Uniform and non-uniform inlet temperature of a vertical hot water jet injected into a rectangular tank
In most of real-world applications, such as the case of heat stores, inlet is not kept at a constant temperature but it may vary with time during charging process. In this paper, a vertical water jet injected into a rectangular storage tank is measured experimentally and simulated numerically. Two cases of study are considered; one is a hot water jet with uniform inlet temperature (UIT) injected into a cold water tank, and the other is a cold water jet with non-uniform inlet temperature (NUIT) injected into a hot water tank. Three different temperature differences and three different flow rates are studied for the hot water jet with UIT which is injected into a cold water tank. Also, three different initial temperatures with constant flow rate as well as three different flow rates with constant initial temperature are considered for the cold jet with NUIT which is injected into a hot water tank. Turbulence intensity at the inlet as well as Reynolds number for the NUIT cases are therefore functions of inlet temperature and time. Both experimental measurements and numerical calculations are carried out for the same measured flow and thermal conditions. The realizable k-ε model is used for modeling the turbulent flow. Numerical solutions are obtained for unsteady flow while pressure, velocity, temperature and turbulence distributions inside the water tank are analyzed. The simulated results are compared to the measured results, and they show a good agreement at low temperatures.
Unsteady Buoyancy-Induced and Turbulent Flow from a Hot Horizontal Jet Entrance into a Solar Water Storage
Experimental visualizations and numerical CFD calculations of a horizontal hot water jet entering cold water into a rectangular storage tank are described. Three different temperature differences and their corresponding Reynolds numbers are considered. Both experimental visualization and numerical calculations are carried out for the same flow and thermal conditions. The realizable ε − k model is used for modeling the turbulent flow while the buoyancy is modeled using a Boussinesq approximation. Polynomial approximation of the water properties are used to compare with the Boussinesq approximation. Numerical solutions are obtained for unsteady flow while pressure, velocity, temperature and turbulence distributions inside the water tank as well as Froude number are analyzed. The experimental visualizations are performed at intervals of five seconds for all different cases. The simulated results are compared with the visualized results, and both of them show the stratification phenomena and buoyancy force effects due to temperature difference and density variation. After certain times, depending on the case condition, the flow tends to reach a steady-state. Key-words:Turbulent flow, realizable ε − k turbulence model, unsteady flow, heat transfer, jet, solar storage, CFD, flow visualization.
Submerged turbulent jets in stagnant linearly stratified fluids
Turbulent round buoyant jets discharging into linearly density-stratified stagnant fluids are studied. The sensitivity of the assumed entrainment relations and profile shapes in traditional integral models is explored. A different representation of the density profile is developed in order to more correctly represent the cross-sectional density distribution. In an experimental study, the dilution of a passive tracer along the jet trajectory, the maximum height of rise, and terminal dilution are measured. Measured center-line dilutions and jet widths are in essential agreement with model predictions with any of several previously proposed entrainment relations. It is found that jet mixing is not significantly influenced by either the ambient density gradient or the gravitational spreading layer from the jet collapse. There is some evidence of re-entrainment of jet fluid for horizontal nonbuoyant discharges. The integral model tends to under-predict the maximum height of jet rise and the associated dilution...