Thermal properties variations in unconsolidated material for very shallow geothermal application (ITER project)

Abstract In engineering, agricultural and meteorological project design, sediment thermal properties are highly important parameters, and thermal conductivity plays a fundamental role when dimensioning ground heat exchangers, especially in very shallow geothermal systems. Herein, the first 2 m of depth from surface is of critical importance. However, the heat transfer determination in unconsolidated material is difficult to estimate, as it depends on several factors, including particle size, bulk density, water content, mineralogy composition and ground temperature. The performance of a very shallow geothermal system, as a horizontal collector or heat basket, is strongly correlated to the type of sediment at disposal and rapidly decreases in the case of dry-unsaturated conditions. The available experimental data are often scattered, incomplete and do not fully support thermo-active ground structure modeling. The ITER project, funded by the European Union, contributes to a better knowledge of the relationship between thermal conductivity and water content, required for understanding the very shallow geothermal systems behaviour in saturated and unsaturated conditions. So as to enhance the performance of horizontal geothermal heat exchangers, thermally enhanced backfilling material were tested in the laboratory, and an overview of physical-thermal properties variations under several moisture and load conditions for different mixtures of natural material was here presented.

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The effect of soil temperature and soil water content on thermal properties in an artificial forestland and a natural regrowth grassland

10.5194/egusphere-egu2020-9352 ◽

2020 ◽

Author(s):

Tangtang Zhang ◽

Xin Ma

Keyword(s):

Thermal Conductivity ◽

Thermal Properties ◽

Soil Temperature ◽

Water Content ◽

Soil Water ◽

Soil Water Content ◽

Soil Condition ◽

Soil Thermal Conductivity ◽

Soil Thermal Properties ◽

Increasing Temperature

Soil temperature, soil water content and soil thermal properties were measured in an artificial forestland and a natural regrowth grassland from November in 2017 to July in 2019. The results show that the effects of soil temperature and soil water content on thermal properties are different in different soil condition. Soil thermal conductivity (K) and soil volumetric heat capacity (C) increase with increasing temperature in unfrozen period, but soil diffusivity (D) has no significant dynamic cycle and it almost keeps a constant level in a certain time. Soil thermal conductivity (K) decreases with increasing temperature during soil frozen period. The C and K increase with increasing soil water content in unfrozen period, while the D decrease with increasing soil water content.

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Physical Properties of Soy-Phosphate Polyol-Based Rigid Polyurethane Foams

International Journal of Polymer Science ◽

10.1155/2012/907049 ◽

2012 ◽

Vol 2012 ◽

pp. 1-8 ◽

Cited By ~ 5

Author(s):

Hongyu Fan ◽

Ali Tekeei ◽

Galen J. Suppes ◽

Fu-Hung Hsieh

Keyword(s):

Thermal Conductivity ◽

Compressive Strength ◽

Thermal Properties ◽

Water Content ◽

Polyurethane Foams ◽

Solid Polymer ◽

Mechanical And Thermal Properties ◽

Blowing Agent ◽

Isocyanate Index ◽

Pu Foams

Water-blown rigid polyurethane (PU) foams were made from 0–50% soy-phosphate polyol (SPP) and 2–4% water as the blowing agent. The mechanical and thermal properties of these SPP-based PU foams (SPP PU foams) were investigated. SPP PU foams with higher water content had greater volume, lower density, and compressive strength. SPP PU foams with 3% water content and 20% SPP had the lowest thermal conductivity. The thermal conductivity of SPP PU foams decreased and then increased with increasing SPP percentage, resulting from the combined effects of thermal properties of the gas and solid polymer phases. Higher isocyanate density led to higher compressive strength. At the same isocyanate index, the compressive strength of some 20% SPP foams was close or similar to the control foams made from VORANOL 490.

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Novel Dual Walling Cob Building: Dynamic Thermal Performance

Energies ◽

10.3390/en14227663 ◽

2021 ◽

Vol 14 (22) ◽

pp. 7663

Author(s):

Kaoutar Zeghari ◽

Ayoub Gounni ◽

Hasna Louahlia ◽

Michael Marion ◽

Mohamed Boutouil ◽

...

Keyword(s):

Thermal Conductivity ◽

Heat Capacity ◽

Thermal Properties ◽

Water Content ◽

Wheat Straw ◽

Numerical Study ◽

Energy Performance ◽

Climatic Conditions ◽

Structural Walls ◽

Hemp Shiv

This paper emphasizes the experimental and numerical study of new cob mixes used for insulation and load bearing wall elements. The experimental study provides complete datasets of thermal properties of the new walling materials, using cob with density ranging from 1107 kg/m3 to 1583 kg/m3 for structural walls and less than 700 kg m−3 for insulation walls. Various mixes of French soils and fibres (reed, wheat straw, hemp shiv, hemp straw, and flax straw) with different water contents are studied. The lowest average thermal conductivity is obtained for the structural cob mix prepared of 5% wheat straw and 31% of water content. The insulation mix, prepared with 25% reed and 31% water content, has the lowest thermal conductivity. Investigation of diffusivity, density, and heat capacity shows that, when thermal conductivity is lower than 0.4 W m−1 K−1, the decrease in cob density leads to better insulation values and higher heat capacity. Little variation is noticed regarding the density and heat capacity for cob mixes with thermal conductivity higher than 0.4 W m−1 K−1. Furthermore, the non-uniformity of local thermal conductivity and heat losses through the samples is due mainly to the non-uniform distribution of fibres inside the mixes inducing an increase in heat loss up to 50% for structural walls and 25% for insulation walls. Cob thermal properties are used in a comparative simulation case study of a typical house under French and UK climatic conditions. The energy performance of the conventional building is compared to a dual walled cob building, showing remarkable reduction in energy consumption as the cob walls, whilst maintaining comfortable indoor conditions without additional heating.

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Comparison between traditional and enhanced Thermal Response Test for ground thermal properties estimation

10.5194/egusphere-egu21-11059 ◽

2021 ◽

Author(s):

Antonio Galgaro ◽

Alberto Carrera ◽

Eloisa Di Sipio

Keyword(s):

Thermal Conductivity ◽

Thermal Properties ◽

Heat Exchangers ◽

Thermal Response ◽

Physical Parameters ◽

Thermal Response Test ◽

Wireless Data ◽

Stratigraphic Sequence ◽

Response Test ◽

Geological Unit

For the design and implementation of an efficient Ground Source Heat Pump (GSHP) system, the local subsoil represents the core element. Since the thermal performance of Borehole Heat Exchangers (BHEs) is site-specific, its planning typically requires the knowledge of the thermal proprieties of the ground, which are influenced by the local stratigraphic sequence and the hydrogeological conditions. The evaluation of the variations of the ground thermal conductivity (TC) along the depth, as well as its undisturbed temperature, are essential to correctly plan the BHEs field and improve the performance of the ground heat exchangers themselves. Thermal Response Test (TRT) is a well-known experimental procedure that allows to obtain the thermal properties of the ground. However, the traditional method provides a single value of the equivalent TC and the undisturbed temperature, which can be associated with the average value over the entire BHE length, with no chance to detect the thermo-physical parameters variations with depth and to discriminate the contributions of the different geological levels crossed by the geothermal exchange probe. Indeed, different layers within a stratigraphic sequence, may have different thermal properties, according to the presence and to the flow rate of groundwater, as well as to granulometry and mineralogical composition, density, and porosity of the lithologies. The identification of the different contributions to the thermal exchange provided by each geological unit, in practice, can further support BHE design, helping to determine the most suitable borehole length and number, achieving the highest heat exchange capability at the lower initial cost of implementing of the entire geothermal plant. In the last years, new improved approaches to execute an enhanced thermal response test have been developed, as the pioneer wireless data transmission GEOsniff technology (enOware GmbH) tested in this study. This measurement method is characterized by its sensors, 20mm-diameter marbles equipped by pressure and temperature transducers combined with a system of data storing and wireless data transmission. Released at regular intervals down the testing BHE, infilled with water, each marble freely floats allowing the measurement of the water temperature variations over time at different depths, in order to identify areas with particular values of thermal conductivity related to distinctive hydrogeological conditions or lithological assessment. This way, the GEOsniff technology allows a high-resolution spatially- distributed representation of the subsoil thermal properties along the BHE. In this work, we present the test outputs acquired at the new humanistic campus of the University of Padova, located in the Eastern Po river plain (Northern Italy). The thermal conductivity data obtained by the GEOsniff method have been compared and discussed, by considering the standard TRT outputs. This innovative technique looks promising to support the optimization of the borehole length in the design phase, even more where the complexity of the treated geological setting increases.

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Mediate relation between electrical and thermal conductivity of soil

Geomechanics and Geophysics for Geo-Energy and Geo-Resources ◽

10.1007/s40948-020-00173-x ◽

2020 ◽

Vol 6 (3) ◽

Author(s):

Hans Schwarz ◽

David Bertermann

Keyword(s):

Thermal Conductivity ◽

Electrical Conductivity ◽

Water Content ◽

Bulk Density ◽

Geophysical Methods ◽

Heat Extraction ◽

Geothermal Systems ◽

Corrective Factor ◽

Thermal Conductivity Model

Abstract Thermal conductivity is a key parameter for many soil applications, especially for dimensioning shallow and very shallow geothermal systems based on the possible heat extraction rate and for modelling heat transfer processes around high voltage underground cables. Due to the limited purview of direct thermal conductivity measurements, for an investigation of extensive areas, usually other geophysical methods like electrical resistivity tomography measurements are applied. To derive thermal conductivity of soil from geoelectrical measurements a relation between electrical and thermal conductivity is needed. Until now only few approaches worked on a direct correlation between both conductivities. Due to the difficulties of a direct relation, within this study a modular approach of a mediate correlation between electrical and thermal conductivity was investigated. Therefore, a direct relationship between a corrected electrical conductivity and water content as well as the standard and simple thermal conductivity model of Kersten (Bull of the Univ Minnesota 28:1–227, 1949) was used. To develop this concept soil types of sand, silt loam and clay were investigated where different saturation steps and pressure loads were applied. For each configuration electrical and thermal conductivity as well as water content and bulk density was determined. To refine the results of the calculated water content a corrective factor was applied. Furthermore, bulk density as an inlet parameter of the Kersten equation was also derived based on electrical conductivity. The suggested proceeding enables the determination of thermal conductivity solely based on electrical conductivity without prior soil property information.

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Physical properties of the mor layer in a Scots pine stand III. Thermal conductivity

Canadian Journal of Soil Science ◽

10.4141/s95-004 ◽

1997 ◽

Vol 77 (4) ◽

pp. 643-648 ◽

Cited By ~ 3

Author(s):

A. Laurén

Keyword(s):

Thermal Conductivity ◽

Thermal Properties ◽

Water Content ◽

Heat Transport ◽

Time Domain ◽

Good Accuracy ◽

Time Domain Reflectometry ◽

Thermal Probe ◽

Water Desorption ◽

Thermal Probes

Thermal conductivity was measured with thermal probes in undisturbed mor samples subjected to water desorption and sorption. The volumetric water content was determined simultaneously with time domain reflectometry. The thermal conductivity increased from 0.06 to 0.24 W m−1 K−1, when the water content increased from 0.10 to 0.40 m3 m−3. There was little spatial variation in the mor layer. The results were similar to those found in the literature for peat and humus materials. The thermal conductivity of the mor layer could be predicted with the de Vries model with good accuracy if the humus and air particles were assumed to be of lamellae shape and latent heat transport in air-filled pores was neglected. Key words: humus, thermal probe, thermal properties, time domain reflectometry

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The Variation Mechanism of Thermal Properties of Loess with Different Water Contents during Freezing

Advances in Civil Engineering ◽

10.1155/2021/9990051 ◽

2021 ◽

Vol 2021 ◽

pp. 1-12

Author(s):

Xihao Dong ◽

Shuai Liu ◽

Yuanxiang Yu

Keyword(s):

Heat Transfer ◽

Phase Transition ◽

Thermal Conductivity ◽

Heat Capacity ◽

Thermal Properties ◽

Water Content ◽

Volumetric Heat Capacity ◽

Soil Particles ◽

Water Ice ◽

Variation Mechanism

The thermal properties of soils are affected by many factors, such as temperature, water content, and structure. Based on the transient plane source method of thermal physics, the thermal properties of loess with different water content during the freezing process were tested. We analyzed the variation mechanism of thermal properties from the perspective of phase change. Based on the Pore/Particle and Crack Analysis System (PCAS) and theory of heat transfer, we then analyzed the microstructure and heat conduction process of loess. And a calculation model of volumetric heat capacity of frozen soil was presented. The results show that, in the major phase transition zone, the variation of the thermal properties of loess with temperature is the most significant. And the thermal diffusivity increases sharply with the significant increase of thermal conductivity and the rapid decrease of volumetric heat capacity. Moisture content not only increases the thermal conductivity and volume heat capacity of loess but also makes the influence of temperature on the thermophysical parameters more significant. The effect of temperature on thermal properties is mainly due to the change of heat transfer media caused by phase transition of water-ice, followed by the change of thermal properties of heat transfer media such as soil particles, water, ice, and air with temperature. Increasing the water content reduces the contact thermal resistance between soil particles because of the increase in the thickness of the water film on the surface of soil particles and the thermal conductivity of the heat transfer medium between particles, thus changing the thermal properties of soils.

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Laboratory thermal conductivity measurements on gravel sample

Acque Sotterranee-Italian Journal of Groundwater ◽

10.7343/as-2018-344 ◽

2018 ◽

Vol 7 (3) ◽

pp. 67-70

Author(s):

Antonio Galgaro ◽

Matteo Cultrera ◽

Giorgia Dalla Santa ◽

Fabio Peron

Keyword(s):

Thermal Conductivity ◽

Thermal Properties ◽

Heat Exchangers ◽

Heat Pumps ◽

Conductivity Measurements ◽

Ground Source Heat Pumps ◽

Ground Source

Modern Ground Source Heat Pumps (GSHPs) systems must be designed by taking into account the ground thermal properties, in order to properly plan the capability of the heat pumps to transfer calories through the Ground Source Heat Exchangers (GSHE) to the subsoil (and vice versa). [...]

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New borehole heat exchanger thermal enhanced grout formulations

10.5194/egusphere-egu21-8234 ◽

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

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 &#8230;) 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.This research focus on assessing the contribution of two specific thermal additives (silica sand and molybdenum disulphide powder) to the thermal properties&#8217; 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.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.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.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.&#160;GEO4CIVHIC project has received funding from the European Union&#8217;s Horizon 2020 research and innovation program under grant agreement No. 792355.

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Analysis of novel shallow geothermal system in coastal fractured limestone aquifer

10.5194/egusphere-egu21-12377 ◽

2021 ◽

Author(s):

Nicola Pastore ◽

Claudia Cherubini ◽

Concetta Immacolata Giasi

Keyword(s):

Heat Exchanger ◽

Heat Exchangers ◽

Industrial Area ◽

Physical Models ◽

Experimental Investigations ◽

Geothermal System ◽

Geothermal Systems ◽

Borehole Heat Exchanger ◽

Limestone Aquifer ◽

Fractured Limestone

In shallow geothermal systems natural and forced groundwater movement as well as the temperature driven flow plays an important role on the borehole heat exchanger efficiency.The analysis of the efficiency of innovative heat exchangers installed in a fractured limestone aquifer was carried out through three-dimensional numerical simulations and experimental investigations on physical models.The coastal fractured limestone aquifer of the industrial area of Bari (Italy) was chosen as benchmark field site in order to identify the aquifer parameter range and the respective combinations. The role of seawater intrusion on the borehole heat exchanger efficiency was deepen .The results disclosed that the efficiency of the innovative heat exchangers is strictly dependent on the aquifer transmissivity and groundwater flow under natural and forced groundwater conditions.Discussion on the performance of the seasonal heat storage and the occurrence of the thermal interference between the borehole heat exchanger was presented.

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