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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.

Accurate estimation of frictional pressure loss in an annulus is crucial for selecting appropriate pump systems, determining horsepower requirements, and controlling hole cleaning. Generally, when calculating the friction factor, the temperature of the fluid and the rotation of the inner pipe are not considered, which can lead to errors in estimating the pressure difference in the annulus. In this study, to ensure accurate pressure drop calculations, the effects of temperature and inner pipe rotation, along with other parameters, were included. An extensive experimental study was conducted at Izmir Katip Celebi University's Flow Loop using two Carboxymethyl cellulose (CMC) solutions, across various fluid velocities, fluid temperatures, diameter ratios, and inner pipe rotation speeds. A dimensional analysis was performed to identify the parameters that affect friction factors in the annulus. Finally, friction factor equations were developed based on the experimental data using optimization algorithms such as interior point (fmincon), genetic, minimax, and simulated annealing. The findings showed that the predictions from all the algorithms tested in the study closely matched the experimental results; however, the interior point algorithm (fmincon) provided the best performance, with an average absolute percentage error of 9.4%. [ABSTRACT FROM AUTHOR]

Fluid temperature is one of the most important parameters influencing the rheological properties of non-Newtonian fluid flow in pipes. If the change in fluid temperature is not considered, it can cause problems in correctly calculating pressure losses and selecting appropriate pump systems. The flow characteristics of carboxymethyl cellulose (CMC), xanthan gum (XG), and partially hydrolyzed polyacrylamide (PHPA) solutions flowing through rough pipes under various fluid temperatures are experimentally studied in this study. A comprehensive experimental study has been conducted using two different CMC solutions for three different pipe diameters, as well as two different XG solutions and two different PHPA solutions for an 80 mm pipe diameter, for fluid temperatures from 20°C to 60°C, and for Reynolds number ranges from 3×103 to 9.7×104. A new friction factor correlation is developed in fully developed turbulent flow as a function of the generalized Reynolds number, the Prandtl number, and the relative roughness to calculate the pressure loss and to select proper pump systems, considering the fluid temperature. The proposed equation obtained from the regression analysis of experimental data shows better prediction with wide ranges of Reynolds numbers and Prandtl numbers than Reed and Pilehvari's (1993) equation. Increasing the accuracy of pressure loss predictions and pump system selection, particularly in diverse temperature conditions, is of paramount importance for efficient fluid transport systems. [ABSTRACT FROM AUTHOR]

Double pipe heat exchangers, or DPHEs, are employed in the power, oil, and process sectors. They cannot handle demanding applications. They have restrictions if they have to be utilized for heavy-duty applications. To get beyond these restrictions and use them for heavy-duty applications, heat transmission must be improved. In this work, a DPHE fitted with bowl-cut twisted tapes at different scale ratios (25, 50, and 75%) width (D) of bowl-cut from the center and circulated with TiO2/CuO hybrid nanofluids (NFs) is studied to assess its friction factor, thermal performance factor and Nusselt number. The working fluid was TiO2/CuO hybrid nanofluids (NFs) at varying concentrations (0.01, 0.03, and 0.05%) with Reynolds numbers from 2000 to 12,000. The bowl-cut twisted tape's twisted ratio (H/D = 3) was kept constant. The hybrid NFs' Nusselt number improvement was 66.09% more than that of the conventional tube. For varying scale ratios, the improvement in heat transfer was found to be 83.35, 115.31, and 172% with the bowl-cut twisted tapes and hybrid NFs. It was discovered that the friction factor penalty was 8.28, 0.83, and 1.075 times greater than that of the carrier fluid. Additionally, it was noticed that the thermal performance factor (TPF) was 1.65 times higher than the original fluid. [ABSTRACT FROM AUTHOR]

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]