Mobilized Thermal Energy Storage Research Articles

Numerical Simulation of an Indirect Contact Mobilized Thermal Energy Storage Container with Different Tube Bundle Layout and Fin Structure

The great development of energy storage technology and energy storage materials will make an important contribution to energy saving, reducing emissions and improving energy utilization efficiency. Mobile thermal energy storage (M-TES) technology finds a way to realize value for low-grade heat sources far beyond the demand side. In this paper, an indirect-contact M-TES container is studied using the computational fluid dynamics (CFD) method. By optimizing the heat exchange tube bundle layout and the installed fin structure of the shell and tube type M-TES container, a method of enhancing the charging and discharging efficiency is identified. The peripheral distribution mode of the heat exchanger tubes improves the efficiency of heat charging by 12.6% compared with the traditional uniform layout. The installation of the Y-shaped fins can improve the heat charging efficiency by 8.3%, better than straight fins. Compared with the horizontal installation of Y-shaped fins, the vertical installation of Y-shaped fins is preferred to improve the heat charging efficiency of the M-TES container.

Mobilized thermal energy storage (M-TES) system design for cooperation with geothermal energy sources

The main focus of this paper is the mobilized thermal energy storage system designed to be applied in the heating system of a single-family residential building. It has been investigated if it is possible to use geothermal heat as a heat source for M-TES based on PCMs. To analyze this possibility, tests were carried out under real conditions. The M-TES with 700 kg of Rubitherm RT70HC PCM filled into the tank equipped with internal heat exchanger was designed and experimentally tested in Szaflary and Zakopane, Poland. Conceptual and research work were carried out in cooperation with innogy Polska S.A., PEC Geotermia Podhalańska S.A. and the startup company Enetech sp. z o. o. The field tests were preceded by the series of laboratory experiments. On their basis and on the basis of literature research, a hypothesis was put forward that: it is possible to supply single-family buildings with the M-TES based on PCM, powered by geothermal sources. This has been confirmed in practice by observing the process of loading the storage in the heat source, its transport and heat collection at the user's location. The process was observed through the acquisition of the temperature data inside the tank. The appropriate distribution of sensors allowed the analysis of temperatures at the entrance, exit and located both centrally and at the walls of the tank. Results show that there can be indicated some important aspects that have a significant influence on the operation and justification of the application of the M-TES. Among them: proper selection of PCM, proper design of the heat exchanger, supply temperature and constancy of the heat source operating conditions, distance between charging and discharging points. An additional goal of this article is to present guidelines for the design of such systems, which were formulated on the basis of measurements and observations. The paper was designed to highlight the weakest points of the tests and areas for improvement.

Mobilized Thermal Energy Storage for Waste Heat Recovery and Utilization-Discussion on Crucial Technology Aspects

Changes observed in the Polish energy sector, including the demand for and use of heat, require the introduction of appropriate measures aimed at diversifying the available heat sources, increasing the share of renewable and low-emission sources in heat production, and increasing waste heat recovery and its usage. There is an increasing emphasis on issues such as reducing the carbon footprint, reducing pollution, reducing the use of raw materials, reducing waste heat, and improving the energy efficiency of businesses. Increasingly, the question arises—what technologies can be used as an answer to the identified problems and needs. The solution proposed in this publication to support these needs is the use of mobilized thermal energy storage (M-TES) technology. The use of this technology has great potential, but also involves a number of conditions that need to be taken into account when undertaking the design, construction, and use of this type of technology. The primary purpose of this publication is to provide a detailed description of mobilized thermal energy storage technology, together with a discussion of the various practical aspects associated with the design and use of M-TES. Technology was discussed both in terms of application, but also in terms of specific areas. In the first case—step-by-step, from the design stage to the end-of-life stage. In the second case—one area at a time, including: technical, legal, economic, and environmental. The discussion of the technology is preceded by an analysis of the existing solutions presented in this area. The state-of-the-art shows that, despite the growing interest in the subject, there are still a small number of solutions in this area that have been implemented and are in use. The conducted analysis shows that M-TES is a solution with great potential. However, it is necessary to develop it, especially in the technological, as well as economical, areas.

Techno-Economic Assessment of Mobilized Thermal Energy Storage System Using Geothermal Source in Polish Conditions

The paper considers technical and economic possibilities to provide geothermal heat to individual recipients using a mobile thermal storage system (M-TES) in Polish conditions. The heat availability, temperature and heat cost influence the choice of location—Bańska Niżna, near Zakopane in the southern part of the Poland. The indirect contact energy storage container was selected with phase change material characterized by a melting temperature of 70 °C and a heat storage capacity of 250 kJ/kg, in the amount of 800 kg. The economic profitability of the M-TES system (with a price per warehouse of 6000 EUR, i.e., a total of 12,000 EUR—two containers are needed) can be achieved for a heat demand of 5000 kWh/year with the price of a replaced heat source at the level of 0.21 EUR/kWh and a distance between the charging station and building (heat recipient) of 0.5 km. For the heat demand of 15,000 kWh/year, the price for the replaced heat reached EUR 0.11/kWh, and the same distance. In turn, for a demand of 25,000 kWh/year, the price of the replaced heat source reached 0.085 EUR/kWh. The distance significantly affected the economic profitability of the M-TES system—for the analyzed case, a distance around 3–4 km from the heat source should be considered.

Experimental study on thermal performance of a mobilized thermal energy storage system: A case study of hydrated salt latent heat storage

A mobilized thermal energy storage (M-TES) system was proposed to utilize the renewable energy or recover the industrial waste heat in this paper. The M-TES system with 215 kg sodium acetate trihydrate as phase change material (PCM) filled into a tube-in-tank heat exchanger was designed and experimental tests were conducted to evaluate its thermal performance. The charging-discharging behavior of M-TES system was observed and temperature evolutions of PCM and heat transfer fluid (HTF) were monitored. The charging process of the M-TES system could be accomplished in 1200 s; while for energy discharging process, it took a little longer (1400 s) due to the prevention of natural convection. It also revealed that the non-uniform temperature distribution of PCM would result in asynchrony of melting/solidification. The PCM in the middle part of the tubes would melt at first, whereas the temperature of the PCM close to the end of the tubes increased much slower. The temperature difference was much more significant during the discharging process. Super cooling could be found easily for the PCM in the ends of tubes. The released heat in the discharging process was applied to heat the cooling water to mimic the domestic consumption of hot water to investigate the thermal performance of energy discharging. With perfect performance of our indirect contact heat exchanger, the thermal efficiency was estimated of 79.4%. Our tests would provide an experimental basis for the application of the low-temperature mobilized LHTES system.

Techno-economic assessment of mobilized thermal energy storage for distributed users: A case study in China

The mobilized thermal energy storage (M-TES) system is a promising alternative to conventional heating systems to meet the heat demand for distributed users. This paper provided a techno-economic assessment of the M-TES system based on a case study in China. According to the analysis of the design specifications of the heating system, the suitability of matching the M-TES with existing heating systems was analyzed. The results show that the M-TES is appropriate for use with heating systems with a fan-coil unit and under-floor pipe. Containers and operating strategies for the M-TES with different transportation schemes were also designed. The maximum allowed load of the M-TES container is 39t according to the discussion of transportation regulations on the road. The cost and income of the M-TES in the study case were estimated, and the net present value (NPV) and payback period (PBP) were also calculated. The best operating strategy is the use of 2 containers and 4 cycles of container transportation per day, with a PBP of approximately 10years. The M-TES is applicable for middle and small-scale heat users in China.

Economic Assessment of Mobilized Thermal Energy Storage for Distributed Users: A Case Study in China

Mobilized thermal energy storage (M-TES) system can be an alternative of the conventional heating system to meet the heat demand for distributed users. This paper conducted a case study of the M-TES system in China. The operating strategies (OS) of the M-TES with different transportation schemes were compared. Moreover, the economic assessment was performed based on the project's net present value (NPV) and payback period (PBP). The OS with 6 trips per day is the most profitable with pay-back time of about 2, 3 and 5 years if the waste heat costs at the level of 0 €/MWh, 3300 €/MWh, and 6600 €/MWh, respectively.

Experimental study on solving the blocking for the direct contact mobilized thermal energy storage container

As a promising technique of the waste heat recovery, the mobilized thermal energy storage (M-TES) can reduce the energy consumption and meet the heat demand for distributed users. With the convective heat transfer in the container, the direct contact M-TES shows a good charging and discharging performance except the blocking by the deposited phase change material (PCM) at the initial stage of the charging process. This paper studied a solution on forming the quick channels (QC) with electric heaters to solve the blocking issue. Phase change behaviors of PCM in the container with and without QC were analyzed and compared. With the QC formed with electric heaters, the charging time at the early and middle stage is obviously shortened compared with that of the experiment without electric heating. However, the solution is not suitable at later stage of charging because of the fading away of QC. The formation of QC takes about 90 s and covers around 5% of the thermal energy stored in the container. The results present that it is a good method to solve the blocking issue for the direct contact M-TES system especially with a low rate of heat release.

Numerical simulation study on optimizing charging process of the direct contact mobilized thermal energy storage

Mobilized thermal energy storage (M-TES) system is considered as an attractive alternative to supply heat to distributed heat users, especially when the waste heat from industries is used as a heat source. From our previous study it was known that the charging time of M-TES system was more than four times of the discharging time, which was a critical issue for the application of M-TES. To improve the charging performance of the system and further understand the mechanism of melting process, a 2-dimensional (2D) numerical simulation model was developed in ANSYS FLUENT. The model was validated by the experimental measurements. The results showed that the model could be used for the engineering analysis. With the validated model, different options to shorten the charging time were investigated including increasing flow rate of thermal oil, creating channels before charging and adding wall heating. Correspondingly, around 25%, 26% and 29% of the charging time could be reduced respectively compared to the experiment with a thermal oil flow rate of 9.8L/min, according to the numerical simulation. In addition, if the last two options could be applied simultaneously, more than half of the melting time might be shortened without changing the flow rate of thermal oil.

Experimental Study on Heat Transfer Enhancement of Heat Exchanger in Indirect Mobilized Thermal Energy Storage System with Fins

To recover waste heat for the distributed users,an indirect mobilized thermal energy storage(M-TES) system is designed incorporating a medium temperature phase change material(PCM) erythritol.Because the low thermal conductivity of the PCM,the copper tube that with double straight fins is chosen to help enhance the heat exchange.The thermal characteristics in the system are analyzed using temperature time curves.The investigation shows that the temperature of the PCM rises rapidly in the solid sensible heat stage in the heat storage process,but there is almost no temperature change in the latent heat stage.The natural convection can make the PCM melt faster.The melt process of the PCM takes 210 min.The temperature of the heat source has influence on the charging time and the temperature gradient of the PCM.In the heat release process,the PCM shows sub-cooling phenomenon.The investigation also shows that 16 790 kJ of heat is released in the initial 120 min of discharging process that accounts for 84 % of heat capacity of the M-TES container,which can heats 0.115 m3of water from 10 ℃ up to 55 ℃.The system shows a good performance in energy storage process.It makes the mobile energy storage car can be truly used for recover industrial waste heat.

Economic assessment of the mobilized thermal energy storage (M-TES) system for distributed heat supply

A conceptual system, mobilized thermal energy storage system (M-TES), was proposed for distributed heat supply. The economic evaluation that is essential to identify the key issues and provide guidelines regarding system improvement was conducted in this paper. Results show that the cost using M-TES to supply heat (COH) is primarily determined by the transport distance and the heat demand. The variation of COH is proportional to the transport distance, but inversely proportional to the heat demand. According to the sensitivity study, COH is more sensitive to the price of phase change material (PCM) than other parameters, such as the transport cost. Moreover, it is possible for an M-TES system to compete with other heat supply methods, such as pellet/bio-oil/biogas/oil boiler systems and electrical air-source heat pump. When using M-TES to replace the existing system, the payback time is mainly determined by the transport distance and the heat demand. Water is another potential working fluid for M-TES system. Comparatively, using PCM is more suitable for cases with larger heat demand or longer transport distance.

Combined heat and power plant integrated with mobilized thermal energy storage (M-TES) system

Energy consumption for space and tap water heating in residential and service sectors accounts for one third of the total energy utilization in Sweden. District heating (DH) is used to supply heat to areas with high energy demand. However, there are still detached houses and sparse areas that are not connected to a DH network. In such areas, electrical heating or oil/pellet boilers are used to meet the heat demand. Extending the existing DH network to those spare areas is not economically feasible because of the small heat demand and the large investment required for the expansion. The mobilized thermal energy storage (M-TES) system is an alternative source of heat for detached buildings or sparse areas using industrial heat. In this paper, the integration of a combined heat and power (CHP) plant and an M-TES system is analyzed. Furthermore, the impacts of four options of the integrated system are discussed, including the power and heat output in the CHP plant. The performance of the M-TES system is likewise discussed.