HEAT TRANSFER DURING TRANSVERSE AIR FLOW AROUND A SINGLE-ROW BUNDLE OF CYLINDERS WITH SPIRAL GROOVES OF VARIOUS CROSS SECTIONS
Abstract
The aim of the work was to study the heat transfer and hydraulic resistance of a single-row bundle of cylinders with spiral grooves of various types on the outer surfaces. The task was to compare the heat transfer and hydraulic resistance of cylinders with spiral grooves with a rectangular cross section and grooves with an oval cross section in a cross-sectional air flow. The experiments were carried out in an open-type wind tunnel in the range of Reynolds numbers 3000 < Re < 16000 at air temperatures from 10 to 20 °С. The calorimetric method of melting ice was used. The heat transfer coefficient and the Nusselt number were calculated from the balance equations, and the Euler number was calculated from the value of the pressure drop. The Reynolds analogy factor was determined from the Nusselt and Euler numbers. An analysis of heat transfer and hydrodynamics during air flow around a bundle of cylinders with grooves was performed. Different types of spiral grooves on the surface of cylinders are considered. It is shown that the best heat transfer results were obtained for cylinders with steps of 10 mm and 40 mm. Cylinders with 20mm groove pitches were midway between 40mm grooved cylinders and smooth cylinders in terms of efficiency. This fact may be due to the peculiarities of the formation of vortices on the rear surface of the cylinder. The effect of groove geometry on hydraulic resistance and heat transfer coefficient was investigated. It was established that the flat side walls of the grooves create greater resistance than the curved ones in the range of Reynolds number change from 3000 to 4500. It is shown that the dependence of the heat transfer coefficient on the air speed is non-monotonic in nature. At the same time, the use of grooved cylinders with straight side walls leads to an increase in heat transfer in the range of Reynolds numbers Re from 7000 to 16000.
References
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