Thermohydrodynamics of continuous-wave CO2 lasers with a closed cycle of the flow

Abstract

The problem of pressure losses upon gas motion along a closed circuit containing channels in which heat is supplied to and removed from the gas is studied. The object where the pressure losses are studied is a CO2 laser with a crossflow.With increasing power of electric-discharge lasers with a closed cycle of the flow, the role of the gasdynamic circuit becomes more important. The gas-dynamic circuit of a powerful continuous-wave CO2 laser with a crossflow and transverse discharge resembles a subsonic wind tunnel with a closed circuit but differs from the latter by configuration of the gas-discharge chamber wherein the electric energy is converted to radiation and thermal energy.There are different approaches to designing the gas-dynamic circuit of the laser, and the choice of its schemes is based on contradictory criteria. The circuit has either a large specific volume (3 m 3 per 1 kW of generated power) and a low specific power for sustaining gas circulation over the closed circuit (1 kW per I kW) or a high (up to 2 kW per 1 kW) specific power and a comparatively small (1-1.5 m 3 kW) specific volume [1][2][3][4][5][6]. Various approaches, which are often incompatible, are proposed to choose the pumping tools that ensure gas circulation over a closed circuit and aerodynamic schemes of gas-discharge channels wherein the pumping of the laser mixture of gases is performed. The results of papers devoted to the problem of calculation of pressure losses upon nonisothermal gas flow are contradictory. In the case of nonisothermal motion of gases, the motion becomes nonuniform because of changes in gas densities and, hence, their velocities. This involves pressure losses for gas acceleration [7][8][9][10]. Another contradiction arises in calculating the drag of the gas motion over the circuit as a whole. For example, Ivanchenko et al. [4] showed that the cross-sectional area of the flow in a channel where the heat is removed is significantly greater than the cross-sectional area of the flow in a channel with heat addition; therefore, the effect of nonisothermality on the coefficient of pressure losses in a channel with heat removal can be ignored. At the same time, heat addition in real devices does not seem to be inevitably accompanied by pressure losses. For example, Bartlma [9] considered the channel with heat addition as a thermal confuser.In the present paper, we study the problem of pressure losses upon circulation of a subsonic gas flow over the circuit of a device with a closed cycle, which contains channels wherein heat is supplied to and removed from the gas. The pressure losses are studied in a COs laser with a crossflow. Here and in what follows, the pressure losses are understood as the total (stagnation) pressure losses, which determine the power necessary for gas pumping (see, for example, [8][9][10][11][12][13]). Nonisothermal motion is understood as a gas flow under conditions of changing stagnation temperature of the flow due to heat addition or removal. The effect of nonisothermality on pressure losses...