Experimental and numerical study of freezing water around a cylindrical tube : application to desalination

Abstract

To face the shortage in fresh water, many techniques are used nowadays for brackish and seawater desalination. One of them which consume the less energy is freezing. This process allows the separation of the different salt water’s components and gives rise to a saltier liquid phase called brine and a solid phase of ice becoming fresh water after melting. The quantity and the quality of the products depend, among other, on the geometry of the surface of the exchanger on which will occur the freezing. In this paper, we present experimental and numerical results of fresh and seawater freezing around a circular Cu cylindrical tube immersed into a cavity filled with water to freeze. The tube is fed by a refrigerant coming from a cryostat. A data logger was used to register temperature at different times. Shadowgraphs allowed to visualize the birth and growth of ice. Numerical simulations were based on Navier- stokes, energy and species equations in transient flow. FLUENT software was used to solve theses partial differential equations using a bi-dimensional formulation and an appropriate mesh. Thus temperature, velocity, concentration and flow visualization were investigated and compared to experimental ones. It was found that: 1) Vertical tube produced more ice than the horizontal one. 2) Less the water is salty, more is the production of ice. 3) Dendrites may appear and delay heat and mass transfer.