ИСТИНА

Numerical and experimental studies of flows in annular and conical channel of variable cross-section have been carried out. The flow is assumed to be continuous, so only small angles of inclination of the channel walls are considered. For the Reynolds numbers in the range 1000- 10000, the velocity profiles, turbulence energies, and Reynolds stresses and the characteristics of turbulent heat transfer determined by them are calculated. Calculations show a strong influence of the opening angle of the channel on the turbulent flow characteristics [1]. An increase in the intensity of turbulence in the case of heat supply to the wall leads to an increase in the heat transfer characteristics [2]. Using numerical simulation, the characteristics of the experimental setup of a counterflow heat exchanger with diffuser channels were determined. Depending on the position of the valve switches, the heat exchanger can operate in two modes: a diffuser in a diffuser (expanding channels) or a confuser in a confuser (converging channels). The calculations were carried out using a three-parameter differential turbulence model [3], supplemented by equations for turbulent heat transfer, and a numerical study of the flow and heat transfer in the annular and conical channels with different degrees of expansion was carried out. Water was considered as the heat medium. It was shown that in expanding channels (annular and conical) for all considered opening angles, the main characteristics of heat transfer - the Nusselt number and the Reynolds analogy coefficient - turn out to be higher than in narrowing channels, with the same Reynolds number. For these two operation modes of the heat exchanger, the heat transfer characteristics were measured and compared with the calculated data. Intensification of heat transfer in such a heat exchanger with diffuser channels is achieved without a noticeable increase in the friction coefficient. This is the fundamental difference between the considered method of heat transfer intensification from many known methods, where an increase in heat transfer is achieved at the cost of a significant increase in hydraulic losses. The study was carried out under the financial support of the Russian Science Foundation, grant no. 20-19-00404