Determination of heat-transfer coefficients in multi-vortex heat-mass-exchange apparatus

Abstract

In this work, heat transfer coefficients from the working surfaces of a multi-vortex heat-and-mass exchange apparatus developed by the authors are determined along with dimensionless equations for calculating the heat transfer coefficients from the inner wall of a housing and bottom when generating. Numerical modelling is carried out using the ANSYS Fluent software package. When determining the velocity profile of a fluid in order to calculate the coefficient of heat transfer, the SST k-ω turbulence model is used. This allows for an adequate convergence in near-wall fluid and gas flow areas when simulating flows in similar constructions used, for example, to classify finely dispersed bulk solids. Dimensionless equations are obtained that relate the Nusselt number to the Reynolds and Prandtl numbers. Relationships are obtained for the increase in the heat transfer intensity as a function of the Reynolds number. It is established that the intensity of heat transfer from the inner wall in the multi-vortex apparatus exceeds the heat transfer from the bottom by 12.7–15.8 % depending on the Reynolds number. The values of heat transfer coefficients at the inner wall of the proposed apparatus can reach 14747 W/(m2 ∙ K) at an average fluid flow rate of 1 m/s. The proposed multi-vortex heat-exchange apparatus ensures swirling gas or fluid flow in the annular gap between the branch pipe and unit housing to provide high heat transfer coefficients and, hence, high intensity of heat transfer, especially through the wall of the contact stage. The numerical studies demonstrate the possibility of achieving high values of specific heat flux through the wall of the contact stage, which enables the most efficient use of the apparatus in the processes associated with the additional heat supply or removal from the contact stage through its external.