E. de los Reyes

Control of citrus surface drying by image analysis of infrared thermography

Citrus surface drying is one of the most important unit operations in a fresh fruit processing plant. A common risk in citrus surface driers (CSD) is using an excessive air temperature or keeping the fruit in the drier too long, since an important loss in sensorial quality may occur as well as a decrease in the fresh fruit shelf life. Nowadays, most of the new CSD use systems to control air temperature, but do not include elements to monitor the process by defining the required drying time. A new system to control the surface drying time by image analysis of the fruit surface temperature distribution, using infrared techniques was tested. The control of fruit surface temperature during drying allowed us to determine the moment when the surface drying finishes and the peel drying begins. Oranges (var. Valencia Late) washed with water or covered with a commercial wax were dried at 20, 25 and 35 °C with 1, 1.5 and 2 m/s air velocities. During the first drying step the lowest surface temperature of the fruit was measured from infrared images captured with an AGEMA 470 camera and was assumed to be the wet bulb temperature. Drying time could be well established when temperature at any point on the fruit surface exceeded this value. An empirical model was developed to correlate drying times with air conditions. Parameters of the model may be used in control systems for industrial CSD equipment.

Heat flux and heat generation characterisation in a wet-laminar body in microwave-assisted drying: an application to microwave drying of leather

Heat fluxes through a laminar body have been modelled from a parabolic temperature distribution assumption when the material is irradiated with microwaves and immersed in a convective air flow. The heat equation has been analysed and a relationship between thermal conductivity, temperatures and net heat flux through the material surface has been established. This study has been successfully applied to leather hides when they are dried in a combined microwave-hot air oven. With regard to the development of this work, dielectric and temperature measurements have been demonstrated to be of the utmost importance.

A new empirical method for extracting unloaded resonant frequencies from microwave resonant cavities

Equivalent circuits traditionally used to model resonators and coupling networks in the vicinity of a resonance provide values of unloaded resonant frequencies which usually do not agree with experimental results. A new empirical method for the extraction of influence of coupling networks on resonant cavities is presented. The characterization of coupling structures is performed directly from measurements without the need of obtaining the electromagnetic fields inside the cavity, which is very interesting from a practical point of view. Results are validated with simulations and experimental measurements. The accuracy of some cavity applications, such as dielectric characterization techniques can be directly improved with this approach.

Continuous monitoring of the progressive degradation of a liquid composite by means of a noninvasive microwave resonator

Microwave control capabilities have been used to monitor the degradation of polyol, an alcohol composite material commonly used in the footwear industry for polymerization purposes. The liquid flows continuously inside a thin pipe and its desirable properties are altered with time associated to moisture absorption processes. Consequently, variations in the dielectric properties are involved, and they can be detected by permittivity measurements. In this paper, in order to obtain high sensitivity and resolution, a rectangular cavity resonator working at a fixed frequency was designed using as sample holder a rectangular pipe containing the liquid going through. Changes in the liquid modify the original response of the cavity with a non- degraded liquid and these differences have been used to determine the degree of degradation of the material. The final response of the microwave resonator was experimentally validated with measurements in a continuous line.

Susceptibility Analysis of Arbitrarily Shaped 2-D Dielectric Screens using the Generalized Scattering Matrix Method

The EMS inside slotted screens has been studied by using a hybrid technique. The screen is characterized, using the FEM, by a generalized admittance or impedance matrix, from which the scattering matrix can be straightforwardly obtained. The scattering matrix is then combined with a modal solution to compute the fields inside and outside the envelope. This circuital approach provides a systematic procedure for the analysis of very complex open structures.

Wood timber disinfestation by microwave power application

Different durations to treat bulk timbers have been assessed. The investigation is based on wood timber samples, woodworm larvae and a circular antenna prototype. The research establishes an initial treatment duration, measures the temperature at such duration and estimates durations and extermination rates at different depths. The current results demonstrate that he heating is more homogeneous in overlapped radiation and the treatment duration is strongly related to timber thickness or treatment depth. The treatment duration ranged from 20 to 50 seconds depending on application method and the applied power.

On the Feasibility of a Bistatic Radar for Detecting Bad Road Conditions

In this paper a study on the feasibility of a bi static radar system for bad road conditions, including water, snow and ice, is presented. First of all, the most suitable frequency is chosen among all the frequencies available for such a system from a regulatory point of view. Then, the best mathematical model for predicting the electromagnetic behaviour of different layers of water, snow or ice over an asphalt basis is presented. The numerical study is focused on the reflexion attenuation (the difference between the direct and the reflected signal levels). Results for linearly polarized waves are presented and some useful design guidelines are presented.