To the mathematical modeling of the area of tubular gas heater in the condensing mode of work

Purpose. During the combustion of inflammable gases in the air stream, the gas-air mixture, which contains water vapor, is formed inside of the emitting pipe of a heater. While the mixture is moving along the pipe its temperature is decreasing, which leads to the condensation of water vapors from the gas-air mixture. Maximum fuel economy can be achieved through the use of the mode of condensation of water vapor from the gas-air mixture in the construction of the heater. In the process of condensation the condition of vapor near the surface of the phase transition is nonequilibrium. In the existing mathematical model of the tubular gas heater in the condensing mode of operation the state of vapor near the surface of the phase transition is not considered. The purpose of the article is to examine the existing mathematical model of the section of tubular gas heater in the condensing mode of operation and make additions in terms of the specifics of the phase transition. Methodology. Existing mathematical model of the tubular gas heater with the condensation of water vapor includes the equations of conservation of mass, motion and energy. The processes of condensation of vapor are characterized by the coexistence of the phases, and as a result, by the presence of the surface of the section, in which the flow does not conform to the laws of classical gas dynamics. The layer of the phase section was taken into the consideration ? the Knudsen layer, in which the parameters of exchanged mass with the condensation inside of emitting pipe of the tubular gas heater. Findings. It has been found that there are jumps on the borders of the Knudsen layer in the parameter changes of the exchanged mass, such as average speed, temperature and enthalpy. To determine these jumps it is necessary to solve the Boltzmann equations inside of the Knudsen layer and unite his decisions for the outer domain in relation to the Knudsen layer. The boundary conditions for the Knudsen layer are the limiting conditions for the equations of gas dynamics. Originality. The question of the possibility of accountability of the nonequilibrium state of vapor near the surface of the phase transition for the mathematical model of the tubular gas heater in the condensing mode has been examined. Practical value. The ways of determining the parameters of exchangeable mass during the condensation of water vapor into tubular heaters were examined. It allows to make appropriate adjustments in the existing mathematical model.