Low Air Flow Rates Research Articles

Use of experimental designs to optimize fluidized bed granulation of maltodextrin

The goal of this study was to use the experimental design approach in order to determine which process parameters are the most influent to granules properties. The agglomeration process was performed with a fluidized bed processor equipped with a top-spray tilted nozzle. The granules were obtained by binding fluidized particles of maltodextrin (DE 12) with an aqueous solution of maltodextrin. The variables considered in the experimental design were fluidization air flow rate, drying air temperature, spraying pressure and binder flow rate. The physical properties of the granules were evaluated in terms of granule size, particle size distribution, dissolution time and flowability. Moreover, the amount of binder for each experiment was noted. The statistical analysis performed with Statgraphics® Centurion version XVI software indicated that the best operating conditions were found for low fluidization air flow rate, high drying air temperature, high spraying pressure and high binder flow rate. The study also revealed the difficult task of acquiring all the optimum properties at the same time.

Research about effect of spray drying conditions on hygroscopicity of spray dry powder of Gubi compound’s water extract and its mechanism

To investigate moisture content and hygroscopicity of spray dry powder of Gubi compound's water extract obtained at different spray drying conditions and laying a foundation for spray drying process of Chinese herbal compound preparation. In the paper, on the basis of single-factor experiments, the author choose inlet temperature, liquid density, feed rate, air flow rate as investigated factors. The experimental absorption rate-time curve and scanning electron microscopy results showed that under different spray drying conditions the spray-dried powders have different morphology and different adsorption process. At different spray-dried conditions, the morphology and water content of the powder is different, these differences lead to differences in the adsorption process, at the appropriate inlet temperature and feed rate with a higher sample density and lower air flow rate, in the experimental system the optimum conditions is inlet temperature of 150 degrees C, feed density of 1.05 g x mL(-1), feed rate of 20 mL x min(-1) air flow rate of 30 m3 x h(-1).

Stability and accuracy of variable air volume box control at low flows. Part 1: Laboratory test setup and variable air volume sensor test

Variable air volume systems with direct digital controllers have been widely adopted in the HVAC system of commercial, industrial, and large residential buildings because they provide better energy efficiency and occupant comfort. Normally, a variable air volume terminal unit defines a minimum airflow rate to satisfy the space ventilation requirement and/or the proper operation of a terminal heating coil, if so equipped. However, it has been found that variable air volume terminal units often fail to perform as expected at the minimum airflow range (below 500 fpm [2.5 m/s]). Under such a flow range, the embedded airflow sensor becomes inaccurate, and the designed minimum airflow rate is less than the minimum controllable airflow rate. This results in a series of problems, including lack of ventilation, uneven airflow control, reduced damper and operator life, and energy waste. Through designed laboratory and field tests, this study (ASRHAE Research Project RP-1353) aims to identify the major factors that cause inaccuracy and instability issues in variable air volume terminal units and the relationship between the major factors and performance of the airflow sensor, controller, and terminal unit system. Laboratory tests performed in this study included a variable air volume sensor test, controller test, and system test. Four variable air volume boxes from three manufacturers and four controllers from four manufacturers were tested systematically. Two identical test beds with high accuracy (±0.5%) reference airflow meters were designed and constructed in the test facility. The size of the reference airflow measuring stations was carefully selected to provide maximum airflow measuring accuracy and maximum available system pressure drop. This article describes the laboratory test setup and summarizes the variable air volume sensor test results. A companion article summarizes the controller test, system test, and field test results. From the variable air volume sensor test, three factors, namely, inlet conditions, low variable air volume damper positions, and low airflow rates, are identified as strongly impacting variable air volume terminal unit performance.

Stability and accuracy of variable air volume box control at low flows. Part 2: Controller test, system test, and field test

This article with its companion paper (Liu et al. 2013), summarizes the findings of ASHRAE Research Project 1353 (Stability and Accuracy of VAV Box Control at Low Flows). This project aims to identify the major factors that cause the airflow measurement in a variable air volume system to be inaccurate and unstable, especially at low airflow conditions. Both a laboratory test (including variable air volume sensor test, controller test, and system test) and field test were conducted; the companion work discussed the variable air volume sensor test. In this article, findings from the controller test, system test, and field test are summarized. The controller tests involved testing of four controllers from four different manufacturers. Testing was performed for accuracy, stability, resolution, and ambient temperature effect. For the system test, the variable air volume box and the controller were operated together and tested as terminal unit systems. Two terminal units were tested, and it was found that the performance of a variable air volume terminal unit is highly dependent upon on controller performance. Zeroing and balancing at a low airflow rate 560 fpm (2.84 m/s) or 200 cfm (0.09 m3/s) for an 8-in. (0.2-m) box were effective for achieving high system accuracy at low airflow ranges. For the field tests, five variable air volume terminal units were tested in real commercial buildings. It was found that system balancing was not always an effective way to reduce the variable air volume airflow sensor error in the field due to the uncertainty of reference airflow measurement methods commonly adopted in the field testing and balancing process.

Investigation of a Gas-Solid Fluidized Bed for Lump Coal Separation

The influences of operating parameters (bed height, air flow rate, and separation time) on the separation effect for lump coal were experimentally studied. The results show that shallow bed takes less time to reach steady separation state comparing with the deep bed. Increasing separation time at low air flow rate and decreasing separation time at high air flow rate could improve the separation effect. Separation effect could get the optimal under the condensation of bed height at 90mm, air flow rate at 8m3/h and separation time at 60s.

Design and optimization of a solar air heater with offset strip fin absorber plate

Solar air heaters are becoming more and more popular in space heating and industrial processes due to their cost effectiveness and easy maintenance. However, how to increase thermal efficiency of solar air heaters becomes a major challenge. In this paper, the design of a solar air heater with offset strip fins was optimized by numerical modeling. Then, a series of experiments based on ASHRAE Standard 93-2003 was conducted to test the detailed thermal performance of the heater in the light of time constant, thermal efficiency, incident angle modifier and the synthetical resistance coefficient. Results indicate that the instantaneous thermal efficiency exceeded 0.40 even when the heater was running at low airflow rate (100m3h−1) under the typical space heating application where the solar irradiance on the collecting area was 600Wm−2, indoor air temperature 14°C, outdoor air temperature −5°C, and solar incidence angle 20°. Such a design would only require fan power of approximately 20W. The work would be useful for developing energy efficient and cost effective solar air heaters.

Factors involving the solids-carrying flotation capacity of microbubbles

Dissolved air flotation (DAF) is a technique used extensively for separating fine particles in water and wastewater treatment, but, unfortunately, its use is still limited for froth flotation of minerals. This appear to be due to the very low lifting power of the microbubbles (40–70μm) and low airflow rate because of the low solubility of air in water. Thus, the efficiency of DAF in treating mineral particles has shown to be poor and as a solid/liquid separation technology is limited to slurries with no more than 3% solids. This work presents results showing (measuring) the limits of DAF as a function of particle size distribution, solids content and air superficial velocity. Interestingly, the microbubbles were found to be not selective with respect to particle size, floating both fine and coarse particles, which is most likely due to the existence of several mechanisms acting on the flotation of particles by these minute bubbles.

Numerical simulations of water droplet dynamics in hydrogen fuel cell gas channel

The droplet dynamics in the cathode gas flow channel of a hydrogen fuel cell has been numerically investigated to obtain ideas for designing a flow channel to effectively prevent flooding. Three-dimensional two-phase flow simulations employing the volume of fluid method have been performed. Liquid droplets emerging from two adjacent pores at the hydrophobic bottom wall are subjected to airflow in the bulk of the gas flow channel. The effects of various parameters (pore distance, locations, sidewall contact angle, and airflow rate) on the liquid water removal from the gas channel have been investigated in terms of liquid water saturation, coverage of liquid water on the gas diffusion layer (GDL) surface, and change in the pressure drop in the channel. The numerical results show that the coalescence of two adjacent droplets enhances the water removal as compared to two separate, small droplets. It is also observed that droplets generated near the hydrophilic sidewall can be attached to the upper corner of the channel walls, which prevents the liquid water from covering the GDL surface, whereas the hydrophobic sidewall may cause clogging of the gas channel with liquid water at a low airflow rate.

Collector Efficiency by Single Pass of Solar Air Heaters with and without Using Fins

This paper presents the study of heat transfer in a solar air heater by using new design of solar collector. The collector efficiency in a single pass of solar air heater without, and with using fins attached under the absorbing plate has been investigated experimentally. Due to adding the fins to the interior of an absorber plate, the desirable effect of increasing the heat transfer coefficient compensates for the undesirable effect of decreasing the driving force (temperature difference) of heat transfer, while the attached fins provide an enlarged heat transfer area. In this study, the absorbing plate of solar collector is attached with fins for further improved performance. The improvements of collector efficiencies in the single pass solar air heaters with, and without fins attached; increase with increasing the mass flow rate, especially for operating at lower air flow rate. Experiments were performed for two air mass flow rates of 0.012 and 0.016 kg/s. Moreover, the maximum efficiency obtained for the 0.012 and 0.016 kg/s with, and without fins were 40.02, 51.50% and 34.92, 43.94% respectively. A comparison of the results of the mass flow rates by solar collector with, and without fins shows a substantial enhancement in the thermal efficiency.

Experimental study of a building-integrated solar air heating system in cold climate of China

A series of experiments were carried out in Harbin, a typical city of the severe cold climate zone of China under real transient outdoor conditions to investigate thermal performance, color effect and energy savings of a building-integrated solar air heating system based on unglazed transpired collectors (UTCs). The average efficiency of black UTC was 77.64% and 68.92% under high and low air flow rate respectively, which are higher than most glazed flat-plate collectors. Collector's surface color had an effect on its thermal performance. However, the thermal efficiency of colored UTC was still competitive, and therefore it is feasible to use colored UTC on building façade for esthetic reasons. Design heating load of a reference building in Harbin can be reduced by 6.4% due to reduced wall loss with the application of UTC. For a first cost less than 200$/m2, it is economically viable to use UTC as an energy efficiency measure in Harbin with net present value of 333$/m2 and payback time of 10.5years. With better coordination with architectural design at early stage in a project, this building-integrated solar air heating system can be both esthetically and technically viable in cold climate of China.

The fouling phenomenon in membrane bioreactors: Assessment of different strategies for energy saving

Membrane fouling represents one of the major issues for a membrane bioreactor (MBR). Membrane fouling and high aeration requirements (for inducing shear stress to limit fouling) make MBR operation economically demanding due to high energy costs. Although several studies on MBR fouling have been performed, comprehensive knowledge on how to reduce membrane fouling and consequently save energy is still lacking.An integrated mathematical model for MBR is applied to a University of Cape Town membrane bioreactor with the final aim to reduce the energy costs. In particular, the influence of the aeration intensity, the duration of filtration/backwashing cycles, and the number of membrane cleanings are investigated. Five scenarios are analyzed and compared, each implementing different operating conditions. The features of the analyzed scenarios are quantified by employing Monte Carlo simulations and performance indices partially drawn from literature. The results provide insights about the role played by the main physical/chemical/biological processes in view of a system optimization. As expected, MBR operation at low air flow rate (qa) leads to a substantial reduction of the operational costs (specifically, 20% with respect to the suggested manufacturers ones in terms of qa). Despite such a reduction of qa, a good effluent quality is also obtained as an effect of a high biological cake thickness. Results also show that the values of filtration time (Tf) higher than those suggested by manufacturers (e.g., Tf=9min) can be used to increase effluent quality. This study demonstrates that both energy savings and effluent quality can be improved by varying the operational variables with respect to those of the suggested manufacture. One of the main insights gained from this study is that the values of the operating variables (i.e., qa, Tb and Tf) suggested by the manufactures can be changed to obtain a system that still respects high effluent quality and is characterized by lower economical cost. The proposed modeling approach can be an useful tool for the optimization of the operating conditions in order to reduce the operational costs for MBR systems.

Use of a Terrestrial LIDAR Sensor for Drift Detection in Vineyard Spraying

The use of a scanning Light Detection and Ranging (LIDAR) system to characterize drift during pesticide application is described. The LIDAR system is compared with an ad hoc test bench used to quantify the amount of spray liquid moving beyond the canopy. Two sprayers were used during the field test; a conventional mist blower at two air flow rates (27,507 and 34,959 m3·h−1) equipped with two different nozzle types (conventional and air injection) and a multi row sprayer with individually oriented air outlets. A simple model based on a linear function was used to predict spray deposit using LIDAR measurements and to compare with the deposits measured over the test bench. Results showed differences in the effectiveness of the LIDAR sensor depending on the sprayed droplet size (nozzle type) and air intensity. For conventional mist blower and low air flow rate; the sensor detects a greater number of drift drops obtaining a better correlation (r = 0.91; p < 0.01) than for the case of coarse droplets or high air flow rate. In the case of the multi row sprayer; drift deposition in the test bench was very poor. In general; the use of the LIDAR sensor presents an interesting and easy technique to establish the potential drift of a specific spray situation as an adequate alternative for the evaluation of drift potential.

Removal of methyl orange from aqueous solution using a 1.6 MHz ultrasonic atomiser

Under 1.6 MHz atomisation, methyl orange (MO, 10 mg L−1) removal was mainly influenced by the calorimetric power, so that as the calorimetric power doubled, MO removal (%) increased three-fold. MO removal was favoured by low pH, low solution volume and high air flow rate. By analysing the effect of a radical scavenger on MO removal, it was found that the major MO removal mechanism was sonochemical degradation of MO in the bulk solution due to cavitation. CCl4 (100 mg L−1) increased MO removal by 22.9% from a 90 mL solution having 10 mg L−1 MO at pH 2. Atomiser design is thus an important factor to consider when implementing sonochemical remediation to ensure that the maximum possible calorimetric energy intensity is obtained within the atomiser.

Fabrication of an Ultra-Flexible ZnO Nanogenerator for Harvesting Energy from Respiration

A novel ZnO nanogenerator (NG) with a flexible and highly lightweight substrate has the potential to harvest energy from human respiration. Previous studies have proposed lift-off and fold-up fabrication methods. The ZnO nanowires (NWs) are transferred to a polydimethylsiloxane (PDMS) layer, which serves as the secondary flexible substrate. The thickness of the 2-fold ZnO NG is approximately 25 μm, whereas the thickness of the 16-fold NG is approximately 200 μm. The 16-fold ZnO NG generates approximately 0.6 V and 0.5 μA at the low air flow rate of 2.0 ms−1, and reaches approximately 1.3 V and 0.8 μA at the air flow rate of 5.0 ms−1.

Photocatalysis of Sub-ppm-level Isopropyl Alcohol by Plug-flow Reactor Coated with Nonmetal Elements Irradiated with Visible Light

This work explored the characteristics and the photocatalytic activities of S element-doped TiO2 (S-TiO2) and N element-doped TiO2 (N-TiO2) for the decomposition of gas-phase isopropyl alcohol (IPA) at sub-ppm concentrations, using a plug-flow reactor irradiated by 8-W daylight lamp or visible light-emitting-diodes (LEDs). In addition, the generation yield of acetone during photocatalytic processes for IPA at sub-ppm levels was examined. The surface characteristics of prepared S- and N-TiO2 photocatalysts were analyzed to indicate that they could be effectively activated by visible-light irradiation. Regarding both types of photocatalysts, the cleaning efficiency of IPA increased as the air flow rate (AFR) was decreased. The average clea- ning efficiency determined via the S-TiO2 system for the AFR of 2.0 L min -1 was 39%, whereas it was close to 100% for the AFR of 0.1 L min -1 . Regarding the N-TiO2 system, the average cleaning efficiency for the AFR of 2.0 L min -1 was above 90%, whereas it was still close to 100% for the AFR of 0.1 L min -1 . In contrast to the cleaning efficiencies of IPA, both types of photocatalysts revealed a decreasing trend in the generation yields of acetone with decreasing the AFR. Consequently, the N-TiO2 system was preferred for cleaning of sub-ppm IPA to S-TiO2 system and should be operated under low AFR conditions to minimize the acetone generation. In addition, 8-W daylight lamp exhibited higher cleaning efficiency of IPA than for visible LEDs.

Factors Affecting Ventilation and Acoustical Quality in a Sustainably-Designed and in Conventional Buildings — A Pilot Study

This paper discusses a pilot study involving direct monitoring of airflow and acoustical quality in a sustainably-designed and in conventional buildings. The objectives were to measure these environmental aspects, determine the factors affecting them and the relationships between them and key building-design concepts, and consider the implications of the results for ventilation-system design. Selected rooms in buildings with natural and mechanical ventilation, without and with acoustical treatment, were monitored. Measurements were made of airflow rates and acoustical quality. Correlations between these environmental aspects, the types of building and ventilation system, and the building window status were investigated. In rooms with natural ventilation, noise levels were lower; however, the rooms had lower airflow rates. Rooms with mechanical ventilation had higher airflow rates, but noise levels were higher; HVAC noise was a problem if the system was not well designed. In naturally-ventilated buildings, airflow rates and noise levels were low with windows closed, but opening the windows to increase the airflow rate resulted in higher noise levels. The results of the study suggest that the acceptability of indoor environments in buildings depends on the degree of compliance of the design and its implementation with standards and design guidelines, whether the original design is ‘sustainable’ or not.

수중 Plasma 공정을 이용한 Ralstonia Solanacearum 불활성화

A dielectric barrier discharge (DBD) plasma reactor was investigated for the inactivation of Ralstonia Solanacearum which causes bacterial wilt in aquiculture. The DBD plasma reactor of this study was divided into power supply unit, gas supply unit and plasma reactor. The plasma reactor consisted of a quartz dielectric tube, discharge electrode (inner) and ground electrode (outer). The experimental results showed that the optimum 1st voltage, 2nd voltage, air flow rate and pH were for 100 V (1st voltage), 15 kV (2nd voltage), 4 L/min, and pH 3, respectively. At a low 1st voltage, shoulder and tailing off phenomena was observed. The shoulder phenomenon was decreased as the increase of 1st voltage. R. Solanacearum disinfection in the lower air flow rate was showed shoulder and tailing off phenomenon because the active species generated less. Under optimum condition, shoulder and tailing off phenomenon was reduced. When the 2nd voltage was less than 7.5 kV, tailing off phenomenon was observed and this was not vanishes even though the increase of the disinfection time. The inactivation efficiency increased as the increase of air flow rate, however, the efficiency decreased when the air flow rate was above 4 L/min. R. Solanacearum disinfection at pH 3 showed somewhat higher than in pH 11. The pH effect of R. Solanacearum deactivation is less than the impact on other factor.

Design and fabrication of a novel flowmeter with corrugated structure

We designed, fabricated and evaluate the novel air flowmeter with corrugation structure for the detection of low air velocity. For measuring the low air flow rate, the sensitivity related factors, the air drag force and the output signal, should be improved at the given air flow. The device has the paddle structure, and the maximized air drag force is obtained with vertical air flow. The output signal is also improved with the corrugation structure and measured with piezoresistive detection. The low air flow rate with less than 1m/s air velocity are applied, and the fabricated flowmeter with corrugation structure shows the better sensitivity and the response time than those of flat one. Various experiments about repeated measurements also show the stabilized signals.

INFLUENCE OFAIRFLOW RATE AND FORWARD SPEED ON THE SPRAY DEPOSIT IN VINEYARDS

The present paper reports the results of some spray application trials carried out in a hedgerow vineyard to assess the influence of airflow rate and forward speed on the foliar deposition, keeping approximately constant the volume application rate. The experimental tests were carried out using an air assisted towed sprayer, fitted with an axial fan and two spray booms equipped with seven turbulence nozzles. A full factorial experimental design with two air flow rates (3.9 and 7.5 m3/s) and three forward speeds (0.9, 1.4, and 2.8 m/s) was adopted, arranged according to a randomised complete block design with four replicates. To take into account the development of the vegetation, the experimental plan was replicated in two phenological stages: “Beginning of berry touch” and “Beginning of ripening”. After spray application (just one spray pass for each replicate, delivering a water solution with a food dye as a tracer and a surfactant), 36 leaves were picked on each sample tree, equally shared among three heights and two depths. The foliar deposition was measured by means of a spectrophotometer. The main results show that neither airflow rate, nor forward speed, significantly influence the average foliar deposition in both phenological stages. The overall variability (coefficients of variation) is also almost constant. However, in the second stage, the greater airflow rate improves the foliar deposition on the inside part of the canopy, suggesting the necessity of using not too low air flow rates at full foliage development. Also the forward speed interacts with the sampling zones, showing that at 2.8 m/s the differences among the three heights and the two depths increase, thus suggesting the opportunity to operate in field at 1.4-1.7 m/s.

FURTHER STUDIES ON THE VARIATION OF SPRAY DEPOSITS IN VINEYARDS WITH AIRFLOW RATE AND VOLUME RATE

The present research, continuing that reported in [2], deals with the spray application subject, so to investigate as volume rate and airflow rate, forward speed being equal, affect the foliar deposition in an espalier vineyard. Experimental trials were carried out by means of an air assisted towed sprayer, equipped with “Albuz ATR” nozzles. To take into account the influence of the development of the trees, the field trials were replicated in two phenological stages with an interval of about one month: “Inflorescences fully developed” (stage 1) and “Beginning of berry touch” (stage 2). A full factorial experiment was carried out for each growth stage, with two airflow rates (3.9 and 7.5 m3/s), three volume rates (103, 216, and 276 L/ha in the first growth stage and 154, 330 and 432 L/ha in the second growth stage), and four replicates, arranged according to a randomised complete block design. Working pressure (1.2 MPa) and forward speed (1.4 m/s) were kept unchanged for all the trials. The foliar deposition was measured by means of a spectrophotometric technique. The leaves were sampled on two depth layers and two or three heights, according to the trees’ development. The results showed that volume rate did not significantly influence the mean foliar deposition in both the two growth stages, while the highest deposits were obtained with the lowest airflow rate. The airflow rate × volume rate interaction, though not statistically significant, showed that low volume rates together with high airflow rates, result in a noticeable reduction in foliar deposition (29% with respect the grand mean), due to an increase of the spry drift, especially at the first growth stage, when the foliar development is little. These second tests, unlike those described in [2], did not show any positive influence of the airflow rate on the foliar deposition in the inner part of the canopy, so further investigations could be necessary to better understand the results. The whole results suggest to operate in field at low airflow rates (some 3.9 m3/s) and low volume rates (some 25 L/ha per active nozzle), so to reduce the power requirements and increase the promptness of intervention.