Thermal Stratification In Storage Tank Research Articles

Investigation of thermal stratification in a thermal storage tank with a curve edge obstacle plate

Nowadays, thermal storage tanks have been widely installed because of high demanding for hot water in the production process or daily activities in a household. Numerous energy has been consumed to produce hot water. To reduce the energy consumption and improve the energy efficiency of the hot water system, the design of thermal stratification in a storage tank can play as an important parameter on its thermal efficiency. The basic concept of the thermally stratified tank is attempted to separate a layer of hot and cold water by means of density variation and gravitational effects which cold water is aimed to existing at the bottom and hot water is at the upper part of the tank. The level of temperature stratification significantly impacts on the thermal efficiency. The higher degree of thermal stratification, the better thermal efficiency of the hot water system. However, there are many factors strongly affected the thermal stratification such as height-to-diameter ratio, the inner structure of thermal storage tank, the water flow rate, and etc. Therefore, the purpose of this study is to design a thermally stratified tank by improvement the inner structural design of the tank. Two influenced factors are focused: i) the different configuration of inlet pipes which can impact on the flow pattern and flow velocity of the water and ii) the different design of obstacle plates which can help control a recirculation area of the water in the tank. To obtain a high thermal efficiency of the stratified tank, the computer simulation program Ansys Fluent is applied for the analysis. The results show that uniform distribution of water flow and lower flow velocity due to the appropriate design of inlet pipe and proper buffer plate design can enhance the temperature stratification in the storage tank which increase the thermal efficiency during discharging processes.

Thermal stratification built up in hot water tank with different inlet stratifiers

Thermal stratification in a water storage tank can strongly increase the thermal performance of solar heating systems. Thermal stratification can be built up in a storage tank during charge, if the heated water enters through an inlet stratifier.Experiments with a test tank have been carried out in order to elucidate how well thermal stratification is established in the tank with differently designed inlet stratifiers under different controlled laboratory conditions.The investigated inlet stratifiers are from Solvis GmbH & Co KG and EyeCular Technologies ApS. The inlet stratifier from Solvis GmbH is a rigid plastic pipe with holes for each 30cm. The holes are designed with flaps preventing counter flow into the pipe. The inlet stratifier from EyeCular Technologies ApS is made of a flexible polymer with openings all along the side and in the full length of the stratifier. The flexibility of the stratifier prevents counterflow.The tests have shown that both types of inlet stratifiers had an ability to create stratification in the test tank under the different test conditions. The stratifier from EyeCular Technologies ApS had a better performance at low flows of 1–2 l/min and the stratifier for Solvis GmbH & Co KG had a better performance at 4 l/min. In the intermediate charge test the stratifier from EyeCular Technologies ApS had a better performance in terms of maintaining the thermal stratification in the storage tank while charging with a relative low temperature.

Experimental performance study on a dual-mode CO2 heat pump system with thermal storage

Performances of a water-source CO2 heat pump coupled with hot and cold thermal storage were investigated experimentally in this study. This combined system was tested by controlling compressor frequency, expansion valve opening, and hot and cold circulated water flow rates. Experimental results shows that higher compressor frequency leads to a shorter energy charging time and a higher overall coefficient of performance (COP) of the combined system during the charging process. Expansion valve opening affects the COPs significantly but affects the thermal stratification in thermal storage tanks slightly. Low hot and cold water flow rates lead to the good thermal stratification in storage tanks, which is beneficial for the overall COP of the combined system during the charging process, although high water flow rates are beneficial for the transient COP of heat pump at the beginning of the charging process. The overall COP reaches maximum when the hot and cold water flow rates were set as 0.1m3/h and 0.2m3/h respectively at the compressor frequency of 50Hz and at the expansion valve opening of 330 pulses. Based on the test data, the correlations of COP with the outlet water temperature of thermal storage tanks were developed for further optimizing this combined system.

Thermal stratification in storage tanks of integrated collector storage solar water heaters

To determine the influence of the shape of the tank, the installation angle, and the magnitude of the absorbed heat flux on thermal stratification in integrated collector-storage solar water heaters, numerical simulation of thermal convection in tanks of different shapes and same volume was carried out. Idealized two-dimensional models were studied; automodel stratification profiles were obtained at the constant heat flux. The shape of the tank, the pattern of the heat flux dynamics, the adiabatic mixing on the circulation rate and the degree of stratification were shown to have significant influence.

유량제어방식에 따른 태양열 급탕시스템의 열성능 평가

In this study, the performance and behavior of solar heating system according to the system control scheme, variable flow control (proportional control) and constant flow control (on-off control) was carried out by experiment. The on-off control is used generally for solar thermal system by now. But the proportional control is used for the solar district heating system which is supplied the higher temperature of water than that of desired. The proportional control logic that pump speed is varied in an attempt to maintain a specified outlet temperature of solar heating system was developed and tested for the use widely for the small and medium solar thermal system. The results are as following. First, the proportional controller which is made here could be adopted the characteristics for setting temperature control. Second, the proportional control is better than the on-off control in the side of the performance of thermal stratification in storage tank. Third, the operating energy(electricity consumption by pump) of solar thermal system can be saved more than 60% using the proportional control comparing to the on-off control.

Performance study of a partitioned thermally stratified storage tank in a solar powered absorption air conditioning system

Accurate modeling of solar heating or cooling with storage generally requires an accounting of the stratification within such storage tank, since overall system performance is significantly affected by the storage temperature distribution. In this study, a simple one-dimensional multi-node approach, taking into account of the axial heat conduction between nodes, has been used to theoretically analyze temperature stratification in the thermal storage tank. The results indicate that, for less collector area, the heat removal factor plays a major role in increasing the system performance, than the thermal stratification. Also, an optimum ratio of tank volume over collector area exists for a solar powered absorption air conditioning system. This paper also reviews the state of the art on different kinds of variable inlet design, and a simple new inlet design (partitioning the tank) has been introduced to effect better thermal stratification in storage tank.

Parametric studies on thermally stratified chilled water storage systems

An analysis of the stratification decay in thermally stratified vertical cylindrical cool storage systems is presented using a one dimensional conjugate heat conduction model. The degree of thermal stratification depends upon the length to diameter ratio, wall thickness to length ratio, the thermo-physical properties of the material of the storage tank, the type and thickness of the insulation and the design of the admission system for both cold and warm water. A parametric study of the stratified chilled water storage tanks in charging, discharging and stagnation modes of operation is made. The thermoclines degrade due to the heat transfer from the ambient, thermal diffusion in the storage tank, axial wall conduction and mixing due to admission of the fluid in the storage tank during charging and discharging. The degree of thermal stratification in storage tanks is expressed in terms of either heat capacity (thermal capacitance ratio) or modified Biot Number. A mixing parameter accounts for the effect of mixing on thermal stratification in both charge and discharge cycles.

Analytical and experimental investigation of thermal stratification in storage tanks

An analytical and experimental investigation of transient turbulent two-dimensional charging and discharging of a sensible heat storage tank has been conducted. Parametric studies showed that the turbulent mixing factor due to hydrodynamic disturbances at the inlet ports is the most significant item in the performance of thermal stratification storage tanks. Furthermore, the effect of the aspect ratio and convection at the walls in promoting stratification have been studied. Comparison with experimental data showed the capability of the present analytic approach to accommodate, with a satisfactory degree of accuracy, such problems.

Unique air conditioning system serves new industrial building

Accurate modeling of solar heating or cooling with storage generally requires an accounting of the stratification within such storage tank, since overall system performance is significantly affected by the storage temperature distribution. In this study, a simple one-dimensional multi-node approach, taking into account of the axial heat conduction between nodes, has been used to theoretically analyze temperature stratification in the thermal storage tank. The results indicate that, for less collector area, the heat removal factor plays a major role in increasing the system performance, than the thermal stratification. Also, an optimum ratio of tank volume over collector area exists for a solar powered absorption air conditioning system. This paper also reviews the state of the art on different kinds of variable inlet design, and a simple new inlet design (partitioning the tank) has been introduced to effect better thermal stratification in storage tank.