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Estolides
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Jakob Bredsguard, Travis Thompson
Because lubricants are typically filled on a volumetric basis, rather than a mass basis, a better value for understanding this thermodynamic property is volumetric heat capacity. While heat capacity describes the energy storing potential of a unit of mass, the volumetric heat capacity represents the energy storing potential of a unit of volume. By multiplying a material’s heat capacity by its density, the volumetric heat capacity can be derived. The density, heat capacity, volumetric heat capacity, and a relative comparison of each base oil is provided in Figure 27.12. Estolide volumetric heat capacities are higher than refined mineral oils, polyalphaolefins, and diesters, but are slightly lower than the polyol ester and the polyalkylene glycol samples tested.
Multidimensional and Unsteady Conduction
Published in Anthony F. Mills, Heat and Mass Transfer, 2018
where α = k/ρc [m2/s] is a thermophysical property of the material called the thermal diffusivity. Table 3.1 gives selected values of the thermal diffusivity. Additional data are given in Appendix A, as are values for k, ρ, and c. from which α can be calculated. Equation (3.6) is called Fourier’s equation (or the heat or diffusion equation) and governs the temperature distribution T(x, y, z, t) in a solid. The relevance of the thermal diffusivity can be seen in Fourier’s equation: when there is no internal heat generation, it is the only physical property that influences temperature changes in the solid. The thermal diffusivity is the ratio of thermal conductivity to a volumetric heat capacity: the larger α. the faster temperature changes will propagate through the solid.
Thermal and electrical properties of soils
Published in Hsai-Yang Fang, John L. Daniels, Introductory Geotechnical Engineering, 2017
Hsai-Yang Fang, John L. Daniels
Once heat is transmitted into the ground, the ability of the soil to retain or dissipate heat is dependent on its heat capacity and thermal conductivity. There are five basic parameters to measure the characteristics of heat: (a) mass heat capacity: the mass heat capacity is defined as the quantity of heat, Q, required to raise a unit weight of material one degree; (b) volumetric heat capacity: the volumetric heat capacity is defined as the quantity of heat required to raise a unit volume of material one degree; (c) specific heat: specific heat is the ratio of mass heat capacity of the material, divided by the mass heat capacity of water. It is a dimensionless quantity, the typical values of specific heat for air = 0.237, ice = 0.463, water = 1.000, wood = 0.327, limestone = 0.216, quartz = 0.188; (d) thermal conductivity or thermal resistivity: for practical application, the values for thermal conductivity and resistivity are important. Detailed discussion of these two parameters will be presented in Section 6.4; and (e) thermal diffusivity: the thermal diffusivity is the quotient of the thermal conductivity and the heat capacity per unit volume.
Measuring moisture content in building insulation materials by a hot film
Published in Science and Technology for the Built Environment, 2022
Kexin Tang, Tengfei (Tim) Zhang
The thermal method determines the moisture content on the basis of thermal conductivity and/or volumetric heat capacity. The volumetric heat capacity is simply the product of density and heat capacity. The thermal conductivity of a porous material depends on the solid frame material, pore structure, trapped gaseous content, moisture, and the gas and moisture distribution, among other factors. There are many models that describe the dependence of thermal conductivity on moisture content (De Vries 1963; Campbell 1985; Hopmans and Dane 1986). However, the thermal conductivities of gases are much lower than those of the solid frames and the moisture, and therefore the presence of gases can cause great uncertainties in measurements of the thermal conductivities of porous materials. In addition, the heat conduction pattern within the porous material is complicated, and convection heat transfer may occur within voids. Hence, measuring moisture content on the basis of thermal conductivity may result in large errors (Yu et al. 2009).
Enhanced Thermochemical Heat Capacity of Liquids: Molecular to Macroscale Modeling
Published in Nanoscale and Microscale Thermophysical Engineering, 2019
Peiyuan Yu, Anubhav Jain, Ravi S. Prasher
where Cp_base is the intrinsic volumetric heat capacity of the reaction mixture. The first term in Equation (5) is the heat absorbed due to the net chemical reaction (shift of equilibrium) from Tlow to T, and the second term is the sensible heat absorbed by the reaction mixture itself (R1, R2, P and solvent). For simplicity, we assume that Cp_base does not vary with temperature, thus can be treated as constant. It should be noted that in practice, the intrinsic Cp of the reaction mixture (Cp_base) will be temperature-dependent. This originates from the fact that the Cp of each component is temperature-dependent and the composition of the reaction mixture (determined by the concentration of each component) is also temperature-dependent. In general, the specific heat capacity of a pure liquid gradually increases with temperature, and its volume expands as well. As a result, the volumetric heat capacity could increase (e.g., ethanol) or decrease (e.g., water) with increased temperature.
A novel numerical approach for investigation of the heat transport in a full 3D brake system of high-speed trains
Published in Numerical Heat Transfer, Part A: Applications, 2019
Peng Ji, Fan Wu, Guoliang Zhang, Xiaofang Yin, Dmitri Vainchtein
The integral of heat conduction power over time gives the total amount of heat transferred into the disc. The thermal conductivity and volumetric heat capacity of cast steel are higher than that of titanium alloy, see Table 1. Higher volumetric heat capacity leads to a smaller increase in temperature for the same amount of heat, and consequently, causes a more intensive heat conduction. Larger thermal conductivity for cast steel also helps the heat conduction from the heat source into the brake disc. Thus the cast steel disc receives more frictional heat than titanium alloy disc. The heat conducted into the cast steel disc and titanium alloy disc is 90.36% and 86.81% of the total heat generated by friction during the first braking period, respectively, and 89.94% and 86.17% during the second braking period. The rest of the heat is transferred into the pad.