Thermal conductivity measurements with different methods: a procedure for the estimation of the retardation time

Abstract

Abstract:As it is known that nowadays, reduction of the heating energy loss of buildings is achieved mainly by thermal insulation. This is one of the most important objectives of buildings constructions and retrofitting of buildings. Therefore research, calculation and simulation on the energy efficiency of buildings are of great importance. In this paper we give an expansive presentation about the measurements of the thermal conductivity, heat flux and thermal resistance of individual insulation materials as well as in-built wall constructions executed in our laboratory. Thermal diffusion coefficients and wall delaying ability of the systems will be given resulting from the measurements. First of all, thermal conductivity measurement results of individual insulation materials achieved by a Holometrix type Heat flow Meter (HFM) will be presented. Afterwards, two different steady-state methods for measuring thermal resistance of wall structures (Calibration hot box method (CC) and Heat Flux measurements by Hukseflux (HF) apparatus) will be introduced. These measurements were accomplished through either an inbuilt plaster/brick/plaster wall construction insulated internally at the first time and later externally with different materials. The main target of this paper is the presented theoretical procedure for the estimation of the retardation time of wall structures. Furthermore in this publication the determination of thermal performance of Expanded Polystyrene Insulation (EPS) applied to walls in building constructions can also be found. Moreover numerical predictions for thermal resistance are presented. Besides, infrared thermographs were used to visualise the insulation ability of the layer structures.2

Thermophysical investigations of nanotechnological insulation materials

“…(10) and (11) are well known equations for the diffusion profiles in nanodiffusion and it was presented earlier that they can be applied with good approximations for thermal diffusions [15].…”

“…It follows then that flux can be described as "the rate per unit area at which mass moves. [15] Numerical calculations were done to predict the thermal diffusivity of the materials and the time lag. If we represent the Onsager equation as Eq.…”

“…Representing the 2nd law of Fick in one dimension and assuming that there are no sources and D A is constant, the following equation can be reached: where t is the time [15].…”

“…In our previous papers [13,15,19,21] the measurements of the thermal conductivities of the aerogel insulations with 1.3 cm and vacuum hollow spheres contaminated insulation paint with 2 mm thickness applied on a brick based wall with hot box method, moreover their measurements with Holometrix Lambda 2000 apparatus were presented also. The measurement order and details can be found clearly in Ref [13,15,19,20].…”

“…Vacuum contaminated nano-ceramic thermal insulation (VCHNS) is sad to be to the most promising thermal insulations. In this article measurements will be presented in order to show the good thermal properties of these materials [14][15][16][17][18]. In Fig.…”