Coefficient of thermal conductivity,

This definition is in terms of a pool of liquid of depth h, where z is distance normal to the surface and ti and k are the liquid viscosity and thermal diffusivity, respectively [58]. (Thermal diffusivity is defined as the coefficient of thermal conductivity divided by density and by heat capacity per unit mass.) The critical Ma value for a system to show Marangoni instability is around 50-100. 

Cross-linked polyester composites have a relatively low coefficient of thermal conductivity that can provide beneficial property retention in thick laminates at high temperatures as well as remove the need for secondary insulation. The coefficient of thermal expansion of glass-reinforced composites is similar to aluminum but higher than most common metals. 

The heat-transfer quaUties of titanium are characterized by the coefficient of thermal conductivity. Even though the coefficient is low, heat transfer in service approaches that of admiralty brass (thermal conductivity seven times greater) because titanium s greater strength permits thinner-walled equipment, relative absence of corrosion scale, erosion—corrosion resistance that allows higher operating velocities, and the inherently passive film. 

Additionally, at higher pressures, the coefficients of thermal conductivity of these deposits gives increasing cause for concern because scales such as serpentine (3MgO2Si02 2H20) may be present and often have particularly poor heat transfer rates. 

As a comparison, Table 4.1 lists the coefficients of thermal conductivity (at room temperature) for some metals employed in heat exchangers, together with some minerals commonly found in boiler deposits. 

Table 4.1 Coefficients of thermal conductivity for some heat-exchanger metals and boiler deposits...

Coefficient of thermal conductivity, 244 Coefficient of thermal expansion (CTE), 280-281... 

Heat is transported through the layers of the ice into the nucleus of the comet. The temperature and rates of heat conduction are controlled by the coefficients of thermal conductivity. 

Nevertheless, encouraging results have been obtained in recent years (see reviews(Bonetto et al, 1961) and the references therein). For example it is now known that in one dimensional systems of the Fermi-Pasta-Ulam (FPU) type (Lepri et al, 1998), heat conduction is anomalous and the coefficient of thermal conductivity k diverges with the system size L as k L2/5 (when the transverse motion is considered n L1/3... 

Heat Conductivity, Specific or Coefficient of Thermal Conductivity (X) is the quantity of heat in gram-calories transmitted per second through a plate of material one centimeter thick and one square centimeter in area, when the temperature differential between the two sides is 1°C. When it is desired to express it in Btu... 

The equation of motion and the equation of energy balance can also be time averaged according to the procedure indicated above (SI, pp. 336 et seq. G7, pp. 191 et seq. pp. 646 et seq.). In this averaging process there arises in the equation of motion an additional component to the stress tensor t(,) which may be written formally in terms of a turbulent (eddy) coefficient of viscosity m(I) and in the equation of energy balance there appears an additional contribution to the energy flux q(1), which may be written formally in terms of the turbulent (eddy) coefficient of thermal conductivity Hence for an incompressible fluid, the x components of the fluxes may be written... 

The coefficient of thermal conductivity can be defined in reference to the experiment shown schematically in Fig. 12.2. In this example the lower wall (at z = 0) is held at a fixed temperature T and the upper wall (at z = a) is held at some higher temperature T + AT. At steady state there will be a linear temperature profile across the gap, with temperature gradient dT/dz = AT/a. Heat will flow from the hot wall toward the colder wall, and the heat flux q is proportional to the areas of the plates, proportional to the temperature... 

According to Jannettaz,6 the thermal conductivity perpendicular to the (111) face of a crystal of metallic arsenic is nearly twice as great as it is parallel to the chief axis. Little7 gives the coefficient of thermal conductivity in absolute units at 20° C. to be 3-68 xlO6. 

Coefficient of Thermal Conductivity or Specif, ic Heat Conductivity ( is the quantity of heat transmitted per second thru a plate of material 1cm thick and 1cm2 in area, when the temp difference between the two sides of the plate is one degree centigrare. Some values are given in Ref and under individual compds described in this Encyclopedia Ref Clift Fedoroff, Vol 2(1943), Table of Physical Constants of Compounds Used in Explosives Industry and Definition of Terms Used in Table of Physical Constants [See also S. Nagayama Y.Mizushima KKK 21, 8-11 (I960) CA 55, 9877 (1961) Explosivst 1964, 2l]... 

The coefficient of thermal conductivity also called specific heat of conductivity is the q uantity of heat in gram calories transmitted per second thru a plate of the material one cm cube, when the temp difference between the two sides of the plate is one degree C (Ref l )... 

We imagine a distribution of a which is characterized by an amplitude o0 and a length scale L which exceeds the maximum scale of the turbulent pulsation, l. We denote the pulsating velocity by u the turbulent coefficient of diffusion, the coefficient of thermal conductivity and the effective turbulent kinematic viscosity are all expressed by the formula k = ul. For an initial uniform distribution of a, obviously,... 

From the technology of combustion we move to the molecular mechanism of flame propagation. We shall give a molecular-kinetic expression for the heat release rate by calculating the frequency v of collisions of fuel molecules with other molecules (v is proportional to the molecular velocity and inversely proportional to the mean free path), further taking into account that only a small (1/j/) part of all collisions are effective. The quantity 1/v—the probability of reaction taken with respect to a single collision— depends on the activation heat of an elementary reaction event, as well as on the fraction of all molecules comprised of those radicals or atoms by means of which the reaction occurs. The molecular-kinetic expression for the coefficient of thermal conductivity follows from formulas (1.2.4) and (1.2.3). 

The initial conditions are at t = 0, T = To, andp = 0. The parameter n characterizes the dimensions of the volume for a parallel plate reactor n = 0 for a cylindrical reactor n = 1 and for a spherical reactor n = 2. In these equations, x is a space coordinate A. is the coefficient of thermal conductivity r is the characteristic size of the reactor k is the heat transfer coefficient and To is the initial temperature of the initial medium. 

High heat conductivity works well if the area over which the fire is impinged is a small part of the total. The low heat-conductive mastic has proved more feasible on a fire over the total area. In order to accomplish low heat conductivity the mastic binder itself must be a poor conductor of heat and preferably nonflowing at high temperatures. The mineral components are selected on the basis of their low k value, the coefficient of thermal conductivity as derived from the following equation ... 

The coefficient of thermal conduction, X, is defined on the basis of the formula ... 

L = %a=%a- (75) The formulas refer (71) to thermal conductance (72) to electric current (73) to diffusion in the two-component mixture (74) to dissolution in the ideal solution (75) to the single-stage chemical reaction. In the formulas k is a coefficient of thermal conductance r is the electric resistance per unit of conductor length D1 is a coefficient of diffusion of substance soluble v and n are the specific volume and the number of moles, respectively Rf eq and Rr eq are the rates of the forward and reverse reactions in the equilibrium state. 

Another well-known example is the coupling between mass flow and heat flow. As a result, an induced effect known as thermal diffusion (Soret effect) may occur because of the temperature gradient. This indicates that a mass flow of component A may occur without the concentration gradient of component A. Dufour effect is an induced heat flow caused by the concentration gradient. These effects represent examples of couplings between two vectorial flows. The cross-phenomenological coefficients relate the Dufour and Soret effects. In order to describe the coupling effects, the thermal diffusion ratio is introduced besides the transport coefficients of thermal conductivity and dififusivity. 

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