Heat gradient

In areas of the system where the heat gradient is less severe, calcium carbonate precipitates in both crystalline and amorphous forms. It may precipitate as a calcite or aragonite sludge, but more usually an aragonite scale is produced. Aragonite is hard and adherent, depositing in FW lines and various boiler surface components such as boiler tubes. 

The latitudinal heat gradient in the atmosphere and ocean remains relatively constant over time despite the short-term and spatial variations in insolation. This steady state is maintained by the net transport of heat from low to high latitudes where it is radiated back into space. Atmospheric currents (winds) are responsible for about half of this meridional net transport of heat. The rest is accomplished by water movement in the... 

The story of the Sun, and indeed of any star, centres around the age-old struggle between the nuclear furnace and gravity. The pressure due to heat, or rather heat gradient, fights back against collapse and a masterful equilibrium is achieved. The vocation of the perfect star is to burn, in the nuclear sense, that is, to transmute elements in nuclear reactions. 

In bulk water portions of the cooling system, where the heat gradient is less severe, calcium carbonate will tend to precipitate in both crystalline and amorphous forms. 

FIGURE 6.25 Experimental setup for measuring heat gradient in an intumescent coating for a cone calorimeter experiment at the beginning of the experiment (a) and at the steady state (b). 

Example A spring of 62 °C emerges in a region with an average annual surface temperature of 22 °C. The local heat gradient has not been measured, hence the value of 3°C/100m may be applied. The depth of circulation is... 

Groundwater that is more than 6°C above local average annual surface temperature circulates to appreciable depths, deducible from the heat gradient (section 4.7). 

The closed system conditions seen in cold groundwater systems may be further checked in warm springs, that is, in waters that are trapped at a depth of 1-2 km and get heated by local (normal) heat gradients. The first study of this type was done on warm springs and wells (up to 60 °Q of the Jordan Rift Valley (Mazor, 1972). The isotopic compositions of the encountered dissolved Ne, Ar, Kr, and Xe were found to be atmospheric, that is, very close (in the range of the analytical accuracy) to the values given in Table 13.2. 

Example The water of the Taninim spring is seen in Table 13.6 to emerge at 23.5 °C, whereas the noble gas deduced temperature at the base of the aerated zone is 21 + 1 °C. How can this difference be explained The additional 2.5 °C resulted from equilibration of the aquifer temperature. The local heat gradient is not known, so let us use the common value of 3 °C/ 100 m. Accordingly, the water circulated to a depth of 80 m or more in the saturated zone. (It might be more because partial cooling during ascent could occur). 

Answer 13.4 As it is a coastal spring and nothing is known about the recharge area, no altitude correction is to be applied. The intake temperature may be directly read from the argon concentration from Fig. 13.1. The outcome 12 °C. Hence, the water was heated 32 °C — 12 °C = 20 °C. As the local heat gradient is not known, we shall use the common value of 3°C/100m. Accordingly, the minimum depth of circulation is 20 x 100/3 = 660 m. 

Different kinds of driving forces tend to bring about different kinds of change. For example, imbalance of meehanical forces such as pressure on a piston tend to cause energy transfer as work temperature differences tend to eause the flow of heat gradients in chemical potential tend to cause substances to be transferred from one phase to another. At equilibrium all sueh forees are in balance. 

One easy extension of equilibrium molecular dynamics is the computation of the properties of condensed matter systems in the presence of external fields. Many experiments are done by applying an external field, whether it be an electric field, heat gradient, or some type of flow. Usually, the experimentalist waits some time for the system under investigation to reach a steady state in the presence of the applied field. Measurements are then performed to deduce structural or dynamical information. Performing this task on a computer is what is commonly known as nonequilibrium molecular dynamics (NEMD). It is nonequilibrium in the sense that, in the presence of an external field, the system at the steady state will be in a state of lower entropy. Upon removing the external field, the system will return to the state of maximum entropy or the equilibrium state. 

When desorption of ammonia starts, the rate increases exponentially with temperature (see Fig. 19.3). The exponential increase stops one-third of the way towards the peak maximum, due to the development of a heat gradient... 

In most lakes the distribution of dissolved substances is dominated by transport due to turbulent motions. Mixing in the horizontal direction is rapid, resulting in nearly homogeneous concentrations horizontally. In the vertical direction, density stratification suppresses turbulence, thus reducing vertical exchange of dissolved substances and heat. As a consequence vertical concentration and heat gradients can build up. Because density stratification varies seasonally, vertical mixing varies substantially over the year. 

TEIAMES was developed originally by Ohnishi et al. (1987) to simulate the coupled THM behaviour in rock media, and later extended to simulate the coupled THM behaviour of a saturated-unsaturated buffer by adding function of taking into account unsaturated water movement by heat gradient in the buffer by Chijimatsu et al. (2000) and swelling characteristics by Komine et al. (2003). 

As a result of these heat gradients it has been found that ceramic fuel elements may melt in the center (2865 °C mp for pure UO2) at high loading even though the surface temperature is much below the melting point. High c iter temperatures, especially in... 

Temperature Apparent mean thermal Total heat gradient conductivity Xa, flux... 

The unclogging temperature is obtained on the heating gradient of the clogging indicator pellet This gradient is reached when the flow in the pellet reaches 55% of the initial flow and terminates when the high temperature level has been reached... 

In industrial plants, generally all essential heat inputs for calculating the absorbed heat Qch are recorded, so that the radiated heat Qp can be estimated by equation (3). The effective heat being absorbed or radiated by each tray is a function of the heat gradient. The circumstance of high heat radiation at the top of the column is also considered by this model. 

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