The presence of suspended particles in solutions significantly affects the crystallization rate. This study investigates the effects of calcium sulphate (crystallizing) particles and alumina (noncrystallizing) particles on calcium sulphate crystallization fouling in a plate heat exchanger. Calcium sulphate particles are formed during the preparation of calcium sulphate solution due to breakage of calcium sulphate crystals growing on the heat transfer surface. These suspended particles settle on the heat transfer surface and act as nuclei. The availability of extra nucleation sites increases the crystallization rate significantly. These particles can be removed with a filter, and the removal of the particles prevents this extra assistance available for crystallization. Therefore, the crystallization rate is reduced markedly. Alumina particles were purposely added during the preparation of calcium sulphate solutions. These particles attach loosely to the heat transfer surface compared with crystalline deposits which adhere strongly. Therefore, calcium sulphate crystals growing on these particles are removed easily. Also, alumina particles settling on the growth faces of calcium sulphate crystals may act as a distorting agent. This slows down the growth of the crystals.
This paper examines the problem of maximising the productivity of a class of fermentation processes described by an unstructured fermentation process model. For a given dilution rate, an extremum seeking adaptive control has been used to maximise the productivity of a fermentation process. The concept behinds the extremum seeking method is to iteratively adjust the feed substrate rate in order to steer the process to yield a maximum productivity. The main advantage of the extremum seeking adaptive control is it does not require any structural information of the modeling uncertainty.
SUMMARYShort electric band heaters (¸/D (1.5) are constructed for the ease of implementation in small scale heating applications. They are usually mounted side-by-side in series along the external wall of a pipe for heating the #uid within the pipe. There are no rules-of-thumb available about designing such a system to achieve good uniformity of the temperature pro"le at the pipe inner surface beforehand. Non-uniformity can cause preferential fouling at hotter spots. This study focuses on the axial uniformity of heating along a pipe inside which the heated #uid if #owing. The situation has been simpli"ed a great deal in mathematical terms from the corresponding conventional conjugate problem considered previously due to the small temperature rise in the #uid #ow through one section of the pipe which is heated by one band heater. Similarity parameter sets have been deduced and veri"ed by numerical simulations. The worst scenario of non-uniformity for such short band heaters, that is when¸/D "1.5, is presented in this paper. This may be used for designing a system to minimize the non-uniformity in terms of choosing the right pipe material, percentage of heater wire coverage in the band heater, etc.
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