scholarly journals Heat flow in a right circular cylinder with arbitrary temperature boundary conditions - applications to the determination of thermal conductivity

1964 ◽  
Vol 68C (4) ◽  
pp. 215
Author(s):  
D.R. Flynn
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Circular Cylinder ◽  
Boundary Conditions ◽  
Arbitrary Temperature ◽  
Temperature Boundary

Measurement of the thermal conductivity of thin layers using a scanning thermal microscope

2001 ◽  
Vol 16 (9) ◽  
pp. 2530-2543 ◽  
Author(s):  
Erwin R. Meinders
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Thermal Structure ◽  
Thin Layers ◽  
Heat Diffusion ◽  
Sputter Deposited ◽  
Relative Differences ◽  
Conductivity Of Thin Films ◽  
Change Material

A scanning thermal microscope (SThM) was used to measure the thermal conductivity of thin sputter-deposited films in the thickness range of 10 nm–10 μm. The SThM method is based on a heated tip that is scanned across the surface of a sample. The heat flowing into the sample is correlated to the local thermal conductivity of the sample. Issues like the contact force, the surface roughness of the sample, and tip degradation, which determine to a great extent the contact area between tip and surface, and thus the heat flow to the sample, are addressed in the paper. A calibration curve was measured from known reference materials to quantify the sample heat flow. This calibration was used to determine the effective thermal conductivity of samples. Further, the heat diffusion through a layered sample due to a surface heat source was analyzed with an analytical and numerical model. Measurements were performed with films of aluminum, ZnS–SiO2, and GeSbTe phase change material of variable thickness and sputter-deposited on substrates of glass, silicon, or polycarbonate. It is shown in the paper that the SThM is a suitable tool to visualize relative differences in thermal structure of nanometer resolution. Determination of the thermal conductivity of thin layers is possible for layers in the micrometer range. It is concluded that the SThM is not sensitive enough to measure accurately the thermal conductivity of thin films in the nanometer range. Suggestions for improvement of the SThM method are given.

The Thermal Transport Properties of Polymers

1977 ◽  
Vol 50 (3) ◽  
pp. 480-522 ◽  
Author(s):  
D. Hands
Keyword(s):  
Thermal Conductivity ◽  
Thermal Diffusivity ◽  
Heat Flow ◽  
Natural Rubber ◽  
Material Selection ◽  
Reliable Data ◽  
Large Scatter ◽  
Structure Property ◽  
Structure Property Relationships

Abstract Values of thermal diffusivity and thermal conductivity are needed for heat-flow calculations, for the determination of structure-property relationships, and for material selection and comparison. However, all aspects are hampered by a dearth of reliable data and anything more than a superficial glance at the literature is apt to be discouraging for the uninitiated. Hardly any thermal diffusivity data exist, and the reported values of thermal conductivity show very large scatter. The present state of confusion can be seen, for example, in Figures 1 and 2, which show the reported thermal conductivity values for polystyrene and gum natural rubber. Not only do the values differ at some temperatures by more than 100%, and in the case of rubber by almost 300%, but different trends are indicated throughout the temperature range. Discrepancies of this size cannot be due to sample variations, and they give some indication of the experimental difficulties associated with thermal property measurements.

scholarly journals Mathematical apparatus for determination of homogenous scalar medium thermal resistance

Vestnik MGSU ◽  
2019 ◽  
pp. 1037-1045
Author(s):  
Tatiana A. Musorina, ◽  
Michail R. Petritchenko ◽  
Daria D. Zaborova
Keyword(s):  
Thermal Conductivity ◽  
Heat Flow ◽  
Thermal Resistance ◽  
Heat Conducting ◽  
Heat Flow Rate ◽  
Conductivity Equation ◽  
Total Thermal Resistance ◽  
Active Resistance ◽  
One Dimensional

Introduction: the article suggests a method for determining a thermal resistance of small and large-sized areas (one-dimensional and multidimensional problems) of wall enclosure. The subject of the study is the thermal resistance of homogeneous scalar medium (homogeneous wall enclosure). The aim is the determination of thermal resistance of a wall structure for areas of arbitrary dimension (by the coordinates xi, where 1 ≤ i ≤ d and d is the area dimension) filled with a scalar (homogeneous and isotropic) heat-conducting medium. Materials and methods: the article used the following physical laws: Fourier law (the value of the heat flow when transferring heat through thermal conductivity) and continuity condition for the heat flow rate leading to the thermal conductivity equation. Results: this method extends the standard definition of thermal resistance. The research proved that the active thermal resistance does not increase with increasing of the area dimension (for example, when switching from a thin shell or plate to a rectangle with length and width of the same order of magnitude). That is the sense of geometric inclusion, i.e., increase of the dimension of an area filled with a homogeneous isotropic medium. Evident expressions are obtained for the determination of active, reactive, and total thermal resistance. It is proved that the total resistance is higher than the active resistance since the reactive resistance is positive, and the wall possesses an ability to suppress the temperature fluctuations and accumulate/give up the heat. Conclusions: the appearance of an additional wall dimension (comparable length-to-thickness ratio) does not increase its active resistance. In the general case, the total thermal resistance exceeds the active thermal resistance no more than four times. Geometric inclusions must be considered in the calculation of wall enclosures that are variant from one-dimensional bodies.

scholarly journals Reverse Task of Heat Conductivity for the Semilimited Bar

2019 ◽  
pp. 27-31
Author(s):  
O. Shevchenko
Keyword(s):  
Thermal Conductivity ◽  
Inverse Problem ◽  
Heat Exchange ◽  
Boundary Conditions ◽  
Heat Conductivity ◽  
Algebraic Equations ◽  
Newton's Law ◽  
Newton’S Law ◽  
Solid Bodies

The article concerns methods and formulas for the calculation of the coefficient of thermal conductivity of solid bodies using the known solutions of direct thermal conductivity tasks. The solution to the inverse problem of heat conductivity is based on the quite complicated methods including both hyperbolic functions and finite-difference methods. Under certain experimental conditions, the task is simplified at the regular thermal modes of 1, 2, or 3 types. Thus final formulas are simplified to algebraic equations. The simplification of the inverse problem of heat conductivity to algebraic equations is possible using other approaches. These me­thods are based on the analysis of the reference points, zero values of temperature distribution function, function inflection points, and its first and second derivatives. Here, we present formulas for the calculations of the temperature field on the assumption of the direct task solution for the half-bounded bar under the pulsed heating followed the re-definition of the boundary conditions. The article describes two methods in which solutions are reduced to simple algebraic formulas when using the specified points on hea­ting thermograms of test examples. These solutions allow algebraic deriving of simple relations for inverse problems of determination of thermophysical characteristics of solid bodies. The calculation formulas are given for the determination of the heat conductivity coefficient determination by two methods: by value of temperature, coordinate, and two moments at which this temperature is reached. The second method uses the values of two coordinates of the test sample in two different points where the equal temperature is reached at different points in time. The final solution of the equation is logarithmic. The analysis of known methods and techniques shows that experimental methods are oriented on the technical implementation and based on facilities of available equipment and instruments. Existing experimental techniques are based on specific constructions of measuring facilities. Simultaneously, there are well-studied methods of solution of thermal conductivity standard tasks set out in fundamental issues. The theoretical methods come from axioms, equations, and theoretical postulates, and they give the solution of inverse tasks of thermal conductivity. This work uses the solutions of direct tasks presented in the monograph by A.V.Lykov “The theory of heat conductivity”. These solutions have a good theoretical background and experts’ credit. The boundary conditions of the problem are next: the half-bounded thin bar is given. The side surface of the bar has a thermal insulation. At the initial moment, the instant heat source acts on the bar in its section at some distance from its end. Heat exchange occurs between the environment and the end of the bar according to Newton’s law. The initial (relative) temperature of the bar is accepted equal to zero. The heat exchange between the free end face of the bar and the environment is gone according to Newton’s law.

Heat Flow Calorimetry

2008 ◽  
Author(s):  
José A. Martinho Simões ◽  
Manuel Minas da Piedade
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Flux ◽  
Heat Flow ◽  
Heat Sink ◽  
Reaction Vessel ◽  
Heat Output ◽  
Large Numbers ◽  
Different Temperatures

Heat flow calorimeters, also known as “heat flux,” “heat conduction,” or “heat leakage” calorimeters, are instruments where the heat output or input associated with a given phenomenon is transferred between a reaction vessel and a heat sink. This heat transfer can be monitored with high thermal conductivity thermopiles containing large numbers of identical thermocouple junctions regularly arranged around the reaction vessel (the cell) and connecting its outside wall to the heat sink (the thermostat). The determination of the heat flow relies on the so-called Seebeck effect. An electric potential, known as thermoelectric force and represented by E, is observed when two wires of different metals are joined at both ends and these junctions are subjected to different temperatures, T1 and T2. Several thermocouples can be associated, forming a thermopile. For small temperature differences, the thermoelectric force generated by the thermopile is proportional to T1 − T2 and to the number of thermocouples of the pile (n): E = nε ′ (T1 − T2) (9.1) where ε′ is the thermoelectric power of a single thermocouple (ε′ = dE/dT).

Sign in / Sign up

Export Citation Format

Share Document