Evaluation of convective heat transfer coefficient of various crops in cyclone type dryer

In this paper, an attempt was made to evaluate the convective heat transfer coefficient during drying of various crops and to investigate the influences of drying air velocity and temperature on the convective heat transfer coefficient. Drying was conducted in a convective cyclone type dryer at drying air temperatures of 60, 70 and 80 °C and velocities of 1 and 1.5 m/s using rectangle shaped potato and apple slices (12.5 × 12.5 × 25 mm) and cylindrical shaped pumpkin slices (35 × 5 mm). The temperature changes of the dried crops and the temperature of the drying air were measured during the drying process. It was found that the values of convective heat transfer coefficient varied from crop to crop with a range 30.21406 and 20.65470 W/m² C for the crops studied, and it was observed that the convective heat transfer coefficient increased in large amounts with the increase of the drying air velocity but increased in small amounts with the rise of the drying air temperature.     

An experimental investigation of the effect of longitudinal fin orientation on heat transfer in membrane water wall tubes in a circulating fluidized bed

Experiments were conducted in a cold model circulating fluidized bed having riser cross-sectional area of 100 mm × 100 mm, height of 4.8 m, bed temperature of 75 °C and superficial velocity of 8 m s^?1. Local sand having average diameter of 231 μm was used as bed material. The experiments were conducted for three tube configurations: membrane tube, membrane tube with a longitudinal fin at the tube crest and membrane tube with two longitudinal fins at 45° on both sides of the tube crest. The results show that membrane tubes with one and two longitudinal fins have higher heat transfer than membrane tubes and the heat is mainly transferred in the combination portion of tube and membrane fins. In addition, the membrane tube has the highest heat transfer coefficient.     

Mathematical modeling of drying characteristics of tropical fruits

In this study, a heat pump dryer was designed and produced in which drying air temperature was controlled with PID. PID controlled heat pump dryer was experimentally tested in drying tropical fruits such as kiwi, avocado and banana. Drying air temperature was kept at 40 °C with the accuracy of ±0.2 °C. Drying air velocity changed between 0.03 m/s and 0.39 m/s. Initial moisture contents of the kiwi, avocado and banana were 4.31, 1.51 and 4.71 g water/g dry matter, which were dried to 0.75, 0.35 and 0.5 g water/g dry matter moisture contents in 6 h. Afterwards the moisture ratios were analyzed with “STATGRAPHIC” computer program by using semi-theoretical models and empirical values. Correlation and standard error of estimation (SEE) and R² values were achieved.     

Waste-to-energy possibilities for industrial olive and grape by-products in Extremadura

The olive and grape agro-industrial sectors have a major economic importance in Extremadura. Annual production of olive oil is more than 50×10³ t, and of wine is more than 3×10⁶ hectolitres. The large amounts of by-products are in most cases under-used, although they could be converted into a zero cost of the waste at the point of origin. In this context, the present work describes an estimate of plant size, and an economic analysis of grate firing+steam turbine (GF/ST) and fluidized bed combustion+steam turbine (FBC/ST) waste-to-energy solutions using industrial olive and grape by-products in Extremadura. The fuel is dry olive husk waste (OH), olive mill wastewater (OMW), OH+OMW sludge, and grape waste from wineries, with total calculated specific costs of 3.28, 8.09, 2.67, and 2.05 € GJ⁻¹ with respect to the lower heating value (LHV), respectively. The logistics component corresponding to trucking the biomass to the power production plant is that of greatest economic importance, even when the logistics strategy includes de-centralized drying plants.For real onsite availabilities of OH 21.084×10³ t, OMW 37.483×10³ t, olive sludge 87.462×10³ t, and grape waste 89.486×10³ t, the gross power is 19.13 MW for a GF/ST plant and 20.46 MW for an FBC/ST plant. The results are compared using standard economic indices—net present value (NPV), profitability index (PI), internal rate of return (IRR), and payback time (PBT). A sensitivity and risk analysis of the proposals showed the GF/ST option to be the better suited to the studied scenario, with better values for all the indicators.     

Mathematical modeling of thin-layer drying of fermented and non-fermented sugarcane bagasse

This work reports hot-air convective drying of thin-layer fermented and non-fermented sugarcane bagasse. For this purpose, experiments were carried out in a laboratory-scale dryer assessing the effects of solid-state fermentation (SSF) on the drying kinetics of the processing material. The fermented sugarcane bagasse in SSF was obtained with the use of Kluyveromyces marxianus NRRL Y-7571. Drying experiments were carried out at 30, 35, 40 and 45 °C, at volumetric air flow rates of 2 and 3 m³ h^?1. The ability of ten different thin-layer mathematical models was evaluated towards representing the experimental drying profiles obtained. Results showed that the fermented sugarcane bagasse presents a distinct, faster drying, behavior from that verified for the non-fermented material at the same conditions of temperature and volumetric air flow rate. It is shown that the fermented sugarcane bagasse presented effective diffusion coefficient values of about 1.3 times higher than the non-fermented material. A satisfactory agreement between experimental data and model results of the thin-layer drying of fermented and non-fermented sugarcane bagasse was achieved at the evaluated experimental conditions.     

Influence of uncertainty in diffusion coefficients on moisture field during wood drying

The paper presents an experimental measurement of diffusion coefficients of wood and theoretical analysis (stochastic analysis) based on influence of uncertainty in these coefficients on moisture field during wood drying simulations. Experimental measurement was used to verify of analytic equations for calculation of diffusion coefficients, which were implemented in the numerical simulations. Histograms show on normal distribution, but stochastic analysis was used for uniform distribution as well. Mean value of diffusion coefficient in tangential direction was calculated as 1.016·10^?10 m² s^?1 and standard deviation as 0.153·10^?10 m² s^?1. Stochastic analysis is based on the Monte Carlo method. The analysis proves that final moisture field has a same probability distribution as the diffusion coefficient (normal or uniform distribution) and also depicts a character of course and distribution of uncertainty in lumber during drying.     

Cynara cardunculus L. genotypes as a crop for energy purposes in a Mediterranean environment

Previous studies indicate biomass and grain production for energy purposes as potential utilizations of the three Cynara cardunculus botanical varieties (globe artichoke, cultivated cardoon, and wild cardoon). In this work, the results of C. cardunculus biomass and grain yield under Sicilian (south Italy) low input conditions are shown. Over a 3 year period on the plain of Catania (South Italy) six genotypes of C. cardunculus, including 1 cultivated cardoon cultivar, 1 globe artichoke line, 1 wild cardoon ecotype, 3 F₁ progenies: “globe artichoke × wild cardoon”, “globe artichoke × cultivated cardoon” and “cultivated cardoon × wild cardoon”, were evaluated for lignocellulosic biomass production, energy yield and grain yield. On a 3 year average, the dry aboveground biomass and grain yield resulted, respectively, about 2000 g plant^?1 and 100 g plant^?1 in “globe artichoke × wild cardoon”, 1720 and 126 g plant^?1 in cultivated cardoon, 1570 and 90 g plant^?1 in “globe artichoke × cultivated cardoon”, 1480 and 109 g plant^?1 in “cultivated cardoon × wild cardoon”, 1116 and 75 g plant^?1 in wild cardoon and 990 and 60 g plant^?1 in globe artichoke. The results showed that genotypes deriving from the cross of globe artichoke with cultivated and wild cardoon improved the performance both of globe artichoke and wild cardoon separately. It is reasonable to expect further improvements for biomass and grain yield in C. cardunculus in the future by breeding work.     

Single layer solar drying behaviour of Citrus aurantium leaves under forced convection

Convective solar drying experiments in thin layers of Citrus aurantium leaves grown in Marrakech, morocco, were conducted. An indirect forced convection solar dryer consisting of a solar air collector, an auxiliary heater, a circulation fan and a drying cabinet is used for the experiments. The air temperature was varied from 50 to 60 °C; the relative humidity from 41% to 53%; and the drying air flow rate from 0.0277 to 0.0833 m³/s. Thirteen statistical models, which are semi-theoretical and/or empirical, were tested for fitting the experimental data. A nonlinear regression analysis using a statistical computer program was used to evaluate the constants of the models. The Midilli–Kucuk drying model was found to be the most suitable for describing the solar drying curves of Citrus aurantium leaves with a correlation coefficient (r) of 0.99998, chi-square (χ²) of 4.664 × 10⁻⁶ and MBE of 4.8381 × 10⁻⁴.     

Energy and exergy analysis of timber dryer assisted heat pump

In this research, poplar and pine timbers have been dried from the moisture contents of 1.28 kg water/kg dry matter and 0.60 kg water/kg dry matter to 0.15 kg water/kg dry matter in heat pump dryer functioning on the basis of 24 h operation. The change in weight in all of the timbers was followed in the drying chamber and drying stopped when the desired weight was achieved. At 40 °C dry bulb temperature, 0.8 m/s air velocity, and initial moisture content of the poplar timbers 1.28 kg water/kg dry matter, the moisture content was reduced to 0.15 kg water/kg dry matter moisture content in 70 h, and the moisture content of the pine timbers which was 0.60 kg water/kg dry matter was reduced to the same amount in 50 h. All data collected while drying were saved on computer and analysed afterwards. For this system, energy analysis was made to determine the energy utilization. Exergy analysis was accomplished to determine of exergy losses during the drying process.     

Hydrothermal preparation and electrochemical properties of Gd3+ and Bi3+, Sm3+, La3+, and Nd3+ codoped ceria-based electrolytes for intermediate temperature-solid oxide fuel cell

The structure, the thermal expansion coefficient, electrical conductivities of Ce_0.8Gd_0.2?xM_xO_2?δ (for M: Bi, x = 0–0.1, and for M: Sm, La, and Nd, x = 0.02) solid solutions, prepared for the first time hydrothermally, are investigated. The uniformly small particle size (28–59 nm) of the materials allows sintering of the samples into highly dense ceramic pellets at 1300–1400 °C. The maximum conductivity, σ_700 °C around 4.46 × 10^?2 S cm^?1 with E_a = 0.52 eV, is found at x = 0.1 for Bi-co-doping. Among various metal-co-dopings, for x = 0.02, the maximum conductivity, σ_700 °C around 2.88 × 10^?2 S cm^?1 with E_a = 0.67 eV, is found for Sm-co-doping. The electrolytic domain boundary (EDB) of Ce_0.8Gd_0.1Bi_0.1O_2?δ is found to be 1.2 × 10^?19 atm, which is relatively lower than that of the singly doped samples. The thermal expansion coefficients, determined from high-temperature X-ray data are 11.6 × 10^?6 K^?1 for the CeO₂, 12.1 × 10^?6 K^?1 for Ce_0.8Gd_0.2O_2?δ, and increase with co-doping to 14.2 × 10^?6 K^?1 for Ce_0.8Gd_0.18Bi_0.02O_2?δ. The maximum power densities for the single cell based on the codoped samples are higher than that of the singly doped sample. These results suggest that co-doping can further improve the electrical performance of ceria-based electrolytes.     

Unsteady conjugate natural convection in a square enclosure filled with a porous medium

Mathematical simulation of unsteady natural convection modes in a square cavity filled with a porous medium having finite thickness heat-conducting walls with local heat source in conditions of heterogeneous heat exchange with an environment at one of the external boundaries has been carried out. Numerical analysis was based on Darcy–Forchheimer model in dimensionless variables such as a stream function, a vorticity vector and a temperature. The special attention was given to analysis of Rayleigh number effect Ra = 10⁴, 10⁵, 10⁶, of Darcy number effect Da = 10^?5, 10^?4, 10^?3, ∞, of the transient factor effect 0 < τ < 1000 and of the heat conductivity ratio k_2,1 = 3.7 × 10^?2, 5.7 × 10^?4, 6.8 × 10^?5 on the velocity and temperature fields. The influence scales of the defining parameters on the average Nusselt number have been detected.     

Numerical modeling of heat and mass transfer during forced convection drying of rectangular moist objects

A two-dimensional analysis of heat and mass transfer during drying of a rectangular moist object is performed using an implicit finite difference method, with the convective boundary conditions at all surfaces of the moist object. The variable convective heat and mass transfer coefficients are considered during the drying process. The external flow and temperature fields are first numerically predicted through the Fluent CFD package. From these distributions, the local distributions of the convective heat transfer coefficients are determined, which are then used to predict local distributions of the convective mass transfer coefficients through the analogy between the thermal and concentration boundary layers. Also, the temperature and moisture distributions for different periods of time are obtained using the code developed to determine heat and mass transfer inside the moist material. Furthermore, the influence of the aspect ratio on the heat and mass transfer is studied. It is found that the convective heat transfer coefficient varies from 4.33 to 96.16 W/m² K, while the convective mass transfer coefficient ranges between 9.28 × 10⁻⁷ and 1.94 × 10⁻⁵ m/s at various aspect ratios. The results obtained from the present analysis are compared with the experimental data taken from the literature, and a good agreement is observed.     

The effects of operating conditions on emissions from masonry heaters and sauna stoves

Emissions from masonry heaters and sauna stoves were studied. In the sauna stove the production of organic gaseous carbon (OGC) at 10 gC kg^?1 (per kilogram of fuel), carbon monoxide (CO) at 55 g kg^?1, fine particle mass (PM₁) at 5 g kg^?1 and number emissions (N) at 1.8 × 10¹⁵ kg^?1 was higher than in other measured appliances. In a modern technology masonry heater with a unique grate, the emissions were very low: 0.4 gC kg^?1 OGC, 14 g kg^?1 CO and 0.7 g kg^?1 PM₁. Conventional masonry heaters, using small logs, clearly produced higher emissions when compared to using large logs. Doubling the fuel load caused emission factors to increase by up to 4- times (OGC), except for the number emission, which decreased from 4.0 × 10¹⁴ to 2.0 × 10¹⁴ kg^?1. From the conventional masonry heater 90% of the PM was emitted during the firing phase. Its combustion process is different to that in stoves or conventional open fireplaces. The insufficient supply of air, due to too fast pyrolysis, and increased ash release, due to the high combustion temperature, are the main parameters which cause high particle and gas emissions in masonry heaters and sauna stoves.     

Solar energy system reduces time taken to inhibit microbial growth in soil

This research studied how to reduce the time consumption and to increase and improve the efficiency of the solarization process. The asymmetry compound parabolic concentrator (ACPC) was developed to produce boiling water to be utilized while the solarization process was in operation. This could decrease the time consumed in the solarization process from 4 to 6 weeks to 4 h, with a temperature of approximately 41.25 °C at the various depth levels, not exceeding 50 cm. The test to inhibit the growth of Ralstonia solanacearum, the causative agent of wilt in crops leaves, indicated that R. solanacearum was reduced from the total bacterial population of 10.9 × 10⁸ colony forming unit/g soil (cfu g^?1) at soil surface to 9.0 × 10⁷, 7.5 × 10⁴ and 4.1 × 10³ cfu g^?1 within 1, 2 and 4 h, respectively.     

Energy and exergy analyses of OMW solar drying process

The energy and exergy analyses of the drying process of olive mill wastewater (OMW) using an indirect type natural convection solar dryer are presented. Olive mill wastewater gets sufficiently dried at temperatures between 34 °C and 52 °C. During the experimental process, air relative humidity did not exceed 58%, and solar radiation ranged from 227 W/m² to 825 W/m². Drying air mass flow was maintained within the interval 0.036–0.042 kg/s. Under these experimental conditions, 2 days were needed to reduce the moisture content to approximately one-third of the original value, in particular from 3.153 g_water/g_{dry matter} down to 1.000 g_water/g_{dry matter}.Using the first law of thermodynamics, energy analysis was carried out to estimate the amounts of energy gained from solar air heater and the ratio of energy utilization of the drying chamber. Also, applying the second law, exergy analysis was developed to determine the type and magnitude of exergy losses during the solar drying process. It was found that exergy losses took place mainly during the second day, when the available energy was less used. The exergy losses varied from 0 kJ/kg to 0.125 kJ/kg for the first day, and between 0 kJ/kg and 0.168 kJ/kg for the second. The exergetic efficiencies of the drying chamber decreased as inlet temperature was increased, provided that exergy losses became more significant. In particular, they ranged from 53.24% to 100% during the first day, and from 34.40% to 100% during the second.     

Temperature imaging of sub-millimeter-thick water using a near-infrared camera

This paper presents a method of imaging temperature distributions of sub-millimeter-thick water using a near-infrared camera and optical narrow-bandpass filter. The principle is based on the temperature dependence of the ν₁ + ν₃ absorption band of water. Temperature images are constructed by measuring the absorbance of water at the wavelength of 1412 nm through the filter for all pixels of the camera. From calibration measurements on 0.5-mm thick water at temperatures from 26.0 °C to 40.0 °C, the temperature coefficient was 6.3 × 10^?4 K^?1 and the standard deviation of absorbance was 1.9 × 10^?4. Thermal diffusion in 0.5-mm thick water caused by a thin heating wire was visualized with this method. The obtained images were verified against temperature distributions calculated by solving a two-dimensional thermal conduction model. This method would be useful for temperature measurement applications and control of aqueous solutions in microchips.     

Numerical simulation on oxygen transfer in a porous scaffold for animal cell culture

Detailed numerical simulations are performed for oxygen transfer around and within a circular scaffold for animal cell culture. The oxygen concentration distribution, minimum oxygen concentration within the scaffold and its corresponding location, as well as the Sherwood number are presented at different Darcy numbers, Reynolds numbers and Damkohler numbers. It is found that if the Reynolds number is increased from 1 to 30, the Sherwood number increases 1 time for a Darcy number of 5 × 10^?6 while 34 times for a Darcy number of 5 × 10^?4. The location of the minimum oxygen concentration is close to the centre of the scaffold when the Darcy number is smaller than about 5 × 10^?5 or the Reynolds number is smaller than about 1, especially for the Damkohler number larger than O(10). The present study may provide useful guidance on design of the bioreactor with scaffold as well as choosing optimal operating parameters.     

Energy and exergy of potato drying process via cyclone type dryer

This paper is concerned with the energy and exergy analyses of the single layer drying process of potato slices via a cyclone type dryer. Using the first law of thermodynamics, an energy analysis was performed to estimate the ratios of energy utilization. An exergy analysis was accomplished to determine the location, type and magnitude of the exergy losses during the drying process by applying the second law of thermodynamics. It was concluded that the exergy losses took place mostly in the 1st tray where the available energy was less utilized during the single layer drying process of potato slices. It is emphasized that the potato slices are sufficiently dried in the ranges between 60 and 80 °C and 20–10% relative humidity at 1 and 1.5 ms⁻¹ of drying air velocity during 10–12 h despite the exergy losses of 0–1.796 kJ s⁻¹.     

Modeling of a flat plate membrane-distillation system for liquid desiccant regeneration in air-conditioning applications

A thermally driven flat plate air gap membrane distillation liquid desiccant regenerator for lithium chloride in dehumidification applications is modeled. Operating conditions and device geometry are optimized, and it is found that membrane materials have little influence on regenerator performance. It is shown that radiation heat transfer across the air gap cannot be neglected. The regenerator removes 11.4 g min^?1 cm^?3 of moisture with a COP of 0.372 for an inlet solution concentration of 0.38, solution flow rate of 50 ml min^?1, and heated solution temperature of 135 °C. This design has negligible desiccant carry-over losses and operates without a blower.     

Comparison of numerical and experimental performance criteria of an ammonia–water bubble absorber using plate heat exchangers

A mathematical model for ammonia–water bubble absorbers was developed and compared with experimental data using a plate heat exchanger. The analysis was performed carrying out a sensitive study of selected operation parameters on the absorber thermal load and mass absorption flux. Regarding the experimental data, the values obtained for the solution heat transfer were in the range 0.51–1.21 kW m^?2 K^?1 and those of the mass absorption flux in the range 2.5–5.0 × 10^?3 kg m^?2 s^?1. The comparison between experimental and simulation results was acceptable being the maximum difference of 11.1% and 28.4% for the absorber thermal load and the mass absorption flux, respectively.