Abstract

In order to reduce the weight-size dimensions of the lasers and apply their atmospheric low temperetures, it is often needed to use air cooled lasers, instead of traditional water cooled ones. It is known [1], that the heat exchange ratio when cooled diffusely by air, is approximately by two orders of magnitude lower than that for the liquid cooling Therefore, creation of air cooled CW lasers with pump power up to 3kW is one of the actual problems of modern laser techniques. The main problem in creation of similar lasers is to obtain high heat transmission ratios in cooling channels, which will ensure for the lasers working temperature regimes to be near the ones when cooled by liquids. For obtaining such high ratios of heat transmission the authors of this paper succeeded in developing of the turbulence of the flow in the channels with straight flow of the air with Reynolds number $R{e}^{0.875}=\frac{d_2-d_1}{v}\sqrt{\frac{P_{max }\left(d_2-d_1\right)2g}{k{L}_{\text{ρ}}}}$ where d₂-d₁- is the hydraulic diameter of cooling channel, v-the kinematic viscosity of the air, P_max-the maximal input pressure of the channel, g-free falling acceleration, k-hydraulic resistance ratio, L-the cooling channel's length, ρ- the air density. The principle of cooling is based on achieving an equality between the times of diffuse propagation of heated air molecule from the cooled object in the plane, perpendicular to the air flow and its running time from the channel's entrance along all its length. Inserting the number Re in the formula for calculating the heat exchange ratio [1] $\alpha =\frac{\text{λ}}{d_2-d_1}\{\dots \}R{e}^{0.875}P{r}^n$, we get its value for cooling channels of various dimensions and configurations, where λ- is the air heat conductivity, Pr - the Prandtl's number, $n=0.4+\frac{0.5}{2Pr+1}$ and figure brackets contain tabulated values of this formula and also constructive-technical parameters of the cooled channel very slightly influencing the heat exchange ratio's value.

© 1996 IEEE