Yndicio 3

difference model which accounts for turbulent mixing in the tank and heat loss to the ambient surroundings. The energy equation for turbulent flow is solving by splitting it in two equations representing the conduction and convection cases, and handling them with different compu- tational time step. The model used by Zurigat et al. was compa- red with the experiment carried out by them. The results show that the model proposed may break down for Ri<3.6 and specific correla- tion for particular inlet configurations could be necessary if the operating conditions require Ri<3.6. A characteristic of this model is that eliminates the numerical diffusion in the finite difference solution introducing the effective diffusivity factor, eff [6]. The comparison be- tween the predicted thermocline and the expe- rimental can be achieved. The Turbulent Mixing Model and the Displacement Mixing Model deve- loped by Alizadeh [10] was used to study the behavior of a cylindrical sto- rage tank. The first model considers a tank divided into a k equal volume layers. Cold water is allowed to enter and is mixed with the initial m bottom layers. This model could be used ne- glecting the fluid thermal conductivity and the heat loss or taking the fluid thermal conductivity and the heat loss into account. The Displacement Mixing Model assumed that at the commencement of the cold inflow a volume V of the inlet water is equally distributed amongst the initial m bo- ttom layers so that no mixing occurs between the layers. Consequently, the cold inflow pushes the top layers up in an ideal plug flow manner. 6, 9, 10, 11, 18]. More complex models have appeared in the literature. The two-dimensio- nal models have been studied to predict the mixing effect of the hot and cold water [7, 8, 12, 13, 14, 15, 16, 17] and the three-dimensional models are used to evaluate the effect of sto- rage tank geometry [2, 15, 19]. While two and three-dimensional models are more capable in accounting for different factors affecting the thermal storage tank performance, they are not suitable for use in larger energy systems load management programs due to computational cost. Simpler one-dimensional model may be advantageous since they are computationally more efficient and predict the effect for indus- trial process. In this paper a survey of several types’ one-dimensional models for thermal stratifications tanks are stu- died, the objective of this study is to give a suggestion for using the model according to the necessity of is case of study, including advantages and disadvantages. ONE-DIMENSIONAL MODELS Oppel et al. [5] developed an explicit finite di- fference model. The model was covered throu- gh-flow conditions for charging or discharging the thermal storage tank and conduction and turbulent mixing model within the water. The authors developed the “buffer-tank” that allows variable rate flow and eliminates the pseu- do-mixing in the algorithm. The energy equa- tion is solving by splitting it in two equations, the conduction and the convection cases. The parameters AMIX and FLOW (Courant number) were used to ensure stability in the numeri- cal simulation. The model was compared with experimental date and there was good agree- ment in the comparison. The model of Zurigat et al. [9] is known like the “effective diffusivity model”. This model is a finite