Dual solutions of the nonlinear problem of heat transfer in a straight fin with temperature-dependent heat transfer coefficient

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Nasibeh Karamollahi ◽  
Ghasem Barid Loghmani ◽  
Mohammad Heydari
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Numerical Scheme ◽  
Lower Solution ◽  
Taylor Formula ◽  
Temperature Dependent ◽  
Content Type ◽  
Approximate Form ◽  
Special Case

Purpose In this paper, a numerical scheme is provided to predict and approximate the multiple solutions for the problem of heat transfer through a straight rectangular fin with temperature-dependent heat transfer coefficient. Design/methodology/approach The proposed method is based on the two-point Taylor formula as a special case of the Hermite interpolation technique. Findings An explicit approximate form of the temperature distribution is computed. The convergence analysis is also discussed. Some results are reported to demonstrate the capability of the method in predicting the multiplicity of the solutions for this problem. Originality/value The duality of the solution of the problem can be easily predicted by using the presented method. Furthermore, the computational results confirm the acceptable accuracy of the presented numerical scheme even for estimating the unstable lower solution of the problem.

Identification of three-dimensional transient temperature fields in thick-walled elements using the inverse method

2018 ◽  
Vol 28 (1) ◽  
pp. 138-150 ◽  
Author(s):  
Magdalena Jaremkiewicz
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Inverse Method ◽  
Thermal Stresses ◽  
Computing Time ◽  
Transient Temperature ◽  
Content Type ◽  
Inner Surface ◽  
The Heat Transfer Coefficient

Purpose The purpose of this paper is to propose a method of determining the transient temperature of the inner surface of thick-walled elements. The method can be used to determine thermal stresses in pressure elements. Design/methodology/approach An inverse marching method is proposed to determine the transient temperature of the thick-walled element inner surface with high accuracy. Findings Initially, the inverse method was validated computationally. The comparison between the temperatures obtained from the solution for the direct heat conduction problem and the results obtained by means of the proposed inverse method is very satisfactory. Subsequently, the presented method was validated using experimental data. The results obtained from the inverse calculations also gave good results. Originality/value The advantage of the method is the possibility of determining the heat transfer coefficient at a point on the exposed surface based on the local temperature distribution measured on the insulated outer surface. The heat transfer coefficient determined experimentally can be used to calculate thermal stresses in elements with a complex shape. The proposed method can be used in online computer systems to monitor temperature and thermal stresses in thick-walled pressure components because the computing time is very short.

Numerical investigation of laminar forced convection for a non-Newtonian nanofluids flowing inside an elliptical duct under convective boundary condition

2019 ◽  
Vol 29 (1) ◽  
pp. 334-364 ◽  
Author(s):  
Haroun Ragueb ◽  
Kacem Mansouri
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Transfer Coefficient ◽  
Fluid Flow ◽  
Transfer Coefficient ◽  
Convective Boundary Condition ◽  
Bulk Temperature ◽  
Convective Boundary ◽  
Content Type ◽  
The Heat Transfer Coefficient

PurposeThe purpose of this study is to investigate the thermal response of the laminar non-Newtonian fluid flow in elliptical duct subjected to a third-kind boundary condition with a particular interest to a non-Newtonian nanofluid case. The effects of Biot number, aspect ratio and fluid flow behavior index on the heat transfer have been examined carefully.Design/methodology/approachFirst, the mathematical problem has been formulated in dimensionless form, and then the curvilinear elliptical coordinates transform is applied to transform the original elliptical shape of the duct to an equivalent rectangular numerical domain. This transformation has been adopted to overcome the inherent mathematical deficiency due to the dependence of the ellipsis contour on the variables x and y. The yielded problem has been successfully solved using the dynamic alternating direction implicit method. With the available temperature field, several parameters have been computed for the analysis purpose such as bulk temperature, Nusselt number and heat transfer coefficient.FindingsThe results showed that the use of elliptical duct enhances significantly the heat transfer coefficient and reduces the duct’s length needed to achieve the thermal equilibrium. For some cases, the reduction in the duct’s length can reach almost 50 per cent compared to the circular pipe. In addition, the analysis of the non-Newtonian nanofluid case showed that the addition of nanoparticles to the base fluid improves the heat transfer coefficient up to 25 per cent. The combination of using an elliptical duct and the addition of nanoparticles has a spectacular effect on the overall heat transfer coefficient with an enhancement of 50-70 per cent. From the engineering applications view, the results demonstrate the potential of elliptical duct in building light-weighted compact shell-and-tube heat exchangers.Originality/valueA complete investigation of the heat transfer of a fully developed laminar flow of power law fluids in elliptical ducts subject to the convective boundary condition with application to non-Newtonian nanofluids is addressed.

Near-Field Radiative Transfer Between Heavily Doped SiGe at Elevated Temperatures

2011 ◽  
Author(s):  
Z. M. Zhang ◽  
E. T. Enikov ◽  
T. Makansi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
State Energy ◽  
Radiative Heat ◽  
Elevated Temperatures ◽  
Near Field ◽  
Temperature Dependent ◽  
Heavily Doped ◽  
The Heat Transfer Coefficient

SiGe alloys represent an important type of high-temperature semiconductor material for solid-state energy conversion. In the present study, the near-field radiative heat transfer between heavily doped SiGe plates is investigated. A dielectric function model is formulated based on the previously reported room-temperature mobility and temperature-dependent electric resistivity of several silicon-rich alloys with different doping type and concentration. The fluctuational electrodynamics is used to evaluate the near-field noncontact heat transfer coefficient. The variation of the heat transfer coefficient with doping concentration and temperature is explained according to the change in the optical constants and in the spectral distribution of the near-field heat flux.

scholarly journals Heat transfer aspects of condensation during vapour phase soldering on aligned PCB-based surfaces

2020 ◽  
Vol 32 (4) ◽  
pp. 247-252 ◽  
Author(s):  
Daniel Straubinger ◽  
István Bozsóki ◽  
Balazs Illes ◽  
Oliver Krammer ◽  
David Bušek ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Vertical Wall ◽  
Initial Pressure ◽  
Vapour Phase ◽  
Circuit Board ◽  
Pressure Measurements ◽  
Transfer Coefficients ◽  
Content Type

Purpose The paper aims to present an investigation on heat transfer in a vapour phase soldering (VPS) oven, focusing on the differences of horizontally and vertically aligned Printed Circuit Board (PCB) surfaces. The investigation can help develop a better understanding of the process and provide information for future modelling of the process. Design/methodology/approach For the investigations, flame retardant grade 4 (FR4) PCB plates and sealed plate–based boxes were immersed into saturated vapour of an experimental oven. The temperature and resulting heat transfer coefficients were analysed according to the sample boxes and the surface orientations. In addition, the boxes’ vapour consumption was investigated with pressure measurements. Findings The horizontal top- and bottom-side heating shows very similar results. In addition, the sides of a box were heated in a manner similar to the top and the bottom sides, but there was a slight increase in the heat transfer coefficient because of the vertical wall alignment. The pressure measurements reveal the dynamic changes in vapour after immersion of the boxes. Practical implications The findings may help to show differences on different surface orientations, pointing to more precise, explicit and multiphysics simulation results. Originality/value The experiments present an aspect of heat transfer coefficient differences in VPS ovens, also highlighting the effect of initial pressure drop inside the workspace of an oven.

scholarly journals Temperature Dependence of the Dynamic Parameters of Contact Thermometers

Sensors ◽  
2019 ◽  
Vol 19 (10) ◽  
pp. 2299 ◽  
Author(s):  
Silke Augustin ◽  
Thomas Fröhlich
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Temperature Dependence ◽  
Dynamic Behavior ◽  
Material Properties ◽  
Convective Heat Transfer Coefficient ◽  
Heat Radiation ◽  
Dynamic Parameters ◽  
Temperature Dependent

Contact thermometers are used in a wide temperature range as well as under various media and environmental conditions. The temperature can range from −200 °C to about 1500 °C. In this case, the dynamic parameters (time percentage values tx and time constants τ) depend on temperature. Several effects are superimposed. Constructional and material properties of the thermometer and the installation location affect the dynamic behavior as well as the type and material properties of the object to be measured. Thermal conductivity λ, specific heat capacity c, and density ρ depend on temperature. This temperature dependence can be mutually compensated for (see Section 3). At the same time, the dynamic behavior is also influenced by the temperature-dependent parameters of the medium. When the thermometers are installed in air, for example, the heat transfer coefficient α decreases with increasing temperature, owing to the temperature-dependent material data of the air, at constant speed v. At the same time, heat radiation effects are so strong that the heat transfer improves despite the decreasing convective heat transfer coefficient. In this paper, a number of examples are used to establish a model for the temperature dependence of the dynamic parameters for various thermometer designs. Both numerically and experimentally determined results for the determination of the dynamic characteristic values are included in the consideration.

Sign in / Sign up

Export Citation Format

Share Document