Hot Air Velocity Research Articles

DRYING REFINED SUGAR ON THE CONTINUOUS PULSED FLUIDIZED BED DRYER: EXPERIMENTAL STUDY ON THE MAIN TECHNOLOGICAL PARAMETERS DETERMINATION

A continuous pulsed fluidized bed (CPFB) dryer with relocated gas stream was employed to conduct the drying of refined sugar. The experiments were carried out according to the 2-level orthogonal experimental plan, combined with multiple response optimization according to Response Surface Method (RSM) to determine the appropriate parameters (hot air temperature, hot air velocity, pulse frequency, particle mean diameter) in the refined sugar drying process. The appropriate conditions of drying process were identified at 71.5C of hot air temperature, 2.1 m/s of hot air velocity, 0.55 Hz of pulse frequency and 467m of particle mean diameter. At these conditions the dried refined sugar reached final moisture content of 0.035% (wet basis), the specific electrical energy and the specific heat value consumption reached 187 Wh/kg product and 1024 kJ/kg product, respectively.

The convective hot air drying of Lactuca sativa slices

ABSTRACTThe storage of fresh agricultural products is not easy because of its high moisture. Dehydration is an efficient preservation method. The investigation of drying modeling and transfer characteristics are important for selecting operating conditions and equipment design. The drying behavior of Lactuca sativa slices, with the thickness of 2 mm, was investigated at 60.0–80.0°C and 0.60–1.04 m sec−1 velocity in a convective hot air drier. The mass transfer during the drying process was described using six thin drying models. The convective heat transfer coefficient α and mass transfer coefficient kH were finally calculated. The results showed that the drying process could be separated into three stages including accelerating rate, constant rate, and falling rate period, which was influenced by hot air temperature and velocity, and the Modified Page model agreed well with the experimental data. When the operating temperature was increased from 60.0°C to 80.0°C, α was found increased from 88.07 to 107.93 W·m−2·K−1, and kH increased from 46.32 × 10–3 to 68.04 × 10–3 kg·m−2·sec−1·ΔH−1. With the increase of air velocity from 0.60 to 1.04 m·sec−1, α was increased from 78.85 to 101.35 W·m−2·K−1, and kH was enhanced from 51.78 × 10–3 to 65.85 × 10–3 kg·m−2·sec−1·ΔH−1.

Investigation of Solar Chimney System and the Effct of Thrmal Storage Capacity on the System Performance Part I: Experimental Investigation

The performance and the thermal behavior of the solar chimney were investigated experimentally. The experimental data were collected from small pilot solar chimney which was designed and constructed at Sabratha Faculty of Engineering-Libya. Solar chimneys need solar radiation in order to work, thus, to have more stable condition, solar energy should be stored during the day and released back during the night. In order to investigate the temperature fild during daylight and hours of darkness, the data were collected for a period of 24 hours for several days of months, May and June 2014. Th investigation also include the effctof thermal storage on the temperature fild. Th solar chimney system contains two main components; the solar collector and the solar chimney. Th solar collector roof has a circular area of 126 m2. A PVC pipe 0.2 m in diameter and 9 m in height was used as a chimney. Water containers were put as thermal blocks to study the effct of thermal storage on the performance of solar chimney. The measurements included the intensity of solar radiation inside/outside the collector, temperature and velocity of heated air at the entrance of the chimney, temperature and speed of wind outside the collector, temperature of the ground inside the collector and temperature measurements of air at particular points at diffrent levels throughout the collector. Solar irradiance was found to affct the chimney temperature and subsequently chimney air velocity. The temperature diffrence between the hot air at chimney entrance and the ambient reached about 45 °C, which generates the driving force of airflw in the chimney. Th hot air velocity in the chimney can reach 3.6 m/s (≈ 0.118 kg/sec). Wind speed was found to have a small inflence on the performance of the solar chimney.The results indicate that the solar chimney system can operate in northwestern Libya. If this type of system is used on a large scale it can trap solar radiation and store a suffient amount of heat through the use of additional heat storage such as water, which raises the air temperature in the collector aftr sunset to a suffient value capable of generating air flw for a long time to run turbines to produce electricity during the day and aftr sunset especially during the summer time.

A Study to increasing the thermal efficiency of the improvements salt boiling stove which the fuel was firewood in Ban Dung area, Udon Thani province by CFD

This research aims a study to compare the thermal efficiency of the original and improvement salt boiling stove by using a mathematical model by computational fluid dynamics (CFD) of the boiling salt process in Ban Dung area, Udon Thani province. This study aimed to compare the thermal efficiency between the original stove and the develop stove, has installed the panels (baffles) that retained heat inside the channel of burning stove. The first study, the original stove has U-shaped channel for heating flow through chimney. The original stove size is 2.4 m of width, 6.0 m of long, 0.8 m of high and cross-sectional area of heating flue was 0.8 x 0.8 m2. The heating flue can be flow through to the space which not installed the panels of U-shaped channel. The second study, the improvement salt boiling stove has a similarly size of the original stove but installed the baffles. The baffles retained heat inside the channel stove which length of 0.2 m and the baffle panel installed every 1.0 m in a zigzag form along of the channel stove. From the experiment of original stove which the fuel was firewood, the average fired temperature is 1,000°C and the average velocity of hot air in the chimney is 0.6 m/s. From the results of mathematical models by CFD found that the original stove have the thermal efficiency, the highest fired temperature and the velocity outlet of hot air of 17.78%, 537.77°C and 4.86 m/s, respectively. Then, the improvements stove have 28.43%, 919.16°C and 2.80 m/s, respectively. it can be calculated the amount of firewood used as fuel to boiled salt that can be reduced to 557.85 kg and calculate cost for boiled salt reduce is 475 baht per one round boiling salt which can reduce the cost of boiling salt production is 37.19%. Comparison between the original and improvement salt boiling stove found that the improvement stove have the thermal efficiency and heating flue more than original stove because the improvement stove have install the baffles retained heat through slowly inside the stove.

Thin-layer isothermal drying kinetics of municipal sewage sludge based on two falling rate stages during hot-air-forced convection

The thin-layer drying behavior of municipal sewage sludge in a laboratory-scale hot-air-forced convective dryer was investigated in between 100 and 160 °C hot air temperatures and hot air velocities of 0.6, 1.4, and 2.0 m s−1. The thin-layer drying of sewage sludge presented a combination of a short warm-up period, and two distinguished falling rate periods. The Modified Page model was the best model to characterize the thin-layer drying of sewage sludge. The thin-layer drying kinetics was evaluated based on two falling rate stages. The effective moisture diffusivities of sewage sludge were from 1.87 × 10−9 to 6.18 × 10−9 m2 s−1 for the first falling rate period, and from 1.15 × 10−8 to 4.40 × 10−8 m2 s−1 for the second falling rate period. The average apparent activation energies of sewage sludge in the first falling rate period and the second falling rate period were 18.25 and 13.79 kJ mol−1.

Drying Characteristics of Agricultural Products under Different Drying Methods: A Review

Purpose: Drying is one of the most widely used methods for preserving agricultural products or food. The main purpose of drying agricultural products is to reduce their water content for minimizing microbial spoilage and deterioration reaction during storage. Methods: Although numerous drying methods are successfully applied to dehydrate various agricultural products with little drying time, the final quality of dried samples in terms of appearance and shape cannot be guaranteed. Therefore, based on published literature, this review was conducted to study the drying characteristics of various agricultural products when different drying methods were applied. Results: An increase in the drying power of sources-for example, increase in hot air temperature or velocity, infrared or microwave power-and the combination of drying power levels can reduce the drying time of various agricultural products. In addition, energy efficiency in drying significantly relies on the compositions of the dried samples and drying conditions. Conclusions: The drying power source is the key factor to control entire drying process of different samples and final product quality. In addition, an appropriate drying method should be selected depending on the compositions of the agricultural products.

Experimental investigation of solar tower with chimney effect installed in CRTEn, Tunisia

This paper studies the performance of a solar tower power plant (STPP) with chimney effect based on renewable energy proposed for electricity production. That's way, a solar tower prototype was constructed and tested in the Research and Technology Centre of Energy (CRTEn), Borj Cédria, northern Tunisia.The design involves heating air using solar energy and the chimney effect to raise the hot air up the chimney stack. The hot air velocity increases by the use of a convergent nozzle to reach a suitable velocity which can run the wind turbine. The kinetic energy of the hot air is then converted to electricity by the wind turbine.During this study, the influence of the climatic conditions of Borj Cédria site (insulation, ambient temperature) as well as the chimney height and the collector diameter on the amount of electricity production were investigated.The distribution and the evolution of the temperature at different positions of the prototype as well as the electrical energy produced were determined.The results reveal that when the temperatures reach 45 °C, the electric power reaches an average value of about 0.3 W/m2 for a solar tower prototype with 8 m of diameter and 2 m of height chimney.

SOME ENGINEERING FACTORS AFFECTING FISH BY- PRODUCTS RECYCLING

The main objective of the present work is to Study the properties of the fish by-products which result from the fish industry (Fillet tilapia) and the proportion of edible parts to non-edible parts tilapia fish from natural. Some physical properties of tilapia fish and its by-products .The drying behavior of Nile fish by- products was investigated in a mechanical dryer and the mathematical modeling by using thin layer drying model (Lewis's models) was used. The impact of the drying air temperature (60, 70 and 80 0C) ,hot air velocity ( 1.0 ,1.5 and 2 ms-1) and The thickness layer(5,7 and 9 mm ) on the fish moisture losses against drying time has been studied. Drying rate, moisture ratio, cost estimation and Chemical assays of the drying process were also considered. The obtained data showed that,average mass fish, skin, trimming, viscera, Head, backbone and meat 373.815, 12.002, 16.325, 34.631, 67.657, 54.88, 187.136 g respectively. The shortest drying time of the fish was recorded at 150 min with 80 0C drying air temperature, thickness layer 5mm and 2 ms-1 air velocity. While, the longest drying time was recorded at 510 min with 60 0C, thickness layer 9 mm and 1 ms-1 treatments .Moisture content decreased from an initial level of about 106.5% (d.b.) to range between 4.4and 2.2% (d.b.) at the end drying process depending on the drying conditions. Moreover, drying rate was increased with the increase of drying air temperature, air velocity and reducing the thickness of the layer. Between tested model, the modified simple exponential model was found to be the most suitable for describing the drying behavior of the fish by-products. The effects of drying air temperature and velocity on the drying constant and coefficient were also shown. On the other hands, the calculated operation cost of the dryer approaches about 2.92 LE/kg of dried whole fish by-product. The protein content in the final product 45%.

Applying Computational Fluid Dynamic to Predict the Thermal Performance of the Nacelle Anti-Icing System in Real Flight Scenarios

Ice accumulation on the inner surface of a nacelle lip-skin can be hazardous. Therefore, it is necessary that the aircraft be protected against the effect of ice accumulation. The Piccolo Tube Anti-Icing (PTAI) is one of the most reliable ice protection systems for nacelle lip-skins and aircraft wings, and is commonly used in commercial aviation. Thus, many researchers studied and developed the empirical correlation of the PTAI system, including Jeffry Brown of Queens University Belfast. He focused on the nacelle lip-skin PTAI system. However, the Brown correlation was developed at room temperature. In present study, on the other hand, the Brown correlation was modified with the help of CFD, in order to make it suitable at different ambient temperatures. CFD analysis can help to save time and effort, as well lower the cost of the nacelle design, by reducing the number of experiments required during the development. The present research executed CFD in 5 different conditions, i.e. Laboratory, Taxi, Climb, Hold, and Descent. Laboratory data closely agree with the Brown correlation, having been run in similar conditions. The average Nusselt number increases as the Reynolds number increases. In conclusion, the research demonstrated that CFD is not only capable of predicting the thermal performance of the PTAI, but it can also be used to investigate some parameters/characteristics that are difficult to obtain from experiments, e.g. the ambient temperature effects and the hot air velocity inside the D-chamber. Keywords: Anti-Icing, CFD, Lip-Skin and Aircraft Crash, Nacelle, Piccolo Tube Anti-Icing

Artificial neural network modeling of thin layer drying behavior of municipal sewage sludge

The back-propagation (BP) and generalized regression neural network models (GRNN) were investigated to predict the thin layer drying behavior in municipal sewage sludge during hot air forced convection. The accuracy of the BP model to predict the moisture content of the sewage sludge thin layer during hot air forced convective drying was far higher than that of the GRNN model. The GRNN models could automatically determine the best smoothing parameters, which were 0.6 and 0.3 for predicting the moisture content and average temperature, respectively. The model type for predicting the average temperature of the sewage sludge thin layer was selected for different sample groups by comparing their MSE values or R2 values. The GRNN model was suitable for predicting the average temperature corresponding to the sample groups at hot air velocity of 0.6m/s, and drying temperatures of 100°C, 160°C; hot air velocity of 1.4m/s, and drying temperatures of 130°C, 140°C; hot air velocity of 2.0m/s, and drying temperatures of 150°C, 160°C. The average temperature for the other sample groups was best predicted by the BP model.

Parameter optimization for microwave coupled with hot air drying process of hawthorn slices using response-surface methodology

The microwave coupled with hot air (MCHA) drying method was used in this test to dry hawthorn slices The effect of initial microwave power density level (6 W/g to 12 W/g), hot air temperature (55°C to 70°C), and hot air velocity (1 m/s to 3 m/s) on the quality attributes of rehydration ratio (Rf), organic acid (OA) and ascorbic acid (AA) of the dehydrated hawthorn slices was analyzed using a response surface methodology. An orthogonal rotatable central composite with three factors and at five levels was used to develop predictive regression models for the responses. The prediction mathematical model of Rf, OA and AA of the hawthorn slice was determined by analysis of variance. Factor and response variables as well as the prediction mathematical model, the optimal drying process of Rf, OA and AA of the hawthorn slice were determined by using the Design-Expert software. The comprehensive optimal conditions were as follows: initial microwave power density 12 W/g, hot air temperature 55°C and hot air velocity 1.56 m/s. Keywords: parameter optimization, response surface methodology, hot air drying, microwave, hawthorn slice DOI: 10.3965/j.ijabe.20150802.1596

Modeling Drying Characteristics of Terebinth Fruit Under Infrared Fluidized Bed Condition

Abstract Advantages of infrared fluid bed drying include high heat and mass transfer coefficients, short process time, high quality and low energy consumption. Since heat and mass transfer and quality changes during drying of terebinth fruit with infrared fluid bed method is not described in the literature. Goals of this research were study the effects of different infrared drying conditions on the drying kinetic and physical parameters of terebinth fruit. To predict moisture during drying process, five mathematical models were used. Experiments were conducted at different levels of hot air velocity (0.93, 1.76 and 2.6 m/s), temperature (40, 55, and 70°C) and infrared radiation power (500, 1000 and 1500 W). Results showed that Demir et al. model had the best performance for predicting of moisture ratio. Effective moisture diffusivity for terebinth samples (6.2×10-11 to 7.3×10-10 m2/s) was achieved. Activation energy of the samples (44.4 to 59.13 kJ/mol) was computed. Maximum rupture force (118.4 N) was calculated at air velocity of 2.6 m/s, infrared power of 1500 W and air temperature of 70°C. The results proved that in addition to short process time, monitoring of terebinth fruit characteristics such as mechanical properties during drying process can be achieved.

Drying Characteristics and Model of Chinese Hawthorn Using Microwave Coupled with Hot Air

Microwave coupled with hot air drying kinetics and characteristics of hawthorn slices at different drying hot air temperatures, hot air velocities, and microwave power densities was investigated. The research results showed that drying occurred mainly in the falling rate period and in the accelerating period. Twelve mathematical models were selected to describe and compare the drying kinetics of hawthorn slices. By comparing three criterions including correlation coefficient, chi-square, and root mean square error, we determined that Weibull distribution model obtained the best fit and could best predict the experimental values. Consequently, Weibull distribution model could be used to aid dryer design and promote the efficiency of dryer operation by simulation and optimization of the drying processes. Moisture transfer from hawthorn slice was described by applying Fick’s second law and the effective diffusivity values were calculated by simplified Fick’s second law. The variable law of effective diffusivity values was consistent with the variable law of moisture ratio.

The Effect of the Width and Number of Gaps on the Characteristics of Swirl Flow Induced Naturally inside Split Channel Using Hot Air Inlet

Split channels are commonly employed in research laboratories to generate fire whirls. The purpose of this computational study is to investigate the effects of the width and number of side gaps on the performance of the split channel when hot air enters at the base of the channel instead of using a fire. Three cylindrical channels are modeled. The first channel includes two identical slots, the second channel has only one gap with a width double that of the first channel, and the third channel comprises one gap identical to that of the first channel. Comparisons between the results of the first and the second channel provide the assessment of the impacts of the number of gaps on the performance of the split channel. Moreover, the comparison between the results of the second and third channels shows the effect of changing the width of the gap. The combined (overall) effects of the number and the width of the gaps on the characteristics of the flow within the channel are also evaluated by comparing the results of the first and the third channel. The results show that increasing the number of the slots without increasing the total area of the gaps leads to an increase in centerline vorticity within the channel. In addition, the inlet velocity of hot air from the base and entrainment ratio decreases with the increase of the number of the side slots. Increasing the width of the gap without changing the number of the slots reduces the entrainment velocity, the inlet velocity, but the entrainment mass flow rate and centerline vorticity increase. The entrainment mass flow rate centerline vorticity and entrainment ratio increases by the increase in the number of identical gaps and the increase of gap width whereas the entrainment velocity and the inlet velocity decrease.

THIN LAYER DRYING OF NILE TILAPIA FINGERLINGS USING MECHANICAL DRYER

In this study, the drying experiments were conducted on fresh fingerlings of Nile tilapia, which does not benefit the consumers (non-marketed and juvenile fish), for production of the fishmeal to be used as an ingredient in feedstuffs in the aquaculture, dairy, and poultry industries. The thin layer drying behaviour of Nile tilapia fingerlings was experimentally investigated in a mechanical dryer and the mathematical modeling by using two thin layer drying models (simple and modified simple exponential models). The butane-gas was used as heat energy source for the dryer. The impact of the drying air temperature (50, 60, 70 and 80oC) and hot air velocity (0.5, 1.0 and 1.5m/s) on the fish moisture losses against drying time has been studied. Drying rate, moisture ratio, cost estimation and microbial assays of the drying process were also considered. The obtained data showed that, the shortest drying time of the fish was recorded at 140min with 80oC drying air temperature and 1.5m/s air velocity. While, the longest drying time was recorded at 280min with 50oC and 0.5m/s treatments. Tilapia moisture content decreased from an initial level of about 84.56%(d.b.) to range between 9.18 and 11.86%(d.b.) at the end drying process depending on the drying conditions. Moreover, drying rate was increased with the increase of drying air temperature and air velocity. Between the two tested models, the modified simple exponential model was found to be the most suitable for describing the drying behavior of the fish. The effects of drying air temperature and velocity on the drying constant and coefficient were also shown. On the other hands, the calculated operation cost of the dryer approaches about 2.88LE/kg of dried whole fish. Also, the final product had a microbial count below allowed level.

The model and mass transfer characteristics of convection drying of peach slices

The influences of drying temperature, hot air velocity and thickness of peach slice on the drying process were studied in a laboratory convective hot air dryer. The experimental data of moisture ratio of peach slices were used to fit the models and the effective moisture diffusion coefficients (Deff) were calculated. Moreover, the relative relations between the Deff and drying temperature was also related. The result showed that the Page model showed the best fit to experimental drying data for drying temperature, with the increase of temperature from 60 to 80°C, the Deff varied from 5.6083×10−10 to 1.3388×10−9m2·s−1, it fitted the Arrhenius equation, which the activation energy was 42.53kJ·mol−1; the Wang and Singh model was found to be the most satisfactory for air velocity, with velocity from 0.423 to 1.120m·s−1, the values of Deff varied from 6.6626×10−10 to 1.1350×10−9m2·s−1; the Logarithmic model was found to be the most satisfactory for the thickness of peach slice, with thickness from 0.002 to 0.004m, the values of Deff varied from 4.1543×10−10 to 1.1007×10−9m2·s−1.

Modeling of mass transfer performance of hot-air drying of sweet potato (Ipomoea Batatas L.) slices

In order to investigate the transfer characteristics of the sweet potato drying process, a laboratory convective hot air dryer was applied to study the influences of drying temperature, hot air velocity and thickness of sweet potato slice on the drying process. The experimental data of moisture ratio of sweet potato slices were used to fit the mathematical models, and the effective diffusion coefficients were calculated. The result showed that temperature, velocity and thickness influenced the drying process significantly. The Logarithmic model showed the best fit to experimental drying data for temperature and the Wang and Singh model were found to be the most satisfactory for velocity and thickness. It was also found that, with the increase of temperature from 60 to 80?C, the effective moisture diffusion coefficient varied from 2.962?10-10 to 4.694?10-10 m2?s-1, and it fitted the Arrhenius equation, the activation energy was 23.29 kJ?mol-1; with the increase of hot air velocity from 0.423 to 1.120 m?s-1, the values of effective moisture diffusion coefficient varied from 2.877?10-10 to 3.760?10-10 m2?s-1; with the increase of thickness of sweet potato slice from 0.002 m to 0.004 m, the values of effective moisture diffusion coefficient varied from 3.887?10-10 to 1.225?10-9 m2?s-1.

Analysis on Gravure Hot-Air Drying Parameters Based on Matlab

This paper illustrated the importance of determining reasonable gravure hot-air drying parameters. On the basis of residual solvent detection via gas chromatographic method, the effect of hot-air velocity, hot-air temperature and primal solvent content on residual solvent was analyzed. According to polynomial regression analysis, curve fitting was conducted, and mathematical model of various parameters, average drying velocity and unit energy consumption was constructed to optimize printing dryer and guide practical production.

ANCHOVY DRYING USING INFRARED RADIATION

The present study investigated the drying of anchovy using infrared radiation experimentally; in addition, the dimensionless heat transfer coefficient in terms of Nusselt’s number was also investigated. The anchovy was dried from 78±1%wb down to 20±1%wb. The drying conditions were infrared power range 400-800 W, hot air temperatures range 50-70°C and hot air velocity range 0.5-1.5 ms-1. The lowest drying time to reduce the moisture content was found at an air temperature of 70°C and velocity of 1.5 ms-1. Drying took 446, 390 and 223 min at 400, 600 and 800 W of infrared power, respectively. The increase in drying temperature, hot air velocity and infrared power were significant factors for decreasing the moisture and darkness of dried anchovy. The modified correlations of Nusselt’s number for the anchovy drying could fit the experimental data quite well within ±10% deviation.

Mathematical Modeling on Hot Air Drying of Thin Layer Fresh Tilapia Fillets

The hot convective drying of fresh tilapia fillets was evaluated in a heat pump dryer. The influence of the drying temperature (35, 45 and 55°C), hot air velocity (1.50, 2.50 and 3.50 m/s) and thickness (3, 5 and 7 mm) of the tilapia fillets on the moisture ratio and drying rate has been studied. It shows that drying process took place in falling rate periods. The experimental drying data of fresh tilapia fillets under different conditions was fitted to nine different commonly used thin-layer drying models by nonlinear fitting methods and all the models were compared according to three statistical param eters, i.e. coefficient of determination, the reduced chi-square and the root mean square error. It was found that the coefficient of determination values of Page were higher than 0.99254, and the corresponding reduced chi-square and the root mean square error values were lower than 0.000632219 and 0.023854, respectively, indicating that the Page model is the best to describe drying curves of fresh tilapia fillets among them. Effective moisture diffusivity ranged from 6.55×10–10 to 1.23×10–9 m2/s calculated using the Fick’s second law. With the increase of the drying temperature and the hot air velocity, the effective moisture diffusivities Deff increased. The value of drying activation energy of tilapia fillets with thickness of 3 mm at hot air velocity 2.50 m/s was 17.66 kJ/mol, as determined from the slope of the Arrhenius plot, ln(D eff ) versus 1/T a . Notations MR – moisture ratio(-), M 0 , M e , M t , M i – initial moisture content, equilibrium moisture content, moisture content of the product at time t, moisture content of the product at time i, (%), U i – drying rate of the product at time i (g/(g·h)), D eff – effective diffusivity (m 2 /s), L 0 – half thickness of slab (m), D 0 – pre-exponential factor of the Arrhenius equation (m 2 /s),