Minimum achievable temperature

Solid CO2, when mixed with organic solvents, provides coohng media of temperatures ranging from — 15°C to — 100°C. Some common mixtures together with the minimum achievable temperatures are shown in Table 5.3. The CO2 and the organic solvent form a slush , which gives excellent contact with flasks and, therefore, efficient cooling. 

Seletskiy, D.V., Melgaard, S.D., Epstein, R.I., Di Lieto, A., Tonelli, M., Sheik-Bahae, M., 2013. Precise determination of minimum achievable temperature for solid-state optical refrigeration. J. Lumin. 133, 5—9. 

For processes under development, the most cost-effective means of avoiding potential risk is to eliminate those materials that are inherently unsafe that is, those materials whose physical or physico-chemical properties lead to them being highly reactive or unstable. This is somewhat difficult to achieve for several reasons. First, without a full battery of tests to determine, for example, flammability, upper/lower explosivity limits and their variation with scale, minimum ignition temperatures, and so on, it is almost impossible to tell how a particular chemical will behave in a given process. Second, chemical instability may make a compound attractive to use because its inherent reactivity ensures a reaction proceeds to completion at a rapid enough rate to be useful that is, the reaction is kinetically and thermodynamically favoured. 

Determine the pinch temperature and the minimum utility requirements for the process set out below. Take the minimum approach temperature as 15 °C. Devise a heat exchanger network to achieve maximum energy recovery. 

Sb precursor Vapor pressure (torr) Minimum achievable growth temperature (alloy grown ) (°C) Comment References... 

The small mismatch between required and achieved minimum operation temperature has the severe consequence that a special preabsorption stage has to be included in the reactor set-up in order to achieve the essential complete conversion. In this manner the partial pressure of the SO3 product is lowered before the last stage of conversion, rendering acceptable incomplete conversion of the overheated catalyst. If the reason why the catalyst docs not operate efficiently down to its solidification point could be eliminated one may circumvent the intermediate absorption stage and thus facilitate the reactor design considerably. 

Make an estimate of the minimum entering temperature at which the reaction will ignite (j.e., achieve a reasonable conversion for a reasonable amount of catalyst). 

Normally, a minimum preheat temperature is required when it is necessary to achieve particular levels of toughness and/or strength in the HAZ or weld metal a maximum value may also be required. Preheat may be local or general. It is recommended that the former should be measured at least 75 mm from the weld line. 

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