Search

Pin-fin cooling is a significant method for managing high temperatures in gas turbine blades during operation. This study recommends the employment of a pencil-shaped and a circular pin fin to improve the channel’s heat transfer efficiency, based on both experimental and computational examinations. Numerical simulations with Reynolds numbers ranging from 10,000 to 80,000 are used to explore and compare the flow and heat transfer properties of a wedge channel with three rows of staggered pencil and circular-shaped pin fins with a diameter of 12 mm. The investigation revealed that staggered arrangement of pencil pin fins affects flow pattern and heat transfer properties differently. Compared to the pencil pin fins, heat transfer is enhanced by 11.72%, and the pressure drop from pencil pin fins is minimized by 72.2%. Furthermore, compared to the smooth channel, the Nusselt number for circular fins shows an increase of 40%. When comparing pencil fins to the smooth channel, the Nusselt number increases by 18%. As a result compared to circular fins, the thermal performance factor increases by 35.2%. [ABSTRACT FROM AUTHOR]

This study presents the thermohydraulic performance enhancement in a triangular duct solar air heater (TSAH) using circular wing vortex generators (CWVGs) on the absorber plate using computational fluid dynamics (CFD) methodology for the Reynolds number (Re) range of 6000–21,000. The use of wing vortex generators offers relatively lower interference with the core flow region, while the circular geometry offers a smooth curved edge, which reduces multiple vortex interactions in the wake region, thereby limiting the pressure drop. This study explores the impact of flow attack angle, longitudinal pitch, transverse pitch, and diameter of CWVG on the thermohydraulic performance of TSAH. The results reveal that a lower flow attack angle exhibits enhanced heat transfer with a lower friction factor penalty. The nondimensional diameter greater than d/Dh = 0.325 tends to limit heat transfer and exhibits an increased friction factor. The transverse pitch parameter also exhibits a similar trend where the threshold nondimensional pitch is found to be 1.5. The highest improvement in Nu is 4.37 times that of smooth duct for d/Dh = 0.433, Pl/d = 1, Pt/d = 1.5 and α = 20° at Re = 6000. The highest rise in friction factor is about 10.23 times that of smooth duct for d/Dh = 0.433, Pl/d = 1.0, Pt/d = 1.5, and α = 20° at Re = 21,000. The highest thermohydraulic performance parameter (THPP) value is about 2.23 at Re = 6000, with THPP values ranging from 1.69 to 2.23 across different CWVG configurations. Finally, mathematical correlations are developed for Nu and friction factors which are in close agreement with CFD results, with deviations averaging 5.03% and 3.69%, respectively. [ABSTRACT FROM AUTHOR]

An inefficient heating system with poor air circulation can significantly hinder transfer of in an air heater. This study aims to evaluate the thermal exchange and frictional performance of air flowing inside a tube by experimenting it with various insert arrangements. According to the literature, twisted tape and helix-shaped tape inserts induce greater turbulence in the airflow, leading to higher heat transfer rates but with a copious pressure drop. Conversely, some inserts produce lower heat transfer rates but with a meager frictional pressure drop. In this study, selection of inserts was made by combining those with high heat transfer efficiency and those with low friction factors. The chosen insert configurations include Continuous Twisted tapes with square Holes (CTH), Discontinuous Twisted tapes with square Holes (DTH), Y-type inserts with holes (Y-TYPE), and Discontinuous Twisted tapes with V-shaped Winglets (DTHW). The study enumerates the functioning of an air heater with various inserts by analyzing the Nusselt number, friction factor, Thermal Enhancement Factor (TEF), and entropy generation. Experimentations were conducted at five various flow rates of air, with Reynolds numbers in the range between 30,000 and 95,000. The findings vindicate that Y-TYPE inserts achieved higher heat transfer with a lower drop in pressure when compared with other inserts. [ABSTRACT FROM AUTHOR]

The thermal lattice Boltzmann method (TLBM) is used to analyze the overall performance for upstream and downstream wedge ribs microchannels (MC) under slip flow conditions. The thermal–hydraulic enhancement criterion is investigated to evaluate the performance of the channel and compare it for various roughness MC. In order to improve the channel performance, two alternative artificial roughness geometry, upstream and downstream wedge ribs, are taken both on the top and bottom walls of the microchannel with aspect ratio (AR) 7, where AR = L/H; L and H are channel length and height respectively in micrometer (μm). This study focused on simulating temperature profiles, velocity vectors in terms of stream lines, pressure gradients, and friction factor in terms of Poiseuille number as well as heat transfer rate in terms of Nusselt number (Nu). The overall performance of the channel is calculated based on flow friction and heat transfer rate for different Knudsen numbers (Kn) ranging from 0.01 to 0.10 with upstream and downstream wedge ribs height up to 20% of channel height. The results have been compared with previously published work and are found a very good agreement. The analysis revels that, the vortices are formed behind each upstream wedge rib, whereas they are created in front of each downstream wedge rib. The size and shape of vortices are influenced by Kn. As Kn increases from 0.0 to 0.10, the fluid circulation area becomes smaller for upstream wedge ribs MC, while it is changing very slowly for downstream wedge ribs MC; hence, the pressure gradient is also responsible for changing Kn. The flow friction is linearly decreased with increasing Kn but significantly increased with ribs height. But compared to the smooth channel, the friction is significantly increased for upstream and downstream wedge ribs MC. The average rate of heat transfer in terms of Nu is also linearly decreased with increasing Kn, but Nu increased with ε for lower Kn and decreased for higher Kn. Therefore, compared to smooth MC, Nu increased and decreased for the same for upstream and downstream wedge ribs MC. Finally, the performance enhancement (η) is calculated, and it is found that η decreased with increasing Kn for upstream and downstream wedge ribs MC. The higher performances are indicated for lower Kn as well as lower ribs height. For all cases, the better performance is noted for downstream wedge ribs MC compared to upstream MC. [ABSTRACT FROM AUTHOR]

In order to reduce size and cost, the heat transfer (HT) capacity of conventional heat exchanger (HE) must be increased. Addition of nanoparticles (NPs) into parent fluids is a potentially effective method of improving HT at a manageable pressure drop. The present study was focused on the comparative analysis of thermal performance factor (TPF) between CuO–water nanofluid (NF) and ZnO–water nanofluids on double-pipe heat exchanger (DPHE) at four volume fractions (0.005%, 0.02%, 0.04%, and 0.07%) in the Reynolds number (Re) range of 5500–15000. The experiment was performed for single-phase fully developed flow in turbulent regime. The maximum enhancement in Nusselt number (Nu) for CuO–water NF was observed as 12.58% higher than ZnO–water NF for volume fraction (VF) of 0.07% at Re = 5000. Maximum augmentation in friction actor was recorded for CuO–water NF as 14.55% superior than ZnO–water NF for VF of 0.07% at lowest Re of 5500. At a Re of 5500, the maximum TPF value for CuO–water NF was found to be 2.61% greater than ZnO–water NF for 0.07% of VF. In order to develop better understanding of the behaviour of NFs, ZnO and CuO-NPs were characterized in the laboratories using XRD, HRTEM, EDS, and FTIR analysis. An empirical correlation for both Nu and friction factor (ƒ) has been developed within the range of given parameters using regression analysis. [ABSTRACT FROM AUTHOR]

A comprehensive analysis of the flow in Schwarz‐D triply periodic minimal surfaces (TPMS) structures based on CFD simulations is presented. The pressure drops and friction factor characteristics of the structure are investigated by employing both full‐scale and representative elementary volume (REV)‐scale CFD setups. The results are validated against experimental data from the literature. An analytical model is developed using hydraulic diameter, porosity, and permeability from the CFD simulation results. The findings contribute valuable insights into the optimization and application of Schwarz‐D TPMS structures in engineering systems. [ABSTRACT FROM AUTHOR]

This research study investigated the impact of various configurations of semi-circular or half-round ribs on the thermal performance and frictional factor characteristics of a rectangular duct. During this research study, the ribs were provided on the inner surface of the test section's bottom wall. Six distinct configurations of semi-circular ribs varying from continuous to hybrid arrangement were used. The range of Reynolds number was varied from 13,500 to 34,800; while the ratio of rib pitch to rib height (P/e ratio) was kept constant at 8. The ratio of the height of rib to hydraulic diameter of duct (also known as blockage ratio) was kept at 0.114. The results of experimental investigation showed that the Nusselt number ratio obtained was ranging from 1.36 to 2.74, while the friction factor ratio ranges from 1.70 to 4.51. The overall enhancement ratio for all configurations obtained was in the range of 1.06–1.80 times to that of plain duct. Among all rib configurations, the hybrid rib configuration showed superior ratio of Nusselt number and intermediate increase in ratio of friction factor as compared to all the other rib configurations. Hybrid rib configuration showed overall enhancement ratio values ranging from 1.45 to 1.80 times as compared to that of plain duct (duct without ribs) within the specified range of Reynolds number. The results of study showed that the hybrid configuration of semi-circular ribs exhibited superior overall thermal enhancement as compared to that of remaining tested rib configurations. [ABSTRACT FROM AUTHOR]

This research paper details an experimental study on airflow dynamics in a solar air heater. The heater's design incorporates unique, discrete V‐shaped ribs with staggered elements to enhance thermal performance. The study investigates the influence of various roughness parameters on flow characteristics. These parameters include a relative coarseness pitch (P/e) ratio of 12, a rib inclination angle (α) of 60°, a relative coarseness height (e/Dh) of 0.043, and a staggered element arrangement with a positioning ratio (p′/P) of 0.65. Additionally, the investigation includes scenarios with three gaps (Ng) between elements and a gap‐to‐rib width (g/e) ratio of 4. The research focuses on how changes to the Reynolds number, ranging from 3000 to 14,000, and alterations to the ratio of staggered element positioning to rib height (r/e), from 2 to 5, impact the flow dynamics. The outcomes indicate a significant boost in heat transfer performance, with the Nusselt number rising to 3.76 compared with a conventional smooth duct. The highest thermal efficiency recorded was 86%, at an r/e ratio of 3.5. These results underscore the potential of using discrete V‐ribs with staggered elements in rectangular ducts to improve heat transfer efficiency. [ABSTRACT FROM AUTHOR]

The effect of a novel ribbed wave tape on the augmentation of heat transfer in a solar air heater operating in a transitional flow regime is experimentally examined. Three different wave ratios are used, and the tube is uniformly heated using heat fluxes while the Reynolds number varied from 521 to 10,194. The transition for plain tube begins at 2810 and ends at 3724. For tube with ribbed wavy tapes, transition begins early and ends at higher Reynolds number than plain tube. For 2 kW/m2 of heat flux, the transition for wavy tape having wave ratio 3 begins at Reynolds number 2589 while at heat flux of 4 kW/m2, the transition begins at Reynolds number 2745. The end of transition takes place at Reynolds number 3969 and 4139 for wave ratio 3 at heat fluxes 2 and 4 kW/m2, respectively. The length of transition decreases with increase in the wave ratio at uniform heat flux. The average enhancement in Nusselt number for ribbed wavy tapes having wave ratio 3 at 4 kW/m2 heat flux was 262% and 85% for laminar and turbulent flow regime, respectively. Two empirical correlations were developed to predict the Nusselt number and friction factor for all the flow regimes. [ABSTRACT FROM AUTHOR]

This research paper aims to investigate the effect of frustum shape roughness geometry on the thermal characteristic (Nusselt no. and friction factor) of solar air heaters (SAH). The study includes experimental and numerical investigation of a solar air heater equipped with frustum roughened absorber plate under varying operating conditions. Frustum shape roughness element produced more disturbances and greater mixing of primary and secondary flow that resulted in greater augmentation in thermal characteristics of SAH. The investigation was conducted in varying Reynolds number range of 2500 -12,500. Dimensionless parameter for Frustrum shaped roughness is varied as relative frustum height (e/Dh) 0.013–0.054, relative frustum pitch (p/e) 8–14, Relative frustum height to base diameter (e/d1) 0.37–0.75 and relative frustum diametral ratio (d1/d2) 1–3. To save time and resources a three-dimensional numerical simulation was also performed. This simulation helped to visualize flow field behavior with the help of streamline, temperature, turbulence kinetic energy and pressure contours. Maximum performance for roughened system was obtained at optimum value of flow and geometric configuration within the range of investigated parameters. The geometric orientation of proposed roughness geometry produced tremendous rise in Nusselt number (Nu) with an acceptable rise in friction (f). Maximum enhancement in Nu for varying p/e, e/Dh, e/d1, and d1/d2 was, 4.58, 5.21, 6.62 and 6.09 times and that of friction was 5.59, 4.69, 4.92 and 4.66 times respectively over conventional smooth SAH. [ABSTRACT FROM AUTHOR]

Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department 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.)

Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department 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.)

Triply periodic minimal surfaces (TPMS) represent an innovative approach to the design of heat exchangers, enabling the optimisation of thermal and hydraulic performance. This study presents a comparative analysis of three geometric TPMS configurations: sheet gyroid, skeletal gyroid, and the newly proposed combined gyroid geometry. Using numerical analysis based on simulations of fluid flow and heat transfer, key parameters such as the heat transfer coefficient, Nusselt number, friction factor, Chilton–Colburn j-factor, and pressure drop were evaluated. The results demonstrated that the combined gyroid geometry achieves the highest heat transfer efficiency, exhibiting significant improvements in the Nusselt number and heat transfer coefficient across the entire flow range. Simultaneously, it maintains low pressure losses, making it well suited for applications demanding high thermal performance with minimal energy losses. This study highlights the potential of TPMS geometries for optimising heat exchanger design and opens new paths for their implementation in industrial systems. [ABSTRACT FROM AUTHOR]

Because of its narrow and aerodynamic design, cooling the trailing edge of a turbine blade offers an essential problem. For the trailing edge internal cooling of gas turbine blades, wedge-shaped channels are used. Pin-fin arrays play a critical role in enhancing heat transmission at the trailing edge of turbine blades. The flow and heat transfer properties of a number of wedge channels with staggered pin-fins of varied shapes are used to develop a design with a more effective heat transfer effect and reduced flow resistance. The present study compares the combination of circular pin fins and oblong pin fins in a wedge duct with a Reynolds number range of 12,000–85,000 and a constant heat flux (surface) of 3280 W/m2 applied to the bottom wall, top wall, and surfaces of the fins. The results indicate that the pressure loss is less in circular fins at the centre and oblong fins side by side, and it is 23.67 % less than circular and oblong fins in opposite positions. The Heat transfer coefficient for circular and oblong fins in opposite positions is 16.72 % higher than circular fins at centre and oblong fin side by side. The thermal performance factor is almost the same for both cases. [ABSTRACT FROM AUTHOR]

The objective of this research is to explore the characteristics of the mean Nusselt number, friction factor, and enhancement efficiency in a double pipe heat exchanger. The emphasis lies in using short twisted tapes featuring round holes and a V-shaped cut. To conduct the experiment, an IoT-based DPHE setup was employed. In the experiment, various twisted tape configurations were examined to investigate their impact on heat transfer and pressure loss. These configurations included a full-length twisted tape and three short-length tapes with different perforation diameters. The full-length tape, with a twist ratio of x / b = 4, spanned throughout length of the tube. In contrast, the plain short-length tape and modified short-length tapes, with the same twist ratio, were inserted in the section's entrance. The shorter inserts, with a length ratio (LR = ls/lf) of 0.50, were compared to the full-length tape. The experimental findings demonstrated that the short-length tapes with LR = 0.50 consistently exhibited lower thermohydraulic performance compared to full-length inserts. Specifically, within the Re range of 4000–24,000, Nusselt numbers and friction factors for the short inserts were approximately 11%, 9.1%, and 6.1% lower, and 20.6%, 16.1%, and 11.2% lower, respectively, compared to the full-length inserts. [ABSTRACT FROM AUTHOR]

This study explores the coupled effects of pressure-driven and electroosmotic flows in a soft nanochannel filled with non-Newtonian ionised liquid, where the inner walls are coated with a polymer layer. The ion partitioning effect occurs due to the Born energy, arising from the dielectric permittivity difference between the polyelectrolyte medium and the ionised liquid. The model incorporates the nonlinear Poisson-Boltzmann equation, the modified Darcy-Brinkman equation in the polyelectrolyte layer (PEL), the Cauchy momentum equation in the electrolyte domains and the continuity equation for incompressible fluids. Using the Debye-Hückel approximation for analytical results, the study validates numerical findings. The study considers the no-slip boundary condition on the walls and examines the impact of volume charge density of PEL, bulk electrolyte concentration, non-Newtonian fluid rheology and polymer layer characteristics and applied pressure gradient on flow modulation and ionic transport in the nanochannel. We provide rigorous mathematical results showing how electrohydrodynamic factors like charged PEL, flow behaviour index, EDL thickness, ion partitioning parameters, Debye-Hückel parameter and softness parameters influence the strength of the potential and the total flow modulation. We illustrate ion selectivity in the soft nanochannel and the friction factor across its walls, considering ion partitioning effects. [ABSTRACT FROM AUTHOR]

The thermal efficiency of conventional solar air heater is very low. This research article concentrates on incorporating V-shaped staggered twisted ribs over absorber surface of solar air heater. Various roughness parameters were tested to determine their effect on the Nusselt number, friction factor, thermo-hydraulic performance index, and thermal efficiency. During experiment, the Reynolds number is varied from 3000 to 21,000; while relative roughness length varied for 4.39 to 10.26 and relative staggered distance for 2 to 6. However, relative roughness pitch, twist length, and angle of attack were kept constant. The Nusselt number and friction factor of the roughened collector enhances to 3.41 and 2.56 times that of the smooth collector, respectively. The thermal efficiency of the roughened solar air heater increases to 73.64% of the roughened plate as it was noticed 42.63% for smooth surface due to breakage of the laminar sublayer. The correlations for Nusselt number and friction factor as function of Reynolds number and roughness parameters are also developed. The maximum thermohydraulic performance gained at the optimum parameters of d/e of 4 and S/e of 6.15 is 2.69. The percentage deviation between the developed correlations and the experimental findings shows very satisfactory outcomes. Therefore, it can be concluded that inclusion of twisted V staggered ribs enhances the thermal performance of solar air heater with the lowest frictional penalty. [ABSTRACT FROM AUTHOR]

This study focuses on improving heat transfer by converting one of the corners of the duct to a rounded structure. To study the effect of dimpled shaped protrusions and intrusions on the rounded corner triangular duct with a constant radius of curvature by varying relative streamwise distance (z/e) with a constant transverse distance x'/e = 10,14 and 18. Steady-state, turbulent flow heat transfer under thermal boundary conditions is to be analyzed by varying different Reynolds numbers (5600 to 21000). The duct with dimple-shaped protrusions and intrusions is compared with a simple triangular duct. Optimization of relative horizontal distance (z'/e) by keeping constant protrusion to protrusion distance as z/e = 28 and relative transverse distance as x/e = 10, 14, and 18. It was noted that there was a significant loss in friction and a rise in heat transfer. The relationship between friction factor and Nusselt number was formulated using operating and roughness parameters, using the data collected from the numerical investigation. The friction factor increases significantly with roughness elements, and it is maximum for x'/e = 20 at a low Reynolds number. Nusselt number increases with roughness elements, and it is maximum for x'/e = 14 for all Reynolds numbers and all the models. Enhancement of Nusselt number is due to increase of local heat transfer because of local vortex neat heat transfer zone. The maximum outlet temperature is obtained at a low Reynolds number. The maximum temperature of the heated surface is obtained for Rc = 0.67 h and the minimum for Rc = 0.33 h. [ABSTRACT FROM AUTHOR]

The study aims to examine how duct length affects the performance of a solar air heater (SAH) with a D‐shaped ribbed absorber plate, compared to a smooth absorber plate. The optimized D‐shaped ribs from previous research investigations are utilized in the present work to explore the absorber plate's length influence on the Nusselt number. The study reveals a slight decrease in the Nusselt number as the length of the absorber plate with D‐shaped ribs is increased. The observed behavior is attributed to the diminishing capacity of air to extract heat from the heated surface within the elongated duct. Moreover, the study calculates the pressure drop and thermo–hydraulic performance parameter (THPP) associated with the D‐shaped ribs and formulates correlations to establish a quantitative understanding of the relationship between duct length and D‐shaped rib performance. The maximum value of THPP was found to be 1.17 within the considered range of duct height. Furthermore, correlations have been derived for the Nusselt number and friction factor in terms of duct length to hydraulic diameter ratio and Reynolds number with maximum deviations of +1.7 and +2.13, respectively. These correlations serve as valuable tool for engineers and researchers seeking to optimize the design of SAHs, enabling them to balance the benefits of D‐shaped ribs with the considerations of duct length. This research contributes to the growing body of knowledge of SAH design, offering insights into the trade‐offs and intricacies of utilizing D‐shaped ribs and adjusting duct length for improved THPP. [ABSTRACT FROM AUTHOR]

Abstract The thermal lattice Boltzmann method (TLBM) is used to analyze the overall performance for upstream and downstream wedge ribs microchannels (MC) under slip flow conditions. The thermal–hydraulic enhancement criterion is investigated to evaluate the performance of the channel and compare it for various roughness MC. In order to improve the channel performance, two alternative artificial roughness geometry, upstream and downstream wedge ribs, are taken both on the top and bottom walls of the microchannel with aspect ratio (AR) 7, where AR = L/H; L and H are channel length and height respectively in micrometer (μm). This study focused on simulating temperature profiles, velocity vectors in terms of stream lines, pressure gradients, and friction factor in terms of Poiseuille number as well as heat transfer rate in terms of Nusselt number (Nu). The overall performance of the channel is calculated based on flow friction and heat transfer rate for different Knudsen numbers (Kn) ranging from 0.01 to 0.10 with upstream and downstream wedge ribs height up to 20% of channel height. The results have been compared with previously published work and are found a very good agreement. The analysis revels that, the vortices are formed behind each upstream wedge rib, whereas they are created in front of each downstream wedge rib. The size and shape of vortices are influenced by Kn. As Kn increases from 0.0 to 0.10, the fluid circulation area becomes smaller for upstream wedge ribs MC, while it is changing very slowly for downstream wedge ribs MC; hence, the pressure gradient is also responsible for changing Kn. The flow friction is linearly decreased with increasing Kn but significantly increased with ribs height. But compared to the smooth channel, the friction is significantly increased for upstream and downstream wedge ribs MC. The average rate of heat transfer in terms of Nu is also linearly decreased with increasing Kn, but Nu increased with ε for lower Kn and decreased for higher Kn. Therefore, compared to smooth MC, Nu increased and decreased for the same for upstream and downstream wedge ribs MC. Finally, the performance enhancement (η) is calculated, and it is found that η decreased with increasing Kn for upstream and downstream wedge ribs MC. The higher performances are indicated for lower Kn as well as lower ribs height. For all cases, the better performance is noted for downstream wedge ribs MC compared to upstream MC.

The objective of this study was to evaluate the performance of a lubricant by defining the value of the friction factor at the interface. Ring compression tests were performed at room temperature for a typical steel in mechanical forming applications. The samples were compressed to 10%, 25% and 40% of their initial height with a constant speed of 3 mm/min. Using the FORGE NxT2.1 finite element software, an optimization procedure was carried out to reduce the computational cost, then simulations were performed by varying the values of the friction factor so that a cost function was minimized. The cost function for this optimization considers a relationship between the internal and external diameters of the specimens for the simulated and experimentally measured cases. The results showed a good relationship between experiments and numerical analysis. After the optimization was performed, the value of the friction factor m varied between 0.001078 and 0.0873, depending on the dimensional measurement method used.

[Purposes] The injection of water and/or CO2 alters the shear characteristics of jointed rock, directly impacting the stability of the sequestered formation. Thus, the influence of water injection and CO2 injection on the shear characteristics of jointed rock mass is explored. [Methods] Shear tests were carried out on flat jointed sandstone under three test conditions: drying, water injection, and CO2 injection. The changes of shear strength with confining pressure, injected fluid type, and injection fluid pressure were investigated. [Findings] The results indicate the following: The shear stress-shear displacement curves for straight jointed sandstone under all three test conditions (dry, CO2 injection, and water injection) exhibit a sliding failure pattern; Water/CO2 injection will weaken the shear strength of straight jointed rock, and the weakening effect of water is stronger than that of CO2; The empirical formula between shear strength and confining pressure, injection fluid type, and fluid injection pressure is proposed. The average error between experimental and theoretical data is 5.69%. [Conclusions] This research work is of great significance for predicting the shear strength of sandstone after water/CO2 injection, optimizing the construction scheme, and improving the construction safety.

Owing to spatial effects and vortex flow, flow in research reactors that use plate-type fuels can be maldistributed to the parallel channels of the core, which significantly impacts the reactor safety. In this study, the core flow of an advanced research reactor was measured in a real-scale facility under various hydraulic conditions. For flow measurement, integrated pressure lines were embedded in the mockups of 22 fuel assemblies and six fission molybdenum assemblies. Each assembly mockup was individually calibrated to obtain the relationship between the pressure drop and flow rate. Real-scale facility, which implements the characteristics of the hydraulic conditions in research reactors, was then used to evaluate the assembly-to-assembly flow distribution under normal operating condition, a partially withdrawn condition for the follower fuel assemblies, no flow for the pool water management system, and 1:1.5 asymmetric inlet flow condition. As a parallel channel system, core flow distribution was analyzed with conventional header design approach. Taking into account the measuring uncertainty, the core flow was uniformly distributed within 5 % under all conditions. This was mainly because the core flow resistance was sufficiently high and the vortex flow was minimized by the perforated plate.

This investigation is conducted to analyze the artificial surface roughness influence on the heat flow and friction characteristics within the ducts of solar air heaters (SAHs). This research aims to investigate the consequences of applying spherical-shaped surface roughness to the absorber in a linear and staggered manner with the intention of enhancing the heat transfer efficiency. The utilization of roughness elements in the shape of spheres is aimed at augmenting the heat transfer characteristics; however, it is crucial to acknowledge that this enhancement is concomitant with an elevation in pumping power due to heightened friction. An experimental campaign encom- passes a diverse set of operational and device parameters. These parameters include the Reynolds number (Re), which varies from 3,000 to 8,000. Additionally, the roughness pitch-to-height ratio (p/h) ranges from 10 to 20, while the roughness gap-to-height ratio (w/h) ranges from 4 to 8. Throughout the trials, a constant value of 0.06 is maintained for the roughness height-to-hydraulic diameter ratio (h/D) and an amount of 5 is maintained for the duct width-to-height ratio (W/H). The outcomes of this study indicate a considerable increase in the Nusselt number, ranging from 50.47% to 69.51%, concurrently with a substantial rise in the friction factor, ranging from 27.76% to 144.75%, when compared to designs using a smooth absorber surface in the context of SAHs. By utilizing the experimental data, relationships between the friction factor and the Nusselt number are established based on the artificial roughness parameters and the operating conditions. The current study’s findings significantly advance our knowledge of and ability to improve SAH systems’ heat transfer and friction characteristics. Thus, this investigation improves our understanding of these systems operational behavior in many situations. [ABSTRACT FROM AUTHOR]

We state the appropriate thermodynamic and transport properties to use for the delivery of hydrogen through pre-existing natural gas distribution networks. We show that the flow is not as fully-turbulent as past work has assumed, that hydrogen makes the flow even less turbulent, and that the pipe friction calculation requires more careful treatment in this partially-turbulent regime. We propose that the relevant final energy demand is the energy delivered as heated water. The different dew points of the flue gases from hydrogen versus natural gas combustion affect the boiler efficiency. This impacts the relative amount of hydrogen required to be delivered. We find that to deliver the same amount of useful energy as hot water, hydrogen requires a gas velocity of 3.076 × and a pressure gradient that is 1.29 × higher. The compression power increase required to deliver hydrogen through the low pressure network can be up to 7.85 × that for natural gas, depending on the flow regime. • Replacing natural gas with hydrogen reduces the Reynolds number. • Hydrogen flue gas changes the efficiency of a condensing boiler. • Replacing natural gas with hydrogen increases the pressure drop 1.29x. • The changing efficiency of condensing boilers affects how much hydrogen is needed. • The Blasius parameter ρ 3 / 4 ⋅ μ 1 / 4 has a very low temperature dependence. [ABSTRACT FROM AUTHOR]

The contact stiffness of the mechanical joint usually becomes the weakest part of the stiffness for the whole machinery equipment, which is one of the important parameters affecting the dynamic characteristics of the engineering machinery. Based on the three-dimensional Weierstrass–Mandelbrot (WM) function, the novel normal contact stiffness model of the joint with the bi-fractal surface is proposed, which comprehensively considers the effects of elastoplastic deformation of asperity and friction factor. The effect of various parameters (fractal dimension, scaling parameter, material parameter, friction factor) on the normal contact stiffness of the joint is analyzed by numerical simulation. The normal contact stiffness of the joint increases with an increase in the fractal dimension, normal load, and material properties and decreases with an increase in the scaling parameter. Meanwhile, the fractal parameters of the equivalent rough surface of the joint are calculated by the structural function method. The experimental results show that when the load is between 14 and 38 N∙m, the error of the model is within 20%. The normal contact stiffness model of the bi-fractal surface joint can provide a theoretical basis for the analysis of the dynamic characteristics of the whole machine at the design stage. [ABSTRACT FROM AUTHOR]

Solar energy as prime energy source draws attention of world due to its availability and eco-friendliness. Low performance of solar air heater create curiosity for researchers to increase its performance. To enhance performance of solar air heater active and passive techniques used by researcher. Surface modification is one of the most prominent passive techniques to improve the performance. Present experimental and numerical investigation explore thermal characteristics of two-sided curvilinear rib roughened solar air heater. An indoor experiment was performed on two side curvilinear rib roughened absorber plate having constant heat flux of 1000 W/m2. Parallelly 2-dimensional numerical simulation was also performed to explore flow behavior and to complete investigation within optimum cost. ANSYS Fluent 2021.R was used for performing this simulation with K-ε RNG model with enhanced wall treatment. Velocity inlet and pressure outlet was selected as boundary condition. Main roughness and flow parameters were relative roughness height (e / D h = 0.21–0.042), relative roughness pitch (p / e = 7.14–35.71), and Reynolds number (Re = 3800–18,000). Maximum value of Nusselt number improvement ratio and friction factor improvement ratio was 3.17 and 3.26 at roughness and flow parameter of (e / D h = 0.042, p / e = 15, Re = 15,000) and (e / D h = 0.042, p / e = 7.14, Re = 3800) respectively. Thermohydraulic performance parameter achieved its maximum value of 2.77 at e / D h = 0.042, p / e = 17.85, and Re = 18,000. [ABSTRACT FROM AUTHOR]

The roughness height plays a crucial role, especially in shallow‐water environments with rough‐bed conditions. Specifically, it is a key parameter for predicting flow velocity and bed shear stress. Therefore, an accurate determination of roughness height is essential for precise predictions of hydraulic phenomena. In this study, we propose a method to estimate form roughness height and friction factor using bathymetry data, with a focus on cross‐sectional data in the transverse direction. To overcome the limitations of using lateral direction data, we derived an empirical formula for estimating bedform length from the bed profiles in the streamwise direction. To assess the validity of bedform analysis and estimated form roughness height based on lateral direction data, we compared the characteristics of bedform and form roughness height analysed using lateral direction data with those analysed using the streamwise direction data. Furthermore, we confirmed the importance of considering the form roughness height in estimating bed shear stress through a comparison with bed shear stress calculations considering only grain roughness height. [ABSTRACT FROM AUTHOR]

Lubricants are necessary for metal forming to avoid direct contact, adhesion, transfer, and scratches from materials and tools. It is also essential for increasing tool durability and reducing energy use. The work aims to study the effects of lubricants and billet geometry on the extrusion of AA6063/5% SiCp. The lubricants were used such as graphite, zinc stearate, and molybdenum disulphide. The friction factor has been determined by the lubricant effect and billet geometry. The simulation was done for the lubricated condition which was compared with experimental results. It was found that improved billet quality was obtained by the graphite-lubricated 12:8 configuration die profile. Also, the friction factor for the graphite-lubricated 12:8 configuration dies profile was 10.5% less compared to other configure profiles. Scanning electron microscopy was used to investigate the surface of the lubricated extruded component, and samples were examined utilizing energy-dispersive X-ray analyses. [ABSTRACT FROM AUTHOR]

Plate heat exchangers have served various industrial applications for decades, with brazed plate heat exchangers (BPHE) emerging as preferred choices due to their favorable operating conditions. While extensive research has been conducted on flow patterns in gasketed plate heat exchangers, similar studies for BPHE have been lacking, given their analogous geometry. However, recent years have witnessed a surge in research focusing on single and multi-phase flow dynamics. Advancements in computational fluid dynamics (CFD) have furthered our understanding by providing insights into flow and heat transfer patterns, while also reducing the need for costly experimental tests of different geometries. This has facilitated the adoption of parametrization, bolstered by the feasibility and accuracy of numerical models. Nevertheless, substantial research remains to be undertaken to develop comprehensive models capable of integrating multiple geometric and flow parameters. This article examines existing research on BPHE and outlines potential areas for future exploration to address current research gaps. [ABSTRACT FROM AUTHOR]

The utilization of solar air heaters are significant due to its capacity to diminish the reliance on fossil fuel-based power usage, hence mitigating pollution and conserving energy. The thermal-performance of a solar heater was analyzed using experimental simulations. Different types of artificial roughness, such as delta-winglet-vortex generators, ribs, or a combination of ribs and delta-winglet, were tested in a single-pass solar air heater. The objective of this study is to identify the optimal design that maximizes the thermal efficiency of a solar air heater. The relative roughness height-ratio remains constant at 0.6, although the pitch ratio is fixed at 10 and various attack angles are used. The experimental investigation was conducted within a range of Reynolds numbers (5000-14000). The usual levels of irradiance varied as 330 W/m2 - 850 W/m2. Based on the results, the average bulk temperature of the roughened solar air heater was 37% greater than that of a smooth SAH under peak sun irradiation. The inclined ribs at a 60° angle exhibited superior thermal efficiency compared to the other instances. These ribs covered a greater surface area and greatly enhanced the convective heat-transfer rate. [ABSTRACT FROM AUTHOR]

This research work aims to optimize double pipe heat exchanger performance using Taguchi, ANOVA, and ANN. Experimental trials involved varying ferric oxide nanoparticles, cut radius, and volume-based flow rate. Twisted tapes with ratios of 3, 5, and 7 were placed within the tube. Assessed heat transfer characteristics included h, Nu, ff, and thermal performance factor. Taguchi, ANOVA, and ANN optimization techniques were applied to the experimental data. A Taguchi optimization using an L9 orthogonal array focused on input attributes (Vol % of nanoparticles, flow rate, radius of cut), with output attributes being heat transfer co-efficient (h), Nusselt number (Nu), friction factor(ff) and thermal performance factor. Results revealed a notable flow rate effect on enhancing h, Nu, and ff, while the addition of nanoparticles significantly influenced thermal performance. Taguchi and ANOVA were conducted using MINI Tab and ANN was implemented through MATLAB. Test data demonstrated that nanoparticle dispersants in nanofluid significantly improved heat transfer properties, consistent with the noteworthy improvement indicated by optimization techniques. The convective heat transfer coefficient parameter showed improvement with a coolant flow rate of 50.29% and a volume of nanoparticles at 27.32%. The enhancement of Nusselt number (Nu) was influenced by a coolant flow rate of 50.34% and a volume percent of nanoparticles at 34.25%. The thermal performance factor was significantly influenced by the volume percent of nanoparticles (79.75%) and the radius of cut (3.83%). The experimental data aligned well with findings from Taguchi and ANN. [ABSTRACT FROM AUTHOR]

The research aimed to explore the thermal performance of a miniature hexagonal tube heat sink (MHTHS) by utilizing three different binary nanofluids. These nanofluids incorporated nanoparticles such as MgO, Al2O3, and CuO, dispersed in base fluids of de-ionized water (DIW) (80 %) and ethylene glycol (EG) (20 %) at different concentrations (0.5 vol %, 1.0 vol %, 1.5 vol %, and 2.0 vol %). Variations in volume flow rate (VFR) and temperature spanned from 10L/h to 50L/h and 10 °C to 50 °C, respectively. Throughout the study, nanofluids circulated through the hexagonal tube side (HTS) at VFR ranging from 10L/h to 50L/h, while hot DIW flowed through the mini passage (MPS) at a constant VFR of 30L/h. Notably, CuO–DIW/EG nanofluid exhibited an 8.7 % increase in density, and MgO–DIW/EG nanofluids demonstrated a 14 % increase in thermal conductivity at a particle concentration of 2.0 vol %. However, at a higher particle concentration of 2.0 vol %, MgO–DIW/EG nanofluids exhibited a 5.6 % decrease in specific heat. Furthermore, MgO–DIW/EG nanofluids displayed a 79.6 % increase in heat transfer coefficient and a 66.7 % increase in Nusselt number. Although the pumping power and friction factor showed 5.1 % to 20.4 % and 7.5 % increases in particle concentration and Reynolds number, this negative impact did not affect the overall thermal performance of the heat sink. Finally, the study determined that MgO–DIW/EG nanofluid stands out as the most suitable heat transfer fluid for the heat sink. [ABSTRACT FROM AUTHOR]

This work examines the fluid flow, heat transfer, and thermal hydraulic performance of turbulent flow through a horizontal pipe integrated with TT that has various cut shapes using numerical analysis. In the current investigation, trapezoidal-cut geometry with single and double cuts is adopted. Three-dimensional simulations have been validated using experimental data from the literature. The equations have been solved using the RNG k-ε model and the finite volume method (FVM). With three distinct types of twisted tape (PT, SC, and DC) and TR (4.0, 6.4, and 8) for a heat flux of 5000 W m−2, the computational findings have been carried out in the range of Reynolds numbers 4000 ≤ Re ≤ 8000. Impact of these factors on Nusselt number, friction factor, and thermal performance are explored and compared to plain pipe under similar conditions. The addition of trapezoidal-cut TTs leads to enhanced mixing of fluid due to swirl flow generation. The result shows that average Nusselt number and friction factor are functions of TR. The thermal performance factor (TPF) for double-cut trapezoidal TT is about 1.2–1.65 which is maximum compared to single-cut and plain TT inserts. [ABSTRACT FROM AUTHOR]

During solar cell operation, most light energy converts to heat, raising the battery temperature and reducing photoelectric conversion efficiency. Thus, lowering the temperature of solar cells is essential. Nanofluids, with their superior heat transfer capabilities, present a potential solution to this issue. This study investigates the mechanism of enhanced heat transfer by nanofluids in two-dimensional rectangular microchannels using the two-phase lattice Boltzmann method. The results indicate a 3.53% to 22.40% increase in nanofluid heat transfer, with 0.67% to 6.24% attributed to nanoparticle–fluid interactions. As volume fraction (φ) increases and particle radius (R) decreases, the heat transfer capability of the nanofluid improves, while the frictional resistance is almost unaffected. Therefore, the performance evaluation criterion (PEC) of the nanofluid increases, reaching a maximum value of 1.225 at φ = 3% and R = 10 nm. This paper quantitatively analyzes the interaction forces and thermal physical parameters of nanofluids, providing insights into their heat transfer mechanisms. Additionally, the economic feasibility of nanofluids is examined, facilitating their practical application, particularly in solar cell cooling. [ABSTRACT FROM AUTHOR]

This study delved into the efficacy of enhanced oil production (EOP) within perforated horizontal wellbores across diverse flow profiles. The authors implemented five distinct configurations, encompassing uniform radial air injection (profile 1) and variable radial air injection (profiles 2–5), with a particular emphasis on the concomitant production of liquid and air phases. Additionally, the study examined the frictional behavior along the perforated wellbore. Liquid production was demonstrably amplified throughout the bubble, plug, and slug flow regimes; however, a decline was observed in the stratified, stratified transition, and stratified wave flow regimes. Notably, the liquid product exhibited a direct correlation with both the mixture flow rate and its associated Reynolds number, signifying an increase with holdup and a decrease with void fraction. Conversely, air production displayed a positive association with a higher air flow rate. Overall, profiles 2 and 4 yielded the most favorable production during the bubble, plug, slug, and stratified flow regimes. In contrast, profile 3 emerged as the optimal configuration for the stratified transition and stratified wave flow regimes. The friction factor remained relatively constant with profile 1, experienced a reduction in profile 2, and exhibited an escalation in profile 3. Additionally, it increased in the middle of profile 4 and decreased at the center of the perforated section in profile 5. The friction factor behavior of profile 1 remained stable and smooth due to the invariant air flow rate throughout the perforated section. Conversely, some fluctuation was observed in profile 2 due to the inherent variability of the radial air injection along the perforated section. Importantly, the experimental and numerical results demonstrated satisfactory agreement across all flow patterns, with some minor discrepancies noted in the static pressure drop behavior during the bubble, dispersed bubble, and slug flow regimes. [ABSTRACT FROM AUTHOR]

This study investigates the performance of a double pipe heat exchanger utilizing TiO2/H2O nanofluid at different concentrations (ϕ = 0.05%, 0.15%, and 0.5%) and v-cut twisted tape inserts with varying width-to-depth ratios (w/h) and rectangular tooth depth to depth of v-cut ratios (z/h). Experimental tests are conducted with hot water at 70 °C and cold water in the range of 30–32 °C, covering Reynolds numbers from 6000 to 13,000 for double pipe flow. Twisted tape with a width-to-depth ratio of w/h = 0.67 increases the Nusselt number by 68.75% compared to a plain tube. Furthermore, combining this twisted tape configuration with a rectangular tooth depth to depth of v-cut ratio of z/h = 0.14 leads to an even greater enhancement of 84%. Introducing TiO2/water nanofluid at a concentration of 0.5% alongside the aforementioned twisted tape arrangement results in a significant increase of 123.64% in the Nusselt number. These findings highlight the positive impact of both twisted tape inserts and nanofluid on heat transfer performance. The friction factor increases up to 7.1 times in the absence of nanofluid, while including nanofluid (0.5% concentration) raises it significantly to 15.41 times relative to a plain tube. Importantly, the established correlations show good agreement with experimental results, with deviations within ± 10% for both the Nusselt number and the friction factor. These findings validate the reliability of the proposed correlations. Overall, this study highlights the effectiveness of toothed v-cut twisted tape inserts and TiO2/water nanofluid in enhancing heat transfer performance in double pipe heat exchangers. [ABSTRACT FROM AUTHOR]

Pin fin arrays, which have a high heat transfer capacity and minimal pressure loss, are currently being used as the primary cooling technique for the turbine trailing edge cooling channel used in modern gas turbines. To enhance the heat transmission efficiency of the channel, this study proposes the use of a circular-shaped pin and a teardrop pin, through both experimental and numerical investigations. The numerical simulations conducted in the Reynolds number range of 10,000 to 80,000 are used to investigate and compare the flow and heat transfer parameters of a wedge channel which has three rows of staggered circular-shaped and teardrop-shaped pin fins with a diameter of 12 mm. The experiment showed that teardrop pin fns with staggered arrangement has different effect on flow pattern and heat transfer characteristics. Heat transfer is increased by 10.45% when compared to the circular pin fins and the pressure drop of teardrop pin fins is reduced by 54.6%.Therefore thermal performance factor exhibits a 25.4% increase when compared to circular fins. [ABSTRACT FROM AUTHOR]

Accurate prediction of the friction factor is fundamental for designing and calibrating fluid transport systems. While the Colebrook–White equation is the benchmark for precision due to its physical basis, its implicit nature hinders practical applications. Explicit correlations like Churchill's equation are commonly used but often sacrifice accuracy. This study introduces two novel modifications to Churchill's equation to enhance predictive capabilities. Developed through a rigorous analysis of 240 test cases and validated against a dataset of 21,000 experiments, the proposed Churchill B(Re) and Churchill B(V,ε) models demonstrate significantly improved accuracy compared to the original Churchill equation. The development of these functions was achieved through generalized reduced gradient (GRG) nonlinear optimization. This optimized equation offers a practical and precise alternative to the Colebrook–White equation. The mean relative errors (MRE) for the modified models, Churchill B(Re) and Churchill B(V,ε), are 0.025% and 0.807%, respectively, indicating a significant improvement over the original equation introduced by Churchill in 1973, which exhibits an MRE of 0.580%. Similarly, the mean absolute errors (MAE) are 0.0008% and 0.0154%, respectively, compared to 0.0291% for the original equation. Beyond practical applications, this research contributes to a deeper understanding of friction factor phenomena and establishes a framework for refining other empirical correlations in the field. [ABSTRACT FROM AUTHOR]

The present investigation employed computational techniques to analyze the heat transfer and fluid-flow properties of a Cu-water nanofluid moving through a rectangular micro-channel. The upper wall of the micro-channel is thermally insulated, while the lower wall is equipped with a ribbed surface maintained at a greater temperature than the fluid entering the channel. The governing equations were discretized using the finite volume method and solved using the ANSYS-FLUENT 16.0 CFD software. The study investigated the influence of many parameters, such as the Reynolds number (20 ≤ Re ≤ 200), volume percentages of nanoparticles (1% ≤ φ ≤ 8%), and rib height. The numerical results demonstrate that when the height of the ribs rises, e = 20 μm, e = 30 μm, and e = 40 μm, the contact surface area between the ribs and the nanofluid similarly increases. As a result, the friction factor of the heated surface rises, regardless of whether the Reynolds numbers are low or high. Furthermore, numerical analysis suggest that the average friction factor diminishes as the Reynolds number rises for all rib heights. Ribs in the micro-channel facilitate improved mixing, resulting in heightened heat transfer. The impact is intensified by augmenting the concentration of nanoparticles and the Reynolds numbers at all rib heights. [ABSTRACT FROM AUTHOR]

Computational fluid dynamics (CFD) simulations were employed to model a novel double sine wave corrugated heat exchanger surface. The turbulent flow within the heat exchanger channels was simulated using the k - ω SST model for the corrugated cases. In contrast, a laminar model was applied to the flat plate heat exchanger without corrugations. The simulation results demonstrate that 3D-printed polymer heat exchangers are effective for heat transfer, with the double-sine wave corrugated surface outperforming the single-sine wave corrugated surface. Specifically, the double sine wave configuration achieved a 20% higher Nusselt number and a 15% lower friction factor than the single sine wave, indicating superior thermal-hydraulic performance. Optimal performance was observed with low amplitude and frequency of the sine waves, suggesting that small protrusions and wider-spaced corrugations enhance heat transfer without significantly increasing pressure drop. These findings have significant implications for the design of efficient and cost-effective heat exchangers, particularly in applications where both thermal performance and energy efficiency are critical. Further experiments with full-scale heat exchangers are necessary to validate these results and explore practical applications. [ABSTRACT FROM AUTHOR]