The purpose of this article is to determine the dependence of heat transfer processes on balance and criterion equations, heat transfer in external and internal heat exchange, criterion equations of heat transfer in heat exchange devices, the dependence of heat on physical parameters, and mathematical modeling of the process. The heat transfer coefficient was calculated based on criterion equations related to the Nusselt, Prandtl (from the table), Grasshoff, Pecle and Reynolds numbers. When a pipe with d_0 = 32 mm was studied, according to the calculations based on criteria, it was determined that the heat transfer coefficient is 14.5 × 103 W/m2 K and the heat flux is 29.14 × 103 W when the Nusselt number is 730.47. When the heat exchange is calculated when the flow crosses a large number of pipe bundles, the Reynolds number for the flow at a speed of 4 m/s is equal to 12.7 × 104, that is, the flow is turbulent. According to the criterion equations, the Nusselt number reaches 749.7, and the value of the heat transfer coefficient reaches 14,021 W/m2 K. Based on the results of mathematical modeling based on the selected boundary conditions, it was determined that the coefficient of heat transfer is greater, it depends on the flow regime of heat carriers, Reynolds, Nusselt criteria and Prandtl number, and graphs of dependence were obtained.