Thermal Diffusivity Measurements on Elastomers

1974 ◽  
Vol 47 (4) ◽  
pp. 849-857 ◽  
Author(s):  
H. K. Frensdorff
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Diffusivity ◽  
Measurement Method ◽  
Volumetric Heat Capacity ◽  
Raw Data ◽  
Diffusivity Measurements ◽  
Thermal Diffusivities ◽  
Heating Up ◽  
Rubber Article

Abstract Thermal diffusivity, rather than thermal conductivity, is the property which governs rates of heating up and cooling down of a rubber article in the mold. It is preferable to measure it directly, rather than to derive it from separate measurements of thermal conductivity and volumetric heat capacity. A straightforward measurement method is described together with procedures for deriving the required results from the raw data. The sources of error are discussed, and ways for minimizing them are suggested. Thermal diffusivities for gum and black EPDM and fluoroelastomer are reported for temperatures from 0° to 100° C.

Effect of timeliness on the thermal properties of paraffin-based Al2O3 nanofluids

2019 ◽  
Vol 33 (05) ◽  
pp. 1950051
Author(s):  
Yangyang Wu ◽  
Baichao Wang ◽  
Dong Li ◽  
Changyu Liu
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Volume Concentration ◽  
Volume Fraction ◽  
Thermal Conversion ◽  
Volumetric Heat Capacity ◽  
Energy Storage Material ◽  
Over Time

Paraffin is an excellent photo-thermal conversion phase change energy storage material, and extensively used in the thermal storage field at the medium-low temperature. However, the low thermal conductivity of paraffin restricts its application in practice. Adding nanoparticles into paraffin is one of the effective methods to improve its thermal conductivity. Nevertheless, the thermal diffusivity, specific heat and volumetric heat capacity of paraffin as well as timeliness were affected after the addition of nanoparticles. In this paper, the influences of volume fraction of Al2O3 nanoparticle and timeliness on these thermal parameters of paraffin were investigated. The results show that the thermal conductivity of paraffin-based Al2O3 nanofluids increases first and then decreases with time, and the maximum thermal conductivity is 0.34 W/[Formula: see text] for volume fraction 1% on third day. The higher volume concentration, the lower specific heat and volumetric heat capacity, all present downtrend over time, until stable in the range of 0.3 MJ/[Formula: see text] and 0.4 MJ/[Formula: see text]. The average enhancement rate of specific heat and volumetric heat capacity are concentrates on −6% to 9%, −10% to 0%, respectively. While increasing the volume concentration, the thermal diffusivity has no obvious regularity, and presents undulatory property over time.

Theoretical Study on Transient Hot-Strip Method by Numerical Analysis

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Gaosheng Wei ◽  
Xiaoze Du ◽  
Xinxin Zhang ◽  
Fan Yu
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Diffusivity ◽  
Numerical Analysis ◽  
Measurement Error ◽  
Transient Hot Strip ◽  
Strip Method ◽  
Hot Strip ◽  
Transient Hot Strip Method ◽  
Thermal Diffusivities

This paper presented the effects of finite dimensions of the sample and nonzero heat capacity of the strip on thermal conductivity determination with the transient hot-strip method. Through the numerical analysis of the temperature field within the system composed of the samples and the strip, the temperature transients at the strip surface were obtained to calculate the thermal conductivities of materials, which were compared with the exact values. The effect of heat losses out of the external surfaces of the sample and the heat capacity of the strip on thermal conductivity determination were then analyzed comprehensively. It is shown that the sample finite dimensions have a great effect on thermal conductivity determination, especially on the materials with relatively higher thermal diffusivities, and the measured thermal conductivity is always lower than the exact value due to the lower convective heat transfer coefficient out of the external surfaces of the sample. The measurement error is estimated to be less than 2.1% for the material with thermal diffusivity less than 4.0×10−6 m2/s with the sample dimensions of 120×60 mm2(width×thickness) and the fitting time interval of 20–300 s. The nonzero heat capacity of the strip has a great effect on thermal conductivity determinations of the materials with relatively lower thermal diffusivities. The measurement error is estimated to be less than 5% for the material with thermal diffusivity larger than 0.8×10−7 m2/s with Cr20Ni80 alloy as the strip.

scholarly journals Effects of sonication and freezing on the color, mechanical and thermophysical properties of osmo-microwave-vacuum dried cranberries

2020 ◽  
Author(s):  
Izabela Anna Staniszewska ◽  
Szymon Staszyński ◽  
Magdalena Zielińska
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Diffusivity ◽  
Moisture Diffusion ◽  
Moisture Diffusivity ◽  
Microwave Drying ◽  
Vacuum Drying ◽  
Volumetric Heat Capacity ◽  
Drying Time ◽  
Microwave Vacuum Drying

The aim of study was to determine the effects of sonication (S), convective freezing (F), convective freezing preceded by sonication (SF) as well as cryogenic freezing (N) on the osmo-microwave-vacuum drying kinetics, energy usage and properties of dried cranberries such as moisture content, moisture diffusion, water activity, density, porosity, thermal conductivity, thermal diffusivity, volumetric heat capacity, lightness, redness, yellowness, total differences in color, saturation and hue, hardness, cohesiveness, springiness, and chewiness. Osmo-microwave-vacuum drying of cranberries took from 13.5 to 16.0 min. All initial treatments increased the moisture diffusivity and thus reduced the drying time. The most energy effective method was osmo-microwave-vacuum drying preceded by sonication (S) of fruits. Osmo-microwave-drying of cranberries subjected to convective freezing preceded by sonication (SF) resulted in the highest lightness (32.5 ± 0.5), redness (33.9 ± 0.7), and yellowness (11.3 ± 0.5) of fruits, as well as the lowest cohesion (the lowest resistant to stress associated with manufacturing, packaging, storage, and delivery). The lowest hardness, i.e. 12.3 ± 0.4 N and the highest cohesiveness and springiness, i.e. 0.38 ± 0.02 and 0.74 ± 0.03 of dried fruits, were noted for berries subjected to initial cryogenic freezing (N). Cryogenic freezing (N) combined with osmo-microwave-vacuum drying resulted in the largest color changes of fruits and the highest thermal conductivity. Sonicated and convectively frozen (SF) fruits were characterized by the highest thermal diffusivity. Sonication (S), convective freezing (F) and their combination (SF) significantly reduced the volumetric heat capacity of cranberry fruits.

Comparison of single and dual probes for measuring soil thermal properties with transient heating

Soil Research ◽  
1994 ◽  
Vol 32 (3) ◽  
pp. 447 ◽  
Author(s):  
KL Bristow ◽  
RD White ◽  
GJ Kluitenberg
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Heat Pulse ◽  
Volumetric Heat Capacity ◽  
Transient Heating ◽  
Single Probe ◽  
Soil Thermal Properties ◽  
Dual Probe

Storage and transfer of heat in soils is governed by the soil thermal properties and these properties are therefore needed in many agricultural and engineering applications. In this paper we discuss solutions of the heat flow equation applicable to single and dual probe transient heating methods, and describe measurements made on air-dry sand to show how these methods can be used to obtain soil thermal properties. Measurements show that the two methods yield similar values of thermal conductivity. When determining thermal conductivity from the single probe data, it is best to use nonlinear curve fitting and to include a correction term in the model to account for the presence of the probe. Measurements of volumetric heat capacity made by using the dual probe heat-pulse method agreed well with independent estimates obtained using the de Vries method of summing the heat capacities of the soil constituents. The advantage of using the dual probe method together with the appropriate heat-pulse theory rather than the single probe is that all three soil thermal properties, the thermal diffusivity, volumetric heat capacity, and thermal conductivity, can be determined from a single heat-pulse measurement. Instantaneous heat-pulse theory can be used with the dual probe method to determine heat capacity from short duration heat-pulse data, but it should not be used to determine the thermal diffusivity and thermal conductivity.

Theoretical Study on Transient Hot-Strip Method by Numerical Analysis

2009 ◽  
Author(s):  
Gaosheng Wei ◽  
Xiaoze Du ◽  
Xinxin Zhang ◽  
Fan Yu
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Diffusivity ◽  
Numerical Analysis ◽  
Measurement Error ◽  
Time Interval ◽  
Strip Surface ◽  
Transient Hot Strip ◽  
Hot Strip ◽  
Thermal Diffusivities

This paper presented the effects of finite dimensions of the sample and non-zero heat capacity of the strip on thermal conductivity determination with the transient hot-strip (THS) method. Through numerical analysis of temperature field within the system composed of the samples and the strip, the temperature transients at the strip surface were obtained to calculate the thermal conductivities of materials, which were compared to the exact values. The effect of heat losses out of the external surfaces of the sample and the heat capacity of the strip on thermal conductivity determination were then analyzed comprehensively. It is shown that the sample finite dimensions have great effect on thermal conductivity determination, especially on the materials with relatively higher thermal diffusivities, and the measured thermal conductivity always lower than the exact value due to the lower convective heat transfer coefficient out of the external surfaces of the sample. The measurement error is estimated less than 2.2 percent for the material with thermal diffusivity less than 4.0×10−6 m2/s with the sample dimensions of 120 mm × 60 mm (width × thickness) and the fitting time interval of 20–450s. The non-zero heat capacity of the strip has great effect on thermal conductivity determinations of the materials with relatively lower thermal diffusivities. The measurement error is estimated less than 5 percent for the material with thermal diffusivity larger than 0.8×10−7 m2/s with Cr20Ni80 alloy as the strip.

scholarly journals Transient method measured thermal properties of concrete with microspheres and latex based addition

2018 ◽  
Vol 196 ◽  
pp. 04037
Author(s):  
Roman Jaskulski ◽  
Wojciech Kubissa
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Fly Ash ◽  
Thermal Diffusivity ◽  
Thermal Conductivity Coefficient ◽  
Transient Method ◽  
Volumetric Heat Capacity

The goal of the performed research was to determine the influence of microspheres from fly ash and the latex based addition on the thermal properties of concrete. The tested additions were used in two different proportions each and they were combined with each other. As a reference two series of concrete were used: one without any addition and another with 0.2% of air entraining agent. The thermal properties were measured using transient method with ISOMET 2114 apparatus. No clear trends were observed in case of the results of the measurements of the thermal diffusivity and the volumetric heat capacity. While the results of the thermal conductivity coefficient show that both additions has a potential of lowering the thermal conductivity but they are not so efficient as air entraining agent.

Thermal conductivity, thermal diffusivity, and volumetric heat capacity of silicone elastomer nanocomposites

2017 ◽  
Vol 30 (3) ◽  
pp. 365-374 ◽  
Author(s):  
Govind Sahu ◽  
VK Gaba ◽  
S Panda ◽  
B Acharya ◽  
SP Mahapatra
Keyword(s):  
Electron Microscopy ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Temperature Response ◽  
Silicone Elastomer ◽  
Positive Temperature ◽  
Volumetric Heat Capacity ◽  
Multiwalled Carbon

Silicone elastomer (SiR) nanocomposites were prepared using multiwalled carbon nanotubes (MWCNT) and nano-graphite (NG). The morphology of the SiR nanocomposites has been studied using scanning electron microscopy and high-resolution transmission electron microscopy techniques. Detailed analysis of the morphology reveals a uniform distribution of the MWCNT and NG filler particles in the silicone matrix. On increasing the filler loading, a continuous network structure is formed and aggregation takes place. The effect of the MWCNT and NG loadings on the thermal properties of the silicone elastomer has been investigated. The thermal properties of the SiR nanocomposites were measured by a thermal properties analyzer based on the transient hot-wire method. Studies also suggest that incorporation of nanoparticles improves the thermal conductivity of SiR nanocomposites. The thermal conductivity of SiR nanocomposites increased from 0.200 W/(m K) to 0.440 W/(m K) and to 0.310 W/(m K) for 6 wt% MWCNT and NG loadings, respectively. Because of the positive temperature coefficient and the conductive nature of the nanoparticles, the thermal conductivity of the material increased on increasing the temperature. The thermal diffusivity and the volumetric heat capacity of the SiR nanocomposites were measured. The thermal diffusivity of the SiR nanocomposites increased from 0.1194 mm2/s to 0.3209 mm2/s and to 0.2050 mm2/s for 6 wt% MWCNT and NG loadings, respectively. This indicates that the temperature response becomes faster with MWCNT and NG loadings. The volumetric heat capacity of the silicone elastomer nanocomposites decreased from 1.80 MJ/(m3K) to 1.34 MJ/(m3K) and to 1.40 MJ/(m3K) for 6 wt% MWCNT and NG loadings, respectively. Thus, MWCNT particles are more effective in increasing the thermal conductivity and diffusivity of the SiR nanocomposites, when compared to NG fillers at any loading.

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