Experimental and theoretical study of the hot-wire method applied to low-density thermal insulators

Coquard, R.; Baillis, Dominique; Quénard, Daniel

doi:10.1016/j.ijheatmasstransfer.2006.05.016

Cited by 85 publications

(45 citation statements)

References 10 publications

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“…That is the reason why we do not detail it here and invite the reader to consult previous works on the subject. [25,26] We used the hot-wire apparatus used for measurements at the CSTB Grenoble. It is composed of a metallic wire of 0.08 m in length and a thermocouple, both embedded in a slab of kapton in order to ascertain that the thermocouple is positioned at a given distance from the wire.…”

Section: Hot-wire Methodsmentioning

confidence: 99%

“…It is composed of a metallic wire of 0.08 m in length and a thermocouple, both embedded in a slab of kapton in order to ascertain that the thermocouple is positioned at a given distance from the wire. This apparatus is described in detail in [25] and has been widely used by the CSTB for the measurement of the conductivity of various materials in a wide range of conductivities. The wire is sandwiched between the foam sample and a slab of cellular concrete ( Fig.…”

Section: Hot-wire Methodsmentioning

confidence: 99%

“…Cont) have been obtained with d = 0. 25 The solid conductivities k solid indicated in Table 1 have been found in the literature. These values vary relatively widely according to the sources, especially for the ceramic materials.…”

Section: Validationmentioning

confidence: 99%

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Conductive Heat Transfer in Metallic/Ceramic Open‐Cell Foams

Coquard¹,

Loretz²,

Baillis³

2008

Adv Eng Mater

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During the last decade, solid foams which are characterized by a relatively high porosity (> 80 %), have known a strong development. Indeed, they allow to envisage a substantial improvement of the performance of standard materials in numerous technological fields. Notably, metallic and ceramic foams exhibit thermal, mechanical and exchange properties, which make them very interesting in lots of applications requiring multifunctionality. To illustrate this, we can cite a non-exhaustive list of functions for which they are usually used: ultra light panels, energy absorbing structures, heat dissipation media, electrodes for electric battery, ultrasound deflector, carrying structure for catalyst, medical prosthesis, heat exchanger _. In most of these applications, the knowledge of the thermal transport properties is of primary importance for the dimensioning of the structures. At ambient temperature, the heat transfer in solid foams is dominated by thermal conduction. To quantify the magnitude of heat conduction, one generally uses the effective conductivity k c which implies that the two-phase material behaves like a homogeneous conductive medium. This assumption is rigorously valid when the size of the pores is much lower than the dimensions of the materials, which is the case in solid foams. The effective conductivity depends on the porosity of the foam, the morphology of the material and on the properties of the two-phases. It is particularly difficult to estimate in solid foams due to the complexity of the geometry encountered and to the large difference between the thermal conductivity of fluid and solid phases.Numerous authors proposed empirical, analytical or numerical model depending on the porous morphology and on the conductivity of the phases to estimate the apparent conductivity of this type of materials. A study was conducted by Schuetz and Glicksmann. [2,3] They were interested in the conductivity of polymeric foams whose porous microstructure is very close to that of metallic and ceramic foams. Indeed, these foams are formed of closed or open cells made of cell struts and/or windows. The porosity of these foams is beyond 95 %. They modeled the foam as a network of thermal resistances and made several simplifications of the morphology and of the solution method to compute overestimating and underestimating values of the exact conductivity. These overestimating and underestimating values, given in, [2] are calculated analytically and are related to the conductivity of air and polymer and to morphological parameters:ek fluid 0:8 × 1 À e 2 À f s 3 k solid < k c

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Section: Hot-wire Methodsmentioning

confidence: 99%

Section: Hot-wire Methodsmentioning

confidence: 99%

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Conductive Heat Transfer in Metallic/Ceramic Open‐Cell Foams

Coquard¹,

Loretz²,

Baillis³

2008

Adv Eng Mater

Self Cite

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“…The cement specimen was cured in the mold with dimensions of 50 mm × 100 mm × 50 mm to measure the thermal conductivity. The QTM-500 thermal conductivity meter adopts the transient hot wire method corresponding to the following line source model (Kestin and Wakeham 1978;Roder 1981;Coquard et al, 2006) [12][13][14]:…”

Section: Laboratory Experimentsmentioning

confidence: 99%

Numerical Investigation on the Effect of Cementing Properties on the Thermal and Mechanical Stability of Geothermal Wells

et al. 2016

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Abstract:In this paper, a two-dimensional (2-D) Finite Element (FE) analysis of a geothermal well was performed with respect to five different cross-sections corresponding to the design specifications for the geothermal well that is currently constructed in Pohang, South Korea. Among the essential components (such as ground formation, casing, and cementing) of a geothermal well, the thermal and mechanical stability of the cementing component was discussed based on a series of parametric studies with consideration of the thermal conductivity and Young's modulus of the cementing component. With increasing number of casing layers, the cementing component experiences less stress concentration. In addition, the lower thermal conductivity of the cementing material is advantageous for effectively controlling radial displacement. Consequently, it should be noted in geothermal well cementing construction that long-term strength degradation of the cementing might cause the severe structural instability of an entire geothermal well.

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“…Most of the existing techniques are empirical. The most popular measuring technique for the thermal conductivity is based on transient measurement of hot wire [11]. Although this technique is widely used for pure fluids, it is yet unreliable for mixtures, since the properties of the mixtures are not well defined; the local concentration of the volatile phase may change together with the fluid local temperature and the various time scales of the heat and mass transfer.…”

Section: Introductionmentioning

confidence: 99%

Heat transfer to sub-cooled binary solution in horizontal tube

Orian

Jelínek

Levy

2009

Applied Thermal Engineering

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Predicted heat transfer coefficients (HTC) are widely used for calculations of various heat transfer processes. Various empirical and semi-empirical models of non-dimensional groups are used for calculating the heat transfer coefficients. The common accuracy of the predicted heat transfer coefficient is usually about ±25%; however, the accuracy is failing by the inaccurate predictions of the fluid properties.In the present study the heat transfer coefficient of subcooled organic mixture chlorodifluoromethane (R22) -dimethylacetamide (DMAC) were predicted. While the solution's pressure-temperature-concentration, densitytemperature-concentration and viscosity-temperatureconcentration relations were previously measured in our laboratory and the heat capacity were calculated from the enthalpy of the solution, the only unknown property that was required for predicting the HTC was the mixture thermal conductivity. Various correlations and mixing rules for the mixture thermal conductivity were adopted for predicting the heat transfer coefficient. In order to validate the predicted heat transfer coefficients, an experimental system was designed, built and successfully operated. The heat transfer coefficient was measured experimentally and compared with the predicted one. Based on this comparison the best fitted thermal conductivity for the working fluid (R22-DMAC) is recommended. As a result, the deviations of the predicted heat transfer coefficients, obtained by the well-known Dittus-Boelter equation, from the experimental values were less than 15%.

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Experimental and theoretical study of the hot-wire method applied to low-density thermal insulators

Cited by 85 publications

References 10 publications

Conductive Heat Transfer in Metallic/Ceramic Open‐Cell Foams

Conductive Heat Transfer in Metallic/Ceramic Open‐Cell Foams

Numerical Investigation on the Effect of Cementing Properties on the Thermal and Mechanical Stability of Geothermal Wells

Heat transfer to sub-cooled binary solution in horizontal tube

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