Physical properties of fluid and boundary conditions

The thermodynamic properties of the water are considered in this study. The velocity and is assumed to be zero at the beginning. The operation pressure in the tank is taken 1 atmosphere and the hot water temperature is assumed to be 320 K when the water usage started. The time between the water is started to be used and the water usage was finished is assumed as calculation region. This time is taken as 30 minute and the problem solved as unsteady.

2.2. The numerical method

The velocity and temperature distributions inside the tank have obtained by using the computer code [12]. Three dimensional unsteady solutions are taken by using implicit method in segregated solver. The discretization is achieved by using standard method for pressure and by using first upwind method for momentum, energy, turbulent kinetic energy and turbulent dissipation rate equations. The SIMPLE (semi-implicit method for pressure-linked equations) algorithm was used for flow calculations.

The convergence is very important in numerical calculation by using the code. Solutions were assumed to converge when the following convergence criterion is satisfied by every dependent
variable at every grid point in the computational domain

pnew — pold


Where (^) in general could be any dependent variable. In this study, ^=10’3 for continuity, momentum. Turbulent kinetic energy and turbulent dissipation rate equations. This value is 10^6 or energy equations.

To under-relaxation factors are assumed as 0.3, 0.7, 1, 0.8, 0.8 and 1 for pressure, momentum, energy equations, turbulent kinetic energy (k), turbulent dissipation rate (s) and turbulent viscosity (pt) as, respectively. This factor has assumed as 1 for body force and density.