Experimental testing of a new solar dryer

Drying of agricultural products is an energy-intensive operation. High prices and shortages in fossil fuels increase the emphasis on using solar energy as an alternative energy source, especially in developing countries. In this respect, a new solar dryer, which consisted of a solar air heater and a drying chamber, was developed and used for drying various fruits and vegetables, i.e., sultana grapes, green beans, sweet peppers and chilli peppers and was successfully tested. In order to make a comparison, the traditional sun-drying experiments were employed. Results showed that the solar dryer reduced the drying time significantly and prevented mass losses, and essentially provided better product quality.     

Evaluation of some of the physical properties of atmospheric plasma treated polypropylene fabric

In this study, atmospheric pressure plasma (APP) treatment was applied to polypropylene (PP) fabric with non‐polymerizing gases, such as air, argon, and nitrogen. Properties of the APP‐treated samples including low‐stress mechanical behavior, air permeability, water vapor permeability, and thermal characteristics were evaluated. Tensile and friction coefficient of the specimens were also measured. The changes in these properties are believed to be closely related to the inter‐fiber and inter‐yarn frictional force induced by the APP. The decrease in the air permeability of the APP‐treated PP fabric was probably because of the plasma action effect on change in fabric surface morphology, which was confirmed by scanning electron microscopy micrographs. The change in the thermal properties of the APP‐treated PP fabric was in good agreement with the earlier findings and can be attributed to the amount of air trapped between the yarns and fibers. This study suggests that the APP treatment can influence the final properties of the PP fabric, and also provides information for developing APP‐treated PP fabric for industrial use.     

The Effect of Atmospheric Pressure Plasma Corona Discharge on pH,Lipid Content and DNA of Bacterial Cells

Effect of plasma corona discharges on the pH, whole cell lipids and DNA of bacteria is investigated. Results showed an increase in the acidity levels of water due to plasma reactive species which, however, were not responsible for bacterial cell death. No changes in the whole cell lipid contents were observed, while DNA after plasma treatment showed deterioration of the amplified sequences, indicating the possible occurrence of DNA degradation. In conclusion, reactive species produced by plasma discharges affects DNA, possibly contributing to cell death.     

Performance analysis of a solar cooker in Turkey

A box‐type solar cooker is designed and its thermal performance is analysed experimentally. The cooker tracks the sun in two axes, altitude and sun azimuth, by hand control for hourly periods. The experimental results show that the tested cooker may be assumed suitable in some cooking processes for specific country conditions. Copyright © 2002 John Wiley & Sons, Ltd.     

Heat transfer and thermal stress analysis in grooved tubes

Heat transfer and thermal stresses, induced by temperature differences in the internally grooved tubes of heat transfer equipment, have been analysed numerically. The analysis has been conducted for four different kinds of internally grooved tubes and three different mean inlet water velocities. Constant temperature was applied from the external surface of the tube. Energy and governing flow equations were solved using finite difference scheme. Finite element method (FEM) was used to compute the thermal stress fields. Grooving effects on the thermal stress ratio have been discussed. As a result, maximum thermal stress occurs in the case ofp =d for all water inlet velocities. The maximum thermal stress ratio positions inside the tube have been indicated as MX for all investigated cases. In the light of the thermal stress values, various designs can be applied to reduce thermal stress in grooved tubes.     

Effect of ambient conditions on the first and second law performance of an open desiccant cooling process

An open desiccant cooling process is presented and applied to ventilation and recirculation modes of the system operation. The cooling system consists of a desiccant wheel, a rotary regenerator, two evaporative coolers, and a heating unit. Certain ideal operating characteristics based primarily on the first law of thermodynamics are assumed for each component. The system with indoor and outdoor ARI conditions has a thermal coefficient of performance (COP) of 1.17 in ventilation mode and 1.28 in recirculation mode. A second law analysis is also performed and at ARI conditions, the reversible COP of the system is determined to be 2.63 in ventilation mode and 3.04 in recirculation mode. Variation of the first and second law based COP terms and cooling load with respect to ambient temperature and relative humidity are investigated in both modes of the system operation. The results of the analysis provide an upper limit for the system performance at various ambient conditions and may serve as a model to which actual desiccant cooling systems may be compared. As an additional study, a non-ideal system operation is considered and it is determined that both the COP and cooling load decrease with increasing ambient temperature and relative humidity, and they approach zero at high values of ambient temperature and humidity.     

Comparison of Legendre polynomial approximation and variational iteration method for the solutions of general linear Fredholm integro-differential equations

In this study it is shown that the numerical solutions of linear Fredholm integro-differential equations obtained by using Legendre polynomials can also be found by using the variational iteration method. Furthermore the numerical solutions of the given problems which are solved by the variational iteration method obviously converge rapidly to exact solutions better than the Legendre polynomial technique. Additionally, although the powerful effect of the applied processes in Legendre polynomial approach arises in the situations where the initial approximation value is unknown, it is shown by the examples that the variational iteration method produces more certain solutions where the first initial function approximation value is estimated. In this paper, the Legendre polynomial approximation (LPA) and the variational iteration method (VIM) are implemented to obtain the solutions of the linear Fredholm integro-differential equations and the numerical solutions with respect to these methods are compared.     

Geotechnical characteristics of the clayey soils and rocks of the North Lefkoşa,Nicosia, Cyprus

This paper outlines the engineering geological properties of the clayey soils of North Lefkoşa (Nicosia, Cyprus). On the basis of their physical properties and their engineering characteristics, the Miocene, Pliocene and Quaternary deposits were divided into six units: unconsolidated man-made fill, unconsolidated surficial recent alluvium, unconsolidated surficial young alluvium, consolidated old alluvium, highly weathered soft rock units and slightly weathered relatively resistant rock units. Laboratory tests indicated a generally high swelling potential, which would account for the damage seen in many single and two-storey buildings as well as major roads.      

Distributed parameter estimation and identification for system with fast and slow dynamics: A tubular,fixed-bed catalytic reactor to form styrene

A simple and efficient on-line scheme is developed to estimate temperature and compositions along a packed bed reactor in which styrene is being produced by the dehydrogenation of ethylbenzene. Slowly varying catalyst activity is also identified. The system is distributed in time and axial position and is nonlinear in the states: temperature and nine compositions. The dehydrogenation rate is augmented with a catalyst activity parameter which is assumed to undergo a long-term exponential decay.Since the decline in catalyst activity is slow when compared to state dynamics, a quasi-steady-state approach is used to derive a state filter equation neglecting process state dynamics and assuming spatially uncorrelated measurements and model uncertainty. For this filter, temperature measurements are available from four locations along the reactor and compositions are measured only at the reactor exit. A second dynamic, Kalman filter is used to identify the slowly varying catalyst activity.The two filters, one for distributed, steady-state, state estimation and the other for dynamic catalyst activity identification, are tested by computer simulation using measurements with added white noise. Several cases for numbers of sensors and noise levels are studied. The overall scheme is efficient and useable for on-line implementation. The steady-state filter is readily extended to distributed systems in more than one spatial variable such as reactor models with axial and radial dependencies. For steady-state or static models, multiple measurements yield significant improvements in the quality of the optimal estimates. Internal measurement locations allow for the subdivision of the spatial domain for the problem and improved profile estimates.