Creation of scientific and technological foundations for the development of advanced high-performance heat transfer surfaces.
The design of flat-oval profile steel tubes with the incomplete fins is investigated for use as heat transfer surfaces. Such surfaces have several important advantages: the material - carbon steel, manufacture of low-cost technology – contact welding of the fins on the tube; improved thermal efficiency as compared with steel tubes of round profile, aerodynamic drag of flat-oval tubes with incomplete fins for 40...50 % below the tube of round profile. Experimental methods and numerical simulations carried out studies of local and surface average convective heat transfer characteristics, aerodynamic resistance and flow structure in the heating surfaces of the flat-oval tubes with an incomplete transverse fins in intervals of the coefficients of fins y = 7...15 and Reynolds numbers . For the first time used to study the structure of the flow with visualization techniques, pneumatic and hot wire anemometry methods on the surface and in the interfins channels of flat-oval tubes. An improved estimates generalizing dependences for determining the rate of heat transfer and aerodynamic resistance of flat-oval tubes with incomplete fins are obtained, taking into account the influence of geometrical parameters of finned tubes and the package as a whole. The experimental and numerical investigations of heat transfer and drag make possible to improve on (2-3) % calculation correlations for determining the convective heat transfer coefficients and pressure losses for staggered bundles of flat-oval tubes with incomplete fins.
In the paper revealed that profile of flat-oval tubes with d2/d1 = 2.8 in their properties, in terms of heat transfer from one meter of finned tubes can be 25% more give or take the heat for the same coefficients of fins than the flat-oval tube with d2/d1 = 2.0 with a slight increase in drag.
On the basis of new relations for calculating heat transfer coefficients and pressure losses carried improving techniques for heat-aerodynamic calculations. The advanced engineering simulation techniques allows more accurate calculation of mentioned factors and mortgage the less factor of safety than on the surface area of the heat exchanger in general.
Study of heat transfer and hydrodynamics of the flow in the heating surfaces of the flat-oval tubes with incomplete fins, given the opportunity to optimize the geometrical characteristics of the fins. Carrying out such studies has revealed that the optimum geometric parameters of natural flat-oval tubes fins have such values: fins step t = 3.6...3.8 мм; fin height h = 20...21 мм; fin thickness d = 0.8...0.9 мм.
On the example of a specific heat exchange equipment carried out a variant heat-aerodynamic calculations for economizer-heat made of flat-oval tubes and placed between the boiler and smoke exhauster and smokestack on one of the Zaporozhye boiler plants. Weight of the tubes decreased by more than 0.5 tons (25%) that in the final version reduced the cost of heat exchanger. In addition, production tests showed that the low impedance of heat transfer surface does not require an additional regulation of exhauster.