Heat Transfer at Film Cooling of an Array of Horizontal Tubes with an Enhanced Surface

The paper presents investigation results about the influence of various methods of surface treatment on heat transfer enhancement in falling films of R21 Freon on an array of horizontal tubes. The experiments were carried out on the aluminum alloy tubes with a ceramic coating obtained by micro-arc oxidation and on copper tubes with a structured surface, treated by deformational cutting. The experiments were carried out in a regime of turbulent film flow at Reynolds numbers from 400 to 1500. The results of measuring the heat transfer coefficients on the surface of samples with a developed surface and on the standard smooth tube are compared. The highest values of heat transfer coefficients in falling films during nucleate boiling were obtained on a structured surface with semi-closed cavities. Heat transfer enhancement on the surface of a tube made of alloy D16T with the MAO coating of 30 μm thick, obtained in a silicate-alkaline electrolyte, is comparable to heat transfer enhancement on the surface of copper tubes with a microstructure applied by the deformational cutting method.

The Temperature in the Cutting Zone when Applying Deformational Cutting to Form a Hardened Layer

Deformational cutting is a promising method of increasing wear resistance of friction surfaces by creating a strain hardened surface layer on them. An important factor influencing the deformational cutting process is the temperature in the cutting zone, therefore, it is necessary to obtain calculation formulas for predicting it. In this paper, the temperature change during deformational cutting of non-hardened austenitic steel in order to form a hardened layer was studied in relation to the cutting parameters: cutting depth, feed and cutting speed. Austenitic steel was selected as a promising material for strain hardening by the deformational cutting method. Temperature measurements were carried out using the natural thermocouple method. An empirical formula for calculating the temperature in the cutting zone depending on the cutting parameters was obtained.