Low Air Velocity Research Articles

A Study on Suitable Habitat for Swiftlet Farming

Swiftlet farming is a new industry in Sarawak as compared to other long-standing industries such as rubber, palm oil and timber. It is one of the businesses that involved a small capital investment that could generate enormous returns in the future. Swiftlet farming involves the conversion of human-centric building into structures for Swiftlet. The purpose of this conversion is to let Swiftlet for nesting and protect them. The design and construction of such building will also helps to accommodate Swiftlets' population. The nest of the Edible-nest Swiftlet rank amongst the world's most expensive animal products. Therefore, in order to increase the productivity of bird nest, study of the suitable habitat for Swiftlet should be done thoroughly. Environmental factors such as air temperature, surface temperature, relative humidity, air velocity and light intensity are the key factors for a successful Swiftlet farm house. Internal air temperature of building should be maintained from 26°C to 35°C, relative humidity from 80% to 90%, low air velocity and light intensity less than 5 LUX. Proper ventilation and installation of a humidifier could help the building to achieve the desirable range of environment factors. Location of structure will also be considered from direct sunlight direction to reduce the internal temperature. Only licensed Swiftlet farming is legal.

Investigation of Combustion Characteristics of Biodiesel and Its Blends

Experiments employing porous sphere technique are carried out to investigate the combustion characteristics of biodiesel produced from karanja oil and its blends with diesel and gasoline. Biodiesel or its blend is transpired to porous sphere surfaces, where it burns. Porous spheres are placed in an air stream blowing with a uniform velocity at atmospheric pressure and temperature under normal gravity conditions. At low air velocities, a flame envelops the entire sphere. Fuel feed rates are recorded for various sphere sizes and air velocities. Overall, the visible flame shape is analyzed with the help of digital flame image. At a particular air velocity, the flame will not envelope the sphere, but establish near the rear region of the sphere and the same is recorded for different sphere sizes. Theoretical correlations are proposed for burning rate as a function of effective Reynolds number and for Damköhler number as a function of Froude number.

Possible role of denitrification on aerobic granular sludge formation in sequencing batch reactor

The aim of this work was to evaluate and quantify the influence of denitrification of nitrate on the aerobic granular sludge development. Two parallel sequencing batch reactors (SBRs) were fed with synthetic wastewater, the first reactor (R1) receiving nitrate at a fixed concentration whereas the second reactor (R2) did not receive any external source of nitrate. Both systems were working at the same operational conditions with a low specific air velocity (0.07 cm s −1), a relatively low and acceptable oxygen concentration (1.8 ± 0.8 mg L −1) and without significant biomass selection pressure (minimal velocity 0.4 m h −1). The results showed that the sludge settling properties of R1 were comparable to granular sludge (settling velocity ≈ 10.6 m h −1, SVI 5 ≈ 13–30 mL g −1, SVI 30 ≈ 11–28 mL g −1 and SVI 5/SVI 30 ratio ≈ 1.05–1.1). In the opposition, biomass of the reactor R2 reveals more traditional properties. Nitrogen measurements revealed that a significant denitrification (up to 80% of fed nitrate) occurred in R1 in the core of aggregates, as aerobic condition was maintained in the bulk. After the mean particle size was reduced from 250 to 125 μm by an increase of mechanical stirring rate, it was shown that denitrification decreased from 80% to 20%. These parallel experiments definitively proved that the presence of nitrate in SBRs can assist the densification of the biological aggregates in aerobic condition. The presence of nitrate (commonly provided by nitrification) should be considered as a possible factor which helps to maintain the granulation process.

Water management studies in PEM fuel cells, Part II: Ex situ investigation of flow maldistribution, pressure drop and two-phase flow pattern in gas channels

Two-phase flow of water and reactant gases in the gas distribution channels of proton exchange membrane fuel cells (PEMFCs) plays a critical role in proper water management. In this work, the two-phase flow in PEMFC cathode parallel channels is studied over a wide range of superficial air velocity (air stoichiometry) and superficial water velocity in a specially designed ex situ experimental setup, which enables the measurement of instantaneous flow rates in individual gas channels and simultaneous visualization of the water flow structure. It is found that the two-phase flow at low superficial air velocities (air stoichiometry below 5) is dominated by slugs or semi-slugs, leading to severe flow maldistribution and large fluctuations in the pressure drop. Slug residence time, measured from the video observation and the instantaneous flow rate data, is found to be a new parameter to describe the slug flow. At higher air velocities, a water film is formed on the channel walls if they are hydrophilic. The pressure drop for the film flow is characterized by smaller but frequent fluctuations, which are found to result from the water buildup at the channel-exit manifold interface. As the superficial air velocity increases further, mist flow is obtained where little water buildup is observed. The water buildup in the gas channels at the two-phase flow is well described by the two-phase friction multiplier, defined as the ratio of the two-phase pressure drop to the single gas phase pressure drop. It is found that the two-phase friction multiplier increases with increasing water flow rate. A flow pattern map is developed using superficial water and air velocities with clearly defined transition regions.

The Purification, Formulation and Drying of Papain

Papain, a proteolytic enzyme was purified from latex of Carica papaya by a variety of techniques such as two-step salt precipitation, organic solvent precipitation (ethanol) and ion exchange chromatography. Fold purity obtained using ion exchange chromatography was in the range of 4.5 to 5 times as compared to the precipitation techniques. The purified papain was entrapped in ionotropically cross-linked alginate beads, in order to develop formulation for site-specific delivery of papain in intestine. The entrapment efficiency for papain in alginate beads was found to be in excess of 86%. Drying at low temperature and low air velocity results into maximum retention of papain activity; however, drying time increases significantly. The dissolution study shows the possible use of alginate beads for site-specific intestinal delivery of papain. The shelf-life of papain can be improved significantly by entrapment in alginate matrix, which was confirmed by an FTIR study.

Effects of low humidity and high air velocity in a heated room on physiological responses and thermal comfort after bathing: An experimental study

Objective In the present study we investigated the effects of low relative humidity (RH) and high air velocity (VA) on physiological and subjective responses after bathing in order to present the evidence for required nursing intervention after bathing. Methods Eight healthy male subjects participated in this experiment. There were four thermal conditions which combined RH (20% of 60%) and VA (low: less than 0.2 m/s or high: from 0.5 to 0.7 m/s). After taking a tub bath, subjects sat for 80 min in the test room under each condition. In addition, one condition under which the subjects were exposed to 20% RH and high VA condition for 80 min without bathing condition was conducted. Results A decrease in mean skin temperature ( T ¯ sk ), dryness of the skin and eyes were observed, though thermal comfort and warmth retained, due to spending time after bathing in a low RH and high VA environment, compared to the condition without bathing. Moreover, dryness of the skin, a decrease in hydration of the skin and an increase in transepidermal water loss (TEWL) after bathing were significantly affected by RH levels, on the other hand subjective coolness, discomfort and perception of dryness in the eye were significantly affected by VA levels. The decrease in T ¯ sk after bathing was significantly affected by both RH and VA. Conclusion From our findings we concluded that low RH and high VA have negative effects on humans after bathing, for example a decrease in body temperature and dryness of the skin and eyes. Moreover, it was indicated that the negative effects could be kept to a minimum and thermal comfort remain higher, if RH and VA levels were controlled within the optimum ranges.

Experimental investigation of burning rates of pure ethanol and ethanol blended fuels

A fundamental experimental study to determine the burning rates of ethanol and ethanol-blended fossil fuels is presented. Pure liquid ethanol or its blends with liquid fossil fuels such as gasoline or diesel, has been transpired to the surface a porous sphere using an infusion pump. Burning of the fuel takes place on the surface of the porous sphere, which is placed in an air stream blowing upwards with a uniform velocity at atmospheric pressure and temperature under normal gravity conditions. At low air velocities, when ignited, a flame envelopes the sphere. For each sphere size, air stream velocity and fuel type, the fuel feed rate will vary and the same is recorded as the burning rate for that configuration. The flame stand-off distances from the sphere surface are measured by post-processing the digital image of the flame photograph using suitable imaging software. The transition velocity at which the flame moves and establishes itself at the wake region of the sphere has been determined for different diameters and fuel types. Correlations of these parameters are also presented.

Effect of biomass particle size and air superficial velocity on the gasification process in a downdraft fixed bed gasifier. An experimental and modelling study

A one-dimensional stationary model of biomass gasification in a fixed bed downdraft gasifier is presented in this paper. The model is based on the mass and energy conservation equations and includes the energy exchange between solid and gaseous phases, and the heat transfer by radiation from the solid particles. Different gasification sub-processes are incorporated: biomass drying, pyrolysis, oxidation of char and volatile matter, chemical reduction of H 2, CO 2 and H 2O by char, and hydrocarbon reforming. The model was validated experimentally in a small-scale gasifier by comparing the experimental temperature fields, biomass burning rates and fuel/air equivalence ratios with predicted results. A good agreement between experimental and estimated results was achieved. The model can be used as a tool to study the influence of process parameters, such as biomass particle mean diameter, air flow velocity, gasifier geometry, composition and inlet temperature of the gasifying agent and biomass type, on the process propagation velocity (flame front velocity) and its efficiency. The maximum efficiency was obtained with the smaller particle size and lower air velocity. It was a consequence of the higher fuel/air ratio in the gasifier and so the production of a gas with a higher calorific value.

Influence of airflow and liquid properties on the mass transfer coefficient of ammonia in aqueous solutions

The influences of airflow and liquid properties on the mass transfer coefficient of ammonia from aqueous solutions were investigated. In the laboratory experiments using a small-scale model, four ventilation rates with three ventilation control strategies were used to estimate the influence of airflow. To evaluate the effects of different model scales and liquid properties, six inlet air velocities with three turbulence intensities and four pH values were studied using a small wind tunnel. In the scale model experiments, the results showed that the mass transfer coefficient increased as the ventilation rate increased and the turbulence intensity had a significant effect on the mass transfer coefficient at low air velocities. To represent the comprehensive influence of airflow on the mass transfer coefficient, a statistical model was developed based on surface air velocity, turbulence intensity and ventilation rate (coefficient of determination R 2 =0.98). It was found that the mass transfer coefficient for ammonia was much more sensitive to the variations in air velocity at lower rather than at higher air velocities. Similar responses were obtained for both turbulence intensity and ventilation rate. Comparative results using different ammonia mass transfer coefficient equations for a constant inlet opening area strategy indicated that it is not sufficient to express the mass transfer coefficient simply in terms of the air velocity and the ventilation rate. In the wind tunnel experiments, the mass transfer coefficient increased with increasing turbulence intensity. However, the mass transfer coefficient increased as the air velocity increased with lower velocities but at higher velocities ammonia emission did not increase with air velocity. It was found that increasing the pH of the solution not only increased mass transfer rates but also increased the peak value of the air velocity that induced the maximum emission of ammonia. The different correlations that were established between the mass transfer coefficient and air velocity in both the scale models and the wind tunnel may have been caused by the use of different model scales. The scale of turbulence found in the scale model cannot be reproduced in the wind tunnel. Therefore, full-scale investigations are necessary to characterise emissions affected by turbulence scale.

Low Air Velocity Measurement Characteristics- Variation Due to Flow Regime

Low Air Velocity Measurement Characteristics- Variation Due to Flow Regime

Assessment of the Electrohydrodynamic Drying Process

Industries using energy-intensive processes are being forced to explore ways for reducing their energy consumption. In the food industry, air drying is one of the more energy-consuming processes. To reduce the energy consumption during this operation, alternative processes should be investigated. One promising alternative consists in the electrohydrodynamic (EHD) enhancement of heat and mass transfer. This paper analyses the literature and describes the great potential of this innovative process based on the generation of an electric wind by a corona discharge. The main aspects of this technique are discussed and special emphasis is given on its benefit for food processes. The main part of this paper concerns experimental investigations carried out to assess the EHD enhancement on the drying process. An experimental set-up was designed to measure the weight losses on a food product submitted to an electrostatic field and to a cross air flow. Present results confirm that, for a low cross air velocity, the ionic wind leads to an enhancement of the drying rate. The best results are obtained for the smaller distance between the food surface and the corona electrode. Nevertheless, the process is less efficient for a high air velocity. The last part deals with a numerical model that was developed to evaluate the electric parameters and the flow field in turbulent regime. This model provides useful information on the coupled phenomena and permits to explain the experimental observations and to help in designing EHD drying processes.

Airflow Inside School Building Office Compartments with Moderate Environments

In this paper, the airflow inside school building office compartments with moderate environments, in steady-state conditions, is experimentally and numerically analyzed. The experimental tests are made in a developed experimental chamber, while the numerical results are obtained in a developed numerical model. The air velocity fluctuations are experimentally measured and the air velocity root mean square, the air turbulence intensity, the draft risk, the air velocity fluctuation frequencies, and the air velocity fluctuation equivalent frequencies are calculated. The mean and local air renovation rates, using the decay tracer gases method with a carbon dioxide concentration, are calculated. The three-dimensional air velocity and the air renovation rate are numerically calculated. Both these experimental and numerical results are compared to better understand the airflow topology inside this kind of compartment and evaluate the comfort level, namely the thermal comfort, local thermal discomfort, and air quality levels, to which occupants are subjected. The analyzed airflow topology, with the air forced inlet and outlet located above the occupants' head level, is divided into two areas: the non-occupied upper area, which contains the airflow inlet and outlet, with high air velocity levels, is developed to facilitate the contaminant extraction released by the occupants, while the occupied lower area, with low air velocity levels, is developed to ensure good thermal comfort and reduced local discomfort levels, with the capacity to transport the occupants' contaminants to the upper area.

Physical properties that govern fiber separation from distillers dried grains with solubles (DDGS) using sieving and air classification

Distillers dried grains with solubles (DDGS) is a coproduct of the dry grind corn to fuel ethanol process. Recently, we showed that Elusieve process, the combination of sieving and elutriation (air flow), was effective in separating fiber from DDGS. DDGS was sieved into different fractions and the sieved fractions were air classified to separate fiber. In this study, we determine relevant physical properties and terminal velocities of fiber and nonfiber that govern fiber separation from DDGS. Particle densities were determined using a pycnometer and equivalent spherical diameters were calculated from mean particle volume, obtained as mean particle mass divided by particle density. Sphericity of fiber was calculated as the ratio of surface area of sphere having the same volume as fiber to the actual surface area of fiber. Sphericity of nonfiber was calculated from experimentally determined terminal velocities of nonfiber and using the correlation between terminal velocity and sphericity. Terminal velocities of fiber and nonfiber are the lowest air velocities at which fiber and nonfiber, respectively, were carried by air. Particle density of fiber was higher than particle density of nonfiber. It was visually observed that fiber was flat and nonfiber was not flat. Sphericity of fiber and nonfiber ranged from 0.19 to 0.47 and 0.72 to 0.92, respectively. Within each sieved fraction, fiber particles had lower or comparable equivalent spherical diameters relative to nonfiber particles. Fiber particles experienced higher drag force and aspirated at low air velocities because: (1) they had lower or comparable mass relative to nonfiber particles and (2) their shape was flatter than nonfiber particles. The difference in shapes and equivalent spherical diameters of fiber and nonfiber within each sieved fraction resulted in difference in their terminal velocities within sieved fractions. This difference in terminal velocities allows separation of fiber from DDGS. Sieving of DDGS into fractions and then blowing air through sieved fractions was effective in separating fiber.

Wpływ aerodynamiki przepływu powietrza przez nos na fizjologię nosa

The ability of the human nose to warm and humidify the respiratory air is important to maintaining the internal environment of the lungs, since ambient air is conditioned to nearly alveolar conditions (body temperature and fully saturated with water vapour) upon reaching the nasopharynx. Because of very short time of the inspiratory phase duration, as well as expiratory phase, only the rich vascularization of the nasal mucosa and specific organization of the submucosal vessels are not able to assure such effective physiological activity. Therefore the type of airflow during the respiration is essential to understanding the functional possibilities of the nasal mucosa. Most studies have investigated the airflow only in steady-flow conditions, where the laminar flow was observed. Anatomically accurate physical models of real nasal cavities and particle image velocimetry allow evaluation of the entire flow field in the nasal cavity. In these investigations a partially turbulent flow was observed even at low air velocities in most part of the nasal cavity. From a physiological perspective, a turbulent flow would seem sensible, since it enhances contact between air and the mucosal layer. By doing so, the nasal physiological functions - humidification, cleaning and warming are optimized.

The Impact of Insect Screens and Ventilation Openings on the Greenhouse Microclimate

The objective of this work was to experimentally investigate the influence of vent type (side, roof, or both) and of anti-aphid insect screens on airflow, air temperature, and air vapor pressure deficit distribution in a round arch, mono-span greenhouse with vertical side walls. The greenhouse was equipped with two side roll-up vents and a flap roof vent. A tomato crop planted in double rows was cultivated inside the greenhouse. The three components of air velocity were measured by a 3-D sonic anemometer, and the air temperature and relative humidity were simultaneously recorded at several positions inside the greenhouse. Concerning the effect of insect screens, it was found that the mean value of the normalized air velocity was 58% lower in the greenhouse with insect screens on the side vent openings than in the case of a greenhouse without screens. Furthermore, the spatial heterogeneity of the microclimate variables was reduced with screens in the vent openings. When the ventilation was provided by side openings only, the air velocity inside the greenhouse was characterized by a strong air current near the greenhouse ground and low air velocity near the roof; when the ventilation was provided by roof vents, a circulating current prevailing at the center of the greenhouse was observed. The combined use of roof and side openings increased air velocity and decreased air temperature inside the greenhouse but also increased the spatial heterogeneity of the greenhouse microclimate compared to the cases with side or roof vents only. The most homogeneous climate conditions were achieved with the use of roof openings only. The results of this study provide a better understanding of the plant environment behavior under different vent configurations and a high-resolution database for validating on-going efforts with computer simulations.

A comparison of a range of models for dispersion in a partially stratified room

A comparative study of models used to predict contaminant dispersion in a partially stratified room is presented. The experiments were carried out in a ventilated test room, with an initially evenly dispersed pollutant. Air was extracted from the outlet in the ceiling of the room at 1 and 3 air changes per hour. A small temperature difference between the top and bottom of the room causes very low air velocities, and higher concentrations, in the lower half of the room. Grid-independent CFD calculations were compared with predictions from a zonal model and from CFD using a very coarse grid. All the calculations show broadly similar contaminant concentration decay rates for the three locations monitored in the experiments, with the zonal model performing surprisingly well. For the lower air change rate, the models predict a less well mixed contaminant distribution than the experimental measurements suggest. With run times of less than a few minutes, the zonal model is around two orders of magnitude faster than coarse-grid CFD and could therefore be used more easily in parametric studies and sensitivity analyses. For a more detailed picture of internal dispersion, a CFD study using coarse and standard grids may be more appropriate.

Air-side performance of louver-finned flat aluminum heat exchangers at a low velocity region

The heat transfer and pressure drop characteristics of heat exchangers having louver fins were experimentally investigated. The samples had small fin pitches (1.0–1.4 mm), and experiments were conducted up to a very low frontal air velocity (as low as 0.3 m/s). Below a certain Reynolds number (critical Reynolds number), the fall-off of the heat transfer coefficient curve was observed. The critical Reynolds number was insensitive to the louver angle, and decreased as the louver pitch to fin pitch ratio (Lp/Fp) decreased. Existing correlations on the critical Reynolds number did not adequately predict the data. The heat transfer coefficient curves crossed over as the Reynolds number decreased. Possible explanation is provided considering the louver pattern between neighboring rows. Different from the heat transfer coefficient, the friction factor did not show the fall-off characteristic. The reason was attributed to the form drag by louvers, which offsets the decreased skin friction at low Reynolds numbers. The friction factor increased as the fin pitch decreased and the louver angle increased. A new correlation predicted 92% of the heat transfer coefficient and 94% of the friction factor within ±10%.

Power Ultrasound Mass Transfer Enhancement in Food Drying

Power ultrasound application could constitute a way to enhance food drying in order to improve not only mass transfer but also product quality, since it does not significantly heat the material. The main aim of this work was to assess the influence of power ultrasound on the mass transfer process during drying of different products, carrot, persimmon and lemon peel. Convective drying kinetics were carried out with ultrasound (US experiments 21.8 kHz, 75 W), or without ultrasound application (AIR experiments) at air velocities ranging between 0.5–12 m s −1. Different geometries were used for each of the products: cubes in carrots (2 L = 8.5 mm), cylinders in persimmon (2 L = 30 mm and 2 R = 13 mm) and slabs in lemon peel (L = 10 mm). Drying kinetics were modelled by considering different diffusion models according to the geometry. The results show that air velocity and raw material characteristics play a role in convective drying kinetics assisted by power ultrasound. Power ultrasound increased effective moisture diffusivity at low air velocities for all the products. However, in the case of lemon peel, ultrasound also improved the drying rate at high air velocities. This behaviour may be explained by the disruption of the acoustic field at high air flow rates and the different level of intensity required due to the structure of the products. Therefore, the raw material constitutes an important variable to establish the influence of power ultrasound on convective drying.

A Preliminary Study of Thermal Comfort in Malaysia′s Single Storey Terraced Houses

In a tropical climate, passive cooling is difficult to achieve with respect to mass housing design. A good house design keeps the indoor environment favorable and comfortable during most of the year without the use of any mechanical devices. Terraced houses are typical examples with low comfort problem that need particular consideration. Low air velocity and high air temperature are experienced during the daytime and the wind effect is not well captured, especially in the single sided ventilation. Use of natural ventilation has been increasingly examined as an energy–efficient means to provide thermal comfort as well as a healthy indoor environment. This paper discusses the validation of Computational Fluid Dynamic (CFD) results and the measurement of thermal comfort in Malaysia′s single storey terraced houses. The thermal environment and comfort conditions were investigated using field measurement and CFD technique. Validation of CFD FloVent was carried out through the comparison of field measurements. Comparison of the results between simulations and measurements illustrated a good agreement. The simulations were performed on a selected day in a one–year climate condition. The results indicated that the design of single storey terraced houses is not effective in providing natural ventilation for achieving thermal comfort. The microclimate condition surrounding the terraced house indicated very low wind speed. Therefore, modification of the natural ventilation mechanism using a solar chimney as induced ventilation needs to be manifested and evaluated.

Indoor air quality in a dentistry clinic

The purpose of this work is to assess, both experimentally and theoretically the status of air quality in a dentistry clinic of the Athens University Dentistry Faculty with respect to chemical pollutants and identify the indoor sources associated with dental activities. Total VOCs, CO(2), PM(10), PM(2.5), NO(x) and SO(2) were measured over a period of approximately three months in a selected dentistry clinic. High pollution levels during the operation hours regarding CO(2), total VOCs and Particulate Matter were found, while in the non-working periods lower levels were recorded. On the contrary, NO(x) and SO(2) remained at low levels for the whole experimental period. These conditions were associated with the number of occupants, the nature of the dental clinical procedures, the materials used and the ventilation schemes, which lead to high concentrations, far above the limits that are set by international organizations and concern human exposure. The indoor environmental conditions were investigated using the Computational Fluid Dynamics (CFD) model PHOENICS for inert gases simulation. The results revealed diagonal temperature stratification and low air velocities leading to pollution stratification, accompanied by accumulation of inert gaseous species in certain areas of the room. Different schemes of natural ventilation were also applied in order to examine their effect on the indoor comfort conditions for the occupants, in terms of air renewal and double cross ventilation was found to be most effective. The relative contribution of the indoor sources, which are mainly associated with indoor activities, was assessed by application of the Multi Chamber Indoor Air Quality Model (MIAQ) to the experimental data. It was found that deposition onto indoor surfaces is an important removal mechanism while a great amount of particulate matter emitted in the Clinic burdened severely the indoor air quality. The natural ventilation of the room seemed to reduce the levels of the fine particles. The emission rates for the fine and coarse particulates were found to be almost equal, while the coarse particles were found susceptible to deposition onto indoor surfaces.