scholarly journals Design Considerations for Borehole Thermal Energy Storage (BTES): A Review with Emphasis on Convective Heat Transfer

Geofluids ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-26 ◽  
Author(s):  
Helge Skarphagen ◽  
David Banks ◽  
Bjørn S. Frengstad ◽  
Harald Gether
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Theoretical Calculations ◽  
High Surface ◽  
High Surface Area ◽  
Volume Ratio ◽  
Thermal Recovery ◽  
Conductive Heat ◽  
Geological Environment

Borehole thermal energy storage (BTES) exploits the high volumetric heat capacity of rock-forming minerals and pore water to store large quantities of heat (or cold) on a seasonal basis in the geological environment. The BTES is a volume of rock or sediment accessed via an array of borehole heat exchangers (BHE). Even well-designed BTES arrays will lose a significant quantity of heat to the adjacent and subjacent rocks/sediments and to the surface; both theoretical calculations and empirical observations suggest that seasonal thermal recovery factors in excess of 50% are difficult to obtain. Storage efficiency may be dramatically reduced in cases where (i) natural groundwater advection through the BTES removes stored heat, (ii) extensive free convection cells (thermosiphons) are allowed to form, and (iii) poor BTES design results in a high surface area/volume ratio of the array shape, allowing high conductive heat losses. The most efficient array shape will typically be a cylinder with similar dimensions of diameter and depth, preferably with an insulated top surface. Despite the potential for moderate thermal recovery, the sheer volume of thermal storage that the natural geological environment offers can still make BTES a very attractive strategy for seasonal thermal energy storage within a “smart” district heat network, especially when coupled with more efficient surficial engineered dynamic thermal energy stores (DTES).

Numerical investigation of induced thermal impacts from high-temperature thermal energy storage in porous aquifers

2021 ◽  
Author(s):  
Bo Wang ◽  
Jens-Olaf Delfs ◽  
Christof Beyer ◽  
Sebastian Bauer
Keyword(s):  
High Temperature ◽  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage Capacity ◽  
Storage Temperature ◽  
Thermal Recovery ◽  
Pumping Rate ◽  
Background Temperature ◽  
C 30

<p>High-temperature aquifer thermal energy storage (HT-ATES) in the geological subsurface will affect the temperature distribution in and close to the storage site, with potential impacts on groundwater flow and biogeochemistry. Quantification of the subsurface space affected by a HT-ATES operation is thus required as one basis for urban subsurface space planning, which would allow to address potential competitive and conflicting uses of the urban subsurface. Therefore, this study shows a quantitative evaluation of induced thermal impacts and subsurface space required for a synthetic ATES operated at varying temperature levels.</p><p>A hypothetic seasonal HT-ATES operation is simulated using the coupled groundwater flow and heat transport code OpenGeoSys. A well doublet system consisting of fully screened “warm” and “cold” wells 500 m apart is used for the storage operation. A sandy aquifer typical for the North German Basin at a depth of 110 m and with a thickness of 20 m in between two confining impermeable layers is used as storage formation. Seasonal cyclic storage is simulated for 20 years, assuming charging and discharging for six months each. During charging, water with the aquifer background temperature of 13°C is extracted at the "cold" well, heated to 70°C and reinjected at the “warm” well using a pumping rate of 30 m³/h. During discharging, the stored hot water is retrieved at the "warm" well using the same pumping rate and reinjected at the “cold” well after heat extraction at aquifer background temperature.</p><p>The simulation results show that during a single storage cycle using a storage temperature of 70°C 7.51 GWh of thermal energy is injected, of which 4.79 GWh can be retrieved. This corresponds to a thermal recovery factor of 63.8% and thus an effective storage capacity of 0.43 kWh/m<sup>3</sup>/K can be deduced in relation to the heat capacity of the storage medium. For storage temperatures of 18°C, 30°C and 50°C, the effective storage capacity is 0.56 kWh/m<sup>3</sup>/K, 0.55 kWh/m<sup>3</sup>/K and 0.49 kWh/m<sup>3</sup>/K, respectively. By delineating the subsurface volume with a temperature increase larger than 1°C, the subsurface space used for and affected by the storage operation at the storage temperature of 70 °C is determined to be 10.56 million m³. In relation to the retrieved thermal energy, a subsurface volume of 2.2 m<sup>3 </sup>is thus required to retrieve one kWh of heat energy at 70 °C injection temperature. At lower temperatures of 18°C, 30°C and 50°C, the subsurface space required is 1.77 m<sup>3</sup>/kWh, 1.54 m<sup>3</sup>/kWh and 1.76 m<sup>3</sup>/kWh, respectively. The lower effective storage capacity and the relatively larger required space, which correspond to a lower thermal recovery factor, are caused by induced thermal convection and higher heat losses by conduction at higher temperatures.</p>

scholarly journals Titanium carbide MXene: Synthesis, electrical and optical properties and their applications in sensors and energy storage devices

2019 ◽  
Vol 9 ◽  
pp. 184798041882447 ◽  
Author(s):  
Johnson Michael ◽  
Zhang Qifeng ◽  
Wang Danling
Keyword(s):  
Energy Storage ◽  
Electrical Properties ◽  
Titanium Carbide ◽  
Inorganic Compounds ◽  
High Surface ◽  
High Surface Area ◽  
Volume Ratio ◽  
Energy Storage Materials ◽  
Post Processing ◽  
Energy Storage Devices

MXenes have been under a lot of scientific investigation due to the novel characteristics that are inherent to two-dimensional nanostructures. There are a multitude of MXenes being studied and one of the most popular among these would be the titanium carbides. The general formula for titanium carbide is Ti n+ 1C n for the nanosheets produced that have undergone much study in the past few years. These studies include how the etching process affects the final MXene sheet and how the post-processing via heat or combining with polymers and/or inorganic compounds influences the mechanical and electrical properties. It is found that different etching techniques can be used to change the electrical properties of the produced MXenes and different post-processing techniques can be used to further change the properties of the nanosheets. The possible application of the titanium carbide MXenes as chemical sensing and energy storage materials will be briefly discussed. MXene nanosheets show promise in such devices due to their high surface area to volume ratio and their specific surface structure with feasible surface functionalization.

scholarly journals Electrospun polyacrylonitrile–lauric acid composite nanofiber webs as a thermal energy storage material

2019 ◽  
Vol 14 ◽  
pp. 155892501882489 ◽  
Author(s):  
Ezgi Ismar ◽  
A Sezai Sarac
Keyword(s):  
Energy Storage ◽  
Phase Change ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Lauric Acid ◽  
Solid Phase ◽  
High Surface ◽  
Attenuated Total Reflection ◽  
Electrospinning Technique ◽  
Composite Nanofiber

Phase-change materials have remarkable characteristics due to their simple phase-changeable nature. Within a certain temperature range, these materials can easily change from solid phase to liquid phase or vice versa. It is possible to build thermal energy storage mechanisms, thanks to their latent heat. In this study, composite nanofiber structures were prepared with lauric acid and polyacrylonitrile blends. Nanofiber webs were fabricated via electrospinning technique and combined with phase-change material due to their light weight and high surface area. Thermal energy storage properties were investigated via differential scanning calorimeter, and structural analysis was studied by Fourier transform infrared–attenuated total reflection spectroscopy. Scanning electron microscope was used to investigate the surface morphology of the fibers. Blended polyacrylonitrile–lauric acid nanofibers were successfully converted to nanofiber formation without losing their properties. Results showed that fabricated polyacrylonitrile–lauric acid composite nanofiber webs can be used as a thermal energy storage patch.

scholarly journals Simulation study of the Lower Cretaceous geothermal reservoir for aquifer thermal energy storage

2021 ◽  
Author(s):  
Elżbieta Hałaj ◽  
Leszek Pająk ◽  
Bartosz Papiernik
Keyword(s):  
Energy Storage ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Lower Cretaceous ◽  
Waste Heat ◽  
Thermal Recovery ◽  
Geothermal Reservoir ◽  
Geothermal Systems ◽  
Geothermal Heating ◽  
Aquifer Thermal Energy Storage

AbstractThe aquifer thermal energy storage (ATES) has gained attention in several countries as an installation for increasing the energy efficiency of geothermal systems and the use of waste heat. The Lower Cretaceous reservoir is known as one of the most prospective for geothermal purposes in Poland. However, in the southern part of the Mogilno–Łódź Trough (Central Poland) is considered to have a lower geothermal potential. The aim of this paper is to study whether the Lower Cretaceous reservoir in this area is suitable for aquifer thermal energy storage. Prior to dynamic simulations in Feflow© software, a regional Petrel© static parametric model which includes a multidisciplinary approach was prepared. A methodology of fitting Petrel’s structural and parametrical model to Feflow requirements is provided within this paper. The performance simulation of 4 systems has been conducted for 30 years. Increasing precipitation potential is expected for aragonite and calcite along with a temperature increase, while silica precipitation carries a much smaller risk. The paper presents potential for ATES systems in the Lower Cretaceous reservoir of the study area with the best doublet location having thermal recovery ratio of 0.47 and 0.34 for 30 and 40 K temperature differential scenario. An imbalance in heat injection/production in the storage system can cause the reservoir to cool faster than in conventional geothermal heating installation. ATES can provide a successful geothermal reservoir boosting in the case of applying a balanced injection of waste heat.

scholarly journals Numerical Modeling of Thermal Energy Storage of CHPs in Porous Concrete

2020 ◽  
Vol 2 (2) ◽  
pp. 191-204
Keyword(s):  
Heat Transfer ◽  
Energy Storage ◽  
Numerical Solution ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Energy Charge ◽  
Mineral Wool ◽  
Discharge Process ◽  
Conductive Heat ◽  
Porous Concrete

Energy storage is essential in the modern age because fossil energy sources are running out, so there are a variety of ways to store energy, such as operating costs, energy consumption. The primary emissions and emissions, or all three, are reduced. In this paper, the heat energy storage method is used as sensible heat. The primary purpose of this study is to use inexpensive and available materials for energy storage. The heat source in this study is the CHP system exhaust gas selected for a 10-unit residential building. Thermal energy storage material is porous concrete that stores thermal energy in perceptible heat. The modeling of the system was also performed for the storage of thermal energy (charge and discharge process) by Schumann equations for fluid and solid storage in the porous medium, and the numerical solution of the equations was done by the characteristic method. For the fluid charge process of the CHP exhaust gases and air for the fluid discharge process, the porous concrete tank is assumed to be coated with mineral wool thermal insulation without loss of thermal energy. Heat transfer is only considered as one-dimensional heat transfer along the vertical axis of the tank, due to the porous solid storage environment, the conductive heat transfer in all dimensions of the tank is ignored. The thermocline property of the storage tank is essential for the numerical solution of the Schumann equations for the tank, with a charging time of 6 and a half hours and a discharge time of 5 hours.

scholarly journals Thermodynamic Analysis of a High-Temperature Latent Heat Thermal Energy Storage System

Energies ◽  
2020 ◽  
Vol 13 (24) ◽  
pp. 6634
Author(s):  
David W. MacPhee ◽  
Mustafa Erguvan
Keyword(s):  
Heat Transfer ◽  
Energy Efficiency ◽  
Energy Storage ◽  
Entropy Generation ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Storage System ◽  
Volume Ratio ◽  
Melting Time ◽  
Inlet Temperature

Thermal energy storage (TES) technologies are becoming vitally important due to intermittency of renewable energy sources in solar applications. Since high energy density is an important parameter in TES systems, latent heat thermal energy storage (LHTES) system is a common way to store thermal energy. Though there are a great number of experimental studies in the field of LHTES systems, utilizing computational codes can yield relatively quick analyses with relatively small expense. In this study, a numerical investigation of a LHTES system has been studied using ANSYS FLUENT. Results are validated with experiments, using hydroquinone as a phase-change material (PCM), which is external to Therminol VP-1 as a heat transfer fluid (HTF) contained in pipes. Energy efficiency and entropy generation are investigated for different tube/pipe geometries with a constant PCM volume. HTF inlet temperature and flow rate impacts on the thermodynamic efficiencies are examined including viscous dissipation effects. Highest efficiency and lowest entropy generation cases exist when when flow rates are lowest due to low viscous heating effects. A positive relation is found between energy efficiency and volume ratio while it differs for entropy generation for higher and lower velocities. Both efficiency and entropy generation decreased with decreasing HTF inlet temperature. The novelty of this study is the analysis of the effect of volume ratio on system performance and PCM melting time which ultimately proved to be the most dominant factor among those considered herein. However, as PCM solidification and melting time is of primary importance to system designers, simply minimizing entropy generation by decreasing volume ratio in this case does not lead to a practically optimal system, merely to decrease heat transfer entropy generation. Therefore, caution should be taken when applying entropy analyses to any LHTES storage system as entropy minimization methods may not be appropriate for practicality purposes.

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