Air Flow Path Research Articles

A Statistical Approach for Predicting Airtightness in Residential Units of Reinforced Concrete Apartment Buildings in Korea

In this study, a model equation is derived that uses a statistical analysis based on empirical models to predict the airtightness of reinforced concrete apartment buildings popular in Asian regions. Airtightness data from 486 units personally measured by the authors in the past eight years are used. As major variables used in the prediction model, two groups of variables are configured for the geometric components of the envelope, which is a major path of airflow in a building and is where air infiltration and leakage occur. The two groups of variables represent (1) the areas of the individual components forming the envelope and (2) the connection lengths between different components of the envelope. For the effective prediction of airtightness, correlation analysis and multiple regression analysis were applied step by step in this study. The results of the correlation analysis indicated that the areas of the slab and the window are the area variables that present the greatest impact, whereas the perimeter length of the window is the connection length variable that presents the greatest impact. Using a multiple linear regression analysis method, airtightness prediction model equations can be derived, and it is found that the model with variables for area is able to predict airtightness more accurately compared to the two models derived from variables for connection length and all variables for area and connection length. Although the statistical approach in this study shows a limitation in that the prediction results may vary depending on the attributes and type of data collected by countries, the methodology and procedure in this study contribute to similar studies for making prediction models and finding the influence of variables in the future with high applicability and feasibility.

Creep compaction and μCT based permeability measurement of aerospace-grade out-of-life prepregs

This paper focuses on the experimental creep compaction behavior and μCT based permeability measurements of an “Out-of-life” aerospace-grade carbon/epoxy prepreg system. The creep compaction experiments were conducted using four different thicknesses (2, 4, 8 and 16 layers) of prepreg at three different temperatures (23, 60, and 90 °C). The effect of varying the number of prepreg layers on the creep compaction strain and fiber volume fraction at various temperatures was determined. An X-ray computed tomography (XCT) technique was carried out on all samples to observe the internal features of the compacted prepreg. It was observed that an increase in the number of layers reduced the overall creep property of the expired prepreg system. An XCT-based model was created to measure air permeability through the voids at room temperature and through-thickness reinforcement permeability at the three different temperatures using computational fluid dynamics. Several unit cells were extracted for image analysis and segmentation for subsequent modeling of the flow through the thickness of the prepreg at elevated temperatures. The flow fields and fluid velocity contours for different numbers of layers at different temperatures were also obtained. The probability of finding connected air flow paths for air permeability decreased as the number of layers increased. It was observed that creep compaction distorted the prepreg architecture at elevated temperatures, pushing the resin out and causing an increase in the through-thickness reinforcement permeability.

Experimental and thermal performance investigations on sensible storage based solar air heater

Abstract The thermal performance of the solar collector for air heating purpose is investigated with and without packed bed through experimental and theoretical methods. A simple flat plate solar air heater was developed with 2m2 corrugated absorber plate and integrated with porous pebble bed in the airflow path to act as a sensible heat storage medium. The experimental studies were carried out for different mass flow rates of air from 0.014 to 0.087 kg/s with the increment of 0.0095 kg/s. Steady-state theoretical models have been established to predict the thermal performance of the air heaters and the results indicated that they are well enough to predict the outlet air temperature with acceptable error percentage. The collector with packed bed storage medium is more efficient than without packed bed in terms of energy efficiency as well as in reducing temperature fluctuation of air at the outlet of the collector. The energy and exergy efficiency of the collector with packed bed veried from 20.35% to 50.92% and +3.97% to −2.807% for the airflow rates 0.014 kg/s to 0.087 kg/s respectively. Solar collectors with packed bed are capable to deliver the hot air in the range of 45 to 60 °C for a longer period and which can be preferred for achieving a better quality of the dried products as well as for space heating applications.

Performance analyses of a combined natural draft hybrid cooling system with serial airflow path

For offsetting the inherent weakness of traditional cooling system, a natural draft hybrid cooling system is introduced to take full advantage of wet and dry cooling technologies, by combining the dry and wet cooling sections in one cooling tower with serial airflow path. The three-dimensional numerical models are developed to evaluate the thermal-flow performance of the hybrid cooling system under different operating and ambient conditions, with the airflow fields and cooling efficiency obtained and analyzed. The results show that the performance of the wet cooling section is superior to the dry one in most cases. The large spraying water flow ratio, low ambient humidity and small wind speed are of benefit to the cooling capacity of the hybrid cooling system, but the cooling efficiency of the hybrid system is more favorable at high ambient humidity and large spraying water flow ratio. At the high ambient humidity, the cooling performance of the dry section in the dry mode can exceed that in the hybrid mode, and the ambient wind even plays a positive role in the wet cooling section with a low spraying water flow ratio. Moreover, the natural draft hybrid cooling system is favorable to the visible plume abatement.

Pin-to-plane self-pulsing discharge in transversal airflow: interaction with a substrate of plasma filaments blown out from the discharge zone

The pin-to-plane electrode system for the multi-sectioned discharge in the transversal airflow at atmospheric pressure has been developed. The airflow is directed perpendicularly to the electric current. As it was revealed, all sections of the multi-sectioned discharge operate identically and independently to each other. For this reason, the spatial-temporal behavior of the discharge excited only in a single section was investigated. The pin-to-plane discharge (PPD) was powered by a positive polarity DC voltage that induces the spontaneously repeating streamer-spark breakdowns in a discharge gap. Each breakdown forms the plasma filament (PF) which is being further blown out of the discharge zone and stretched by the airflow. The PF impacts a dielectric plate located in the path of the airflow at different distances away from the discharge zone. Two modes in the behavior of the blown-out PF have been revealed. When the plate is close to the discharge zone, the blown-out PF is tightly pressed by the flow to the plate. In this case, both the brightness and electric current of the PF are periodically pulsing with a high frequency up to the plasma filament breaking up due to its strong elongation by the flow. If the plate is far away, the quasistationary regime happens. During the PF elongation in this regime, plasma filament keeps both the brightness and current approximately changeless till the filament breaking up. At In this regime, the blown-out PF is being stretched in parallel to the surface without contacting it. The release of energy into the PF continues also in the course of its blowing out until its impinging the object located in the path of airflow. Due to that, the PPD pulsing mode generates a lot of reactive species inside the PF up to its impinging the object to be treated. This is a reason why the self-pulsing PPD can be highly effective for surface processing by non-thermal plasma.

Proposal and Prototyping of Self-Excited Pneumatic Actuator Using Automatic-Flow-Path-Switching-Mechanism

Robots currently have a wide range of practical applications. However, their widespread use is limited by long design and manufacturing times as well as increasingly complex drive system electronics and software, which have led to high development costs. Therefore, simpler manufacturing, driving, and control methods are required. In this study, we design a pneumatic actuator drive system that combines the printing technique and self-excited vibration. In the proposed actuator, a mechanism for automatically switching the airflow path is used to induce self-excited vibration. Moreover, the actuator is integrally molded by a 3D printer; therefore, no assembly process is required. This actuator can be used to easily build robots in a short time, contributing to more widespread use of robots. In this study, we also calculate the theoretical value of the moving frequency by modeling the actuator and verify the validity of this value through experiments using a prototype actuator. Based on the results, we were able to freely design the operating frequency of the actuator; by using this knowledge, we designed a flapping robot. The robot is also integrally molded by a 3D printer. Finally, we validate its motion through experiments, in order to illustrate one of the many applications of the proposed actuator.

Experimental study on the frosting characteristics of round tube in confined circular flow path at low temperature

Frosting in confined spaces usually takes places on the cold surfaces in heat exchangers and other equipment. In order to study the frosting characteristics on the surface of a round tube in a confined space, a test rig is developed capable of visualizing transient frosting. The periodic melting and refrosting phenomena are captured and analyzed with the wall surface temperature of −60 °C. The roles of humid air velocity, air temperature, relative humidity and cold surface temperature on frosting have been expounded independently. Along the air flow path, the frosting thickness, accumulation, heat transfer rate and average density are compared under different air velocities, air temperatures, clod surface temperature and relative humidity and the correlations are proposed from dimensionless parameters. The results show that obvious stepwise periodic frosting and frost-melting appear due to the thermal resistance and heat transfer between the frost and the humid air when the frosting entered the mature stage. At a higher tube temperature, air temperature and relative humidity, the frosting melting and undulations emerged more frequently and the frost accumulation, heat transfer rate and average density increased. The frost layer thickness is uneven along the air flow path, which possesses the highest value in the middle position of tube and the lowest near the air inlet.

Ventilation and laboratory confirmed acute respiratory infection (ARI) rates in college residence halls in College Park, Maryland

Strategies to protect building occupants from the risk of acute respiratory infection (ARI) need to consider ventilation for its ability to dilute and remove indoor bioaerosols. Prior studies have described an association of increased self-reported colds and influenza-like symptoms with low ventilation but have not combined rigorous characterization of ventilation with assessment of laboratory confirmed infections. We report a study designed to fill this gap. We followed laboratory confirmed ARI rates and measured CO2 concentrations for four months during the winter-spring of 2018 in two campus residence halls: (1) a high ventilation building (HVB) with a dedicated outdoor air system that supplies 100% of outside air to each dormitory room, and (2) a low ventilation building (LVB) that relies on infiltration as ventilation. We enrolled 11 volunteers for a total of 522 person-days in the HVB and 109 volunteers for 6069 person-days in the LVB, and tested upper-respiratory swabs from symptomatic cases and their close contacts for the presence of 44 pathogens using a molecular assay. We observed one ARI case in the HVB (0.70/person-year) and 47 in the LVB (2.83/person-year). Simultaneously, 154 CO2 sensors distributed primarily in the dormitory rooms collected 668,390 useful data points from over 1 million recorded data points. Average and standard deviation of CO2 concentrations were 1230 ppm and 408 ppm in the HVB, and 1492 ppm and 837 ppm in the LVB, respectively. Importantly, this study developed and calibrated multi-zone models for the HVB with 229 zones and 983 airflow paths, and for the LVB with 529 zones and 1836 airflow paths by using a subset of CO2 data for model calibration. The models were used to calculate ventilation rates in the two buildings and potential for viral aerosol migration between rooms in the LVB. With doors and windows closed, the average ventilation rate was 12 L/s in the HVB dormitory rooms and 4 L/s in the LVB dormitory rooms. As a result, residents had on average 6.6 L/(s person) of outside air in the HVB and 2.3 L/(s person) in the LVB. LVB rooms located at the leeward side of the building had smaller average ventilation rates, as well as a somewhat higher ARI incidence rate and average CO2 concentrations when compared to those values in the rooms located at the windward side of the building. Average ventilation rates in twenty LVB dormitory rooms increased from 2.3 L/s to 7.5 L/s by opening windows, 3.6 L/s by opening doors, and 8.8 L/s by opening both windows and doors. Therefore, opening both windows and doors in the LVB dormitory rooms can increase ventilation rates to the levels comparable to those in the HVB. But it can also have a negative effect on thermal comfort due to low outdoor temperatures. Simulation results identified an aerobiologic pathway from a room occupied by an index case of influenza A to a room occupied by a possible secondary case.

Cooling performance of natural draft hybrid system with parallel air path

The flexibility of the dry cooling system in thermal power plant needs to be improved to suit the load undulation caused by the increased renewable energy power. For overcoming the weakness of conventional cooling system, a natural draft hybrid (dry/wet) cooling system (NDHCS) is proposed to fully take advantage of dry and wet cooling technologies, which comprises the wet and dry cooling sections with parallel air flow path. The three-dimensional numerical models are developed to investigate the thermal-flow performances of the NDHCS under various environment and operation conditions, by which the flow fields near the NDHCS as well as the heat and mass transfer between circulating water and cooling air are obtained. The results show that both the dry and wet cooling sections dominate the cooling capacity of the hybrid system but the performance of the former is inferior to the latter in most of the cases. Low ambient humidity, large spraying water flow ratio in the wet cooling section and small wind speed are of benefit to the thermal performance of hybrid cooling system. For the dry and wet cooling sections themselves, the cooling performance can be improved thanks to the ambient wind under specific conditions. Besides, NDHCS can effectively avoid visible plume especially under windy conditions.

An Investigation into the Influence of the Airflow Path on the Convective Heat Transfer for an Eddy Current Retarder Turntable

An Investigation into the Influence of the Airflow Path on the Convective Heat Transfer for an Eddy Current Retarder Turntable

Preferential Paths of Air-water Two-phase Flow in Porous Structures with Special Consideration of Channel Thickness Effects

Accurate understanding and predicting the flow paths of immiscible two-phase flow in rocky porous structures are of critical importance for the evaluation of oil or gas recovery and prediction of rock slides caused by gas-liquid flow. A 2D phase field model was established for compressible air-water two-phase flow in heterogenous porous structures. The dynamic characteristics of air-water two-phase interface and preferential paths in porous structures were simulated. The factors affecting the path selection of two-phase flow in porous structures were analyzed. Transparent physical models of complex porous structures were prepared using 3D printing technology. Tracer dye was used to visually observe the flow characteristics and path selection in air-water two-phase displacement experiments. The experimental observations agree with the numerical results used to validate the accuracy of phase field model. The effects of channel thickness on the air-water two-phase flow behavior and paths in porous structures were also analyzed. The results indicate that thick channels can induce secondary air flow paths due to the increase in flow resistance; consequently, the flow distribution is different from that in narrow channels. This study provides a new reference for quantitatively analyzing multi-phase flow and predicting the preferential paths of immiscible fluids in porous structures.

Thermohydraulic performance enhancement of a new hybrid duct solar air heater with inclined rib roughness

In this work, a new hybrid duct configuration of solar air heater is analytically investigated to improve the thermal performance of the system. The proposed design consists of parallel pass air flow paths with rectangular and triangular cross sections at upper and lower sides of the absorber plate. Both the sides of the absorber plates are roughened with inclined shape ribs. The roughness parameters are configured with relative roughness pitch at the bottom of the plate (Pb/eb) of 4–16, relative roughness height of e/Dh ranges from 0.021 to 0.050 and relative angle of arc of (α/60) 0.5–1. Based on the analytical results it is concluded that the maximum effective efficiency is 80.1% for roughness pitch of 8, relative roughness height of 0.021 and relative angle of arc of (α/60) 0.5, at the mass flow rate of 0.045 kg/s at the upper and lower duct. The effect of the mass flow fraction (i) on the thermal performance of the solar air heater is also analyzed. The system improves the thermal and effective efficiency by 22.4% and 18.1% when compared to conventional rectangular duct parallel pass SAH. The design plots are developed to find the optimum values of roughness parameters with respect to ambient conditions.

열풍건조기의 내부 공기유로 개선을 위한 연구

Hot air drying, which circulates hot air in a dryer, removes water contents inside a substance by causing evaporation on the surface. For dryers, reducing power consumption, drying time and the amount of water contents between distributed drying materials are the most significant aspects for better performance. To achieve this goal, the time for the air to reach the drying material and dryness of the air become important factors when designing air flow path inside a dryer. In this study, 3 cases of air flow path were proposed and water evaporation quantity and evaporation differences of 15 locations in a dryer were compared by computational fluid dynamic simulation. Simulation results were first verified by experiments which were carried out with 15 glass dishes filled with 30 g of water, in the same locations as the simulation. Computational results indicated that Case 2 which supplied hot air from the left side and generates uniform horizontal flow from left to right, and finally exiting to the right side showed the best performance among 3 cases in terms of evaporation quantity and evaporation uniformity.

Spatiotemporal dynamics of odor responses in the lateral and dorsal olfactory bulb.

The mammalian olfactory bulb (OB) plays an essential role in odor processing during the perception of smell. Optical imaging of the OB has proven to be a key tool in elucidating the spatial odor mapping and temporal dynamics that underlie higher-order odor processing. Much is known about the activation of olfactory sensory neuron (OSN) glomerular responses in the dorsal olfactory bulb (dOB) during odor presentation. However, the dorsal bulb provides access to only approximately 25% of all glomeruli, and little is known about how the lateral bulb functions during this critical process. Here, we report, for the first time, simultaneous measurements of OSN glomerular activity from both the dOB and the lateral olfactory bulb (lOB), thus describing odor-specific spatial mapping and the temporal dynamics of olfactory input to both the dorsal and lateral bulb. Odor responses in the lateral bulb tended to be most prominent in the dorso-lateral (D-L) region. Lateral glomeruli became active in a dorso-ventral (D-V) sequence upon odor inhalation, unlike the anterio-posterior (A-P) activity wave typical of the dorsal glomeruli. Across the entire D-L bulb, the spatial organization of these dynamics can be explained neither by the purely mechanosensitive dynamics (to breathing clean air) nor by the response amplitudes across glomeruli. Instead, these dynamics can be explained by a combination of zonal receptor distributions, associated OB projections, and air flow paths across the epithelium upon inhalation. Remarkably, we also found that a subset of OSN glomeruli in the lOB was highly sensitive to extranasal air pressure changes, a response type that has not been reported in dorsal glomeruli.

A Study on the Thermal Performance of Air-Type BIPVT Collectors Applied to Demonstration Building

Research on existing air-type PVT (photovoltaic/thermal) collectors has mainly focused on improving the efficiency of the collector itself and on using the energy produced by the collector in heating and cooling facilities and building energy. The first consideration in an air-type PVT system applied to a building facade is the collector arrangement and the flow path considering the collector performance. It is necessary to design the flow inside the air-type BIPVT (building integrated photovoltaic/thermal) collector so that it runs smoothly so as not to cause a dead space and a pressure drop inside the collector, which deteriorate the thermal performance. This study analyzed the thermal characteristics of an air-type BIPVT collector applied to a demonstration building (educational buildings) according to the air flow path and inlet opening ratio. For this purpose, the uniformity of the airflow in the collector was compared through the NX computational fluid dynamics (CFD) program, and the acquired thermal calories and thermal efficiency of the BIPVT collector were compared and analyzed. Based on the simulation results, the temperature and thermal characteristics of the BIPVT collector were compared.

Innovative cathode flow-field design for passive air-cooled polymer electrolyte membrane (PEM) fuel cell stacks

A novel cathode flow-field design suitable for a passive air-cooled polymer electrolyte membrane (PEM) fuel cell stack is proposed to enhance the water-retaining capability under excess dry air supply conditions. The innovative cathode flow-field is designed to supply more air to the cooling channels and further enables deceleration of the reactant air in the gas channels and acceleration of the coolant air in the cooling channels simultaneously along the air flow path. Therefore, the design facilitates the waste heat removal through the cooling channels while the water removal by the reactant air is minimized. The conceptual cathode flow-field design is validated using a three-dimensional PEM fuel cell model. The detailed simulation results clearly demonstrate that the new cathode flow-field design exhibits superior water-retaining capability compared with a conventional cathode flow-field design (parallel flow channel configuration) under typical air-cooled fuel cell operating conditions. This study provides a new strategy to design cathode flow-fields to alleviate notorious membrane dehydration and unstable performance issues in a passive air-cooled PEM fuel cell stack.

Experimental Study on the Thermal and Electrical Characteristics of an Air-Based Photovoltaic Thermal Collector

A photovoltaic thermal (PVT) system is a technology that combines photovoltaics (PV) and a solar thermal collector to produce thermal energy and generate electricity. PVT systems have the advantage that the energy output per unit area is higher than the single use of a PV module or solar thermal collector, since both heat and electricity can be produced and used simultaneously. Air-based PVT collectors use air as the heat transfer medium and flow patterns are important factors that affect the performance of the PVT collector. In this study, the thermal and electrical performance and characteristics of an air-based PVT collector were analyzed through experiments. The PVT collector, with bending round-shaped heat-absorbing plates, which increase the air flow path, has been developed to improve the thermal performance. The experiment was done under the test conditions of ISO 9806:2017 for the thermal performance analysis of an air-based PVT collector. The electrical performance was analyzed under the same conditions. In the results, it can be found that the inlet flow rate of the PVT collector considerably affects the thermal efficiency. It was analyzed that as the inlet flow rate increased from 60 to 200 m3/h, the thermal efficiency increased from 29% to 42%. Then, the electricity efficiency was also analyzed, where it was determined that it was improved according to operating condition of PVT collector.

Eddy Current Loss Effect in Foil Winding of Transformer Based on Magneto-Fluid-Thermal Simulation

The foil winding temperature distribution is crucial to the life of power transformer since local heating can accelerate aging of insulation materials. However, based on the traditional 3-D electromagnetic model and the principle of heat transfer, the non-uniform losses and temperature distribution of foil windings are difficult to estimate because of complex magnetic leakage flux. In this paper, the magneto-fluid-thermal coupling model has been established to calculate the temperature rise and predict the potential hotspots of a simplified dry-type power transformer rated at 2500 kVA. Moreover, the influence of insulation barrier is considered to reshape the air-flow path and to affect the radiative effect between the high-voltage and low-voltage windings. Experimental temperature rises are measured with infrared thermography to verify the simulation results, which achieved reasonable hotspot predictions and provide the theoretical method for transformer designers.

Diesel Engine Acoustic Emission Airflow Clogging Diagnostics With Machine Learning

A diesel engine electrical generator set (“gen-set”) was instrumented with in-cylinder indicating sensors as well as acoustic emission microphones near the engine. Air filter clogging was emulated by progressive restriction of the engine's inlet air flow path during which comprehensive engine and acoustic data were collected. Fast Fourier transforms (FFTs) were analyzed on the acoustic data. Dominant FFT peaks were then applied to supervised machine learning neural network analysis with matlab-based tools. The progressive detection of the air path clogging was audibly determined with correlation coefficients greater than 95% on test data sets for various FFT minimum intensity thresholds. Further, unsupervised machine learning self-organizing maps (SOMs) were produced during normal-baseline operation of the engine. The degrading air flow engine sound data were then applied to the normal-baseline operation SOM. The quantization error (QE) of the degraded engine data showed clear statistical differentiation from the normal operation data map. This unsupervised SOM-based approach does not know the engine degradation behavior in advance, yet shows clear promise as a method to monitor and detect changing engine operation. Companion in-cylinder combustion data additionally shows the degrading nature of the engine's combustion with progressive airflow restriction (richer and lower density combustion).

Multiphysics Field Distribution Characteristics within the One-Cell Solid Oxide Fuel Cell Stack with Typical Interdigitated Flow Channels

Generally, the manufacturing technology of fuel cell units is considered to satisfy the current commercialization requirements. However, achieving a high-performance and durable stack design is still an obstacle in its commercialization. The solid oxide fuel cell (SOFC) stack is considered to have performance characteristics that are distinct from the proton exchange membrane fuel cell (PEMFC) stacks. Within the SOFC stack, vapor is produced on the anode side instead of the cathode side and high flow resistance within the fuel flow path is recommended. In this paper, a 3D multiphysics model for a one-cell SOFC stack with the interdigitated channels for fuel flow path and conventional paralleled line-type rib channels for air flow path is firstly developed to predict the multiphysics distribution details. The model consists of all the stack components and couples well the momentum, species, and energy conservation and the quasi-electrochemical equations. Through the developed model, we can get the working details within those SOFC stacks with the above interdigitated flow channel features, such as the fuel and air flow feeding qualities over the electrode surface, hydrogen and oxygen concentration distributions within the porous electrodes, temperature gradient distribution characteristics, and so on. The simulated result shows that the multiphysics field distribution characteristics within the SOFC and PEMFC stacks with interdigitated flow channels feature could be very different. The SOFC stack using the paralleled line-type rib channels for air flow path and adopting the interdigitated flow channels for the fuel flow path can be expected to have good collaborative performances in the multiphysics field. This design would have good potential application after being experimentally confirmed.