İnci Türk Toğrul

Modelling of drying kinetics of single apricot

Abstract In this work, the drying behaviour of single apricots, hanging in the flow direction of hot air in a drying chamber, was investigated. In the experiments, the air was passed through the chamber at a variety of flow rates (0.2, 0.5, 1.0 and 1.5 m/s) and temperatures (50, 60, 70 and 80 °C). In order to obtain drying data, the changes in the mass and inner temperatures of the apricots were recorded as well as the drying air properties. The variations of drying rates with time and moisture content were used to test fourteen different one-layer drying models given in the literature and a new model was developed. Among all the models, the logarithmic model was found the best for explaining the drying behaviour of apricots. The effects of drying air flow rates and temperatures on the constants and coefficients of the models were also studied by multiple regression analysis. It was found that the new model could represent single apricot drying kinetics within 99.9% accuracy. The moisture transfer from the apricots occurring during the falling-rate period of drying was characterised by determining experimentally the apparent diffusion coefficient into the air. It was found, by multiple regression analysis, that the diffusion coefficients could be expressed within 97.3% accuracy, depending on the air flow rates and inside temperatures of the single apricot. In studying the consistency of all the models, some statistical tests, such as reduced χ 2 , mean bias error and root mean square error were also used as well as correlation coefficients. The results of these tests have also confirmed the consistency of the logarithmic model.

Mathematical modelling of solar drying of apricots in thin layers

Abstract Solar drying experiments in thin layers of apricots grown in Elazig, Turkey, were conducted. An indirect forced convection solar dryer consisting of a solar air heater with conical concentrator and a drying cabinet were used in the experiments. Air was forced into the solar air heater by a blower and hot air obtained there was passed over the apricots. The changes in the mass of apricots and principal drying parameters were recorded continuously from morning to evening in each test day. Drying curves obtained from the data were fitted to a number of mathematical models and the effects of drying air temperature, velocity and relative humidity on the model constants and coefficients were evaluated by the multiple regression and compared to previously given models. The logarithmic drying model was found to satisfactorily describe the solar drying curve of apricots with a correlation coefficient ( r ) of 0.994. The constants and coefficients of this model could be explained by the effect of drying air temperature, velocity and relative humidity with a correlation coefficient ( r ) of 1.000.

A study for estimating solar radiation in Elazig˘ using geographical and meteorological data

Abstract In this study, the effect of geographical and meteorological parameters on the monthly mean global solar radiation in Elazig was investigated. A multiple linear regression was applied to six geographical and meteorological data sets, which were monthly mean extraterrestrial radiation, the ratio of ‘bright sunshine hours to daylength’, ambient and soil temperatures, humidity and sine of declination angle. The global solar radiation estimated from the models was compared with the values measured by the Kipp–Zonen pyranometer between April 1994 and March 1995. It has been determined that these equations which express the 99th percentile of the incident solar radiation, have a −9% deviation from our measured values.

Global solar radiation over Turkey: comparison of predicted and measured data

In this study, various regression analyses were applied to estimate monthly mean solar radiation in Turkey, by using n/N and n/Nnh parameters. Also, equations which represent two periods of the year, winter and summer, were developed by using these parameters. The equations developed by using n/Nnh ratio showed good results for the whole country, but, those which included n/N ratio at different cities showed better results. Even better results were obtained when the equations were applied to the summer and winter. In addition to RMSE and MBE statistics, the t-test method and the harmonic analysis were employed to prove that the results are reliable.

Estimation of global solar radiation under clear sky radiation in Turkey

In this study, the usability of clear sky radiation for predicting the average global solar radiation was investigated. For this aim, the various regression analyses were applied by using n/N and n/Nnh parameters. Also, equations which represent the two periods of the year, winter and summer, were developed by using these parameters.

The performance of a solar air heater with conical concentrator under forced convection

Abstract In this work, the efficiency of a new solar air heater with a conical concentrator, which can track the sun from sunrise to sunset, was investigated under forced convection conditions of air. The collector, whose absorber was arranged as a two-pass exchanger and mounted on the focal axis of the conical concentrator, was tested for a number of tilting angles and a variety of air mass flow rates. In addition, major operation parameters related to efficiencies of the collector and heat flow in the absorber were determined and correlated with each other and compared with flat-plate solar collectors. The highest efficiencies and maximum increase in the air temperatures were obtained at 28.4° tilting and the lowest mass flow rate, respectively. Although, the efficiencies were similar, the maximum outlet temperatures of the air were found to be approximately twice and heat transfer rates inside the absorber were higher than those reached by conventional flat-plate solar air heaters.

DETERMINATION OF CONVECTIVE HEAT TRANSFER COEFFICIENT OF VARIOUS CROPS UNDER OPEN SUN DRYING CONDITIONS

In this study, an attempt has been made to evaluate the conveetive beat transfer coeffieient operating in crop drying in open sun drying conditions (natural convection). Values of the constant. C and n were obtained by linear regression analysis from experimental data obtained for nine crops. namcly marrow, auberginc. carrot. green bean. Albanian pepper, green pepper, potato, onion and pear. Based on the values of C and a convective heat transfer coefficients for these crops were determined. We observed that the values of convective heat transfer coefficient varied from crop to crop with a range of °C for the crops studied. The data have also been analysed in terms of per cent uncertainty.

Convective Heat Transfer Coefficient of Apricots Under Open Sun Drying Conditions

ABSTRACT In this work, the convective heat transfer coefficients of apricots in open sun drying conditions were determined. Convective heat transfer coefficients were found at different initial moisture contents and at ambient temperature for apricots with various pretreatments. Convective heat transfer coefficient for apricots was found to increase exponentially with increasing moisture content. The coefficients of the exponential model were determined by using the Statistica program. To test the consistency of the models developed for apricots, some statistical tests were also used as well as correlation coefficients. The experimental error in terms of percent uncertainty was also calculated.

THERMAL EFFICIENCY OF AN AIR SOLAR COLLECTOR WITH EXTENDED ABSORPTION SURFACE AND INCREASED CONVECTION

A modified solar air heater, which incorporated aluminium wool on a perforated plate placed diagonally on the passageway of the air to serve as a front absorbing medium above the absorber plate was designed, constructed and tested. Its efficiency was compared with the same sized conventional solar collector. The efficiencies of these two collectors were evaluated in terms of the effects of temperatures and duration times for the same airflow rates. It was found that the heat transferred to the air was increased greatly in the case of solar air heater with front absorbing surface.

Determination of Moisture Transport Parameters of Some Fruits Under Open Sun Drying Conditions

In order to determine the behavior of fruits during drying under natural conditions, open sun drying experiments were conducted on apricots, grapes, peaches, figs, and plums. The drying rate curves of these fruit did not contain constant rate period, but showed a falling rate period. In the present work, Biot numbers and the mass transfer characteristics—namely moisture diffusivity and moisture transfer coefficient—of selected fruits were evaluated by drying coefficients (S) and lag factors (G). The experimental results exhibited mass transfer Biot numbers in the range of 0.115–0.158, thus indicating the presence of finite internal and external resistances.