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Physical Properties of Steel
Published in Vladimir B. Ginzburg, Metallurgical Design of Flat Rolled Steels, 2020
Thermal conductivity can be described as the capability of a material to transfer heat by conduction. The quantity of heat that passes through a cross-sectional area per unit of time is determined by Fourier’s law as follows [12]:q=kAdTdLBtu/h where dT/dL = temperature gradient, °F/in.A = cross-sectional area, ft2k = thermal conductivity, Btu-in./ft2/h/°F.
The Laws of Thermodynamics
Published in Robert E. Masterson, Nuclear Reactor Thermal Hydraulics, 2019
Heat transfer in nuclear power plants can occur through the processes of conduction or convection. In conduction, the material through which the heat is transferred is at rest, while in convection, it is in motion (that is, natural or forced). When heat is added to a system, it increases its internal energy, and when heat is removed from the system, it decreases it. The heat gain (or loss) is represented by a change in the kinetic energy of the molecules within the system. In practice, the amount of heat transfer to and from the system is represented by the symbol Q, and the rate at which this heat is transferred is represented by the symbol Q′, where Q′ = dQ/dt. The heat transfer rate is expressed in J/s or W, and the absolute amount of heat transferred is given in J. In other words, the value of Q is given by
Broadband Global Irradiance
Published in Frank Vignola, Joseph Michalsky, Thomas Stoffel, Solar and Infrared Radiation Measurements, 2019
Frank Vignola, Joseph Michalsky, Thomas Stoffel
For accurate solar irradiance measurements, the heat flow should be only between the disk and the pyranometer’s heat sink that has considerable thermal mass compared to the disk. A thinner sensor (less thermal mass) results in a faster response time. Heat losses by other means such as convection, advection, conduction, and radiation reduce the accuracy of the measurements. Convection is the movement of heat in a medium such as water or air. An example of convection is using a ceiling fan to circulate warm air near the ceiling of a room to the lower part of the room. Advection is the process that transfers heat from a surface to a gas or liquid. An example of advection is when a fan is used to blow air across hot elements in a heater, resulting in the transfer of heat to the air. Conduction is the movement of heat in a material. An example of conduction is when a spoon is put in a hot cup of coffee and the handle of the spoon becomes hot as heat travels up the spoon. Heat also is transferred through electromagnetic radiation. An example of radiative heating is microwave heating of water or sunlight heating a solar collector to heat water (see Section 2.12 in Chapter 2 for more information on thermodynamic fundamentals).
Investigation of the optimal configuration of a highly conductive material embedded in a triangular fin
Published in Numerical Heat Transfer, Part A: Applications, 2023
M. Ahmadian-Elmi, M. Mohammadifar, K. Vafai, S. S. Nourazar
Also, it is possible to improve thermal performance by utilizing highly conductive materials in systems that are required to enhance heat transfer. The idea of inserting highly conductive materials was investigated by Bejan [50]. Almogbel and Bejan [51] proposed a constructal theory to reduce the global resistance between a point and an entire volume and suggested tree-shaped structures as an efficient method. This method has been used among researchers for the last two decades and helps with the increase of the heat transfer coefficient leading to the manufacturing of small-scale devices with a high rate of heat flux [52, 53]. You et al. [54] used constructal optimization on a triangular element and applied it to a triangular body with nonuniform heat generation. A cooling channel with semi-circular sidewall ribs on a rectangular heat-generating body was studied with constructal designs to optimize the temperature difference and pump power [55]. Wei et al. [56] combined constructal and entrancy theories to solve heat conduction problems on volume-point heat conduction, disk cooling, and heat exchangers. The constructal theory was first utilized in fins by Hajmohammadi et al. [57, 58] to insert a highly conductive material into a rectangular and annular fin to achieve the best configuration of highly conductive material which has the maximum heat transfer rate in a fixed volume.
Construction, testing and performance analysis of a multi-stage traveling-wave thermo-acoustic generator
Published in International Journal of Green Energy, 2023
Miniyenkosi Ngcukayitobi, Lagouge Tartibu
In practice, heat is transferred to the system via a hot fluid such as hot water or thermal oil in most thermo-acoustic devices (Abduljalil 2012; Dhuchakallaya and Saechan 2017). In this experimental investigation, electrical heaters were chosen to supply the required heat. These cartridge heaters are constructed to slot easily into drill holes, and have the following specifications: 10mm 150mm, 200W, 220AC. The amount of heat was adjusted through a VARIAC (variable and adjustable voltage transformer). Each engine stage has four cartridge heaters connected in parallel at one side of the regenerator (see Figure 2). Heat is transferred to the regenerator by conduction through copper strips. The conduction process refers to the transfer of heat from a hotter to colder part of an object by direct molecular contact (Arun and Nagaraja 2015; Book 2014). Between the regenerator and the heat exchangers, a number of holes have been drilled to accommodate thermocouples used for temperature measurement. The maximum operating temperature for the hot heat exchanger is between 650 and 1000. Copper strips have been selected because of their high thermal conductivity properties. The machining process and the layout of the HHX arrangement are shown in Figures 2 and 3.
Magnetic dipole aspect of binary chemical reactive Cross nanofluid and heat transport over composite cylindrical panels
Published in Waves in Random and Complex Media, 2022
Syed Latif Shah, Assad Ayub, Sanaullah Dehraj, Hafiz A. Wahab, K. Martin Sagayam, Mohamed R. Ali, Rahma Sadat, Zulqurnain Sabir
Figure 3 is plotted on the basis of the important thermic conductivity parameter for different values of n on temperature profile. Physically thermal conductivity is the rate of heat transferred through a unit area by conduction. Increasing the numerical values temperature goes up. The Figure 3 is divided in two subfigures: Figure 3(a) and (b) for n = 0.5 and n = 1.5. Figure 3(a) gives shear thinning domain of fluid, which disclose that variation to thermic conductivity parameter tracked to increase in temperature profile, while Figure 3(b) gives a shear thickening domain of fluid that disclose the same behavior. It is summarized that thermic boundary layer grows up with the increment in the normal temperature.