Modelling water evaporation during frying with an evaporation dependent heat transfer coefficient

In this study a cylindrical crust-core frying model was developed including an evaporation rate dependent heat transfer coefficient. For this, we applied a Nusselt relation for cylindrical bodies and view the release of vapour bubbles during the frying process as a reversed fluidised bed. The characteristic length and velocity for the Reynolds number are taken as the average diameter of the vapour bubbles and vapour bubble release frequency multiplied with the bubble diameter, respectively. The model assumes limited conductive heat transfer and convective water vapour flow through the crust following Darcy's law. The predictions of temperature profiles and water loss in potato cylinders of different size and at varying frying temperature were found in good agreement with experimental data. Extensions to the crust-core model are suggested to improve prediction of the heat transfer coefficient and water vapour flux; however this should be balanced to keep the model simple for engineering purposes.