•The effect of particle contact on heat storage tank performance was studied.•The evolutions of apparent thermal resistance were studied.•The evolutions of average heat flux were studied.
Energy ...Internet can guarantee the efficient and stable use of renewable energy, and the energy storage device bears an important linking task. In order to achieve a fast response to Energy Internet, energy storage devices often use metal particle heat storage tanks. The contact between particles is complicated, which directly affects the heat storage performance of the particle tank. Therefore, it is very important to study the effects of the contact between the particles on the performance of the fast-response heat storage tank. In this paper, a 2D steady-state heat storage and release model of the elliptical particles tank was established. The influence of particle contact coefficient on the performance of the heat storage tank was studied. The results showed that with increases of the particle contact coefficient, the average heat flux increases, and the apparent thermal resistance decreases. The work performance and dynamic response performance of the heat storage tank increase. The effect of vacancy on the performance of the heat storage tank is basically not affected by the change of particle contact coefficient.
Thermocline sensible heat storage (SHS) systems are usually utilized in parabolic trough solar power systems. Liquid lead–bismuth eutectic (LBE) is a potential heat transfer medium for SHS systems, ...but its influences on the performances of SHS systems are rarely studied. In this study, a simulation model of thermocline SHS tank using liquid LBE as the heat transfer fluid is established, and the influences of initial cold and hot LBE temperatures on the operation and mechanical performances of the tank are estimated. The results reveal that when the liquid LBE is used as the heat transfer fluid, the SHS tank can operate stably. The initial cold LEB temperature has almost no influence on both the total heat storage and heat release durations of the tank, while the initial hot LBE temperature has proportional relationships with the total heat storage and heat release durations. The heat storage performance as well as the heat release behavior of the tank can be improved by increasing the initial cold LBE temperature, or by decreasing the initial hot LBE temperature. The peak maximum mechanical stress of the tank can be decreased by increasing the initial cold LBE temperature, or by decreasing the initial hot LBE temperature.
This paper presents an effect evaluation of initial hot molten salt temperature on behaviours of a thermally stratified latent heat storage (LHS) tank using phase change material (PCM) capsules. The ...influence of initial hot molten salt temperature on the heat storage, heat release and mechanical behaviours of the LHS tank are evaluated. The simulation results show that the initial hot molten salt temperature has relatively great influences on both the heat storage and heat release behaviours of the LHS tank. A higher initial hot molten salt temperature can reduce both the thermocline thickness and total heat storage duration of the tank in the heat storage process, and can increase the maximum heat storage and heat release powers, final effective heat storage and heat release quantities and peak maximum mechanical stress of the tank. When the initial hot molten salt temperature reaches 873.0 K, the peak maximum mechanical stress of the tank is 141.7 MPa. Therefore, to achieve a better operation behaviour of the LHS tank, the initial hot molten salt temperature should be appropriately increased while ensuring that the peak maximum mechanical stress of the tank does not exceed the yield stress and a certain margin can be kept.
It is necessary to satisfy the flexible requirements of solar heat storage systems to provide efficient heating and constant-temperature domestic hot water at different periods. A novel heat storage ...tank with both stratified and mixing functions is proposed, which can realize the integration of stable stratification and rapid mixing modes. In this research, a three-dimensional heat transfer model of the heat storage tank with stratified and mixed dual modes was established, and a thermal performance test system for the tank was built in the State Key Laboratory of Green Building in Western China. Moreover, a new evaluation index representing the mixing speed is proposed. The stratification effect and mixing characteristics of the tank were studied under different comprehensive conditions. The results show that the exergy efficiency of the tank with a stratified pipe can be increased by 10%–15% compared to that of a conventional tank. Additionally, the recommended optimal flow rate range for well-stratified tanks is 4–6 L/min. The mixing nozzle of the tank reduces the mixing reaction coefficient by 0.27 and significantly reduces the mixing time. This study provides critical guidance to meet the flexible thermal needs of users and implement high-performance applications using the stratified and mixing modes of heat storage tanks.
Renewable energy sources (RES) and their transformation technologies become more attractive in building sector as energy demand and emissions to the environment increase. Along with renewable energy ...transformation technologies, the importance of energy storage also arises as these RES are characterized by volatility and energy mismatch over time. For this reason, engineering systems which use RES are becoming increasingly dynamic. This study examines ongoing processes in a vertical cylindrical storage tank designed to cover domestic hot water demand in a building. Simultaneous dynamic mode of operation when the energy is being charged and at the same time discharged from the storage tank is analysed. Experiments are performed and stratification number describing thermal stratification is calculated. The obtained data are used for the development and validation of the numerical model. Using Ansys Fluent software, the influence of different discharge rate on operation mode of the storage tank is investigated. Graphical and numerical interpretation of results is performed.
•We design the schematic diagram of solar desalination system with evacuated tube collectors.•Mathematical and economic models of the collector and desalination subsystem are proposed.•The method of ...desalination is low temperature multi effect distillation.•The cost constitution of solar desalination system is shown.•The water cost given appreciate the economic performance of the system.
Conventional seawater desalination technology could solve the problem of fresh water shortage, but consumes a large amount of fossil fuel and causes the environmental problems such as global warming and acid rain. On account of this, solar desalination is one of the promising methods. The thermal and economic performance on solar desalination system with evacuated tube collectors and low temperature multi-effect distillation is researched in this paper. Mathematical and economic models are established based on mass and energy conservation, which conclude evacuated tube collector model, heat storage tank model, flash tank model, multi-effect distillation model and electrical heating and cooling model. Taking actual operation into account, the influence of the heating steam temperature of the first effect and the effect number of multi-effect distillation system on system performance is analyzed. The cost constitution of solar desalination system with evacuated tube collectors is shown, and the proportion of the cost of evacuated tube collector is the largest. The water cost is given out to appreciate the economic performance of the solar desalination system. The conclusions are helpful to the design and operation of solar desalination plant.
A heat storage tank (HST), described in this paper, may be applied to numerous systems used for thermal energy generation and storage. Working principle and heat-flow processes of the HST remain the ...same and are independent of the systems in which the HST is being used. This paper presents a thermal-flow analysis of a heat storage tank (HST) operating in an air compressor heat pump (ACHP) and a dry cooler (DC) combined cycle. The HST is operated under transient conditions for four different ACHP steady states. The HST was analysed using lumped capacitance method. The heating power of a single coil varied from 2.2 to 3.2 kW. 50% increase in mass flow rate of heating water in the coils increased the HST water mean temperature by 5.6 °C. A differential equation for the HST water temperature variation was solved analytically and it was presented with the use of dimensionless numbers. The presented solution is of a general form. An important parameter such as number of the coils may be varied easily. Additionally, a Mathcad computational program was proposed for the estimation of HST-ACHP-DC system thermodynamic and thermal-flow parameters. System dynamics was studied using MATLAB/Simulink. An optimal operating parameters of the HST were found and are presented in the paper. The aforementioned parameters are as follows: mass flow rates of heating and cooling media in all three coils, mass flow rate of freshwater supplying the HST, number of loops in coils and resulting heat transfer area, diameter of the loops of the coils, diameter of the coils, time after which water in the HST reaches a steady value, time period within which the HST may fulfil demand for central heating and domestic hot water (DHW) preparation without being charged simultaneously. The presented analytical model was validated based on the available data in the field literature and a high compliance was reached. For this purpose theoretical model results were compared to results of HST computational fluid dynamics (CFD) simulations. The temperature calculated using the presented model differed from the one obtained by the CFD analysis by 2.96 K.
The central heating technology with thermal storage technology is an important means to realize thermoelectric decoupling, meet heating demand, reduce primary energy consumption, and protect the ...ecological environment. For this paper, the numerical simulation method was used to study the temperature variation of large-capacity hot water storage tank (HWST) in an actual combined heat and power system. The influence of various factors, including the length diameter ratio, water supply temperature, and water supply flow, as well as the orifice diameter and number of the water distributor, on the flow uniformity and performance of the HWST was investigated. The results show that the heat storage efficiency and flow uniformity of the HWST can be improved by properly increasing the water supply flow, the orifice diameter, and number of the water distributor. Increasing the length diameter ratio can improve the flow uniformity, but it will reduce the heat storage efficiency of the HWST. Increasing the water supply temperature can increase heat storage efficiency of the HWST and accelerate the stratification of cold and hot water in the tank. Besides, the comprehensive analysis of the non-dimensional exergy loss calculation results, velocity field, and temperature field show that there is a certain coupling relationship between the non-dimensional exergy loss and flow uniformity at the initial stage of heat storage. In practical application, the influence of these factors on flow uniformity, heat storage efficiency, and non-dimensional exergy loss should be comprehensively considered in order to achieve the best heat storage and release performance of the HWST. This paper provides some engineering guidance for the application of large-capacity heat storage tanks in the combined heat and power (CHP) system.
A ground source heat pump system is one of the high-efficient technologies for space heating and cooling since it uses stable underground temperature. However, in actual application, many situations ...cannot be achieved due to the unsuitable design of operation. In particular, the design characteristics of buildings with different building load patterns are not reflected by the conventional design method. Moreover, the design capacity of the heat pump can be reduced by designing less capacity than the peak load through the introduction of the heat storage tank, but there is no related quantitative design method. Therefore, in this study, the effect of the ground source heat pump system design factors such as shape, length of the ground heat exchanger, and the capacity of the heat storage tank on the system performance was analyzed. To quantify the effect of such factors on system performance, an experimental plant was constructed and case studies were conducted for each design factor.
Heat storage systems with multiple heat sources play an important role in consuming extra wind power. A reasonable scheduling strategy for a hybrid system with multiple heat and electric sources ...could provide greater economic benefits. However, the present scheduling methods primarily focus on extra wind power consumption alone. This paper aims to develop a coordinated dispatching method that targets the maximum extra wind power consumed and highest economic benefit of the hybrid energy system as the optimization objective. A two-step coordinated dispatching method is proposed, where the first step focuses on optimizing the extra wind power consumed by coordinating the consumption quota for different types of energy sources at the system level and distributes the consumption share for every unit within each type of energy source, thereby maximizing fuel savings and economic benefits in the second step. The effectiveness of the approach is demonstrated using simulation results for an electric-heat hybrid system. Compared with two existing dispatching methods, the scheduling strategy presented in this paper could consume more extra wind power and provide higher fuel savings and economic benefits.
PDF
