S. Yanniotis

Air humidification for seawater desalination

This paper presents the study of two types of air humidifiers, namely a tubular spray humidifier and a pad humidifier. These two humidifiers were studied as a part for a multiple stage solar desalination process. Comparative experimental results for the evaporation capacity of both humidifiers are presented for different operating conditions of air and seawater flow rate, air and seawater temperature and dimensions of equipment. Some results of a CFD simulation of the pad humidifier are also presented.

Analysis of thermal processing of table olives using computational fluid dynamics.

In the present work, the thermal processing of table olives in brine in a stationary metal can was studied through computational fluid dynamics (CFD). The flow patterns of the brine and the temperature evolution in the olives and brine during the heating and the cooling cycles of the process were calculated using the CFD code. Experimental temperature measurements at 3 points (2 inside model olive particles and 1 at a point in the brine) in a can (with dimensions of 75xa0mmxa0× 105xa0mm) filled with 48 olives in 4% (w/v) brine, initially held at 20xa0°C, heated in water at 100xa0°C for 10xa0min, and thereafter cooled in water at about 20xa0°C for 10xa0min, validated model predictions. The distribution of temperature and F-values and the location of the slowest heating zone and the critical point within the product, as far as microbial destruction is concerned, were assessed for several cases. For the cases studied, the critical point was located at the interior of the olives at the 2nd, or between the 1st and the 2nd olive row from the bottom of the container, the exact location being affected by olive size, olive arrangement, and geometry of the container.

Numerical Simulation of Variable Water Diffusivity during Drying of Peeled and Unpeeled Tomato

UNLABELLEDnA mathematical model was formulated for the estimation, in conjunction with experimental measurements, of water diffusivity parameters during convective drying of peeled and unpeeled tomatoes. Ficks 2nd law of diffusion was solved numerically for a sphere, by explicit finite differences, considering shrinkage effect, variable diffusivity, and constant boundary conditions. Experiments were performed in a laboratory tunnel dryer. The equivalent radius of tomato decreased by 50% until the end of the process, which explains the necessity for shrinkage inclusion in the mass transfer model. The mean estimated diffusivities varied between 2.03 × 10(-10) and 15.1 × 10(-10) m(2)/s for peeled tomatoes and 0.59 × 10(-10) and 15.2 × 10(-10) m(2)/s for unpeeled tomatoes. The estimated water diffusivities and their variation with the tested drying temperatures (45, 55, and 65 °C) provide an insight of peeling effect during air-drying. Peeling was beneficial since yielded greater drying rates and shortened significantly drying times, thus saving energy during drying. In all the studied cases, good agreement was found between experimental and predicted drying curves (≥ 0.99, mean relative deviation [MRD]≤ 0.12, and root mean square error [RMSE]≤ 0.03). In overall, the proposed methodology provides a reliable and easy estimation of temperature and moisture-dependent mass transfer properties and drying simulation of shrinkable food products such as tomato.nnnPRACTICAL APPLICATIONnWater diffusivity is a food property, difficult in estimation but essential in drying processing optimization. This property was estimated as a function of moisture content and drying temperature employing a numerical simulation procedure. The peeling effect was also studied and found beneficial for lower temperature drying (<55 °C) which is useful in the energy optimization of the drying process as well as the retention of the end-product quality.

Energy consumption of absorption-driven multiple-effect evaporators

Abstract Theoretical and experimental studies of absorption-driven multiple-effect evaporators were carried out. Theoretical predictions for such units were compared with existing industrial-scale conventional evaporators. It was calculated that the total energy consumption of an absorption-driven evaporator is considerably lower than that of a conventional multiple-effect evaporator. Theoretical predictions were also verified with an experimental four-effect absorption-driven evaporator, coupled with a two-effect regenerator, using sodium hydroxide solution as the absorptive medium. Energy savings of 30% to 45% were obtained.

Pistachio deterioration detected by X-ray absorption.

Proshlyakov A., Yanniotis S., Blahovec J. (2013): Pistachio deterioration detected by X-ray absorption. Czech J. Food Sci., 31: 126–131. The measurement of the absorption coefficient of X-rays in healthy and fungus infected pistachio kernels was the main objective of this work aimed at detecting the potential injury by insects and/or fungi in the kernel. It was found that the absorption coefficient in the injured parts is about half of that in the healthy parts. The absorption coefficient is also affected by the position in the kernel due to the variations in cell dimensions and the oil and moisture contents in the kernels.