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Öğe A new model for single-layer drying(2002) Midilli A.; Kucuk H.; Yapar Z.This paper presents a new empirical model for single layer drying process, which was verified with selected experimental data. The present model is also compared with other single layer drying models available in the literature, using laboratory as well as field data from literature.Öğe Energy and exergy analyses of solar drying process of pistachio(Elsevier Ltd, 2003) Midilli A.; Kucuk H.This paper is concerned with the energy and exergy analyses of the drying process of shelled and unshelled pistachios using a solar drying cabinet. Using the first law of thermodynamics, energy analysis was carried to estimate the amounts of energy gained from solar air collectors and the ratios of energy utilization. However, exergy analysis was accomplished to determine the location, type, and magnitude of exergy losses during the solar drying process by applying the second law of thermodynamics. It was deduced that the exergy losses took place mostly in the 15th shelf where the available energy was less utilized. Moreover, the shelled and unshelled pistachios are sufficiently dried in the ranges between 40 and 60 °C and 37 and 62% of relative humidity at 1.23 m s-1 of drying air velocity in 6 h despite the exergy losses of 0.15-3.08 kJ kg-1. © 2003 Elsevier Science Ltd. All rights reserved.Öğe Energy and exergy analyses of sugar production stages(2003) Bayrak M.; Midilli A.; Nurveren K.This paper presents the energy and exergy analyses of sugar production stages by using the operational data from Bor Sugar Plant, Turkey. For these purposes, all stages of sugar production, considered as a steady-state open thermodynamic system, were analysed by employing the first and second law of thermodynamics. In this regard, the first and second law efficiencies, the magnitude and place of exergy losses in these production stages were estimated and discussed in detail. It was concluded that the exergy loses took place mostly during the sherbet production process (?I.sp = 96.8% ?II.sp = 49.3%) because of the irreversibility in the sub-operation stages, which are vapour production, circulation sherbet mixing and bagasse compression. Therefore, it is generally suggested that the irreversibility, mostly stem from the finite temperature differences at the production stages, should be reduced to conduct more productively the sugar production process. © 2003 John Wiley and Sons, Ltd.Öğe Experimental investigation of drying behaviour and conditions of pumpkin slices via a cyclone-type dryer(2003) Akpinar E.K.; Midilli A.; Bicer Y.This paper describes an experimental investigation of the drying behaviour and conditions of pumpkin slices via a convective cyclone-type dryer. Drying experiments were conducted at air inlet temperatures of 60, 70 and 80°C and air velocities of 1 and 1.5 ms-1. Samples of 200 g of cylindrical pumpkin slices (thickness 5 mm x diameter 35 mm) were arranged in a single layer on each of two trays. The least squares method was applied to derive the drying curve equation of samples. During the experiments the following parameters were measured: weight loss, temperature, relative moisture and velocity. From these parameters, dimensionless mass loss, moisture content, mass shrinkage and drying rate of samples were calculated and are discussed in detail. Additionally, the transport of water during dehydration was described by the diffusion mechanism, and Fick's equation was used for evaluation of the experimental data. The linear sections of drying curves were analysed by linear regression to obtain the moisture diffusivities. It was found that pumpkin slices would dry perfectly within 340-720 min under these drying conditions. The convective cyclone dryer could also be used to dry other products. Thus it is expected that this new dryer will help farmers and producers to reduce the cost of drying. © 2003 Society of Chemical Industry.Öğe Gasification of sewage sludge using a throated downdraft gasifier and uncertainty analysis(2002) Dogru M.; Midilli A.; Howarth C.R.The most important objectives to gasify sewage sludge are to produce a clean gas of acceptable composition for synthesis or combustion, and to convert this solid resource into combustible-clean gas at high efficiency. The experiments of the gasification were conducted using a 5 kWe-throated downdraft gasifier. It was concluded that sewage sludge can be gasified to produce low-quality combustible gas, and would be an acceptable alternative source to fossil fuels for the production of the clean energy. It is suggested that the downdraft gasifier should be operated at 3.69-3.71 kg/h ± 1.43% of the feed rate, at 2.28-2.34 N m3/kg ± 1.84% of the air fuel ratio, around 497.74-514 N m3/m2 h ± 1.50% of specific gasification rate and around 93.64-94.15% ± 1.92% of turndown ratio in order to achieve good quality gas and to avoid clinker formation at the throat of the gasifier because of high ash content of sludge. The thermal efficiency was calculated as between 39% and 40% at the optimum operation levels given above. © 2002 Elsevier Science B.V. All rights reserved.Öğe Global warming: Engineering solutions(2010) Dincer I.; Midilli A.; Hepbasli A.; Karakoc T.H.[No abstract available]Öğe Hydrogen production from sewage sludge via a fixed bed gasifier product gas(2002) Midilli A.; Dogru M.; Akay G.; Howarth C.R.The main objective pursued in this work is to investigate the hydrogen production potential from sewage sludge by applying downdraft gasification technique. An experimental study was conducted using a pilot scale (5 kWe) throated downdraft gasifier. During the experiments, all data were recorded with an analog to digital (ATD) converter linked to a computer for every 15 s. The flow rates of the wet product gas, the mass flow rate and volumetric percentage of hydrogen were determined and illustrated. The effects of temperatures of oxidation zone on the production of hydrogen were discussed, and the conversion ratios of dried sewage sludge to hydrogen and ash were also designated. It was concluded that substantial amount of hydrogen gas could be produced utilizing a renewable biomass source such as dried and undigested sewage sludge pellets by applying air blown downdraft gasification technique. The product gas obtained mainly consists of H2, N2, CO, CO2 and CH4 with a maximum average gross calorific value of 4 MJ/m3. Around 10-11%(V/V) of this product gas is hydrogen which could be utilized for fuel cells. Moreover, sewage sludge can be assumed as an alternative renewable energy source to the fossil fuels, and the environmental pollution originating from the disposal of sewage sludge can be partially reduced. © 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.Öğe Mathematical modeling of thin layer drying of pistachio by using solar energy(2003) Midilli A.; Kucuk H.This paper presents a mathematical modeling of thin layer forced and natural solar drying of shelled and unshelled pistachio samples. In order to estimate and select the suitable form of solar drying curves, eight different mathematical models, which are semi-theoretical and/or empirical, were applied to the experimental data and compared according to their coefficients of determination (r,?2), which were predicted by non-linear regression analysis using the Statistica Computer Program. It was deduced that the logarithmic model could sufficiently describe thin layer forced solar drying of shelled and unshelled pistachio, while the two term model could define thin layer natural solar drying of these products in evaluation by considering the coefficients of determination, rsfsd = 0.9983, ?2sfsd = 2.697 × 10-5; rufsd = 0.9990, ?ufsd2 = 1.639 × 10-5 for thin layer forced solar drying and rsnsd = 0.9990, ?snsd2 = 3.212 × 10-6; runsd = 0.9970, ?unsd2 = 4.590 × 10-5 for thin layer natural solar drying. © 2002 Elsevier Science Ltd. All rights reserved.Öğe Natural vacuum distillation technique - Part I: Theory and basics(John Wiley and Sons Ltd, 2004) Midilli A.; Ayhan T.This part of the study presents the theory, design and appropriate models of a new distillation system with natural vacuum technique. Natural vacuum distillation (NVD) system is considered as ? (opposite U) to obtain 10.33m of water elevation and create natural vacuum. Theoretical models of this system are investigated and appropriate models are selected for practice applications. In the scope of this study, the theory and design criteria of NVD system which include balance design and selection of distillation method, natural vacuum formation, balancing and feeding processes are introduced and discussed in detail. Additionally, P-v and T-s diagrams including the process flow of each model are obtained by depending on thermodynamic behaviours of the system. Consequently, the operation height between the tanks and columns should be stable and conserved as 10.33 m of water in order to create the natural vacuum and keep the natural balance of the system for a long time. Hence, the water is transported throughout the system due to the pressure differences between evaporation and distillation parts. The pressure losses that are caused by the water-level differences between tanks and columns should be taken into account and absolutely reduced. Moreover, the system should be definitely operated in the natural vacuum to efficiently conduct the production of distilled water from wastewater with the high temperature. © 2004 John Wiley and Sons, Ltd.Öğe Natural vacuum distillation technique - Part II: Experimental investigation(2004) Midilli A.; Ayhan T.This part of the study is concerned with the experimental investigation and uncertainty analysis of natural vacuum distillation process. Natural vacuum distillation (NVD) system is operated in the forms of free and forced mass convection. The experiments are conducted at temperatures of 20 and 40°C of network water as fluid in the system. During the experiments, total pressure losses are measured as 15.33 kPa during free mass convection distillation while 14 kPa during forced mass convection distillation. Depending on time and temperature, the ratios of vapour/wastewater (v/ww)free, distilled water/wastewater (dw/ww)forced and total energy/distilled water (te/dw) are experimentally determined. Moreover, the ratios of mass and energy balances are experimentally obtained. Accordingly, it is found that the ratios of (dw)forced/(dw)free vary between 1.4 and 1.6 depending on the wastewater temperatures. In addition, 2.5 kWh kg-1 distilled water is experimentally used in the NVD system with free mass convection while 2.6 kWh kg-1 distilled water in the NVD system with forced mass convection. In case of reduction of heat and pressure losses in the systems, 0.7 kWh is needed for the former while 1.3 kWh of energy is required for the latter. © 2004 John Wiley and Sons, Ltd.Öğe Single layer drying behaviour of potato slices in a convective cyclone dryer and mathematical modeling(2003) Akpinar E.; Midilli A.; Bicer Y.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. © 2002 Elsevier Science Ltd. All rights reserved.
