Cooling, natural

Control of supersaturation is an important factor in obtaining crystal size distributions of desired characteristics, and it would be useful to have a model relating rate of cooling or evaporation or addition of diluent required to maintain a specified supersaturation in the crystallizer. Contrast this to the uncontrolled situation of natural cooling in which the heat transfer rate is given by... 

Vk, Vk2 and Vk (W. when considering the outdoor part) can thus be determined. The total heal, Vk, so generated can be naturally dissipated through the enclosure by radiation and convection. If natural cooling is not adequate, forced cooling can be adopted through forced air or water. But precautions must be taken to ensure that the system is protected from absorbing dirt, dust or moisture from the atmosphere. 

The rate of natural cooling is proportional to the surface area of the vessel and is represented by... 

The predicted transient supersaturation levels (and corresponding nucleation rates) are also shown in Figure 7.3. These considerations predict that the high levels in the early period of natural cooling can be avoided by controlled cooling. 

Although programmed cooling crystallization clearly results in a larger mean crystal size than that from natural cooling it is also evident that some fines i.e. small crystals are also present in the product. Since the solution was seeded these fine crystals must clearly have arisen from crystal attrition or secondary nucleation (see Chapter 5). 

Selbst-kosten, f.pl. cost of production, prime cost. -kUhlung, /. self-cooling, natural cooling. -laut, -lauter, m. vowel. 

The availability of very small areas of control can be advantageous where electronic apparatus with mild chimney effect would have its natural cooling upset by strong downdrafts, by confining air supply to gangways. 

The product crystal size from a batch crystalliser can also be controlled by adjusting the rates of cooling or evaporation. Natural cooling, for example, produces a supersaturation... 

For illustrative purposes, consider that the protocol for a cooling crystallizer can involve either natural cooling— cooling resulting from exposure of the crystallizer contents to a heat sink without intervention of a control system—or manipulation of cooling to reduce the system temperature in a specific manner. In both cases, the instantaneous heat-transfer rate is given by ... 

H. Ottinger, A. Bareth, and T. Hofmann, Characterization of natural cooling compounds formed from glucose and L-proline in dark malt by application of taste dilution analysis, J. Agric. Food Chem., 2001, 49, 1336-1344. 

In California, temperatures of the secondary fermentation range from 10° to over 25° C in different wineries. Cool, slow fermentations are preferred by some, and warm, quick fermentations by other wineries. Bottle-fermented processors commonly chill the cuvee to 10°-15° C before bottling. One cellar is temperature controlled to 10°-13°C and another at 18° C. Other cellars are naturally cool summer and winter. Unfortunately, a few cellars are not temperature-controlled or well-insulated, and the temperaures can vary from 10° C in winter to as high as 22° C in summer. Bulk wine processors may or may not chill the cuvee before fermenting in insulated tanks. Most do not chill during fermentation and report temperaure increases of 3°-8° C (theoretical is about 3° C). 

Pyrolysis conditions Heating al 24 "CVmin until 500 ° C. held for 30 min. natural cooling. ... 

Figure4.14 Atypical rapid thermal anneal temperature program, which consists of a stabilization step and a spike-anneal (i.e. a fast linear heating step followed by a natural cool down step).

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