Mathematical modeling of controlled charge cooling in a vacuum-compression resistance furnace
The article presents the mathematical model of an unsteady complex heat transfer process in subjecting a product (charge) to controlled cooling in the gas stream formed inside a vacuum-compression furnace. The results obtained from studying the process on the model are given, and the gas distribution system configuration version ensuring the best quality of controlled cooling process has been selected. Furnaces the thermal processes in which can be carried out both in vacuum, and at excess pressure are called vacuum-compression furnaces. Heating in vacuum-compression resistance furnaces is necessary for carrying out many production processes, in particular, soldering operations performed using solid solders and with the use of fluxes in order to obtain reliable soldered joints of parts in the rocket, nuclear, aerospace, and other industries. The technological process realized in the majority of vacuum-compression furnaces includes heating of a product, its holding, and controlled cooling in protective medium. One of important conditions for achieving a successful result (for example, obtaining high-quality soldered joints) is to set up a uniform temperature field in the product---both in heating and cooling it. Another no less important condition consists in maintaining a preset cooling rate. A highly uniform temperature field in combination with the cooling rate exactly complying with the preset schedule can be achieved by properly choosing the design and parameters of a charge blowing system. This involves the configuration of gas-passage bores, the necessary cooling medium flow rate, and the spatial arrangement of inlet and outlet holes corresponding to the furnace chamber geometry and charge layout. Controlled cooling of a bulky charge in the vacuum-compression furnace for soldering is investigated using the mathematical modeling method with the aid of the ANSYS finite-element computation software package. The simulation of a controlled charge cooling process in a gas stream is reduced, subject to the adopted assumptions, to solving the problem of unsteady heat conductivity with the boundary conditions of the 3rd kind that take into account the convective and radiating components of complex heat transfer. The field of gas velocities and the temperature field pattern in the charge for different configurations of gas-passing bores and at different cooling gas flow rates are obtained on the model. The configuration with four outlet holes, preferable from the viewpoint of obtaining a highly uniform temperature field in combination of the optimal cooling rate, has been found, and the necessary cooling gas flow rate has been determined.