Air Mass Flow Rate Research Articles

Numerical simulation of an innovative design of solar air heater using spiral duct inserts for enhancing thermal efficiency

ABSTRACT An innovative design of solar air heater (SAH) with spiral shape is numerically analyzed in this paper. The spiral-shaped SAH hydro-thermal performance is studied for different air mass flow rates using CFD COMSOL Multiphysics software. The outlet air temperature difference, thermal efficiency, flow structure, thermal field and pressure drop are the main parameters which are considered to estimate the fluid flow and heat transfer behaviors of the SAH. The simulation is realized for 1000 W/m2 of solar heat flux and 25°C of ambient temperature as typical climatic conditions in a middle day. The results show that the maximum outlet temperature difference of the SAH reached 93.08°C with 0.0083 kg/s of air mass flow rate. For the range of 0.0083–0.0332 kg/s, the thermal efficiency is varied from 91.41% to 99.01%. The ambitious percentage of the thermal efficiency of 99.01% was observed for 0.012 kg/s. The proposed design provides high thermal efficiency of SAH compared to other configurations of SAH.

The Influence of the Intake Geometry on the Performance of a Four-Stroke SI Engine for Aeronautical Applications

In this work, the influence of plenum and port geometry on the performance of the intake process in a four-stroke spark ignition engine for ultralight aircraft applications is analyzed. Three intake systems are considered: the so-called “standard plenum”, with a relatively small plenum volume, the “V1 plenum”, with a larger plenum volume, and the “standard plenum” equipped with a large curvature manifold called the “G2 port”. Both measurements and 3D CFD simulations, by using Ansys® Academic Fluent, Release 20.2, are performed to characterize and analyze the steady-flow field in the intake system for selected valve lifts. The experimental data and the numerical results are in excellent agreement with each other. The results show that at the maximum valve lift, i.e., 12 mm, the V1 plenum allows an increase in the air mass flow rate of 9.1% and 9.4% compared to the standard plenum and the standard plenum with the “G2 port”, respectively. In addition, the volumetric efficiency has been estimated under unsteady-flow conditions for all geometries at relatively high engine rpms. The difference between numerical results and measurements is less than 1% for the standard plenum, thus proving the accuracy of the model, which is then used to study the other configurations. The V1 plenum shows a fairly constant volumetric efficiency as the engine speed increases, although such an efficiency is lower than that of the other two geometries considered in this work. Specifically, the use of the “G2 port” leads to an increase of 1.5% in terms of volumetric efficiency with respect to the configuration with the original manifold. Furthermore, for the “G2 port” configuration, higher turbulent kinetic energy and higher swirl and tumble ratios are observed. This is expected to result in an improvement of air–fuel mixing and flame propagation.

Pressure Change in a Duct with a Flow of a Homogeneous Gaseous Substance in the Presence of a Point Mass and Momentum Sink of Gas

The flow characteristics of homogeneous gases in complex systems are an important issue in many areas, including underground mines. The flow in mine excavations and ventilation systems is described by known mathematical relationships that could be applied to various cases. In this paper, a flow in a duct with a local sink of mass and momentum for multiple variants of cooperation of a mechanical fan was analyzed. The relationships for the total and static pressure of air in the duct were derived. In the next stage, a calculation example of how the mass flow rate of air, and the total and static pressure of the flowing air will change in the tested sections for the duct with and without a sink, is presented. The derived formulas and calculated values for the considered calculation case allow the verification of the obtained relationships at the measurement station. Analyzing the results of the examples presented in the article, it can be concluded that the total and static pressure at the sink point differ depending on the equation of motion used. In the case of the classic equation, the value of total pressure is lower than the value calculated from the new equation of motion, and the difference between them is about 20 Pa. In the case of static pressure, this difference is about 46 Pa. Qualitative differences in the static pressure distribution at the release location were also demonstrated. Depending on the applied approach, positive or negative changes in the static pressure are noticed. The presented form of the equation of motion made it possible to determine the flow characteristics in the duct with a point mass and momentum sink in the case of the operation with and without a fan.

Enhancing building energy efficiency: Numerical analysis of a hybrid thermoelectric ventilation system and earth-air heat exchange with photovoltaic-thermoelectric power integration for heating and cooling loads

The lack of studies on hybrid systems combining thermoelectric ventilation (TEV) and earth-air heat exchangers with a photovoltaic-thermoelectric generator (PV-TEG) as the power supply for the hybrid system is addressed in this research. This study aims to investigate the effectiveness and performance of such a combined system in providing the required thermal load of a building. To simulate the performance of TEV and PV-TEG systems, energy conservation equations for various components of the system were formulated for the quasi-state mode. The performance of the earth-air heat exchanger system was evaluated using the effectiveness-number of transfer units method. The resulting set of algebraic equations was then solved using a MATLAB code. Results indicated significant preheating (5.41–15.03 °C) and precooling (0.7–10.22 °C) effects during the daily hours of 15-February and 15-July, respectively. Additionally, the TEG component effectively reduced PV temperatures by 3.54 °C–16.99 °C in 15-February and 3.99 °C–21.54 °C in 15-July. The system also demonstrated a high monthly useful thermal energy output (1215–1584 kWh) in the cold months (December to March), contrasting with higher monthly useful thermal exergy (712–763 kWh) in the summer months. Furthermore, increasing the number of TEGs from 10 to 50 resulted in significant improvements in the yearly average energy and exergy proficiency indexes (PIya,en and PIya,ex) by 164.97 % and 459.82 %, respectively. The supply air mass flow rate and the length and depth of the earth-air duct were identified as the second and third most influential parameters affecting these indexes. Moreover, the system at CPV concentration ratio of 3 provided the highest PIya,en and PIya,ex of 1.512 and 14.65, respectively.

Experimental study on thermal performance of reverse flow solar collector for dual heating applications

AbstractThe present study investigated the performance of dual function reverse flow solar collector (RFSC). The impact of the mass flow rate of air and water on outlet temperature, thermal performance, and overall performance of dual‐function solar air heater (SAH) has also been investigated. An experimental investigation of three different working models namely, Model‐A: SAH, Model‐B: solar water heater (SWH), and Model‐C: integrated solar air‐water heater (SAWH) for dual heating applications was performed to analyze the actual performance of these models. The investigation of the impact of time intervals on the water inlet and outlet temperatures at various mass flow rates of water is conducted to analyze the time‐varying efficiency of SWH systems. Furthermore, the effect of solar intensity on the performance of the dual‐function heating system has also been explained. The result reveals that the maximum thermal efficiency of Models: A and B can be achieved at about 78.8% and 67.9%, at a mass flow rate of 0.0644 and 0.10 kg/s, respectively, according to the experimental findings. The maximum temperature rise of air and water reaches about 52.4 and 55.58°C for Models A and B, respectively. The total efficiency of Model C reaches 81.69%, exceeding that obtained in Models A and B individually. The efficiency, outlet temperature of the fluid, and heat transfer effectiveness of the system strongly depend on the mass flow rate. The increase in heat removal factor is negligible for a higher flow rate (more than 0.10 kg/s).

Airflow Characteristics in Conveyor Type Damper for Hot Air Temperature Changes

The aim of this study was to present the characteristics of a hot airflow in a conveyor type dampers under the hot air temperature changes. The amount of space occupied by the damper was reduced by 50 %, and by efficiently managing the damper's airflow rate even in the face of extreme external conditions and constant air volume proportional control, a conveyor-type damper with a significant energy-saving effect has been explored. It was configured to control the degree to which it was opened by operating the folding conveyor drive mechanism, enabling the damper to modify airflow. In this study, the mass flow rate of heated air through the conveyor-type damper increased in proportion to the damper port's expansion. The mass flow rate of air decreased as the temperature of air intensified. In addition, the thermal energy of the air flowing in the conveyor-type damper improved in ratio to the increase in the damper opening. The findings indicate a 50 % reduction in the damper's occupied space, indicating a significant energy-saving impact of the conveyor-type damper. This is because the damper's air volume is effectively controlled even in the face of severe external conditions, as it is proportionately controlled throughout. The understanding of the properties of airflow for the hot temperature change is strengthened by this research. Furthermore, this study may provide useful direction for future research and industry optimization.

A Numerical Study on the Flow Field and Classification Performance of an Industrial-Scale Micron Air Classifier under Various Outlet Mass Airflow Rates

In this study, the gas−particle flow field in a real-size industrial-scale micron air classifier manufactured by Phenikaa Group using 3D transient simulations with the FWC-RSM–DPM (Four-Way Coupling-Reynold Stress Model-Discrete Phase Model) in ANSYS Fluent 2022 R2 and with the assistance of High-Performance Computing (HPC) systems is explored. A comparison among three coupling models is carried out, highlighting the significant influence of the interactions between solid and gas phases on the flow field. The complex two-phase flow, characterized by the formation of multiple vortices with different sizes, positions, and rotation directions, is successfully captured on the real-size model of the classifier. Additionally, analyzing the effects of the vortices on the flow field provides a comprehensive understanding of the gas–solid flow field and the classification mechanism. The effect of the outlet mass airflow rate is also investigated. The classifier’s Key Performance Indicators (KPIs: d50, K, η, ΔP) and the constrained condition of the particle size distribution curve of the final product are used to evaluate the classification efficiency. The contributions of this work are as follows: (i) a simulation analysis of a real-size industrial-scale classifier is conducted that highlights its advantages over a lab-scale one; (ii) a comparison is conducted among three coupling models, showing the advancement of four-way coupling in providing accurate results for simulations of interactions between the gas phase and particles; and (iii) the particle size distribution curve performances of a classified product under different simulation models and outlet airflow rates are addressed, from which optimal parameters can be selected in the design and operation processes to achieve the required efficiency of an air classifier.

Experimental Study of the Effect of Porous Media on the Performance of Single-Pass Solar Air Heater

Solar energy is harnessed to heat the air, which is then utilised for warming greenhouses and drying crops. Solar air heaters may readily increase their performance using an absorbent plate design with a front pass of steel wools. This kind of SAH has been investigated and compared to a conventional flat absorbent plate. Steel wool, a cost-effective and permeable substance, possesses excellent heat conductivity, and it can be utilised in ongoing initiatives to enhance convection and thermal efficiency. The analysis in this research is based on data from experiments, focusing on the single-pass SAH technique and considering two scenarios: traditional system and porous system, with air mass flow rates of 0.015 Kg/s and 0.035 Kg/s. The experimental findings show that employing porous materials increases the exhaust temp by 12.28% and 21.32 % form of air 0.015 and 0.035 Kg/s, respectively. Moreover, the solar radiation readings for non-porous and porous medium SAHs were recorded as 905.32-912.92 and 979.04-945.6 W/m2, respectively, at 1:30 p.m. Furthermore, thermal efficiency is between 33.29 % and 64.36 % in the porous scenarios and between 30.12% and 57.36% for non-porous cases. Porous media increases the thermal efficiency by 10 % and mass flow rate by 14 %.

Solar air heater energy and exergy enhancement using a v-corrugated wire mesh absorber: An experimental comparison

In this paper, the energy and exergy performance of a double-pass solar air heater (SAH) using a novel model of a v-corrugated wire mesh absorber (CM-SAH) is investigated experimentally. The v-corrugated wires are adjacent to each other in one layer along the airflow direction to reduce the hydraulic resistance. Simultaneously, this arrangement increases the surface absorptance rate of solar radiation and expands the heat exchange area. To evaluate the performance of CM-SAH, a standard SAH having a v-corrugated absorber plate (CP-SAH) and the same configuration dimensions is compared with CM-SAH. The comparison is achieved under the same operating conditions and using different air mass flow rates of (0.01, 0.02, and 0.03 kg/s). The results show that the CM-SAH outperformed the CP-SAH in terms of thermal efficiency, exergy efficiency, and output air temperature. The maximum thermal efficiencies reach 87.3 % and 65.1 %, while the maximum exergy efficiencies reach 4.4 % and 3.4 %, for CM-SAH and CP-SAH, respectively. In addition, the thermal efficiency of CP-SAH decreased after midday while that of CM-SAH continuously increased.

An approach of analyzing gas and biomass combustion: Positioned of flame stability and pollutant reduction

Biomass, as a renewable energy source, has gained attention as a sustainable alternative to conventional fuels due to its global availability and usability in rural areas. However, biomass combustion presents challenges such as flame instability and pollutant emissions. This study compares the use of methane gas, wood shavings, and a combination of these two fuels, examining the effects of preheating and flame stability in the combustion of natural gas, biomass, and their co-firing using numerical methods. An equivalence ratio of 1 has been used to avoid a rich-fuel mixture, and an air mass flow rate of 0.0001 kg/s are considered to ensures a sufficient supply of oxygen for the combustion process. Biomass fuel particles are injected from the surface of the fuel and its particle diameter ranging between 5 and 10 μm. The results showed that using the combined fuel not only increased the flame temperature at the beginning of the combustion chamber but also achieved more complete and stable combustion, with over 97 % of the fuel consumed at the start of combustion. As a result of this complete combustion, the emissions of toxic gases CO and NOx in the combustion products reached zero. Additionally, preheating the air increased the flame temperature by 14 %, while preheating the fuel reduced NOx emissions by 24 %.

Effects of motive flow temperature on holding steam ejector Performance under Condenser temperature change by considering Entropy generation and Non-equilibrium condensation

The condenser plays a crucial role as one of the key components in a power plant, directly influencing its overall efficiency. Any alteration in the power plant’s efficiency has a substantial impact on both energy consumption and the environment. The holding steam ejector (HSE) is essential for condenser operation by creating a vacuum and effectively removing air. The primary objective of this study is to evaluation the motive flow temperature (MFT) by considering various parameters such as steam price, production entropy, air suction, and entrainment ratio (ER). The investigation focuses on different temperatures within the power plant condenser. The study examines the changes in MFT within the range of 350 ˚C to 400 ˚C, as well as the variation in condenser temperature (CDT) spanning from 47 ˚C to 67 ˚C. The results demonstrate that varying the MFT impacts the functional parameters of the HSE. As the MFT increases, there is an increasing trend in the ER. Simultaneously, there is a decreasing trend observed in the cost of steam production, production entropy, and air suction. When the MFT increased from 350 ˚C to 400 ˚C, the suction air mass flow rate for temperatures of 47 ˚C, 57 ˚C and 67 ˚C decreases by 2.22%, 2.09% and 1.99%, respectively. These results highlight the influence of temperature on various parameters, showcasing how adjustments in the MFT and CDTs can affect the flow characteristics and associated factors in the system.

Exergy efficiency and sustainability indicators of forced convection mixed mode solar dryer system for drying process

The study investigates the effectiveness of a mixed-mode solar dryer (MSD) featuring two double-pass solar air collectors in series, with a focus on dehydrating cluster figs characterized by high moisture content and rapid deterioration. Exergy analysis is a powerful tool to assess the efficiency and sustainability of drying systems. The study involves experimental data obtained from the drying process under different air mass flow rates (0.018–0.062 kg/s). The solar radiation intensity ranged from 120 W/m2 to 750 W/m2 during these experiments. The solar air collectors and mixed mode dryer exergy efficiency is found to be dependent on solar radiation intensity, showing increased efficiency with higher air mass flow rates due to enhanced heat removal and reduced losses to the surroundings. The findings reveal that the optimal air mass flow rate of 0.062 kg/s yields the highest exergy efficiency in the solar air collectors. The overall exergy efficiency of the mixed-mode solar drying chamber increases with higher air mass flow rates, ranging from 18.8 % to 41.4 %. Improvement potential (IP) analysis indicates that, as the air mass flow rate increases, the potential for reducing exergy losses decreases. The sustainability index (SI), measures the environmental impact, and it ranges from 1.26 to 1.71, with higher values associated with higher exergy efficiency.

Study on the Effects of Inflow Parameters on the Auto-Initiation of Hydrogen-Rich Gas Rotating Detonation

ABSTRACT To obtain a comprehensive understanding of the auto-initiation characteristics of rotating detonation with the high-temperature hydrogen-rich gas. The experiment was carried out with hydrogen-rich gas as fuel and ambient temperature air as oxidant. The high-temperature hydrogen-rich gas was a kind of fuel-rich gas produced by the pre-combustion of hydrogen and oxygen. The effects of inflow parameters such as air mass flow rate, hydrogen mass flow rate, and hydrogen-rich gas temperature on the auto-initiation delay time and velocity of rotating detonation waves (RDWs) were experimentally studied. The experimental results showed that when the hydrogen and air mass flow rates were 6.3 ~ 17.4 g/s and 314 ~ 610 g/s, respectively, auto-initiation could be successfully achieved and a stable RDW could be formed. As the hydrogen and air mass flow rates increased, the auto-initiation delay times decreased from 40 to 5 ms and from 45 to 19 ms, respectively. When the temperature of the hydrogen-rich gas increased from 460 to 690 K, the auto-initiation delay time decreased from 100 to 10 ms, the RDW velocity decreased from 1368.5 to 1231 m/s. Hydrogen-rich gas has a high temperature, which is easy to cause the non-detonative combustion ahead of the wave of air and hydrogen-rich gas in the RDC, which consumes part of the fuel and resulting in a decrease in the RDW velocity.

Thermal analysis of constant surface area tapered helical Coils: Insights from numerical modelling

Helical coils are integral to numerous engineering and domestic applications, from room heaters and vehicle suspensions to nuclear reactors, owing to their high surface area-to-volume ratio that facilitates efficient heat transfer. This study investigates the natural convection heat transfer characteristics of tapered helical coils under radiative heat loss, focusing on both straight and inverted configurations, within an unconfined air medium. The numerical simulations were validated against experimental results with a maximum deviation of 5 % before proceeding to establish the numerical findings. The analysis considers geometric parameters such as non-dimensional pitch (p*), cone angle (θ), and emissivity (ε), along with Rayleigh number (Ra), to elucidate their impact on average Nusselt number (Nu), mass flow rate of air through the coil core, and heat transfer mechanisms. Results reveal distinct behaviors for straight and inverted coils, with varying Ra and θ influencing heat transfer dynamics and airflow patterns. Notably, inverted coils exhibit enhanced heat transfer characteristics compared to straight coils. For straight coils, Nu initially decreases with increasing θ at lower Ra but rises beyond a critical θ at higher Ra due to independent heat dissipation by the coil turns. When θ changes from 0° to 50° at p* = 6, the change in average Nu is approximately 3 % and 10 % for Ra = 108 and 104 respectively. In contrast, for inverted coils, Nu increases with θ across all Ra, owing to the wider top opening facilitating airflow. Furthermore, empirical correlations are developed to predict Nu based on key parameters, achieving high accuracy with deviations of ± 6 % and ± 4 % for straight and inverted coils, respectively. These correlations provide robust tools for optimizing thermal management in diverse applications. Overall, this study contributes significant insights into tapered coil performance, essential for advancing heat transfer technology and design optimization.

A novel solar tower simulator for hydrogen regeneration by thermo-catalytic cracking of Ammonia: Energy, Exergy, and CFD investigations

This paper presents a novel concept of a central solar tower-based hydrogen regeneration system by thermo-catalytic cracking of ammonia. This includes a closed volumetric receiver for ammonia heating and cracking, a 2.45 kWe high-concentration radiation source, and an air-cooling system for the radiation source. The thermodynamic analysis shows that the net solar-to-hydrogen generation efficiency, first law efficiency, and exergy efficiency are 31 %, 82 %, and 79.8 %, respectively, for the optical efficiency of 35 %, the conversion efficiency of 99 %, and the waste heat recovery fraction of 20 %. The simulations with an ammonia flow rate of 1 kg/hr and flux concentration of 1200 Suns show the regeneration of 1.27 kg H2/day at Jodhpur and 1.57 kg H2/day at Ladakh. Monte Carlo ray tracing simulations revealed that the developed radiation source provides an average flux of ∼ 2 MW/m2 onto a spot size of 20 mm with an efficiency of about 31 %. Reynolds-averaged Navier Stokes-based analyses are used to design a novel air-cooling system for the radiation source. The computations show that (a) an unequal distribution of air mass flow rates at the front mḟ and back mḃ, should be preferred with mḟ>mḃ, and (b) for a total mass flowrate of 0.1 kg/s with mḟmḃ = 4, the maximum surface temperature of reflectors and Xe-arc lamps is less than 315 K and 610 K, respectively. The investigations revealed the feasibility of the concept and provided valuable insight for the planned experimental assessment and scale-up of the solar tower simulator.

Thermodynamic analysis of lined rock caverns for initial inflation and cyclic operational conditions in compressed air energy storage

With the irreversible trend towards cleaner and lower carbon energy alternatives on a global scale, the Lined Rock Cavern (LRC) compressed air energy storage technology emerges as a promising solution, offering vast prospects for large scale energy storage. This study explores the thermodynamic behaviors that arise from complex factors under high-frequency charging and discharging conditions in compressed air energy storage. It comprehensively considers transient gas flow, heat transfer, and real air properties, employing Computational Fluid Dynamics (CFD) methods. The simulations and analyses focus on the temperature and pressure variations inside the cavern during the initial inflation and cyclic operational conditions, along with the heat transfer characteristics of the sealing layer steel plate, concrete lining, and surrounding rock. As revealed by the research results, the inlet temperature and the air mass flow rate are two key factors affecting the average temperature inside the cavern during the initial inflation. Specifically, the inlet temperature shows a linear relationship with the average temperature while the air mass flow rate exhibits a nonlinear relationship. By fitting the simulation results, expressions that enable effective control of the average temperature are obtained. Under cyclic operational conditions, the pressure inside the cavern fluctuates within the range of 6 MPa to 10 MPa, displaying regular oscillations. With an increase in the number of cycles, the average temperature inside the cavern exhibits a decreasing trend, eventually stabilizing within a fixed range of fluctuations, indicating that the cavern has reached a steady state. The temperature of the steel plate and concrete lining undergoes significant changes throughout the entire operational cycle, influenced by both convective heat transfer and thermal conduction. With an increase in the number of cycles, their temperature variations align with the changes in the average temperature inside the cavern. In contrast, the temperature of the surrounding rock fluctuates within a narrow range throughout the process. The research findings of this study enable a more accurate estimation of the temperature variation range inside the cavern, facilitating the optimization of cavern design and providing crucial guidance for the application of lined rock caverns compressed air energy storage systems.

Microcontroller-based integrated data logging system for solar air heater performance assessment

ABSTRACT Efficiency curves for assessing solar air heater (SAH) performance are determined by measuring different parameters under certain operating conditions recommended by different test standards such as American Society of Heating, Refrigerating and Air-Conditioning Engineers. In this work, development and testing of a low cost integrated datalogging system for tracing efficiency curves are presented. Pyranometer (CMP11) and temperatures sensors (DS18B20) are integrated with microcontroller (AT89S52) for continuous data recording at desired time interval. Switching devices are integrated to automatically control operations of electric heater for maintaining inlet air stream temperature as per testing requirements. Using the system, efficiency curves of a 1.46 m2 SAH installed in Tezpur University, India, are determined at two mass flow rates of air. Results are comparable with published literatures revealing negative slope (energy loss component, F R U L ) and positive intercept (energy absorption component, F R (τα) n ) of efficiency curves. SAH shows better performance at lower mass flow rate of air (0.0235 kg/m2-s), with F R U L as 13.5 W/m2-K compared to operation at 0.0430 kg/m2-s mass flow rate of air where slope increases by around 23% with same intercept. Higher slopes of the SAH demonstrate its highest sensitivity to prevailing wind compared to three previously published designs. Present study shows that the integrated system can replace individual traditional measuring instruments for respective parameters like solar irradiance and temperatures as well as additional control equipment required to maintain desired test conditions. Further development of the system can lead to a modular and portable efficiency curve tracer for SAH performance assessment.

Examining the impact of filling ratio on thermosyphon performance in passive energy recovery processes with dual effects of evaporative cooling: An experimental study

AbstractThe thermosyphon heat exchanger contributes significantly to the improvement of energy conservation technology and has been used in multiple applications, raising the possibility of further studies to contribute to increasing the efficiency of heat pipes. This experimental study examines the different filling ratios of pure Acetone liquid inside a WHPHE integrated with the double‐effect of evaporative cooling to improve the energy‐saving technology. This work studies changing the filling ratio of pure acetone working fluid to investigate the effect of the filling ratio on heat exchanger performance in waste energy recovery technology. The heat exchanger was used with four rows and five tubes per row arranged in a staggered manner. The filling ratio of acetone inside the heat pipe was changed from 50% to 100%. The effect of the mass flow rate of air flowing in direct evaporative cooling on energy conservation technology was studied while the mass flow rate of air through indirect cooling remains constant in addition to the effect of ambient temperature. The results showed that the best filling percentage was between 80% at different temperatures, and the highest energy recovery percentage was when it was at the filling percentage of 80% in the presence of evaporative cooling.

Thermo-Economic Analysis of Thermoelectric-Based Atmospheric Water Harvesters: Flow Configuration Impacts

In recent years, thermoelectric cooling has seen significant growth, driven by advancements in nanoscience and manufacturing. Concurrently, the increasing water crisis in various regions has led to a surge in research on Atmospheric Water Harvesters (AWHs) for decentralized water harvesting. This study presents a comprehensive thermodynamic and economic analysis of Thermoelectric-based Atmospheric Water Harvesters (TAWHs) with different Heat Exchanger (HX) configurations with different flow configurations. Our research identifies five types of HXs, each characterized by its own optimal geometrical and controlling parameters. These HXs are evaluated based on economy, eco-friendliness, productivity, air cooling efficiency, and compactness. We provide new insights into the hidden potential and performance of Thermoelectric Coolers (TECs) in desalination, particularly highlighting the effect of increasing the ratio of surfaces mounted with TECs to the total surface area of the channels. Our results indicate that among the HX configurations, the counter flow HX is the most economical option, capable of water harvesting at a cost of $0.230 USD per liter from an 80% humidity level. The parallel flow HX demonstrates higher efficiency according to the second law of thermodynamics and environmental friendliness, while the crossflow HX exhibits lower overall efficiency. We found that the optimum cold channel incoming air flow rate varies with humidity in a detailed analysis of a counter flow HX with 2 columns and 15 rows. Interestingly, we found that humidity and incoming air mass flow rate have a negligible effect on power consumption. This work can be used as a guideline for future engineering problems involving the design and optimization of TAWHs.

CFD modeling of a modern wood stove - Soot formation

Wood stoves are important domestic heating appliances using renewable bioenergy. However, the emission of Particulate Matter (PM) is the major concern for the application of wood stoves. Thus, improvements in the design of wood stoves are required for the reduction of PM emissions (mainly soot) to fulfill the increasingly stringent pollutant emission limits. To achieve low PM emission of the wood stove, a 3D steady-state CFD model is used to simulate the wood stove with a focus on soot formation in this study. The model is evaluated with the experimental data, the results of which show that the CFD model provides a reasonable prediction of wood stove experiments, indicating that the CFD model can be used as an efficient tool to optimize the design of the wood stove. The model is further used to study the effects of injection direction and mass flow rate of the tertiary air on the soot particle emission. It is found that the horizontal- and down-direction injectors can effectively reduce soot formation and an optimized tertiary air mass flow rate exists in the modern wood stove system. These conclusions are very useful in designing and developing the intelligent control system of the modern wood stove.