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Coupling crystallization-foaming within a scraped surface heat exchanger during sorbet production.

Couplage cristallisation-foisonnement au sein d’un échangeur de chaleur à surface raclée lors de la production de sorbet.

Author(s) : HERNANDEZ PARRA O.

Type of monograph: Doctoral thesis

Summary

During sorbet production, a crucial step is the initial freezing in a scraped surface heat exchanger (SSHE), whose main goals is to generate small ice crystals (by crystallization) and air bubbles (by foaming) to obtain a product with a smooth texture. The crystallization-foaming coupling undertake diverse interactions which lead to a modification of the product in terms of flow, mixing, phase change, heat transfers and rheology, which in turn, can affect the crystallization mechanisms and therefore the size distributions.The objective of this thesis is to provide a better knowledge of the mechanisms involved during crystallization and simultaneous foaming in an SSHE and their impact on the structural and textural properties of the final product. This thesis made possible a better understanding the phenomena induced by the foaming on the crystallization processes during the manufacture of sorbet in an SSHE, thanks to a combined approach of experimentation and modeling.The study of the influence of the operating conditions of the freezing process on the size distributions of ice crystals and air bubbles was carried out through the development of a discriminatory granulometry technique using a refrigerated glove box. It demonstrated the strong coupling between the mechanisms of crystallization and foaming.The overall characterization of the flows within the SSHE was made through an experimental and numerical study of the residence time distribution (RTD) during the simultaneous process of crystallization and foaming. In particular, the RTD revealed the presence of an almost stagnant air pocket inside the heat exchanger.A 3D digital flow model was developed to study the thermal transfer flow coupling in the absence of air. It made it possible to highlight recirculation zones which can influence the transfers and the dynamics of air bubble formation.Another model based on local air bubble fragmentation mechanisms has been developed using a CFD approach. It allows, as a first approach, to identify the zones of formation of the first air bubbles and to predict the order of magnitude of the size of the largest air bubbles.

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Pages: 211 p.

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Details

  • Original title: Couplage cristallisation-foisonnement au sein d’un échangeur de chaleur à surface raclée lors de la production de sorbet.
  • Record ID : 30032277
  • Languages: French
  • Subject: Technology
  • Publication: AgroParisTech - Antony - France
  • Edition statement: Institut agronomique, vétérinaire et forestier de France
  • Publication date: 2018/11/13

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