Design of a Calibration System for Heat Flux Meters

Abstract

Accurate heat flux measurements are needed to gain a better knowledge of the thermal performance of buildings and to evaluate the heat exchange among various parts of a building envelope. Heat flux meters (HFMs) are commonly used both in laboratory applications and in situ for measuring one-dimensional heat fluxes and, thus, estimating the thermal transmittance of material samples and existing buildings components. Building applications often requires heat flux measurements below 100 W center dot m(-2). However, a standard reference system generating such a low heat flux is available only in a few national metrology institutes (NMIs). In this work, a numerical study aimed at designing an HFM calibration apparatus operating in the heat flux range from 5 W center dot m(-2) to 100 W center dot m(-2) is presented. Predictions about the metrological performance of such a calibration system were estimated by numerical modeling exploiting a commercial FEM code (COMSOL(A (R))). On the basis of the modeling results, an engineered design of such an apparatus was developed and discussed in detail. The system was designed for two different purposes: (i) for measuring the thermal conductivity of insulators and (ii) for calibrating an HFM with an absolute method (i.e., by measuring the applied power from the heater and its active cross section) or by a relative method (i.e., by measuring the temperature drop across a reference material of known thickness and thermal conductivity). The numerical investigations show that in order to minimize the uncertainty of the generated heat flux, a fine temperature control on the thermal guard is needed. The predicted standard uncertainty is within 2% at 10W center dot m(-2) and within 0.5% at 100 W center dot m(-2)

Experimental and numerical analysis in heat flow sensors calibration

“…Liu [21] performed numerical simulations with turbulence methods to study the effect of unsteady thermal boundary conditions on the temporal behaviour of heat transfer coefficient on a flat plate. Some authors of the present paper, designed a standard system for HFM calibration [22]. The results were affected by a high heat flux distortion and showed that in order to minimize the uncertainty of the generated heat flux, a very fine temperature control on the side thermal guard was needed.…”

“…The computational domain and the boundary conditions employed are available in Figure 3. The temperature fields are obtained by solving the well-known energy conservation equations [22][23][24], not reported here for brevity. In order to accurately reproduce experiments, three generation terms are applied in correspondence of the main and guard heaters indicated in yellow in Figure 1.…”

7.2 - Kalibriereinrichtung für Wärmestromsensoren

“…Es gibt verschiedene Verfahren zum Kalibrieren von WSS, deren Aufbau der Gradienten Methode entspricht. Ein weit verbreitetes Verfahren ist die Guarded Hot Plate (GHP) Methode [10], bei der ein definierter Wärmeeintrag in Form von elektrischer Leistung in den WSS eingeprägt wird. Eine weitere Möglichkeit ist der Vergleich des Sensors gegen einen Referenzsensor [11] oder Referenzmaterial [12], dies ist in verschiedensten Variationen möglich.…”

A novel calibration system for heat flow meters: Experimental and numerical analysis

“…The proposed standard for HFM calibration relies on the GHP method. It was discussed in a previous work by one of the authors [28] who presented its design together with a preliminary CFD analysis in a heat flux range between 10 W/m 2 and 100 W/m 2 . The design of the apparatus was flexible enough to be used for different applications, such as: i) the measurement of the thermal conductivity of insulating materials by generating a known heat flux and measuring the temperature difference across the thickness of the material under test; ii) the HFM calibration by an absolute method (i.e., by measuring the power generated by the main heater once the surface of the measuring section is known) or by a relative method (i.e., by measuring the temperature difference across a certified reference material with known thermal conductivity).…”

“…On the basis of the analysis results in [28], the authors developed a novel setup for the HFM prototype, with the objective of improving its potential applications and metrological performances.…”