scholarly journals Innovative Solutions for Improving the Heat Exchange in Closed-Loop Shallow Geothermal Systems

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 108
Author(s):  
Giovanni Floridia ◽  
Federica Blandini ◽  
Salvatore Iuculano ◽  
Giuseppe M. Belfiore ◽  
Marco Viccaro
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchange ◽  
Carbon Fibre ◽  
Thermal Characteristics ◽  
Experimental Tests ◽  
Geothermal Systems ◽  
Thermal Exchange ◽  
Ground Source ◽  
Innovative Solutions ◽  
Drilling Operations

Thermal conductivity, hydraulics properties and potential use in low-enthalpy geothermal applications of single and double U geothermal probes enhanced with carbon fibre are discussed in this work. Although the efficiency of a shallow geothermal installation is chiefly based on chemical and physical characteristics of rocks and hydrogeological aspects of the subsurface, the total heat extracted from the subsoil also depends on the intrinsic thermal characteristics of probes. New configurations and solutions aimed at enhancing the performance of components are therefore of considerable interest in this field of research. As a consequence of the economic and versatility advantages of the components, geothermal probes have been generally developed with materials like polyethylene, which presents, however, isolating behaviour that does not allow ideal heat exchange in ground source heat pump systems (GSHP). Innovative combinations of different materials are therefore necessary in order to improve thermal conductivity and to preserve the exceptional workability and commercial advantages of the finest elements available on the market. This work presents results coming from experimental tests involving standard polyethylene geothermal probes integrated with radial rings of polyacrylonitrile-based carbon fibre (PAN). Our evaluations are aimed at finding the best solutions for thermal exchange and adaptability with respect to traditional systems. Hydraulic and thermal performances and the response in a geo-exchange system have been verified. The new solutions appear to be highly suitable as geothermal exchangers in shallow geothermal systems and contribute to significantly reduce the total costs pertaining to the drilling operations.

New borehole heat exchanger thermal enhanced grout formulations

2021 ◽  
Author(s):  
Eloisa Di Sipio ◽  
Enrico Garbin ◽  
Laura Fedele ◽  
Davide Menegazzo ◽  
Ludovico Mascarin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Heat Exchange ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Operation Mode ◽  
Silica Sand ◽  
Geothermal Systems

<p>In shallow geothermal systems, especially ground source heat pumps (GSHP), cementitious grouts play a decisive role in guaranteeing an efficient heat transfer between the probe and the surrounding ground. Several studies have been devoted to understand the effect of different additives (silica sand, graphite, fluorspar, glass and fly ash …) in improving especially the thermal conductivity of such mixtures, maintaining at the same time physical properties as viscosity and workability suitable for in situ application. In fact, when continuous operation mode is running, thermal conductivity shows a positive effect on the mean heat exchange rate of vertical borehole heat exchangers (BHE). However, when an intermittent operation mode is selected, the BHE performance improves when a high thermal conductivity is coupled with a high specific heat capacity.</p><p>This research focus on assessing the contribution of two specific thermal additives (silica sand and molybdenum disulphide powder) to the thermal properties’ improvements of a specific commercial cementitious grout. These components are added in different proportion to the grout, up to the creation of 6 different mixtures. For each mixture 3 specimens are prepared, in order to perform the thermo-physical analyses. In addition, other 3 commercial grouts are considered. A total of 10 mixtures, leading to the creation of 30 specimens, have been analyzed. Then, thermal conductivity, thermal diffusivity and specific heat capacity of each specimen measured in anhydrous and saturated conditions are considered.</p><p>The commercial grouts prepared as stated by the producers show, as expected, a minimum variation of their thermal properties in wet and anhydrous conditions. Instead, when the additives are used, a noticeable improvement of the thermal properties is observed in saturated conditions, where the effect of silica sand seems dominant. The best thermal properties improvement obtained by combining the two additives is also considered.</p><p>However, the grouts suitability to be easily managed on site must be considered because, even if the new mixtures show a general gain of the thermal properties, these can be difficult to apply going from laboratory to full scale.</p><p>Anyway, the characterization of the grouts thermal properties based on composition and saturation variations is important not only in numerical simulations, but also in analytical approaches, typical of the heat exchange probe fields sizing processes. In fact, the cementitious grouts play a key role in determining the shallow geothermal systems efficiency in transient mode operation, often neglected by sizing programs. In fact, those characterized by better thermal performances will contribute to the reduction of the borehole thermal resistances, interposed in the heat exchange processes between the heat transfer fluid and the ground. Finally, this research contributes to fill the gap between numerical simulation and experimental data, providing real data to be used as database for further numerical modelling analysis improvement.</p><p> </p><p>GEO4CIVHIC project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 792355.</p>

scholarly journals Comparative Analysis of Different Methodologies Used to Estimate the Ground Thermal Conductivity in Low Enthalpy Geothermal Systems

Energies ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1672 ◽  
Author(s):  
Cristina Sáez Blázquez ◽  
Ignacio Martín Nieto ◽  
Arturo Farfán Martín ◽  
Diego González-Aguilera ◽  
Pedro Carrasco García
Keyword(s):  
Thermal Conductivity ◽  
Thermal Properties ◽  
Thermal Response ◽  
Ground Source Heat Pump ◽  
Thermal Response Test ◽  
Geothermal Systems ◽  
Ground Source ◽  
Accurate Comparison ◽  
The One ◽  
Alternative Solutions

In ground source heat pump systems, the thermal properties of the ground, where the well field is planned to be located, are essential for proper geothermal design. In this regard, estimation of ground thermal conductivity has been carried out by the implementation of different techniques and laboratory tests. In this study, several methods to obtain the thermal properties of the ground are applied in order to compare them with the reference thermal response test (TRT). These methods (included in previous research works) are carried out in the same geological environment and on the same borehole, in order to make an accurate comparison. All of them provide a certain value for the thermal conductivity of the borehole. These results are compared to the one obtained from the TRT carried out in the same borehole. The conclusions of this research allow the validation of alternative solutions based on the use of a thermal conductive equipment and the application of geophysics techniques. Seismic prospecting has been proven as a highly recommendable indicator of the thermal conductivity of a borehole column, obtaining rate errors of below 1.5%.

Evaluation of compression-recovery and thermal characteristics of multilayer bedding textiles

2020 ◽  
Vol 32 (5) ◽  
pp. 631-643
Author(s):  
Sedat Özer ◽  
Yaşar Erayman Yüksel ◽  
Yasemin Korkmaz
Keyword(s):  
Thermal Conductivity ◽  
Sleep Quality ◽  
Thermal Comfort ◽  
Sleep Duration ◽  
Human Body ◽  
Design Methodology ◽  
Thermal Characteristics ◽  
Air Permeability ◽  
Content Type ◽  
Thermal Comfort Properties

PurposeDesign of bedding textiles that contact the human body affects the sleep quality. Bedding textiles contribute to comfort sense during the sleep duration, in addition to ambient and bed microclimate. The purpose of this study is to evaluate the effects of different layer properties on the compression recovery and thermal characteristics of multilayer bedding textiles.Design/methodology/approachIn this study, woven and knitted multilayer bedding textiles were manufactured from fabric, fiber, sponge and interlining, respectively. Different sponge thickness, fiber and interlining weight were used in the layers of samples. Later, the pilling resistance, compression and recovery, air permeability and thermal conductivity of multilayer bedding textiles were investigated.FindingsThe results indicated that samples with the higher layer weight and thickness provide better compression recovery and lower air permeability properties. It was also found that knitted surfaces show the higher air permeability than the woven surfaces depending on the fabric porosity. Layer properties have insignificant effect on the thermal conductivity values.Originality/valueWhile researchers mostly focus on thermal comfort properties of garments, there are limited studies about comfort properties of bedding textiles in the literature. Furthermore, compression recovery properties of bedding textiles have also a great importance in terms of comfort. Originality of this study is that these properties were analyzed together.

scholarly journals Field Test and Numerical Simulation on the Long-Term Thermal Response of PHC Energy Pile in Layered Foundation

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3873
Author(s):  
Guozhu Zhang ◽  
Ziming Cao ◽  
Yiping Liu ◽  
Jiawei Chen
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchange ◽  
Temperature Variation ◽  
Thermal Response ◽  
Ground Temperature ◽  
Short Term ◽  
Energy Pile ◽  
Backfill Soil ◽  
Short And Long Term

Investigation on the long-term thermal response of precast high-strength concrete (PHC) energy pile is relatively rare. This paper combines field experiments and numerical simulations to investigate the long-term thermal properties of a PHC energy pile in a layered foundation. The major findings obtained from the experimental and numerical studies are as follows: First, the thermophysical ground properties gradually produce an influence on the long-term temperature variation. For the soil layers with relatively higher thermal conductivity, the ground temperature near to the energy pile presents a slowly increasing trend, and the ground temperature response at a longer distance from the center of the PHC pile appears to be delayed. Second, the short- and long-term thermal performance of the PHC energy pile can be enhanced by increasing the thermal conductivity of backfill soil. When the thermal conductivities of backfill soil in the PHC pile increase from 1 to 4 W/(m K), the heat exchange amounts of energy pile can be enhanced by approximately 30%, 79%, 105%, and 122% at 1 day and 20%, 47%, 59%, and 66% at 90 days compared with the backfill water used in the site. However, the influence of specific heat capacity of the backfill soil in the PHC pile on the short-term or long-term thermal response can be ignored. Furthermore, the variation of the initial ground temperature is also an important factor to affect the short-and-long-term heat transfer capacity and ground temperature variation. Finally, the thermal conductivity of the ground has a significant effect on the long-term thermal response compared with the short-term condition, and the heat exchange rates rise by about 5% and 9% at 1 day and 21% and 37% at 90 days as the thermal conductivities of the ground increase by 0.5 and 1 W/(m K), respectively.

scholarly journals Experimental Study on the Heat Exchange Mechanism in a Simulated Self-Circulation Wellbore

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2918
Author(s):  
Liang Zhang ◽  
Songhe Geng ◽  
Jun Kang ◽  
Jiahao Chao ◽  
Linchao Yang ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Exchange ◽  
Convective Heat Transfer Coefficient ◽  
Injection Rate ◽  
Circulation Rate ◽  
Similarity Analysis ◽  
Published Data ◽  
Outlet Temperature ◽  
Hot Dry Rocks ◽  
Mining Capacity

Self-circulation wellbore is a new technique for geothermal development in hot dry rocks (HDR), which uses a U-shape channel composed of tubing and casing as the heat exchanger. In this study, a self-circulation wellbore in HDR on a laboratory scale was built, and a serial of experiments were conducted to investigate the heat exchange law and the influencing factors on the heat mining rate of the wellbore. A similarity analysis was also made to estimate the heat-mining capacity of the wellbore on a field scale. The experimental results show that the large thermal conductivity and heat capacity of granite with high temperature can contribute to a large heat-mining rate. A high injection rate can cause a high convective heat transfer coefficient in wellbore, while a balance is needed between the heat mining rate and the outlet temperature. An inner tubing with low thermal conductivity can significantly reduce the heat loss to the casing annulus. The similarity analysis indicates that a heat mining rate of 1.25 MW can be reached when using a 2000 m long horizontal well section in a 150 °C HDR reservoir with a circulation rate of 602.8 m3/day. This result is well corresponding to the published data.

A Model for a Geothermal Well in a Hydraulic Groundwater Flow for Ground Source Heat Pump Systems

2011 ◽  
Author(s):  
Kevin D. Woods ◽  
Alfonso Ortega
Keyword(s):  
Thermal Conductivity ◽  
Analytical Solution ◽  
Groundwater Flow ◽  
Heat Pump ◽  
Temperature Response ◽  
Ambient Air ◽  
Heat Pumps ◽  
Thermal Reservoir ◽  
Geothermal Well ◽  
Ground Source

Heat pumps are mechanical systems that provide heating to a space in the winter, and cooling in the summer. They are increasingly popular because the same system provides both cooling modes, depending on the direction of the cycle upon which they operate. For proper operation, the heat pump must be connected to a constant temperature thermal reservoir which in traditional systems is the ambient air. In ground source heat pumps however, subterranean ground water is used as the thermal reservoir. To access the subterranean groundwater, “geothermal” wells are drilled into the formation. Water from the building heating or cooling system is circulated through the wells thereby promoting heat exchange between the coolant water and the subterranean formation. The potential for higher efficiency heating and cooling has increased the utilization of ground source heating ventilating and air conditioning systems. In addition, their compatibility with a naturally occurring and stable thermal reservoir has increased their use in the design of sustainable or green buildings and man-made environments. Groundwater flow affects the temperature response of thermal wells due to advection of heat by physical movement of groundwater through the aquifer. Research on this subject is scarce in the geothermal literature. This paper presents the derivation of an analytical solution for thermal dispersion by conduction and advection from hydraulic groundwater flow for a “geothermal” well. This analytical solution is validated against asymptotic analytical solutions. The traditional constant linear heat source solution is dependent on the ground formation thermal properties; the most dominant of which is the thermal conductivity. The results show that as hydraulic groundwater flow increases, the influence of the ground formation thermal conductivity on the temperature response of the well diminishes. The diminishing influence is evident in the Peclet number parameter; a comparison of thermal advection from hydraulic groundwater flow to thermal conduction by molecular diffusion.

scholarly journals Improving the quality of alumina-containing sinter using water-cooled furnace shell

2012 ◽  
Vol 44 (3) ◽  
pp. 281-286
Author(s):  
A.V. Aleksandrov ◽  
V.V. Aleksandrov
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Heat Exchange ◽  
Energy Balance ◽  
Cold Water ◽  
Sintering Temperature ◽  
Radiant Heat ◽  
Thermal Processes ◽  
Technical Solutions

This article deals with the use of computer modeling to develop technical solutions to ensure better quality of alumina-containing sinter. The simulation accounted for the influence of the feed materials on the thermal processes in the furnace. The energy balance (including thermal conductivity, heat convection and radiant heat exchange) was solved assuming steady state. A good correlation was observed for the actual and calculated temperatures of the solids and gases, with less than 15% discrepancy. Using the model of the furnace investigated the possibility of lowering the temperature of sintering by removing heat from the outside of the furnace shell. To reduce the sintering temperature to 1000 ?C length of the refractory lined steel is 5 m, the height of the lining should not exceed - 0.06 m, the required rate of cold water - 54.7 m3/h

scholarly journals Thermal Analysis of AlGaN/GaN HEMTs Considering Anisotropic And Inhomogeneous Thermal Conductivity

2021 ◽  
Author(s):  
Yao Li ◽  
Zixuan Zheng ◽  
Qun Li ◽  
Hongbin Pu
Keyword(s):  
Thermal Conductivity ◽  
Temperature Rise ◽  
Power Dissipation ◽  
Thermal Characteristics ◽  
Maximum Temperature ◽  
Base Temperature ◽  
Initial Growth ◽  
Boltzmann Transport ◽  
Growth Interface ◽  
Anisotropic Thermal Conductivity

Abstract To examine the differences of thermal characteristics introduced by material thermal conductivity, anisotropic polycrystalline diamond (PCD) and GaN are analyzed based on the accurate model of grain sizes in the directions of parallel and vertical to the interface and an approximate solution of the phonon Boltzmann transport equation. Due to the space-variant grain structures of PCD, the inhomogeneous-anisotropic local thermal conductivity, homogeneous-anisotropic thermal conductivity averaged over the whole layer and the typical values of inhomogeneous-isotropic thermal conductivity are compared with/without anisotropic GaN thermal conductivity. The results show that the considerations of inhomogeneous-anisotropic PCD thermal conductivity and anisotropic GaN thermal conductivity are necessary for the accurate prediction of temperature rise in the GaN HEMT devices, and when ignoring both, the maximum temperature rise is undervalued by over 16 K for thermal boundary resistance (TBR) of 6.5 to 60 m2K/GW at power dissipation of 10 W/mm. Then the dependences of channel temperature on several parameters are discussed and the relations of thermal resistance with power dissipation are extracted at different base temperature. Compared with GaN, SiC and Si substrates, PCD is the most effective heat spreading layer though limited by the grain size at initial growth interface.

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