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Achieving a quick temperature increase is a burning issue for biophysical applications, like germ inactivation and tumor ablation, and for energy performances, like solar collectors and steam generators. Based on the plasmon resonance phenomenon, noble metallic nanoparticles have emerged as promising weapons due to their very high biocompatibility, optical properties, and high surface-to-volume ratio, increasing energy conversion and allowing the maximum temperature to be reached faster. This work examines the energy conversion in sandwiched glassy platforms with gold nanorods. The platforms are kept vertically in the air and illuminated by a 0.5 W near-infrared laser (808 nm). To describe this aspect theoretically, the size and conversion efficiency of the electromagnetic properties are compromised between the proposed model and the stability of the nanorods. As a research approach, our model of cross-sections and polarizability for the surface effect is proposed, coupled with classical CFD numerical calculations. The results of the proposed model, validated by a thermal camera and spectroscopy measurements, indicate that as long as the energy conversion is visible with relatively low-power lasers (ΔT = 18.5 °C), the platforms do not offer fast heat dissipation. The results indicate that, despite the flow forcing by the air inflow, the entropy generation due to heat conduction is more than three orders higher than the dynamic entropy production. Flow forcing corresponds to the value of the velocity for classical convective motions. Therefore, the delivered heat flux must be distributed via convective transport or the associated high-conductive materials. [ABSTRACT FROM AUTHOR]

Wind machines based on the air disturbance method are progressively employed to mitigate frost damage within the agricultural machinery frost protection. These devices are utilized during radiative frost nights to disrupt near-surface thermal inversion through air mixing. Despite this application, the fundamental mechanisms underlying these mixing processes are not well comprehended. In this research, numerical simulations were conducted using COMSOL Multiphysics software version 6.0 to simulate the flow and heat transfer processes between the thermal airflow and both the tea canopy and stems. The results indicated that due to obstruction from the canopy cross-section, the airflow velocity on the contact surface rapidly increased. As the airflow further progressed, the high-speed region of the airflow gradually approached the canopy surface. Turbulent kinetic energy increased initially on the windward side of the canopy cross-section and near the top interface. On the windward side of the canopy, due to the initial impact of the thermal airflow, rapid heating occurred, resulting in a noticeable temperature difference between the windward and leeward sides within a short period. In the interaction between airflow and stems, with increasing airflow velocity, fluctuations and the shedding of wake occurred on the leeward side of the stems. The maximum sensible heat flux at the windward vertex of the stem increased significantly with airflow velocity. At an airflow velocity of 2.0 m/s, the maximum heat flux value was 2.37 times that of an airflow velocity of 1.0 m/s. This research utilized simulation methods to study the interaction between airflow and tea canopy and stems in frost protection, laying the foundation for further research on the energy distribution in tea ecosystem under the disturbance of airflow for frost protection. [ABSTRACT FROM AUTHOR]

In cold regions, the flow of outside air into a tunnel often causes freeze–thaw damage to the surrounding rock, and insulation methods are usually adopted to avoid this damage. In this study, the heat transfer in a multilayer tunnel structure that includes a rock layer, an initial lining, an insulation layer, and a secondary lining was investigated, and convection between the tunnel air and the inner surface of the tunnel lining was considered. A mathematical model describing the heat transfer process was established, and an analytical solution for the temperature field was developed using Duhamel's principle and the separation-of-variables method. The model and the solution were verified by comparing the computational results of the analytical solution with the computational results and in situ measurements available in the literature. By treating the minimum temperature of the inner surface of the surrounding rock as a function of the insulation thickness, a procedure to determine the minimum insulation thickness that ensures no freeze–thaw damage to the surrounding rock was developed based on the analytical solution using the bisection method. Computational examples were presented, and the effects of different factors on the minimum temperature of the inner surface of the surrounding rock and minimum insulation thickness were investigated. [ABSTRACT FROM AUTHOR]

The industry is faced with the task of introducing novel products with significant added value due to the rising customer demand for ingredients derived from sustainable sources and organic processes. Lycopene, a red pigment with well-known antioxidant effects, is particularly abundant in watermelon. They are also a remarkable source of different nutrients, but because of a specific harvesting period, seasonal production in certain agro-climatic zones, watermelon fruit have a relatively short shelf life. Therefore, the fruits are processed into juice concentrates, which extends their shelf life, lowers the cost of transportation and storage, and makes the fruit available year-round, even when it is out of season. Evaporation is the typical process used for producing juice concentrates. The main drawbacks of various evaporators, however, include the increase in viscosity brought on by the concentration of the juice and the fouling of the heat transfer surface. In this study, concentration is achieved by stripping water from the juice by an unsaturated air stream, under a high centrifugal field in a rotating packed bed with wire mesh packing. The performance of the contactor is studied by varying the operating parameters (rotating speed, air flow rate, juice flow rate, and temperature). The highest concentration obtained in the study after two hours of operation is ~21.9 °Brix which is remarkable. [ABSTRACT FROM AUTHOR]

The current study uses numerical methods to evaluate the thermal and flow characteristics of air jet impingement on concave multi-protruded surfaces. A two-dimensional numerical analysis is carried out with the help of commercially available FLUENT package. The impact of different geometric parameters is studied, including protrusion shape (convex and triangle), protrusion height and central angle by protrusions (α). Multiple protrusions on a surface lead to a series of peaks and valleys in the local Nu variation, which governs the overall thermal performance of jet impingement. It is found that protrusions with lower central angle by protrusions improve the heat transfer attributes compared to smooth surface, irrespective of protrusion size and shape. A drastic improvement in thermal performance is noted by replacing convex protrusion with triangle protrusion, particularly at the larger central angle by protrusions (α). [ABSTRACT FROM AUTHOR]

This study analyses Compound Fins (CFs) in turbulent airflows using numerical and experimental methods. CFs combine Novel Plate Fin Heatsinks (NPFHSs) [1] and Slotted fins (S8 and S9) [2] and are compared to plain plate fins. Numerical modelling of turbulent airflow is conducted using Reynolds-Averaged Navier-Stokes equations, and ANSYS is used for the analysis. The CFs are manufactured using selective laser melting and validated experimentally. CF variations are categorized as CF18, CF19, CF28 and CF29 as described in Table 1. CFs outperform plain fins, with CF18, CF19, CF28, and CF29 showing higher Nu numbers by 52.7%, 51.2%, 44.8%, and 47.9%, respectively. CF18 and CF19 have 22.9% and 21.7% higher heat transfer coefficients than NPFHS1, respectively. CF28 and CF29 have 19.1% and 22.4% higher heat transfer coefficients than NPFHS2, respectively. CF18 and CF19 have higher air pressure drops than plain fins, while CF28 and CF29 have lesser pressure loss. The study concludes that CFs perform better than plain fins and are lighter. The methodology ensures the accuracy and reliability of the findings, making the study a valuable contribution to electronic cooling. [ABSTRACT FROM AUTHOR]

Stenter machines are used to remove moisture from fabrics produced in the textile industry. Following the drying process, the cooling process, which is applied to fabrics using injector channels, is conducted in the last section of a stenter machine, preventing fabrics from expanding and the degradation of their quality. The present study mainly aimed to investigate the fabric-cooling process in a stenter machine used actively in a textile company. First, industrial data were obtained with some experiments, and computational fluid dynamics (CFD) simulations were then conducted by validating the industrial data. All CFD models were simulated using ANSYS Fluent commercial CFD software. A total of four parameters, including two geometric and two operating parameters, were considered in order to investigate their effects on the fabric-cooling performance of the stenter machine. While the geometric parameters were the porosity (β) and injector angle (α), the operating parameters were the velocity of the airflow that cools the fabrics and fabric velocity, representing the movement of the fabric. As outputs of CFD simulations, fabric surface temperature values, the distributions of fabric surface temperatures, and some streamlines were illustrated. Although low values of porosity (β1 = 0.05) and injector angle (α1 = 0°) provided better performance, airflow velocity could be increased one or two times for the range of these constant parameters. [ABSTRACT FROM AUTHOR]

The ambient temperature's impact on the power output of gas turbines is significantly pronounced, particularly in hot and dry climates such as Iraq. This study seeks to elucidate the potential enhancement of heat transfer and performance improvement in gas turbines through the implementation of an inlet air fogging system. By cooling and humidifying the inlet air, it is hypothesized that the air's density and mass flow rate will be augmented, thereby increasing the power output and overall cycle efficiency. A comprehensive experimental and numerical investigation was undertaken, employing the inlet fogging technique which introduces a mist of fine water droplets into the incoming airflow. The heat exchange between the water droplet surface and the hot air-up until the droplet's evaporation - was examined meticulously. The results underscored differential improvements when using 9 and 5 nozzles, which modified the air velocity flow. These improvements were attributed to the enhancement in heat exchange between the hot air and the evaporating water droplets, leading to an increase in electrical energy output. Computational fluid dynamics (CFD) was employed to analyze the thermal behavior inside the wind tunnel using the commercial software Fluent 22 R1. The model predictions and experimental observations along the duct exhibited satisfactory agreement, with the most significant discrepancies being a temperature drop of 2.5% and a heat transfer rate difference of 3.8%. [ABSTRACT FROM AUTHOR]

The article presents numerical simulations of the flow and heat transfer for beds with an ordered and shifted arrangement of elements. The numerical model applied is based on the unsteady equation of heat conduction (3D) and the Navier-Stokes equations. A high-order compact method in combination with the weighted essentially non-oscillatory scheme and predictor-corrector method is applied for the spatio-temporal discretisation. The flows of air and heat in the bed are modelled using the immersed boundary technique, which allows the use of Cartesian meshes for objects with very complex geometric shapes. The influence of the shift of elements in the bed on the temperature and velocity field was analysed. For two of the selected beds, the influence of arrangements of elements on the flow and heat exchange was analysed, which can lead, for example, to an improvement in the heating properties and to eliminating defects in the construction of reactor fillings. [ABSTRACT FROM AUTHOR]

To study the heat and mass transfer characteristics of an evaporative cooler for cooling high-temperature working fluids, an experimental device of the evaporative cooler was built, and a corresponding test system was constructed. Then, the experimental study was carried out based on an orthogonal experimental design, and the law and extent of the influence of water flow in the tube, the spray water flow rate, the inlet water temperature in the tube, and the air flow rate on the heat dissipation, cooling efficiency, and heat and mass transfer coefficients were obtained. The correlation equations of the heat and mass transfer coefficients were obtained by fitting the orthogonal experimental data, and the validity of the correlation equations was confirmed by the verification experiment. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

As the electronics industry gravitates towards smaller yet more powerful devices, the need to enhance traditional heat sink cooling capabilities without enlarging their footprint has become increasingly urgent. This necessity stems from the adverse effects of high temperatures on electronic performance and the limitations of traditional heat sinks' thermal transfer. This study addresses the challenge by investigating modifications to heat sink design, specifically through the strategic perforation of fins to increase their surface area, thereby improving heat dissipation without augmenting size. A series of lateral plate fins, perforated for increased surface area, were positioned on the base of a heat sink. The thermal performance of these modified heat sinks was then tested experimentally within a long, square cross-sectioned channel, facilitating forced air passage at manually controlled speeds. Three heat sink samples were compared under variable airflow rates to ascertain the cooling efficiency of the perforated fins. Three distinct rectangular heat sinks were utilized. The first featured holes of varying diameters arranged horizontally (PHS-HV), while the second had vertically varying diameters, with smaller ones at the top and larger ones at the bottom (PHS-VV). These perforated heat sinks were contrasted against a nonperforated heat sink under different thermal loads and Reynolds numbers. Results demonstrated enhanced heat dissipation, Nusselt number, and heat transfer coefficient in perforated fins compared to non-perforated ones. Notably, the use of different hole diameters in the same fin positively impacted heat dissipation, with horizontal diameter expansion (PHS-HV) outperforming vertical expansion (PHS-VV). The heat transfer improvement was 8.53% for PHS-HV and 4.36% for PHS-VV at Re 20000. Furthermore, perforation contributed to a decrease in heat sink mass compared to solid heat sinks, indicating cost and material savings. This study underscores the potential of strategic perforation in augmenting heat sink performance for next-generation electronics. [ABSTRACT FROM AUTHOR]

In order to reduce the rain zone noise of wet cooling towers and enhance the heat transfer and ventilation, the influence of sound barriers on the thermal performance of wet cooling towers with synergistic optimization of fillers and water distribution was studied based on threedimensional numerical calculations. It is found that under the working conditions of this research, the sound barrier and the two zone synergistic efficiency scheme can uniformly distribute the temperature field, air flow velocity distribution, and water vapor mass fraction distribution inside the cooling tower;The two zone synergistic efficiency enhancement scheme can to some extent counteract the adverse effect of the noise barrier on the heat transfer performance of the cooling tower, resulting in an average increase of 0. 06℃ and 3. 8% in the circulating water temperature drop and cooling number compared to the original tower, respectively;Although the ventilation capacity of the entire tower has been reduced after the renovation, the distribution of the aerodynamic field is more reasonable, which is more conducive to the heat exchange of the cooling tower. This study can provide reference for the design of a two zone synergistic cooling tower with sound barriers. [ABSTRACT FROM AUTHOR]

In order to optimize the heat transfer characteristics of regenerative evaporative coolers under different climatic conditions and provide reference data for numerical simulation research. The dynamic coupling of heat and humidity parameters of the air flow in the regenerative evaporative cooler is the fundamental factor affecting the efficiency of evaporative heat transfer, and mastering its law can guide the structure optimization of the heat exchanger. In this paper, a simulation model is constructed based on the structure of regenerative evaporative cooler, and the variation of heat and humidity parameters in the airflow passage is studied by numerical simulation method with the application background of representative cities at home and abroad under different climate conditions. It is found that the relative humidity increases rapidly in the wet channel, and the length of 40 cm wet channel can meet the full evaporation demand under most working conditions. The evaporation cooling effect is greatly affected by the inlet air parameters, and the saturation degree of ambient air has a significant influence on the cooling effect. Keeping the latent heat exchange process in the high efficiency evaporation section and the sensible heat exchange process in the high temperature difference section of the channel can effectively improve the heat exchange efficiency of the evaporative cooler and shorten the length of the heat exchanger. [ABSTRACT FROM AUTHOR]

In this study, roughness in the form of multi-V ribs having trapezoidal slots were crafted over the surface of absorber plate for enhancing the heat transfer rate in a solar air heater. An experimental setup was designed and fabricated for demonstrating the performance of this plate with respect to smooth absorber plate. The setup has a double glazed-double pass air flow arrangement. The experiments were conducted under Indian climatic conditions (Latitude = 28.53°N and Longitude = 77.39°E) in September and October 2021 at various rates of air flow through the duct. The results of the roughened absorber plate were compared with the smooth absorber plate. It shows that the multi-V ribs with trapezoidal slots have higher efficacy as compared to smooth absorber plate in the order of 10.42% at an air flow rate of 0.078 kg/s. In addition, the present data of proposed roughness were also compared with data of various roughness available in the literature. It was found that the maximum thermo-hydraulic performance parameter of the proposed roughness texture is higher than other shapes of roughness texture. It was also found that the combination of double-glass cover and double-pass arrangement with the proposed roughness geometry increases the efficiency of the solar air heater at least by one order of the present solar air heating system. [ABSTRACT FROM AUTHOR]

Copyright of International Journal of Advances in Engineering & Pure Sciences is the property of Marmara University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The detailed understanding of heat transfer in the pulsating airflow in the pipe is critical to reducing heat losses in the engine exhaust stream and improving catalyst performance. In the present investigation, we have scrutinized the impact of pulsation frequencies ranging from 0-90 Hz on the flow velocity field and the consequent heat transfer through a horizontal pipe wall. The Nusselt numbers were evaluated at three distinct cross-sectional points moving from upstream to downstream, by systematically modulating the frequency. Temporal variations in the velocity field and temperature were captured utilizing particle image velocimetry (PIV) and dual-thermocouple probes, respectively. Intriguingly, while the Nusselt number for steady flow at 0 Hz closely adhered to Gnielinski's equation, the pulsating flow demonstrated a peak between 25-35 Hz, a pattern not predicted by the prevailing quasi-steady-state theory. The observed frequency response of turbulence was found to be congruous with the Nusselt number, indicating that the heightened heat transfer at frequencies of 25-35 Hz could be attributed to the enhanced turbulence and the temperature gradient between the fluid and the wall surface during the deceleration phase in the hysteresis of turbulence in the pulsating flow. The unique frequency characteristics of heat transfer that were uncovered in this study, with respect to both flow velocity and temperature, offer valuable insights for devising strategies to mitigate heat loss during ignition and idling. Furthermore, these findings provide robust benchmarks for validating numerical simulations of pulsating flows in real-life automotive engines. [ABSTRACT FROM AUTHOR]

This study presents an experimental and numerical investigation into the thermofluid characteristics of airflow over an inclined, heated plate, mimicking a solar panel. The inclination of the plate was systematically adjusted from 0° to 90°, and the heat flux was varied from 1000 to 4000 W/m², with Reynolds number ranging from 63,000 to 650,000. The study employed a second-order finite volume method for discretization and resolution of steady fluid dynamics problems, with simulations conducted using Ansys Fluent software. The k-ε RNG turbulence model was utilized for these simulations. The numerical results, validated against experimental data, were extrapolated to assess the behaviour at a wide range of attack angles and flow rates. Correlations were established between the average Nusselt number and friction coefficient, as functions of Reynolds number and attack angles. It was observed that heat transfer was optimized at lower attack angles. Conversely, higher inclination angles resulted in increased skin friction, thereby reducing airflow and negatively impacting heat convection. For larger Reynolds numbers, convective flow enhanced and the resistance of the plate was found to be lower at smaller attack angles. These findings have significant implications for the improvement of solar panel efficiency, offering valuable insights into the optimal configuration for maximizing convective heat transfer. [ABSTRACT FROM AUTHOR]

Current investigation aims to introduce and analyze an oblique-finned corrugated to evaluate numerically an unique method for improving heat transfer. Vertical gap ratios (V) of 0.15, 0.20, and 0.25; horizontal gap ratios (H) of 0.03, 0.04, and 0.05 as well as oblique-angle (θ) values of 10°, 20°, and 40° are just a few of the design factors that are examined. The targeted channels are subjected to turbulent air flows that are simulated using the finite volume technique (FVM) and the κ- ε model under constant temperature circumstances (T = 300 K). The data show that the novel approach enhances fluid mixing, which enhances heat transfer and, ultimately, thermal-hydraulic performance (PEC). The outcomes also show that frictional loss was employed to stimulate the target system's overall performance in the way of reducing the impact of heat transfer. Additionally, the findings uncover that, in comparison to other gap ratios, a moderate vertical gap ratio and a large horizontal gap ratio have a greater impact on heat transfer rate and PEC, respectively. Accordingly, the Nusselt number enhances by 73 %, 74 %, and 72 % across the same range of Reynolds number at a group of gap ratios (V = 0.15, h = 0.04), (V = 0.2, h = 0.05), and (V = 0.25, h = 0.05), respectively. Besides, the design parameters V = 0.2, H = 0.05, and θ = 40° yielded the best PEC of 2.547. New correlations for the innovative oblique-finned corrugated model are also presented. [ABSTRACT FROM AUTHOR]

The air-based photovoltaic-thermal collector (PVTC) is a system that can generate electricity and heated air simultaneously from solar energy. This study investigates the electrical and thermal performances of an air-based single-pass double-flow photovoltaic-thermal collector (SPDFPVTC) coupled with a nonuniform cross-section rib (NUCSR) under various operating conditions. The rib is installed at the rear of the photovoltaic panel to enhance the heat transfer performance between the photovoltaic panel and the flowing air. Based on the energy balance equations, a mathematical model of the proposed SPDFPVTC is established and validated by experimental results. The solar intensity, air mass flow rate, and wind speed are selected as operating conditions. The effects of these operating conditions on the electrical and thermal performance of the SPDFPVTC have been discussed. In addition, this study evaluates the daily performance of SPDFPVTC with and without NUCSR. The average electrical, thermal, and overall efficiency were 17.59%, 43.96%, and 61.55%, respectively, for SPDFPVTC with NUCSR and 16.97%, 38.87%, and 55.83%, respectively, for SPDFPVTC without NUCSR. Consequently, installing NUCSR could enhance the daily electrical, thermal, and overall energy output of SPDFPVTC by 4.33%, 13.23%, and 10.63%, respectively. [ABSTRACT FROM AUTHOR]

The paper presents the results of calculating the thermal-hydraulic heat exchange efficiency processes for direct and swirl (using an inserted twisted tape) pipe air flows at the same transferred heat fluxes and temperature conditions. The calculated energy efficiency, which characterizes the thermal-hydraulic heat exchange efficiency, demonstrated the ratio of transferred heat and energy consumption for pumping the coolant during the heat exchange for these two cases to be almost the same for coolant-flow Reynolds numbers up to 2.5 ⋅104. At large Reynolds numbers, the thermal-hydraulic efficiency of a direct flow heat exchange is higher. [ABSTRACT FROM AUTHOR]

A non-tubular prototype cavity receiver absorber with extended internal surfaces (fins) is proposed to enhance heat transfer in Stirling engine-based Concentrated Solar Power systems. There is limited research on the realization of downsized absorbers in terms of their design and manufacturing. The objective of the absorber solution proposed in this paper is to address the issue of inadequate comprehension regarding the impacts of the geometric and flow parameters on thermohydraulic efficiency. These impacts are numerically investigated in a 100 mm long heat transfer channel with a 10 mm × 10 mm section. The prototype absorber is fabricated using a wire electrode-discharging manufacturing approach, and is experimentally investigated using the enthalpy method. Numerical results indicate that heat transfer to the working fluid in the novel absorber can reach 482 W at the reasonable cost of 0.391% pressure drop per 100 mm (air flow at 0.0015 kg/s and 5 bar). In the experimental investigation, the prototype realizes a 1113.033 W heat transfer rate at 8 bar and 12 kg/h. This implies that a non-tubular design with extended internal surfaces can increase the internal surface area to enhance heat transfer while downsizing the volume to reduce heat loss. [ABSTRACT FROM AUTHOR]

The use of solar air heater systems brings with it the convenience of having hot air at discretion for heating households with quite low prices compared to the use of conventional heating sources. The researchers desire to achieve the highest thermal efficiency of these systems has led to the emergence of different ways of improvement. The present work is focused on the available literature in the field of SAH systems made with different types of air flow. The paper also presents the different designs for the realization of airflow types used by researchers for high efficiency during the years 2017-2021. [ABSTRACT FROM AUTHOR]

This work provides a comprehensive overview of various aspects of airfoil CFD simulations. The airflow around a 2D NACA 0012 airfoil at various angles of attack is simulated using the RANS SST turbulent flow model and compared to experimental data. The airfoil is then modified with a slotted flap and additionally the angle of the flap is altered. The flow model is subsequently coupled to a heat transfer model to compare the isothermal versus non-isothermal performance. The airfoil with the slotted flap shows increased C L and C D values compared to the standard NACA 0012. Larger flap angles further increase the C L and C D . The lift and drag coefficients show no difference in the non-isothermal model compared to the isothermal model, indicating the isothermal model is sufficient for this system. The 3D model without wingtips shows a similar C L to the 2D model as it effectively has an infinite span. Adding a wingtip reduces the lift coefficient, as the air can flow around the wingtip, increasing the pressure on top of the wing. Overall, these results match the behavior expected from wing theory well, showing how CFD can be effectively applied in the development and optimization of wings, flaps, and wingtips. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement using curved ribs of different cross sections, viz., square, rectangular, triangular, and circular, is a crucial study for designing heat-exchanging devices for various applications, and their thermohydraulic performance prediction using machine learning technique is a vital part of the modern world. An experimental study on using curved ribs suitable for heat transfer enhancement for the circular tube is presented for turbulent airflow with Reynolds numbers varying from 10,000 to 50,000. The machine learning methodology is used to predict the thermohydraulic performance assessment of curved ribs. The square cross-sectioned curved ribs produce the highest performance factor R3 of 1.5 to 2.65 to the equivalent Reynolds number Rec value of 20,000. It is observed that most of the curved rib configurations show a performance ratio R3 maximum and are suitable at a low Reynolds number value. At moderate and high Reynolds number values, the performance factor values decrease due to a rise in the pressure drop values for a few curved rib configurations. An artificial neural network (ANN) model predicts with an accuracy of 95% with the present study experimental values for the heat transfer performance indicators like average heat transfer enhancement Nua/Nus, average heat transfer enhancement fa/fs, and performance ratio R3, i.e., Nua/Nuc. [ABSTRACT FROM AUTHOR]

Air-to-air fixed plate enthalpy membrane exchanger is considered one of the equipment used in energy recovery services. Thermal performance of air-to-air energy recovery ventilator is examined numerically using a 3D CFD simulation. Air flow inside the exchanger is tested using four numerical turbulence models: Standard k-ε, k-ε renormalization group (RNG), k-ε realizable and k-ω shear-stress transport (SST) models. The adopted heat and mass exchange element within the ventilator (membrane) is a thin 98 μm porous 60 gsm Kraft paper. A user defined function (UDF) has been developed to enable the CFD model to estimate amounts of mass exchanged between the two sides of the membrane. Grid dependency study is conducted and results have shown that a perpendicular distance of 50 μm or less from the membrane surface would result in a negligible variation in the ERV thermal effectiveness. The validated CFD model and UDF code against experimental measurement resulted in a maximum difference in thermal effectiveness of 3.6%. Results have shown that the SST k-ω turbulence models under enhanced wall treatment showed more sensitivity to flow at all Re values when compared with the k-ε simulated models. [ABSTRACT FROM AUTHOR]

Microchannel heat exchangers (MCHX) are increasingly being used in refrigeration and heat pumps due to their superior thermal-hydraulic properties. However, when the MCHX surface temperature drops below the freezing point, frost will accumulate on the fin surface, which significantly affects the heat transfer performance. In this study, a modified MCHX with extended windward fins was developed to improve the frosting performance. The thermal-hydraulic performance of the modified MCHX and conventional MCHX were compared and evaluated under frosting conditions. Results show that the extended fins on the windward side capture a large amount of frost and delay the rapid blockage of air flow passage by frost. The modified MCHX structure makes the frost more evenly distributed. During the 60 min frosting cycle, the total heat transfer capacity and the mass of the accumulated frost of the modified MCHX are 9.6–49.7% and 10.3–46.9% higher than the conventional MCHX, respectively. Furthermore, the modified MCHX has greater potential to improve the thermal-hydraulic performance under the condition of more uneven frost layer distribution. The purpose of this work is to provide useful guidance for the optimal design of MCHX under frosting conditions. [ABSTRACT FROM AUTHOR]

The exploitation of natural resources is associated with many natural hazards. Currently, the copper ore deposits exploited in Polish mines are located at a depth of about 1200 m below the surface. The primary temperature of the rocks in the exploited areas reaches 48  ∘ C, which constitutes a major source of heat flux to the mine air. However, another important source of heat is the machine plant, which mainly consists of machines powered by diesel engines. Following the results of in situ measurements, boundary conditions for a simulation were determined and a geometric model of the cabin was created. Furthermore, an average human model was created, whose radiative heat transfer was included in the analysis. Three cases were studied: the first covering the current state of thermal conditions, based on the measurement results, and two cases of forecast conditions. In the second case, the temperature of the conditioned air was determined, and in the third, the flow velocity required to ensure thermal comfort was found. The results of the simulation indicated that for the microclimatic conditions established based on the measurements (ambient air temperature in the excavation 35.0  ∘ C, air-conditioned airflow 2.4 × 10 − 2  m 3 /s, and temperature 10.0  ∘ C), the temperature of the air inside the air-conditioned operator's cabin would be 20.4  ∘ C. Based on the personal mean vote (PMV) index, it was concluded that the thermal sensation would range from neutral to slightly cool, which confirmed the legitimacy of the actions taken to reduce the adverse impact of the microclimatic conditions on workers in the workplace. However, for the case of predicted conditions of enhanced heat flux from strata and machinery, resulting in an average ambient temperature increased to 38.0  ∘ C, it would be necessary to lower the temperature of air from the air conditioner to 8.00  ∘ C or increase the flow rate to 3.14 × 10 − 2  m 3 /s to maintain thermal comfort at the same level of PMV index. [ABSTRACT FROM AUTHOR]

Stenter machines are used to remove moisture from fabrics produced in the textile industry. Following the drying process, the cooling process, which is applied to fabrics using injector channels, is conducted in the last section of a stenter machine, preventing fabrics from expanding and the degradation of their quality. The present study mainly aimed to investigate the fabric-cooling process in a stenter machine used actively in a textile company. First, industrial data were obtained with some experiments, and computational fluid dynamics (CFD) simulations were then conducted by validating the industrial data. All CFD models were simulated using ANSYS Fluent commercial CFD software. A total of four parameters, including two geometric and two operating parameters, were considered in order to investigate their effects on the fabric-cooling performance of the stenter machine. While the geometric parameters were the porosity (β) and injector angle (α), the operating parameters were the velocity of the airflow that cools the fabrics and fabric velocity, representing the movement of the fabric. As outputs of CFD simulations, fabric surface temperature values, the distributions of fabric surface temperatures, and some streamlines were illustrated. Although low values of porosity (β1 = 0.05) and injector angle (α1 = 0°) provided better performance, airflow velocity could be increased one or two times for the range of these constant parameters.

Today, reciprocating internal combustion engines are used in many branches of the economy (power engineering, machine engineering, transportation, and others). In order for piston engines to meet stringent environmental and economic regulations, it is necessary to develop complex and accurate control systems for the physical processes in engine elements based on digital twins, machine learning, and artificial intelligence algorithms. This article is aimed at preparing and analysing experimental data on the gas dynamics and heat transfer of pulsating air flows in a piston engine's intake system for modelling and machine learning. The key studies were carried out on a full-scale model of a single-cylinder piston engine under dynamic conditions. Some experimental findings on the gas-dynamic and heat-exchange characteristics of the flows were obtained with the thermal anemometry method and a corresponding measuring system. The effects of the inlet channel diameter on the air flow, the intensity of turbulence, and the heat transfer coefficient of pulsating air flows in a piston engine's inlet system are shown. A mathematical description of the dependences of the turbulence intensity, heat transfer coefficient, and Nusselt number on operation factors (crankshaft speed, air flow velocity, Reynolds number) and the inlet channel's geometric dimensions are proposed. Based on the mathematical modelling of the thermodynamic cycle, the operational and environmental performance of a piston engine with intake systems containing channels with different diameters were assessed. The presented data could be useful for refining engineering calculations and mathematical models, as well as for developing digital twins and engine control systems. [ABSTRACT FROM AUTHOR]

Caves and their surrounding fracture systems in the vadose zone of karst regions host a unique atmospheric environment. Understanding the airflow patterns in caves is critical to understanding the properties of the subsurface atmosphere and the chemical interactions between air, water, and rock. The most common driver of airflow in caves is the density difference between the subsurface and the outside air, known as the chimney effect. Observations show that seasonal airflow patterns in caves also depend on the geometry of passages. In this work, I present and use a numerical model of a passage embedded and thermally coupled to a rock mass to study the relationship between the airflow pattern and passage geometry. As the outside air enters the subsurface, it approaches thermal equilibrium with the rock mass along a characteristic relaxation length. This determines the temperature and density contrast between the inside and outside air, and the resulting pressure difference, which drives the airflow. In passages with non-uniform outlines and/or cross-sections, the relaxation length may depend on the flow direction, resulting in different airflow velocities in cold and warm periods for the same absolute temperature difference between the massif and the external temperature. In a passage with a V-shaped longitudinal profile, the airflow is triggered by instability which causes the feedback between the relaxation length and airflow velocity. The airflow pattern can also be altered by snow and ice. Heat transfer in the rock and the thermal inertia of the rock also change the relaxation lengths and cause hysteresis in the curve presenting the airflow velocity vs. temperature difference. [ABSTRACT FROM AUTHOR]

Various external-recycle configurations of multi-pass flat-plate solar air collectors were studied theoretically to examine the optimal thermal performance under the same working dimension and operation conditions. An absorber plate and insulation sheet were implemented horizontally and vertically, respectively, into an open rectangular conduit to conduct a recycling four-pass operation, which the device lengthens the air flow channel and increases the air mass flow rate within the collector, and thus, a more heat transfer efficiency is obtained. Four recycling types with different external-recycle patterns were introduced and expected to augment the heat transfer rate due to the turbulent convective intensity through four subchannels in the present study. Coupling energy balances into one-dimensional modeling equations were derived by making the energy-flow diagram within a finite element, which the longitudinal temperature distributions for each subchannel were obtained. The theoretical predictions show that the improved four-pass device is accomplished due to the multiple heating pathways over and under the absorber plate, from which the turbulence intensity augmentation results in the heat transfer rate as compared to that in the device without inserting the absorber plate and insulation sheet (say a downward-type single-pass solar air collector). The theoretical results also show that the external-recycle configuration (say Type C in the present study) acts as an optimal collector thermal efficiency and leading to a beneficial design in multi-pass solar air collectors for improving heat-transfer rate and increasing resident time under the same operation conditions. Theoretical predictions show a higher heat-transfer efficiency for the present recycling configurations up to a maximum 115% device enhancement in comparison to that of a single-pass device. Examination of implementing the absorber plate and insulation sheet on the heat-transfer efficiency enhancement as well as the hydraulic dissipated power increment were also delineated, and deliberated the suitable external-recycle configuration with respect to an economic consideration. [ABSTRACT FROM AUTHOR]

Experimental studies of free-convective heat exchange between single-row bundles of bimetallic tubes with spiral rolled aluminum fins of different heights (2–14.6 mm) and a vertical air flow created by an exhaust shaft with adjustable height H = 0.52, 1.16, and 2.12 m are presented. The tubes were layed out with a constant relative transverse spacing σ1 = 1.14 (6 pipes). The data of measurements were used to calculate the average reduced heat transfer coefficient, which ranged from 0.78 to 17.30 W/(m2∙°C) at Rayleigh numbers (19–360)·103. A similarity equation is obtained for describing the dependence of heat emission of single-row bundles with different fin heights in a free convection regime on the relative height of the bundle–shaft system. It is found that intensification of free convection of air by installing an exhaust shaft above the bundle of tubes allows one to increase the heat emission intensity by 2.3 times. Expressions are obtained for determining the energy and aerodynamic efficiencies of the bundle–shaft system. The optimal height of finning (about 8 mm) for bundles of studied tubes with an exhaust shaft was determined. [ABSTRACT FROM AUTHOR]

This paper performed a three-dimensional numerical analysis of the flow structure and heat transfer enhancement of turbulent airflow through a rectangular channel (without baffles, with baffles). Two partially inclined baffles with different orientations are mounted on the bottom and top walls of the channel. The location of the baffles in the direction of flow through the channel of a heat exchanger is of great importance. It depends mainly on the geometrical parameters and the orientation of the baffles. Hence, our study focused on analyzing the effects of the baffles on the thermal–hydraulic behavior in the exchanger by choosing a flat baffle and four configurations of different orientations. Numerical results are presented in terms of axial velocity U, isotherms (T), turbulent kinetic energy (k), amount of heat dissipated by the channel surfaces (Q), average Nusselt number (Nu), friction factor (f), and thermal performance factor (ƞ). The results show that the insertion of the partially inclined baffles into the channel causes the generation of vortices in the upstream and downstream areas of the baffle location point. Thus the mixing phenomenon occurs, which induces an increase in the heat transfer rate and generates a pressure drop simultaneously. Furthermore, the analysis of the results shows that compared to the smooth case (without baffles), the thermal performance factor (η) is significantly higher in the four configurations with baffles. Thus, for the different cases studied: (2); (3); (4); (5) and (6), the factor (η) is equal to 2.18; 2.16; 2.19; 2.27; and 2.25, respectively, for a Reynolds number equal to 87,300. The results also indicate that the transmitted relative heat quantities are equal to 116.08, 113.93, 118.2, 121.71, and 109.39%, respectively, for the same cases considered. Therefore, the configuration corresponding to case (5) performs better in heat transfer than the others. Finally, new correlations for predicting friction factor and Nusselt number as a function of Reynolds number and configuration are found at the end of this study. [ABSTRACT FROM AUTHOR]

A 3D computational fluid dynamics (CFD) model was developed to predict the airflow and heat transfer in half of a pallet layer of tomatoes. The numerical and experimental results were compared, and a good agreement was obtained between both results using the root-mean-square error (RMSE) and absolute relative deviation (ARD) values as criteria. The validated CFD model was then used to minimise the product temperature heterogeneity by optimising the airflow rate and the crate design. A downward flow of the air along the central parts of the crates and an upward flow close to the lateral walls of the crates were observed. Three different total ventilated areas (TVAs) were tested to study their influence on the product temperature uniformity and cooling rate. The MTD and ATD decreased from 6.8 to 3.5 °C and from 1.5 to 0.7 °C, respectively, when the TVA was increased from 11 to 15%. [ABSTRACT FROM AUTHOR]

With the aid of the COMSOL program, the laminar mixed convection heat transfer in a channel-open cavity with two heat sources of constant 20 W each and varying input air velocity ranges (0.1, 0.5, 1.0, and 1.5 m/s) is numerically determined. In this study, the effect of varying inlet air velocity on the heat transfer characteristics is investigated. Numerical results show that the temperature starts to fall steadily as one moves farther and further away from the site of the two heat sources and closer to the horizontal channel. The higher the velocity of the air entering the cavity, the greater the natural convection that will be created by the heated heat sources. The increase in inlet air velocity will increase the turbulence of airflow and thus increases the pressure distribution. The increase in absolute y-direction decreases the velocity distribution. The rise in the inlet velocity of air will increase the transfer of heat; thus, the Nusselt number will be great when increasing air flow velocity. The maximum Nusselt number is at the interface and reduces with increasing the absolute value of y. A reduction in air temperature and an increase in air density result from an increase in natural convection from the cavity into the air stream caused by an increase in air input velocity. [ABSTRACT FROM AUTHOR]

At present, China's high-speed rail is in a period of rapid development. Most of the refrigerants used in Chinese motor train units at this stage are still R134a and R407c, which have an impact on the environment. In response to the environmental protection concept of green travel, it is of great significance to study the air conditioning system of motor train units using CO2 refrigerant. Using CFD simulation analysis technology, the heat transfer performance of the air side of the CO2 finned tube evaporator used in the air conditioning system of the motor train unit is studied. We select the air outlet temperature, pressure drop, heat transfer factor, and resistance factor as the objective function, in addition, monitoring points are set up in the air flow channel to monitor the turbulent flow field and pipe wall pressure. Our research shows that the cooling capacity of the CO2 evaporator can reach up to 29.76 kW, which can meet the heat exchange required in the air conditioning system of the motor train unit. In order to obtain a better structure and the conditions of the heat transfer effect, structural optimization was conducted. The simulation results demonstrate several trends: (i) With the augment of the air inlet velocity, the cooling capacity of the evaporator increases and the heat exchange effect improves; when the air inlet ve > 2.2 m/s, the effect of continuing to augment ve on heat exchange is weak. (ii) Following appropriate reduction of the diameter of the heat exchange tube, the wind resistance is reduced and the cooling capacity of the evaporator is improved. (iii) With the enlargement of the fin spacing, the turbulent motion in the flow channel can be fully developed, there is a peak in the change in the heat exchange tube area optimization factor, and the optimal fin spacing is between 1.6 mm and 1.7 mm; at this time, the average turbulent kinetic energy of the air side is larger and the turbulent dissipation rate is smaller. These results provide a reference for the practical application of CO2 refrigerant in the motor train unit. [ABSTRACT FROM AUTHOR]

In the typical structure of a turboshaft aero-engine, the mass flow of the cooling air in the rotor-stator cavity is controlled by the inlet seal labyrinth. This study focused on the swirl flow and heat transfer characteristics in a rotor-stator cavity with considerations of the inlet seal thermal deformation effect. A numerical framework was established by integrating conjugate heat transfer (CHT) analysis and structural finite element method (FEM) analysis to clarify the two-way aero-thermo-elasto coupling interaction among elastic deformation, leakage flow, and heat transfer. Simulation results showed that the actual hot-running clearance was non-uniform along the axial direction due to the temperature gradient and inconsistent structural stiffness. Compared with the cold-built clearance (CC), the minimum tip clearance of the actual non-uniform hot-running clearance (ANHC) was reduced by 37–40%, which caused an increase of swirl ratio at the labyrinth outlet by 5.3–6.9%, a reduction of the Nusselt number by up to 69%. The nominal uniform hot-running clearance (NUHC) was defined as the average labyrinth tip clearance. The Nusselt number of the rotating disk under the ANHC was up to 81% smaller than that under the NUHC. Finally, a clearance compensation method was proposed to increase the coolant flow and decrease the metal temperature. [ABSTRACT FROM AUTHOR]

In this investigation, the effect of replacing the conventional solar absorber with a new solar absorber on the thermal performance of a double-pass solar air heater has been studied experimentally and numerically. Three configurations have been introduced, the first configuration is a double pass solar air heater with a flat plate solar absorber (DPSAHWFP) for the aim of comparison, and the second configuration is a double pass solar air heater with a tubular absorber that includes a set of tubes which are fitted perpendicularly to the direction of airflow (DPSAHWT-1), and the third configuration is double-pass solar air heater with a tubular absorber that involves set of tubes which are fitted in parallel to the direction of airflow (DPSAHWT-2). The experiments have been carried out under indoor conditions at a constant heat flux equal to 1000 W/m2 and different air mass flow rates (0.01– 0.03 kg/s). The results revealed that the air mass flow rate has a substantial impact compared to the rise in air temperature, hence, the thermal performance of solar air heater is directly proportional to increase air mass flow rate. In addition, the experimental and numerical outcomes indicated that for all air flow rates. The (DPSAHWT-2) offers higher thermal performance as compared to other models, where the maximum effective efficiency has been obtained at 0.03 kg/s equal to 80.9 %. Moreover, (DPSAHWT-2) is more efficient than DPSAHWFP and DPSAHWT-1 by 4.2 % and 9.8 % respectively. [ABSTRACT FROM AUTHOR]

This research work deals with the performance of high-density polyethylene sheets arranged in splash used as a fill for a cooling tower. “A forced-draught counterflow cooling tower” of 400 mm × 400 mm cross-sectional area and 1.7m in height was built. The fill has been studied theoretically and experimentally. Air rates of 0.6, 1.2, and 1.8 kg/s.m2 were utilized with water flow rates within the range of 1 to 1.6 kg/s.m² . The overall volumetric heat transfer coefficient, volumetric mass transfer coefficient (Mt), and the tower characteristics (Mt/L) are shown to be functions of the air and water flow rates concurrently. Four available input parameters were inlet water temperature, airflow rate, water flow rate, and full height. A computer program was prepared to perform numerical analysis for reducing data sets obtained from the plant. In addition, analysis was carried out for evaluating the volumetric heat and mass transfer coefficients along with the performance coefficient. [ABSTRACT FROM AUTHOR]

The present study investigates the effect of outer diameter (10 mm and 15 mm) and 5 positions of cylindrical vortex generators (CVGs) installed to the wavy channel in order to improve heat transfer parameters in conjunction with low-pressure drops. The wavy channels with and without CVGs are compared in terms of the local heat transfer coefficient, mean Nusselt number, Colburn factor, friction, and thermal performance for Re in the range of 857 to 8001. Furthermore, the effect of the cooling air flow direction (forward and backward) is assessed. Inserting the CVGs to the channel causes the enhancement of Nusselt numbers and Colburn factors for all CVGs positions and Re in comparison with the channels without CVGs. The maximum thermal performance factor TPFB = 0.8229 was achieved for the channel with CVGs position '5' and 15 mm diameter, backward air flow, and Re = 1677. The backward air flow is more efficient compared with forward air flow since the cooling air gets into the valleys to a greater extent, and thus, better mixing of the fluid occurs. The numerical investigation, conducted with Ansys Fluent software, is compared with the experimental one acquired by holographic interferometry at good agreement of the local heat transfer coefficients. Finally, new correlating equations for the mean Nusselt number were created. [ABSTRACT FROM AUTHOR]

Homogeneity and temperature levels within a refrigerated facility are vital in preserving the quality of horticultural products throughout the cold chain to the consumer. These temperatures are affected by different factors at different scales, including the shape and thermal properties of the horticultural products, package design, pallet arrangement, or characteristics of the cold chain unit of operation. Therefore, airflow and heat transfer studies are valuable in evaluating these factors to optimize the cold chain and achieve and maintain an optimal product temperature. This paper provides an overview of the different scales of the numerical model and experimental setup used to assess the influence of the different factors on the cooling performance, as well as any challenges and limitations of each scale. The importance of considering other aspects in the cold chain studies, such as product quality, energy consumption, and package mechanical strength, will be discussed through an integrative approach. Finally, we propose new perspectives on how multi-scale modelling approaches can be helpful in tackling different challenges and how to investigate the effects of different factors on the cooling efficiency. [ABSTRACT FROM AUTHOR]

The demand for resource circulation of heat exchangers in air conditioners is expected to grow rapidly; however, the market stocking time is relatively long. Therefore, this scenario was used as a case study for sustainable products design. A material flow analysis was conducted to estimate the balance between global relative resource consumption for shipment, waste, and installed stock from publicly available information up to 2050. Based on the projected demand through 2050, the shipment volume for each year was calculated on a cooling capacity basis. From this analysis, the waste volume was calculated. Using the shipment volume on the basis of yearly cooling capacity, the shipment volume on a resource basis was calculated considering the heat transfer coefficient. The balance between the waste volume and the installed stock was estimated. The resource circulation was simulated by defining variables such as the ratio of units that can be converted from waste to shipment and the ratio of heat exchangers using circulated resources in the total number of shipments. The results indicate that the shipment, waste, and installed stock of resources projected for 2050 were greater than those at the 2021 levels by factors of 2.2, 2.8, and 2.9, respectively. In addition, they were greater than those of the 2021 levels in the scenarios by factors of 1.8, 2.2, and 2.8 accounting for the increase of heat transfer coefficient into account, indicating the importance of improvement of heat transfer. The simulation of circulation showed that a fully closed loop in 2050 would be difficult to achieve owing to the shortage of heat exchangers for waste-to-shipment. Sensitivity analysis also indicated that even under conditions where there is no predicted shortage of circulated resources for 2050, achieving the target in a short period of time may cause a rapid increase in demand for circulating resources. This would subsequently, lead to a shortage of supply compared to demand. Thus, it is important to account for these dynamics relating resource circulation and strategy planning during analysis. [ABSTRACT FROM AUTHOR]

The gas-dynamic and heat-exchange behaviours of air flows in gas-dynamic systems have a significant impact on the efficiency and environmental performance of most technical equipment (heat engines, power plants, heat exchangers, etc.). Therefore, it is a relevant task to obtain reliable experimental data and physical laws on the influence of cross-sectional shape and initial turbulence intensity on gas dynamics and the level of heat transfer. In this study, data were experimentally obtained on the instantaneous values of the local velocity and local heat transfer coefficients of stationary air flows in straight pipes with circular, square, and triangular cross-sections at different initial values of the turbulence intensity. The measurements were carried out with a constant temperature hot-wire anemometer, thermocouples, and pressure sensors. Based on the research results, data on the turbulence intensity and averaged local heat transfer along the length of pipes with different cross-sections were summarised. It has been established that turbulence intensity in a square pipe is up to 40% higher than in a round channel; in a triangular channel, on the contrary, it is up to 28% lower. After the air flow's initial turbulence, the relaxation of the flow in square and triangular pipes occurs faster than in a round channel. It is found that the initial intensity of turbulence leads to an increase in the averaged local heat transfer, which is typical of all investigated pipe configurations and initial conditions. [ABSTRACT FROM AUTHOR]

For heat rejection, small air-cooling towers are widely used in mine ventilation systems. However, the thermal efficiency of the cooling towers can be significantly affected by their geometrical arrangement and crosswind conditions. In certain ambient conditions, heated air coming from an exit of one tower can flow to intakes of other towers, which leads to a reduction in the thermal efficiency of the entire ventilation system. The aim of this study was to investigate the influence of crosswind speed and tower spacing on the temperature and moisture content of intakes of cooling towers. For this purpose, a three-dimensional CFD model of the non-isothermal turbulent flow of moist air around cooling towers is proposed. The model is based on the Reynolds-averaged Navier–Stokes equations with a standard turbulence model which are supplemented by heat transfer and moisture transport equations. The investigation of the effects of the crosswind speed and the tower spacing was carried out for two cooling towers by multiparametric numerical simulation using the CFD model. It was shown that the upstream tower protects the downstream one from the effect of the crosswind. The increase in the crosswind speed causes a rise in temperature and moisture content at the intakes of the downstream tower. The increase in the tower spacing, in general, contributes to a decrease in air temperature at the intakes of the downstream tower. However, at low crosswind speed, the heat transfer at the intakes can rise with the tower spacing due to a reduction in the protection possibilities of the upstream tower. Results of the numerical simulation of airflow around three cooling towers indicated that the increase in the number of cooling towers contributes to a rise in temperature and moisture content at the intakes. [ABSTRACT FROM AUTHOR]

The present study focused on researching a technique that can make a cooling system more efficient in terms of heat transfer. To achieve this, it is possible to modify the thermal conductivity of its cooling fluid or the structure of its flow. In this study, we have opted for the second technique. To do this, we sought to create singularities in the flow by inserting vertical and rotating baffles around the vertical. The study field is a channel of rectangular section, placed horizontally, and crossed by the incompressible and turbulent flow of a fluid (air) in forced convection. Geometrically, the physical problem describes mathematically. A system of hyperbolic equations governs it; Navier–Stokes equations derive from the laws of conservation of mass and momentum and the state's law that derives from the principle of conservation of energy. A finite volume scheme ensures the discretization of the governing equations and the numerical analysis's boundary conditions. The turbulence is modeled using the standard k-ɛ model, while the pressure–velocity coupling problem solves by applying the SIMPLE algorithm. The proposed numerical computational model validates by comparing the computed results with those of literature correlations. The model was then applied to practical cases where a Reynolds number in the range (12,000, 16,000) has chosen. The orientation angle (θ) of the baffles is chosen equal to (0°, 5°, 7°, 13°, 15°) with a different orientation direction. The calculated results are presented in map form for the different physical fields (of axial velocity, temperature) or in graphical form for the different factors and coefficients (friction factor, amount of heat removal, average Nusselt numbers, and thermal performance factor). The results obtained show that the system is made more efficient with a thermohydrodynamic behavior that varies significantly with the baffles' orientation. The heat transfer rate increased, and the pressure drops reduced. For an orientation angle of (θ = 5°), the thermal performance factor is around 2.323, and 2.45, for Re = 12,000, and 16,000, respectively. [ABSTRACT FROM AUTHOR]

The focus of this work is on developing a nonlinear grey model for the laminar flow regime of carrier fluid across the flat plate collector. The trust region reflective algorithm was used to solve the nonlinear laminar flow problem and handle the sparse matrix. The stream function, dimensionless velocity, gradients of velocity components, carrier fluid temperature, and the absorber plate temperature were estimated for a flat plate collector operated with and without a circular chimney. Similarly, the same technique was adopted to determine a model for heat transfer across the absorber plate. The numerically obtained solution was also compared with the parameters obtained through the instrumental measurement. The relative tolerance was kept at 10−5 for the white and grey box solutions. The developed model was noticed to have a smaller deviation than the conventional analytical model to predict the experimental values. The slip condition was observed for the proposed scheme. The uncertainty in the temperature measurement through the proposed model varies from ±0.53 to ±1.47 K. The minimum absolute percentage error (MAPE) lies in the domain of 0.52–1.67% for the nonlinear grey model, whereas the linear grey model for measuring absorber plate temperature has a percentage error of 0.0011–0.02%. [ABSTRACT FROM AUTHOR]

The present experimental paper is officiated to study the heat characteristics and performance of air flow through a square cross-sectional heated channel under natural heat convection conditions. The influence of baffles arrangement and perforated baffles on the rate of heat transfer through a channel are studied. Four cases of a heated channels are studied, one is a plain channel and other three channels with a baffle namely, three inline baffles, three staggered baffles and three staggered perforated baffles arrangements. The outer tested channels surfaces are electrically heated with a constant surface heat flux condition. All tested channels are fabricated by cold forming with constant dimensions using aluminum plate has thickness of 1.0 mm. The heat performance is assessed for all tested channels. The results of present paper are approved than the available data in the previous paper and a good convergence are noticed. Obtained experimental results appear that a three staggered perforated baffles arrangement is a best selection as it improves heat transfer rate in expression of Nusselt number, it higher about 22% to 27% than that the plain channel for same conditions. [ABSTRACT FROM AUTHOR]

This research proposes a new type of clear block wall (CBW) based on natural ventilation to compare the temperature reduction caused by heat transfer into a building and indoor light, increasing the ventilation efficiency. A house with a single glass wall (SGW) and another with a CBW were considered. The SGW was composed of a clear glass pane. The CBW had three block types, a translucent upper block that served to ventilate the outside, a middle block that served as the vent gap, and a lower block that acted as an air vent from the test house, and each block was 0.20 × 0.20 × 0.08 m in size. The air gap and block openings were 0.068 m in width. The experimental comparative thermal performance between the houses with an SGW and CBW had a surface area of approximately 1.60 m². The wall faced south to obtain the most sunlight in the afternoon. Data were collected every 15 minutes. The experimental results showed that the CBW could reduce heat flux through the façade wall up to 58 W/m². With the CBW, velocity field measurements indicated that the airflow rate varied between 0.010- and 0.021 m³/s. The indoor illumination level varied between 300- and 1,054 lx. The indoor temperature of the room equipped with the CBW was lower than that equipped with the SGW by 1.9°C on average and up to 2.9°C while receiving the natural light and reduced glare. A proposed configuration of the CBW is recommended for architecture. [ABSTRACT FROM AUTHOR]

Robust metal oxide particles can provide low-cost and stable thermal energy storage (TES) to temperatures up to 1200 ∘C or higher. The transfer of heat into and out of the particles in cost-effective high-temperature particle heat exchangers remains a principal challenge to implementing particle-based TES. The present work expands on prior studies of particle-wall heat transfer in narrow-channel fluidized beds operated in the bubbling fluidization regime. Batch-mode experiments with various oxide particles over a range of temperatures and airflow rates indicate that particle-wall heat transfer increases with higher bed temperature and decreasing particle size. Measured particle-wall heat transfer coefficients in a 12 mm deep channel are fit to a Nusselt number correlation proportional to a non-monotonic function of excess fluidization velocity. Particle-wall heat transfer coefficients rise rapidly with excess fluidization velocities until reaching a maximum at intermediate air velocities due to a trade-off between enhanced transverse particle mixing and decreasing particle volume fraction with increased fluidization velocity. The heat transfer coefficient reaches a maximum of ≈ 400 % of values without fluidization for oxide particles ranging in diameter d p from 159 to 408 μm. For the smallest particles tested, composed of olivine sand, particle-wall heat transfer coefficients peak above 1100 W m−2 K−1 at 450 ∘C. 100-h tests at 500 ∘C and near-optimal heat transfer fluidization velocities indicated minimal wall wear or oxide scaling. High particle-wall heat transfer coefficients suggest narrow channel fluidized beds as a potential pathway for reducing the required surface area and cost of high-temperature particle heat exchangers, as needed in large-scale thermal energy storage applications. • Particle-wall heat transfer coefficients can exceed 1000 W m−2 K−1 at 450 ∘C in a narrow channel fluidized bed. • A Nusselt number correlation captures the peak in heat transfer coefficients at intermediate fluidization velocities. • Wear testing at 500 ∘C for 100 h indicated minimal wall oxide scaling or particle attrition due to mild fluidization. [ABSTRACT FROM AUTHOR]