decided to heat process, and decided to gas dynamic process. Simply speaking, influence on the flow and heat transfer factors have two aspects: (1) the fluid physical properties, such as density, viscosity, expansion coefficient, thermal conductivity, specific heat; (2) the fluid flow condition, is natural the flow is forced to flow, flow is turbulent flow is also layer. Because the layer flow, heat transfer and to rely on each other to do the flow between the heat conducting layer; and the turbulent flow, the wall close to the bottom layer of the outer layer flow, fluid production vortex intensified heat transfer. In general, it is the same one in the circumstances, the turbulent flow heat transfer coefficient than the layer flow heat transfer coefficient is several times, even more.

3) radiation heat shot caused by difference in temperature of electric magnetic wave propagation for radiation heat radiation. Its process than the thermal conduction and the convection complex much. It is the body part of the heat energy is converted into electric magnetic wave energy, can transfer the electric magnetic wave medium such as air, really cool one’s heels, to pass broadcast to, when you encounter the object, a divided by again transformed into heat energy, the remaining is anti shot back. On the surface of the table, at B) (sigma, namely the object scattered hair to the red line is the thermal radiation of a kind. In the real space or air, radiation to the radiation ability of phi, decided to matter, surface condition (such as color, rough degree), surface area and surface temperature. Phi epsilon = BA T14- T24 and the sigma is wave Er hereby Mann constant, the value of 5.67 x 10 8, a radiation surface deposition [m2] t two body surface of absolute temperature [k] and E as a surface black degree. Body color is deep, the more rough, radiation force is strong.

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