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- Elustondo, Diego, et al.
(författare)
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Drying with superheated steam : Maximum drying rate as a linear function of pressure
- 2002
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Ingår i: Chemical Engineering Journal. - 1385-8947 .- 1873-3212. ; 86:1-2, s. 69-74
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Tidskriftsartikel (refereegranskat)abstract
- Drying with superheated steam (SS) as heating agent is controlled through three operative variables, the steam temperature, the recycle velocity, and the system pressure. Once the other conditions are fixed, there is an optimum pressure at which drying rate reaches its maximum value. The exact optimum conditions can be found through a differential mass and energy balance over the heat exchange area, resulting in two equations. The first one to calculate the drying rate as function of the operating conditions and the second one to find the values of those conditions which make the operation optimum. Then, using these equations, this paper shows that the relationship between maximum drying rate and pressure can be rewritten in a unique linear equation. Experiments were performed in a model system to obtain a family of drying rates versus pressure curves, and in accordance with the predicted behaviour, it was observed that all maximum drying rates lay on a straight line
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| 3. |
- Elustondo, Diego, et al.
(författare)
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Mathematical modeling of moisture evaporation from foodstuffs exposed to subatmospheric pressure superheated steam
- 2001
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Ingår i: Journal of Food Engineering. - 0260-8774 .- 1873-5770. ; 49:1, s. 15-24
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Tidskriftsartikel (refereegranskat)abstract
- In this work, a reduced expression to calculate the drying rate of foodstuffs being dried with low pressure superheated steam is developed. It is based on a theoretical drying mechanism which assumes that water removal is carried out by evaporation in a moving boundary making the vapor to flow through the dry layer built as drying proceeds. The theoretical model can be applied to any form and features dimensionless parameters to allow for the influence of form, shrinking effect and boiling point rise. To make the application easier, a simplified expression was derived, which has only two experimentally determined parameters and allows the calculation of the drying rate of a given product. Different foodstuffs were dried with this technique and the empirical parameters were calculated from the experimental data fitting equation. Interestingly, those parameters can be considered constant within the 10000-20000 Pa pressure range and the 60-90°C temperature range
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| 4. |
- Elustondo, Diego, et al.
(författare)
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New thermal conductivity probe design based on the analysis of error sources
- 2001
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Ingår i: Journal of Food Engineering. - 0260-8774 .- 1873-5770. ; 48:4, s. 325-333
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Tidskriftsartikel (refereegranskat)abstract
- The thermal conductivity determination by means of the thermal probe is a classical non-stationary method, suitable for foodstuffs because of the relatively short period of time and the small temperature rise required during experimental measurements. Even though its simplicity, this method has theoretical and practical implicit errors, their main sources being evaluated in this paper. The theoretical analysis shows that experimental errors can be kept within acceptable values, if the testing time period is within certain limits, out of which the errors grow quite rapidly. The error arising from the calculation of the thermal conductivity by means of an approximate equation is studied and a new way to express it is presented. Also, testing times were calculated for different probe dimensions. Finally, on the basis of two former probe which exhibits some advantages upon each other, a new probe design is proposed which recoveries those features.
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