Analysis of the Applicability of the Hot-Wire Technique for Determination of the Thermal Conductivity of Diathermanous Materials

2009 ◽  
pp. 147-147-7 ◽  
Author(s):  
HA Fine
Keyword(s):  
Thermal Conductivity ◽  
Hot Wire

HOT WIRE METHOD FOR DETERMINATION OF THE THERMAL CONDUCTIVITY OF SUGAR CANE FIBERS

2020 ◽  
Author(s):  
Marcelo Borges dos Santos ◽  
CLAUDIA BITTENCOURT ◽  
Ana Carolina Mendonça Mansur ◽  
Luís Mauro Moura ◽  
Carlos Augusto Castro Ferreira
Keyword(s):  
Thermal Conductivity ◽  
Sugar Cane ◽  
Hot Wire ◽  
Wire Method

scholarly journals Estimation of thermal conductivity of short pastry biscuit at different baking stages

2014 ◽  
Vol 45 (2) ◽  
pp. 64 ◽  
Author(s):  
Chiara Cevoli ◽  
Angelo Fabbri ◽  
Simone Virginio Marai ◽  
Enrico Ferrari ◽  
Adriano Guarnieri
Keyword(s):  
Thermal Conductivity ◽  
Thermal Processing ◽  
Physical Property ◽  
Physical Models ◽  
Hot Wire ◽  
Line Heat Source ◽  
Food Material ◽  
Wire Method ◽  
Thermal Conductivity Probe

Thermal conductivity of a food material is an essential physical property in mathematical modelling and computer simulation of thermal processing. Effective thermal conductivity of non-homogeneous materials, such as food matrices, can be determined experimentally or mathematically. The aim of the following research was to compare the thermal conductivity of short pastry biscuits, at different baking stages (60-160 min), measured by a line heat source thermal conductivity probe and estimated through the use of thermo-physical models. The measures were carried out on whole biscuits and on powdered biscuits compressed into cylindrical cases. Thermal conductivity of the compacted material, at different baking times (and, consequently at different moisture content), was then used to feed parallel, series, Krischer and Maxwell-Eucken models. The results showed that the application of the hot wire method for the determination of thermal conductivity is not fully feasible if applied directly to whole materials due to mechanical changes applied to the structure and the high presence of fats. The method works best if applied to the biscuit component phases separately. The best model is the Krischer one for its adaptability. In this case the value of biscuit thermal conductivity, for high baking time, varies from 0.15 to 0.19 Wm<sup>–1</sup> K<sup>–1</sup>, while the minimum, for low baking time, varies from 0.11 to 0.12 Wm<sup>–1</sup> K<sup>–1</sup>. These values are close to that reported in literature for similar products.

scholarly journals The effect of accommodation on heat conduction through gases

1934 ◽  
Vol 143 (850) ◽  
pp. 517-540 ◽  
Keyword(s):  
Thermal Conductivity ◽  
Solid Surfaces ◽  
True Temperature ◽  
Hot Wire ◽  
Absolute Value ◽  
Temperature Discontinuity ◽  
Double System ◽  
Wire Method ◽  
Gas Molecules

An experimental determination of the thermal conductivity of a gas necessarily involves a number of corrections which must either be determined or eliminated before an absolute value can be obtained. With the " hot-wire " method the inherent errors are: (1) the beat lost by radiation ; (2) the beat losses due to convection; (3) the temperature discontinuity between the gas and solid surfaces ; and (4) the fact that the interchange of energy between the gas molecules and the solid surfaces is not perfect. The true temperature attained by a molecule striking a bot surface always being less than the temperature of that surface. previous investigators using this method have applied a correction for the beat lost by radiation, determined by measuring the beat loss in the best obtainable vacuum ; while the convective beat loss has been eliminated, either by simply reducing the pressure or by using a double system of tubes. Both methods are debatable, for the first is very inaccurate, while the second necessarily complicates the experimental arrangement.

Inverse analysis for the determination of heat transfer coefficient

2013 ◽  
Vol 91 (12) ◽  
pp. 1034-1043 ◽  
Author(s):  
Ali Fguiri ◽  
Naouel Daouas ◽  
M-Sassi Radhouani ◽  
Habib Ben Aissia
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Source Strength ◽  
Hot Wire ◽  
Source Power ◽  
Heating Source ◽  
The Heat Transfer Coefficient

The parallel hot wire technique is considered an effective and accurate means of experimental measurement of thermal conductivity. However, the assumptions of infinite medium and ideal infinitely thin and long heat source lead to some restrictions in the applicability of this technique. To make an effective experiment design, a numerical analysis should be carried out a priori, which requires a precise specification of the heating source strength and the heat transfer coefficient on the external surface. In this work, a more accurate physical and mathematical modeling of an experimental setup based on the parallel hot wire method is considered to estimate the two above-mentioned parameters from noisy temperature histories measured inside the material. Based on a sensitivity analysis, the heating source strength is estimated first using early time measurements. With such estimated value, determination of the heat transfer coefficient using temperatures measured at later times is then considered. The Levenberg–Marquardt (LM) method is successfully applied using a single experiment for the inverse solution of the two present parameter estimation problems. Estimates of this gradient-based deterministic method are validated with a stochastic method (Kalman filter). The effects of the measurement location, the heating duration, the measurement time step, and the LM parameter on the estimates and their associated confidence bounds are investigated. Used in the traditional fitting procedure of the parallel hot wire technique, the estimated heating source power provides a reasonable agreement between fitted and exact values of the thermal conductivity and the thermal diffusivity.

scholarly journals Evaluation of the influence of the degree of saturation, measuring time and use of a conductive paste on the determination of thermal conductivity of normal and lightweight concrete using the hot-wire method

2021 ◽  
Vol 71 (344) ◽  
pp. e260
Author(s):  
D. Revuelta ◽  
J.L. García-Calvo ◽  
P. Carballosa ◽  
F. Pedrosa
Keyword(s):  
Thermal Conductivity ◽  
Lightweight Concrete ◽  
Probe Method ◽  
Degree Of Saturation ◽  
Hot Wire ◽  
Measuring Time ◽  
Needle Probe ◽  
Cement Based Materials ◽  
Wire Method

The determination of thermal conductivity of cement-based materials is relevant from the perspective of buildings’ energy efficiency. The absence of unified tests for its measurement in mortars and concrete results in a heterogeneity of the data available in the literature. This work’s purpose is to determine the relevant influence from a a statistical viewpoint that three factors; degree of saturation, measuring time and use of a conductive paste, have in the measurement of the conductivity using the hot-wire needle probe method in two concretes with different thermal behavior: standard-weight concrete and lightweight concrete. The results obtained allow for the establishment of recommendations for future researchers on the minimum information to be included in their reports of thermal conductivity of cement-based materials by the needle probe method, the need to treat outliers, the most favorable saturation conditions and measuring times, as well as the possible benefits of using conductive pastes.

Study of Thermal Technical Properties of Lightweight Concrete with Utilization of Non Stationary Hot-Wire Method

2013 ◽  
Vol 650 ◽  
pp. 333-339 ◽  
Author(s):  
Jiri Zach ◽  
Michala Hubertova ◽  
Jitka Peterková
Keyword(s):  
Thermal Conductivity ◽  
Thermal Insulation ◽  
Thermal Conductivity Coefficient ◽  
Lightweight Concrete ◽  
Measurement Methods ◽  
Hot Wire ◽  
Volume Weight ◽  
Wire Method ◽  
Stationary Measurement

This paper describes the results of research that was focused on the study of thermal insulation properties and behaviour of lightweight expanded clay aggregate concrete. During the research it was carried out a determination of the thermal conductivity on a series of test samples with different volume weight and different mechanical properties. Determination of the thermal conductivity coefficient at lightweight concrete is quite difficult due to high in homogeneousness of the tested material being result of high open structure. Stationary and non-stationary measurement methods were used to determine the thermal insulation properties, which were reviewed for their relevance to the application.

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