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Thermal conductivity coefficient of sand, loamy sand and clay for different humidity in laboratory environment
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To meet the challenges of earth sheltered and green roof buildings, application of the heat pumps that use the heat of soil it is necessary to have the thermo physical characteristics of the soils. The studies in this field are extremely insufficient.
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... A better understanding of the movement of water and heat through soil would benefit the management of the soil and the water used in irrigated agriculture [3]. Moreover, to study green roof buildings, it is required to know about the thermal conductivity of the soils [4]. Soil thermal characteristics affect germination, plant growth, and crop development and significantly affect microclimate [5,6]. ...
The present study used three well-known white-box data-driven models, including multivariate adaptive regression splines (MARS), gene expression programming (GEP), and group method of data handling (GMDH), for generating explicit formulas for the prediction of thermal conductivity of the soil \((\lambda )\). Therefore, 40 soil samples and three input variables, such as moisture content \((\omega )\), porosity \((n)\), and the natural density of soil \((\rho )\), were used to predict \(\lambda \). The performance of the proposed formulas was assessed via statistical indicators such as the determination of coefficient (R2), root mean square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE). Statistical criteria have shown that all proposed models provided almost identical results. However, the MARS model was marginally more accurate than the GEP and GMDH models. In addition, the error measures of MARS with RMSE = 0.021, MAE = 0.018, and MAPE = 1.191% were slightly more accurate than GA-ANN (RMSE = 0.030, MAE = 0.025, and MAPE = 1.750%) that reported in the previous study for estimation of \(\lambda \). However, the prominent feature of the suggested white-box data-driven models compared to black-box models such as ANN is to provide explicit equations for estimating \(\lambda \).
... The soil temperature at the surface depends mainly on solar radiation and on geographical characteristics such as latitude and longitude, altitude, and slope orientation. Furthermore, soil temperature is influenced by soil characteristics including soil type and soil water content [9][10][11]. The soil temperature at the surface is also influenced by the type and height of vegetation, surface colour (albedo), amount of precipitation, snowfall, and urbanization [12]. ...
This study aimed at the analysis and modelling of the groundwater temperature at the water table in different regions of Slovakia. In the first part, the analysis of the long-term trends of air and soil/ground temperature to a depth of 10 m is presented. The average annual soil/groundwater temperatures at different depths were the same but lower than the annual average air temperature by about 0.8 °C. The long-term trend analysis of the air temperature and soil temperature at a depth of up to 10 m in Slovakia showed that the air and soil/ground water temperature have risen by 0.6 and 0.5 °C, respectively, per decade over the past 30 years. The second part of the study aimed at modelling the daily groundwater temperatures at depths of 0.6–15 m below the surface. The simple groundwater temperature model was constructed based on a one-dimensional differential Fourier heat conduction equation. The given model can be used to estimate future groundwater temperature trends using regional air temperature projections calculated for different greenhouse gas emission scenarios.
... Therefore, the outer envelope of the buildings is exposed to intense heat waves for periods, which causes a large difference between the air temperatures in contact with the outer and inner part of the building structure during daylight hours [Iraq]. The daily range of temperature changes (day and night), reaching more than 20 °C, as shown in Figure 1 [8], [29]. The maximum and minimum temperatures for each month, the maximum temperatures for six months for each day, and the maximum temperatures for five months and every hour of the day for 2020 in Baghdad are shown in Figures 1, 2, and 3, respectively. ...
This paper aimed to study how to reduce the amounts of heat transfer from or to the internal space of the building by covering its external walls with many locally available materials, thus reducing the rate of consumption of electrical energy used in adaptation, which leads to reducing energy consumption costs. The researcher built a model room with dimensions (1 x 1 x 2) m on the third floor of a building in Baghdad (L = 33.2 N), the dimensions of its walls (1 x 2 m) east for the installation of the sample, and the other surfaces are insulated with 200 mm polystyrene sheets. Use a 0.5 ton air conditioner to provide the room thermal comfort. The researcher found that the metal sheet with a thickness of 10 mm and covered with an insulating layer of thermoplastics is considered the best among the materials used in construction, as it saves 57% of the electrical energy consumed in air conditioning. While the use of marble, porcelain, Helen stone, and fiberglass slabs with a thickness of 10 mm, comes last because it saves less than 30% of electrical energy.
... He [9] measured and analyzed the effective thermal conductivity of sand with different moisture contents using a thermal constant analyzer. Nikiforova T et al. [10] used the MIT-1 m to determine the thermal conductivity of various types of earth materials and analyzed the variation in their thermal conductivity with the moisture content. Loam has a thermal conductivity change of up to 380%, with moisture content from 0% to 40%. ...
As environment-friendly building materials, earth materials are attracting significant attention because of their favorable hygrothermal properties. In this study, the earth materials in northwest Sichuan were tested and curves of thermal conductivity and water vapor permeability with relative humidity were obtained. The function curves and constants of the two coefficients were substituted into the verified nonstationary model of heat and moisture transfer in rammed earth walls and indoor air for calculation. The difference in the calculation results when the hygrothermal parameters are functions and constants were analyzed, and the influence of the non-constant hygrothermal parameters on the heat and moisture transfer in rammed earth walls, was obtained. The test results show that thermal conductivity is linearly related to moisture content, and water vapor permeability has a small variation in the relative humidity range of 0–60% and increases exponentially above 60%. The calculation results indicate that the non-constant hygrothermal parameters have little influence on the internal surface temperature of the rammed earth walls and Mianyang City’s indoor air temperature and humidity during the summer and winter. The heat transfer on the internal surface will be underestimated by using a non-constant for the hygrothermal parameter when the moisture content of the wall is low, and vice versa. In hot-humid areas or seasons with large differences in temperature and humidity between indoors and outdoors, non-constant hygrothermal parameters have a more obvious effect on heat transfer on the internal surface of the wall. The results of this study demonstrate the necessity of parameter testing.
... Heat transfer by radiation or convection amounts only an insignificant part of the total and could be neglected [25,26]. The area of external surfaces, the material of the partitions and its temperatures, and the soil type, its specific heat capacity and thermal conductivity [27,28], and temperatures must be known to find the heat transfer intensity to the soil. These parameters and their dependence on soil density and moisture are known for the most common soils, such as clay, loam, sand, or gravel [28]. ...
... The area of external surfaces, the material of the partitions and its temperatures, and the soil type, its specific heat capacity and thermal conductivity [27,28], and temperatures must be known to find the heat transfer intensity to the soil. These parameters and their dependence on soil density and moisture are known for the most common soils, such as clay, loam, sand, or gravel [28]. It should be noted that some simplifications are applied in the calculations: the soil is homogeneous in a layer, and the properties are the same in all directions. ...
The cold climate countries require high energy consumption for buildings’ heating. According to EU directives and national law, buildings’ energy efficiency is increasing due to higher investment in the sector. Primary energy consumption for space heating still comprises a large part of global energy consumption. It is essential to develop technological solutions and innovations to reduce energy consumption by using newer, smarter, more natural energy generation and accumulation. The soil layer could be used as a natural material for thermal energy accumulation. The soil’s temperature is higher than atmospheric air in the heating season and is lower in the non-heating season. Underground buildings placed in a soil medium could use less thermal energy for buildings’ heating and cooling during its life cycle. The impact of the wind is eliminated in this underground building case. As the soil temperature rises, the difference in temperature of the building’s inside air and the soil decreases. This means that the heat loss into the soil generates the conditions acting against the heat loss. However, heat spreads further and dissipates in the surrounding soil medium. The analysis of this research results showed that the savings in energy could reach 28 percent in the case of the underground building. Heat loss to the soil could be treated as the charge of the soil by thermal energy. The charging by heat and heat dissipation in the soil was researched experimentally. The dependence of the intensity of the charge on time was analysed and presented in this paper also.
... Electronic copy available at: https://ssrn.com/abstract=4281980 P r e p r i n t n o t p e e r r e v i e w e d Luo et al., 2018;Nikiforova et al., 2013;Zhang et al., 2014), and normal thermal properties are investigated (Table 3). ...
Considering groundwater flow in the soil, the amount of energy extracted from an energy pile is still vague. Therefore, this paper has examined the energy produced considering different design parameters in the presence or lack of groundwater flow by employing the finite element method (FEM). The results illustrate that increasing groundwater flow velocity is ineffective in energy extraction from the ground in some conditions. Moreover, lengthening the pile height after a certain height has a negative effect on the average output power. Porosity has negligible influence on the energy output; however, changing the pipe diameter shows two different behaviors
... The experiments described in Section 2.1 used clayey soil since it is reported that clayey soil has similar density [28,29], thermal conductivity [30,31] and specific heat [32,33] as scumbergs. The thermal properties of each material are summarised in Table 5. ...
... The geometry of the FE model is shown in Figure 4 with a mesh size of 1 mm. The experiments described in Section 2.1 used clayey soil since it is reported that clayey soil has similar density [28,29], thermal conductivity [30,31] and specific heat [32,33] as scumbergs. The thermal properties of each material are summarised in Table 5. ...
Large sheets of high-density polyethene geomembrane are used as floating covers on some of the wastewater treatment lagoons at the Melbourne Water Corporation’s Western Treatment Plant. These covers provide an airtight seal for the anaerobic digestion of sewage and allow for harvesting the methane-rich biogas, which is then used to generate electricity. There is a potential for scum to develop under the covers during the anaerobic digestion of the raw sewage by microorganisms. Due to the nature of the operating environment of the lagoons and the vast size (450 m × 170 m) of these covers, a safe non-contact method to monitor the development and movement of the scum is preferred. This paper explores the potential of using a new thermographic approach to identify and monitor the scum under the covers. The approach exploits naturally occurring variations in solar intensity as a trigger for generating a transient thermal response that is then fitted to an exponential decay law to determine a cooling constant. This approach is investigated experimentally using a laboratory-scale test rig. A finite element (FE) model is constructed and shown to reliably predict the experimentally observed thermal transients and cooling constants. This FE model is then set up to simulate progressive scum accumulation with time, using a specified scumberg geometry and a stepwise change in thermal properties. The results indicate a detectable change in the cooling constant at different locations on the cover, thereby providing a quantitative basis for characterising the scum accumulation beneath the cover. The practical application and limitations of these results are briefly discussed.
... Indicating that, for the fine-grained sand, the influence of the change of moisture content on the heat transfer performance of that is almost negligible. There are also experimental studies [29,30] have shown that, as the moisture content of fine-grained sand increases from drying state to saturated state, the air in the pores is gradually replaced by liquid water, and the overall thermal conductivity increases obviously for the thermal conductivity of liquid water is about 20 times that of air. After reaching a certain level, most of air is replaced by liquid water, and the thermal conductivity of fine-grained sand almost no longer increases with the increase of moisture content. ...
The soil temperature distribution characteristics were experimentally studied, during heat storage and release processes in the fine-grained sand with different moisture content. Results showed that, the soil temperature distributions in the process of soil heat storage and release are almost symmetric under the same excess temperature. The excess temperature is the main factor affecting the soil temperature change, and the influence of the moisture content variation is almost negligible. At each set of excess temperature, the soil temperature change in heat storage and release processes have a good logarithmic relationship with the heat transfer time, radial distance and longitudinal distance. The soil temperature change shows a linear increase trend with the excess temperature, and the soil temperature disturbance in radial direction is far greater than that in longitudinal direction. Based on the hypothetical multivariate nonlinear power function regression model, the experience formula for predicting the soil temperature was proposed. The prediction deviation was within 10 %.
... Prior studies have identified the variables affecting the thermal conductivity of porous materials, such as temperature, pressure, moisture content, porosity, density, the geometry of the pore structure, and the geometrical distribution of the void and solid phases. ese studies have adopted the experimental approach to characterize the thermal conductivity of a variety of products [9][10][11][12][13][14][15][16][17]. ...
This paper discusses an experimental investigation to determine regression models for thermal properties of phosphate particles and to analyze the performances of the phosphate flash dryer. For this purpose, the specific heat capacity and thermal conductivity of phosphate particles were experimentally determined by the modulated differential scanning calorimetry (MDSC) and the modified transient plane source method (MTPS), respectively. Multiple regression models were developed to correlate the specific heat and thermal conductivity to moisture content, particle size, and temperature. Experimental results showed that the measured thermal conductivity and dry specific heat were found in the range of 0.07–0.61 W/m K and 510–630 J/kg·K, respectively. Furthermore, the specific heat increased almost linearly with temperature but decreased with particle size, while the thermal conductivity increased with moisture content and temperature but decreased with particle size. These correlations were integrated to the phosphate flash dryer mathematical model and used to analyze the thermal behavior of phosphate drying. Simulation results were compared to experimental data obtained on a bench-scale dryer, where the model exhibits an average error of 2% and 4% for moisture content and air temperature estimation, showing good fitting for practical data.
... When we test the flow rate of 2 LPM (0.0333 kg/s) we get the results as in the table below: After the system reached a state of stability every day and for the same flow, the results of the entry temperature ranged between ˚C and the exit temperature, which was between (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40) ˚C and noting the differences between them, where the highest temperature difference was (13.6˚C) and higher. The rate of heat transfer (1894.97 ...
Several techniques have been tested to transfer heat and over a period of
years for purpose of obtaining a good heat transfer and a low operating cost, and
of these technologies the underground heat exchangers for various types and
purposes for their use, which depend on the transfer heat of fluid inside them to
the depths of the soil and vice versa
A two-layer horizontal underground heat exchanger was designed and tested as a
closed system to reduce the required area. The installation of a single layer
horizontal heat exchangers, needs to sufficient area to bury the exchanger, which
increase the economic cost of this type of underground heat exchangers that is one
of the disadvantages of a horizontal heat exchangers (not having enough space at
times).
The temperature gradient of the soil was recorded during the year, and its relative
stability was observed at the specified depth from 2m to 3.5 m, in addition to
measuring the thermal conductivity of a sample of the same soil and knowing its
properties.Polyethylene MLC pipes have been used with an external diameter of
16 mm and a thickness of 2 mm and a length of 100 m for each layer.
Two networks are designed in the form of a serpentine each network is 100 m
long, where the pipes of the two networks facing each other in a staggered
arrangement (at V shape side view) to increase the contact area of the tubes to
obtain a greater heat transfer. And by using the COMSOL program, assuming 2D
system and inserting the design properties of the pipes and soil, fined the optimum
distance between the pipes was proposed to be (0.3-0.5) m, The dimension 0.4m
was chosen for the design ground heat exchanger GHE.
The first layer of the system pipes was buried at a depth of 3 meters and the
second layer system pipes buried at a depth of 2.5 meters, from the ground
surface.The tests were done on every layer separately and then for the two layers
together, by changing the inlet water temperature approximately from 30, 40 and
50°C and with different flow rates from 2, 3, 4 and 5ℓ/𝑚𝑖𝑛, that was achieved at
the period (12/6/2019 - 22/7/2019).for the purpose of cooling in the hottest months
of the region.
When operate the system in a double layer mode a high temperature difference
was obtained (the average is 15.96 °C), and when operate the system with single layer mode the average of temperature difference obtained is (15.8) and (13.4) °C
for the first and the second layer, respectively, under different circumstances
In order to record the coefficient of performance (COP), the system was tested
for both layers to record the highest value, the (COP) was 8.59 in the doublelayers mode of operation and,5.9, 5.2 for the first and second layers respectively
in the same conditions, Due to the increased flow when testing each pipe layer
separately, compared with testing the double-layers together.
