Study of heat exchange in cooling systems of heat-stressed structures

Resumo

Increasing working parameters of the cycle of gas-turbine engines, complicating design of gas-turbine plants, as well as growing aerodynamic, thermal, static, and dynamic loads, necessitate the development of promising cooling systems for heat-stressed structures. This work is devoted to an experimental study of heat exchange in ducts equipped with systems of inclined and cross walls (fins). It has been found that an increase in the Reynolds number Re from 3000 to 20000 leads to a decrease in the heat exchange, which is characterized by the relative Nusselt number \(\overline{Nu}\), by 19–30% at the angle of inclination of the walls φ = 0, 40°, 50°, and 90° if the length of the walls x_w is comparable to the spacing b_s and by 12–15% at φ = 30° and 90° if x_w ≫ b_s. If cross walls are used in cooling ducts, the length of the walls x_w plays the governing role; an increase in this characteristic from 1.22 × 10^–3 to 3.14 × 10^–3 m leads to an increase in the intensity of heat exchange by 30–40% and to a decrease in the capacity of the entire system of the walls. It has been shown that, on surfaces with wavy fins, the intensity of heat exchange is closest to that determined in the models under study. For example, values of the Colborne criterion StPr^2/3 for ducts equipped with wavy fins and for the models under study differ only slightly (by 2–20% depending on the value of the angle φ). However, the difference for surfaces with short plate fins and ducts equipped with inclined walls is high (30–40%). This is due to the design features of these surfaces and to the severe effect of the inlet portion on heat exchange, since the surfaces are characterized by a higher ratio of the duct length to the hydraulic diameter L/d_h at small fin thicknesses ((0.1–0.15) × 10^–3 m). The experimental results can be used in developing designs of nozzle and rotor blades of high-temperature gas turbines in gas-turbine engines and plants.