Parametric study on the thermal gradient of a small stratified domestic oil storage tank
A simplified one dimensional model for a small stratified domestic oil storage tank is used for a parametric study on the thermal gradient in the storage tank. The model is validated with experimental results and reasonably good agreement between experiment and simulation is obtained. The effects of measurable and physically adjustable parameters of the average charging flow-rate, the inlet charging temperature and the heat loss factor on the thermal gradient are investigated with the model.
Simulation of thermocline storage for solar thermal power plants: From dimensionless results to prototypes and real-size tanks
Abstract A single-phase one-dimensional model called CIEMAT1D1SF has been developed for characterizing the behaviour of thermocline tanks with an effective storage medium formed by either a liquid or a liquid and a packed-bed. Despite its simplicity, this model has been validated with experimental data and the results of tank performance are similar to those obtained by other authors using more complex simulation models. In order to obtain general results the thermal equation has been nondimensionalized and the resulting expression only depends on the parameter called dimensionless velocity, v ∗ . It has been observed that thermocline thickness decreases as v ∗ increases attaining a minimum value when v ∗  ⩾ 2350 while tank efficiency increases with v ∗ up to a maximum of about 87% also for v ∗  ⩾ 2350. From these results the design equation for building thermocline storage tanks with maximum theoretical efficiency has been established. Since this design equation depends on tank dimensions and thermal power, small thermocline tanks and hence prototypes are not expected to behave in the same way as large or real-size tanks. Therefore maximum efficiency guideline plots for thermocline tanks with different storage media have been presented for various temperature intervals. In these plots thermal power has proven to be the critical design parameter because the larger the power the higher the degree of freedom for choosing tank dimensions and hence storage capacity and charging/discharging time. Therefore, we strongly recommend the use of these guideline plots in the design process of thermocline prototypes.
Estimating correlations for the effective thermal conductivity of granular materials
Based on the well-known solution of Maxwell [1] for the thermal conductivity of dilute dispersions of spheres and the improved form of Maxwell’s equation developed by Chiew and Glandt [2], two general correlation for keff estimation are proposed. One of them apply to medium dense dispersions (0.15≤φ≥0.85) and the other one for dense porous materials (φ>0.9). Both correlating equations encompass a wide range of phase conductivity ratio values. The comparison with experimental measurements shows very good agreement.