Fac-simile Scheda Linee di Ricerca - Federalimentare

This practice is actually aimed to check and set sterilization plants in which layout is already defined but itwould be desirable to extend this approach to plant design. This procedure, put on plant design, would allow toapply optimized processes with large decrease of product thermal damage.8. Rozzi S., Massini R., Paciello G., Pagliarini G., Rainieri S., Trifirò A. (2007) Heat treatmentof fluid foods in a shell-and-tube heat exchanger: comparison between smooth and helicallycorrugated wall tubes. J. of Food Engineering 79, 249-254Fluid foods are often subjected to thermal treatment inside surface heat exchangers. Besides the need for highheat transfer performance, also low friction losses and easy cleaning and sanitizing properties of the surface areimperative. In food process industry these requirements are often met by the shell and tube heat exchangerequipped with helically corrugated walls. The present work concerns convective heat transfer and friction lossesin helically enhanced tubes for both Newtonian and non-Newtonian fluids. Four fluid foods, namely, whole milk,cloudy orange juice, apricot and apple puree, are tested in a shell and tube heat exchanger. Both fluid heating andcooling conditions are considered. The experimental outcome confirms that helically corrugated tubes are particularlyeffective in enhancing convective heat transfer for generalized Reynolds number ranging from about800 to the limit of the transitional flow regime.9. Rinaldi M., Trifirò A., Rainieri S., Bozzoli F., Massini R. (2005) An experimental approachfor the estimation of apparent thermal diffusivity in frozen food. Proceedings of the EurothermSeminar 77 – Heat and Mass Transfer in Food Processing, June 20-22 2005 Parma,Ed. EPS, Pisa 2005, 117-122.The thermal diffusivity value can be determined theoretically, by the weighted sum of thermal properties of eachfood component or experimentally, by elaborating heat penetration curves for thermal diffusivity calculation.However, both methods can’t be directly applied to freezing or thawing treatments, because the water/ice ratiowill continuously change and a correspondent latent heat is released or absorbed. Freezing and thawing tomatopuree thermal diffusivity values were obtained by using a finite differences mathematical method. However,within the freezing or thawing range, thermal diffusivity values presented a linear trend versus samples temperature.From DSC data the ice content inside the sample was calculated for each temperature step of the experimentalthawing tests, and an empirical function between thermal diffusivity and temperature was developed. Byusing thermal diffusivity values corrected for temperature, it was possible to simulate temperature history insidethe samples with good accuracy.10. Rinaldi M., Betta G., Chiavaro E., Barbanti D., Massini R. (2005) Experimental determinationof thermal diffusivity using a numerical technique to solve heat tranfer equatio in conductivefoods. Proceedings of the Eurotherm Seminar 77 – Heat and Mass Transfer in FoodProcessing, June 20-22 2005 Parma, Ed. EPS, Pisa 2005, 111-115The use of mathematical models for optimizing of thermal processes is fast and low-cost, but it is necessary toknow thermal properties with good approximation because they are the most important input. Generally, in foodstuffsthe value of thermal diffusivity (α) strictly depends on cell structure, intracellular air content, water content,operating pressure and temperature; it varies also along system directions cause of physical anisotropy andcomposition heterogeneity. Numerical simulation is the best way to obtain thermal diffusivity data from experimentaltime-temperature data. An hardware-software apparatus for the calculation of the thermal diffusivity ofconductive foods on the basis of experimental data was developed. The proposed method allows to calculate theα value even in cases for which Ball & Olson equation is not applicable. We were able to determine “only product”thermal diffusion values for a tomato puree and starch suspension in agree to the Singh’s theoretical ones.For potatoes samples it was been possible to correlate the thermal diffusivity values with the recorded relativehumidity obtaining an “effective diffusion coefficient” useful for cooking simulation. The proposed method issimple and reproducible and could be an alternative of traditional methods but the accuracy of the calculationstrongly depends on the thermocouples positioning errors along the radius of the container.SISTAL - SOCIETA’ ITALIANA DI SCIENZE E TECNOLOGIE ALIMENTARIDipartimento di Scienze e Tecnologie Agroalimentari, Università degli Studi della TusciaVia San Camillo de Lellis, 01100 ViterboTel.: 0761- 35 74 94/7 , Fax: 0761- 35 74 98, e-mail: mmoresi@unitus.it345