Heat flow meter

A semi-automatic heat meter apparatus was described by Howard et al35 and a guarded heat flow meter by Foreman36. Calibration of heat flow meter apparatus has been discussed by Lackey et al37 and Scott and Bell38. 

ISO 8301, 1991. Thermal insulation - Determination of steady state thermal resistance and related properties - Heat flow meter apparatus. 

BS EN 12664, 2001. Thermal performance of building materials and products. Determination of thermal resistance by means of a guarded hot plate and heat flow meter methods. Dry and moist products of medium and low thermal resistance,... 

ASTM C518, 2004. Standard test method for steady state thermal transmission properties by means of the heat flow meter apparatus. 

To eliminate the effects of external temperature fluctuations in the calorimetric block, the calorimeter has two heat-flow meters, which are connected in opposition. The process under investigation is carried out in one of two identical calorimeter vessels, the other serving as the tare or reference element. This differential arrangement permits the compensation of parasitic phenomena such as external connections and reagent introduction heat, and it provides a good stability of the baseline. (From the development in Section II,A on thermodynamics it follows that for adsorption of gas in a Calvet calorimeter the heat measured corresponds to a differential molar enthalpy of adsorption because all other effects are compensated.)... 

Usually the power generated in the cell is not constant, and then the experimental cell and the heat flow meter can be respectively represented by a heat capacity, M, and a conductivity, C, connecting the vessel to the calorimetric... 

ASTM C 518-85 Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus, 17 pp (Comm C16)... 

ISO 2581-75 Rigid Cellular Plastics — Determination of Apparent Thermal Conductivity by Means of a Heat-Flow Meter, 7 pp... 

As no universal heat flow meter exists, it is necessary to make differential measurements by measuring the heat flow between the sample and an inert reference. The magnitude of the heat flow will be governed by the thermal resistance of the system, and the difference in temperature between the sample and reference... 

Cookson, R. A., Dunham, P G., and Kilham, J. K. "Stagnation Point Heat Flow Meter." Journal of Scientific Instruments 42 (1965) 260-62. 

Method 7B describes a heat flow meter method for the determination of the apparent" thermal conductivity. This is a much faster method of determining this property and is the usual method employed. It uses a heat flow meter as for example described in BS 874, 1973. Appendix C. An international standard. ISO 8301, 1991 [39]c. ists that defines the use of heat flow meters and the calculation of the heat transfer properties of specimens. The... 

Heat loss is a function of sample thickness, hot and cold face temperatures, and ambient temperature. These factors must be taken into account by making calibration measurements over a range of thicknesses and temperatures. If the losses are known to say 10%, and only represent 10% of the heat input, the error in the calculated conductivity is only I o. A further refinement is to use heat How meters on one or both sides of the sample [1.1 15]. Calibration of heat flow meters is discussed in ASTM Cl 1.12 [16] and bv Scott [17],... 

ISO 2581 (1975), Rigid cellular plastics—Determination of apparent thermal conductivity by means of a heat-flow meter. 

Steady State Heat Flux Measurement and Thermal Transmission Properties by Measure of Heat Flow Meter Apparatus, ASTM C518, Am. Soc. Testing and Materials. Goodrich B, Toyama B. Liquid encapsulation considerations. Dexter Technology Paper, Dec. 1994. 

The constant, k, is a material constant called the coefficient of thermal conductivity. It is the time rate of heat flow under steady-state conditions through a unit area and unit thickness per unit temperature gradient. Several methods for measuring thermal conductance are available, of which the guarded-hot-plate and heat-flow-meter methods are the most widely used. The most accurate method for plastics having thermal conductivities of 3.4 x 10 cal/(second)(cm)(°C) [1.4 W/m K] or less (most filled and unfilled polymers) is the guarded-hot-plate method as described in ASTM Cl77. A comparable method is described in ISO 8302. ... 

HEM heat flow meter H2SO4 hydrogen sul te (sulfuric acid)... 

The direct measurement of the thermal conductivity or X factor is one of the most common ways to check the quality of a vacuum panel. Several test methods are available, such as the heat flow meter [45], guarded hot-plate and guarded-calibrated hot box [46, 47] procedures, which measure the heat transferred under steady state conditions through the sample whose surfaces are kept at two different given temperatures. 

In the heat flow meter technique, the sample is placed between two plates controlled at different temperatures. Thermocouples placed just below the plate surfaces measure the temperature drop across the sample. One (or more) heat flow transducers mounted on the plate measures the voltage which is proportional to the heat flow through the sample. Knowing the relationship between the voltage signal of the transducer and the heat flow through it, which can be obtained by calibrating the transducer to a known thermal conductivity standard, the thermal conductivity for the specimen can be obtained. 

Heat flow meter test results generally agree well with those generated hy absolute methods. The technique, which is easier to use and is a universally recognised standard test procedure [45], is also usable either for high accuracy measurements to support VIP analytical modelling/development or for fast tests for QA/QC programs. 

Guarded heat flow meters are variants on the guarded hot-plate technique, which utilize a heat flow meter to measure the heat flux. These techniques are comparative in nature because a reference material is needed to calibrate the heat flux meter. They utilize smaller samples and are thus able to equilibrate faster, improving the versatility of the guarded hot-plate method. 

Figure 2 Schematic diagram of the guarded heat flow meter. (Courtesy of Holometrix Corp.)...

Thermal contact resistance is an issue with the heat flow meter. Some of its eifects can be calibrated out by applying the same load to the test stack as was used during calibration of the instrument. Further, a heat transfer compound can be applied if needed. 

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