Improvement of the Method of Calculating Heat Transfer Coefficients Using Glycols Taking into Account Surface Forces of Heat Carriers

Abstract

This study compares the classic calculating method of the heat transfer coefficients of the shell-and-tube heat exchanger tubes using the classic Nusselt, Reynolds, and Prandtl similarity numbers with a new method that takes into account the coefficients of surface tension of heat carriers, their transitional, turbulent viscosity and thermal conductivity, as well as the average thickness of the laminar boundary layer (LBL). The classic method shows a better efficiency of water as a heat carrier com-pared to a 45% aqueous solution of propylene glycol. Instead, the new calculation method shows that a 45% aqueous solution of propylene glycol at the same Rey-nolds numbers has higher heat transfer coefficients com-pared to water in the temperature range of 273–353 K. We divided the "live cross-section" of the flow of the liquid coolant into a medium-thick LBL, where the Fourier equation of thermal conductivity is applied, and into its turbulent part, where the equation of thermal conductivity with turbulent thermal conductivity is also applied. A new formula (14) is proposed for calculating the average thickness of the LBL based on the radius of the "live cross-section" of the coolant flow, as well as the Blturb similarity number obtained by us in previous works. A new formula (15) is also proposed for calculating the heat transfer coefficient, which includes the transitional and turbulent thermal conductivity of the corresponding zones of the flow "live section", as well as the average thickness of the LBL.