Low Air Flow Rates Research Articles

The role of smoldering in the ignition of Pinus palustris needles

The pyrolysis process and the critical ignition conditions of dead Pinus palustris needles were studied experimentally to understand the role of smoldering in the onset of flaming combustion. The results obtained show that methane (CH4), carbon monoxide (CO), carbon dioxide (CO2), and water vapor (H2O) are the main constituents of the pyrolysis gases generated. The predominance of these compounds was found to be independent of the external heat flux, while their concentrations were sensitive to it. The heat of combustion of the pyrolysis gas and the pyrolysis reaction rate increased with increasing external heat fluxes. Visual observations and parameter measurements during testing hinted at the significance of smoldering to flaming ignition under forced flow conditions. The contribution of smoldering to flaming ignition was quantitively analyzed by combining the measured parameters during testing with the characterized pyrolysis process. The quantification results suggested a significant contribution of smoldering combustion to the flaming ignition under low heat fluxes and high airflow rate conditions.

Membrane bubble aeration unit: Experimental study of the performance in lab scale and full-scale systems

The transfer of oxygen is limited at the gas/liquid interface by the low solubility of oxygen in water. Fine bubble diffusers have a standard oxygen transfer efficiency (SOTE) lower than 30% in a full-scale system. Porous membranes can be employed as diffusor to improve the efficiencies taking the advantage of the high exchange interfacial area and the low volume of equipment. The aim of this work is to study the feasibility of membrane systems for aeration in a full-scale system. Several membrane modules were prepared using hollow fibers hydrophobic membranes and compared with the traditional disk diffusor currently employed in wastewater treatment. The mass transfer coefficient (KLa) and SOTE were assessed by carrying out the aeration tests in both lab-scale and full-scale systems exploring different operating parameters such as system flow rate, the geometry of the module and the surface of the device. The advantage and disadvantages of employing membranes in the aeration process were highlighted. The membrane unit showed better overall mass transfer efficiency increasing from 28% at the lab-scale to 34% in the full-scale system. Unlike the conventional disk diffusers, it has been found that the membrane aerator can operate with significantly lower air flow rates, which leads to a doubling of the efficiency. Moreover, the membrane surface generating the bubbles can be easily increased while maintaining the same module footprint, which in turn allowing a further increase of efficiency from 9% to 24%. However, important phenomena of scaling were observed on the membrane surface.

Automated fault detection and diagnosis of airflow and refrigerant charge faults in residential HVAC systems using IoT-enabled measurements

While automated fault detection and diagnosis (AFDD) in residential heating, ventilation, and air-conditioning (HVAC) using smart thermostat data is gaining increasing attention in recent times, it still requires in-depth investigation for market adoption, especially with real-life data. This paper proposes an Internet of Things (IoT) - based approach that adds a smart sensor to the smart thermostat data to carry out AFDD. The approach uses a model which predicts enthalpy change across the evaporator and compares the prediction to the measured enthalpy change. Deviations which exceed analytically determined thresholds then signal faults in the HVAC system. The faults detected are either installation related or degradation related. Experimental tests were carried out in four homes located in Norman, Oklahoma. From the tests, installation issues like indoor/outdoor mismatch were detected in two homes, while a 30% low charge and low indoor airflow rate were detected in one home. The results show that the proposed AFDD algorithm was able to successfully detect two prevalent faults, namely low indoor airflow and low refrigerant charge. Unlike most of the smart thermostat-based approaches, the proposed IoT-based approach can detect and diagnose both faults but only require one additional sensor which is provided by smart thermostat manufacturers.

Modeling of closed-circuit ball milling of cement clinker via a PBM with a variable Tromp curve for classification

Full-scale closed-circuit cement ball milling was modeled using a true unsteady-state simulator (TUSSIM), based on a transient cell-based population balance model (PBM) with a set of differential algebraic equations (DAEs). As a major novelty, the PBM for the mill was coupled with a dust load-dependent, variable Tromp curve for the air classifier. Results from the dynamic simulations suggest that lower air flow rate or higher rotor speed of the classifier not only led to a finer product but also increased the dust load of the classifier feed. When the dust load was too high, operational failure due to overloading of the whole circuit was detected. Finally, TUSSIM was used for process optimization with a global optimizer-DAE solver to identify the air classifier's parameters that yielded desirable cement quality while maximizing production rate. We have demonstrated that the optimization could increase production rate by 7% compared to the baseline process.

Experimental study and modeling analysis of sewage sludge smoldering combustion at different airflow rates

Sewage sludge is a major by-product of wastewater treatment, and its unfavorable properties are frequently a key restriction of disposal technologies, resulting in high costs and ineffective waste management. Smoldering combustion is a new technique for disposing of organic solid waste with high moisture content, which efficiently recovers energy with minimal igniting energy requirements. The objective of this study is to investigate the effects of airflow rate on sewage sludge (SS) smoldering combustion by combining experimental and modeling analyses. Results show that air channeling easily forms at the reactor's edge, intensifying the smoldering reaction and forming a concave smoldering front. The minimum airflow rate required for self-sustaining smoldering is 0.3 cm/s. As the airflow rate increases, convective heat transfer becomes dominant over conduction and radiation, resulting in a surge in smoldering temperature and velocity at 0.6 cm/s, followed by a linear increase. The maximum airflow rate at which the smoldering process can propagate stably during SS disposal is 8 cm/s. The expressions of the smoldering characteristics are obtained by using the activation energy asymptotic approach, and the calculated and experimental values show the same trend of variation, with good agreement at low airflow rate conditions. Sensitivity analysis shows that porosity φ is the most crucial parameter affecting smoldering temperature and velocity.

Temperature and flame structure imaging in kerosene swirl-stabilized spray flames at low air flow using TLAF and OH-PLIF

Air flowrate is an important parameter for airbrast nozzles and low air inlet flow rate in airbrast type combustors will lead to worse atomization, combustion instability, and increased pollutant emissions. Using non-linear excitation regime two-line atomic fluorescence (NTLAF) thermography imaging and planar laser-induced fluorescence of hydroxyl radical (OH-PLIF), temperature and flame structure in the near-nozzle area are investigated at different low air flow rate to study the combustion deterioration of kerosene swirl-stabilized spray flames. In this concerned area, combustion occurs mainly at the near-wall region but a few OH signals are present at the centerline region except for the kerosene LIF particles. With the air supply getting low, the near-wall OH signals get low, corresponding to the change of indium Stokes and anti-Stokes fluorescence. The temperature in the centerline region is presented to be reduced and the region for the temperature threshold filter expands, indicating the reduction of the downstream hot combustion products brought back by weak swirl, which is closely related to the extremely low air flowrate. Under extremely low air flow rate, the highly fluctuating temperature and weak gas-liquid mixed combustion at the centerline area may tend to cause combustion instability or ignition failure.

Numerical comparison of an office cooled with and without a ventilated slab using a model predictive controller

Ventilated slabs are Thermally Activated Building Systems (TABS) that use the supply air as the heating/cooling medium for taking advantage of the thermal inertia of a slab. The objective for the ventilated slab is to maintain the indoor temperature within the desired range for a minimal energy consumption, at least equal or lower than with a regular (non-ventilated) slab. To achieve such objectives, an efficient control is required but the latter is challenging for TABS because of the delay brought by their thermal inertia. While advanced control techniques are available and suitable with TABS, it is not always clear if the final performances are driven by the control technique itself or the inherent thermal potential of the ventilated slab. The present paper numerically analyses the behaviour of the ventilated slabs controlled with a Model Predictive Controller, and provides a comparison with a non-ventilated slab combined with the same controller. This comparison was extended to four other airflow rates, since it significantly changes the thermal dynamic of a ventilated slab. The indoor temperature requirements were satisfied most of the time and energy demand differences observed between the two systems were minor. However, a lower airflow rate is preferable as it decreases the consumption of the fans, which was significant for this test case. The most important improvement brought by the ventilated slab was the smoothed temperature variation at the outlet of the slab, resulting in a smaller blown air – room air temperature difference with ventilated slabs and thus favouring indoor comfort.

A High-Performance Vortex Adjustment Design for an Air-Cooling Battery Thermal Management System in Electric Vehicles

To boost the performance of the air-cooling battery thermal management system, this study designed a novel vortex adjustment structure for the conventional air-cooling battery pack used in electric vehicles. T-shape vortex generating columns were proposed to be added between the battery cells in the battery pack. This structure could effectively change the aerodynamic patterns and thermodynamic properties of the battery pack, including turbulent eddy frequency, turbulent kinetic energy, and average Reynolds number, etc. The modified aerodynamic patterns and thermodynamic properties increased the heat transfer coefficient with little increase in energy consumption and almost no additional cost. Different designs were also evaluated and optimized under different working conditions. The results showed that the cooling performance of the Design 1 improved at both low and high air flow rates. At a small flow rate of 11.88 L/s, the Tmax and ΔT of Design 1 are 0.85 K and 0.49 K lower than the conventional design with an increase in pressure drop of 0.78 Pa. At a relative high flow rate of 47.52 L/s, the Tmax and ΔT of the Design 1 are also 0.46 K and 0.13 K lower than the conventional design with a slight increase in pressure drop of 17.88 Pa. These results demonstrated that the proposed vortex generating design can improve the cooling performance of the battery pack, which provides a guideline for the design and optimization of the high-performance air-cooling battery thermal management systems in electric vehicles.

Enhanced electro-Fenton degradation of sulfamethazine using Co-based selenite modified graphite cathode via in-situ generation of •OH

Electro-Fenton (EF) reaction has been regarded as a promising technology for practical wastewater treatments. However, the generation of H2O2 and •OH was limited by low O2 utilization and protonation efficiency in the conventional EF system. This research synthesized a novel electrocatalyst, Co12(OH)2(SeO3)8(OH)6 (CoSeO) to achieve efficient wastewater treatment via in-situ H2O2 generation in the EF system. The modified graphite plate-based cathode (CoSeO@GP) was fabricated by using a facile hydrothermal method combined with a simple coating. The CoSeO@GP cathode that had both hydrophilic and aerophilic properties achieved efficient H2O2 production (26.15 mgL-1h−1) at low air flow rate. Moreover, the average protonation rate was significantly improved to 0.00803 molH-1min−1 with this cathode. The presence of Co2+/Co3+ could significantly promote the in situ H2O2 decomposition, and boost the production of •OH. Sulfamethazine (SMZ) was completely degraded in 90 min with the kinetic constant of 0.05959 min−1 by using the CoSeO@GP cathode. In addition, this cathode maintained high stability and applicability after a 10-cycle continuous operation. This study provided a proof-of-concept design strategy for developing novel EF cathodes for the treatment of recalcitrant pollutants.

Tracing the origin of large respiratory droplets by their deposition characteristics inside the respiratory tract during speech.

Origin of differently sized respiratory droplets is fundamental for clarifying their viral loads and the sequential transmission mechanism of SARS-CoV-2 in indoor environments. Transient talking activities characterized by low (0.2 L/s), medium (0.9 L/s), and high (1.6 L/s) airflow rates of monosyllabic and successive syllabic vocalizations were investigated by computational fluid dynamics (CFD) simulations based on a real human airway model. SST k-ω model was chosen to predict the airflow field, and the discrete phase model (DPM) was used to calculate the trajectories of droplets within the respiratory tract. The results showed that flow field in the respiratory tract during speech is characterized by a significant laryngeal jet, and bronchi, larynx, and pharynx-larynx junction were main deposition sites for droplets released from the lower respiratory tract or around the vocal cords, and among which, over 90% of droplets over 5 µm released from vocal cords deposited at the larynx and pharynx-larynx junction. Generally, droplets' deposition fraction increased with their size, and the maximum size of droplets that were able to escape into external environment decreased with the airflow rate. This threshold size for droplets released from the vocal folds was 10-20 µm, while that for droplets released from the bronchi was 5-20 µm under various airflow rates. Besides, successive syllables pronounced at low airflow rates promoted the escape of small droplets, but do not significantly affect the droplet threshold diameter. This study indicates that droplets larger than 20 µm may entirely originate from the oral cavity, where viral loads are lower; it provides a reference for evaluating the relative importance of large-droplet spray and airborne transmission route of COVID-19 and other respiratory infections.

Maintenance of the required indoor air exchange rate by using compact regenerative heat exchangers

Introduction. Ventilation systems of civil buildings experience problems of air exchange interruption and high heat losses. A solution to this problem is the use of compact decentralized ventilation units with the function of heat recovery from exhaust air. They are called stationary switching regenerative heat exchangers (SSRHEs). SSRHEs ensure high energy saving at low air flow rates. However, the required air exchange rate can be substantial even for one person. Therefore, a study was conducted to determine values of the energy efficiency coefficient of SSRHEs for the range of characteristic air flow rates.
 
 Materials and methods. The analysis of regulations and research papers, focused on determining the indoor air exchange required for one person was conducted. The air exchange rate is mainly determined through the recommended level of carbon dioxide concentration in a room. The energy efficiency coefficient of SSRHEs is determined by means of mathematical modeling of the heat exchange process in a single channel of a regenerative nozzle.
 
 Results. Values of the energy efficiency coefficient of SSRHEs are provided for a wide range of air flow rates. Efficiency reduction, accompanied by an increase in the rate of the air flow through the SSRHE, as well as a decrease in the nozzle length and an increase in the diameter of a single channel are shown. Recommendations are provided on the design of a regenerative nozzle that ensures extensive thermal energy savings at high air flow rates through the SSRHEs.
 
 Conclusions. Taking into account a wide range of values of the amount of air required per person, SSRHE capacity control is recommended. Research results can be used to modernize existing devices and develop new configurations of nozzles for such SSRHEs. The authors have found that experimental studies of the proposed configurations are needed to evaluate the level of noise generated by SSRHEs and the optimal nozzle design mitigating the risk of clogging.

In situ probing of atmospheric-pressure warm air glow discharge for nitrogen fixation by multiple laser spectroscopies

The fixation of atmospheric nitrogen into valuable compounds through reactive plasma processes has attracted intense interests due to its easy operation and compatibility with distributed renewable energy sources. However, practical implementation of plasma-assisted nitrogen fixation is hampered because of its relatively low throughput, which is dominantly limited by the unclear underlying mechanisms. In this study, effort was focused on the in situ production of key species in a DC-driven warm air glow discharge at atmospheric pressure with the help of advanced laser spectroscopic diagnostics. Laser Rayleigh scattering was applied to determine the gas temperature distribution in the discharge column. And mid-infrared quantum cascade laser absorption spectroscopy and one/two-photon absorption laser-induced fluorescence were performed on molecular nitric oxide (NO), atomic oxygen and nitrogen (O, N) for their absolute densities in the discharge. It is found that the spatial distributions of gas temperature, O and N atoms show peaks in the hot discharge center. In contrast, a hollow ‘doughnut’ shape characterized by the NO molecule was observed, particularly under conditions of high discharge current but low airflow rate. The steady-state simulation shows that the hollow pattern of NO is dominantly induced by the radial diffusion of species due to the steep spatial gradient of gas temperature in the discharge cross-section. Moreover, the reverse conversion by atomic N leads to a negative effect on the NO synthesis, especially at the discharge center where the N density and gas temperature are high. From the steady-state modeling, a similar hollow distribution of NO2 was depicted in the air glow discharge. These results demonstrate the strong dependence on atomic O for the major formation process of NO, and the importance of suppressing the reverse paths dominated by atomic N for higher NO production in the studied warm air plasma.

Combined Energetic and Exergetic Performance Analysis of Air Bubbles Injection into a Plate Heat Exchanger: An Experimental Study

This paper aims to give a comprehensive energetic-exergetic performance analysis on the impacts of injecting-submillimeter of air bubbles into both sides of cold and hot water streams before the entrance port of a corrugated plate heat exchanger (C-PHE) having ten plates within counterflow configuration. Hence, optimize the energy and exergy effectiveness at different operating conditions for counter and parallel fluid flow configurations. Hot streams were studied in seven flow rates ranging from 280 L/h to 880 L/h with a regular step of 100 L/h, and constant hot water temperature and cold-water stream of 50 °C and 290 L/h, respectively. Hence, the air was discharged with four flow rates ranging between 150 and 840 L/h. The obtained results showed the vital role of the ABI technique in enhancing the NTU and effectiveness by 59% and 18.6%, respectively, for CWS. The entropy generation was reduced to 0.038 W/K and the augmentation entropy generation number to 0.087 at the low airflow rate for CWS, which are the main parameters for evaluating the EGM. These two parameters increase the Witte-Shamsundar-efficiency to a maximum value of 98.6% at the same operating conditions. Moreover, the exergy effectiveness was enhanced to a maximum value of 80.9% at a high ABI flow rate and low volumetric rate of the hot stream at CWS. The thermo-economic assessment has been carried out, which revelers the positive effects of ABI on the combined energetic and exergetic performance on both sides, i.e., hot and cold sides.

Introducing a Novel Rice Husk Combustion Technology for Maximizing Energy and Amorphous Silica Production Using a Prototype Hybrid Rice Husk Burner to Minimize Environmental Impacts and Health Risk

Rice husk is the main by-product of the postharvest stage in rice production, which causes environmental impacts due to improper management as a solid waste. However, potential economic applications of rice husk combustion have been identified for energy generation and amorphous silica production in several industries. To minimize hazardous gaseous emissions and crystalline silica availability, rice husk combustion conditions should be properly controlled which also effect for efficient heat production. This study was conducted under different conditions of temperature, airflow, combustion time, and bulk density of rice husk in the combustion process using an experimental prototype hybrid rice husk burner with a fluidized bed. The availability of crystalline silica in rice husk charcoal and the CO and O2 compositions in the exhaust gas were analyzed using XRD analysis and gas analysis, respectively. Furthermore, elemental and thermogravimetric analyses were conducted to find the most efficient combustion parameter for the optimum conditions of rice husk combustion using the experimental rice husk burner. Therefore, the most efficient heat generation was achieved with the observation of the lowest CO emission, the nonavailability of crystalline silica in rice husk charcoal, at a low temperature and air flow rate (430 °C; 0.8 ms−1), high bulk density (175 kgm−3 and 225 kgm−3) and short combustion time (30 s).

Multi-sections solar distiller integrated with solar air heater: numerical investigation and experimental validation

ABSTRACT A numerical investigation for a solar air heater integrated with a multi-section solar distiller has been conducted with a novel design of solar distiller with interior sections. A mathematical description of the solar distiller is made and solved with a MATLAB code. The air flow in the solar air heater, the water height in the solar distiller, and the number of interior sections have all been studied. To validate the numerical system, an experimental system was built. The theoretical model and the experiment performed appear to be in satisfactory correlation. The best working conditions occur when the system is run with a lower air flow rate, a lower saline water height, and a greater number of interior sections with productivity reaching 1242.6 ml/m2 per day, a gain output ratio (GOR) about 0.622 and air heater efficiency about 35%. In the normal case of output salinity between 0 and 500 ppm, the cost was reduced by 96.7%, and by 96.3% in the case of four interior sections. Water cost reduction is also observable at the same output salinity, with 54.1% at 0 ppm and 62.4% at 200 ppm between number of interior sections = 0 and 4.

SIMULATION OF THE DRYING PROCESS OF WALNUTS IN A CONVECTION DRYER

Walnuts are valued in the world for the nutritional and medicinal properties of the fruits and the versatile character of their use. In particular, they are widely used in confectionery, oil and fat, flour milling, pharmaceutical, chemical, fodder, paint and other industries. To ensure the safety of the walnut crop, it is necessary to condition them. Moisture requirements for whole walnuts are not higher than 10%. Moisture content of whole nuts after harvesting can reach 35-45%. Therefore, it is necessary to carry out drying to bring them to condition. Drying of whole nuts in Ukraine is usually carried out under natural conditions in covered, ventilated rooms. This is due to the fact that it is physically difficult to significantly speed up the process of drying whole nuts with the help of special equipment. In addition, it is economically inefficient, as it requires significant expenditure on energy carriers. However, if the volume of walnuts is significant, it is difficult to do without special drying equipment. Therefore, some enterprises apply forced drying of whole nuts with the help of various drying chambers in order to prevent their spoilage. The purpose of the research is to justify the structural and technological scheme of a convective dryer for walnuts and carry out a simulation of the technological process of drying. Based on the results of the research, the structural and technological scheme of the convective dryer for walnuts, which is made in the form of a mixer with a vertical screw working body with a lower flow of warm air, has been developed and substantiated. Using the Star CCM+ software package, the technological process of drying was simulated in the developed convective dryer. A visualization of the process of redistribution (mixing) of walnut fruits in the drying chamber under the action of the screw working body and the distribution of air flow speed and temperature in the drying chamber of the convective dryer was obtained. According to the coefficient of variation, it was established that the quality of mixing is the best (δ = 0.92±0.02) and remains at this level after 392 s from the moment of the start of rotation of the screw working body. It was established that there is a temperature gradient in the working area of the dryer: the temperature in the lower part is 58±2 °С, in the upper part - 43±2 °С. Given the rather fast mixing (392 s), such a temperature difference is not critical. For a more detailed substantiation of the structural and technological parameters of the developed convective walnut dryer, it is necessary to carry out a full-fledged numerical simulation. It is proposed to choose the following research factors: the angle of the cone-shaped grid, the volume of the drying chamber, the diameter, the step and speed of rotation of the screw working body, the speed and temperature of the incoming air flow. The evaluation criteria should be the coefficient of variation of the redistribution of walnut layers, their average temperature, and the lowest air flow rate in the loaded volume of walnuts.

Three-dimensional numerical analysis of fin-tube desiccant-coated heat exchanger for air dehumidification in tropics

High-performance desiccant-coated heat exchangers (DCHEs) can be employed in air-conditioning systems to improve energy efficiency. While there are significant developments in experimental studies, theoretical approaches for analyzing the DCHE are impeded by the complex and coupled heat and mass transport mechanisms. Therefore, a 3D mathematical model has been developed in this work to study the dehumidification performance of a DCHE. Unlike other works reported in the literature, the developed model is able to simulate the complex coupling between heat and mass transfers in the entire volume of the heat exchanger. The model is calibrated and validated with experimental data, and a maximum discrepancy of ±8 % is recorded. A time-dependent study on the performance of the DCHE is carried out to understand the distribution of temperature, reaction rates, and water uptake in the heat exchanger. Effects of key influencing operational factors are investigated and discussed. It is indicated that the DCHE enters a stable performance state regardless of its initial adsorption state. The regeneration time should be equal to the dehumidification time to optimize the performance. A higher thermal COP is achieved under lower cooling/regeneration temperature, lower air flowrate, and shorter half-cycle time, while higher inlet air humidity ratio. Higher coated desiccant mass also provides a higher thermal COP, but this enhancement levels off once the coating grows. For DCHEs with less coating, reducing cycle time is recommended over increasing the coating amount.

Cost-effective instant air disinfection for building ventilation system by a combination of UV and micro-static electricity

The increased threats of pathogenic bioaerosol make air disinfection in heating, ventilation, and air conditioning (HVAC) systems crucial to occupants’ health. To satisfy the high efficiency, superspeed, and wide temperature range of HVAC air disinfection, UV irradiation (UV254/ UV185+254) and its combination with micro-static electricity were studied in two full-scale ducted ventilation systems. UV254 could efficiently disinfect S.albus (>99 %) at high temperatures (31 ± 2 °C) and low airflow rates (1.2 m s−1) but was weakened at lower temperatures and higher airflow rates. Its combination with micro-static electricity could remarkably overcome these adverse factors and realize efficient disinfection within the retention time of 0.21 s. Especially for the relatively stubborn B.subtilis var. niger, the combination process improved the disinfection efficiency to 82 % at 16 ± 2 °C and the airflow rate of 2.4 m s−1, while UV254 was only 52.9 %. Since the UV185+254 disinfection was more effective than that of UV254, the UV185+254-based combination could further enhance the B.subtilis var. niger to 93.1 %. Besides the disinfection stability, the combination process has advantages in pressure drop (around 50 Pa), energy consumption (e.g., 0.115 kW·h km−3), and equipment costs (1,500–3,000 CNY), making it potentially cost-effective for air disinfection in HVAC systems.

Multi-objective optimization of U-type air-cooled thermal management system for enhanced cooling behavior of lithium-ion battery pack

The forced air cooling of U-type BTMS (battery thermal management system) with 12 prismatic lithium-ion batteries is considerably improved by adjusting the distribution of battery spacing and/or the tapered inlet/outlet manifolds. The temperature and velocity distributions of BTMS with an inlet temperature of 25 °C and various inlet airflow rates are calculated by computational fluid dynamics (CFD). High inlet airflow rate reduces the average temperature of the hottest battery (Tave,max) but increases the maximum average temperature difference between batteries (ΔTave,max), and vice versa for low inlet airflow rate. Multi-objective optimization using Nelder-Mead algorithm combined with CFD is performed to minimize the objective functions including ΔTave,max, Tave,max, and power consumption of fan without changing the BTMS volume. Taking an inlet airflow rate and independent battery spacings as design variables (13 variables), the Tave,max and ΔTave,max of optimized module are reduced to 38.2 °C and 0.3 °C, respectively, with a power consumption of about 1.51 W. Taking a linearly dependent battery spacing, inlet airflow rate, and tapered inlet/outlet manifolds as design variables (3 variables), the multi-objective optimization is carried out in short time and the power requirement of fan is reduced to 1.05 W without sacrificing the cooling performance of U-type BTMS.

Impact of heat generation and use of experimental instruments in a fume hood on pollutant capture efficiency

AbstractA fume hood is a local ventilation system that is typically installed in a laboratory space to ensure the safety of workers from chemical exposure. A fume hood is designed to capture hazardous gas‐phase pollutants generated inside a box‐like enclosure, and the pollutant capture efficiency is regulated by the average opening surface air velocity. However, few cases exist in which the pollutant capture efficiency inside the fume hood is precisely analyzed and quantitatively visualized. In this study, the capture performance of a fume hood under actual use conditions was evaluated using computational fluid dynamics (CFD). The factors that could affect the performance, that is, the exhaust airflow rate, experimental instruments inside, worker in front, and heat source within the fume hood, were parametrically considered. The numerical analyses revealed that experimental instruments near the opening surface significantly affected the airflow into the fume hood and decreased its capture performance. Under the inadequate condition of a low exhaust airflow rate, pollutant leakage inside the chamber was observed due to the presence of a worker in front of the fume hood and the heat source inside. Furthermore, the pollutant capture performance was slightly improved by changing the layout/position of the experimental instrument.