Thermal coefficient of capacitance

Mica capacitors consist of mica, KAl2(Si3Al)0,o(OH)2, plates with fired-on silver electrodes. The metallized plates are stacked together in a multilayer fashion. Mica capacitors are extremely stable over time, have low thermal coefficient of capacitance, and have relatively low loss. 

A key factor in the suitabihty of cokes for graphite production is their isotropy as determined by the coefficient of thermal expansion. After the calcined coke was manufactured into graphite, the axial CTE values of the graphite test bars were determined using a capacitance bridge method over a temperature range of 25 to 100°C. The results are summarized in Table 24. Also included in the table are bulk density measurement of calcined cokes and the resistivity values of their graphites. 

In case of a homogeneous temperature distribution in the heated area, h corresponds to the temperature coefficient of the heater material, otherwise h includes the effects of temperature gradients on the hotplate. As a consequence of the aheady mentioned self-heating, the applied power is not constant over time, and the hotplate cannot be simply modelled using a thermal resistance and capacitance. Replacing the right-hand term in Eq. (3.28) by Eq. (3.35) leads to a new dynamic equation ... 

According to Fourier law, the scalar coefficient of thermal conductivity k rel s the thermal flux density Q [in erg/cm s] to the gradient of temperature Q = —kVT [units of k erg/cm.s.K], The corresponding thermal diffusion coefficient [in cm /s] includes density of substance p and heat capacitance Cp (at constant pressure)... 

The temperature dependence of the lattice constants a and c and the thermal expansion coefficients of hexagonal ZnO have been determined by the capacitive method [138]. The thermal expansion coefficients measured between 4 and 800 Rare shown in Figure 1.25. Reeber [30] has employed X-ray powder diffraction methods instead to measure the temperature dependence of the lattice parameters of ZnO in the range of 4.2-296 K. The results are shown in Figure 1.26. When analyzing the dependence of the lattice parameters on temperature, fourth-order polynomials... 

The heat exchanger is quite large because of the low heat transfer coefficient found in these gas-phase systems. Therefore the mass of metal in the tubes is quite significant in terms of thermal capacitance. Table 7.3 gives design details of the heat exchanger. The tube diameter is 0.0254 m, length is 5 m, wall thickness is 0.000524 m, and heat capacity is 0.05 kJ kg-1 KT1. 

The kink observed around 367 K corresponds to a change of the thermal expansion coefficient from a glassy to a liquid-like state and, by that, marks the position of the glass transition temperature. Usually, the 7g is calculated as a intersection point between two linear dependencies. Nevertheless, a more convenient method is the calculation of the first and second numerical derivatives of the experimental data (Fig. 15b,c). In this case, the Tg is defined as the minimum position in the second numerical derivative plot (Fig. 15c). Down to a thickness of 20 nm, no shifts of 7g as determined by capacitive scanning dilatometry were found (Fig. 16). 

There will be one integration with respect to x and two with respect to y, so we will need to provide one piece of boundary information in the x direction and two in the y direction. The x condition appears to be straightforward We assume that at X = 0 the melt is uniformly at the reservoir temperature, which we denote T (for initial). The thermal boundary condition at a wall is typically written as an equality between the heat flux into the wall from conduction in the fluid and the heat flux from the wall to the surrounding heat transfer medium. It is an equality because the wall is assumed to have no thermal capacitance, so the flux into the wall must equal the flux out. The heat flux in the fluid is equal to -KdT/dy. (This is known as Fourier s law, but it is an empirical constitutive equation, not a law of nature.) The flux to the surroundings is usually written as U T - To), where Ta is the temperature of the ambient environment, which might be air or a heat exchange fluid. U is an overall heat transfer coefficient, which is characteristic of the particular geometry, materials, and flow. The appropriate boundary conditions are then... 

Hi) The thermal capacitances of the tank contents and the jacket contents are signiflcant relative to the thermal capacitances of the jacket and tank walls, which can be neglected, (iv) Constant physical properties and heat transfer coefficients can be assumed. 

The time constant of the measuring element equals the thermal resistance times the capacitance. The thermal resistance can be modelled as a function of area and the heat transfer film coefficient ... 

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