Contents 4 Temperature gradient

The dewpoint for the flue products from gas is a maximum of 60°C and will, in most cases, be lower because of excess air. There is no acid dewpoint because the sulfur content is negligible. It would be thought that condensation would be most unlikely, and this is so for the bulk flue gases. However, the temperature gradient across the flue wall can be such that the skin temperature at the inside wall can be considerably less than the bulk temperature, and condensation will take place. 

The reasons for such a layered structure are, in our view [20, 21], the lateral temperature gradients that are observed when the extrudate is cooled upon leaving the channel and lateral pressure gradients. The resultant effect of both gradients determines layer order in the flow with intermittent gas content (0.5 to 1 %). The lateral pressure gradient is conditioned by normal stresses in the flow. This was discussed in [8, 9]. 

Wherever heat is involved temperature also fulfils an important role firstly because the heat content of a body is a function of its temperature and, secondly, because temperature difference or temperature gradient determines the rate at which heat is transferred. Temperature has the dimension 9 which is independent of M,L and T, provided that no resort is made to the kinetic theory of gases in which temperature is shown to be directly proportional to the square of the velocity of the molecules. 

The level of vapor movement in the unsaturated zone is much less important than transport in liquid form. However, this might not be true if the water content of the soil is very low or if there is a strong temperature gradient. The movement of vapor through the unsaturated zone is a function of temperature, humidity gradients, and molecular diffusion coefficients for water vapor in the soil. 

Next we look at how temperature gradients along an aquifer might affect the silica content of flowing groundwater. We consider a symmetrical aquifer that descends from a recharge area at the surface to a depth of about 2 km and then ascends to a discharge area. Temperature in the calculation varies linearly from 20 °C at the surface to 80 °C at the aquifer s maximum depth. 

Owing to vertical (turbulent) diffusion, heat is transported from regions of warm water to adjacent colder layers. Mathematically this appears as a heat flux against the vertical temperature gradient (remember Fick s first law, Eq. 18-6). Thus, at a later time, ti+u we expect to find warmer water between z and zB. The change of the heat content with time A is ... 

B12 Cell B12 contains the value of the Nusselt number, which is the nondimen-sional temperature gradient evaluated at the stagnation surface. The contents of B12 is computed as =(E48-E47) /dz. 

Agitated jacketed vessel the main resistance to heat transfer is located at the wall, where there is practically no resistance to heat transfer inside the reaction mass. Due to agitation, there is no temperature gradient in the reactor contents. Only the film near the wall presents a resistance. The same happens outside the reactor in its jacket, where the external film presents a resistance. The wall itself also presents a resistance. In summary, the resistance against heat transfer is located at the wall. 

The heat flow dissipated by the central heater is then calculated by measurement of current and voltage (see section 9.3). The thermal conductivity is then computed based on the heat flow, temperature gradient, and known radial distances. The outer furnace then heats the contents to a higher (e.g. 100°C) temperature and the process repeats. The thermal conductivity of the specimen as a function of temperature is thus determined by a series of isothermal steps. 

From equation 7, it may be seen that the tendency toward constitutional supercooling increases as the freezing rate increases, the temperate gradient G decreases, the impurity content w increases, the separation (w i) between Hquidus and soHdus in the phase diagram increases, and the stirring decreases (5 increases). This explains why zone melting is limited to purification of materials with low impurity contents, and why substantial temperature gradients and low zone-travel rates are necessary. 

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