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Thermally-based Modification Processes
Published in Dick Sandberg, Andreja Kutnar, Olov Karlsson, Dennis Jones, Wood Modification Technologies, 2021
Dick Sandberg, Andreja Kutnar, Olov Karlsson, Dennis Jones
The thermal conductivity (2,) of a material is a measure of its ability to conduct heat, i.e., the quantity of heat which flows in one second through a cube one cubic metre in size with a temperature difference of one Kelvin between the opposite sides. The unit of conduction is Wm1K-1. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal conductivity. Materials with high thermal conductivity are widely used in heat-sink applications, and materials with low thermal conductivity are used for thermal insulation. The reciprocal of thermal conductivity is called the thermal resistivity. Thermal conductivity is calculated from Fourier’s Law for heat conduction: q=−λΔT
The Laws of Nuclear Heat Transfer
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
where ∇ is the gradient operator. Here, q″ is the heat flowing through a unit area of the material, and it is defined by q″ = q/A. In some textbooks, q″ is referred to as the heat flux, and in reactor work, it is referred to as the nuclear heat flux. In the SI system, it has the units of kW/m2. However, in nuclear science and engineering, it is also expressed in W/cm2—particularly when it pertains to nuclear fuel rods and radiation shields. The constant of proportionality between the heat flux and negative temperature gradient is called the thermal conductivity k. The thermal conductivity is material dependent and it has the units of W/m-°K. In nuclear applications, the thermal conductivity is also expressed in W/cm-°C. Sometimes the degree symbol (°) is suppressed when quoting the temperature in SI units, but we will not adhere to this convention here. In many applications the thermal conductivity is constant, but in nuclear applications involving uranium or plutonium fuel, this is not always the case. Fourier’s law in integral form is
Short Review of Atomic and Semiconductor Theory
Published in Vijay B. Pawade, Sanjay J. Dhoble, Phosphors for Energy Saving and Conversion Technology, 2018
Vijay B. Pawade, Sanjay J. Dhoble
This is the property of a material to transfer a flow of heat from one end to another. It is expressed in the form of the law of heat conduction, also called Fourier’s law of heat conduction. The rate of heat transfer is lower across a material having low thermal conductivity than one with high thermal conductivity. Materials with high thermal conductivity can be applied as heat sinks, and those with low thermal conductivity are used as thermal insulators in most electrical equipment. Therefore, this property of the materials depends on temperature. Thermal resistivity is defined as the reciprocal of thermal conductivity. In general, metals, such as copper, aluminum, gold, and silver, are good conductors of heat; however, materials such as wood, plastic, rubber, and so on are poor heat conductors, so-called insulators.
Sound absorbing and thermal insulating properties of recycled cotton/polyester selvedge waste chemical bonded nonwovens
Published in The Journal of The Textile Institute, 2023
Meseret Bogale, S. Sakthivel, S. Senthil Kumar, B. Senthil Kumar
The thermal insulation properties of the samples were measured in terms of the thermal conductivity. The thermal conduciveness of various samples is shown in Figure 11. The thermal conductivity better is the insulation property. Low values of the thermal conductivity imply higher resistance to conduction of the heat through the material. With the increase in temperature, the thermal conductivity increases for all samples. Two-layer mats with 50% recycled cotton fiber along with 50% recycled PET fiber provided one of the best insulation properties. These results showed that it is possible to develop samples that show similar thermal conductivity as that of 100% recycled cotton and PET fiber. The thermal conductivity for the color PET material is about 0.13 W/mK which has a SAC value of 0.33 which is higher than that of the S1C, S2P, S3C/P, S4C/P, S5C/P, and S6 C/P these samples were suitable for roof ceiling insulation applications in a building. The study has conducted by Küçük et al. (2012) and Sakthivel et al. (2020), and Dhanapiriya et al. (2021).
Comprehensive review of phase change material based latent heat thermal energy storage system
Published in International Journal of Ambient Energy, 2022
Pitambar Gadhave, Firojkhan Pathan, Sandeep Kore, Chandrakant Prabhune
Salt hydrates are inorganic compounds, with melting point temperature range from C to C. These are widely in use due to their higher thermal conductivity, high latent heat of fusion/, and less expensive compared to paraffin. Another inorganic compound is metallics consist of either low melting point temperature metal or metal eutectics. Metallics have a high-value thermal conductivity as compared to other materials. The significant advantages of metallics are low specific heat, high thermal conductivity and less vapour pressure. However, due to the low latent heat of fusion/unit mass, they are rarely used as storage materials. Two or more components with fixed freezing/melting points called eutectic mixtures.
CFD study on heat transfer and pressure drop of nanofluids (SiO2/H2O, Al2O3/H2O, CNTs/H2O) in a concentric tube heat exchanger
Published in International Journal of Ambient Energy, 2022
Ankit Kumar Gupta, Bhupendra Gupta, Jyoti Bhalavi, Prashant Baredar, Hemant Parmar, Ramalingam Senthil
In both conduction and convection heat transfer mechanism, thermal conductivity of material plays a vital role in heat transfer. The higher thermal conductivity material transfers more heat compare to the lower thermal conductivity material. Conventional fluid has lower thermal conductivity so convective heat transfer by the conventional fluid is low; the main purpose of using nanofluid over the conventional fluid is their improved thermal conductivity. Due to the importance of thermal conductivity of nanofluids, it is necessary to determine the accurate value of thermal conductivity; for this, there are many correlations developed by different research. In this analysis, the Hamilton and Grosser model is used, as shown in equation (1), who studied the effect of sphericity as mentioned by Kakaç and Pramuanjaroenkij (2009). The empirical shape factor (n) can be calculated by n=3/ψ, where ψ is the sphericity of the nanoparticle