Increasing Air Velocity Research Articles

Design of a separation machine using pneumatic system combined with sieve vibration for removing parchment coffee from Robusta green coffee bean

The hulling process for coffee bean extraction may not effectively release the bean from parchment. This might negatively affect the aroma or taste of coffee in the coffee beans roasting process. Consequently, the objectives of this work were to design and construct a machine for separating parchment coffee from Robusta green coffee bean using a pneumatic separation system combined with sieve vibration. The performance of the separation machine was investigated under different operating conditions such as air velocity, vibration frequency, and the angle of sieve inclination. The samples were fed into the machine at a feed rate of 20 kg/h. The testing conditions were set at air velocities of 2 to 4 m/s, vibration frequencies of 36 to 40 Hz, and sieve inclination angle of 4° to 8°. The results showed that the purity and separation efficiency of parchment increased with increasing air velocity. Conversely, decreasing vibration frequency and sieve angle increased the purity and separation efficiency. The appropriate conditions for parchment coffee separation from Robusta green coffee bean using a pneumatic-sieve vibration system were 4 m/s air velocity, 36 Hz vibration frequency, and 8° sieve angle with the highest overall effectiveness of 92%.

Fragmentation dynamics of single agglomerate-to-wall impaction

The de-agglomeration characteristics of single agglomerate-wall impaction are examined using high-resolution shadowgraph imaging. Experiments are performed to investigate the effects of constituent particle size (D50 from 3 to 7 μm) and air velocity on the individual size and velocity of de-agglomerated fragments at conditions relevant to dry powder inhalation systems. De-agglomerated fragment area and trajectories were used to differentiate between pseudo-elastic and inelastic collisions during de-agglomeration. Advanced image processing techniques have enabled provision of joint population distributions of fragment area and aspect ratio, which identify a bimodal dispersion of fragments during de-agglomeration. The bimodality is destroyed with increasing air velocity and also generally diminishes with time after impact. The experiment presented forms a platform for the detailed quantitative characterisation of de-agglomeration behaviour and can be useful towards the development and validation of related computational models for pharmaceutical dry powder inhalers.

Effect of air velocity, temperature, and relative humidity on drying kinetics of rubberwood

Kiln drying of rubberwood lumbers is a complex transport phenomenon for realistic modeling and simulation. To decouple this complexity, researchers usually divide their research into two parts. The first one is single-lumber drying kinetics to describe how wood lumber responds to its surface conditions. Then they combine this drying kinetics with a lumped transport model or dispersion model or computational fluid dynamics. The mathematical models are then solved numerically to predict the industrial kiln drying behaviors. This work focuses on the drying kinetics of stacked rubberwood lumbers using hot air at different air velocity (0.5, 1.5, 2.5, 3.5, 4.0 m/s), relative humidity (6–67% relative humidity (RH)) and temperature (60–100 °C). The drying kinetics followed the conventional drying theory. However, the two drying periods, namely constant and falling rate (CRP and FRP), were not distinct. As the air velocity increased, the transition from CRP to FRP is faster. The middle of the transition period (at critical moisture content, CMC) moves closer to the fiber saturation point (FSP). The overall mass transfer coefficients in the falling rate period for stacked rubberwood drying were lower than those predicted by the Ananias correlation. Hence, a modified formula was proposed, representing the overall moisture transfer coefficients as a function of air velocity, temperature, relative humidity, and lumbers thickness for the range of variables under investigation satisfactorily. In general, the drying rate and the overall moisture transfer coefficient increased with increasing air velocity, drying temperature, and decreasing RH. Relative humidity directly affects the driving force of moisture transfer rate because higher RH is associated with higher equilibrium moisture content. A lumped parameter model for kiln drying was also developed. After being integrated with the estimated mass transfer coefficient, the model can predict the moisture profiles in lab-scale kiln drying satisfactory, although the model needs more validation data. These kinetic parameters and correlation for stacked rubberwood drying can be used in more complex models and process optimization in future research.

CFD-DEM Simulation of Reverse Circulation Pneumatic Cuttings Removal during Coal Seam Drilling

To solve the problems that the borehole depth is shallow and the borehole formation rate is low during the gas drainage drilling in soft coal seam with current cuttings removal method, a new technology of reverse circulation pneumatic cuttings removal is put forward. The CFD-DEM coupling method is used to establish the simulation model of cuttings-air two-phase flow in drill pipe. The effects of the air velocity for cuttings removal and the mass flow rate of cuttings on the flow characteristics, cuttings removal effect and pressure drop of cuttings-gas two-phase flow are analysed. The results show that the drag force of drilling cuttings becomes larger with the increase of air velocity and the stratified flow characteristic is obvious. The drill cuttings migration ratio is positively correlated with the air velocity for cuttings removal and negatively correlated with the mass flow rate of cuttings. When the mass flow rate of cuttings is constant, the increase of air velocity for cuttings removal leads to the increase of pressure drop in the inner hole of drill pipe. When the air velocity of cuttings removal is constant, the mass flow rate of cuttings and the pressure drop in the inner hole of drill pipe increases. Therefore, the appropriate air velocity should be selected considering the energy consumption during cuttings removal.

Analytical investigation of the influence of natural gas leakage & safety zone in a pipeline flow

Natural gas transportation is complex process which involves building long pipelines with various diversions and joints. Sometimes due to environmental factors like moisture, humidity cracks do initiate causing pipelines to rupture. Such ruptures result in natural gas leakage causing risks of infestations and fire due to methanation reaction. The current research investigates the effect and zone of influence of natural gas leakage from pipeline using techniques of Computational Fluid Dynamics. The CAD model is developed in ANSYS design modeller and CFD analysis is conducted using ANSYS CFX software. The mass fraction and pressure variations in ambient zone depicted the zone of influence of leakage and also specifies the safety zone of operation. The analysis is conducted for three different external air velocities i.e. 5 m/s, 10 m/s and 20 m/s and the combustion model used for analysis is eddy dissipation. The analysis has shown that external air velocity has significant effect on gas leakage zone which increased with increase in external air velocity. The leakage zone was deflected towards windward direction. It is recommended that during any such leakage, the staff personnel should maintain a minimum distance of 0.2 m away from leakage zone to avoid any infestation.

Effect of front air attack angles on heat transfer coefficient of the cross‐flow of four flat tube

AbstractHeat transfer coefficients are studied experimentally for airflow over a four‐flat‐tube configuration with different inlet attack angles. The range of Re numbers was from 1668 to 3782. The heat fluxes are 13.2, 38.5, and 99.8 W/m2. In this paper, 45 samples of a flat tube with inlet airflow angles (30°, 45°, and 90°) are set up to investigate its thermal performance. The design of experimental approach was used to conduct the heat transfer parametric study by designing 45 experiments, analyzing the empirical model, and optimizing heat transfer. The response was modeled using a general factorial design model based on experimental data. From analysis of variance (ANOVA), we obtained significant coefficients by performing the 5% test of level of significance. The results indicated that both the Nu and Re numbers increase for all heat flux cases and these decrease with increasing the air attack. Also shown are that the Colburn j‐factor decreases with increase of air velocity. It was found that the ANOVA results are appropriate to the collected experimental data, as the R2 and R2‐adjusted statistics are found to be 92.61% and 90.97%, respectively, for Nu number. In a similar manner, for Colburn j‐factor, the R2 and R2‐adjusted statistic are 96.97% and 96.29%, respectively.

Ignition Delay of Fluorinated Ethylene Propylene Wire Insulation in a Forced Flow Field in Microgravity

Fluorinated ethylene propylene (FEP) wire insulation ignition is investigated in a forced flow field in microgravity and normal gravity with a continuous current. First, FEP insulation melts and decomposes, causing jet bursting in both normal gravity and microgravity. Second, the forced flow and gravity produce minor effects on the core heating and bursting time, while the pyrolysis time increases slightly with increasing air velocity. Third, the positively stretch rates in terms of the velocity gradients are higher in microgravity. Both the forced flow and gravity have significant effects on the induction time, which is dependent on the stretch rate and Damkohler number. The induction time increases with increasing air velocity, and it is higher in microgravity. Finally, the ignition delay time is dominated by the core heating and bursting time, while its bigger value and faster increase in microgravity with increasing air velocity are dominated by the induction time.

Effect Analysis on Combustion and Emission Characteristics of a Rotary Burner Fueled by Biomass Pellet Fuel

A biomass pellet rotary burner was chosen as the research object, in order to study the influence of excess air coefficient on the combustion phenomenon of biomass rotary burner, the finite element simulation model of a biomass rotary burner was established, and simulation results of a biomass rotary burner were verified by the experiment. The computational fluid dynamics software was applied to simulate the combustion characteristics of biomass rotary burner in a steady-state condition, and the effect of excess air coefficient on temperature field and component concentration field in biomass rotary burner was analyzed. The results show that the flue gas flow rate inside the burner gradually increases with the increase of air velocity, the area with large temperature is mainly concentrated in the middle region of the rotary burner, and the maximum combustion temperature also appeared in the middle region of the combustion chamber, and the formation area of CO decreases with the increase of excess air coefficient. CO2 is mainly concentrated in the middle region of the burner, and the CO2 generating region decreases with the increase of excess air coefficient. The experimental value of the combustion temperature of the biomass rotary burner is in good agreement with the simulation results.

Experimental investigation of battery thermal management and safety with heat pipe and immersion phase change liquid

This paper presents a battery thermal management system (BTMS) with heat pipe and phase-change-liquid to control temperature and inhibit thermal runaway (TR). The proposed BTMS utilizes the cooling capacity and flame retardancy of fluid immersion and the high heat-transfer efficiency of heat pipes. An aged cell is overcharged at 60 A under an ambient temperature of 10 °C. The results show that the proposed BTMS inhibits TR and its propagation effectively, the temperature of overcharge-cell surface remains below 185 °C, and it remains above 60 °C for only 14 s. The experimental results of normal operation indicate that the BTMS operates with heat-pipe & liquid-phase-change mode under high discharge rates and high-power cycle, and the maximum temperature of batteries is limited to 47 ± 1 °C. The corresponding temperature difference of all observation points is below 2.1 °C. The effectiveness of an increase in air velocity is limited in boiling state owing to heat dissipation and vapours pressure, however, it significantly mitigates the temperature rise in non-boiling state; meanwhile, it demonstrates a slight non-monotonic effect on temperature consistency. These results provide an insight into the optimization of BTMS to manage batteries with high power and long safe-operating-life requirements.

HEAT TRANSFER INSIDE BUILDING- CLADDING SOLAR COLLECTOR

In this work numerical and experimental investigation have been adopted to collect and store solar energy in exterior-wall cladding, Various improvements have been investigated inside and outside the duct to increase the efficiency of thermal heating. ANSYS software has been used to simulate current case. Results show that there is a good agreement between experimental and numerical results and this agreement increases as air velocity increases. The average percentage error for air inside duct at velocity of air 1 m/s, 3 m/s and 5 m/s is 8%, 16.5% and 5% respectively. Several vertical cooper cylinders with 12 mm diameter were added inside basin to increase the surface area. It has been found that the enhancement in temperature of air between this case and Smooth Duct, Smooth Cover base model for air velocity of 1,3and 5 m/s is 3, 4 and 11 % respectively. The effect of increasing surface area by using granular (corrugated) duct on the air temperature distribution along the duct. Have been also investigated the percentage enhancement in temperature of air between this case and previous base smooth duct case for velocities of 1, 3 and 5 m/s is 19.4, 28.6 and 16.5 % respectively. The enhancement in heat transfer when using both granular hollow sphere duct with vertical metal cylinders for air velocity of 1, 3 and 5 m/s is 27.5, 33 and 35.2 % respectively.

Impacts of longitudinal air velocity and fuel flow rate on flame radiative fraction in tunnel

Fires in tunnels have attracted special attention in recent years due to catastrophic fires, which cause huge human and economic losses. For accurate fire modelling and ventilation system design, it is critical to understand the correct radiative fraction (Xr) of the flame. Recent study has proved that Xr decreases with the increase of longitudinal air velocity in heptane pool fires. However, the impacts of longitudinal air velocity and fuel flow rate on Xr in propane or liquefied petroleum gas tunnel fires have not been studied. To fill the gap, this paper conducts two sets of fire experiments in a 1/20 reduced-scale wind tunnel using a porous burner. Unique visible flame shapes are observed and described by the ‘back-to-back conical frustum’. The geometric parameters and their variations with the momentum flux ratio are discussed. In comparison with the experimental results, the radiation model using the proposed flame shape shows an 80 % accuracy. The predictive radiative fractions of the two tests are calculated and compared with other tests from literature. The coupling effects of longitudinal air velocity and fuel flow rate on the flame radiative fraction are studied in detail. And their influences on key parameters of smoke extraction system are analyzed.

Experimental and computational studies on gas–solid fluidization in a cylindrical column with and without internals

Gas-solid fluidization often suffers from inherent drawbacks like channeling, bubbling and slugging which affect the quality of fluidization. Efforts have been made in this present investigation to improve the quality of fluidization in gas–solid fluidized beds by conducting hydrodynamic studies in cylindrical fluidized bed column with and without internals. The effect of hydrodynamic parameters such as inlet air velocity, bed height and internal spacing on pressure drop, expansion ratio, fluctuation ratio, minimum fluidization velocity and fluidization index were studied. The pressure drop was found to increase with an increase in bed height regardless of presence or absence of internals. But in the presence of Internals (More Number of internals or less spacing) pressure drop initially decreases but beyond a certain level the resistance offered by the internals is more, and it caused a slight increase in pressure drop. The expansion ratio and fluctuation ratio reduces significantly with a decrease in the spacing of internals. The effect of the internals on quality of fluidization has been studied. By the introduction of internals, the quality of fluidization in terms of fluidization index has improved. The experimental data was used in the CFD simulations and the results obtained are in good agreement with the experimental observations. It is found from the simulation results that the bed height increased with increase in air velocity. The solids are more evenly fluidized in the presence of internals with smaller bubble size and lower bed height than the beds without internals.

INFLUENCE OF DESIGN AND OPERATING PARAMETERS ON SEPARATING THE COARSE WHEAT BRAN BY CYCLONE

Experimental study and predicted models were used to investigate the effect of cyclone geometry and operating parameters such as cone height (30, 50 and 70 cm), vortex finder length (0, 10, 20, 30 and 40 cm), dipleg length (25, 40 and 55 cm) and inlet air velocity (14, 16, 18 and 20 m/s) on separating the coarse wheat bran from air stream. The performance parameters via cut-off diameter (d50), overall collection efficiency (ηo) and pressure drop (ΔP) were evaluated to determine the appropriate design of the cyclone under local operating conditions. The results showed that, ΔP increased with the increase of inlet air velocity and cone height. The optimum operating and design parameters at cone height of 70 cm were inlet air velocity 14 m/s and vortex finder length 40 cm, which lead to high ηo 99.93 % and low ΔP 80.63 Pa. While at cone height of 50 cm, the optimum operating and design parameters were: inlet air velocity 18 m/s under vortex finder length 40 cm which lead to high ηo 99.97 % and low ΔP 121.52 Pa. whereas the cone height 30 cm and vortex finder length zero cm were undesirable because they have low ηo. The d50 decreased with increase inlet air velocity and lead to increase ηo; for instance at cone height of 30 cm the d50 of Lapple model were 31.95, 29.88, 28.17 and 26.73 µm for coarse wheat bran at inlet air velocity 14, 16, 18 and 20 m/s, respectively. Moreover the statistical indicators presented that the Hoffmann & Stein model was the best model and more validation to predict coarse wheat bran ηo at cone height 30 and 50 cm. The Lapple model was the best model and more validation to predict coarse wheat bran ηo at cone height 70 cm. There is a wide range of the optimum ηo depend on the design, operating parameters and the price of the separated material and this is subject to the operator's decision; in other words balancing operating economics cost and the price of the separated material.

Natural Ventilation Design: Predicted and Measured Performance of a Hostel Building in Composite Climate of India

Natural ventilation is recognized for improving the thermal comfort of the built environment and indoor air quality. It provides comfortable conditions for building occupants and reduces energy consumption for air-conditioning. Therefore, it is important to study and explore effective means of ventilation to improve the building designs. This study investigates the thermal comfort of a naturally ventilated hostel operational building in the composite climate of Jaipur, India using Computational Fluid Dynamics (CFD) simulation tool ‘Cradle scSTREAM’. A 3D building model has been developed to analyze the thermal comfort for different natural ventilation strategies with advanced mesh algorithms which generate fewer mesh elements and maintain good mesh quality. A field study was carried out to collect the actual data and to validate the model which was further used to evaluate the thermal comfort range based on the ASHRAE-55 standard. Several design strategies have been applied to enhance thermal comfort. It was found that an increase in air velocity up to 0.5 m/s was achieved by Cross Ventilation while a drop of 2.0–2.5°C in the air temperature was found using Night Ventilation. It can be stated that cross ventilation increases the air movement while night ventilation gives comparatively higher comfort regarding air temperature and relative humidity.

Numerical investigation of particles characteristics on cyclone performance for sustainable environment

In this paper, a three-dimensional turbulent gas flow with solid particles was numerically simulated to optimize the performance of a cyclone preheater. The numerical approach for the flow development was based on unsteady simulations using the Reynolds Stress Model (RSM). The Discrete Phase Model (DPM) was used for the dispersion of particles due to turbulence in the fluid phase. The size of raw material solid particles ranged from 1 µm to 30 µm and the inlet gas velocity ranged from 10 m/s to 20 m/s were considered for parametric study. The main objective of this study consists of the performance evaluation of the cyclone pre-heater in terms of collection efficiency, pressure drop across the cyclone, heat transfer rate. The results indicate that the increase of particle size leads to increase collection efficiency of the particles up to 99.89% and temperature difference of about 212 K with the slight variation of pressure drop. The heat transfer rate decreases with increase in inlet air velocity due to less particles residence time inside the cyclone pre-heater. For a given cyclone design and working conditions, the maximum heat transfer was 87 W for 30 µm particle size with hot air velocity of 10 m/s.

Effects of drying conditions in low-temperature microwave-assisted drying on bioactive compounds and antioxidant activity of dehydrated bitter melon (Momordica charantia L.).

Bitter melon (Momordica charantia L.) is a fruit that brings health benefits to consumers because the fruit is rich in bioactive compounds. In this work, a combination of low‐temperature convective drying and microwave radiation was used to dehydrate sliced bitter melon. One‐factor‐at‐a‐time design was performed to evaluate the influence of microwave power density (1.5, 3.0, 4.5 W/g), drying temperatures (20, 25, and 30°C), and air velocity (1.0, 1.2 and 1.4 m/s) on the change of moisture content, nutrient levels (vitamin C and total phenolics), and the antioxidant activities (DPPH and FRAP assays) of the bitter melon. The obtained results showed that all investigated factors affected the rate of moisture removal. Microwave power density output and air‐drying temperature strongly participated in the retention of nutrients. In this study, the drying process was driven by both heat and mass transfer processes, so the increase of air velocity prolonged the drying time causing more loss of nutrient levels and antioxidant activities. It was found that DPPH free radical scavenging ability directly correlated with total phenolic content, but the ferric‐reducing antioxidant power was related to the presence of reductants including phenolic compounds, vitamin C, and other phytochemicals in bitter melons. This work determined that microwave power density and the air‐drying temperature are the main two factors that should be used for further investigations.

Pengaruh Kecepatan Udara pada Alat Pengering Jagung dengan Mekanisme Penukar Kalor

The purpose of this study was to design and determine the performance of a dryer for drying corn with biomass burning energy sources. The dryer consists of a biomass stove, a heat exchanger, and a drying cabinet. The dimensions of the biomass stove are 500 x 500 x 800 mm with a diameter and hole distances of the biomass stove wall is 10 mm and 50 mm, respectively. The heat exchanger pipe diameter is 25.5 mm, the drying cabinet 500 x 500 x 600 mm, and the biomass was rice husk. The heat exchanger is made of stainless steel pipes arranged in a parallel arrangement. A heat exchanger pipe connects the biomass stove to the drying cabinet in order to avoid drying products from burning biomass contamination. The results showed that the drying rate could be faster if the air velocity increases. Drying corn in order to reduce water content from 19% to 12% takes 47 minutes with an air velocity of 3 m/s.

Thermo-hydraulic characteristics of radiator with various shape nanoparticle-based ternary hybrid nanofluid

Water-based ternary hybrid nanofluid with various shape nanoparticles, i.e., spherical (Al2O3), cylindrical (CNT), and platelet (Graphene) as a new radiator coolant has been investigated in the present analysis. Effect of thermo-hydraulic (pressure drop and heat transfer rate) performance along with exergetic analysis (irreversibility, entropy generation, exergy loss) on ternary hybrid nanofluid vol. concentrations, coolant flow rate, and frontal air velocity has been considered. Furthermore, the XRD and SEM morphology analysis have been conducted for 1% vol. fraction of ternary hybrid nanofluid. The comparative theoretical analysis revealed that the change in ternary hybrid concentrations play an important role in thermal performance due to its shape configuration and 18.45%, 6.3% increment in the heat transfer rate, the second law of efficiency respectively, are observed for 1%–3% vol. fractions range. The irreversibility of the system increases with the application of ternary hybrid nanofluid on coolant flow rate and frontal air velocity. However, a 42.45% increase in irreversibility is observed for a change in ternary hybrid concentrations within the range of 1%–3%. Change in entropy for air is higher compared to the coolant entropy change and results in an increment of 27.27% in entropy change for ternary hybrid nanofluid. Similarly, an increase in air velocity also has the least effect on fan power. Thus, the particle shape in ternary hybrid nanofluids has a significant impact, and its application is more effective in enhancing the thermo-hydraulic performance for an automotive cooling system.

Rudimentary analysis for solar chimney enhancement

This paper presents fundamental results for solar chimney enhancement. Solar radiation proves to be an important factor in influencing the efficiency of the solar chimney power plant, but its effects on the ambient conditions outside the system has not been considered. Using the Discrete Ordinates radiation model on the semi-transparent collector component of the two-dimensional system, the work presented in this paper simulates the velocity and temperature inside the solar chimney as the ambient temperature of air outside is varied from 307 K to 314 K. At the highest ambient temperature, results show an increase in air velocity of 0.55 m/s at ground level and 1.85 m/s at a height of 1 m along the chimney. To further investigate of this study, a simulation model to include the ambient domain is proposed as a conclusion.

The cooling effect of a spray fan in an indoor hot environment

The aim of this study is to evaluate the cooling effect of a spray fan in an indoor hot environment. An experimental workplace with a thermal environment of high temperature and radiation intensity was set up. The hot environment of the experimental workplace could not meet occupational health requirements when the heat source temperature exceeded 150°C. The effects of air velocity and relative humidity on the natural wet bulb temperature, black globe temperature and wet bulb globe temperature (WBGT) were investigated. The maximum reduction of the WBGT was about 1.7°C, with an air velocity increase by 1 m/s. There was a notable cooling effect on the hot environment for low air velocities (e.g. 0–2 m/s), while the cooling effect only increased slightly for high air velocity (e.g. 2–5 m/s). We also found that the indoor WBGT declined by 0.2–0.8°C when the relative humidity was increased by about 10%. These results may provide guidance for reducing heat stress in industrial hot environment.