Increasing Air Flow Rate Research Articles

Influence of twisted tape inserts on energy and exergy performance of an evacuated Tube-based solar air collector

Energy and exergy behaviour of an Evacuated Tube with Inserted Baffles Solar Air Collector (ETIBSAC) with various design configurations of twisted tape is analyzed through an analytical model. Among those configurations, Loose-Fit Perforated Twisted Tape (LFPTT) exhibits better performance in terms of energy effectiveness. Hence, LFPTT was selected for further investigation to identify the influence of helical twist ratio (y/D) and tape hole diameter ratio (d/D). The analytical model predicts the energy and exergy performance of the ETIBSAC with LFPTT inserts (y/D) = 2, 2.5 and 3 & (d/D) = 0.0714, 0.107 and 0.143. The results show that ETIBSAC with LFPTT produces the highest effective thermal and exergy efficiencies at lower airflow rates. The peak thermal efficiency of 62.33% was attained at 400 kg/h with (y/D) = 2 & (d/D) = 0.0714. The exergy efficiency attained its peak value of 3.91% and reduces with increasing airflow rate due to more exergy destruction. It is concluded that the proposed insertion of twisted tapes can be adopted for enhancing the performance of the system.

Influence of air layer on temperature and humidity characteristics of outer envelope structure with internal heat insulation

Objective. The article addresses the process of heat and mass transfer in outer envelope structure with internal heat insulation. To prevent condensate formation, it is proposed to use a ventilated air duct inside the wall structure. Methods. The study was carried out using numerical simulation methods. Air movement in the duct was described by solving the Navier-Stokes equation in k-ε approximation. Condensate formation was analysed via joint resolution of heat conduction and diffusion equations. The problem of heat and mass transfer was addressed for a structure with internal heat insulation, behind the layer of which an air duct was located with air movement occurring due to natural or forced convection. Results. As part of the work, it was shown that the use of an air duct significantly reduces the thermal resistance of the structure, and an increase in the airflow rate leads to a decrease in thermal resistance and the likelihood of condensate formation. A decrease in thermal resistance with an increase in air flow rate into interlayers occurs faster than an increase in the amount of air-entrained moisture. Conclusion. Results of the work have shown that the use of an air duct throughout the entire period of operation of a building is not effective, but it is proposed to use this duct periodically in winter to dry the condensate.

Heat transfer of a coil-tube heat exchanger in the freeboard zone of a rice husk fluidized-bed combustor

This research presents an investigation on heat recovery from a fluidized-bed combustor by using coil-tube heat exchangers positioned inside the freeboard zone. Rice husk was used as a fuel at a constant mass flow rate of 8 kg/h. Heat recovery experiments were performed at four different air mass flow rates (6.0248, 6.8077, 7.8163, and 8.8646 kg/h) using coil-tube heat exchangers wrapped around with steel wires in three different configurations (2_Coil wires, 4_Coil wires and Full length). Air was supplied to the coil-tube heat exchanger with two different air flows corresponding to flue gas flow: co-flow and counter-flow. The results showed that the outlet temperature tended to decrease with an increase in air flow rate in the coil-tube heat exchanger. The outlet temperatures obtained from the system with co-flow were greater than the one with counter-flow by 7–17 °C (2–15%) depending on the coil-tube heat exchanger configuration. The heat transfer rates in heat recovery process were in the range of 279–425 J/s. In addition, it was found that the heat transfer rate and the outlet temperature of the air from the coil-tube heat exchanger increased with an increase in the number of coil wires wrapped around the outer surface of the coil-tube heat exchanger.

Cultivation of Synechococcus HS-9 in a novel rectangular bubble column photobioreactor with horizontal baffle

As a source for third-generation biofuel, microalgae can assist island countries to overcome their energy crisis. In this study, a novel photobioreactor having three segments is designed and Synechococcus HS-9 growth in the photobioreactors with and without a baffle is compared. The aims of this study are to investigate how the baffle influences bubble size, distribution, and velocity, to explain the bubble coalescence phenomena, and verify the effect of the baffle on Synechococcus HS-9 growth. The results showed that bubble size distribution in the photobioreactors paralleled the increasing air flow rate. At a flow rate of 1.0 L/min, most bubbles had a diameter of 200–400 μm; however, at 2.5 L/min, the typical size was 1400–2000 μm. Bubble velocity was observed through imaging techniques. The intake air flow rate of 1 LPM has a mass transfer coefficient value of 0.00075 m/s for the photobioreactor without the baffle and 0.00089 m/s for the baffle-bearing photobioreactor. The Sauter mean diameters at three different heights (A, B and C section) in the photobioreactors were 675 μm, 1001 μm, and 1125 μm. Synechococcus HS-9 growth was 2.17 times higher in the baffle-bearing photobioreactor than that in the photobioreactor without the baffle.

Study on Two-Phase Mixing Inside Flow Focusing/Blurring Nozzle by Gray Distribution Analysis Method

The application prospect of a flow focusing/blurring nozzle is broad but research on gas-liquid flow inside the nozzle is not comprehensive. The gas-liquid mixing inside the nozzle is difficult to study by visualization experiment, so this paper proposes to study the gas-liquid flow or mixing inside the nozzle by the gray scale level distribution of the experimental images. The results show that the increase of air flow rate is beneficial to two-phase mixing inside the nozzle, while the influence of water flow rate, tube hole distance (the distance between inner tube and nozzle outlet) and orifice diameter increase is opposite. The influence of air inertia force on two-phase mixing is weaker than the water inertia force under different parameters, the effect of the air inertia force on two-phase mixing is similar to tube hole distance under a small flow rate, the effect of the orifice diameter on two-phase mixing is relatively weak. In addition, the analysis of the gas-liquid flow field in the mixing zone shows that the gas-liquid flow in the nozzle is stable in the flow focusing mode. In the flow blurring mode, the gas-liquid flow inside the nozzle has radial stability but axial pulsation. In the transition mode, the gas-liquid flow inside the nozzle is unstable, but the gas-liquid flow is close to the flow blurring mode.

Rock and roll: Incipient aeolian entrainment of coarse particles

Aeolian transport of coarse grains is an important topic, finding applications in nature (for infrastructure exposed to wind scour) as well as industry (e.g., considering pneumatic transport). Incipient particle entrainment due to turbulent winds refers to the wind conditions where aeolian transport initiates, and as such, it is at the core of such studies. The research presented herein focuses on identifying and quantifying the dynamical processes responsible for coarse particle entrainment. Specifically designed wind tunnel experiments are conducted for a range of wind conditions near the aeolian transport thresholds. A high-resolution laser distance sensor is employed to provide information for the displacement of an exposed particle ranging from small simple rocking motions to complete entrainments (rolling). Measurements of the exposed particle's angular displacements are acquired, which allow the probabilistic study of incipient motion. The variation of statistical parameters, such as the frequency of entrainments, duration of dislodgements, magnitude of displacements, and time between displacements, is studied for a range of increasing airflow rates. The main findings from these experiments suggest that rocking can be observed only up to a limit angular displacement (equal to 0.41π for the conditions tested herein), which defines the position beyond which the resistance force can be overcome by just the mean aerodynamic forcing. Following this experimental framework to establish aeolian thresholds for a wider range of environments may be useful for the identification of the wind conditions under which aeolian transport may start occurring.

A comparison of partially premixed methane/air combustion in confined vane-swirl and jet-swirl combustors

ABSTRACT The characteristics of partially premixed methane/air combustion in aconfined geometry are experimentally investigated in two types of swirling flows introduced by using avane swirl (VS) and tangential jet swirl (TJS), respectively. To make acomparison, acoaxial jet (CJ) burner is also employed. The fuel and air are individually injected through their own inlets, partially premixed in amixing chamber, and then burned in aconfined cylindrical combustor. In VS and CJ combustors, the fuel is axially injected from the center; while in the TJS combustor the fuel is injected through either acentral inlet or tangential inlet. The geometry swirl number varies from 0 to 3.38. The flame structures, extinction limits, temperature distribution, NOx, CO concentrations and flow velocities are systematically examined to compare the flame characteristics. The detailed observations show that the swirl plays asignificant role in the fuel mixing, flame stabilization, and flame structures. As fuel is axially injected, ayellow flame is established at low airflow rate regardless of the swirl number values. As the airflow rate increases, ablue flame is obtained; the flame extinguishes at avery low global equivalence ratio of 0.25 in the VS and TJS combustors. When fuel and air are tangentially injected, ablue flame similar to premixed one is established; asteady flame is obtained from lean to rich limits (equivalence ratio of 0.5 to 1.68). The temperature is distributed more uniformly in the high swirl TJS combustor, particularly for the one adopts pure tangential jets of fuel and air, in which the measured NOx and CO concentrations are the lowest. The differences were mainly attributed to different mixing modes.

DEM-CFD simulation of wood pellet degradation by particle-wall impact during pneumatic conveying

A numerical degradation model based on two key-functions, the so-called selection and breakage functions, is developed and implemented into a coupled DEM-CFD approach for investigating wood pellet degradation and fines formation during pneumatic conveying by particle-wall impact. The influence of operating conditions like air flow, product flow and solids loading ratio as well as of pipe component geometry on degradation is examined. Detailed insights into the flow field and particle motion are obtained. The inter-particle and particle-wall collisions are statistically analysed since they are the major cause of particle degradation.Apart from operating conditions, the bend radius is varied in four steps, supplemented by a 90°-Elbow as the worst-case scenario and a straight pipe section for reference. Increasing air flow rates, and thus higher particle velocities, as well as decreasing pellet mass flows and smaller bend radii result in progressive particle degradation. Particle-wall collisions turned out to be the major reason for particle breakage. Numerical results are compared to experimental data and show good agreement.

INFLUENCE OF JET FAN INSTALLED ON A CUTTER-LOADER ON AIR DRAG IN VERY LONG LONGWALL PANELS

The article presents studies into aerodynamic processes in very long longwall panels. The computations in ANSYS using the finite volume method show that air drag in longwalls varies versus position of the longwall mining system in the panel. Enhancement of ventilation efficiency in longwalls requires reduction in air drag. The longwall air drag is governed by the air drags of the powered roof support and cutter-loader. The latter have very large dimensions which are technologically unchangeable. For this reason, it is necessary to ensure forced air flow to by-pass the cutter-loader in the longwall panel. The estimate of advantages of the proposed method for the air drag reduction in very long longwall panels is presented. The method consists in increasing air flow rate in the longwall with the help of an axial jet fan mounted on the cutter-loader.

Performance evaluation of a seasonal residential space heating system based on thermochemical energy storage

Abstract Performance of a novel configuration of residential seasonal space heating system based on open thermochemical energy storage (TCES) is numerically investigated. The system comprises two open TCES reactors and a humidifier operating in a complete closed-loop or in partial recirculation to maintain a comfortable temperature in a detached room. A detailed three-dimensional model for flow and heat transfer in a detached room is coupled with a model of the reactive bed undergoing exothermic reaction. The thermal and breathing comfort requirements in the room are obtained simultaneously by operating the system on partially recirculated air. A comparative study of the closed-loop configuration with its open-loop counterpart for the detached room indicates a significant energy saving of 76.61% (92.90 W) for the former. A realistic case study is conducted by operating the system with 10% fresh air, subject to ambient conditions for a winter night in Pune, India. Numerical studies conducted for constant ambient conditions reveal improvement in the room’s heat distribution with increased airflow rate. Employment of two TCES reactors instead of one reactor enhances the Coefficient of Performance (COP) by a factor of 1.39. Adiabatic humidification in the humidifier eliminates its external heat requirement with the increase in the blower power input. Investigation of different locations for the exhaust vent is carried out for minimum heat loss to the surroundings. The system’s energy consumption reduces by 10.18% using a cross-flow air-to-air heat exchanger for pre-heating fresh air. An annual heating cost of 0.44 USD.kWh−1 is estimated for the system.

Effects of Operating Parameters on the Froth and Collection Zone Recovery in Flotation: An Industrial Case Study in a 10 m3 Cell

The effects of flotation operation parameters, including froth depth, air flowrate, and frother dosage, on the froth and collection zone recovery and the flowrate of particles into the froth phase were investigated in a 10 m3 industrial cell. The results showed that froth recovery increases upon increasing air flowrate and frother dosage, as well as reducing froth depth. While all tested parameters affected the particles that entered into the froth phase, air flowrate and frother dosage showed the most and least significance, respectively. When the air flowrate, frother dosage, and froth depth were 146 m3/h, 150 mL/min, and 5 cm, respectively, froth recovery was found to be above 84%. Also, the effect of the parameters studied on collection zone recovery was different from their effect on the froth zone, with air flowrate having the greatest impact on the former.

Open Space Scenario on Riverside Settlement to Access Comfortable Wind Environment

Beyond confines of the geography, urban form has direct impact to its microclimatic condition. The constituted set of buildings and open spaces contribute to its comfortable wind environment. This paper examines incorporation of open spaces as passive urban ventilation to infiltrate wind into a riverside settlement. The research conducted in warm-humid riverside settlement: Pasar Lama Tangerang. The actual wind environment is below desired breezes for outdoor activity like strolling. Upon actual site conditions, such as prevailing wind and morphology of existing buildings, we established three urban morphology scenarios: (1) ground floor open space, (2) pocket open space, (3) combination scenario. The research coupled with Computational Fluid Dynamics (CFD) simulation to calculate air flow rate and wind flow direction in every scenario. Study results reveal the three scenarios can prevent air flow from stagnating and allow better permeability of urban air. Reducing land coverage (open space) is one of the most efficient strategy to increase air flow rate up to 2 times the existing case. CFD simulation provide comprehensive data and help to understand systems, performance and implication of design. The capacity to measure climatic parameters compared and correlated with morphological and topography characteristic can improve the quality of built environment.

Model of thermal buoyancy in cavity-ventilated roof constructions

Timber roof constructions are commonly ventilated through an air cavity beneath the roof sheathing in order to remove heat and moisture from the construction. The driving forces for this ventilation are wind pressure and thermal buoyancy. The wind driven ventilation has been studied extensively, while models for predicting buoyant flow are less developed. In the present study, a novel analytical model is presented to predict the air flow caused by thermal buoyancy in a ventilated roof construction. The model provides means to calculate the cavity Rayleigh number for the roof construction, which is then correlated with the air flow rate. The model predictions are compared to the results of an experimental and a numerical study examining the effect of different cavity designs and inclinations on the air flow rate in a ventilated roof subjected to varying heat loads. Over 80 different test set-ups, the analytical model was found to replicate both experimental and numerical results within an acceptable margin. The effect of an increased total roof height, air cavity height and solar heat load for a given construction is an increased air flow rate through the air cavity. On average, the analytical model predicts a 3% higher air flow rate than found in the numerical study, and a 20% lower air flow rate than found in the experimental study, for comparable test set-ups. The model provided can be used to predict the air flow rate in cavities of varying design, and to quantify the impact of suggested roof design changes. The result can be used as a basis for estimating the moisture safety of a roof construction.

Numerical investigation of electrostatic effect on particle behavior in a 90 degrees bend

Particle behavior in a turbulent circular-sectioned 90° bend under electrostatic field at three air flow rates (1600 L/min, 1100 L/min and 950 L/min, the corresponding bulk Reynolds numbers are 58,000, 40,000, 34,000) is simulated by a Large Eddy Simulation-Lagrangian particle tracking technique (LES-LPT) method coupled with electrostatic field model by Coulomb’s law. This numerical simulation is dedicated to study the electrostatic effect on particle behavior and erosion occurred in the dilute particle-laden bend flow. Forces considered acting on particles includes drag, lift, gravity and electrostatic force. Results obtained for the fluid phase are in good agreement with experimental and numerical data. Predictions show that electrostatic field does affect the particle motion in the pipe bend. At higher air flow rate with higher electrostatics at the inner arc the increasement of impact angle is lower than that at lower flow rate with lower electrostatics. The same conclusion can be found at the outer arc. In addition, electrostatic effect does increase particle-wall impact velocity while such trend decreases with flow rate. Erosion rate increases with increasing air flow rate, which is independent of electrostatics. However, given the same flow rate, the electrostatics reduces the occurrence of erosion at the bend. The erosion rate under electrostatic effect is found to approach that without electrostatics as the flow rate increases. Therefore, the effect of electrostatics on erosion decreases with the air flow rate.

On the Energy Performance of Micro-Encapsulated Phase Change Material Enhanced Spackling with Night Ventilation

Phase change material (PCM) is an attractive solution for improvement of thermal performance in buildings, and have excited a vast amount of research in recent years. There are however practical challenges with ensuring adequate phase transitions of the PCM to exploit the passive heat storage benefits. Night ventilation (NV) with free cooling have surfaced as one of the most promising methods to properly utilize PCMs and maximize energy savings. This work deals with a novel spackling compound enhanced with microencapsulated PCM. The product is intended for use at inner walls and ceiling surfaces of buildings and is suited for new and retrofitting building applications. Ensuing former experimental studies, a validated simulation model is developed and used to study the PCM with natural and hybrid NV strategies in an office building during summer conditions in Oslo, Norway. Cooling load reduction and energy savings are analyzed with varying air flow rates of 0.5–5 air changes per hour (ACH) and 2–4 mm PCM layer thickness. It is shown how increasing air flow rates and PCM thickness greatly enhances energy performance, but at a diminishing rate. Although the NV alone can reduce the cooling load by 11.5% at 1 ACH, 40.2% at 3 ACH and 59.8% at 5 ACH, one can achieve further reduction up to 19.5%, 78.2% and 95.5% for the respective ACHs with 4 mm PCM. The natural NV provides more energy savings compared to the hybrid strategy. As energy requirement by fans increases with the increase of air flow rates in the hybrid strategy, the energy savings eventually start to reduce. The hybrid strategy can save 38% energy at most with 3 ACH, and the savings is increased to 50% with the inclusion of 4 mm PCM. On the other hand, the natural strategy saves 56% of energy at the same air flow rate, and 69% with 4 mm of PCM.

Investigation on solar humidification dehumidification water desalination system using a closed-air cycle

Recently, many regions of the world have become in an urgent need of desalination systems. Humidification-dehumidification desalination plants are considered the most suitable choices for many countries. Many of the previous studies have worked on the study of humidification-dehumidification desalination systems based on the open-air cycle. The current research presents a theoretical and experimental study of a solar humidification-dehumidification water desalination system based on a closed-air cycle. The impact of air flow-rate, water to air mass ratio, and cooling water flow-rate on gain output ratio and water productivity has been investigated. The results show that the productivity is enhanced with increasing air flow-rate, while the gain output ratio decreases. The gain output ratio and productivity improve with raising the water temperature. The average value of gain output ratio is 0.71, 0.74, 0.78, and 0.81, and the productivity reaches 1.46 kg/h, 2.59 kg/h, 4.40 kg/h, and 6.99 kg/h at water temperatures of 40 °C, 50 °C, 60 °C, and 70 °C, respectively. The maximum gain output ratio of 0.86 is recorded at water to air mass flow-rate ratio of 5. Increasing the cooling water flow-rate has a positive effect on both productivity and gain output ratio. Moreover, the results indicate that the fresh water cost is 0.012 $/L. Finally, a good agreement is noted between the theoretical and experimental results.

Thermal performance of a fixed‐plate air‐to‐air energy recovery system for building application in hot and humid environment

An analysis of the performance of a fixed-plate air-to-air energy recovery system on its efficiency and recovered energy for potential building applications in the hot and humid environment was performed. Investigations were executed under controlled laboratory conditions in an energy testing chamber. Tests were carried out with varying operating parameters in terms of airflow rates that ranged from 1.0 to 3.0 m/s, intake air temperature of 28°C, 31°C, 35°C, 40°C and intake relative humidity of 70%, 75% and 80%. The performance was analysed by adopting the calculation methods of the ASHRAE Standard. This study showed that increased airflow rate decreased efficiency. The increase of airflow rate raised the recovered energy of the system. The study indicated that increasing values of intake air temperature (Tin) resulted in the increase of efficiency and recovered energy. A decrease in the efficiency of the system was observed, notably when the intake relative humidity (RHin) increased.

Effect of Flow Bypass on the Performance of a Shrouded Longitudinal Fin Array.(Dept.M)

Theoretical and experimental studies were carried out 10 investigate the effects of duct velocity, sin density and tip-to-shroud clearance on the flow bypass and its impact on the pressure drop across a longitudinal aluminum fin array and its thermal performance. The clearance was varied parametrically, stating with the fully shrouded case and variations of the channel height giving partially shrouded configuration of different clearance ratios were also carried out. The slow bypass was found to increase with increasing sin density and insensitive to the air slow rate. That effect of fin density decreased as the clearance increased. The calculated total pressure was greatly affected by fin density. For fully-shrouded sin array, with H/S equals to 8 and 12.72, the pressure drop increased by a factor of 4.3 and 20 of that with Hf/S equals to 3.4, respectively. The total pressure drop and the average convective heat transfer coefficients corresponding to the fully and partially shrouded fin array of Hf /S=3.4 were compared. Going from fully to partially shrouded one of the largest clearance ratio (C/Hf =0.89), the total pressure drop reduced by about 50%. For clearance ratios equal to 0.36, 0.56, and 0.89, the average heal transfer coefficients were reduced by about 12, 17, and 30 percent of those for the fully shrouded configuration at ReD of about 3x103. That percentage reduction in heat transfer coefficients decreased with the increase of air flow rate.

Dehumidification performance of liquid desiccant system with aqueous-CaCl2 solution in a humid climatic condition

The liquid desiccant solution can able to dehumidify the air by absorbing the water vapour content present in the air. The current work aims to test the dehumidification performance of liquid desiccant system with aqueous CaCl2 and ABS (Acrylonitrile butadiene styrene) packing in a humid climatic condition of India i.e., Kozhikode. The experimental setup is made with packed type dehumidifier. The dehumidification performance such as specific moisture removal, moisture removal rate and dehumidification effectiveness are studied with the effect of variation of solution flow rate, air flow rate, outdoor humidity ratio and solution temperature. The increase in solution flow rate and outdoor humidity ratio positively affect the dehumidification performance whereas the increase in solution temperature negatively affects the dehumidification performance. The increase in air flow rate increases the moisture removal rate but decreases the specific moisture removal and the effectiveness. The dehumidification performance shows a promising results, particularly performs better in higher outdoor humidity conditions. The dehumidification performance can be further improved by adding the cooling system.

Retrieval of Phase and Temperature Distributions in Axisymmetric Flames From Phase-Modulated Large Lateral Shearing Interferogram

A precise phase modulation and demodulation method was proposed to retrieve temperature distributions in axisymmetric flames by using a single-wavelength large lateral shearing interferometer. A spatial light modulator (SLM) was employed to vary the phases in each pixel continuously in the flame-phase measurement. The uniqueness of the phase extraction was mathematically proved for the first time, and a least square method was applied to recover the profile of flame phase in the interferometer. The ambiguity of the phases at different cycles of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\pi $ </tex-math></inline-formula> was eliminated. The phase shift at each pixel was uniquely determined and verified by using simulated data. Further, precise-phase distributions were utilized to retrieve the temperature distribution in a laminar flame. In actual experiments, four axisymmetric laminar flames from diffused to premixed flames were generated by using a Bunsen burner. Profiles of temperature distribution in the flames were extracted and agreed well with the results scanned by using a thermocouple. With the increase of airflow rate, the position of high-temperature zone was observed moving down, and the thermal structure of the premixed flame became more and more obvious. The preheating zone, reaction front, and reaction zone inside the flames were clearly captured.