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• Numerical modeling of an integrated refrigerated container. • Different cargo pallet arrangements and cargo packaging boxes are tested. • Airflow short-circuiting has both positive and negative effects on cargo cooling. • Improving vertical airflow in cargo pallets enhances cargo cooling than air gaps. Improving the performance of a refrigerated container is crucial in effectively preserving thermal-sensitive cargo. The combined effect of vertical airflow resistance and airflow short-circuiting in air gaps play a vital role in cargo cooling. This study numerically investigates the effects of cargo vertical airflow resistance and air gaps between cargo pallets using two commonly used apple packaging boxes, each stacked in six different cargo pallet arrangements. A heat transfer enhanced refrigerated container design and a numerical model developed from the present authors' previous studies are used. The numerical model uses the porous medium model to incorporate the refrigeration unit and cargo within the refrigerated container. Additionally, the numerical domain includes the T-bar floor in the refrigerated container. Initially, the airflow characteristics based on vertical airflow resistance and air gaps are discussed. Then, the corresponding effects on cargo cooling are addressed. Results show that the air gaps between the cargo pallets have positive and negative effects on cargo cooling. In cargos with lower vertical airflow resistance, an increase in air gaps leads to reduced cargo cooling and elevated temperature non-uniformity. Conversely, cargos with higher vertical airflow resistance experience increased cooling rates and reduced temperature non-uniformity with the increase in air gaps. However, avoiding airflow short-circuiting through the air gaps between the cargo pallets and improving the vertical airflow inside the cargo pallets can provide better cargo cooling, which outweighs the positive cooling effect of the air gap. [ABSTRACT FROM AUTHOR]

The application of turbulators to improve thermal performance and thermal enhancement in heat exchangers because of the significance of energy management and optimization is one of the interesting topics for researchers. Analysis of aerodynamic turbulator in internal flow has been less discussed in previous studies. Therefore, the present work focuses on the effect of a perforated sphere turbulator in a circular pipe with square, circular, oval, and hexagonal geometry holes on turbulent flow characteristics and thermal performance. These turbulators are placed with equal obstruction against the flow of air passing inside the pipe at Re = 6000–24000 in wall conditions of constant heat flux. Ansys Fluent software is used for numerical solutions, and the results are validated with an experimental paper. According to the results, the hexagonal geometry creates less pressure drop than other geometries. The thermal performance in the pipe with innovative aerodynamic turbulators is improved compared to the smooth pipe and the pipe equipped with conventional turbulators. The highest thermal performance of 1.256 is obtained for the turbulator with an oval hole. Also, the range of Nusselt number compared to the plain pipe for turbulator with circular, hexagonal, square, and oval holes increases by 1.97–2.46, 2.24–2.65, 1.58–1.89, and 2.48–2.81 times, respectively. The effect of the proposed new turbulators was compared with previous studies in this field, and the results are promising. [ABSTRACT FROM AUTHOR]

Unsteady gas-dynamic phenomena in pipelines of complex configuration are widespread in heat exchange and power equipment. Therefore, studying the heat transfer level of pulsating air flows in round and triangular pipes with different turbulence intensities is a relevant and significant task for the development of science and technology. The studies were conducted on a laboratory stand based on the thermal anemometry method and an automated system for collecting and processing experimental data. Rectilinear round and triangular pipes with identical cross-sectional areas were used in the work. Flow pulsations from 3 to 15.8 Hz were generated by means of a rotating flap. The turbulence intensity (TI) of the pulsating flows varied from 0.03 to 0.15 by installing stationary flat turbulators. The working medium was air with a temperature of 22 ± 1 °C moving at a speed from 5 to 75 m/s. It was established that the presence of gas-dynamic unsteadiness leads to an increase in the TI by 47–72% in a round pipe and by 36–86% in a triangular pipe. The presence of gas-dynamic unsteadiness causes a heat transfer intensification in a round pipe by 26–35.5% and by 24–36% in a triangular pipe. It was shown that a significant increase in the TI of pulsating flows leads to an increase in the heat transfer coefficient by 11–16% in a round pipe and a decrease in the heat transfer coefficient by 7–24% in a triangular pipe. The obtained results can be used in the design of heat exchangers and gas exchange systems in power machines, as well as in the creation of devices and apparatuses of pulse action. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis of a finned heat exchanger fed with synthetic refrigerant R410a and environmentally friendly refrigerant R290. Analyses of the performance of the heat exchanger operating as an evaporator in a refrigeration system were carried out. Simulation studies were performed using SOLIDWORKS software with the Flow Simulation library. The analysis was conducted for various design parameters of the device. The performance of the exchanger was examined for different fin materials (aluminium alloys: alloy 1060, 1060-H12, alloy 2014, alloy 2024), number of fins (78 and 39), and fin spacings (2.5 mm and 5 mm). The studies were conducted under various operational parameters of the exchanger (varying volume flow of air and refrigerant mass flow). Based on the results obtained, it was found that the material of the exchanger does not significantly affect its performance. The next conclusion is that when the heat exchanger is fed with an environmentally friendly refrigerant, the heat transfer surface area can be reduced by 50%. As a result, the reduction in heat transfer surface area can be achieved by increasing the fin spacing, which will reduce the electricity consumed in the defrost process under operating conditions, or by reducing the size of the exchanger, which will positively translate into a reduction in the weight of the refrigerant in the system. The possibility of reducing the dimensions of the heat exchanger by up to 50% indicates that replacing R410a refrigerant with environmentally friendly R290 is a promising direction for development. It advocates for ongoing investigations to refine these systems and maximize the operational advantages presented by natural refrigerants. [ABSTRACT FROM AUTHOR]

uDALES is an open-source multi-physics microscale urban modelling tool, capable of performing large-eddy simulation (LES) of urban airflow, heat transfer, and pollutant dispersion. We present uDALES v2.0, which has two main new features: (1) an improved parallelisation that prepares the codebase for conducting exascale simulations and (2) a conservative immersed boundary method (IBM) suitable for an urban surface that does not need to be aligned with the underlying Cartesian grid. The urban geometry and local topography are incorporated via a triangulated surface with a resolution that is independent of the fluid grid. The IBM developed here includes the use of wall functions to apply surface fluxes, and the exchange of heat and moisture between the surface and the air is conservative by construction. We perform a number of validation simulations, ranging from neutral, coupled internal–external flows and non-neutral cases. We observe close agreement with the relevant literature, both in cases in which the buildings are aligned with the Cartesian grid and when they are at an angle. We introduce a validation case specifically for urban applications, for which we show that supporting non-grid-aligned geometries is crucial when solving surface energy balances, with errors of up to 20 % associated with using a grid-aligned geometry. [ABSTRACT FROM AUTHOR]

The primary heat transfer source in the conventional multi-cylinder drying of paper and board is conduction. Conduction is facilitated by high-tension contact with steam-heated cylinders, while convective drying, the main mass transfer source, operates as heated air flows over the article web in the pockets. This conduction process occurs at elevated temperatures and contact pressures to ensure effective contact between the wet paper web and the heated cylinders. The contact pressures and temperatures of the hot surface significantly influence the conductive drying characteristics. This research paper presents an experimental study that involves designing a simple lab-scale setup with in-situ and continuous sensing capabilities for various commercially available grades of paper and board. Embedded thermocouples measure the temperatures of the heated platen and the sheet, allowing the collection of flux data to determine heat transfer characteristics. The goal of this study is to ascertain the instantaneous contact coefficients for different basis weights as a function of moisture content. The acquired data will provide valuable insights and information toward process development, design, and simulation of the article drying process. [ABSTRACT FROM AUTHOR]

The cooling problem of hot-end components has become an important factor restricting the aero-engine performance, life and reliability. In order to improve the cooling quality of the cooling air, the supercritical aviation kerosene was used as a heat sink to cool the cooling air in a spiral heat exchanger. The flow and heat transfer process of the air-oil heat exchanger with spiral tube were numerically simulated using Fluent software. The flow and heat transfer situation of air and aviation kerosene were analyzed in detail. The optimized spiral heat exchanger with the diaphragm was presented to enhance the heat transfer capacity of the air side. It is found that the heat transfer performance of the air-oil heat exchanger is greatly enhanced by the spiral tube due to the secondary flow effect. With the increase in the turning angle of the spiral tube, the effect of the secondary flow for the heat transfer enhancement is strengthened. The PEC index of the spiral heat exchanger increases with the increase in the air flow rate. The spiral heat exchanger with the diaphragm can effectively improve the heat transfer performance of the heat exchanger, and increase the PEC index of the air side by more than 20%. [ABSTRACT FROM AUTHOR]

Chinese Baijiu industry is undergoing industrial modernization. However, the key processes including Daqu processing are directly modified based on empirical knowledge, and the lack of engineering mechanisms lead to the inability of rational design. Here, this study quantitatively analyzed the heat generation and flow during Daqu solid-state fermentation, tracked and recorded the parameters during Daqu processing, simplified the biochemical reactions of the fermentation process, and built a Daqu heat balance model. Through the model, the heat generated during the whole fermentation process was transferred outside of the system through three ways: Water evaporation (54. 22% ), conduction of wall and air flow (42. 00% ), and air temperature rising ( < 1% ). The remaining heat (3. 77% ) was the cumulative heat, which was positively correlated with the temperature rise of the Daqu ( R² =0.85). It was verified that the average error of the model for the temperature change of dacquoise was 5. 05% with R² = 0. 94. Based on the model, the effect of regulating moisture parameters on the temperature of Daqu was explored, which showed the importance of moisture control for regulating the temperature during Daqu preparation. Through the preliminary exploration of the feasibility of regulating and optimizing the future production of Daqu from the perspective of mathematical modeling, the results of the study can provide theoretical support for the construction of modern fermentation process. [ABSTRACT FROM AUTHOR]

In engineering phase-change phenomena are found in a multitude of applications, ranging from refrigeration and air conditioning to steam turbines and petroleum refining. This study investigates the flow of moist air in a circular duct where water vapour condenses in contact with the cold wall of the duct. The investigation delves into the relationship between the condensation mass transfer rate, the heat transfer between the bulk flow and the wall, and the temperature of the wall. The volume of fluid model coupled with the Lee evaporation-condensation model was employed. Five simulations were carried out, involving different wall temperatures while maintaining the same inlet conditions. Condensation was more pronounced at lower wall temperatures, which aligns with the expectations. The heat transfer between the bulk flow and the wall decreased with the decreasing temperature difference. Interestingly, the findings revealed that the surface heat transfer coefficient increased as the wall temperature approached the temperature of the bulk flow. The success of the study suggests potential applications in optimising thermal management systems, with implications for industries where accurate predictions of moisture behaviour and heat transfer are crucial. [ABSTRACT FROM AUTHOR]

In order to have a heat transfer per volume, heat exchangers have to have high overall heat coefficient. The effects of a transverse wedge on the heat transfer, the pressure drop, and the thermal efficiency factor (TEF) of air flow through a tube bundle heat exchanger was investigated. TEF increases continuously with the wedge aspect ratio (α). Form α = 0.275, 0.550, 0.758 to 1, TEF increases continuously from 1.157 to 1.84, 1.11 to 1.72, 1.05 to 1.42, and 1.02 to 1.39 for x/L = 1/3, 2/3, 1, and 0, respectively. [ABSTRACT FROM AUTHOR]

Snow avalanche run-out is controlled by flow regime, which is heavily dependent on snow temperature and water content. Existing avalanche models calculate temperature change and snow melting arising from frictional work, snowcover entrainment and particle collisions, but ignore the influence of the ambient air temperature. Here, we propose an experimentally-based relationship to describe the sensible heat flux between the flowing avalanche and the ambient air. A snow avalanche case study and a sensitivity analysis are performed using the proposed model. Modeling results suggest a marginal contribution of heat to the avalanche core, but one, that nonetheless can have significant effect on avalanche runout. For wet (warm) avalanches, higher air temperature will amplify water lubrication effects, leading to longer avalanche run-out. Warmer air temperatures also influence the behaviour of dry, cold avalanches, as the presence of meltwater increases snow cohesion, restricting the formation of strong powder clouds and reducing the avalanche run-out. Colder air temperatures facilitate the formation of more fluidized powder snow avalanches with long run-out and strong air-blasts. The proposed model quantifies the temperature change in the avalanche and can be included in avalanche hazard assessments in which temperature and flow regime are important elements, including the understanding of air temperature and avalanche flow in a changing climate. [ABSTRACT FROM AUTHOR]

In this paper, a novel air‐cooled supercapacitor thermal management system (STMS) based on the corner deflectors and the inclined inlet and outlet was proposed. The temperature and velocity fields were simulated and analyzed by CFD. Moreover, the heat dissipation effect of different STMSs was analyzed against each other. The results showed that the STMS proposed had a better heat dissipation effect when the inclined angle of inlet and outlet was appropriate, in which the maximum temperature (Tmax) and the maximum temperature difference (ΔTmax) of the module could be reduced by 10.3% and 34.6%. And it is shown that the structure with inclined inlet and outlet plays an important role for the heat dissipation capability of the STMS proposed. And it has experimentally proven its heat dissipation ability. Consequently, the impacts of inclined angle (α), monomer spacing (dc), and the distance between monomer and module shell (dx, dy, and dz) on the heat dissipation effect were deeply analyzed. For the STMS arranged in four rows and three columns, it had a better heat dissipation effect when inclined angle was in the range of 40° to 50°. The results showed that the structural parameters had a large influence on the Tmax and ΔTmax. Besides, it had shown that the temperature curves of the Tmax and ΔTmax had a main trend of “decreasing and then increasing” when the monomer spacing as well as the distance between monomer and module shell are taken from 1 mm to 5 mm. It implies that a small spacing (1 mm to 2 mm) will hinder the air circulation and reduce heat dissipation, and a large spacing (3 mm to 5 mm) will reduce the average flow rate of air and reduce the efficiency of heat transfer. [ABSTRACT FROM AUTHOR]

Breaking laminar sub-layer and creating turbulence flow is the main characteristic of solar air heater to increase heat transfer. Several geometries have been employed, and their effect on heat transfer has been studied by researchers. These effects are studied in form of Nusselt number (Nu) and friction factor (Fr) rise and correlations for them are developed. In current experimental study, a novel geometry in shape of rhombus is used as roughness. Rhombus shape is selected because of its feature of v shape and converging nature on its end sides which helps to guide the flow of air and offer more secondary flow and less resistance. The geometrical and flow parameters are varied as number of elements (W/Vr), relative diagonal length (dr/e), Reynolds number (Re), relative roughness height (e/Dh), relative roughness pitch (P/e) within range of 8–12, 6–13.33, 2500–14200, 0.0202–0.0337 and 6–14, respectively. Variation of 258–378% and 215–148% more compared to smooth plate is achieved for Nu and Fr, respectively. Nu increases when values of P/e increases and attains maxima at P/e = 10, e/Dh = 0.03375, W/Vr = 10 and dr/e = 9.6. Experimental correlations are grounded in actual data making them applicable to real-world scenarios and practical applications. The deviation between Nu and Fr calculated from the correlation and experimentation was ± 12% and ± 10%, respectively. [ABSTRACT FROM AUTHOR]

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]

This paper compares the performance of a vertical-finned microchannel heat exchanger (VMHX) and a 2-row fin-tube heat exchanger (FTHX) under wet and frosting conditions. The VMHX features vertically oriented fins with an extension at the windward side and parallel microchannel tubes, allowing for efficient water drainage and better performance than conventional microchannel heat exchangers with parallel serpentine fins. However, the performance of the VMHX has not been sufficiently compared to that of FTHX. After conducting experiments under specific operating conditions, the VMHX exhibits better water drainage performance than the FTHX at higher inlet air velocities, higher maximum heat flow, and time-integrating heat flow under certain operating conditions. Although the heating time is relatively shorter than the 2-row FTHX, these results suggest that the VMHX may be a more suitable option for applications requiring efficient water drainage and heat transfer. Additionally, the operating conditions significantly affect the heat exchanger's performance. The performance of VMHX is analyzed under different inlet air velocities, inlet air temperatures, and evaporation temperatures. The results indicate that frost itself had no effect on the heat exchanger performance and that the decrease of the inlet air flow rate was the main factor that decreased the heat exchanger performance. Overall, the results of this study provide valuable insights into the performance of VMHX and FTHX under wet and frosting conditions and the impact of various operating parameters on VMHX performance. These findings can inform the development of more efficient and reliable heat exchangers for various applications. [ABSTRACT FROM AUTHOR]

In heating processes using superheated steam, a practical heat transfer model for predicting the change in the material temperature taking condensation/evaporation into consideration is required. This study observed the behavior of condensed water and verified a simple but practical heat transfer model to predict the heating time of materials. The one-dimensional model, which comprehensively includes the conductive, convective, radiative, and latent heat fluxes, was utilized. For simplicity, film condensation was assumed. To conduct experiments covering a wide humidity range, the humidity of the airflow was regulated by mixing superheated steam with high-temperature air. The sample material having 50 mm of length, 50 mm of width, and 10 mm of thickness was placed under this airflow, and the change in temperature over time was measured. During the initial stages of heating via superheated steam, condensation, and subsequent evaporation were observed. The time required for the evaporation of condensed water increased with the humidity, owing to the large amount of condensed water. The ending time of evaporation was successfully estimated within about −30% error. Although some modifications will be required in the future, the model is expected to be a powerful tool in various industries where superheated steam is applied. [ABSTRACT FROM AUTHOR]

This paper explores the influence of design variations on the electrical and thermal efficiencies of PV/T (Photovoltaic-Thermal) systems. Utilizing COMSOL Multiphysics, three different PVT configurations with varying air duct designs were studied. The results demonstrated significant enhancements in both electrical and thermal efficiencies, with the PVT-3 configuration outperforming PVT-1 and PVT-2. Specifically, PVT-3, incorporating fin-shaped air ducts, exhibited the lowest recorded panel temperature of 55 °C, indicating improved electrical efficiency and thermal performance. Also, PVT-3 achieved the highest average thermal efficiency of 46.35% and the best electrical performance of 13.91%. Furthermore, the study highlights ameliorated airflow dynamics and uniformity within the ducts, particularly with the redesigned air inlet. These findings underscore the importance of design innovations in optimizing temperature management and energy output in PVT systems. It is worth noting that the tests were conducted under identical operating conditions, including air velocity, inlet temperature, ambient temperature, and solar irradiation. [ABSTRACT FROM AUTHOR]

The present study focuses on heat transfer in ventilated caves for which the airflow is driven by the temperature contrast between the cave and the external atmosphere. We use a numerical model that couples the convective heat transfer due to the airflow in a single karst conduit with the conductive heat transfer in the rock mass. Assuming dry air and a simplified geometry, we investigate the propagation of thermal perturbations inside the karst massif. We perform a parametric study to identify general trends regarding the effect of the air flowrate and conduit size on the amplitude and spatial extent of thermal perturbations. Numerical results support the partition of a cave into three regions: (a) a short (few meters) diffusive region, where heat mainly propagates from the external atmosphere by conduction in the rock mass; (b) a convective region where heat is mainly transported by the air flow; (c) a deep karst region characterized by quasi‐constant temperatures throughout the year. Numerical simulations show that the length of the convective region is approximately proportional to the amplitude of the flowrate annual fluctuations divided by the square root of the cave radius. This result is tested against field data from a mine tunnel and two caves. Our study provides first estimates to identify climate sensitive regions for speleothem science and/or ecosystemic studies. Plain Language Summary: Karsts are landscapes formed from the dissolution of soluble rocks. The chemical erosion due to rainwater results in the formation of an extensive network of caves traversed by air and water flows. Understanding heat transfer in karst is a key issue in many fields, as diverse as study of underground biota or paleoclimate reconstruction. The present work focuses on heat transfer in ventilated caves for which the airflow is driven by the temperature contrast between the cave and the external atmosphere. In winter, the air inside the massif is hotter (and thus lighter) than the air outside. This situation results in an upward airflow as in a chimney. The airflow is reversed in summer (colder and thus heavier air inside the massif). Assuming a simplified geometry, we investigate by numerical simulations the propagation of thermal perturbations inside a single ventilated conduit. The results of the numerical simulations are tested against field data from a mine and two caves. We show that in ventilated caves, the airflow can propagate the annual temperature fluctuations over distances from the entrance ranging from a few tens to a few hundreds of meters. In extreme cases, it could go up to kilometers. Our study provides first estimates to identify climate sensitive regions for speleothem science and/or ecosystemic studies. Key Points: A numerical model was developed to investigate heat transfer inside ventilated caves driven by chimney effectThe airflow can propagate annual temperature fluctuations over a few tens to a few hundreds of meters from the cave entrance (over kilometers in extreme cases)The distance of propagation (the convection length) is approximately proportional to the airflow rate and inversely proportional to the square root of the cave diameter [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]

This study focuses on the development of an advanced high heating rate thermobonding process for the manufacture of preforms and the metrological characterisation of the process. The process involves passing hot air, driven by pressure differential, through a textile stack consisting of several plies of a quadraxial fabric coated with a binder. Heat is transferred into the stack and into the binder by forced convection, melting the binder. The process is used in the same way to cool the stack and binder so that the plies are bonded together. The pressure differential compacts the stack. The comprehensive methodological characterisation of the process includes first determining the air permeability of the stack and thus the volume flow of air as a function of the number of plies stacked. Further characterisation focuses on a comprehensive determination of the heating behaviour in the individual plies as a function of time, using thermocouples and thermal imaging to determine the temperatures of hot air and textiles. These are compared and related using a mathematical approach as different values have been found. The results indicate high heating rates, reducing process time by at least 85% compared to previous binder activation methods. In addition, the cantilever method assesses the flexural stiffness of the processed stacks and shows a twofold improvement in bond strength compared to uncompacted stacks. Results and discussions include orifice based volume flow determination, thermography calibration, mathematical modelling, stiffness of bonded textile plies, process comparison, process control and potential energy savings. [ABSTRACT FROM AUTHOR]

This paper presents the results of thermal performance study of a solar air heater having absorber plate with inclined fins fitted in equilateral triangular flow passages in parallel using the governing equations under transition to turbulent flow and compares the same with the conventional solar air heater having low aspect ratio rectangular air flow duct at equal pumping power condition. The equal pumping power condition for the equilateral triangular passages of width w and rectangular duct height H has been found to be w = 2.65 H. The finned absorber plate solar air heater has been found to provide 7.3-25.8% better thermal efficiency than the conventional air heater because of the substantial increase in the effective heat transfer surface area due to the fins. The effects of variation of design, ambient, and operating parameters on the performance of the finned solar air heater show that the triangular passage width w must be increased with the increase in the collector length L to satisfy the condition of equal pumping power according to the relation w³/L2.75 = constant. The results of the present study can be utilized for the development of enhanced-performance finned solar air heater with triangular passages. [ABSTRACT FROM AUTHOR]

The roughness geometry has been introduced to improve the rate of heat transfer in a solar air heater duct. In the current work, circular and triangular shape geometries are used as roughness elements in the rectangular channel to enhance the thermal performance of reversed flow solar air heater (RFSAH). The important parameters selected for the research are Reynolds number (Re = 5000-18,000 (5 values)), pitch ratio (P/e = 4-12 (5 values)), and height ratio (e/D = 0.0392-0.1571 (4 values)). A 2D-computational fluid dynamics (CFD) model was developed using ansys (fluent 2022r1), and simulation was performed using the (RNG) turbulence model and validated with one set of experimental results for smooth duct and previous research. The findings revealed that the highest value of heat transfer was augmented about 2.18 times and 2.35 times for circular and triangular roughness geometry, respectively, as compared to the smooth channel at a Reynolds number of 12,000. The thermohydraulic performance factor (TPF) is 1.58 and 1.7 at pitch ratios of 6 and 5 for circular and triangular roughness geometry respectively, at Re of 12,000. [ABSTRACT FROM AUTHOR]

Rapid development of the anomalous enhancement of separated turbulent Re = 6000 air flow and heat transfer in an in-line single-row package of 31 inclined grooves, 0.2 in dimensionless depth, in a singled-out longitudinal region of the wall of a narrow channel is studied. It is due to the interference of vortex wakes behind the grooves and the acceleration in the channel flow core with the formation of a zone of ultrahigh longitudinal velocity. The wave-shaped parameter characteristics are stabilized in the region of approximately 15th groove, whereupon the oscillation amplitudes are moderately reduced. The return flows in the grooves are enhanced with distance from the entry section, the minimum negative friction diminishing from −2 to −4. The total relative heat removal from the structured region increases at q = const by a factor of approximately 2.75 and by the factor of two at T = const with increase in the relative hydraulic losses by the factor of 1.7, as compared with the case of a plane–parallel channel. The relative heat removal from the surface bounded by the contour of the 20th inclined groove amounts to 3.7 (q = const) with increase in the hydraulic losses by the factor of 2.2. An increase in the local maximum of the longitudinal velocity up to a factor of 1.5, as compared with the mean-mass velocity, can be observable. [ABSTRACT FROM AUTHOR]

fThe traditional solar air heater (SAH) has poor thermal performance due to low heat transfer coefficient. Artificial roughness, flow passage alteration, absorber modification, etc. can enhance it. Thus, an experimental investigation is performed to study the thermohydraulic characteristics of a reverse flow SAH with perforated absorber and delta wing (DW) structure. The present study investigates the effect of attack angle (15°–75°) at constant streamwise pitch (35 mm), transverse pitch (70 mm), height (h), and width (w) of DW 20 mm, under Reynolds number (Re) ranging from 4000 to 20 000. The perforation index (PI = ADW/Aap) for inline and staggered arrangements are 9.52 and 4.76, respectively. The results indicate that the concept of perforated absorber and DW leads to enhanced heat transfer, reduced pressure drops, and enhanced utilization of solar energy. The Nusselt number (Nu), friction factor (f), and thermohydraulic performance enhance about 6.6, 9.4, and 3.06 times, respectively, at attack angle 75o for inline arrangement of DW over the smooth duct. Thermohydraulic performance of reversed‐flow SAH is compared with previously published works, and it highlights that the full‐length inline and staggered arrangement of the DW offers the most significant improvements in heat transfer and friction factor. [ABSTRACT FROM AUTHOR]

This study prepares an experimental examination of thermal and hydraulic analysis of an absorber plate integrated with different arrangements of twisted turbulators, including longitudinal, transversal, and oblique orientations. These arrangements are considered for both the integral and the interrupted turbulators over Reynolds number range from 9174 to 55048. Nu ratio and f ratio range from 1.15–2.21 and 1.73–7.79, respectively. The interrupted turbulators with oblique arrangements with the attach angles of 30° and 60° come in the second and third places, respectively, and the maximum criterion value in the latter cases is 1.29 and 1.21. [ABSTRACT FROM AUTHOR]

This study investigates time-dependent free convection heat transfer and buoyancy-assisted flow over a horizontal heated plate within a vertical channel for two distinct scenarios: one stand alone and second involving tilted plates and varying plate positions. The temperature difference between the plate and air induces buoyant airflow. The study explores the impact of plate tilt angles and positions on time-dependent heat transfer coefficients due to varying buoyant airflow. The primary focus of the research for both classes of study is on the effects of the tilt angles (which control the change in flow blockage ratio) and positions of the heated plate on the time-dependent heat transfer coefficients due to the time-dependent buoyant airflow. As the blockage ratio increases and the positions of the heated plate in the vertical channel decreases, the influence of time-dependent buoyancy on the time-dependent Nusselt number weakens. The time-dependent Richardson's number varied from 7.4 to 9.6 throughout the tests. Based on the experimental data gathered from corresponding flux geometries and test conditions, the CFD model was validated. We have also developed a set of empirical correlations for predicting time-dependent Nusselt numbers for a time-dependent Rayleigh number range of 2000 < Ra < 7500, the dimensionless height of the heated plate from 0.507 ≤ ϕ ≤ 0.551, and a flow blockage ratio of 0.08 ≤ χ ≤ 0.024. At orientations where γ = π/2 and γ = π/4, it has been observed that the heat transfer at position ∅ 1 is higher, whereas at γ = 0 orientation, ∅ 1 heat transfer value is lower compared to the others. When the time required for the heated plate at all positions (∅) to reach thermal equilibrium with the ambient environment is compared with respect to orientation angles, it has been observed that the γ = π/2 orientation angle reaches thermal equilibrium in the shortest time compared to the γ = π/0 and γ = π/4 orientation angles. [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]

uDALES is an open-source multi-physics microscale urban modelling framework, capable of performing large-eddy simulation (LES) of urban airflow, heat transfer, and pollutant dispersion. We present uDALES v2.0, which has two main new features: 1) an improved parallelisation that prepares the codebase for conducting exascale simulations; and 2) a conservative immersed boundary method (IBM) suitable for an urban surface that does not need to be aligned with the underlying Cartesian grid. The urban geometry and local topography are incorporated via a triangulated surface with a resolution that is independent of the fluid grid. The IBM developed here includes the use of wall functions to apply surface fluxes, and the exchange of heat and moisture between the surface and the air is conservative by construction. We perform a number of validation simulations, ranging from neutral, coupled internal-external flows and non-neutral cases. Good agreement is observed, both in cases in which the buildings are aligned with the Cartesian grid and when they are at an angle. We introduce a validation case specifically for urban applications, for which we show that supporting non grid-aligned geometries is crucial when solving surface energy balances, with errors of up to 20 % associated with using a previous version of uDALES. [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]

This research presents a detailed transient experimental and computational study of heat transfer and airflow in a scaled room linked with a double-duct vertical roof solar chimney (SC). The analysis was made in the coupled system, varying the heat flux supplied to the roof SC absorber during the day. Experimental temperature profiles were obtained at six different depths and heights, the empirical heat transfer coefficient was computed for the SC absorber, and the variation of air changes per hour was determined. A good agreement between experimental and numerical temperature profiles and average Nusselt number (Nut) is shown in the latter of average difference of 3.41%. The validated computational model was used to analyze the effect of the transient heating of the SC on temperature fields and flow patterns in the thermal system. Almost symmetrical temperature and y-velocity profiles are formed in the ducts at different hours of the day, with thermal boundary layers of about 4 mm. Correlations of the Nusselt number and air changes per hour (ACH) are provided as a function of the modified Rayleigh number. [ABSTRACT FROM AUTHOR]

The setting machine exhaust gas contains a large number of fiber particles and micro oil droplets, which are adhesive and flammable. This leads to difficulties in waste heat recovery of the exhaust gas. In this article, numerical and experimental studies of a non-uniform plate heat exchanger with dimples/protrusions for waste heat recovery of setting machines are carried out. Based on the three-dimensional fluid-thermal-structural coupling method, the regenerative process between gas and air are investigated numerically with low Reynolds number turbulence model. The effect of the structural parameters (protrusions diameters, protrusions spacing and plate spacing) and operation parameters (air inlet temperature, gas and air flow rate) on the heat transfer performance are discussed. The multi-objective optimization of the plate regenerator is conducted by Box-Behnken Design and Nondominated Sorting Genetic Algorithm II to maximize the thermal performance coefficient and minimize entransy dissipation number. It is found that when D1, H1 S1, D2, H2, S2 are 9 mm, 7 mm, 161 mm, 9 mm, 8 mm and 153 mm respectively, the heat exchanger has the best heat transfer performance. Compared with the original model, the heat transfer rate of the optimized heat exchanger is increased by 3.9%, the thermal performance coefficient of the air side and flue gas side is increased by 5.7% and 5.9% respectively, and the entransy dissipation number is reduced by 24.6%. [ABSTRACT FROM AUTHOR]

Anomalous heat transfer enhancement in turbulent separated air flow over a long groove of moderate depth made in a plate inclined at an angle of 45° to the freestream is revealed both experimentally and numerically. The region under investigation includes a rectangle heated to 100°C by saturated water vapor. The Reynolds number varied from 103 to 3 × 104. Using the gradient heatmetry the twofold increase, as compared with the case of a flat plate, of the heat transfer coefficient on the groove bottom is established at the Reynolds number Re = 3 × 104. The relative Nusselt number in different regions of the groove is determined both in the physical experiment and in the RANS calculations with the application of multiblock computational technologies and the SST model in the VP2/3 software package. The results are in good agreement in the turbulent flow regime at Re = (5, 10, and 30) × 103. [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]

Air-based photovoltaic thermal(PVT) solar collectors can convert solar energy into both electrical and thermal energy. However, the output efficiency was often low due to the limitation of the heat transfer capacity for air. Therefore, in this paper, an air-based PVT with the application of a novel rib was modeled and numerically simulated. The innovation of this paper was proposing a novel rib, which was based on the Venturi effect. First, the effects of the new rib control parameters on the performance of the PVT system were analyzed using orthogonal design tests. The result showed that the thermal efficiency of the best factors combination test was 51.16% when the solar radiation was 500W=m²and the air inlet rate was 0:09m=s. Second, analyzing the fluid flow characteristics and the enhanced heat transfer mechanism, this study found that the increased air velocity under the novel rib and the low-velocity vortex formed between the rib both negatively affected heat transfer. Consequently, this paper proposed a novel fin design coupled with curved fins to address the issues with the novel rib design, which achieved 55.12% thermal efficiency with the combination structure. Finally, we applied the combined structure to the PVT system, studied its thermal efficiency under real-world conditions, and compared it with the empty channel collector. The results showed significant improvement, with a 16.38% increase in thermal efficiency and the model exhibited excellent, stable performance. [ABSTRACT FROM AUTHOR]

With the increasing number of high-temperature mines, there has been a growing focus on research into thermal environment management and prediction in long-distance ventilation roadways. Mastering the principles of heat transfer in roadways is crucial for enhancing ventilation performance and achieving energy savings in mine heat hazard control. A onedimensional ventilation ultra-long roadway with high precision and low weight is presented in this study, which accurately depicts the dynamic heat transfer between the airflow and three-dimensional surrounding rock (SR) of roadway. The calculation time of the one-dimensional roadway numerical model is reduced by over 90%. The accuracy of the proposed numerical model is verified by the heat convection within roadway wall and the heat transfer in SR. In addition, the evolution of the temperature field and Nusselt (Nu) number of ultra-long roadway wall regarding ventilation time and periodic fluctuation of initial temperature of airflow (TA) are analyzed. The results indicate that the temperature of SR and Nu number of ultra-long roadway wall both periodic changes with the fluctuation of TA, and the TA and Nu number of ultra-long roadway wall fluctuate in opposite phases. When the TA temperature ranges from 15 to 25°C, the Nu number of ultralong roadway wall changes in the range 90 in a year. The Nu number of ultralong roadway wall decreases with the increase of ventilation distance. Additionally, the TA in ultra-long roadway exhibits a linear relationship with both the initial TA, the thermal conductivity of SR, and the initial temperature of SR, but it is subject to negative exponential decay in relation to ventilation speed. As the length of the roadway increases, fluctuations in the initial TA have less impact on the thermal environment within the longdistance ventilation roadway, while ventilation speed, thermal conductivity of SR, and initial temperature of SR become more influential factors. [ABSTRACT FROM AUTHOR]

This research is mainly concerned on studying the effects of heating surface area of immersing heater and particles size of bed packing on values of heat transfer coefficient (HTCs) under different air flow rates. Experiments were conducted in a gas-solid fluidized bed to study the steady-state heat transfer between gas and solid, along with the surface of the bed at various velocities, ranging from static bed to fluidized bed conditions (0.024– 0.387 m/s). The bed column was 172 mm in diameter and 1000 mm in height, attached with a horizontal heating tube of different diameters (19.5, 25.4, and 30 mm). Three different sizes of sand particle were employed (i.e. 200, 300 and 400 µm). HTCs are shown to rise with fluidizing air velocity while exhibiting a reverse association with particle size. The influence of heating tube diameter on HTC has been examined with remarkable fluctuations revealing the bed's hydrodynamic characteristics. [ABSTRACT FROM AUTHOR]

Unsteady gas-dynamic phenomena in pipelines of complex configuration are widespread in heat exchange and power equipment. Therefore, studying the heat transfer level of pulsating air flows in round and triangular pipes with different turbulence intensities is a relevant and significant task for the development of science and technology. The studies were conducted on a laboratory stand based on the thermal anemometry method and an automated system for collecting and processing experimental data. Rectilinear round and triangular pipes with identical cross-sectional areas were used in the work. Flow pulsations from 3 to 15.8 Hz were generated by means of a rotating flap. The turbulence intensity (TI) of the pulsating flows varied from 0.03 to 0.15 by installing stationary flat turbulators. The working medium was air with a temperature of 22 ± 1 °C moving at a speed from 5 to 75 m/s. It was established that the presence of gas-dynamic unsteadiness leads to an increase in the TI by 47–72% in a round pipe and by 36–86% in a triangular pipe. The presence of gas-dynamic unsteadiness causes a heat transfer intensification in a round pipe by 26–35.5% and by 24–36% in a triangular pipe. It was shown that a significant increase in the TI of pulsating flows leads to an increase in the heat transfer coefficient by 11–16% in a round pipe and a decrease in the heat transfer coefficient by 7–24% in a triangular pipe. The obtained results can be used in the design of heat exchangers and gas exchange systems in power machines, as well as in the creation of devices and apparatuses of pulse action.

Particle-to-supercritical carbon dioxide (sCO2) heat exchanger is a critical component in next-generation concentrating solar power (CSP) plants. The inherently low heat transfer between falling particles and sCO2 imposes a challenge toward economic justification of levelized cost of electricity produced through solar energy. Introduction of integrated porous media with the walls bounding particle flow has the potential to enhance the overall particle-to-sCO2 heat exchanger performance. This paper presents an experimental study on heat transfer characterization of additively manufactured lattice frame material based on Octet-shaped unit cell with particles and air as working fluids. The lattice structures were additively manufactured in stainless steel (SS) 316L and SS420 (with 40% bronze infiltration) via Binder jetting process, where the lattice porosities were varied between 0.75 and 0.9. The mean particle diameters were varied from 266 µm to 966 µm. The effective thermal conductivity and averaged heat transfer coefficient were determined through steady-state experiments. It was found that the presence of lattice enhances the effective thermal conductivity by 2-4 times when compared to packed bed of particles alone. Furthermore, for gravity-assisted particle flow through lattice panel, significantly high convective heat transfer coefficients ranging from 200 W/m2K to 400 W/m2K were obtained for the range of particle diameters tested. The superior thermal transport properties of Octet-shape-based lattice frame for particle flow makes it a very promising candidate for particle-to-sCO2 heat exchanger for CSP application. [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 effect of the boundary conditions of the first and second kind on the predicted characteristics of anomalous heat transfer intensification in the case of turbulent low-velocity air flow over an inclined groove in the hot wall of a narrow channel is numerically investigated. It is shown that the isothermality conditions lead to a considerable underestimation of the thermal efficiency of a surface structured with narrow grooves, compared with the conditions of heat flux constancy. [ABSTRACT FROM AUTHOR]

To investigate the effects of under‐clothing airflows on the thermal protection performance (TPP) and thermal aging of flame‐retardant fabrics, we constructed an under‐clothing air‐gap ventilation device based on the TPP tester. This device can generate different levels of airflow velocities such as 0.17, 1.0, and 2.0 m/s. The flame‐retardant fabrics were exposed to a heat flux of 30 kW/m2 to simulate an indoor fire scene. The impacts of under‐clothing airflows on the heat transfer behaviors of fabrics were analyzed with the temperature rise measured by thermocouples. The thermal aging behavior of the fabric was investigated based on the outer‐shell morphology, mass loss, and residual tensile strength. The results of this study indicated that the under‐clothing airflow enhanced the TPP of flame‐retardant fabric and the best TPP was achieved under the airflow of 1.0 m/s. Under‐clothing airflow increased the post‐thermal‐exposure mass loss of the fabric but did not further decrease the tensile strength. Higher severity thermal aging occurred for 2.0 m/s airflow than for 1.0 m/s airflow. The findings of this study are important for TPP prediction for firefighters' clothing and will help optimize firefighters' clothing design. [ABSTRACT FROM AUTHOR]

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