Numerical modeling of coolant parameters in helicoid heat exchangers

Abstract

The article is devoted to the numerical simulation of heat exchange processes in a helicoid heat exchanger. An intensified heat exchanger is used here. The heat exchanger used is an intensified one, consisting of a bundle of profiled tubes fixed in a spiral-seam housing made of corrosion-resistant material. The article presents the case of one tube for heating and one tube for heated heat carriers. Heat transfer occurs from the flow of the heating medium to the flow of the heated one through tubes with a helicoid profile. The main difference between heat exchangers of this design is the profiled heat exchange surface of the tubes. This paper employs a hybrid approach to obtain dependencies for complex transients of the flow of a coolant (oil) with highly variable viscosity from a numerical experiment and constructing a closed mathematical model of heat transfer for a heat exchanger. The paper presents the results of calculations of the oil temperature field depending on various hydrodynamic parameters. Numerical modeling of oil dynamics was solved in the Ansys Fluent software package, where stationary Navier-Stokes equations averaged by Reynolds were used. The numerical simulation of fluid flow and heat transfer includes the numerical solution of the equations of continuity, momentum and energy transfer in the computational domain in Cartesian coordinates. To achieve this, we use the finite volume method on unstructured grids and the Coupled method to discretize the basic equations. The discretization of inviscid flows is carried out using the MUSCL scheme (Monotonic Upstream Schemes for Conservation Laws), and viscous flows are a centered scheme of the 2nd order of accuracy. The calculations use an uneven grid in which the thickening of the grid cells is performed near the walls of the pipe, where the oil temperature gradient is significant. To control the convergence of the iterative process, the level of discrepancy of the desired physical quantities and compliance with the mass balance equation are checked. The grid sensitivity study consists of running the same simulation using grids with different resolutions and analyzing how much the convergent solution changes with each grid. The resolution of the grid near the wall is fixed at y+<1, and the number of grid cells in the remaining part of the calculation area (part of the area outside the inflation layer) varies. The sensitivity of the grid to the result is estimated by the temperature distribution in the outlet section of the pipe. Calculations are completed when the level of discrepancy of all physical quantities decreases by three orders of magnitude, and the mismatch of mass expenditures at the input and output boundaries of the calculated area becomes less than $10^{-3}$ kg/s.