A fixed-grid frost formation model is presented. In constrast to the previous studies, the present work accounts for a unified domain composed by both frost that is being formed due to phase changes under a saturation state and free humid air. Moreover, a porous treatment is given to the frost structure in which advective terms are taken into account as well as variable thermophysical properties. A 2D numerical test consisting on a duct flow with a cooled lower boundary is performed. Aspects related to the rate of growth as well as to the implemented finite volume approach have been analysed, proving the method to
be a valid candidate to simulate the free-air-frost coupled problem.
An Arbitrary Lagrangian-Eulerian formulation has been posed to solve the challenging problem of the three-dimensional Taylor bubble, within a Conservative Level Set (CLS) framework. By employing a domain optimization method (i.e. the moving mesh method), smaller domains can be used to simulate rising bubbles, thus saving computational resources. As the method requires the use of open boundaries, a careful treatment of both inflow and outflow boundary conditions has been carried out. The coupled CLS - moving mesh method has been verified by means of extensive numerical tests. The challenging problem of the full three-dimensional Taylor bubble has then been thoroughly addressed, providing a detailed description of its features. The study also includes a sensitivity analyses with respect to the initial shape of the bubble, the initial volume of the bubble, the flow regime and the inclination of the channel.
A three-dimensional transient formulation of the frost formation process is developed by means of a finite volume approach. Emphasis is put on the frost surface boundary condition as well as the wide range of empirical correlations related to the thermophysical and transport properties of frost. A study of the numerical solution is
made, establishing the parameters that ensure grid independence. Attention is given to the algorithm, the discretised equations and the code optimization through dynamic relaxation techniques. A critical analysis of four cases is carried out by comparing solutions of several empirical models against tested experiments. As a result, a discussion on the performance of such parameters is started and a proposal of the most suitable models is presented.
Published under licence in Journal of Physics: Conference Series by IOP Publishing Ltd.
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