Transient Response of a Steady Vertical Flow which is Subjected to a Change in Surface Heat Flux in Porous Media

1996 ◽  
Author(s):  
Simon D. Harris ◽  
Derek B. Ingham ◽  
Ioan Pop
Keyword(s):  
Heat Flux ◽  
Porous Media ◽  
Transient Response ◽  
Surface Heat Flux ◽  
Surface Heat ◽  
Vertical Flow

scholarly journals New analytical solution for natural convection of Darcian fluid in porous media prescribed surface heat flux

2011 ◽  
Vol 15 (suppl. 2) ◽  
pp. 221-227 ◽  
Author(s):  
Domiry Ganji ◽  
Hasan Sajjadi
Keyword(s):  
Heat Flux ◽  
Porous Media ◽  
Differential Equations ◽  
Iteration Method ◽  
Surface Heat Flux ◽  
Nonlinear Differential Equations ◽  
Variational Iteration Method ◽  
Surface Heat ◽  
Variational Iteration ◽  
He’S Variational Iteration Method

A new analytical method called He's Variational Iteration Method is introduced to be applied to solve nonlinear equations. In this method, general Lagrange multipliers are introduced to construct correction functional for the problems. It is strongly and simply capable of solving a large class of linear or nonlinear differential equations without the tangible restriction of sensitivity to the degree of the nonlinear term and also is very user friend because it reduces the size of calculations besides; its iterations are direct and straightforward. In this paper the powerful method called Variational Iteration Method is used to obtain the solution for a nonlinear Ordinary Differential Equations that often appear in boundary layers problems arising in heat and mass transfer which these kinds of the equations contain infinity boundary condition. The boundary layer approximations of fluid flow and heat transfer of vertical full cone embedded in porous media give us the similarity solution for full cone subjected to surface heat flux boundary conditions. The obtained Variational Iteration Method solution in comparison with the numerical ones represents a remarkable accuracy.

Transient Response Characteristics of a Surface Junction Probe

2019 ◽  
Author(s):  
Anil Kumar Rout ◽  
Niranjan Sahoo ◽  
Pankaj Kalita ◽  
Vinayak Kulkarni
Keyword(s):  
Heat Flux ◽  
Transient Response ◽  
Time Scale ◽  
Surface Heat Flux ◽  
Scale Up ◽  
Surface Heat ◽  
Temperature History ◽  
Transient Temperature ◽  
Time Data ◽  
Response Characteristics

Abstract The present work highlights the transient response phenomena captured by a coaxial surface junction thermocouple (CSJT) and subsequent use of the thermal probe for prediction of surface heat flux. To accomplish the objective, an E-type CSJT has been fabricated in-house in a laboratory scale from its thermo-elements with constantan (0.91mm diameter and 15mm length) serving as the inner element and chromel as outer element (3.25mm diameter and 10mm length). Both the thermo-elements are clubbed together coaxially which are separated by a thin layer of insulation in between them along the length. The junction between the thermo-elements is created at the surface through abrasion technique which forms a firm contact through formation of cold weld. The junction feature is then examined through a field emission scanning electron microscope (FESEM). The sensitivity of the probe is found experimentally to be 59 μV/°C. The transient response characteristics are observed through water plunging and water droplet tests at 55°C for 20ms and 2s time scale. The voltage time data is recorded and with the help of sensitivity value, the temperature history is calculated. The temperature histories from plunging and droplet experiments are used for calculation of heat flux by analytically modeling the sensor as semi-infinite substrate and assuming heat conduction through it is one dimensional. The heat flux is also calculated from the same temperature history by using numerical analysis and compared with the previous one. The measured data provides substantial evidence for usage of these CSJT probes in transient temperature and surface heat flux recoveries within experimental time scale up to 2s with reasonable accuracy.

Analysis of significant measures for thermal conductivity

2020 ◽  
pp. 35-42
Author(s):  
Yuri P. Zarichnyak ◽  
Vyacheslav P. Khodunkov
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Surface Heat Flux ◽  
Heat Flux Density ◽  
Measurement Method ◽  
Conductivity Measurement ◽  
Surface Heat ◽  
Measuring Instrument ◽  
New Class ◽  
Achievable Accuracy

The analysis of a new class of measuring instrument for heat quantities based on the use of multi-valued measures of heat conductivity of solids. For example, measuring thermal conductivity of solids shown the fallacy of the proposed approach and the illegality of the use of the principle of ambiguity to intensive thermal quantities. As a proof of the error of the approach, the relations for the thermal conductivities of the component elements of a heat pump that implements a multi-valued measure of thermal conductivity are given, and the limiting cases are considered. In two ways, it is established that the thermal conductivity of the specified measure does not depend on the value of the supplied heat flow. It is shown that the declared accuracy of the thermal conductivity measurement method does not correspond to the actual achievable accuracy values and the standard for the unit of surface heat flux density GET 172-2016. The estimation of the currently achievable accuracy of measuring the thermal conductivity of solids is given. The directions of further research and possible solutions to the problem are given.

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