scholarly journals Analysis of moisture and temperature fields coupling process in freezing shaft

2019 ◽  
Vol 23 (3 Part A) ◽  
pp. 1329-1335
Author(s):  
Yugui Yang ◽  
Dawei Lei ◽  
Haibing Cai ◽  
Songhe Wang ◽  
Yanhu Mu
Keyword(s):  
Heat Capacity ◽  
Temperature Field ◽  
Specific Heat ◽  
Temperature Change ◽  
Frozen Soil ◽  
Temperature Fields ◽  
Freezing Time ◽  
Coupling Process ◽  
Evolution Characteristics ◽  
Initial Freezing

The temperature change of frozen soil wall and the evolution characteristics of the specific heat capacity are analyzed. The frozen soil cylinders form surrounding freezing pipes at initial freezing stage, and the temperature field of frozen soil presents a non-linear decrease. With the increase of freezing time, the radius of the frozen soil cylinder increases and a frozen soil wall is enclosed. After freezing 30 days, the thickness of the frozen soil wall is obtained as 1.7 m. After freezing 250 days, the thickness of frozen soil wall increases to about 11.0 m.

scholarly journals Numerical simulation of the temperature fields in the shielding walls of frozen soil with multi-circle-pipe freezing in shaft sinking

2019 ◽  
Vol 23 (Suppl. 3) ◽  
pp. 647-652 ◽  
Author(s):  
Yugui Yang ◽  
Mengke Liao ◽  
Haibing Cai ◽  
Peijian Chen
Keyword(s):  
Numerical Simulation ◽  
Temperature Field ◽  
Numerical Method ◽  
Frozen Soil ◽  
Temperature Fields ◽  
Freezing Time ◽  
Frozen Soils ◽  
Soil Walls ◽  
Shaft Sinking ◽  
Initial Freezing

In this study, the temperature fields of frozen soil wall were calculated by using numerical method, and were analyzed after the soil was actively frozen with different freezing time. The results showed that the temperature field evolved from the freezing pipes, and then formed into frozen soil cylinders. After a certain freezing duration, the cylinders of frozen soil began to connect, and frozen soil walls started to form. At initial freezing stage, the thickness of frozen soil wall was mainly determined by the freezing pipes of the inner two circles. Then, connections were found to have occurred between the inner and outer frozen soil walls. Finally, the temperature fields of the unfrozen and frozen soils reached a state of stability. The results also showed that it was feasible to use numerical method to simulate the temperature fields of frozen soil walls during shaft sinking process, and potentially provided important references for the design and construction of deep alluvium shaft.

scholarly journals A simple model for predicting soil temperature in snow-covered and seasonally frozen soil: model description and testing

2004 ◽  
Vol 8 (4) ◽  
pp. 706-716 ◽  
Author(s):  
K. Rankinen ◽  
T. Karvonen ◽  
D. Butterfield
Keyword(s):  
Heat Capacity ◽  
Simple Model ◽  
Soil Temperature ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Frozen Soil ◽  
Model Description ◽  
Freezing And Thawing ◽  
Catchment Scale ◽  
Soil Temperatures

Abstract. Microbial processes in soil are moisture, nutrient and temperature dependent and, consequently, accurate calculation of soil temperature is important for modelling nitrogen processes. Microbial activity in soil occurs even at sub-zero temperatures so that, in northern latitudes, a method to calculate soil temperature under snow cover and in frozen soils is required. This paper describes a new and simple model to calculate daily values for soil temperature at various depths in both frozen and unfrozen soils. The model requires four parameters: average soil thermal conductivity, specific heat capacity of soil, specific heat capacity due to freezing and thawing and an empirical snow parameter. Precipitation, air temperature and snow depth (measured or calculated) are needed as input variables. The proposed model was applied to five sites in different parts of Finland representing different climates and soil types. Observed soil temperatures at depths of 20 and 50 cm (September 1981–August 1990) were used for model calibration. The calibrated model was then tested using observed soil temperatures from September 1990 to August 2001. R2-values of the calibration period varied between 0.87 and 0.96 at a depth of 20 cm and between 0.78 and 0.97 at 50 cm. R2-values of the testing period were between 0.87 and 0.94 at a depth of 20cm, and between 0.80 and 0.98 at 50cm. Thus, despite the simplifications made, the model was able to simulate soil temperature at these study sites. This simple model simulates soil temperature well in the uppermost soil layers where most of the nitrogen processes occur. The small number of parameters required means that the model is suitable for addition to catchment scale models. Keywords: soil temperature, snow model

The study of thermal stresses and parameters of refractory structures for the formation of the temperature field when changing the heating rate of the working surface of products

2020 ◽  
pp. 34-38
Author(s):  
A. Kh. Akishev ◽  
S. M. Fomenko ◽  
S. Tolendiuly
Keyword(s):  
Temperature Field ◽  
Specific Heat ◽  
Heating Rate ◽  
Thermal Stresses ◽  
Thermomechanical Properties ◽  
Heat Fluxes ◽  
Temperature Fields ◽  
Experimental Setup ◽  
Working Surface ◽  
Refractory Structures

An experimental setup for micro- and macro-studies of specific heat fluxes and thermomechanical properties of refractories has been developed. The influence on the heat resistance of refractory structures of thermal stresses, temperature field, shape and size of products under various heating conditions of their working surface is studied. It is shown that reducing the width of the side of the working surface of the refractory allows you to increase the speed and specific heat flux without violating the integrity of the structure of the refractory material. The distribution of the temperature fields of the refractory with a change in the heating rate of its working surface, as well as its shape, is studied. Ill. 5. Ref. 11.

Thermochemistry

2009 ◽  
Author(s):  
Christopher O. Oriakhi
Keyword(s):  
Heat Capacity ◽  
Specific Heat ◽  
Temperature Change ◽  
Chemical Reactions ◽  
Molar Heat Capacity ◽  
Physical Object ◽  
Heat Energy ◽  
Chemical Bonds ◽  
Quantity Of Heat

All chemical reactions involve energy changes. Some reactions liberate heat to the surroundings; others absorb heat from the surroundings. The breaking of chemical bonds in reactants and the formation of new ones in the products is the source of these energy changes. Calorimetry is the experimental determination of the amount of heat transferred during a chemical reaction. This measurement is carried out in a device called a calorimeter, which allows all the heat entering or leaving the reaction to be accounted for. This is done by observing the temperature change within the calorimeter as the reaction takes place; if we know how much energy is needed to change the calorimeter’s temperature by a given amount, we can calculate the amount of energy involved in the reaction. The relation between energy and temperature change for the calorimeter or for any other physical object is known as its heat capacity (C), which is the amount of heat energy required to raise the temperature of that object by 1°C (or 1 K). This can be expressed in mathematical terms as: C = q/ΔT where q is the quantity of heat transferred and ΔT is the change in temperature, calculated as ΔT = Tf − Ti. The larger the heat capacity of a body, the larger the amount of heat required to produce a given rise in temperature. The heat capacity of 1 mol of a substance is known as the molar heat capacity. Also, the heat capacity of 1 g of a substance is known as the specific heat . To determine the specific heat of a substance, measure the temperature change, ΔT, that a known mass, m, of a substance undergoes as it gains or loses a known quantity of heat, q. That is: Specific heat (c) = Quantity of heat gained or lost/Mass of substance (in grams)×Temperature change (ΔT) or c = q/m×ΔT The unit of specific heat is J/g-K or J/g°C.

Теплофизические характеристики теплозащитного материала корпуса ракетного двигателя при температурах до 1000 оС

2021 ◽  
pp. 11-18
Author(s):  
Геннадий Александрович Фролов ◽  
Юрий Игоревич Евдокименко ◽  
Вячеслав Михайлович Кисель ◽  
Ирина Александровна Гусарова
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Temperature Fields ◽  
Thermophysical Characteristics ◽  
Furnace Heating ◽  
Temperature Dependences ◽  
Good Agreement

An experimental determination of the temperature dependences of the specific heat capacity and the thermal conductivity coefficient of the multifunctional coating MFP-92 at temperatures up to 1000 °C has been carried out. At temperatures up to 450 °C, an IT-c-400 device was used to determine the specific heat capacity. IT-l-400 device was used for the determination of thermal conductivity. At higher temperatures, the determination of the thermophysical characteristics (TPC) was carried out by solving the inverse problem of thermal conductivity (IPT) in a flat plate under conditions of one-sided heating in a muffle furnace. Composite material MFP-92 is a multilayer structure with upper layers based on silica fabric and chromophosphate binder and lower layers based on mullite-silica fabric and aluminosilicate binder. The TPC of the layers also differ from each other, and, accordingly, the properties of this material as a whole can be determined only in the form of their effective values, averaged in one way or another over the thickness of the coating. In addition, during heating, the material undergoes significant physicochemical transformations associated with the thermal destruction of its components, manifested in the form of abundant gas release, and a decrease in the density of the material, which significantly changes its TPC and determines its dependence on the heating rate. Therefore, studies of the thermophysical characteristics of the MFP-92 material were carried out with several (2-5) consecutive heating cycles. It was found that in four heating cycles of the MFP-92 material up to 450 °C for 75 minutes when measuring the specific heat on the IT-c-400 device, its temperature dependence significantly changes qualitatively and quantitatively. With furnace heating to 1000 °C, the temperature dependences of the TPC of the material, determined in the first and second heating cycles, have a different form, but change insignificantly in subsequent heating cycles. This makes it possible to ascribe to the MFP-92 material a set of two sets of TPC related to its initial (phase A) and annealed after heating to 1000 °C (phase B) states. Using the obtained TPС of phase A (including the magnitude of the thermal effect of irreversible endothermic phase transition at 100 °C) and phase B, good agreement was obtained between the calculated and experimental temperature fields in the samples under furnace heating conditions.

THE MECHANISM OF RAISING AND QUANTIFICATION OF SPECIFIC HEAT FLUX AT BOILING OF NANOFLUIDS IN FREE CONVECTION CONDITIONS

2017 ◽  
pp. 25-34
Author(s):  
V.N. Moraru
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Capacity ◽  
Specific Heat ◽  
Chemical Properties ◽  
Heating Surface ◽  
Physical Models ◽  
Superheated Liquid ◽  
Two Phase ◽  
Boiling Process

The results of our work and a number of foreign studies indicate that the sharp increase in the heat transfer parameters (specific heat flux q and heat transfer coefficient _) at the boiling of nanofluids as compared to the base liquid (water) is due not only and not so much to the increase of the thermal conductivity of the nanofluids, but an intensification of the boiling process caused by a change in the state of the heating surface, its topological and chemical properties (porosity, roughness, wettability). The latter leads to a change in the internal characteristics of the boiling process and the average temperature of the superheated liquid layer. This circumstance makes it possible, on the basis of physical models of the liquids boiling and taking into account the parameters of the surface state (temperature, pressure) and properties of the coolant (the density and heat capacity of the liquid, the specific heat of vaporization and the heat capacity of the vapor), and also the internal characteristics of the boiling of liquids, to calculate the value of specific heat flux q. In this paper, the difference in the mechanisms of heat transfer during the boiling of single-phase (water) and two-phase nanofluids has been studied and a quantitative estimate of the q values for the boiling of the nanofluid is carried out based on the internal characteristics of the boiling process. The satisfactory agreement of the calculated values with the experimental data is a confirmation that the key factor in the growth of the heat transfer intensity at the boiling of nanofluids is indeed a change in the nature and microrelief of the heating surface. Bibl. 20, Fig. 9, Tab. 2.

Experimental Study on the Specific Heat Capacity Measurement of Water-Based Al2O3-Cu Hybrid Nanofluid by using Differential Thermal Analysis Method

2019 ◽  
Vol 15 ◽  
Author(s):  
Andaç Batur Çolak ◽  
Oğuzhan Yıldız ◽  
Mustafa Bayrak ◽  
Ali Celen ◽  
Ahmet Selim Dalkılıç ◽  
...  
Keyword(s):  
Heat Capacity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Thermophysical Properties ◽  
Volume Concentration ◽  
Pure Water ◽  
Heat Capacity Measurement ◽  
Experimental Results ◽  
Hybrid Nanofluid ◽  
Capacity Measurement

Background: Researchers working in the field of nanofluid have done many studies on the thermophysical properties of nanofluids. Among these studies, the number of studies on specific heat are rather limited. In the study of the heat transfer performance of nanofluids, it is necessary to increase the number of specific heat studies, whose subject is one of the important thermophysical properties. Objective: The authors aimed to measure the specific heat values of Al2O3/water, Cu/water nanofluids and Al2O3-Cu/water hybrid nanofluids using the DTA method, and compare the results with those frequently used in the literature. In addition, this study focuses on the effect of temperature and volume concentration on specific heat. Method: The two-step method was used in the preparation of nanofluids. The pure water selected as the base fluid was mixed with the Al2O3 and Cu nanoparticles and Arabic Gum as the surfactant, firstly mixed in the magnetic stirrer for half an hour. It was then homogenized for 6 hours in the ultrasonic homogenizer. Results: After the experiments, the specific heat of nanofluids and hybrid nanofluid were compared and the temperature and volume concentration of specific heat were investigated. Then, the experimental results obtained for all three fluids were compared with the two frequently used correlations in the literature. Conclusion: Specific heat capacity increased with increasing temperature, and decreased with increasing volume concentration for three tested nanofluids. Cu/water has the lowest specific heat capacity among all tested fluids. Experimental specific heat capacity measurement results are compared by using the models developed by Pak and Cho and Xuan and Roetzel. According to experimental results, these correlations can predict experimental results within the range of ±1%.

Development of the room temperature protocol based on room temperature ionic liquids and surfactant ionic liquids for the synthesis of derivatives of 2-amino-thiazoles and thermo-physical analysis of the synthesized derivatives using TGA-DSC.

2020 ◽  
Vol 10 ◽  
Author(s):  
Chandrakant Sarode ◽  
Sachin Yeole ◽  
Ganesh Chaudhari ◽  
Govinda Waghulde ◽  
Gaurav Gupta
Keyword(s):  
Thermal Analysis ◽  
Heat Capacity ◽  
Ionic Liquids ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Room Temperature ◽  
Heat Capacity Data ◽  
General Strategy ◽  
Capacity Data ◽  
Derivatives Of

Aims: To develop an efficient protocol, which involves an elegant exploration of the catalytic potential of both the room temperature and surfactant ionic liquids towards the synthesis of biologically important derivatives of 2-aminothiazole. Objective: Specific heat capacity data as a function of temperature for the synthesized 2- aminothiazole derivatives has been advanced by exploring their thermal profiles. Method: The thermal gravimetry analysis and differential scanning calorimetry techniques are used systematically. Results: The present strategy could prove to be a useful general strategy for researchers working in the field of surfactants and surfactant based ionic liquids towards their exploration in organic synthesis. In addition to that, effect of electronic parameters on the melting temperature of the corresponding 2-aminothiazole has been demonstrated with the help of thermal analysis. Specific heat capacity data as a function of temperature for the synthesized 2-aminothiazole derivatives has also been reported. Conclusion: Melting behavior of the synthesized 2-aminothiazole derivatives is to be described on the basis of electronic effects with the help of thermal analysis. Additionally, the specific heat capacity data can be helpful to the chemists, those are engaged in chemical modelling as well as docking studies. Furthermore, the data also helps to determine valuable thermodynamic parameters such as entropy and enthalpy.

scholarly journals Influence of alkaline modification on selected properties of banana fiber paperbricks

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Abayomi A. Akinwande ◽  
Adeolu A. Adediran ◽  
Oluwatosin A. Balogun ◽  
Oluwaseyi S. Olusoju ◽  
Olanrewaju S. Adesina
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Moisture Absorption ◽  
Water Volume ◽  
Banana Fiber ◽  
Fiber Loading ◽  
Banana Fibers ◽  
Alkaline Modification

AbstractIn a bid to develop paper bricks as alternative masonry units, unmodified banana fibers (UMBF) and alkaline (1 Molar aqueous sodium hydroxide) modified banana fibers (AMBF), fine sand, and ordinary Portland cement were blended with waste paper pulp. The fibers were introduced in varying proportions of 0, 0.5, 1.0 1.5, 2.0, and 2.5 wt% (by weight of the pulp) and curing was done for 28 and 56 days. Properties such as water and moisture absorption, compressive, flexural, and splitting tensile strengths, thermal conductivity, and specific heat capacity were appraised. The outcome of the examinations carried out revealed that water absorption rose with fiber loading while AMBF reinforced samples absorbed lesser water volume than UMBF reinforced samples; a feat occasioned by alkaline treatment of banana fiber. Moisture absorption increased with paper bricks doped with UMBF, while in the case of AMBF-paper bricks, property value was noted to depreciate with increment in AMBF proportion. Fiber loading resulted in improvement of compressive, flexural, and splitting tensile strengths and it was noted that AMBF reinforced samples performed better. The result of the thermal test showed that incorporation of UMBF led to depreciation in thermal conductivity while AMBF infusion in the bricks initiated increment in value. Opposite behaviour was observed for specific heat capacity as UMBF enhanced heat capacity while AMBF led to depreciation. Experimental trend analysis carried out indicates that curing length and alkaline modification of fiber were effective in maximizing the properties of paperbricks for masonry construction.

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