Hot-air Chamber Research Articles

PRORAČUN KOMORNE SUŠARE ZA PEČURKE

U okviru rada prikazan je primer proračuna i konstrukcije jedne konvektivne komorne sušare sa podovima za sušenje pečurki. Cilj rada je razmatranje više mogućih rešenja za zagrevanje agensa sušenja, sa fokusom na upotrebu obnovljivih izvora energije umesto konvencionalnih goriva, pre svega toplotnih pumpi. Na osnovu definisanog sistema, odabrana je odgovarajuća konstruktivna izvedba sušare.

Mechanical activation of two different types of fly ash and their effect on alkali activation.

The article aim is to analyze the influence of mechanical activation of a fly ash, with different proportion of mechanically activated and not mechanically activated material on alkali activation. The paper describes fly ash based geopolymers and their mechanical properties. Fly ashes were mixed in four different ratios with mechanically activated fly ash. Activation solution was constant in all specimens. Compressive and flexural strengths of the hardened product were tested after 7 and 28 days of the storage in laboratory conditions and samples were cured after activation in hot air chamber for 6 hours in 80°C temperature. The results show how mechanical activation of materials affects their strengths with highest amount achieved was 44 MPa.

Effect of different drying methods on the nutritional and physicochemical properties of unpeeled banana flour

This work was conducted to evaluate the effect of drying methods on the nutritional values and physicochemical properties of unpeeled banana flour. Proximate, amylose content, phenolic compound, resistant starch, total dietary fibre, functional properties, pasting properties, and thermal properties of dried banana flour samples were evaluated. Three different drying methods of whole banana with the intact peel were studied including 1) hot-air unpeeled flour (HAU) (dried at 60oC for 2 h in hot-air chamber), 2) microwave-vacuum unpeeled flour (MVU) (36,000 W under vacuum -600 mmHg for 15 min in a pilot microwave-vacuum dryer), and 3) infrared unpeeled flour (IRU) (600 W for 15 min in infrared channel dryer). The HAU and MVU showed the highest yield. Drying methods did not affect the compositions of the flour but significantly affected the total dietary fibre, resistant starch, amylose content and phenolic compound of the flour. Among samples, HAU contained the highest nutritional values with outstanding functional properties, and pasting properties. The unpeeled banana flour can be utilized in various food products such as noodle, bakeries, snack or used as functional ingredients for nutritional purposes.

Modelling of hot air chamber designs of a continuous flow grain dryer

The pressure loss, flow distribution and temperature distribution of a number of designs of the hot air chamber in a continuous flow grain dryer, were investigated using CFD. The flow in the dryer was considered as steady state, compressible and turbulent. It is essential that the grain is uniformly dried as uneven drying can result in damage to the end-product during storage. The original commercial design was modified with new guide vanes at the inlets to reduce the pressure loss and to ensure a uniform flow to the line burner in the hot air chamber. The new guide vane design resulted in a 10% reduction in pressure loss and a γ-value of 0.804. Various design changes of the hot air chamber were analysed in terms of pressure loss and temperature distribution with the aim of a temperature variation of ±5 K at the outlet ducts. An obstruction design was analysed, which improved mixing and gave a temperature distribution within the limits. However, the pressure loss was six times larger than the original design with new guide vanes. Finally, The static mixer design resulted in a 23% reduction in the pressure loss, but had a mean absolute deviation of 22.9 K.

Numerical simulation of 3D hot-air anti-icing chamber based on Eulerian wall film model

Numerical simulation of 3D hot-air anti-icing chamber based on Eulerian wall film model

Forced hot-air treatment against Bactrocera papayae (Diptera: Tephritidae) in papaya

The Asian papaya fruit fly, Bactrocera papayae Drew and Hancock, was treated with hot-water immersion and forced hot air to develop a phytosanitary heat treatment schedule. Hot-water immersion tests were conducted with 12- and 24-h-old eggs and with first and third instar larvae to compare the relative thermotolerances of this fruit fly among these life stages. The 24-h-old eggs, the most thermotolerant among the four life stages tested, were subjected to time and temperature tests using cage-infested papaya fruits in a forced hot-air chamber. Heating the papayas to a minimum core temperature of 47.7 °C (95% confidence interval 47.2–48.3 °C) was estimated to induce probit-nine mortality based on a probit analysis of the data. Confirmatory tests in which papayas infested with 24-h-old eggs were heated to a minimum fruit core temperature of 47.2 °C that was maintained for 0–30 min followed by hydrocooling to a fruit core temperature of ≈25 °C resulted in the complete mortality of an estimated treated population of 43,425 eggs aged 24 h (99.9931% mortality at the 95% confidence level). Therefore, heating the papaya fruits to a core temperature of 47.2 °C for a minimum dwell time of 30 min, which was the longest dwell time in the confirmatory tests, may serve as a phytosanitary heat treatment schedule for the control of B. papayae in papaya fruits.

Lipid characterization of chestnut and willow honeybee-collected pollen: Impact of freeze-drying and microwave-assisted drying

Honeybee-collected pollen is gaining attention as functional food, due to its high content of bioactive compounds, such as essential amino acids, antioxidants, vitamins and lipids. Traditional conservation methods include drying in a hot air chamber or freezing. These techniques influence the pollen organoleptic properties and its content of nutraceutical compounds. We analysed the lipid component of two honeybee-collected pollens, Castanea sativa and Salix alba. Chestnut pollen was characterized by a higher level of omega-6 fatty acids, while willow pollen showed a higher concentration of omega-3 fatty acids and carotenoids. Furthermore, two novel conservation methods, freeze-drying and microwave-assisted drying, were proposed and their impact on the pollen lipid profile was assessed. Only the microwave treatment showed a damaging action on antioxidant compounds (i.e. reduction of tocopherols). Overall, this research shed light on the lipid profile of honeybee-collected pollen, highlighting the nutraceutical importance of pollen as a source of omega-6 and omega-3 polyunsaturated fatty acids.

Activation Energy of Thin-layer Drying Kinetics of Belimbing Dayak Fruit (<em>Baccaurea angulata</em>)

Drying using a hot air chamber was tested on samples of belimbing dayak (Baccaurea angulata). The drying experiments were performed at drying air temperature 40, 45 and 50°C, respectively and at a constant relative humidity of 20% and constant air velocity of 1 m/s. The drying kinetics of B. angulata were investigated and obtained. The time required to dry B. angulata from an initial moisture content of about 89% (wb) to the final moisture content of around 8% (wb) was 13, 11.5 and 7 h at 45, 50 and 55°C of drying air temperature respectively. The effective moisture Diffusivity (Deff) of B. angulata increased from 1.99×10-9 to 3.71×10-9 m2/s as the drying air temperature increased from 45 to 55°C. The activation energy of diffusion (Ea) was calculated about 54 kJ/mol.

Drying Kinetics and Drying Models of Terong Dayak (<em>Solanum lasiocarpum</em>)

Drying using a hot air chamber was tested on samples of terong dayak (<em>Solanum lasiocarpum</em>). Drying kinetics curves of drying <em>S. Lasiocarpum</em> demonstrated that drying at 55°C and relative humidity of 10% were the optimum values for drying <em>S. Lasiocarpum</em>, with the appropriate equations using the Page’s model drying equation $MR = exp (-0.5494t^{1.4052})$ that produced 96.8% accuracy. According to the results which showed the highest average values of $R^2$ and the lowest average values of MBE and RMSE, therefore it can be stated that the Page model could describe the drying characteristics of S. lasiocarpum in the drying process at a temperature of 55°C and relative humidity of 10%.

Mathematical Modeling of Belimbing Dayak Fruit (&lt;em&gt;Baccaurea angulata&lt;/em&gt;) Influence of Different Drying Air Temperature

Drying using a hot air chamber was tested on samples of belimbing dayak fruit (<em>Baccaurea angulata</em>). The drying experiments were performed at various air temperature drying (40 to 50oC). Drying kinetics of belimbing dayak fruit were investigated and obtained. Ten drying models were compared with experiments data belimbing dayak fruit drying. A new model was introduced, which is an offset linear logarithmic (offset modified Page model). The fit quality of the models was evaluated using the coefficient of determination (R2), Root Mean Square Error (RMSE) and Sum of Squared Absolute Error (SSAE). The result showed that the new model was comparable with two or three-term exponential drying models.

Microwave-Assisted Drying for the Conservation of Honeybee Pollen.

Bee pollen is becoming an important product thanks to its nutritional properties, including a high content of bioactive compounds such as essential amino acids, antioxidants, and vitamins. Fresh bee pollen has a high water content (15%–30% wt %), thus it is a good substrate for microorganisms. Traditional conservation methods include drying in a hot air chamber and/or freezing. These techniques may significantly affect the pollen organoleptic properties and its content of bioactive compounds. Here, a new conservation method, microwave drying, is introduced and investigated. The method implies irradiating the fresh pollen with microwaves under vacuum, in order to reduce the water content without reaching temperatures capable of thermally deteriorating important bioactive compounds. The method was evaluated by taking into account the nutritional properties after the treatment. The analyzed parameters were phenols, flavonoids, with special reference to rutin content, and amino acids. Results showed that microwave drying offers important advantages for the conservation of bee pollen. Irrespective of microwave power and treatment time, phenol and flavonoid content did not vary over untreated fresh pollen. Similarly, rutin content was unaffected by the microwave drying, suggesting that the microwave-assisted drying could be a powerful technology to preserve bioprotective compounds in fresh pollen.

Effect of different drying methods on moisture ratio and rehydration of pumpkin slices

This study was carried to determine the influence of hot air drying process and combined methods on physicochemical properties of pumpkin (Cucurbita moschata) samples. The experiments in hot air chamber were lead at 50, 60 and 70°C.The combined method consists of a triple combination of the main drying techniques. Thus, in first stage the samples were dried in hot air convection at 60°C followed by hot air ventilation at 40°C simultaneous with microwave.The time required to reduce the moisture content to any given level was highly dependent on the drying conditions. So, the highest value of drying time in hot air has been 540min at 50°C, while the lowest time has been 189min in hot air combined by microwave at 40°C and a power of 315W.The samples dried by hot air shows a higher rehydration capacity than samples dried by combined method.

The Influence of Hot Air Environment and Humidity towards the Performance of Folding Endurance for Polypropylene Hinges

Folding endurance is very important in terms of the indication for durability and performance of plastics and papers. The objective of this research is to study the performance of polypropylene hinges with the influence hot air in the fabricated chamber and high humidity condition. The performance of this sample was analysed by using folding endurance tester with hot air chamber, adopting the Design of Experiment L9 (34) Taguchi Method for the selected factors which are temperature, relative humidity, breaking time and motor speed. All of these factors were selected with a constant force. Based on the findings, the best combination of parameters which signify the performance of folding endurance test in humidity environment is 70°C for temperature, 60 N for relative humidity, 2 days of breaking time and 850 rpm for motor speed. As for hot air environment, the best setting is 70°C for temperature, 55 N for relative humidity, 3 days of breaking time and 700 rpm for motor speed. For Signal to Noise ratio, the result showed that the temperature was the most influential factor for humidity effects and hot air environment, whereby the Signal to Noise ratio value obtained for the humidity and hot air environment are 129.5 dBi and 130.5 dBi respectively. The conclusion of this research is the polypropylene hinges have performed better with hot air environment as compared with higher humidity environment condition.

DRYING CHARACTERISTICS OF THE BORNEO &lt;i&gt;CANARIUM ODONTOPHYLLUM&lt;/i&gt; (DABAI) FRUIT

The quality and shelf-life of an underutilized frui ts are compromised by the conventional method of drying. We therefore proposed using hot-air chamber to develop the drying curves of Canarium odontophyllum (dabai) fruit. Present study provides evidence of the best mathematical model to demonstrate the drying characteristi cs of this indigenous fruit and thus, may generate or add to t he existing database. The drying experiments were performed at three different relative humidity of 10, 20 and 30% and a constant air velocity of 1 m sec -1 . Drying kinetics of C. odontophyllum fruit were investigated and obtained. A non-linear regression procedure was used to fit three different one-term exponential models of thin layer drying models. The models were compared with experimental data of C. odontophyllum fruit drying at air temperature of 55°C. The fit qu ality of the models was evaluated using the coefficient of determination (R 2 ), Mean Bias Error (MBE) and Root Mean Square Error (RMSE). The highest value of R 2 obtained was 0.9348, the lowest MBE value was 0.0018 and the value for RMSE was 0.0420. Page model is the best mathematical model to describe the drying behavior of C. odontophyllum fruit.

A temperature-sensitive tracer suitable for two-colour laser-induced fluorescence thermometry applied to evaporating fuel droplets

This paper reports an extensive spectroscopic study of the fluorescence of pyrromethene 597-8C9, which can be used as a dye in two-colour laser-induced fluorescence thermometry. This technique requires a single dye and two spectral bands of detection to measure the droplet temperature. The selection of a fluorescent tracer is a critical issue. To achieve measurements with a reasonable accuracy, a tracer should exhibit a fluorescence spectrum that is particularly dependent on the temperature. Another important feature is the possibility of using the same dye and the same optical components with a large variety of fuels, including multi-component fuels which are commonly used in industrial applications, which was not possible with usual tracers like rhodamine B. This paper demonstrates that pyrromethene 597-8C9 is relevant for measuring the temperature of droplets made of alkanes (dodecane), ketones (3-pentanone) or alcohols (ethanol). It can also handle mixtures of ethanol and 3-pentanone. In this study, demonstration experiments are performed on droplets injected into a hot air chamber (645 K).

03/01636 Combustion characteristics of droplets composed of light cycle oil and diesel light oil in a hot-air chamber: Xu, G. et al. Fuel, 2003, 82, (3), 319–330

03/01636 Combustion characteristics of droplets composed of light cycle oil and diesel light oil in a hot-air chamber: Xu, G. et al. Fuel, 2003, 82, (3), 319–330

Burning Droplets of Heavy Oil Residual Blended with Diesel Light Oil: Analysis of Coke Behaviors

Isolated droplet burning was conducted in a hot-air chamber for blended oils formed from mixing a heavy oil residual (HOR) and a diesel light oil (LO) at different fractions to investigate the burn...

Burning droplets of heavy oil residual blended with diesel light oil: Distinction of burning phases

This work succeeds a previous report in Combustion Science and Technology (Vol. 174, pp. 115-145, 2002), and aims at distinguishing between the liquid and solid phases of burning heavy fuel oil (HFO) droplets in terms of burning times. The durations of the two burning phases were determined from the previously measured component times for burning steps that prevailed inburning droplets of blend oils between a heavy oil residual (HOR) and adiesel light oil (LO). A hot-air chamber was employed to acquire the high-temperature conditions of droplets occurring in actual burners. The result showed that the duration of the solid phase is generally larger than, and in some particular cases it is comparable to, that of the liquid phase. As for the examined blend oils, the pure HOR exhibited comparable phase durations, while the other blend oils had longer durations for the solid phase than for the liquid phase. Under the tested conditions, the durations of both phases tended to decrease with increasing LO fraction and ambience temperature and decreasing the initial droplet diameter. For typical HFOs, such as those equivalent to the blend oils with LO fractions greater than 26 wt. %, the relative ratio of durations between the solid phase and the liquid phase appeared weakly dependent on oil composition, temperature, and droplet size. This resulted in an average ratio of about 1.3 and a corresponding fluctuation from 1.0 to 1.6. The pure HOR slightly deviated from such values, however, manifesting an average of 1.0 and a fluctuation of 0.8 to 1.3. Furthermore, the HOR amount in the oil droplets determined the duration of the solid phase, whereas the initial droplet diameter was linearly correlated with the duration of the liquid phase. This work finally compared the ember times for burning out soot and coke particles, which further verified the dominance of coke burning over the solid phase.

Combustion characteristics of droplets composed of light cycle oil and diesel light oil in a hot-air chamber☆

Development of gas turbines fueled with light cycle oil (LCO) and oil mixture of LCO and diesel light oil (LO) requires an understanding of the droplet burning and vaporization characteristics of those oils. The present study is devoted to comparing the burning characteristics of isolated fuel droplets composed of an LCO and an LO. The tests were conducted in an atmospheric hot-air chamber preset at 1173 K, and the examined LCO had a lower cetane number but higher volatility and aromatics content compared to LO. It was demonstrated that the burning of the LCO droplet was sootier, while that of the LO droplet was more disruptive. At the tested temperature, coke formation was indistinct for both the oils, whereas slightly higher ignition delay time was shown for the LO droplet. The microexplosive burning more or less complicated the time-series droplet size d, an explicit burning rate constant, however, was still definable according to the d 2-law to show the overall regression speed of the droplet surface area d 2 with burning time t. The rate constant exhibited little difference for smaller LCO and LO droplets but was greater for LO when the droplet was larger. The rate constant also gradually increased with increasing the initial droplet diameter d 0, which caused the relative size d/ d 0 to be unified (normalized) into a single curve by a burning time t/ d 0 n (1.0< n<2.0). Analysis revealed that this unification resulted from the respective overlaps of the unsteady and quasi-steady burning phases for differently sized droplets. Further, it was clarified that the unification and analysis are generally valid to isolated liquid fuel droplet burning in hot ambiences.

Burning droplets of heavy oil residual blended with diesel light oil: Characterization of burning steps

Highlighting the burning process of heavy oil droplets resulted in the resolution of the whole process into four burning steps that in turn defined four component times (in succession): the ignition delay, flame lifetime, coke glowing delay, and coke ember time. The present work was devoted to measuring the component times in an atmospheric hot-air chamber, and to further analyzing their constitutional characteristics with respect to oil compositions and burning conditions by using hybrid oils blending a heavy oil residual (HOR) and a diesel light oil (LO) at different fractions to simulate the diversified heavy oils. The four burning steps generally prevailed during burning, but their time durations relative to the total burning time varied with oils, temperatures, and droplet sizes. The increase in the LO fraction considerably reduced the ignition delay and coke ember time but little affected the flame lifetime and coke glowing delay. Notwithstanding, the ratios of component times to total burning times appeared independent of the LO fraction when the fraction was definitely higher, such as greater than 30 wt.%. Increasing the chamber temperature much decreased the ignition delay and coke glowing delay but little changed the flame lifetime. This led the coke ember time and flame lifetime to become dominant in the total burning time at higher temperatures. The initial droplet diameter influenced the component times and their relative values, but the influence appeared secondary to the effects of oil composition and chamber temperature. With these results, the article suggested that the burner designs for different heavy oils should focus on the oil-induced differences in fuel ignition and coke burnout rather than in volatile burn-up.