Influence of Convective and Radiative Cooling on Heat Transfer for a Thin Wire with Temperature-Dependent Thermal Conductivity

In this study, a numerical prediction of temperature profiles in a thin wire exposed to convective, radiative and temperature-dependent thermal conductivity is carried out using a finite-difference linearization approach. The procedure involves a numerical solution of a one-dimensional nonlinear unsteady heat transfer equation with specified boundary and initial conditions. The resulting system of nonlinear equations is solved with the Newton-Raphson’s technique. However unlike the traditional approach involving an initial discretization in space then in time, a different numerical paradigm involving an Euler scheme temporal discretization is applied followed by a spatial discretization. Appropriate numerical technique involving partial derivatives are devised to handle a squared gradient nonlinear term which plays a key role in the formulation of the Jacobian matrix. Tests on the numerical results obtained herein confirm the validity of the formulation.

Flow and thermal analysis of Jeffrey nanofluid in a microchannel: Buongiorno's Model

The present consideration explores the thermal energy and mass transfer process in conducting Jeffrey nanofluid flows through a microchannel. The slip boundary conditions, Brownian motion and temperature-dependent thermal conductivity were considered. The dimensionless governing models have been solved to the best possible investigative solutions using the Runge-Kutta-Fehlberg 4 −5th order numerical procedure. The impact of physical parameters on the momentum, energy, concentration, irreversibility and irreversibility ratio was revealed graphically in detail. It is concluded that the resultant momentum profile is augmented with the relaxation and retardation times parameter all over the flow region. The temperature-dependent thermal conductivity contributes to the resulting thermal energy of the flow system ever-growing to high. The concentration profile was diminutions through growing in the Brownian motion parameter. The irreversibility and irreversibility ratio were obtained mathematically and explained concerning the notable parameters. The magnetic parameter was to diminish the irreversibility rate, but it was augmented by increasing the parameter for the relaxation and retardation times ratio. Effect of thermal radiation, variable thermal conductivity, pressure gradient, buoyancy force and thermophoresis on the Jeffery nanofluid in a microchannel by the Buongiorno model have been inspected for the first time. The effects of this works are innovative and original.

A Linear Approach Suitable for a Class of Steady-State Heat Transfer Problems with Temperature-Dependent Thermal Conductivity

This work presents an useful tool for constructing the solution of steady-state heat transfer problems, with temperature-dependent thermal conductivity, by means of the solution of Poisson equations. Specifically, it will be presented a procedure for constructing the solution of a nonlinear second-order partial differential equation, subjected to Robin boundary conditions, by means of a sequence whose elements are obtained from the solution of very simple linear partial differential equations, also subjected to Robin boundary conditions. In addition, an a priori upper bound estimate for the solution is presented too. Some examples, involving temperature-dependent thermal conductivity, are presented, illustrating the use of numerical approximations.

On the Stefan Problem With Nonlinear Thermal Conductivity

The solution is obtained and validated by an existence and uniqueness theorem for the following nonlinear boundary value problem \[ \frac{d}{dx}(1+\delta y+\gamma y^{2})^{n}\frac{dy}{dx}]+2x\frac{dy}{dx}=0,\,\,\,x>0,\,\,y(0)=0,\,\,\,y(\infty)=1, \] which was proposed in 1974 by [1] to represent a Stefan problem with a nonlinear temperature-dependent thermal conductivity on the semi-infinite line (0;1). The modified error function of two parameters $\varphi_{\delta,\gamma}$ is introduced to represent the solution of the problem above, and some properties of the function are established. This generalizes the results obtained in [3, 4].

Entropy generation analysis for peristalsis of magneto Jeffrey materials

This article communicates peristalsis of Jeffrey material in curved geometry. Here, material has temperature-dependent thermal conductivity and viscosity. Mathematical modeling of an inclined magnetic field in curved configuration has been presented in this article. Irreversibility effects have been analyzed through entropy generation. Slip conditions are entertained both for velocity and thermal fields. Problem is first reduced in wave frame and then lubrication approach has been utilized. Numerical solution of dimensionless problem is obtained and important parameters of curiosity are examined. It is noticed that velocity enhances for higher viscosity whereas temperature decreases for higher thermal conductivity coefficient. Velocity of the flow is maximum for inclination of magnetic field to be zero and it is minimum for [Formula: see text] Heat transfer parameter enhances both for thermal conductivity parameter and Hartmann number. Temperature is high for curved configuration when compared with straight channel. It is observed that entropy remains unchanged in center of the channel and it is maximum near the channel walls. Entropy generation decays near the channel walls by higher viscosity and thermal conductivity parameters. However, entropy is more for higher inclination of magnetic field.

Study of the Structure, Microstructure and Temperature Dependent Thermal Conductivity Properties of SrTiO3: Via Y3+ Substitution

Yttrium (Y) modified strontium titanate (SrTiO3) powders with initial concentration of Y in the range of 0 to 15 mol% were produced through sol-gel technique. X-ray diffraction (XRD) studies show that all the prepared compounds have a perovskite cubic structure with the space group (Pm3m). The lattice constant, lattice strain and crystallite size of the as-prepared samples were estimated from the XRD pattern which reveals the incorporation of Y into SrTiO3 system, moreover to investigate the quality of the prepared SrYT ceramics powder, the scanning electron microscopy (SEM) was used to determined investigate the morphology, grain size and its distribution. The analysis of the thermal conductivity measurements performed on the obtained powders revealed the effect of the combination of temperature and Y content on the thermal conductivity value, Indeed, the minimum thermal conductivity was 4.12 W/(mK) obtained with 15%Y at 464 K.

Dynamic Thermal Properties Estimation Using Sensitivity Coefficients for Rapid Heating Process

Thermal conductivity determination of food at temperatures >100 °C still remains a challenge. The objective of this study was to determine the temperature-dependent thermal conductivity of food using rapid heating (TPCell). The experiments were designed based on scaled sensitivity coefficient (SSC), and the estimated thermal conductivity of potato puree was compared between the constant temperature heating at 121.10 °C (R12B10T1) and the rapid heating (R22B10T1). Temperature-dependent thermal conductivity models along with a constant conductivity were used for estimation. R22B10T1 experiment using the k model provided reliable measurements as compared to R12B10T1 with thermal conductivity values from 0.463 ± 0.011 W m−1 K−1 to 0.450 ± 0.016 W m−1 K−1 for 25–140 °C and root mean squares error (RMSE) of 1.441. In the R12B10T1 experiment, the analysis showed the correlation of residuals, which made the estimation less reliable. The thermal conductivity values were in the range of 0.444 ± 0.012 W m−1 K−1 to 0.510 ± 0.034 W m−1 K−1 for 20–120 °C estimated using the k model. Temperature-dependent models (linear and k models) provided a better estimate than the single parameter thermal conductivity determination with low RMSE for both types of experiments. SSC can provide insight in designing dynamic experiments for the determination of thermal conductivity coefficient.