• Transactions of the KSME C: Technology and Education
• /
• v.2 no.1
• /
• pp.65-72
• /
• 2014

The purpose of this study is to design a heat insulator for reducing available energy loss in stratified thermal storage tank. Heat insulator is operated by buoyancy effect from density difference between hot and cold water without extra equipment. Analysis model using the Matlab Simulink was developed to estimate the internal temperature distribution in thermal storage tank and also used to select proper material and thickness of the heat insulator. Operational feasibility was confirmed through reduced scale experiment. As a result, heat insulator can effectively delay the formation of thermal boundary layer between hot and cold water. In reduced scale experiment, heat insulator can preserve additional 1540J of available energy. When applied to the real thermal storage tank, increase of 6% thermal storage efficiency can be expected.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.37 no.4
• /
• pp.331-341
• /
• 2013

In a solar domestic hot water (SDHW) system, solar energy is collected using collector panels, transferred to a circulating heat transfer fluid (brine), and eventually stored in a thermal storage tank (TST) as hot water. In this study, a computational fluid dynamics (CFD) model was developed to predict the solar thermal energy storage in a hybrid-type TST equipped with a helical jacket heater (mantle heat exchanger) and an immersed spiral coil heater. The helical jacket heater, which is the brine flow path attached to the side wall of a TST, has advantages including simple system design, low brine flow rate, and enhanced thermal stratification. In addition, the spiral coil heater further enhances the thermal performance and thermal stratification of the TST. The developed model was validated by the good agreement between the CFD results and the experimental results performed with the hybrid-type TST in SDHW settings.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.17 no.11
• /
• pp.990-997
• /
• 2005

The stratified effect was investigated with three different types of diffuser shape in a thermal storage tank with variation of diffuser diameter, velocity, Froude number etc. Its effect was estimated by the degree of stratification. No matter of diffuser diameter and shape, the degree of stratification was the best as the Froude number gets closer to 1. In the case of a curved diffuser, when its diameter is a quarter of tank diameter and ejection velocity in a diffuser is approximately 0.2 m/s, the Froude number was almost 1. In the case of a flatted diffuser, when ejection velocity was 0.05 m/s, the Froude number was 1.5. Both cases which Froude number were nearer 1, showed the good degree of stratification.

• 한국태양에너지학회:학술대회논문집
• /
• 2008.04a
• /
• pp.300-303
• /
• 2008

The stratification effect was investigated with four different types of diffuser shape in a thermal storage tank. For this study, experimental facility was constructed, which was composed of experimental thermal storage tank, hot and cold water storage tanks, boiler, chiller, data acquisition system, etc.. Visualization and lab scale experimental result showed that radial curved type diffuser was the highest degree of stratification among the four diffuser shapes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.26 no.1
• /
• pp.8-14
• /
• 2014

We have performed experiments to enhance the stratification in a storage tank in order to raise the collector efficiency and solar fraction in solar thermal systems. The storage tank with a spiral jacket in the side wall has a scroll-shaped heat exchanger coil added to the upper part. The performance was compared between only the side and upper-side heating part through simulation using TRNSYS under the same weather conditions and initial conditions. As a result, the upper-side heating has a 4.2% advantage in solar fraction, but almost no increase in collector efficiency.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.22 no.7
• /
• pp.468-473
• /
• 2010

This paper deals with approximate integral solutions to the one-dimensional model describing the charging process of stratified thermal storage tanks. Temperature is assumed to be the form of Fermi-Dirac distribution function, which can be separated to two sets of cubic polynomials for each hot and cold side of thermal boundary layers. Proposed approximate integral solutions are compared to the previous works of the approximate analytic solutions and show reasonable agreement. The approach, however, has benefits in mathematical difficulties, complicated solution form and unstable convergence of series solution founded in the previous analytic solutions. Solutions for a semi-infinite region, which have simple closed form solutions, give close agreement to those for a finite region. Thermocline thickness is obtained in closed form and shows proportional behavior to the square root of time and inverse proportional behavior to the square root of flow rate.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.1
• /
• pp.42-51
• /
• 1995

In order to establish a theoretical basis for the analyses of transient behaviors in stratified thermal storage tanks, analytical approaches to an improved one-dimensional model are made. In the present model the storage tank is treated as a finite region with an adiabatic tank exit, whereas it has been considered as a simple semi-infinite region previously. Application of the Laplace transformation and the Inversion theorem to the governing equations makes it possible to obtain an exact infinite-series solution, which is convergent only at sufficiently large time. Accordingly a complementary solution which is available for short times, i.e., the time range of this study is sought by an approximate method. The approximate solution which is rigorously validated through the examination of neglected terms in the solution procedure agrees quite well with the exact one. Moreover, it is simpler to use and more convenient to interpret the physical meaning of the solution. Comparison of the present solution with the previous ones shows relatively large difference near the tank bottom, which results from the more realistic boundary condition adopted in the present model. Some representative results by the approximate solution including effects of the Peclet number on temperature distrbutions are illustrated to show the utility of this study. In consequence, it is expected that the present results based on the improved model replace the foregoing ones as a new theoretical reference for studies of thermal stratification fields.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.4
• /
• pp.336-342
• /
• 2012

Large-scale active solar heat systems are generally using heat exchanger between collector and storage tank loops to prevent damage by freezing. It is difficult to maintain stratification in a storage tank in the system owing to greater flow rate enhancing heat transfer. In the previous study, we introduced a spiral-jacketed storage tank and obtained good results to keep system performance of general level without better stratification. We added a scroll-shaped heat exchanger coil on the upper part in the spiral-jacketed storage tank. As a result of the experiment, it was verified that degree of stratification of the new type storage tank is higher than that of the previous one with a possibility of better collector efficiency and solar fraction.

• Solar Energy
• /
• v.14 no.2
• /
• pp.3-16
• /
• 1994

The major objectives of the study are to suggest the optimal basic design conditions for the horizontal storage tank system. For this purspose computer simulation has been carried out to find the characteristics of flow patterns in horizontal storage tank, and experiments have been carried out for the duration of one turnover, Experimental parameters are volume flow rate(1 LPM to 4 LPM), amount of heat generated from heat sources(0 W to 100 W), and inlet and outlet port types of the storage tank(DD type, DO type, ID type, IO type).

• 한국태양에너지학회:학술대회논문집
• /
• 2008.11a
• /
• pp.178-183
• /
• 2008

The purpose of this study is to compare the effect on the thermal stratification under various aspect ratios in the solar storage tank using FLUENT. Numerical calculations of three designs with different aspect ratio were carried out to show the behaviour of stratification in a solar storage tank. The calculation results show that the thermal stratification of the 2.5:1 aspect ratio solar storage tank can be 6.22% higher then that of the 1.5:1 aspect ratio solar storage tank and 2.68% higher then that of the 2:1 aspect ratio solar storage tank.