Study On The Flow And Heat Transfer Behavior For The Ice Slurry In The Piping Systems

Ice slurry, a mixture of water, ice crystals(with diameter of no more than 1×10-3 m) and some kind of depressions, is a new promising second refrigerant in the refrigeration field and the district cooling field for its good character of pumping and flexible ability. Furthermore, the ice slurry also plays an important role in the phase change material field for its high latent heat, high to 3.35×105 J/kg, discharged in the melting process of the solid ice particles. However, it has not yet been widely used in practical use because of that the model of flow and heat transfer behavior is unsolved in piping systems with resistance components. The study of flow and heat transfer behavior aims at increasing heat transfer capacity, as well decreasing the pressure drop. Hence, the research on flow and heat transfer behavior is carried out for the ice slurry in series of pipes with resistance components, by numerical simulation and experiments method in this paper. The following is the details:(1) Numerical simulation is conducted by two steps: mesh drawing and fluid computation. Firstly, hexahedral mesh is created in each geometric model of tubes, with mesh quality of high to 0.7. Secondly, commercial software Ansys Fluent is employed to simualte the flow condition of the ice slurry. Two-phase Euler-Euler model is selected, combined with granular dynamic model, to solve this problem. Diameter of ice particles is set to be 1×10-4 m. Phase change of solid ice crystals is considered in the simulation for the heat transfer characteristics, by writing a UDF profile into the solver.Simulation results of pressure drop and temperature variation are respectively obtained for the ice slurry in straight tubes, elbow tubes and T-type tubes, with varying IPF, flow rates and tube diameters. Results show that pressure drop increase with the IPF and flow rates, which keep accordance with experimental data. Simulation results on the heat transfer show that temperatures at the resistance components are the highest, which indicates the great energy loss.(2) In order to observe and predict the risk of the ice blockage, distribution of ice particle in the tubes is obtained by simulation, which is difficult to test in the practical experiments. First critical velocity( about 1~2m/s) and Second critical velocity( about 10m/s) are proposed to describe the risk of ice blockage, which provide a theoretical basis and reference on the future practical application to some extent.(3) Experiments are carried out to make analyses on the flow and heat transfer behavior practically. The test rig includes 3 parts, namely the ice slurry making device, the flow and heat transfer test section and the data collection system.On the research of flow behavior, pressure drop is measured under varied velocities, IPF and tube shapes. Results show that pressure drop increases with the number of resistance components, of which pressure drop in T-type tubes is the highest, then elbow tubes, and straight tubes is the lowest. As for the ice slurry in the same type of tubes, pressure drop increases at higher flow rates and IPFs. In addition, experimental results show good agreement with the numerical simulation data.On the research of the heat transfer character, the flow condition of straight tube is studied under a electric heater which can be adjusted to provides constant heat flux of 1000 W/m2 and 2000W/m2. Temperature difference and heat transfer coefficient is considered to be influenced by heat flux and flow velocities. Results show that the temperature difference rises up with increasing speed, however, it firstly increases and then decreases with the increasing heat flux. It can also be observed that heat transfer coefficient keep rising with increasing heat flux and flow rates. Specially, the flow rates of the coefficient also increases with growing heat flux.