THE EFFECT OF USING DIFFERENT OBSTACLES INTO. THERMAL STRATIFICATION IN HOT WATER STORAGE. TANK WITH FORCED CONVECTION

Mevlut ARSLAN1, Necdet ALTUNTOP1, Veysel OZCEYHAN1,

1 Dept. of Mechanical Engineering, Erciyes University, 38039 Kayseri, Turkey

Abstract

The numerical analysis of thermal stratification in the cylindrical hot water storage tank with using different kind of obstacles has been presented. The heat transfer is carried out by forced convections in the tank. To obtain higher thermal stratification inside the tank, optimum obstacle type has been determined between 30 different kinds of obstacles. The forced convection effect into the temperature distribution inside the tank has also obtained for different obstacle types. The temperature relations between water exit from the tank and, the water enter to the collector and the water return to the collector have presented according to obstacle type in the graphs. The temperature differences of these waters have also presented to determine thermal stratification according to the obstacle types and angles. The temperature distributions between tank with using obstacle and smooth tank have also been analyzed to compare to get high thermal stratification. At the results, Obstacle type 11 has been found that it has best thermal stratification inside the tank between all investigated cases in forced convection.

1. Introduction

Solar energy applications are widely used in industry. Water heating is one of the solar energy applications. Energy storage is much more important where the energy source is intermittent, such as solar energy. In solar energy storage tank, the temperature of the hot water in the tank stars to decrease while the use of the hot water from the tank starts because of the cold water entering from the main line. The hot water and cold water would mix each other and the hot water temperature will decrease. In present study, using different kinds of obstacles have been proposed to obtain high thermal stratification in the storage tank.

Some researcher presented some works about there fields as; ALIZADEH, has investigated the thermal behavior of a horizontal cylindrical storage tank both experimentally and numerically. He used one dimensional the Turbulent Mixing Model and Displacement Mixing Model in numerical calculations [1].

AL-NIMR has solved and presented some mathematical models to determine the effect of the different design parameters on the thermal stratification within the tank and the time required by tank to supply water within a specified outlet temperature [2].

MISRA has analyzed the thermal stratification both theoretically and experimentally in hot water storage tank for the thermo siphon effect in solar water heating systems. He has given the analytical expressions to obtain temperature distributions in the tank [3].

HELVA ad MOBARAK have investigated the effect of the amount of the hot water using into the temperature distribution in solar water heating storage tank [4].

HARIHARAN and BADRINARAYANA have analyzed the thermal stratifications numerically and experimentally in the hot water storage tank. They have observed that stratification improves with increasing AT and water flow rates [5].

Mo and MIYATAKE have carried out the transient numerical analysis for the thermal stratifications in the storage tanks. They have used turbulence model (k-s model). They have presented the effect of exchange cold water with hot water into the thermal stratifications [6].

YOO and KIM have presented analytical solution to model describing the charging process of stratified thermal storage tank with variable inlet temperature [7].

EAMES and NORTON have investigated the effect of the tank geometry into the thermal stratification for sensible heat storage for low Reynolds number. They have presented the effect of inlet and outlet port locations on store performance [8].

In present study, numerical analysis of using the different obstacles into the thermal stratification has been presented in the storage tank. The different kinds of obstacles are placed in the cylindrical tank to get the best performance for thermal stratifications inside the tank between all investigated cases. The water was used as fluid.

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