The design and experimental measurements of the novel low-pressure thermal energy storage for the heating of electric vehicles

Electric vehicles (EVs) are receiving more attention these days because they are environmentally friendly (no emissions) and are much quieter than internal combustion engine vehicles with rapidly decreasing prices. One of the serious limitations of EVs is the limited driving range. When conventional heating and air conditioning systems are used in winter and summer, the driving range is reduced further because they consume a lot of electric energy stored in the batteries. A thermoelectric cooling system integrated with thermal energy storage has been identified as an attractive alternative to traditional air conditioning in electric vehicles. The main goal of such a system is to minimize the amount of electricity that is drawn for air-conditioning from the electric battery of the vehicle, thus eliminating further reduction in driving range. Not only is the alternative more light weight than the conventional vapor compression based air-conditioning system, it also reduces the amount of electricity drawn from the battery. The proposed system is comprised of thermal energy storage (TES) employing phase change materials (PCMs), thermoelectric electric modules, and a fan. The TES, also referred to as a thermal battery here, can be charged before at home or at a charging station before driving like the electric battery, and is discharged when used in driving. This study involved the design and development of a TES for EVs employing computational fluid dynamics and heat transfer analyses. The model includes all the key components such as thermoelectric (Peltier) modules, heat sinks and the PCM. Various simulations for thermal battery charging and discharging have been conducted to demonstrate the feasibility of incorporating TES coupled with thermoelectric modules.

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Solid Media Thermal Energy Storage System for Heating Electric Vehicles: Advanced Concept for Highest Thermal Storage Densities

Applied Sciences ◽

10.3390/app10228027 ◽

2020 ◽

Vol 10 (22) ◽

pp. 8027

Author(s):

Volker Dreißigacker

Keyword(s):

High Temperature ◽

Energy Storage ◽

Thermal Insulation ◽

Electric Vehicles ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Storage Systems ◽

Temperature Level ◽

Solid Media ◽

Thermal Energy Storage Systems

The integration of thermal energy storage systems enables improvements in efficiency and flexibility for numerous applications in power plants and industrial processes. By transferring such technologies to the transport sector, existing potentials can be used for thermal management concepts and new ways of providing heat can be developed. For this purpose, technology developments for solid media high-temperature thermal energy storage systems are taking place for battery-electric vehicles as part of the DLR Next Generation Car (NGC) project. The idea of such concepts is to generate heat electrically, to store it efficiently and to discharge it through a bypass concept at a defined temperature level. The decisive criterion when using such solutions are high systemic storage densities which can be achieved by storing heat at a high temperature level. However, when storing high temperature heat increasing dimensions for thermal insulation are required, leading to limitations in the achievable systemic storage density. To overcome such limitations, an alternative thermal insulation concept is presented. Up to now, conventional thermal insulations are based on sheathing the storage containment with efficient thermal insulation materials, whereby the thickness results from safety restrictions with regard to the permitted maximum surface temperature. In contrast, the alternative concept enables through the integration of the external bypass into the thermal insulation systemic advantages during the charging and discharging period. During discharging, previously unused amounts of heat or heat losses within the thermal insulation can be integrated into the bypass path and the insulation thickness can be reduced during loading through active cooling. Using detailed models for both the reference and the alternative thermal insulation concept, systematic simulation studies were conducted on the relevant influencing variables and on the basis of defined specifications. The results confirm that the alternative thermal insulation concept achieves significant improvements in systemic storage densities compared to previous solutions and high potentials to overcome existing limitations.

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Molten Nitrate Salt Development for Thermal Energy Storage in Parabolic Trough Solar Power Systems

ASME 2009 3rd International Conference on Energy Sustainability, Volume 2 ◽

10.1115/es2009-90140 ◽

2009 ◽

Cited By ~ 21

Author(s):

Robert W. Bradshaw ◽

Joseph G. Cordaro ◽

Nathan P. Siegel

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Energy Storage ◽

Thermal Energy ◽

Thermal Energy Storage ◽

Molten Salts ◽

Experimental Measurements ◽

Nitrate Salt ◽

Parabolic Trough ◽

Salt Mixtures

Multi-component molten salts have been formulated recently that may enhance thermal energy storage for parabolic trough solar power plants. This paper presents further developments regarding molten salt mixtures consisting of common alkali nitrates and either alkaline earth nitrates or alkali nitrite salts that have advantageous properties for applications as heat transfer fluids in parabolic trough systems. We report results for formulations of inorganic molten salt mixtures that display freeze-onset temperatures below 100°C. In addition to phasechange behavior, several properties of these molten salts that significantly affect their suitability as thermal energy storage fluids were evaluated, including chemical stability and viscosity. The nitrate-based molten salts have demonstrated chemical stability in the presence of air up to 500°C. The capability to operate at temperatures up to 500°C may allow an increase in maximum temperature operating capability vs. organic fluids in existing trough systems and will enable increased power cycle efficiency. Experimental measurements of viscosity were performed from near the freeze-onset temperature to about 200°C. Viscosities can exceed 100 cP near the freezing temperature but are 4 to 5 cP in the anticipated operating temperature range. Experimental measurements of density, thermal conductivity and heat capacity are in progress and will be reported at the meeting. Corrosion tests were conducted for several thousand hours at 500°C with stainless steels and at 350°C for carbon and chromium-molybdenum steels. Examination of the specimens demonstrated good compatibility of these materials with the molten nitrate salt mixtures. Laboratory studies were conducted to identify mixtures of nitrate and nitrite (NO2−) salts as additional candidates for a low-melting heat transfer fluid. Mixtures in which the cations were potassium, sodium and lithium, in various proportions, demonstrated freezing points as low as 70°C for a particular nitrate/nitrite anion composition. Development has emphasized mixtures that minimize lithium content in order to reduce the cost as the lithium salt is the most expensive constituent. Work is in progress to explore the phase diagram of the 1:1 mol ratio of nitrate/nitrite and to evaluate physical properties such as viscosity, density and thermal conductivity. Results to date indicate that the viscosity of these mixtures is considerably less than nitrate-only melts, which necessarily contain calcium cations to suppress freezing to similarly low temperatures.

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