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Temperature, Work, and Heat
Published in Jeffrey Olafsen, Sturge’s Statistical and Thermal Physics, 2019
Thermal physics (Thermodynamics) can be defined as the study of all physical processes involving temperature or heat. From Latin, we know thermodynamics concerns itself with the flow of heat resulting in a change in temperature. However, the precise meaning of these two words needs to be examined carefully. We start with temperature.
An analytical heat-transfer model for coaxial borehole heat exchanger with segmented method
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2020
Xianwen Huang, Zhishu Yao, Haibing Cai, Weipei Xue, Xuesong Wang
The temperature distribution and heat-transfer efficiency of CBHE are related to the cross-section size (Li et al. 2020), fluid inlet (Pan et al. 2019), and fluid characteristics of the coaxial pipe. However, research on the effect of thermophysical parameters of the coaxial pipe material on the temperature distribution and heat-transfer efficiency of the heat exchanger is not comprehensive. Therefore, on the basis of the analytical model proposed in this paper, the influence of CBHE fluid-inlet direction and material thermophysical properties on its heat-exchange efficiency was studied. The basic parameters and the construction process of the model are described in Section 3.3. The control variable method was used to study the influence of the thermal physics of the coaxial pipe material on the heat-transfer effect and temperature distribution. In analysis, as shown in Table 4 the thermal conductivity of the coaxial pipe was selected according to the different materials (ShiMing and Wenshuan 2006) (Copper, 399 W/m·K; iron 36.7 W/m·K; SiO2, 7.6 W/m·K; high-density polyethylene, 0.4 W/m·K and heat insulation material, 0.02 W/m·K), and the thermal conductivity of the backfill material and outer soil was designed in the range of common soisl thermal conductivity (0.4 ~ 8 W/m·K).
Nanostructure design for drastic reduction of thermal conductivity while preserving high electrical conductivity
Published in Science and Technology of Advanced Materials, 2018
Thermoelectric conversion is an important item for thermal management (Figure 1) and offers the possibility for waste heat to be reused as electrical energy. This can be an ideal energy source. The issue in this thermoelectric conversion, which is a function of temperature difference and the dimensionless figure of merit (ZT) determined by a material, is an insufficient efficiency. ZT is described as S2σT/κ, where S is Seebeck coefficient, σ is electrical conductivity, κ is thermal conductivity, and T is the absolute temperature. To enhance the thermoelectric conversion efficiency of a material, the value of ZT must be increased and thus materials with low thermal conductivity and high electrical conductivity are required. Conventionally, to realize this, heavy elements were used for low thermal conductivity [9,10]. In general, however, heavy elements are often rare elements, the use of which prevents the industrial application to thermoelectric materials. Recently, introduction of nanostructures that can reduce the thermal conductivity is expected as a promising approach for the realization of rare-element-free thermoelectric material. Therefore, the thermal physics of phonon transport in nanostructured materials must be understood to allow for independent control of electrical and thermal transport, which will lead to non-conventional thermoelectric materials with high efficiency.
Multiscale modeling of in-room temperature distribution with human occupancy data: a practical case study
Published in Journal of Building Performance Simulation, 2018
Yohei Kono, Yoshihiko Susuki, Mitsunori Hayashida, Igor Mezić, Takashi Hikihara
First of all, we introduce a mathematical model of in-room temperature distribution based on fluid and thermal physics. In the target space denoted by , the dynamics of temperature at position and time t are represented by the following energy equation (Hensen and Lamberts 2011): where D is the thermal molecular diffusion coefficient of air, is the air velocity field in the target space, is the vector differential operator in Cartesian coordinates , is the Laplacian operator, ρ and are the density and the specific heat at constant pressure. Also, stands for the heat input per unit time and volume from indoor and outdoor sources. The second term of the left-hand side of Equation (1) represents the advective heat transfer. Note that the advective transfer has been commonly analysed by CFD programmes: see, e.g. Srebric et al. (2008) and Zhang et al. (2013).