Influence Of Thermal Conductivity Research Articles

Frost heave model and frost heaving force analysis of permafrost tunnel based on segregated ice

Bi-directional freezing occurs when a tunnel portal passes through an active layer in cold region, or when the tunnel passes through permafrost. The surrounding rock of tunnel portal is frozen by air inside of the tunnel and earth surface. The freezing-thawing cycle of permafrost tunnels is frozen by the permafrost and air inside the tunnel. To investigate the frost heave force on the lining of permafrost tunnels, and verify the layered segregation ice in the surrounding rock of these tunnels, a one-dimensional hydrothermal stress model of bi-directional freezing is established, so as to study the evolution law of segregated ice from the surrounding rock in permafrost tunnels based on the theory of hydro-thermal coupling and segregated ice. After that, based on the mechanical theory, a frost-heave elastic mechanical model including secondary lining, freeze–thaw zone, freezing zone and segregated ice is established. The results show that there is layered segregated ice in the surrounding rock after the lining of permafrost tunnel. The annual difference and the annual average temperature have a great influence on the thickness of segregated ice, while the influence of thermal conductivity is relatively small. The thickness of thawing cycle should be less than 5 m, so that the frost heaving force acting on the lining will not be too large. Good water plugging quality can decrease the thickness of segregated ice. The frost-heaving force acting on the lining increases as the thickness of segregated ice increases. When the thickness of segregated ice is 10 cm, the maximum frost heaving force generated on the lining of single-layer segregated ice is 1.39 times that of non-segregated ice. The frost-heaving force caused by the segregated ice should be considered to guarantee the safety of tunnel structure.

Novel algorithm for compressible Newtonian axisymmetric thermal flow

In this paper, we mainly focus on the development of the Taylor-Galerkin/Pressure-Correction method (TG/PC) method to solve the flow of a compressible Newtonian fluid under nonisothermal conditions. The process of development needs applying the two-step Lax–Wendroff method on the energy equation, after which two new steps for energy equations will be obtained within the TG/PC algorithm. In addition, for the density component, the Tait equation of state is adopted to relate density to pressure, which also yields a new step within the novel method to give the correction formula of compressible pressure. To perform the analysis of the new algorithm, Poiseuille flow through axisymmetric rectangular channel for the Newtonian thermal flow is utilized as a simple problem test. The effect of nondimensional factors such as Reynolds number (Re) and Prandtl number (Pr) is discussed in this study. The influence of thermal conductivity [Formula: see text] and viscosity [Formula: see text] on the solution components is presented as well. Also, comparison for both compressible and incompressible flows is provided in addition to a comparison between both cases’ convergence, as it turns out that the convergence of the incompressible case is better than the compressible case. All the results of the effects presented in this study agree well with the approved physical trend.

Finite difference analysis on radiative flow on a perpendicular plate using the influence of thermal conductivity

This study aims to investigate the influence of radiation, thermal conductivity and variable viscosity on natural convective flow on a semi-infinite perpendicular plate. Variable viscosity, thermal conductivity and thermal radiation are considered for the given study. The dimensional governing equations are framed with the use of the mentioned parameters and then these equations were converted into dimensionless equations by applying non dimensional quantities. The main aim of this study is to find the Nusselt number and skin friction for both air and water for considered parameters. Using the finite difference method through Fortran software, numerical solutions to the governing heat equations and dimensionless momentum equations were computed. The results for the parameters thermal conductivity, variable viscosity, radiation, and Prandtl number for both air and water are displayed via various graphs. The skin friction coefficients, Nusselt parameter, and local Nusselt numbers were discussed for both the air and water. The key conclusions of this study are that the succeeding velocity declines as the radiation's increases. By increasing the radiation value and the fluctuation time, the temperature distribution increases. Notably, the temperature profile increases significantly when the variable viscosity parameter decreases.

The influence of thermal conductivity on the thermal state of Central and Eastern geological units of the Rif belt (Morocco)

The influence of thermal conductivity on the thermal state of Central and Eastern geological units of the Rif belt (Morocco)

Влияние теплопроводности материалов контактных поверхностей на тепловой баланс элементов гидросъемника для струйной цементации грунтов

The paper is deals with the influence of thermal conductivity and the materials of the contact surfaces of the drill shaft and the sealing element on the change in the thermal balance of the structural unit «drilling string» used in the jet grouting technology to fix weak and unstable types of soils. A model with nodes for the computational grid of the “hydraulic puller” assembly unit is shown, part of which are the considered drill shaft and sealing elements. The temperature values are calculated by the finite element method in the «Siemens Femap’s» environment depending on the change in the thermal conductivity coefficients of the contacting elements. Calculations were carried out for the fourth part of the indicated model, due to the axisymmetry of the problem being solved, this made it possible to significantly reduce the amount and time of calculations. Graphs of the corresponding dependence are constructed for a number of points located in the characteristic areas of the hydraulic stripper. Also, by power regression, expressions were obtained that allow calculating the temperature values in the indicated areas of the considered assembly. The obtained dependencies will make it possible in the future to select the material for the drill shaft of the hydraulic puller based on the optimal ratio of the thermal conductivity of the shaft, its corrosion resistance, determined by the chemical composition of the steel and the thermal conductivity of the sealing.

Influence of thermal conductivity on transient mixed convection in a vented cavity with a hollow cylinder and filled with CNT-water nanofluid

This study is aimed to perform a numerical time-dependent investigation thermal conductivity effect of the annular cylinder within a vented cavity using CNT based-water nanofluid. For demonstrating the effect of thermal conductivity, four distinct hollow cylinder materials such as Ks = 0.5(Plastic tiles), Ks = 0.84(Clay tiles), Ks = 1.1(Concrete tiles), and Ks = 2(Slate tiles) are introduced together with a suitable variation of dimensionless time (0 ≤ τ ≤ 1). The governing equations of the model with associated boundary conditions is solved using finite element based Galerkin's weighted residual method. Different contour plots for thermal and flow field transformation and mean Nusselt number, mean fluid temperature, bulk convective field temperature, temperature gradient, pressure gradient, vortices, and fluid velocity magnitude are presented for qualitative and quantitative thermal performance analysis. With the decrease of solid thermal conductivity, 27.3% thermal transport enhancement is noted from the heated surface of the cylinder. However, a 16.3% increase in the bulk fluid temperature has been recorded with the increase in cylinder conductivity. The numerical outcomes from this investigation propose a better thermo-fluid efficiency compared to the existing methodology which can be suggestive to engineers and researchers for designing heat exchangers, heat pipes, and other thermal systems.

Effect of thermo-physical parameters on heat transfer characteristics of the wall implanted with heat pipes

• A new evaluate index (ITRR) is proposed to reflect the thermal response. • The actual environmental of WIHP dynamic experiment system is tested and validation. • The influence of thermal conductivity on the heat transfer of WIHP is analyzed. • The influence of density on the heat transfer of WIHP is analyzed. • The influence of specific heat capacity on the heat transfer of WIHP is analyzed. The heat transfer characteristics of a wall implanted with heat pipes (WIHP), a new passive natural energy utilization technology, significantly differ from that of an ordinary wall. It features effective heat transfer between indoor and outdoor environments due to the pipe’s unidirectional thermal conductivity. The thermal performance of the wall is crucial in terms of reducing a building’s energy consumption. In this paper, the experiment and theoretical analysis were combined, and the numerical simulation calculation was used to analyze the effects of material thermo-physical parameters on WIHP heat transfer performance. The results show that for the inside surface temperature, density and specific heat capacity are negatively related to it, and thermal conductivity is also negatively related to it before the heat pipe is in optimum working condition, and then the thermal conductivity is positively related to it. For the inside surface heat flux, it is opposite to the variation of inside surface temperature. The inside surface temperature rise rate (ITRR) is proposed to reflect the thermal response of the inside surface temperature to the variation of outdoor air temperature. When the thermal conductivity increases, the difference between the maximum and minimum ITRR is 0.053 °C/h. When the density increases, the trend of ITRR decreases first and then increases, and the average value is 0.062 °C/h. When the specific heat capacity gradually increases, the difference between the maximum and minimum of ITRR is 0.006 °C/h.

The effect of water droplets geometry on the performance of solar still

The present mathematical model includes heat and mass balance equations for the different elements of the simple solar still, such as the basin, water, humid air, the inner condensation surface and the external one. The performance of the still, as well as its components temperatures profiles are then analysed for two typical days of March and June. The effect of different parameters such as the contact angle and thermal conductivity of the condensation surfaces, the water thickness, the basin absorption coefficient and the insulation material and its thickness were studied. Simulation results show that the contact angle or the water droplets geometry affects greatly the solar distiller performance for both days. The total production in June is about 5058 ml/m2 d for a glass surface with a 0° contact angle, while it is only about 2414 ml/m2 d for a polystyrene surface with a 90° contact angle. The reduction of production for polystyrene is due to the large decrease in droplets transmittance for contact angles higher than 40°. Besides, it was demonstrated that the thermal conductivity of the condensation surfaces does not have a significant effect on the overall solar still production. The influence of thermal conductivity on different components temperatures was also interpreted.

Optical and thermal insulation properties of silica aerogel under a 7 kW·cm-2 power laser irradiation

Laser technology has made great progress over the past decades. However, corresponding defense systems have lagged slightly behind. Therefore, there is significant room for research with respect to the principles and bases of existing laser protective materials. In this paper, a kind of silica aerogel material is prepared with the acid-base sol-gel process. Considering the influence of thermal conductivity and the porosity of the aerogel materials on the laser irradiation results, the best laser resistance times of the materials were obtained. The concept of the maximum energy transfer radius is proposed to build a preliminary laser irradiation model for porous materials. It indicates that under the irradiation of a continuous wave laser with a power of 7 kW·cm−2, the silica aerogel materials with the thickness of 3, 6, and 9 mm can withstand the laser for maximum times of 26, 61, and 100 s, respectively. After 7 s of irradiation, the surface temperature of 3 mm from the laser incident point is 226.9 °C. Aerogels, especially silica aerogels, should be considered as future laser protection materials. The extremely low thermal conductivity and the strong scattered ability for laser of these materials will provide a good defensive effect against large-energy laser weapons.

TEMPERATURE-DEPENDENT PHYSICAL CHARACTERISTICS OF THE ROTATING NONLOCAL NANOBEAMS SUBJECT TO A VARYING HEAT SOURCE AND A DYNAMIC LOAD

In this article, the influence of thermal conductivity on the dynamics of a rotating nanobeam is established in the context of nonlocal thermoelasticity theory. To this end, the governing equations are derived using generalized heat conduction including phase lags on the basis of the Euler–Bernoulli beam theory. The thermal conductivity of the proposed model linearly changes with temperature and the considered nanobeam is excited with a variable harmonic heat source and exposed to a time-dependent load with exponential decay. The analytic solutions for bending moment, deflection and temperature of rotating nonlocal nanobeams are achieved by means of the Laplace transform procedure. A qualitative study is conducted to justify the soundness of the present analysis while the impact of nonlocal parameter and varying heat source are discussed in detail. It also shows the way in which the variations of physical properties due to temperature changes affect the static and dynamic behavior of rotating nanobeams. It is found that the physical fields strongly depend on the nonlocal parameter, the change of the thermal conductivity, rotation speed and the mechanical loads and, therefore, it is not possible to neglect their effects on the manufacturing process of precise/intelligent machines and devices.

An Experimental Investigation to Determine the Effect of Tube Material on the Tubeside Heat Transfer Performance of the Enhanced 1EHT Three Dimensional Heat Transfer Tube

Condensation heat transfer characteristics were experimentally investigated over a wide range of operating conditions in order to determine the heat transfer performance inside horizontal, smooth and enhanced heat transfer tubes; using R410A in tubes produced of copper and stainless steel. Experimental data was verified and results were compared to the performance measured in a smooth tube. Results indicate that the condensation heat transfer coefficient (HTC) enhancement ratio is in the range from 1.15 to 2.05 for the 1EHT tube and for the HX tube it ranged from 1.18 to 1.69. Smooth tube heat transfer performance was slightly affected by the thermal conductivity of the tube; however, larger enhancements are found in the enhanced tubes.Heat transfer coefficients increase with an increase of mass velocities. When the mass flux increases, the liquid flow becomes more turbulent and the liquid film becomes thinner; this reduces the thermal resistance and enhances the heat transfer. Heat transfer performance for low mass velocities rise slowly, showing only a small difference in magnitude. Performance increase is larger at high mass flux rates than that those found at low mass fluxes. The influence of thermal conductivity on the condensation heat transfer of the enhanced horizontal tubes was discussed. Better heat transfer performance occurs in tubes produced of a higher thermal conductivity material (copper) or in tubes with a smaller diameter.

Principles for designing CO2 adsorption catalyst: Serving thermal conductivity as the determinant for reactivity

CO2 is a representative prototype model in energy and environmental fields. Many factors for CO2 capture and activation have been investigated extensively but the research on the influence of thermal conductivity is still absence. We herein have calculated many properties, including dipole moment, electric structure, and adsorption energies, on Pt doped graphene and 2D BC3N2 substrates and served the thermal conductivity as the bridge. Our results have demonstrated that the lower (higher) thermal conductivity for 2D BC3N2 (graphene) corresponds to larger (lower) dipole moment, which is beneficial for CO2 activation (capture) process. Our research have not only revealed the dominant role of heat conductivity for CO2 capture and activation, but also paved the way for further catalyst design of various areas.

Numerical evaluations on the effects of thermal properties on the thermo-mechanical behaviour of a phase change concrete energy pile

Energy pile is a kind of economic and efficient geothermal utilization technology that the ground heat exchanger (GHE) used in ground source heat pump (GSHP) is embedded into building pile foundation to realize heat exchange with surrounding soil. Adding phase change material (PCM) into the energy pile can not only reduce the temperature variation and thermal deformation range of energy pile, but also improve its energy storage and heat transfer performance. In this work, phase change concrete energy pile (PCCEP) is proposed by using PCM as a part of backfill material of energy pile. A three-dimensional numerical model is developed to find the influences of thermal properties of PCCEP on its thermo-mechanical behaviour. According to the model, the influences of thermal conductivity, phase change latent heat (PCLE) and phase change temperature (PCT) on the thermal performance and mechanical characteristics of PCCEP are numerically investigated. It can be seen that for improving heat transfer performance of PCCEP, the thermal conductivity should be increased, but from the perspective of reducing change of pile displacement, axial force and side friction resistance, the thermal conductivity should be reduced. Under heat release mode, lower PCT and larger PCLE contribute to the improvement of thermal performance of PCCEP, and accordingly the rise range of pile temperature, pile displacement change and pile thermal stress can all be reduced. The experimental validation on the model shows that the simulation values of pile wall middle temperature(PWMT) and pile top displacement are agreed well with the corresponding experimental results, the real-time relative error of PWMT and pile top displacement are respectively within 5.1 and 12%.

Conjugate fluid, heat and species transports inside an enclosure containing miscellaneous solid arrays: General models of electronic cooling and pollutant removals

Double-diffusive natural convection in a vertical enclosure containing various solid block arrays is numerically and analytically investigated in present work, where heat and species source and sink are simultaneously attached on the walls. Rayleigh number, buoyancy force ratio, number of inner solid blocks, solid thermal conductivity and mass diffusion coefficient have been varied to observe inherent flow structures and mechanism of thermal and mass transports, regarding of different levels of solid-to-fluid volume ratios. Correlations have been presented for different flow regimes, namely thermal buoyancy driven flow and solutal buoyancy driven flow. Simulation and correlation results demonstrate that influences of thermal conductivity and mass diffusion coefficient of the solid block arrays on average Nusselt and Sherwood numbers are not evident compared with that of Rayleigh number. Furthermore, there is a positive correlation between average Nusselt number and Sherwood number. In addition, under certain values of Rayleigh number, absolute values of buoyancy force ratio close to unity will cause multiple steady solutions in pure natural convection. This research could benefit the future thermal and species management for electronics and built environment.

Using the flammability potential and the exergy indicator to assess the fire hazard of the rail transportation of cargoes

Introduction. Problems of fire safety of dangerous goods (DG) in the process of their rail transportation have not been fully resolved. The flammability assessment of substances and materials is insufficiently impartial; an integrated indicator, that allows to apply a consolidated methodological standpoint to improve their energy efficiency and environmental/fire safety is unavailable.The purpose of this work is to substantiate the feasibility and advantages of the exergy approach to assessing the fire hazard of the exhaust gas emitted from railroad transport.Materials and methods. The use of the flammability potential as an integrated indicator of the fire hazard of cargoes has a number of limitations. The exergy approach has a strong potential if applied to the assessment and prediction of fire hazards. Present-day and potential railroad cargoes serve as examples that substantiate the feasibility of this approach.Results and its discussion. Dependences between fire hazard indicators (flash points, flame propagation limits, auto-ignition points, heat of combustion) demonstrated by the components of liquid and gaseous fuels and the chemical exergy were identified.A study of changes in the physical exergy triggered by spills and combustion were illustrated by liquefied natural gas and liquefied hydrocarbon gases having various compositions. Physical exergy change patterns depending on the temperature and pressure of the above products were developed.For self-ignitable cargoes, dependences between the physical exergy and activation energy, critical ambient temperature, and heat capacity of self-heating materials were identified. The influence of thermal conductivity and humidity coefficients on the exergy value is established.Exergy changes were determined depending on the elemental composition of solid municipal waste, ash, volatile matter and fixed carbon content. Polymers and rubbers have the highest values of this indicator.An exergy indicator was introduced to assess fire and environmental hazards of substances and materials; it serves as the basis for the classification of cargoes.Conclusions. The use of the exergy indicator allows to increase the objectivity of assessments and take account of technical, economic, environmental criteria and indicators of fire hazards within an integrated system.

Triple Diffusive MHD Casson Fluid Flow Over a Vertical Wall with Convective Boundary Conditions

In this article, we study, effects of triple diffusive on a mixed convective viscous flow of an MHD Casson fluid through a vertical permeable wall numerically with convective BC’s. The governing equations are modeled and derived for the triple diffusive boundary layer flow to examine the fluid's nature under the influence of thermal conductivity and solutal diffusivity. Using an effective and suitable similarity transformation, highly non-linear coupled PDE’s are reduced to a series of coupled ODE’s and are solved by the Shooting technique with the help of the integral scheme of Runge Kutta-Fehlberg. To know the fluid properties' behavior, a numerical computation has been carried out for the non-dimensional parameters, which control the flow and demonstrated through plots such as permeability, convective parameter, Casson parameter, and buoyancy ratio parameters of the physical system. In the absence of a few non-dimensional parameters, present findings are compared with previously published work to validate our numerical scheme and found to be in good agreement with up to six decimal places of accuracy.

Numerical study of radiative non-Darcy nanofluid flow over a stretching sheet with a convective Nield conditions and energy activation

Abstract Numerous industrial processes such as continuous metal casting and polymer extrusion in metal spinning, include flow and heat transfer over a stretching surface. The theoretical investigation of magnetohydro-dynamic thermally radiative non-Darcy Nanofluid flows through a stretching surface is presented considering also the influences of thermal conductivity and Arrhenius activation energy. Buongiorno’s two-phase Nanofluid model is deployed in order to generate Thermophoresis and Brownian motion effects [1]. By similarity transformation technique, the transport equations and the respective boundary conditions are normalized and the relevant variable and concerned similarity solutions are presented to summarize the transpiration parameter. An appropriate Matlab software (Bvp4c) is used to obtain the numerical solutions. The graphical influence of various thermo physical parameters are inspected for momentum, energy and nanoparticle volume fraction distributions. Tables containing the Nusselt number, skin friction and Sherwood number are also presented and well argued. The present results are compared with the previous studies and are found to be well correlated and are in good agreement. The existing modelling approach in the presence of nanoparticles enhances the performance of thermal energy thermo-plastic devices.

Influence of Thermal Conductivity on the Thermal Behavior of Intermediate-Temperature Solid Oxide Fuel Cells

Influence of Thermal Conductivity on the Thermal Behavior of Intermediate-Temperature Solid Oxide Fuel Cells

Investigation on the cooling and temperature uniformity of power battery pack based on gradient phase change materials embedded thin heat sinks

In order to further increase the temperature uniformity of power battery, a thermal management method based on thin heat sink embedded with PCM was investigated in this paper. The thermophysical property and distribution of PCM are the key factors affecting the thermal management performance. A comparative study on the cooling and homogenization performance of the battery thermal management system under different thermal conductivities, melting temperature and distributions of PCM were explored carefully. The main results show that the maximum temperature and temperature standard deviation (STD) of the battery can be decreased with the function of heat sink embedded with PCM. Comparing to air cooling method, the maximum temperature and STD of the battery can be decreased by about 11.2% and 78.3% at 600 s, respectively. The influence of thermal conductivity can be neglected. Lowering the melting temperature and increasing latent heat can reduce the maximum temperature and STD. In additional, it is found that the distribution of PCM with different melting temperature or latent heat can obviously affect the maximum temperature and temperature uniformity of the battery. It could be a useful way to optimize the thermal management performance.

Thermal Mode Optimization of Combustion Chamber Walls for Power-Plants Using Semitransparent Porous Ceramics

The paper examines control and management by thermal mode of the internal surface of heat-insulated combustion chamber walls for green & efficient diesel and gas turbine engines due to the application of opaque or semitransparent thermal barrier materials (coatings). The authors’ model is devoted to combined radiant heat transfer both inside the heat-insulated combustion chamber and its ceramics walls, which could be scattering and absorbing for penetrating radiant component in the subsurface volume of optically heterogeneous porous material. The influence of thermal conduction, scattering (absorption) and external convective effects on the increase of the internal overheating zone in subsurface layers is simulated under intensive radiation. The unique set of optical, thermal-physical and mechanical properties of structural ceramics, depending on their porosity, were first proposed. The radiation fields of the absorbed energy in the near IR region and the corresponding temperature distributions in the modeled opaque and semitransparent ceramics walls were calculated under a stationary radiant-convective heat load during the active combustion phase at time intervals 0.01…0.1 s (diesel engines) and 10...100 s (turbine ones). In order to control the emission of nitrogen oxides, the authors propose a generation model of NOx, its growth or reduction caused by the management of radiant overheating inside semitransparent heat-insulation in which surface temperature is due to volumetric radiant absorption. It is shown that for semitransparent materials (coatings), the optimal thermal mode is determined first of all by thermal radiant characteristics in near IR at heating small times and it begins to correct at long ones due to the effect of thermal conductivity. This process may be modeled and regulated by the selected microstructural porosity of ceramic heat insulation.