Heat exchange rate in a round pipe of heat exchanger in a biogas plant

The aim of the work is to develop a reliable method for predicting the intensity of heat exchange in a round tube of a natural heat exchanger in various technological regimes that occur in biogas technologies (using the criterion equations of heat exchange, but with limited information on the thermophysical properties of the substrate). Research materials and methods. The presented work uses an improved experimental and computational method based on the combined use of the theory of similarity and the analysis of the parameters of the regular thermal regime. During the research, a real substrate from an operating biogas plant was used. The reason for the high intensity of heat exchange is the direct contact of substances on the boundary surfaces of the phases, which must be supported by the continuous renewal of these surfaces thanks to the constant mixing of the substrate. The experiment was carried out on a portable experimental setup. The heat exchange of model fluids and substrate from an operating biogas plant was investigated. An array of experimental data on the heat transfer coefficient of model fluids and the substrate was obtained. The results of experiments on the heat transfer coefficient for model fluids are summarized. The criterion equation of heat exchange was obtained. It is hypothesized that the criterion equation of heat exchange also corresponds to the substrate. For the substrate, the density, thermal expansion coefficient, specific heat capacity, and additive thermal conductivity were determined experimentally. Using the criterion equation of heat exchange and determined thermophysical properties, the viscosity of the substrate in the temperature range is determined. Using the known criterion equations of heat exchange and the determined viscosity, the parameters of the intensity of heat exchange in the round tube of the heat exchanger of the biogas plant are determined. The use of the proposed experimental and calculation method provides an opportunity, in conditions of limited information on the thermophysical and rheological properties of the liquid medium, to predict the parameters of the heat exchange intensity in the heat exchanger pipe used in biogas technologies.