The mechanical effects of short-circuit currents in open air substations.

SHort-circuit mechanical effects in substation is investigated by tests and simulations. Simplified equations are deduced to prepare standardisation of a procedure forthe design of substation against short-circuit mechanicle effects

Modeling of drying thin layer of tomato slices using solar and convective driers

This paper presents a mathematical modelling of thin layer drying of tomato (Solanum lycopersicum L.). To this end, two different methods are used to dehydrate tomato slices namely the solar drying (in an indirect solar dryer), and the forced convective drying (in a convective dryer). In the solar dryer, the experiments are carried out at a constant air velocity of 1 m/s and average temperatures of 37.2, 39.9, 42.5 °C. In the convective dryer, the experiments are performed with five different temperatures (30, 40, 50, 60 and 70 °C) at a constant air velocity of 1 m/s. In order to estimate and select the appropriate drying curve equation, fifteen different thin layer mathematical drying models available in the literature are applied to the experimental data. The models are compared using the correlation coefficient (r) and the standard error (s) and are predicted by a non-linear regression analysis using the Curve Expert software. The Midilli-Kucuk model shows a better fit to the experimental drying data according to (r) and (s) for the two drying methods. The effect of the drying temperature on the parameters of this model is also determined. The experimental drying curves show only a falling drying rate period. On average, tomatoes are dried until the moisture content of 0.15 kg water/kg dry matter from 14.36 kg water/kg dry matter in the solar drying, and to the moisture content of 0.10 kg water/kg dry matter from 12.66 kg water/kg dry matter in the convective drying.

IMPACT OF SLUDGE CONDITIONING ON MECHANICAL DEWATERING AND CONVECTIVE DRYING

Management of sludge produced within wastewater treatment plants hasbecome a key issue. After thickening, the removal of remaining water using mechanicaldewatering and/or thermal drying is essential before any type of valorization. Polymersare usually employed in the conditioning step in order to promote particle aggregation,making the dewatering easier. In this work the impact of the polymer dosage and natureon dewatering and convective drying of sludge is studied. Results clearly show the impactof conditioning on dewatering performances, however no effect on drying has beenobserved within the range of tested experimental conditions

apis 1 -Automatic Production of Information Systems

The objective of the apis research project is to develop a case tool that generates executable information systems (IS) from formal specifications (abstract models). In other words, apis aims at automating as much as possible the production of IS by lifting the level of abstraction at which software designers work. Instead of spending most of their time designing, programming and testing at a very low level of abstraction, software designers will be able to concentrate on specifying and validating; the apis case tool will take care of generating an executable system from the specification. The foundations of the case tool are abstract models of IS (formal functional specifications) and algorithms that generates an executable system from these models (modelbased interface development environment -MB-IDE), and specification interpretation. The apis project has to a) define a comprehensive set of integrated models for information systems, b) develop new algorithms for specification interpretation and code generation, and c) implement them in a case tool. The eb 3 specification language will be the foundation for the models The apis project will be the first to study the automation of information systems production from formal specifications. The success of the apis project would represent a significant breakthrough in terms of productivity and quality in IS development. apis could cut up to 50 % of the cost of IS development, because it would relieve software designers from design, programming and testing. Consequently, it would also avoid faults introduced during these activities. Background and Related Work Information Systems IS are generally characterized by large data structures which are modified or queried by several users in concurrency. The difficulty of these systems typically resides in managing complex relationships between data structures, in complex calculations involving several data structures, in processing large volume of data, and in preserving data integrity through concurrent updates by several users. IS typically have little hard real-time constraints or interprocess communication. An IS can be decomposed in three parts: i) the functional behavior (also called business logic), ii) the user interface , and iii) the database. The functional behavior defines the transactions of the system, which are of two types: a) update transactions modify the internal state of the system which is stored in a database, b) inquiry transactions display information about the system state (database). The recent technological developments in IS mostly apply to the programming phase. Database management systems (DBMS), key elements of IS, now offer sophisticated distribution and concurrency control mechanisms, support very large databases, and offer sophisticated querying facilities. Technical breakthroughs like INTERNET, JAVA, CORBA, COM, EJB, frameworks and others make it easier to program distributed information systems or deploy them on the web on various platforms. Some DBMS case tools can generate forms to update-modify-delete records in a table, but this is insufficient to build a real GUI for an information system. 1 Egyptian mythology -a god depicted as a bull, symbolizing fertility and strength in war [OED]. Drawings by Pablo Picasso, 1945

Convective drying of cherry tomato: Study of skin effect

A whole single cherry tomato is dried in a forced convective micro-dryer. The experiments are carried out under temperatures of 50, 60, 70 °C and a constant air flow and humidity. In order to study the effect of the skin two sets of experiments were performed using original tomatoes or after skin was handly removed. The drying kinetics show the existence of two main phases, which are: adaptation phase and falling drying rate phase with an increase of the drying rate with the temperature increase. The observation of the product behavior shows that shrinkage effect is largely happening during the process. It is possible to follow this effect represented by variation of the product volume with its moisture content using X-ray microtomography. This non destructive imaging technique has been proved to find interesting applications in the drying field. In a second part, mathematical modeling using diffusion equation based on Fick’s law is studied. Consequently and using the analytical solutions proposed by Crank (1975), the diffusion coefficient is determined and written as function of the drying air temperature under Arrhenius form permitting by this way the calculus of the activation energy. The skin effect is clearly determined as the calculated diffusion coefficient of an original tomato with skin is largely smaller than the one without skin

ISOTHERMS AND ISOSTERIC HEAT OF DESORPTION OF WATERMELON FRUIT

In this paper, a new unpublished study on the watermelon fruit is presented. It concerns the experimental determination of the water desorption isotherms at three different temperatures, using the dynamic method requiring the Dynamic Vapor System device (DVS). In order to select the appropriate desorption curve equation, 11 different models available in the literature were applied to the experimental data. The models were compared using the correlation coefficient, the standard error, the reduced chi-squared, the mean bias error and the root mean square error; they were predicted by a non-linear regression analysis using the Curve Expert software. The effect of the temperature on the constants of the found equation is also examined. Finally, the desorption isosteric heat of watermelon is determined using the Clausius-Clapeyron relation. Contrary to long times taken in the static method, the results show that 4.5 days are widely sufficient to reach the equilibrium via the DVS device. In addition, the obtained curves are of the type III and the Henderson model is the most appropriate model representing them. In the interval 0.05 - 0.45 kg of water/kg d.m of equilibrium moisture, the values of the isosteric heat vary from 65.02 to 113.25 kJ/mol. Finally, the equation giving the isosteric heat of desorption v.s. the equilibrium moisture content is obtained

Modeling of drying thin layer of tomato slices using solar and convective driers

peer reviewedThis paper presents a mathematical modeling of thin layer drying of tomato (Solanum lycopersicum L.). To this end, two different methods are used to dehydrate tomato slices namely the solar drying (in an indirect solar drier), and the forced convective drying (in a convective drier). In the solar drier, the experiments are carried out at a constant air velocity of 1 m s-1 and average temperatures of 37.2°C, 39.9°C and 42.5°C. In the convective drier, the experiments are performed with five different temperatures (30°C, 40°C, 50°C, 60°C and 70°C) at a constant air velocity of 1 m s-1. In order to estimate and select the appropriate drying curve equation, fifteen different thin layer mathematical drying models available in the literature are applied to the experimental data. The models are compared using the correlation coefficient (r) and the standard error (s) and are predicted by a non-linear regression analysis using the Curve Expert software. The Midilli-Kucuk model shows a better fit to the experimental drying data according to (r) and (s) for the two drying methods. The effect of the drying temperature on the parameters of this model is also determined. The experimental drying curves show only a falling drying rate period. On average, tomatoes are dried until the moisture content to 0.15 kg water kg-1 dry matter from 14.36 kg water kg-1 dry matter in the solar drying, and to the moisture content of 0.10 kg water kg-1 dry matter from 12.66 kg water kg-1 dry matter in the convective drying

Étude par microtomograpie aux rayons X durétrécissement de tranches de tomates durant le séchage convectif

In this study, the shrinkage phenomenon taking place during the convective drying of tomato slices is investigated with three different temperatures (40, 50 and 60 °C) at constant air velocity of 1 m.s-1 and very low humidity. Indeed, the shrinkage curves showing the evolution of the volume ratio (V/V0) v.s. the water content ratio (X/X0) are determined by X-ray microtomography. The results show that the tomato presents an anisotropic and independent of temperature shrinkage and then a single shrinkage curve is proposed. On average, the volume decreases of 70 % of its initial value.The height and the diameter shrinkages have a linear dependence with the water content until X/X0 = 0.2, but for X/X0 < 0.2, the diameter and especially the thickness decrease rapidly, following a polynomial and a logarithmic trend, respectively

Convective drying of cherry tomato: Study of skin effect

A whole single cherry tomato was dried in a forced convective micro-dryer. The experiments were carried out at constant air velocity and humidity and temperatures of 50, 60, 70 °C. In order to study the effect of the skin, two sets of experiments were performed using a tomato with and without skin (easily removed). Shorter drying times were obtained when increasing drying temperatures as well as when removing sample skin. X-ray microtomography, a non-destructive 3D imaging technique was used to follow shrinkage of the samples. This phenomenon was introduced in the modelling part of this study. Analytical solutions of the Fick’law were used to determine the diffusion coefficient at the three temperatures studied, and then the activation energy was obtained through fitting the Arrhenius equation. The skin effect was clearly evidenced by showing that the mass transfer parameter values of an original tomato with skin were largely smaller than the one without skin. Indeed, the moisture effective diffusivity ranged from 2.56×10-11 to 7.67×10-11 m2·s-1 with activation energy of 50430 J·mol-1 for tomato with skin an ranged from 4.59×10-10 m2·s-1 to 6.73×10-10 m2·s-1 with activation energy of 17640 J.mol-1 for tomato without skin