Cooling velocity

To freeze a substance, it must be cooled to such a temperature at which the water and the solids are fully crystallized, or at which areas of crystallized ice and solids are enclosed in zones in which amorphous concentrated solids and water remain in mechanically solid state (see Section 1.1.2). In the zone of freezing, the ice crystals are growing first, thus concentrating the remaining solution, which can vary the pH value. In many substances a eutectic temperature can be determined, but in many others this value does not exist. The crystallization depends on several factors which influence each other cooling velocity, initial concentration, end temperature of cooling, and the time at this temperature. In several products no crystallization takes place and the product remains in an amorphous, glasslike phase, or a mixture of both occurs. 

Amount of Heat, Heat Conductivity, Heat Transfer and Cooling Velocity... 

Riehle [1.6] has calculated the theoretically possible cooling velocities for small objects between 1 and 10-3 mm as shown in Figure 1.7. These calculations are made for a substance consisting of water only and Ksu is assumed to be infinitely large for the geometric dimensions shown in (a) a sphere, (b) a square cylinder of infinite length... 

Figure 7 Comparative effects of cooling velocity on the survival of various cells cooled to -196°C and thawed rapidly. The yeast and human red cells (RBC) were frozen in distilled water and blood, respectively. The marrow stem cells and hamster cells were suspended in balanced salt solutions containing 1.25 M glycerin. (From Ref. 22.)...

Figure 10 Survival of S. cerevisiae as a function of cooling velocity. The highest rate indicated is an estimate. Cells were suspended in water in most cases and cooled to -30°C or below. Data are from various sources. The different symbols represent. separate experiments. (From Ref. 21.)...

Fig. 4. Calculated percentages of the original water remaining in 6-M-diameter spherical cells as a function of temperature and cooling velocity. Details on the parameters used in the calculation may be obtained from [ ]. VjVi is the ratio of the water content to the initial water content. Eq is the curve of equilibrium water content. (Reprinted by permission of Journal of General Physiology,)...

With some cells, especially smaller ones, there seems to be an interval of cooling velocities between the two injurious processes, so that an optimum velocity can be chosen... 

Flow Through Safety Rods. The shim-safety rods afso require a cooling velocity of 30 ft/sec through the fuel section. Measurements in a previous experiment indicated a pressure drop of 40 psi for this velocity. Calibration of the Mock-Up rods agreed with this figure. The curve of velocity versus pressure drop is presented in Fig. A4.L. 

We conclude that the cooling velocity in the rapid solidification process has a strong relationship with the reaction velocity and/or the velocity of the movement of solidification fronts, which decides the stable phase under the given conditions. More attention, therefore, should be paid to the reaction velocity of phase formation for controlling the microstructures of the rare-earth permanent magnets. 

The structure of cirrus and PSCs particles is defined by the growth conditions and cooling velocity [1]. Observation of polycrystalline ice particles in the cirrus clouds at T s-83 C and the identification of the conditions of PSC formation have indicated a common mechanism of ice production by submicron water drop freezing [2]. The ice particles in the aircraft contrails are formed by condensation of supersaturation water vapors and followed by fast freezing that can lead to a polycrystalline ice structure. 

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