Mixing scraped surface heat exchanger

Scraped surface heat exchangers (SSHE) have been used as tubular reactors for plastics pyrolysis. SSHE overcome coking and carbon deposits forming on heat exchanging surfaces when the plastic pyrolyzes to hot gases. A tubular reactor with a special internal screw mixer has been developed in Poland [5]. The purpose of the specially shaped internal mixer is to mix the molten plastic and to scrape coke from the internal surface... 

As the mix is frozen and aerated its viscosity increases both because the temperature is decreased and also because ice crystals and air bubbles are formed. The viscosity of an aerated mix increases according to Einstein s equation (equation 2.11) for low air volume fractions. Figure 7.22 shows what happens as an aerated ice cream mix is frozen. The storage modulus, G starts to rise at about — 0.5 C when the first ice crystals form, and continues to increase as the temperature decreases. This data was obtained by using a scraped surface heat exchanger that is simultaneously a rheometer G was calculated from the torque on the dasher. 

Dasher A mixing device that rotates inside the barrel of a scraped surface heat exchanger and to which scraper blades are attached. The dasher has two functions to scrape ice crystals off the barrel wall and to shear the ice cream as air is injected thereby breaking up large air bubbles and mixing in the ice crystals. Dashers may be open (i.e. they occupy a small proportion of volume of the barrel, typically 20-30%)... 

In one continuous method (17), the waxy oil charge—for example, in the case of a topped crude—is diluted with an equal volume of propane and the mixture is chilled to about —25° F. by means of heat exchange with cold filtrate in double-pipe scraped-surface equipment. This chilled mixture is then mixed with propane which has been chilled by autorefrigeration to —45° F. to bring the ratio of propane to oil to about 5 to 1. Ninety per cent of the refrigeration required is accomplished in this manner the remaining 10% is obtained by evaporating propane from the diluted mixture. 

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