Tag Archives: thermal properties.

1119–1126 P. Neuberger and P. Kic
The use of unsteady method for determination of thermal conductivity of porous construction materials in real conditions
Abstract |
Full text PDF (312 kB)

The use of unsteady method for determination of thermal conductivity of porous construction materials in real conditions

P. Neuberger¹* and P. Kic²

¹ Czech University of Life Sciences Prague, Faculty of Engineering, Department of Mechanical Engineering, Kamýcká 129, CZ165 21 Prague, Czech Republic
² Czech University of Life Sciences Prague, Faculty of Engineering, Department of Technological Equipment of Buildings, Kamýcká 129, CZ165 21 Prague, Czech Republic
*Correspondence: neuberger@tf.czu.cz

Abstract:

The possibility to determine the thermal conductivity of construction materials outside the laboratory conditions is useful for professional practice mainly for control and inspection activities on real existing buildings. The requirement to determine the thermal conductivity can be useful above all for different thermal insulation materials but for other materials as well, even for compact soils or rocks. This paper describes methods and instrument which can be used for these measurements, as well as the results of measurement of porous building materials. Measurements presented in this paper were carried out by the needle and surface sensor. Four different materials were selected for verification of technical parameters of Isomet 2104. Besides the thermal conductivity there were determined also thermal diffusivity and volume-specific heat capacity of materials. The carried out measurements confirmed the applicability of this device for practical measurements of thermal conductivity in real conditions. For porous materials, there were determined significant differences between the data presented by the manufacturer or in the literature and measured values, in some cases. Differences between the measured values of thermal diffusivity and volume-specific heat capacity of porous materials were always statistically significant. Authors tested different materials including thermal insulation based on agricultural products.

Key words:

, , ,




639-653 H. Kallakas, M.A. Shamim, T. Olutubo, T. Poltimäe, T.M. Süld, A. Krumme and J. Kers
Effect of chemical modification of wood flour on the mechanical properties of wood-plastic composites
Abstract |

Effect of chemical modification of wood flour on the mechanical properties of wood-plastic composites

H. Kallakas*, M.A. Shamim, T. Olutubo, T. Poltimäe, T.M. Süld, A. Krumme and J. Kers

Department of Polymer Materials, Tallinn University of Technology, Ehitajate tee 5, EE19086 Tallinn, Estonia;
*Correspondence: heikko.kallakas@ttu.ee

Abstract:

The poor compatibility between the highly hydrophilic wood fibres and the hydrophobic polymers is associated with a loss of mechanical properties. Therefore, to improve the interfacial adhesion between the polymer matrix and wood flour (WF), a chemical modification of WF is an appropriate solution. This study analyzes the influence of different chemical modifications of WF on the mechanical properties of wood-plastic composites (WPCs). WPC test samples were prepared from birch (Betula) WF with a mesh size of 0.⁶³ mm as the filler material and polypropylene (PP) as the matrix material. WF was chemically modified by six different methods to increase its adhesion to, and compatibility with, the polymer matrix. The six chemical methods used were: alkaline (NaOH) modification, polyvinyl alcohol (PVA) modification, silane treatment with ³-aminopropyltriethoxysilane (APTES), acetylation with acetic anhydride, cyanoethylation, and wood fibre esterification. The composites were produced using a twin-screw extruder and the test samples were prepared by injection moulding. The composites’ mechanical properties (three-point bending test), Charpy impact strength and thermal properties were tested. In addition, SEM micrographs of WPC surfaces were generated. WF as a filler material enhanced the flexural properties, while impact strength decreased, making the material more rigid and brittle. The test results revealed that the chemical modifications of WF improved the mechanical properties and crystallinity of WPC materials, while the melting temperature decreased. However, the influence of the chemical modification on the mechanical and thermal properties of WPC varied by method.

Key words:

, , , ,




769-779 L. Brazdeikis
Thermal properties and temperature regime of champignon cultivation substrate
Abstract |
Full text PDF (818 kB)

Thermal properties and temperature regime of champignon cultivation substrate

L. Brazdeikis

Institute of Agricultural Engineering Lithuanian University of Agriculture, Raudondvaris, LT-54132 Kaunas reg., Lithuania;
e-mail: autlab@mei.lt

Abstract:

In designing and analysing the systems of automatic regulation of substrate
temperature for champignon cultivation it is necessary to know substrate thermal properties
(thermal conductivity and specific heat), intensity of substrate self-heating and the distribution
of overtemperature caused by self-heating within a substrate briquette. It is proposed to estimate
substrate thermal properties by the nonsteady method of combined determination of thermal
characteristics using a flat constant power heat source. The scheme of experiments,
mathematical expressions for calculating thermal indicators, examples of temperature variation,
examples of thermal indicators calculations and the established mean thermal indicators for
champignon cultivation substrate are presented.
An electrical analogy model of thermal process in substrate briquette was made for selfheating
investigations. It was established by modelling that the distribution of overtemperature
caused by self-heating within the thickness of a briquette is parabolic. The mean specific heat of
substrate self-heating was established by comparison of modelling and experiments results. An
equation to assess the overtemperature of substrate briquette centre in engineering calculations
is presented. 

Key words:

, , ,