Gas dynamics and heat transfer of stationary and pulsating air flows in round and triangular straight pipelines at different turbulence degrees

RELEVANCE of the study is determined by the fact that non-stationary gas-dynamic phenomena in pipelines of complex configuration are widespread in heat exchange and power equipment. Therefore, the study of the level of heat transfer of pulsating air flows in round and triangular pipes with different degrees of turbulence is an urgent and significant task for the development of science and technology.

THE PURPOSE. The influence of gas-dynamic nonstationarity (flow pulsations) on the degree of turbulence and the intensity of heat transfer of air flows in straight pipes with different cross-sectional shapes had to be assessed.

METHODS. The studies were conducted on a laboratory bench based on the thermal anemometry method and an automated system for collecting and processing experimental data. Rectilinear round and triangular pipes with identical cross-sectional areas were used in the work. Flow pulsations from 3 to 15.8 Hz were generated by means of a rotating damper. The degree of turbulence of pulsating flows varied from 0.03 to 0.15 by installing stationary flat turbulators. The working environment was air with a temperature of 22-24 ^оC moving at a speed of 5 to 75 m/s.

RESULTS. Experimental data on instantaneous values of velocity and local heat transfer coefficient of stationary and pulsating air flows with different levels of turbulence in straight pipes with different cross-sectional shapes were obtained.

CONCLUSION. It has been established that the presence of gas-dynamic non-stationarity leads to an increase in the degree of turbulence by 47-72% in a round pipe and by 36-86% in a triangular pipe. The presence of gas-dynamic non-stationarity causes an intensification of heat transfer in a round pipe by 2635.5% and by 24-36% in a triangular pipe. It has been shown that a significant increase in the degree of turbulence leads to an increase in the heat transfer coefficient of pulsating flows in a round pipe by 11-16% and, conversely, a decrease in the heat transfer coefficient by 7-24% in a triangular pipe. The obtained results can be used in the design of heat exchangers and gas exchange systems in power machines, as well as in the creation of pulsed action devices and apparatus.

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