Heat Conduction Parameter Research Articles

Self-similar flow behind a shock wave in a gas under the effect of viscosity, heat conduction, and variable ambient density

Self-similar solutions have been investigated to describe the propagation of planar shock waves in a non-ideal gas generated by a piston under viscous stress and heat flux. The equation of state for non-ideal gas incorporates the correction in pressure and volume of the gas. The piston position and ambient density vary exponentially with time. Newton’s law of viscosity is used for the viscous stress and Fourier’s law of heat conduction is taken for heat flux. The viscosity coefficient is taken as constant whereas the thermal conductivity coefficient varies with temperature and density following the power law. The shock jump conditions have been derived for the viscous non-ideal gas using integral form of conservation laws. The shock Reynolds number Re s has been introduced to study the effect of viscosity on shock propagation in non-ideal gas. It is found that similarity solution exists only in an ideal gas under the condition that the ambient density exponent is equal to twice the shock position exponent. This study shows that shock Reynolds number Re s and heat conduction parameter Γ c can be used to control the variation of the flow variables and piston position significantly. The shock strength decreases with increase in the value of shock Reynolds number Re s but is independent of the heat conduction parameter Γ c . The pressure, density, and adiabatic compressibility have significant deviations from high to low viscous flow of ideal gas but the velocity and heat flux undergo negligible change. The results do not support the claim of negligible effect of viscosity in earlier studies and establish the impact of viscosity and heat flux on shock propagation in an ideal gas.

Generalized thermoelastic damping in micro/nano-ring resonators undergoing out-of-plane vibration

Micro/nano-ring or ring-based resonators are popular core components of sensors and actuators. Accurately predicting the quality factor (Q) based on thermoelastic damping (TED) is intensively crucial for designing high-performance micro/nano-ring resonators. In this work, adopting the modified-couple-stress (MCS) and nonlocal-dual-phase-lagging (NDPL) models, analytical TED expressions are developed for circular cross-section micro/nano-rings undergoing out-of-plane vibration for the first time. Multiple effects are considered in the modeling procedure, which are size-dependence effects in the mechanical and thermal fields, the non-Fourier effect of heat conduction, and three-dimensional temperature gradients in the circumferential, radial, and tangential directions. Therefore, the proposed TED models are more comprehensive compared to existing TED models. The coefficients (CC and CM) associated with the out-of-plane vibration mode are examined from an energy-ratio perspective. Moreover, the investigation is focused on the impacts of the MCS and NDPL non-Fourier effects on the fluctuation temperature and TED spectra. The results indicate as CC and CM approach one, the bending energy emerges as the predominant component of the stored energy. Notably, the NDPL non-Fourier effect significantly affects the fluctuation temperature within the ring operated in high-order modes. In special, the distributions of fluctuation temperature in the circumferential direction exhibit periodic patterns that are closely correlated with the modal order. Furthermore, TED can be suppressed by the MCS size-dependence effect. Meanwhile, the behavior of TED at high frequencies is simultaneously determined by the dimension of heat conduction, phase-lagging times, and nonlocal thermal-length parameter.

Real-time temperature field and thermal deformation of slab track on cable-stayed bridge

This study aimed to master the real-time temperature fields of slab tracks on cable-stayed bridges and analyze the thermal deformations. The pivotal heat conduction parameters of the geotextile and rubber pad were obtained through testing, and the governing equations for heat conduction considering temperature variations were improved. A thermal-fluid-solid coupling model for slab track on cable-stayed bridge was proposed. The results indicated that the high temperatures of the track were concentrated within 0.05 m depth of the slab. Under the resistance of the isolation layer, the temperature on both sides of the geotextile isolation layer appeared obvious abrupt change. The time of maximum and minimum temperatures of the truss beam were the same as those of the air. The effects of real-time temperature change on the irregularity of the rail were obvious. In summer, the maximum vertical rail deformation was 201.88 mm and the transverse deformation was 17.87 mm. The temperature change in just one day caused vertical deformation of rail with a range of more than 60%. On a single day in summer, the maximum horizontal irregularity was 1.74 mm, which was less than the 2.0 mm specified in the code.

Non-Newtonian Casson Fluid Behaviour in the Presence of Nanofluid Particles During MHD Flow Through a Vertical Cone Filled With Porous Material

The flow of nanofluids around a vertical cone with porous media and Casson fluid characteristics is being looked at in this study. Thermophoresis, Brownian motion, and chemical reactions are also looked at. There are some ways to change the connected partial differential equations into a set of third-order ordinary differential equation with variable coefficients. This is called a similarity transformation. The Runge-Kutta method is used to solve third-order boundary layer equations. Physical processes, such as Epidermis slippage, velocity, temperature, but instead fluid density, mass transfer, heat transference coefficients, besides rate of heat handover coefficients, may be studied in this research. These processes may be looked at in this study. There are graphs that show a lot of different physical processes. Current numerical results are compared to results that have been published in the past to make sure computer programmes work. The resultant velocity profiles are decreasing utilising an increasing trendy captivating field as a result of Lorentz potency. Species concentration of Casson-When the oxidizing agent factor is increased, the microspheres decrease. Temperature profile areas a result of the rise in Thermo Scattering movements but instead heat conduction and Brownian motion parameters. Also, roles about increasing values of Biot number and this same criterion of radiant heat would be to surge the room’s temperature hybrid Nanofluid flow as well as rate of heat flows so at exterior. Concentration profiles remain rising with increasing the morals of Thermo migration limitation and contrary effect occurs as a consequence of Brownian motion parameter.

Quasi-P wave through orthotropic piezo-thermoelastic materials subject to higher order fractional and memory-dependent derivatives

This study uses the triple-phase lag model to investigate how higher-order fractional order and memory-dependent derivatives affect reflection at the free surface of an orthotropic piezo-thermoelastic medium. The performance of both kinds of derivatives is studied using the normal mode analysis technique. Four different types of coupled reflected plane waves are identified and explore the impact of various parameters, fractional order parameter, kernel function, the higher-order time differential fractional, and memory-dependent heat conduction parameters on energy distribution with respect to the angle of incidence. The results are presented graphically, providing numerical data for reflected waves, amplitude, and energy ratios.

Response of thermal conductivity of loess after high temperature in northern Shaanxi burnt rock area, China.

Spontaneous combustion of coal seams can produce a high temperature of about 800 ℃, which greatly changes the thermal conductivity of the overlying loess layer. The thermal conductivity of loess plays an important role in ecological restoration design and the calculation of roadbed and slope stability. In this study, loess in northern Shaanxi, China was taken as the research object to measure the mass-loss rate and heat conduction parameters of loess specimens after high temperature. The test results show that, between 23 and 900°C, with temperature increasing, the mass-loss rate is reduced. And the heat conduction coefficient (λ), specific heat capacity (c), and thermal diffusion coefficient (α) decreased by 48.9%, 23.1%, and 35.6%. This is due to the air thermal resistance effect caused by the increase of pores and cracks in loess specimens after high temperature.

Modeling on cryogenic heat exchangers considering variable properties, axial heat conduction and viscous heating

Cryogenic heat exchangers are key components of low temperature refrigerators and determine the ultimate refrigeration performance. Accurate modeling on the cryogenic heat exchangers in sub-Kelvin regime has important theoretical and applied values, yet is still short of study. This study proposes local thermal nonequilibrium models of the heat exchangers in sub-Kelvin regime, including continuous and discrete ones. The effects of the variable properties, axial heat conduction, and viscous heating were investigated. The finite volume method was employed to solve the models numerically; in addition, the temperature and pressure distributions were obtained and analyzed. The proposed models were validated using a comparison of the obtained simulation results with experimental results in the literature. The analysis of the obtained results revealed that: (1) for continuous heat exchangers, the variable Kapitza thermal conductance leads to a large temperature gradient at the entrance. The outlet temperature was negligibly affected by applying different inlet temperature. (2) The axial heat conduction significantly degrades the performance of discrete heat exchangers. The performance was found to be limited by the axial heat conduction when the axial heat conduction parameter was larger than 0.02. (3) For the sintered heat exchanger, both the dimensionless temperature and pressure drop are obviously affected by the geometric impedance when it is greater than 4 × 1014 m−4. Consequently, the proposed mathematical models are useful for the accurate prediction and optimization of cryogenic heat exchangers.

MATHEMATICAL MODELING OF THERMO-SOLUTAL TRANSPORT IN PULSATING FLOW IN THE HYDROCEPHALUS

Cerebrospinal fluid (CSF) is a symmetric flow transport that surrounds brain and central nervous system (CNS). Hydrocephalus is an asymmetric and unusual cerebrospinal fluid flow in the lateral ventricular portions. This dumping impact enhances the elasticity over the ventricle wall. Henceforth, compression change influences the force of brain tissues. Mathematical models of transport in the hydrocephalus, which constitutes an excess of fluid in the cavities deep within the brain, enable a better perspective of how this condition contributes to disturbances of the CSF flow in the hollow places of the brain. Recent approaches to brain phase spaces reinforce the foremost role of symmetries and energy requirements in the assessment of nervous activity. Thermophysical and mass transfer effects are therefore addressed in this paper to quantify the transport phenomena in pulsatile hydrocephalus CSF transport with oscillating pressure variations that characterize general neurological activity and transitions from one functional state to another. A new mathematical model is developed which includes porous media drag for brain tissue and solutal diffusion (concentration) effects. A classical Laplace transform method is deployed to solve the dimensionless model derived with appropriate boundary conditions. The analysis reveals that with increasing permeability of the subarachnoid space, the CSF velocity is increased, and a significant fluid flux enhancement arises through the brain parenchyma as the pressure of the fluid escalates drastically due to hydrocephalus disorder. Stronger thermal buoyancy (Grashof number) also results in deceleration in the flow. CSF temperature is reduced with progression in time. Particle (e.g. ion) concentration is suppressed with increasing Schmidt number. As heat conduction parameter increases, there is a substantial depletion in CSF velocity with respect to time. Increasing Womersley parameter displaces the CSF velocity peaks and troughs. The present effects are beneficial in determining the thermo-fluidic transport mechanism of the pathological disorder hydrocephalus. Also, the present results are compared with those clinical studies for some cases. We have confirmed that our validity provides a decent justification with the neurological studies.

Stability analysis of diamond-silver-ethylene glycol hybrid based radiative micropolar nanofluid: A solar thermal application

The current study emphasizes the stagnation point flow and heat transmission properties of a hybrid-based micropolar nanofluid over a porous Riga plate that is capable of both shrinking and stretching. A mathematical modeling of diamond-silver-ethylene glycol/water hybrid nanofluid has been explored. Here 20% of ethylene glycol and 80% of water are considered as the base fluid. Heat transfer proficiency of airplane wings is evaluated with the inclusion of distinguished effects like viscous dissipation and solar-based thermal radiation, so we included them in this paper. By employing some suitable transformations, the system of nonlinear ordinary differential equations are attained and numerically solved by using MATLAB software. The dual nature of skin friction, Nusselt number, and micro-rotation gradient solutions are demonstrated for a wide variety of relating parameters. The boundary-layer separation happens when number of results fails to happen ahead of the critical value of the contracting parameter. To show the effect on flow and heat transfer of appropriate parameters, graphs are used. Stability is shown to be better in solution one than in the second, according to the results. It is detected that the temperature has decelerated in the presence of micropolar heat conduction parameter for both solutions The radiation parameter reduces the Nusselt number of the hybrid nanofluid for the first solution and a contrary for second solution. The array of the skin friction values are moving downwards for fluctuating values of heat source/sink. Sun based energy is the chief source of heat from the sun, and it utilizes in photovoltaic cells, sun-based power plates, photovoltaic lights and sun-based hybrid nanofluids. Specialists are currently exploring the utilization of nanotechnology and sun-based radiation to further develop flight effectiveness.

Numerical study of natural convection dissipative electro‐magnetic non‐Newtonian flow through a non‐Darcy channel

AbstractInspired by simulating duct thermal processing of novel functional polymers, a novel mathematical model is developed for buoyancy‐driven heat transfer in non‐Newtonian Williamson fluid flow in a vertical parallel plate duct containing a permeable medium, under mutually orthogonal electrical and magnetic fields. The momentum equation features electrical and magnetic body force terms, and the Darcy–Brinkman–Forchheimer mode is used for non‐Darcy effects. The energy balance equation includes thermal buoyancy (natural convection body force) and a modified viscous dissipation term. The conservation equations with associated boundary conditions are reframed into a system of coupled non‐linear ordinary differential equations via appropriate similarity transformations. The emerging dimensionless boundary value problem is then solved with a differential transform method (DTM). Validation of DTM solutions with the bvp4c MATLAB collocation solver is included. The influence of key parameters on velocity, temperature and average Nusselt number, are computed and illustrated graphically. With elevation in Weissenberg (non‐Newtonian) number, velocity and temperature are reduced. Velocity is suppressed with increasing non‐Darcian parameter (Forchheimer effect) whereas it is enhanced with increment in buoyancy convection parameter. With increasing Forchheimer, Darcy number and Hartmann number, the average Nusselt number is boosted whereas it is decreased with higher values of buoyancy convection parameter, Brinkman number and Weissenberg number. A strong reduction in temperature is computed with increment in ratio of Joule electrical heating to heat conduction parameter. DTM is shown to be an exceptionally accurate and versatile approach for simulating non‐Newtonian electromagnetohydrodynamic transport in ducts.

Effect of salt fingers on heat transfer for different non‐uniform concentration profiles in a micropolar liquid

AbstractThis paper discusses the theoretical aspects of the effect of salt fingers on heat transfer for different non‐uniform concentration profiles in a micropolar liquid layer kept between two parallel plates of infinite extent separated by a thin layer, heated and soluted from above. The onset of salt finger convection (convection due to the salt finger process) is studied through the linear stability analysis theory. The system of partial differential equations is solved numerically using the normal mode analysis method and the required solution is found by applying the Galerkin method. The effect of heat transfer and concentration of micropolar liquid is obtained for (i) free–free, (ii) rigid–rigid, and (iii) rigid–free isothermal, permeable with no‐spin boundary conditions. The effect of different micropolar parameters (i.e., coupling parameter, micropolar heat conduction parameter, couple stress parameter, and inertia parameter) has been analyzed on the onset of stationary convection, and the results are depicted graphically. It is shown that different non‐uniform concentration gradients, diffusivity ratio, coupling parameter, and solutal Rayleigh number influence the heat transfer in the system. The phase of concentration flow for different boundary conditions is compared and analyzed.

IoT-based Peat Soil Heat Conduction Parameter Delivery System As Land Fire Mitigation Effort

IoT-based Peat Soil Heat Conduction Parameter Delivery System As Land Fire Mitigation Effort

Classical Linear Stability Analysis of Energy Based Internally Heated Distributions on Bénard Porous Convection in a Micropolar Fluid Layer

The theoretical and numerical analysis is carried out on the effect of three types of configurations of Rayleigh-Bénard (RB) convection driven by the boundary combinations of Rigid-Rigid (R-R), Rigid-Free (R-F) and Free-Free (F-F). The RB convection models are distinguished by the three different temperature boundary conditions like: 1) RB1: lower and upper at fixed-temperature, 2) RB2: lower and upper with fixed-heat flux, or perfectly insulating and 3) RB3: bottom surface is fixed-temperature and top surface is fixed-heat flux. A Galerkin-type is based on the weighted residual method (WRM) which has been used to obtain the eigenvalue for gravity thermal Rayleigh number. It is noted that the porous medium of Darcy parameter and spin diffusion (couple stress) parameter N3 is to hasten coupling parameter N1 and micropolar heat conduction parameter N5 is to delay the onset of convection. Further, increase in the value of N1, N5, and as well as decrease in N3 is to diminish the size of convection cells.

Numerical study on regenerative effectiveness of parallel-plate regenerator for Stirling engine

ABSTRACT Due to the excellent heat transfer performance and low pressure drop, the parallel-plate regenerator (PPR) is very suitable for use in Stirling engines. At present, researches on the application of PPR in Stirling engines are rare. The axial heat conduction loss in PPR is a key factor that affects the heat transfer performance. Therefore, in this paper, the theoretical model of PPR operated under the Stirling engine working conditions is studied numerically, the regenerative effectiveness is taken as the target parameter, and the influence of axial heat conduction and other important parameters are explored. The results show that the axial heat conduction is detrimental to regenerative effectiveness, the regenerative effectiveness does not vary monotonically with the increase in the thermal conductivity, the copper regenerator with higher thermal conductivity has a lower regenerative effectiveness because of its higher axial thermal conductivity. The working frequency and the thermal properties of the working fluids have a comprehensive effect on the regenerative effectiveness, for high thermal diffusivity working fluids, such as helium and hydrogen, the regenerative effectiveness is high, while for low thermal diffusivity working fluid, such as carbon dioxide, the regenerative effectiveness is relatively low, and does not vary monotonously with frequency. The regenerative effectiveness increases with the reduction of the plate spacing, the plate spacing should be determined by considering the regenerative effectiveness and the pressure drop comprehensively. It is recommended that the stainless steel be a suitable material for the plates, and helium be the suitable working fluid.

Elastic shakedown analysis of two-dimensional thermo-elastic rolling/sliding contact for a functionally graded coating/substrate structure with arbitrarily varying thermo-elastic properties

The elastic shakedown analysis of rolling/sliding contact with friction heat is essential for the safety evaluation of tribological components with a functionally graded (FG) coating. However, the corresponding works are still lacking due to the complexity of thermo-elastic contact stress calculation and residual stress optimization induced by the non-homogeneity of material properties. An effective multi-layered model for the thermo-elastic rolling/sliding contact of two similar elastic cylinders with the FG coating involving arbitrarily distributed thermo-elastic properties is established, and the corresponding thermo-elastic stress field is obtained subsequently by using the conjugate gradient method and fast Fourier transform algorithm. Then, a specific bisection iteration procedure is applied to evaluate the elastic shakedown limit (ESL), and the effects of friction coefficient, rolling speed, distribution gradient indexes of various thermo-mechanical properties, and FG coating thickness on the ESL are discussed, respectively. The results show that the increases of friction coefficient and rolling speed can cause the decrease of ESL, the ESL can be improved significantly by adjusting the distribution gradients of shear modulus and yield stress appropriately, and the relations between the ESL and various heat conduction parameters show a strong dependence on the sliding velocity.

Dynamic evolution simulation of sintering pool in selective laser sintering walnut shell/Co-PES composite

In view of the difficulties in the observation of sintering pool and too many factors influencing the dynamic evolution process of sintering pool during the selective laser sintering (SLS) process of biomass composite materials, the structural morphology of sintering pool during the SLS process of walnut shell/Co-PES (WSPC) powder and its dynamic evolution process were studied. Based on the DFLUX subprogram, a moving double ellipsoid heat source model was established. Considering heat conduction, heat radiation, heat convection and thermophysical parameters changing with temperature, the three-dimensional finite element model of WSPC powder was numerically simulated in the process of SLS. Through numerical simulation analysis, the surface shape of sintering pool is circularand the cross section one is deep bowl, and the sintering forming process is a process in which the sintering pool is continuously superposed along the sintering direction. By comparing the experimental results with the numerical simulated results, the experimental results are in good agreement with the simulated results. The dynamic evolution law of sintering pool during SLS process of WSPC powder and the change law that sintering pool size increases with the increase of preheating temperature and laser power and the decrease of scanning speed were obtained.

Mathematical modeling and analysis of microwave-assisted freeze-drying in biopharmaceutical applications

Freeze drying is an essential unit operation for the storage of biopharmaceuticals, with its main weakness being the very long primary drying times required to sublimate all of the ice formed in the initial freezing step. This study investigates the use of microwave irradiation to reduce drying times. Mechanistic models are derived in a proposed freeze-drying process in which two energy transfer mechanisms – microwave irradiation and heat conduction – occur simultaneously. For this design, a mechanistic model derived in this article predicts an 83% reduction in primary drying time compared to conventional freeze drying. The influence of microwave power and design parameters associated with heat conduction parameters on the primary drying time are investigated and discussed. The model is implemented as open-source software in Julia and is available for engineers to use for designing such equipment.

Temperature Prediction Model for Two-Phase Flow Multistage Fractured Horizontal Well in Tight Oil Reservoir

Distributed temperature sensing (DTS) has been used for fracture parameter diagnosis and flow profile monitoring. In this paper, we present a new model for predicting the temperature profile of two-phase flow multistage fractured horizontal wells in the tight oil reservoirs. The homogeneous reservoir flow/heat transfer model is extended to the tight oil reservoir-fracture-wellbore coupled flow/thermal model. The influence of SRV area on reservoir and wellbore is considered, and the Joule-Thomson effect, heat convection, heat conduction, and other parameters are introduced into the improved model. The temperature distributions of reservoir and wellbore with different production times, water cut, and locations of water entry are simulated. The simulated results indicate that the Joule-Thomson effect will cause wellbore temperature to rise; the temperature of fractures with more water production is significantly lower than that of other fractures, and the water outlet location can be judged according to the temperature change of the wellbore. By using the improved temperature prediction model, the DTS monitoring data of two-phase flow multistage fractured horizontal well in the tight reservoir has been calculated and analyzed, and the accurate production profile has been obtained.

Energy Processes of Self-Organization of Vortex Structures in the Problem of Compressor Stability

The extended micro- and macroscopic model of laminar and stationary non-equilibrium turbulent processes of gas motion, which includes cascade cooperative processes of molecules energy self-organization, is suggested here. The model is based on the energy conservation law taking into account the fact that emission and absorption of energy are occurring during change of phases. Potential energy of thermodynamic potential of gas layers velocities difference is transformed into gas molecules rotational motion by overcoming the dynamic viscosity of laminar movement process as a result of the first self-organizing process and non-equilibrium phase change on micro-level. The second process of self-organization phase, which leads to the macroscopic dynamic spiral-vortex structure formation, is initiated when the heat conduction parameter (energy flux density) has reached its critical value

Estimating sensor number and spacing for inverse calculation of thermal boundary conditions using the conjugate gradient method

The conjugate gradient method is a popular tool for solving inverse heat transfer problems which arise for example from the estimation of unknown thermal boundary conditions or temperature dependent material properties. Depending on the desired accuracy of the results, input data of numerous temperature sensors need to be considered. However, due to limited access and available space many systems offer only a few temperature measurement spots. Therefore, this paper focuses on the question how changes in the number of temperature measurements affect the inversely estimated boundary condition. This behavior is studied by two numerical test cases with different boundary conditions, thermal properties and geometries, investigating also varying resolutions of the boundary condition and the effect of measurement errors. The results of both test cases show, that for undisturbed measurement data as well as superimposed measurement errors, fewer temperature readings than unknowns are sufficient to accurately estimate the boundary condition. Also, after exceeding a threshold in sensor number, only little improvement of inverse estimated results can be observed in both test cases. To transfer these findings on further inverse heat transfer scenarios, the key heat conduction parameters are summarized in a characteristic parameter, the Fourier number. This number supports the estimation of necessary sensor count in future inverse investigations with varying thermal parameters, geometries and investigation time.