Air Channel Research Articles

Design and optimization of a bionic-lotus root inspired shell-and-tube latent heat thermal energy storage unit

Thermal energy storage (TES) is crucial in the efficient utilization and stable supply of renewable energy. This study aims to enhance the performance of shell-and-tube latent heat thermal energy storage (LHTES) units, particularly addressing the issue of the significant melting dead zones at the bottom, which are responsible for the long charging time. This paper proposed a new heat transfer enhancement technique inspired by the air channel distribution inside the root of the lotus. Numerical simulations are used to explore its melting behavior and heat storage performance, and a comparison is made with conventional shell-and-tube TES units. The results indicate that compared to the single-tube type, the bionic-lotus root type reduced the total melting time by 89.1 %, increased the average temperature by 13.2 °C, and enhanced the average effective power density by 7.6 times. Subsequently, multi-objective optimization was conducted based on response surface methodology, and an industrial standard type was constructed according to existing pipeline products to meet the manufacturing standards for mass production. The melting time was further decreased by 5.8 %, and the average effective power density increased by 6.6 %. The results of this study provide a promising and prospective solution for enhancing shell-and-tube LHTES units, with the potential to increase the efficiency, reduce the footprint and manufacturing costs of energy systems equipped with TES.

Experimental investigation of the thermoelectric and double-glazed glass effects on the performance of a solar still

Due to water scarcity, the use of solar stills and their improvements have been widely taken into account. In this regard, researchers are always looking for solutions to improve the performance of solar stills because of their low efficiency. Hence, this study experimentally investigated the effect of adding thermoelectric coolers, a cold air channel, and double-glazed glass on increasing the performance of a conventional solar still. The modified solar still was equipped with six thermoelectric cooler modules under the solar still. The hot sides of the modules were connected to the solar still plate to increase the temperature of the inside water, while the cold parts were used to cool the air blown from a channel toward the double-glazed glass on the solar still. The performance of two solar stills (solar still and the modified solar still) was compared for 2 days in Sabzevar city, in the northeast of Iran. The important analyses, including freshwater production, energy and exergy performances, and economic view are compared. Based on the results, the daily freshwater production, energy efficiency, and exergy efficiency of the modified solar still were improved by 570 %, 137 %, and 215 %, respectively, compared to those in the conventional solar still. The economic analysis results indicated that under optimal conditions (i = 5 %), the cost of distilled water was 0.0326 $/L and 0.0739 $/L for the modified solar still and conventional solar still, respectively. Also, using the modified solar still, the payback period reduced by about 1.74 years (payback period for the modified solar still and conventional solar still was obtained at 1.30 and 3.04 years, respectively).

Enhancing Heat Transfer of Photovoltaic Panels with Fins

Photovoltaic power generation can directly convert solar energy into electricity, but most of the solar energy absorbed by the photovoltaic panel is converted into heat, which significantly increases the operating temperature leading to a reduction in the power generation efficiency of the panels. To reduce the working temperature of photovoltaic panels and improve the photoelectric conversion efficiency, this paper installs aluminum fins and air channels at the traditional photovoltaic cell back sheets and cools them with forced-circulation cooling through fans. The relationships between fin spacing, fin height, air channel inlet wind speed and panel temperature, power generation, and electrical efficiency were investigated. The results show that the temperature of the photovoltaic panel decreases and then increases with the decrease of the fin spacing during natural convection and gradually decreases with the increase of the fin height. The use of forced-circulation cooling technology can effectively reduce the PV panel temperature and increase the net power generation. When the solar radiation intensity is 1000 W/m2, the ambient temperature is 35°C, the fin spacing is 6 mm, the height is 80 mm, the inlet wind speed is 1 m/s, the net generating power reaches the maximum value, and the net generating power and the electrical efficiency are increased by 14.6% and 2.25%, respectively.

Optimization of simultaneous utilization of air and water flow in a hybrid cooling system for thermal management of a lithium-ion battery pack

The present study provides a simulation of a battery pack (BCK) comprising lithium-ion battery cells positioned within an air channel utilizing Finite Element Method (FEM). A tube containing a flowing liquid, which serves the purpose of cooling BCK, sits at center of the BCK. Laminar nanofluids (NFs) or water flow enters tube, and air flows inside channel. A transient investigation is conducted on BCK temperature, heat transfer coefficient (HTC), and air and liquid outlet temperatures by varying airflow rate (AFR). The results demonstrate that raising airflow decreases the BCK's average temperature (TAE) and maximum temperature (TMM). The TAE of the BCK is more sensitive to changes in flow rate. Furthermore, as the AFR increases, the HTC increases because liquid and air leaving the outlet are cooled. Using NFs instead of water in the tube causes the average and TMM of the BCK to decrease and the HTC to enhance. The results show that The TMM and the TAE of the BCK are increased until the first 25 min and then are reduced. Using NFs instead of water reduces the outlet air and water temperature when AFR is low. Using NFs for battery cooling typically results in better performance than water.

Vertical water entry of a cylinder considering wind and linearly sheared flow effect: A numerical investigation

Objects entering water is a complex multiphase flow event that exhibits nonlinear and transient characteristics. This study examines the impact cavities, multiphase flow characteristics, and motion behaviors of a cylinder during vertical water entry, considering different flow and entry velocities. A three-dimensional model was carried out using OpenFOAM® framework, taking into account the effects of wind and linearly sheared flow through newly customized initial and boundary conditions. The overset mesh technique was applied to capture the water entry trajectories of the moving cylinder. Numerical results for the cavity evolution and cylinder motion behaviors were validated against published laboratory tests. The cavity closure patterns were classified into four categories based on the evolution characteristics, which were found to be more complex than those observed under calm water and uniform current conditions. Furthermore, the rapid closure of the splash dome results in a unique cavity flow phenomenon, which creates a suction air channel. The velocities of the flow and water entry have a noticeable impact on the closure modes and time of the cavity. This, accordingly, affects the motion characteristics of the cylinder, as well as the evolution of the velocity field, pressure field, and vortex structures.

Feasibility Analysis of Indirect Evaporative Cooling System Assisted by Liquid Desiccant for Data Centers in Hot-Humid Regions

The rapid development of data centers (DCs) has led to a marked increase in energy consumption in recent years, which poses a direct challenge to global efforts aimed at reducing carbon emissions. In regions with hot and humid climates, the energy demand is largely driven by air conditioning systems necessarily to maintain appropriate operational temperatures. This study proposes a novel multi-stage indirect evaporative cooling (IEC) system, incorporating a liquid desiccant in the primary air channel to address the cooling demands of such DCs. Our approach involves a two-stage process where the first stage uses a liquid desiccant-based IEC (LD-IEC) for air dehumidification and the second stage utilizes the treated air from the first stage as the secondary air to enhance the cooling effect. A simulation model of the proposed system is established with validation, and the performance of the multi-stage system was also discussed based on different operation modes. Furthermore, a case study was conducted to investigate the feasibility of using this system in the DC under a typical hot and humid zone. The findings reveal that the first-stage LD-IEC is capable of diminishing the wet-bulb temperature of the ambient air. Furthermore, the case study demonstrates that the proposed system can greatly improve the temperature drop by 72.7% compared to the single IEC, which noticeably reduces the operation time of energy-intensive supplementary cooling equipment from 5092 h to 31 h given the supply air temperature threshold of 25 °C. In summary, the proposed system could substantially decrease reliance on traditional cooling systems, which demonstrates a promising avenue to fully use this passive cooling technology for cooling DCs.

Performance and exergy analysis of vacuum-assisted sweeping air membrane distillation and bubble column dehumidifier

This study provides a comprehensive theoretical analysis of an integrated Sweeping Gas Membrane Distillation (SGMD) and Bubble Column Dehumidifier (BCD) system for cost-effective water desalination. Analytical investigations on this novel system are not available in the literature which represents a knowledge gap. The current analytical study offers insights into the efficiency of the integrated SGMD-BCD system, identifies optimal operational conditions, and provides benchmark data for future scaling-up and commercialization. The theoretical model, based on solving heat and mass transfer equations, is validated against the experimental data. An exergy analysis of the integrated SGMD-BCD is considered to explore the possible improvements in the design and operation for enhanced performance. Results reveal a peak GOR of 0.41 under maximal tested feed flow rates and temperatures, coupled with minimal air flow rates and air channel pressures. The BCD achieves maximum effectiveness in the range of 0.95–0.98 at feed temperature of 90 °C. Exergetic efficiency reaches its peak at 3.25%, observed at the lowest feed flow rate (1 L/min) and temperature (40 °C). Notably, the SGMD process exhibits 18 to 20 times the exergy destruction compared to the BCD at a 90 °C feed temperature, highlighting the need for improvements in its design and operation.

Numerical research on air-based cooling photovoltaic roof

As a new type of building material for plants, photovoltaic roof building materials can be used as roofs of ordinary plants to reduce damage caused by secondary construction to the roofs, and can also absorb and utilize solar radiation to make full use of renewable energy. This article combines photovoltaic modules with air channels to form building material structures with ventilation ducts, establishes physical and mathematical models for photovoltaic roofs in three different inlet modes, and studies the flow and heat transfer characteristics inside air cooling integrated photovoltaic roofs. The simulation results show that the staggered-overlap-joint waterproof double-inlet photovoltaic roof can prevent rain and snow infiltration, and meanwhile, has a cooling effect on the PV panels significantly better than that of the traditional single-inlet air cooling system and the ordinary parallel double-inlet system, and its temperature difference between the inner and outer surfaces of the PV panels is increased by 19.88% compared to the traditional single-inlet air cooling system and by 15.12% compared to the parallel double-inlet system at the maximum. When the included angle between the PV panels of the staggered-overlap-joint waterproof double-inlet photovoltaic roof and the roof is 3°, the change in average temperature difference between the inner and outer surfaces of the PV panels is maximum, which is increased by 3.88% compared with that at 2°. The thickness of the air channel has small influences on the temperature change inside the air channel, the temperature difference between the inner and outer surfaces of the PV panels, and the outlet temperature. When the thickness increases from 50 mm to 200 mm, the change in outlet temperature does not exceed 0.3 K, but the increase in thickness of air layers increases the airflow velocity, which helps to take away more heat.

Evaluation of drying performance of sports bras

Introduction
 Fabrics used for manufacturing sports bras have to be lightweight, breathable, have fast drying behaviour, and moisture management properties (Uttam, 2013). Therefore, thermo-physiological comfort is an important quality criterion for sports bras (Carneiro et al., 2017). In addition, sports bras have to provide support to stabilize breasts during various physical activities (Ancutiene et al., 2017). These requirements lead to challenges in finding the best sports bra fabric, as bra support (Norris et al., 2021) and thermo-physiological comfort require contrasting fabric properties (Carneiro et al., 2017).
 This work aims to compare drying characteristics of different sports bras types (compression, encapsulation and combination) and fabrics used. A newly developed methodology to investigate the drying behaviour of sports bras in the lab has been taken for their examination.
 Methods
 The measurement set-up was built up in a climatic chamber (at 23°C and 50% RH). It consists of the upper body part of a female manikin, the air channel with fans and a balance to measure the weight change of the sports bra over time (indicative of the amount of moisture evaporated). The Infrared (IR) camera was used to record local surface temperature. Based on these measurements, the local and general drying performance of the sports bras were assessed based on dry fabric weight, moisture uptake, moisture absorption, drying time and drying rate.
 Results
 The results show that type of sports bra and material composition can have influence on better drying performance studied. The range of drying time for the different sport bra types was observed between 13 and 66 min for compression bras, 25 and 42 min for encapsulation bras, and between 35 and 43 min for combination bras. The moisture uptake was detected in a range between 6% and 15% for compression bras, 13% and 15% only for encapsulation bras, while between 7% and 19% for combination bras.
 Discussion/Conclusion 
 We were able to show that there is a significant difference in drying performance between sports bras. In combination with additional data about sensorial comfort and breast support, these findings provide a scientific basis for developing sports bras meeting specific requirements for various sports.
 References
 Ancutiene, K., Koldinska, M., & Havelka, A. (2017). Investigation of tensile resilience properties of stretch denim fabrics. Indian Journal of Fibre & Textile Research, 42, 175-182.
 Carneiro, L. P., Miranda, T. M. R., & Catarino, A. A. (2017). Comparative thermophysiological study in sport bras for running. IOP Conference Series: Materials Science and Engineering, 254(7), Article 072006. https://doi.org/10.1088/1757-899X/254/7/072006
 Norris, M., Blackmore, T., Horler, B., & Wakefield-Scurr, J. (2021). How the characteristics of sports bras affect their performance. Ergonomics, 64(3), 410-425. https://doi.org/10.1080/00140139.2020.1829090
 Uttam, D. (2013) Active sportswear fabrics. International Journal of IT, Engineering and Applied Sciences Research, 2(1), 34-40.

Performance evaluation of a passive air conditioning module integrating radiative sky cooling and indirect evaporative cooling

Amidst escalating global warming challenges, the demand for sustainable, carbon-free cooling technologies in buildings has become pressing. While radiative cooling (RC) and indirect evaporative cooling (IEC) are carbon–neutral, their efficacy is constrained by a limited cooling capacity. This study introduces an innovative passive air conditioning module that integrates RC and IEC to boost efficiency. The RC-IEC module unifies the air-conditioning process in both the RC and dry channels of the IEC unit, ensuring air cooling with a constant humidity ratio. A portion of the IEC dry channel outlet air is redirected to the wet channel to augment the efficiency of the IEC process. The outlet air from the wet channel is directed to the secondary RC air channel for cold energy recovery instead of being directly exhausted. The developed mathematical model, validated with experimental data, demonstrates that the RC-IEC system lowers the supply air temperature by 0.88 °C compared to the IEC-only system. This corresponds to an 11.91 % and 9.94 % improvement in dew-point effectiveness and cooling energy gain, respectively. A parametric study indicates the system's suitability for hot, arid climates, with optimal performance at a wet channel air mass fraction of 0.31. The analysis of the annual cooling performance of the RC-IEC system across diverse climates, spanning from Athens to Singapore, spotlights Dubai's system as the most efficient, achieving a remarkable annual gain of 1081.09 MJ. The study emphasizes the need for tailored strategies, such as advanced air dehumidification technologies, to optimize cooling in humid regions like Singapore.

Topology optimization of acoustic bandgap crystals for topological insulators

Recent advances in topology optimization methods have driven the development of bandgap crystals. These artificial materials with maximized operational bandwidth provide the basis for wave manipulation and investigating the topological phase of matter. However, it is still challenging to efficiently design acoustic bandgap crystals via existing topology optimization methods. Most previous studies considering only a volume fraction constraint on the constituent material may have impractical wide band gaps due to the pseudo-air resonant modes. To solve this issue, this paper establishes a new topology optimization method for creating acoustic bandgap crystals periodically composed of solid and air. We adopt a constraint on air permeability to ensure the connective air channels within the periodic microstructures, which is more applicable in engineering practice. The optimized unit cells from the proposed method are further analyzed to realize topologically protected states, providing opportunities for multi-dimensional wave manipulation in acoustic systems. Numerical examples demonstrate the effectiveness of the proposed method in designing acoustic crystals with broad bandgaps on any given band orders, and gapped/gapless edge states and corner states can be achieved in resulting topological insulators.

Effects of the position and melting point of the PCM layer on the comprehensive thermal performance of a Trombe wall under mixed dry climate

PCM Trombe walls have been an effective passive technology to achieve energy efficiency. However, the majority of previous research investigated the PCM Trombe walls primarily focused on structural improvement, and very few studies have focused on mixed-dry climate Therefore, in this study, ten scenarios were created and simulated by the validated CFD model under a mixed dry climate. The findings indicate that in summer, an external PCM layer with a melting point of 38 °C could reduce the maximum peak load by 48.9 %, decrease the fluctuation amplitude by 76 %, reduce the cooling load by 14.4 %, compared to the reference case, and yields time lags of 4.5 h and 6.1 h for the maximum and minimum indoor temperatures, respectively. In winter, an external PCM layer with a melting point of 30 °C can reduce the thermal load by 38.2 %, decrease the fluctuation amplitude by 28.5 %, compared to the reference case, and achieve time lags of 4.0 h and 1.7 h for the minimal and maximum indoor temperatures, respectively. Overall, the PCM layer should be placed adjacent to the air channel, and the appropriate PCM melting points in summer and winter are different.

The Activity Test of Dewandaru Fruit (Eeugenia uniflora L.) in Trachea of Male Mice (Mus musculus L.) Which Exposed to Cigarette Smoke

Smoking has a serious negative impact on health because cigarettes contain harmful chemical compounds. To combat these negative effects, using natural antioxidants such as Dewadaru fruit has become the research focus. Dewandaru contains high antioxidants, namely flavonoids, anthocyanins, saponins, and tannins, which can fight free radicals in the body. The trachea is an air channel between the larynx and bronchi. To identify the activity test of dewandaru fruit (Eugenia uniflora L.) in the trachea of male mice (Mus musculus L.) exposed to cigarette smoke. This study employed true experimental di laboratory with post-test only control group design, probability sampling. The data were analyzed by using Shapiro Wilk and followed by the ANOVA test and Duncan's test. The finding showed that administering a Dewadaru fruit filter could maintain the histopathology of the male mice trachea exposed to cigarette smoke (P<0.05). Dewandaru fruit filter (Eugenia uniflora L.) has activity in the trachea exposed to cigarette smoke among male mice. Using a Dewadaru fruit filter also affects the presence of cilia, goblet cells, epithelial height, and lumen diameter in the trachea of male mice.

Numerical Investigation of Influence of Extent and Position of a Bypass on the Performance of a Single Unit Liquid Desiccant Based Evaporative Cooler

Air-conditioning of buildings is more energy-consuming with widely used vapour compression refrigeration systems in hot and humid areas. Alternatively, evaporative cooling does not show much effect in sultry regions because of increased humidity despite the minimum energy consumption. Indirect evaporative cooling is a promising alternative to direct evaporative cooling systems, but it suffers from low cooling effectiveness and is unsuitable for highly humid regions. Considering the above facts an alternative liquid desiccant-assisted modified M-cycle cooling system is proposed and examined numerically in the present work. The proposed cooling and dehumidification system is a simple unit incorporating chemical dehumidification and regenerative evaporative cooling in a single unit. A simultaneous heat and mass transfer model is developed for the numerical analysis. The numerical code is written in MATLAB and is validated with results available in the literature. Further, numerical analysis was carried out for the effect of various parameters on the performance of the proposed cooling system. The study shows an improvement of 19.2% in dew point effectiveness by incorporating an intermediate opening in the plate separating the product air and working air channels.

Self-channeling of a multi-Joule 10 µm picosecond pulse train through long distances in air.

In the long-wave infrared (LWIR) range, where, due to wavelength scaling, the critical power of Kerr self-focusing Pcr in air increases to 300-400 GW, we demonstrate that without external focusing a train of picosecond CO2 laser pulses can propagate in the form of a single several-centimeter diameter channel over hundreds of meters. The train of 10 µm pulses, for which the total energy ≥20 J is distributed over several near-terawatt picosecond pulses with a maximum power ≤2Pcr, is generated naturally during short pulse amplification in a CO2 laser. It is observed that the high-power 10 µm beam forms a large diameter "hot gas" channel in the ambient air with a ≥ 50 ms lifetime. Simulations of the experiment show that such filamentation-free self-channeling regime has low propagation losses and can deliver multi-Joule/TW-power LWIR pulses over km-scale distances.

Programmable inverse-designed acoustic coding metasurfaces for multifunctional broadband reflection

In this paper, we develop tunable reflection-type broadband acoustic coding metasurfaces (BACMs) using a bottom-up topology optimization method. These metasurfaces enable flexible configuration switching between the antiphase coding units of “0” and “1” across a wide frequency range through electromagnetic regulation. By introducing a customized dispersion design, the optimized structure exhibits broadband properties. The optimized coding units consist of irregular air channels and connected air cavities. The coding bits of “0” and “1” show a constant opposite phase difference over a wide frequency range through the coupling resonances. By adjusting the electromagnets, arbitrary coding sequences in the BACMs can be rapidly reconstructed. We numerically and experimentally demonstrate the acoustic focusing and splitting properties within the frequency range of 2.2 kHz–4.4 kHz.

Fluorescence and lasing of neutral nitrogen molecules inside femtosecond laser filaments in air: mechanism and applications.

High power femtosecond laser pulses launched in air undergo nonlinear filamentary propagation, featuring a bright and thin plasma channel in air with its length much longer than the Rayleigh length of the laser beam. During this nonlinear propagation process, the laser pulses experience rich and complex spatial and temporal transformations. With its applications ranging from supercontinuum generation, laser pulse compression, remote sensing to triggering of lightning, the underlying physical mechanism of filamentation has been intensively studied. In this review, we will focus on the fluorescence and cavity-free lasing effect of the plasma filaments in air. The different mechanisms underlying the fluorescence of the excited neutral nitrogen molecules will be throughly examined and it is concluded that the electron collision excitation is the dominant channel for the formation of the excited nitrogen molecules. The recently discovered "air lasing" effect, a cavity-free bidirectional lasing emission emitted by the filaments, will be introduced and its main properties will be emphasized. The applications of the fluorescence and lasing effect of the neutral nitrogen molecules will be introduced, with two examples on spectroscopy and detection of electric field. Finally, we discuss the quenching effect of the lasing effect in atmosphere and the mechanisms responsible will be analyzed. An outlook for the achievement of backward lasing in air will be briefly presented.

CYLINDRICAL CROSS-BARS FOR THERMAL PERFORMANCE AUGMENTATION IN AIR CHANNEL

Experiments of the heat transfer and pressure drop are performed in a rectangular channel employing eight different arrays of cylindrical cross-bars as inserts. Numerical simulations are also performed to examine the secondary flow caused by the cylinders. The objectives are to investigate the enhancement of the channel-wall heat transfer and pressure drop caused by the local flow, cylinder array geometry, and flow Reynolds number. Two different cylinder diameters of 1.0 mm and 2.0 mm are employed. The diameter of 2.0 mm is used to create four in-line arrays while the diameter of 1.0 mm is used to create four staggered arrays of the cylinders. The cylinder arrays employ different diameter-to-pitch ratios (0.025 to 0.2) and cylinder orientations (45°, 90°) relative to the main flow direction. The flow Reynolds number is varied between 600 and 13,000. Only two array geometries, one in-line and one staggered, with the cylinders oriented at 90° to the flow are modeled for the numerical study. The numerical results show that the local flow accelerates in the gap between the cylinder and channel wall. The vortex shedding downstream of the cylinders interacts with the channel wall. The Nusselt number on the channel wall and the friction factor are measured with and without the cylinders. The ratios of Nusselt numbers and friction factors increase with the Reynolds number when the Reynolds number is less than 3000. The ratios always increase with the diameter-to-pitch ratio.

In-depth investigations into symmetrical labyrinthine acoustic metamaterial with two micro-slit entries for low-frequency sound absorption.

Sound absorption below 1000 Hz has been extremely difficult through traditional barriers and absorbers, but it is required for noise control of appliances and machineries. Existing passive acoustic metamaterials attenuate low-frequency noise but with narrow bandwidths and bulky sizes. Hence, this paper proposes an acoustic metamaterial with enclosed symmetrical labyrinthine air channels and two micro-slits (configuration 1, identical slits; configuration 2, unequal length slits) at the end channels. Its theoretical model is established by acoustic impedance analysis using electro-acoustic analogy and validated numerically and experimentally. Sound absorption is found to happen as a result of impedance matching, Fabry-Perot-like labyrinthine resonances, and thermo-viscous losses in micro-slits. Parametric investigations reveal that increase in the number of channels, channel length, total height, and outer panel thickness shifts sound absorption peak to lower frequency but also decreases the magnitude and frequency range of absorption. Decreasing the channel width and slit width increases the sound absorption magnitude without changing absorption frequencies. Interestingly, unequal slit lengths perform better than equal slits by giving a lower frequency sound absorption with increased magnitude and frequency range, which is unlike that in existing labyrinthine metamaterials. Therefore, the proposed unequal slit metamaterial has enhanced low-frequency sound absorption and can be applied to appliances and machineries.

Magnetically controlled systems for CO2 absorption

In this paper is presented a conceptual model of magnetically controlled system for CO2 absorption. A design of magnetic air contactor is considered and internal magnetic field in its channels is modelled. It is a closed domain contactor design with controllable internal thermodynamic conditions, additionally influenced by magnetic field. Considered design is providing huge specific surface for dynamic interaction with the processed airflow. Results on magnetic field distribution inside air channels are calculated in order to estimate field homogeneity and force directions on used particles.