scholarly journals Thermal Step Response of N-Layer Composite Walls—Accurate Approximative Formulas

2020 ◽  
Vol 142 (3) ◽  
Author(s):  
Carl-Eric Hagentoft ◽  
Simon Pallin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Flow ◽  
Numerical Solutions ◽  
Step Change ◽  
Step Response ◽  
Surface Boundary ◽  
Multilayer Composites ◽  
Flow Through ◽  
Multiple Variables

Abstract For many industrial applications, heat flow through composites relates directly to energy usage and thus is of highest interest. For multilayer composites, the heat flow is a result of multiple variables, such as the temperature gradient over the surface boundaries and each material's thermal conductivity, specific heat, and thickness. In addition, the transient heat flux also depends on how the materials are aligned together. The heat flow through composites can be estimated using advanced computer simulations for applied heat transfer. Although these tools are powerful, they are also time consuming. Therefore, approximations that allow the estimation of heat flow through composites can be very useful. This paper presents approximations to solve transient heat transfer in multilayer composites, with and without an interior surface resistance. Since the energy use for various applications relates to the heat transferred at the surface boundary, the main focus of this paper is to define approximate solutions for interior heat flow. In other words, these approximations are found by applying a unit step change in temperature on one side of a composite and then in real-time emulating the surface heat flux on the opposite side from which the step change occurs. The approximations are presented based on lumped analyses and Laplace network solutions and are validated against analytical and numerical solutions.

Measurement of Thermal Conduction Through Polymeric Nanowires With the Dual Cantilever Technique

2014 ◽  
Author(s):  
Carlo Canetta ◽  
Arvind Narayanaswamy
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Flow ◽  
Thermal Conduction ◽  
Thermal Conductance ◽  
High Sensitivity ◽  
Conductance Measurement ◽  
Electrospinning Technique ◽  
Flow Through ◽  
Thermal Stimuli

Bi–material microcantilevers, with their high sensitivity to thermal stimuli, are ideally suited sensors for investigating nanoscale heat transfer. We have designed and fabricated low thermal conductance bi–material microcantilevers by minimizing their width and thickness. Using such cantilevers, we have demonstrated heat flux resolution of less than 1 picowatt. A pair of such cantilevers is proposed as a configuration for measuring thermal conductance of a nanostructure suspended between the two. In this technique, two lasers are focused, one on each cantilever. One laser is modulated to vary the temperature at the end of one cantilever, while the second laser senses variation in heat flow through the second cantilever due to thermal conduction along the nanowire. We have determined the resolution of such a conductance measurement by measuring the background conductance between the two cantilevers in the absence of a nanostructure suspended between them. The background conductance is due to other pathways for heat transfer between the cantilevers besides nanostructure conductance. We have measured the background conductance to be as low as 0.05 nWK−1. We present measurements of thermal conductance of polystyrene nanowires performed using the dual cantilever technique. The nanowires are fabricated via electrospinning technique with diameters varying in the range of 150–300 nm. While the polystyrene nanowires present a demonstration of the cantilever technique for measuring thermal conductance, the technique we have developed can be extended to other types of nanostructures so long as they can be suspended between two cantilever ends.

Heat Flux Sensor With Minimal Impact on Boundary Conditions

2003 ◽  
Author(s):  
Arash Saidi ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Heat Flux Sensor ◽  
Inverse Heat Conduction ◽  
Minimal Impact ◽  
Sensor Performance ◽  
Flow Through ◽  
Flux Sensor ◽  
The Ideal

A technique for determining the heat transfer on the far surface of a wall based on measuring the heat transfer and temperature on the near wall is presented. Although heat transfer measurements have previously been used to augment temperature measurements in inverse heat conduction methods, the sensors used alter the heat flow through the surface, disturbing the very quantity that is desired to be measured. The ideal sensor would not alter the boundary condition that would exist were the sensor not present. The innovation of this technique in that it has minimal impact on the wall boundary condition. Since the sensor is placed on the surface of the wall, no alteration of the wall is needed. The theoretical basis for the experimental technique as well as experimental results showing the heat flux sensor performance is presented.

scholarly journals A study of sensing heat flow through thermal walls by using thermoelectric module

2015 ◽  
Vol 19 (5) ◽  
pp. 1497-1505 ◽  
Author(s):  
Noppawit Sippawit ◽  
Thananchai Leephakpreeda
Keyword(s):  
Heat Transfer ◽  
Heat Flow ◽  
Thermoelectric Module ◽  
Plane Wall ◽  
Thermal Engineering ◽  
Transfer Coefficients ◽  
Thermoelectric Effects ◽  
Flow Through ◽  
Flow Detection ◽  
Engineering Practices

Demands on heat flow detection at a plane wall via a thermoelectric module have drawn researchers? attention to quantitative understanding in order to properly implement the thermoelectric module in thermal engineering practices. Basic mathematical models of both heat transfer through a plane wall and thermoelectric effects are numerically solved to represent genuine behaviors of heat flow detection by mounting a thermoelectric module at a plane wall. The heat transfer through the plane wall is expected to be detected. It is intriguing from simulation results that the heat rejected at the plane wall is identical to the heat absorbed by the thermoelectric module when the area of the plane wall is the same as that of the thermoelectric module. Furthermore, both the area sizes of the plane walls and the convective heat transfer coefficients at the wall influence amount of the heat absorbed by the thermoelectric module. Those observational data are modeled for development of sensing heat flow through a plane wall by a thermoelectric module in practical uses.

The Reynolds Analogy Applied to a Cylinder Rotating in Air

1954 ◽  
Vol 58 (519) ◽  
pp. 205-208 ◽  
Author(s):  
Y. R. Mayhew
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Heat Flow ◽  
Solid Surface ◽  
Fluid Flows ◽  
Flat Plates ◽  
Reynolds Analogy ◽  
Transfer Data ◽  
Turbulent Fluid ◽  
Flow Through

When a turbulent fluid flows past a solid surface whose temperature differs from that of the fluid, the shear stress at the surface and the heat flow from it can be related by means of the Reynolds analogy. This analogy has been improved by Prandtl, Taylor, von Kármán and others, and its validity has been tested for flow through tubes and past flat plates by several investigators. In this note the analogy is checked against shear stress data and heat transfer data for a cylinder rotating in “still” air, when the flow is turbulent.

Modeling Transient Heat Transfer Through the Skin and Superficial Tissues—1: Surface Insulation

1986 ◽  
Vol 108 (2) ◽  
pp. 183-188 ◽  
Author(s):  
D. A. Hodson ◽  
G. Eason ◽  
J. C. Barbenel
Keyword(s):  
Heat Transfer ◽  
Blood Flow ◽  
Analytical Solutions ◽  
Numerical Solutions ◽  
Transient Heat Transfer ◽  
Transient Problem ◽  
Finite Slab ◽  
Infinite Slab ◽  
Flow Through ◽  
Superficial Tissues

Two models of transient heat transfer through the skin and superficial tissues are presented. One model comprises a finite slab and semi-infinite slab, representing the epidermis and subdermal tissues, respectively, and a heat-generating interface representing the thermal effect of blood flow through the dermis. A model is also considered where the three tissue regions are represented more conventionally by three finite slabs. A transient problem arising from surface insulation is examined and analytical solutions derived from the first model are compared with numerical solutions derived from the second.

Conjugate heat transfer analysis for laminar flow in pipes having a step change in boundary conditions and wall conductivity

2007 ◽  
Vol 221 (8) ◽  
pp. 919-925 ◽  
Author(s):  
M E Arici ◽  
M E Kaya
Keyword(s):  
Heat Transfer ◽  
Laminar Flow ◽  
Solid Wall ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Step Change ◽  
Heat Transfer Analysis ◽  
Heated Wall ◽  
Surface Boundary ◽  
Wall Conductivity

The current procedure is to examine the effects of wall axial conduction on heat transfer for laminar flow in pipes. The procedure combines the analytical solution of the problem of the fluid region with a numerical approximation of conduction of the solid wall and has the capability of handling the step change in outer surface boundary condition and wall thermal conductivity. The pipe under investigation is divided into two sections: non-heated and heated ones, and the conductivities of the sections are assumed to be different. The obtained results show that the local heat transfer parameters such as wall and fluid temperatures, and Nusselt number are greatly influenced by the step change in wall conductivity and the partially heated wall arrangement. The results of the present study may have applications in the design of heat transfer devices.

Thin Disk On A Convectively Cooled Plate—Application To Heat Flux Measurement Errors

1979 ◽  
Vol 101 (2) ◽  
pp. 346-352 ◽  
Author(s):  
D. A. Wesley
Keyword(s):  
Heat Flux ◽  
Heat Flow ◽  
Measurement Errors ◽  
Heat Conduction Problem ◽  
Flux Measurement ◽  
Thin Disk ◽  
Plate Temperature ◽  
One Dimensional ◽  
Solid Plate ◽  
Flow Through

An analysis is made of the steady-state thermal processes associated with a thin disk affixed to a convectively cooled solid plate. The disk represents a thermopile heat flux gauge. In the first part of the paper, the heat conduction problem of the plate is solved for the simplified condition where the heat flow through the disk is axially one-dimensional. It was found that the local divergence of the heat flux field within the plate owing to the presence of the disk may result in a gauge reading that underestimates the heat transfer rate. Also, a sizeable local plate temperature augmentation can occur. Furthermore, the analysis yields dimensional estimates of the region where the temperature and heat flux fields within the plate are significantly altered by the presence of the disk. An adjunct to the foregoing analysis develops a one-dimensional conduction factor which is useful in determining when the heat flow through the disk can be considered to be axially one-dimensional.

Performance Indicators for Steady-State Heat Transfer Through Fin Assemblies

1996 ◽  
Vol 118 (2) ◽  
pp. 310-316 ◽  
Author(s):  
A. S. Wood ◽  
G. E. Tupholme ◽  
M. I. H. Bhatti ◽  
P. J. Heggs
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Heat Flow ◽  
Performance Indicators ◽  
Physical Parameters ◽  
State Heat ◽  
Extended Surface ◽  
Flow Through ◽  
Steady State Heat ◽  
Steady State Heat Transfer

A comparative study is presented of several models describing steady-state heat flow through an assembly consisting of a primary surface (wall) and attached extended surface (fin). Attention is focused on the validity of four performance indicators. The work shows that the augmentation factor is the only indicator capable of correctly predicting the behavioral trends of the rate of heat flow through the assembly as the influencing physical parameters are varied.

scholarly journals ANALYTICAL STUDY FOR THE BOUNDARY LAYER FLOW IN THE PRESENCE OF HEAT TRANSFER THROUGH A POROUS MEDIUM

2021 ◽  
Vol 8 (65) ◽  
pp. 15142-15146
Author(s):  
Ram Naresh Singh
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Porous Medium ◽  
Boundary Layer Flow ◽  
Numerical Solutions ◽  
Finite Difference Schemes ◽  
Local Similarity ◽  
High Porosity ◽  
Flow Through ◽  
Layer Flow

In this paper we study a problem of the boundary layer flow through a porous media in the presence of heat transfer. Here we consider high porosity bounded by a semi-infinite horizontal plate. The main aim of this study is to point out local similarity transformations for the boundary layer flow, through a homogeneous porous medium. Here we applying finite difference schemes to find out the numerical solutions of the problem. The free stream velocity and the temperature far away from the plate are exponential function of variables.

scholarly journals Groundwater flow equation, overview, derivation, and solution

2021 ◽  
Vol 314 ◽  
pp. 04007
Author(s):  
Lhoussaine El Mezouary ◽  
Bouabid El Mansouri
Keyword(s):  
Heat Transfer ◽  
Differential Equation ◽  
Groundwater Flow ◽  
Numerical Solutions ◽  
Flow Equation ◽  
Heat Transfer Equation ◽  
Flow Equations ◽  
Basic Law ◽  
Flow Through ◽  
Groundwater Flow Equation

Darcy’s law is the basic law of flow, and it produces a partial differential equation is similar to the heat transfer equation when coupled with an equation of continuity that explains the conservation of fluid mass during flow through a porous media. This article, titled the groundwater flow equation, covers the derivation of the groundwater flow equations in both the steady and transient states. We look at some of the most common approaches and methods for developing analytical or numerical solutions. The flaws and limits of these solutions in reproducing the behavior of water flow on the aquifer are also discussed in the article.

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