Ebru Kavak Akpinar

Thin layer drying of red pepper

The thin layer drying behaviour of red pepper slices is experimentally investigated in a convective dryer and the mathematical modelling by using thin layer drying models in literature is performed. Drying experiments were conducted at inlet temperatures of drying air of 55, 60 and 70 °C and at a drying air velocity of 1.5 m/s. Eleven different thin layer mathematical drying models were compared according to their coefficient of correlation to estimate drying curves. The effects of drying air temperature on the model constants and coefficients were predicted by regression models. According to the results, an approximation of the diffusion model could satisfactorily describe the drying curve of red peppers with a correlation coefficient (r) of 0.9987. The constants and coefficients of this model could be explained by the effect of drying air temperature.

Single layer drying behaviour of potato slices in a convective cyclone dryer and mathematical modeling

Abstract The main objective pursued in this paper is to investigate the single layer drying behaviour of potato slices experimentally in a convective cyclone dryer and also to perform mathematical modeling by using single layer drying models in the literature. Drying experiments of potato slices with the thicknesses of 12.5 and 8 mm were conducted at inlet temperatures of drying air of 60, 70 and 80 °C and with drying air velocities of 1 and 1.5 m/s. It was concluded that potato slices with thickness of 12.5 mm would dry perfectly in the range of 460–740 min, while those with thickness of 8 mm would dry in the range of 280–520 min in these drying conditions in the convective type cyclone dryer. Additionally, the mathematical model describing the single layer drying curves was determined by non-linear regression analysis, and an approximation of the diffusion model was selected as the most suitable model to describe the drying curve equation of potato slices.

Mathematical Modeling and Experimental Study on Thin Layer Drying of Strawberry

This paper presents mathematical modeling and the thin layer convective drying of strawberry. The experiments are conducted at drying air temperatures of 60, 75 and 85 deg.C in drying air velocities of 0.5, 1 and 1.5 m/s in a convective cyclone type dryer. The data of sample mass, temperature and velocity of the drying air were recorded continuously during each test. The experimental drying curves show only a falling drying rate period. The main factor in controlling the drying rate was found to be the drying air temperature. Also, the experimental drying curves obtained were fitted to eleven mathematical models. The Modified Page (I) drying model was found to satisfactorily describe the drying curves of strawberry with a correlation coefficient (R) of 0.98042, chi-square (2) of 0.0035 and root mean square error (RMSE) of 0.0588. The constants and coefficients of this model could be explained by the effect of drying air temperature and velocity with a correlation coefficient (R) of 0.998. The effective diffusivity coefficient of moisture transfer varied from 4.528x10-10 to 9.631x10-10 m2/s over the temperature and velocity range in this study.

HEAT TRANSFER ENHANCEMENTS IN A CONCENTRIC DOUBLE PIPE EXCHANGER EQUIPPED WITH SWIRL ELEMENTS

The effect of heat transfer rates of swirl generators with holes for the entrance of fluid were investigated by placing them at the entrance section of inner pipe of heat exchanger. Various swirl generators having different arrangements of boles were used. Hot air and cold water were passed through the inner pipe and annulus respectively. Experiments were carried out for both parallel and countercurrent flow models of the fluids at Reynolds numbers between 8500-17500

EXPERIMENTAL DETERMINATION OF CONVECTIVE HEAT TRANSFER COEFFICIENT OF SOME AGRICULTURAL PRODUCTS IN FORCED CONVECTION DRYING

A simulation study has been made for determination of the convective heat transfer coefficients of eight agricultural products, namely, mulberry, strawberry, apple, garlic, potato, pumpkin, eggplant and onion under forced convection drying. Data obtained from experimentation under open simulated condition have been used to determine values of the coefficients C and n and, consequently, convective heat transfer coefficient. The values of convective heat transfer coefficient determined 2.007 W/m 2 °C for mulberry, 3.615 W/m 2 °C for strawberry, 2.874 W/m 2 °C for apple, 0.644 W/m 2 °C for garlic, 4.897 W/m 2 °C for potato, 3.530 W/m 2 °C for pumpkin, 4.026 W/m 2 °C for eggplant and 7.121 W/m 2 °C for onion. The experimental error in terms of percent uncertainty was also calculated

Exergy analysis associated with heat transfer during heating of slab products

This study deals with an exergy analysis associated with the transient heat transfer taking place during heating of slab shaped products. First, the Dincer and Dosts analytical technique is applied to determine the heat transfer coefficient and surface temperatures using the centre temperatures measured during the heating of slab products. Second, an exergy analysis is conducted as associated with the transient heat transfer to study the change of Exergetic Heating Effectiveness (ExHE) and exergy efficiency with temperature, velocity and time.

Experimental Investigation of Convective Heat Transfer Coefficient of Various Agricultural Products Under Open Sun Drying

Abstract In this article, the convective heat transfer coefficients of various agricultural products were investigated under open sun drying conditions. Data obtained from open sun drying experiments for eight agricultural products, namely, mulberry, strawberry, apple, garlic, potato, pumpkin, eggplant, and onion were used to determine values of convective heat transfer coefficient. The value of convective heat transfer coefficient was determined as 1.861 W/m2°C for mulberry, 6.691 W/m2°C for strawberry, 11.323 W/m2°C for apple, 1.136 W/m2°C for garlic, 8.224 W/m2°C for potato, 8.613 W/m2°C for pumpkin, 6.981 W/m2°C for eggplant, and 6.767 W/m2°C for onion. The experimental error in terms of percent uncertainty was also calculated.

Effects of Meteorological Parameters on Air Pollutant Concentrations in Elazig, Turkey

In the present study, air pollutant concentrations have been analyzed statistically with meteorological factors in the city of Elazig, which is located in the east Anatolia region of Turkey, for the months of September, October, November, December, January, February, March, and April during the years 2003 and 2004. SPSS code was used for statistical analyses. The relationship between monitored air pollutant concentrations, such as SO2 and the total suspended particles (TSP) data, and meteorological factors such as wind speed, temperature, relative humidity and pressure was investigated. According to the results of linear and non-linear regression analysis, it was found that there is a moderate and weak level of relation between the air pollutant concentrations and the meteorological factors in Elazig. The correlation between the previous days SO2, TSP concentrations and actual concentrations of these pollutants on that day was investigated and the coefficient of determination R was found to be 0.80 and 0.76, respectively. The statistical models of SO2 and TSP, including all of the meteorological parameters, gave an R of 0.50 and 0.40, respectively. Further, in order to develop this model, the previous days SO2 and TSP concentrations were added to the equations. The new model for SO2 and TSP was improved considerably with R = 0.85 and 0.80, respectively.

Thermal and mechanical properties of lightweight concretes produced with pumice and tragacanth

Abstract This study was carried out to determine the possibilities of using tragacanth and pumice aggregate in lightweight concrete producing. The samples were produced with mixture combinations of materials such as pumice, tragacanth, and cement. The prepared material samples were subjected to some tests such as thermal conductivity, compressive strength, tensile strength, abrasion loss, and water absorption (WA). It was determined that density, thermal conductivity, compressive strength, tensile strength, abrasion loss, and WA varied as 0.728–1.772 g/cm3; 0.177–0.433 W/mK; 6.1–258.80 kg/cm2; 2.73–17.81 kg/cm2; 0.0–19.9%; and 20–56.8%, respectively. The results showed that the produced material samples were in lightweight concrete class according to thermal and mechanical properties. As to the observations, tests, experiments, and evaluations on lightweight concrete material samples, it was concluded that the lightweight concrete with tragacanth and pumice additive can be used as a coating and dividing material in buildings because of its insulating features.

Experimental and theoretical study for the determination of thermal conductivity of porous building material made with pumice and tragacanth

Abstract In this study, porous solid materials were produced with mixture combinations of materials such as tragacanth, cement, and pumice aggregate. Thermal conductivities of the produced materials were determined using hot wire methodology. The thermal conductivities of the produced samples ranged from 0.433 to 0.177 W/mK, depending on pumice diameter, pumice, tragacanth, and cement rates. A new model was developed to determine the effective thermal conductivities of the produced samples. The thermal conductivities obtained by the measurements were compared to the ones predicted by the model. The predicted values deviated as 1–31% from the measured values. It was finally shown that the experimental results were in good agreement to the predicted results.