Friction Factor Research Articles

Heat transfer and flow characteristics of a plate-fin heat sink equipped with copper foam and twisted tapes

The objective of this paper is to present new heat transfer enhancement approaches in plate-fin heat sinks (PFHS) using copper foam and twisted tapes. The motivation behind these concepts is to reduce pressure drop while enhancing heat transfer compared to PFHSs fully inserted with copper foam. The impact of twisted tape type, twist ratio, and Reynolds number (Re) on the heat and flow behaviors inside the PFHS equipped with copper foam (PFHSCF) is investigated. Copper foam has a porosity of 0.932 and a pore density of 40 pores per inch. Stationary and rotating twisted tapes with twist ratios between 2.7 and 4 are tested at Re between 3000 and 6000. The experimental results indicated that the pressure drop of the airflow inside a PFHS equipped with copper foam and a stationary twisted tape (PFHSCF_STT) as well as a PFHS equipped with copper foam and rotating twisted tapes (PFHSCF_RTT) decreased by an average of 34.8 % and 37.9 %, respectively, compared to a PFHSCF. When the twist ratio is decreased from 4 to 2.7, the thermal resistances of PFHSCF_STT and PFHSCF_RTT are reduced by 14.2 and 14.8 %, respectively. Based on assessment, the thermal-hydraulic performance of a PFHSCF_RTT with twist ratios of 2.7 and 3.3 is higher than that of a PFHSCF. To facilitate practical applications, correlations are proposed to predict the Nusselt number and friction factor. Additionally, considering the outcomes of the current study, conducting numerical investigations on the thermal performance of PFHS under different pore densities of copper foam and wider twist ratios of twisted tapes is recommended to determine optimal working conditions for future research.

Contribution to the Thermal and Hydraulic Study of Forced Convection in Corrugated Configuration Using Nanofluids

In this article, a research on characteristics of the flow and heat transfer of SiO2, Al2O3 and CuO nanoparticles with 5% of volume fraction, in a right and wavy channel with different shapes (trapezoidal, triangular, square) was conducted. Water, glycerin, and ethylene glycol are among the base fluids investigated. Constant temperature was imposed on the top and bottom of the ducts. The investigation covers Reynolds numbers between 100 and 5000 and the particle diameter is 30 nm. The governing equations are resolved using the SIMPLE algorithm, which is based on the finite volume method. The effects of channel shape, base fluids and shape of nanoparticles on the fluid flow and heat transfer are investigated. The findings say that as the Reynolds number increases, the friction factor reduces and the average Nusselt number rises. Also, in comparison to the triangular, straight and square channel, the trapezoidal-corrugated channel provides greater convective heat transfer. Moreover, the total entropy generation and the entropy due to heat transfer decreases with a rise in the Reynolds number unlike that the generation of entropy due to friction increases with the rise in the Reynolds number. When Reynolds’ number rises, the number of Bejan falls. Furthermore, against other base fluids, the nanofluid SiO2-glycerin improves the most heat transferring. The spherical shape gives the highest convective heat transfer performance as opposed to the cylindrical shape. The numerical results from this investigation were used to create two correlations. The current findings are compared to those found in the literature, and there is a strong agreement.

Efficiency and mass optimization for space nuclear power systems with closed Brayton cycle loops

Space nuclear power systems should be strictly limited in mass and size. Lack of detailed designs, mass estimation in the general design phase usually relies on simple and empirical models that leave too much design margin from the limits. Accurate mass estimation of space nuclear power systems is key to minimize the design margin and maximize the system performance in the general design phase. In this paper, new mass estimation models are proposed for the main components of space nuclear power systems, including nuclear reactor, shield, turbine, compressor, heat exchanger, and thermal radiator. The mass estimation models are more accurate by incorporating principles of nuclear physics, thermal hydraulics, and structural mechanics to the component designs. Combined with thermodynamic models and genetic algorithm, the MEGREZ code is developed to optimize the system performance by setting efficiency and mass as dual objectives. The code verification results indicate that the deviations between and the Jupiter Icy Moons Orbiter project parameters and the code calculated values are only 0.4% for system efficiency and 2.1% for system mass. The optimization for the Jupiter Icy Moons Orbiter project shows that the optimal molecular weight of helium-xenon mixture is the minimum value for single-stage turbomachinery limits. Additionally, the impacts of potential technological degradation, such as increased heat exchanger thermal resistances, higher frictional factors, and decreased turbomachinery efficiency, on system performances are discussed. The results show that turbomachinery efficiency presents the strongest influence on the system-specific mass; a 0.04 reduction in the polytropic efficiency of the compressor or turbine results in more than a 10% increase in system-specific mass.

Acclimatize experimental approach to adjudicate hydraulic coefficients under different bed material configurations and slopes with and without weir

The primary purpose of this study was to evaluate the hydraulic coefficient of coarse aggregate grain size beds and hydraulic parameters under random and perpendicular bed configurations, as well as to explore the discharge coefficient for rectangular weirs. The research objectives were to compare flow resistance coefficients, evaluate the discharge coefficient for rectangular weirs, investigate the relationship between roughness coefficient and hydraulic parameters, and validate the theoretical hydraulic equation for the rectangular weir. This was achieved by analysing different bed configurations, bed slopes, and 20 and 30-mm bed materials. Sieve analysis was conducted on bed materials using American-standard sieves to determine their particle size distribution. The experiment was performed in a rectangular flume measuring 12 m in length, 0.31 m in width, and 0.45 m in depth. In a laboratory experiment, water was pumped into a flume using centrifugal pumps, and a rectangular weir was attached downstream for discharge measurement. The experiment investigated factors such as Manning roughness coefficient, bed material geometry, bed slope, and weir shapes. Approximately 1680 tests were conducted to analysed the impact of these factors on discharge and the coefficient of discharge. The average Manning's roughness coefficients for a grain size of 20 mm were 0.019 (with weir) and 0.019 (without weir) in a random bed configuration, and 0.028 (with weir) and 0.027 (without weir) in a perpendicular flow bed configuration. For a grain size of 30 mm, the coefficients were 0.023 (with weir) and 0.022 (without weir) in a random bed configuration, and 0.033 (with weir) and 0.026 (without weir) in a perpendicular flow bed configuration. The presence of a weir has affected Manning's roughness coefficients and discharge coefficients. With a weir, the roughness coefficients have generally been higher compared to without a weir, indicating increased roughness in the channel. The discharge coefficient for a rectangular weir with a grain size of 20 mm ranged from 0.39 to 0.84 (random bed) and 0.27 to 0.68 (perpendicular flow bed), while for a grain size of 30 mm it ranged from 0.31 to 0.81 (random bed) and 0.23 to 0.48 (perpendicular flow bed). The discharge coefficients have varied depending on the grain size and bed configuration, reflecting different flow efficiencies over the weir. Rough particles influenced flow and Manning's roughness coefficient value, then reduced discharge and velocity values. Under two bed configurations and slopes, beds with a grain size of 30 mm have higher roughness coefficients compared to those with a grain size of 20 mm. The models have shown that the roughness coefficient is inversely proportional to the discharge and directly proportional to the tailgate water levels. The coefficient of roughness and discharge coefficient are mainly influenced by the channel slopes, bed roughness, bed grain size, and bed configuration. A randomly configured bed with a 20 mm grain size gravel bed is preferred over a perpendicular bed configuration to handle high discharges. Using a 20 mm grain-size gravel bed in open-channel flow is more suitable than a 30 mm grain-size bed. Relying on the constant friction factor, Manning's n, is not recommended as it may result in design errors. These findings have the potential to improve hydraulic engineering design practices, enhancing the accuracy and efficiency of open-channel flow systems.

Experimental and numerical investigation of hydrothermal performance of a microchannel heat sink with pin fins

The hydrothermal performance of the microchannel heat sinks with different pin fins (PF-MCHS) is studied experimentally and numerically. Five pin fins, namely rectangular pin fin (RPF), backward triangular pin fin (BTPF), forward triangular pin fin (FTPF), diamond pin fin (DPF) and ellipsoidal pin fin (EPR) are integrated in the microchannel for enhancing heat transfer. The results show that the PF-MCHSs possess 51.8–94.8 % higher average Nusselt number than the conventional microchannel (CMC) without pin fins, which indicates that these pin fins all can cause significant heat enhancement in the microchannels. Among all finned microchannels, the MC- RPF and MC-BTPF can offer the larger Nusselt number than the other microchannels. In addition to the improved thermal performance, the pin fins also result in the larger apparent friction factor. Furthermore, taking the MC-RPF and MC-BTPF as examples, three non-dimensional parameters α = P/L, β = wp/hc and γ = lp/hc are proposed for optimizing the global characteristics of microchannels. The rise of Nussle number and apparent friction factor is often accompanied by a decrease in α, or an increase in β and γ.

Effect of Upwind and Downwind Directions of Right-Trapezoidal Winglet-Vortex-Generators in a Solar-Air-Heater

Two directions of right-trapezoidal winglet vortex generators, namely, upwind and downwind directions, were numerically investigated to understand how they affect the thermo-hydraulic performance of the heat exchanger in a solar air heater. The results showed that the Nusselt number, friction factor, and thermal enhancement factor were higher when the vortex generator was installed in an upwind direction. This was because of the magnitude and the position of the airflows’ velocity. That is, faster airflows were induced in the region adjacent to the absorber plate when the vortex generator was installed in the upwind direction. As a result, high convection rates occurred and then increased the overall convective heat transfer rates of the solar air heater. Therefore, Nusselt number and thermal enhancement factor were higher. Nevertheless, the faster airflows also caused increased form drags due to vortex generator blockage, resulting in higher friction factor.

Improved performance evaluation of a dual passage solar thermal collector using staggered turbulators

Energy exists in various forms and plays a crucial role in global economic development and modernization. Solar energy is a prominent choice among several alternatives as an energy source to meet the demand. To harness solar energy for heating applications, the most basic approach is to transform it into thermal energy through the use of solar thermal collectors (STC). The thermal effectiveness of the dual passage solar thermal collector (DP-STC) is particularly poor. An effective approach to enhancing its thermohydraulic performance (ηTHPP) involves employing turbulators on the absorber plate (AP). This study investigates the impact on ηTHPP of DP-STC providedwith single V-shaped staggered baffles (SVSSBs). The impact of various geometrical elements, such as relative staggered baffle position (PB′/PB) ranging from 0.45 to 0.75, relative staggered baffle size (B/HB) from 2.5 to 4.0, and relative roughness pitch (PB/HB) from 1.0 to 2.5, are investigated for Reynolds numbers (ReX) ranging from 3000 to 19000. The remaining geometrical parameters, including the relative roughness height (HB/HC) = 0.40, relative gap position (Gd/Lv) = 0.67, relative gap size g/HB = 1, and angle of attack (αB) = 60°, remained fixed. Notable among the findings of this research is the fact that, SVSSBs performed best in comparison to other turbulators reported in the literature review. The ηTHPP reached its maximum value of 3.67 for the case with SVSSBs with PB/HB = 1.5, PB′/PB = 0.65, andB/HB = 3.5 atReX = 17000. The correlations are also developed for the Nusselt number (NuBP) and friction factor (fBP), using experimental data.

Twisted tape inserts in parabolic trough solar collectors: Assessment of Energy, Exergy, and Environmental impacts

The parabolic trough solar collector is a solar technology extensively employed to focus and harness solar energy for diverse heating purposes. One effective technique to enhance its thermal performance involves the insertion of swirl generators within its absorber tube. In this research, experimental investigation on performance enhancement of parabolic trough solar collector using single twisted tape and dual twisted tape insert across Reynolds number values ranging from 1,000 to 9,000 is performed. Collector efficiency, Nusselt number, friction factor, performance improvement factor, and exergy efficiency are examined for single twisted tape inserts with pitch to width ratios (y/w) of 1, 1.5, 2, 2.5, and 3, and dual twisted tape inserts with y/y0 ratios of 2, 3, and 4. Maximum enhancement in collector efficiency is reported at the lowest flow rate for both inserts. The single twisted tape insert with pitch to width ratio of 1 and the dual twisted tape insert with a pitch ratio of 2 exhibit the most notable enhancements in the evaluated performance parameters. Specifically, at lower flow rates (Re < 4400), the dual twisted tape insert (y/y0 = 2) outperforms the single twisted tape insert (y/w = 1). This dual twisted tape insert configuration provides a thermal efficiency enhancement of 14 %, while the Nusselt number and friction factor enhancement are found to be 372 % and 1600 % compared to bare tube. Additionally, the exergy efficiency exhibits a peak increase of 20.8 % at the lowest flow rate using the dual twisted tape insert (y/y0 = 2). This improvement translates to an annual CO2 reduction between 1.53 tons/year offering a highest enviro-economic benefit of 22.19 US dollars per year.

Experimental and numerical investigation on turbulent convection enhancement in minichannel heat sink with staggered V-shaped pin fins

With the continuous advancements in new energy vehicle technology, the insulated gate bipolar transistor (IGBT) thermal properties have a direct impact on power system reliability. In this article, a minichannel heat sink with staggered V-shaped pin fins (SVPF) is investigated through both experimental and numerical approaches. Initially, the heat transfer performance of SVPF and conventional minichannel heat sink was analyzed using the CFD numerical simulation method. Subsequently, numerical and experimental validation was carried out by assessing the Nusselt number and turbulence characteristics of SVPF. Finally, an in-depth analysis was conducted to investigate the effects of SVPF geometric parameters on the turbulent characteristics and heat transfer performance of the minichannel heat sink. The results demonstrate that SVPF exhibits superior hydrothermal performance, which could maintain better heat transfer performance while simultaneously reducing the friction factor of minichannels. These findings provide valuable insights for the design of three-dimensional pin fins minichannels heat sink.

PENGARUH LAMA WAKTU TAHAN NORMALIZING PADA BAJA ST 41 PENGELASAN FRICTION WELDING TERHADAP SIFAT MEKANIS

The development and application of science and technology, especially in the industrial world, is currently experiencing very rapid progress, especially in the world of welding. Welding is the process of joining two or more metal parts using heat energy. In the current era, welding developments are increasingly developing, such as liquid welding, resistance welding, solid welding, and forging welding. For solid welding, there are friction welding and cold welding. The joining process using friction welding involves friction factors, pressing force, and surface quality. To improve the mechanical properties of steel after welding, Normalizing heat treatment is carried out, namely a heat treatment process on steel which aims to refine the grain, homogenize the structure and obtain steel with mechanical properties as desired, or called normalization. This research method uses the Experimental Testing method. This sample was obtained from the normalizing friction welding process which was tensile tested, namely samples with varying holding times of 15 minutes, 30 minutes and 45 minutes with an engine speed of 2100 rpm and a pressure of 35 MPa with tensile testing of the material and microphotographs. The results of the friction welding research are as follows. The normalizing holding time of 15 minutes produces a maximum tensile stress value of 325.16 N/mm2, the fracture that occurs is in the form of a ductile fracture, the normalizing holding time of 30 minutes produces a maximum tensile stress value of 327.66 N/mm2, the fracture that occurs is in the form of a fracture ductile, the normalizing holding time of 45 minutes produces a maximum tensile stress value of 329.53 N/mm2, the fracture that occurs is in the form of a ductile fracture. The long holding time of normalizing will increase the tensile strength of the steel and tensile test fractures mostly occur in the weld area

An experimental investigation of the convective heat transfer augmentation in U-bend double pipe heat exchanger using water-MgO-Cmc fluid

One of the major problems of using nanofluids in heat exchange applications is the forming and deposition of nanoparticles on the inner surface of the heat exchanger. In this paper, Water-Cmc fluid is used as a surfactant for nanoparticles to prevent deposition and congregation. The pressure drops and heat transfer in U-bend double pipe heat exchanger based on water-MgO-Cmc fluid, are examined. Nanoparticles of Magnesium Oxide (MgO) and Carboxymethyl Cellulose (Cmc) are used with pure water as a base fluid. The experimental rig and procedures are designed to facilitate various operational conditions such as flow rate, volume concentration of MgO particles and weight concentration of Cmc particles. Furthermore, convective heat transfer coefficient, heat exchanger effectiveness, pressure drop, friction factor, under different conditions, are measured. The results demonstrate convective heat transfer coefficient of U-bend double pipe heat exchangers is enhanced by 35% for 1 MgO vol.% and 0.2 Cmc wt.% compared to base fluid (Water-Cmc). It is concluded that pressure drops are directly proportion to the increase of MgO nanoparticles at same Cmc concentration by 23% at 0.2 wt.%. Whilst, friction factor of the system is inversely proportion to the increase of volumetric flow rate of water-MgO-Cmc fluid. An increase in MgO nanoparticle concentration increases the friction factor, hence maximum friction factor enhancement by 38% for MgO concentration of 1 vol.%. The effectiveness of heat exchanger is slightly increased by 8% with increase of MgO concentration and flow rate. Finally, thermo-physical characteristics of water-MgO-Cmc fluid at various temperatures, are measured

Bingham plastic fluids flow analysis in multimembranes fitted porous medium

A mathematical analysis is presented for the flow of a Bingham plastic fluid propelled by the multi-membranes pumping mechanism through porous media. Two successive membranes with different amplitude, diameter, and phase lag, are fitted at the upper wall of the channel, and the lower wall is stationary. Due to the simultaneous propagation of both membranes, the pressure is generated at the membrane's position, which helps in propelling the fluids in forward and backward directions depending upon the compression and expansion cycles of the membranes. The low Reynolds number assumption and lubrication theory are utilized to linearize the governing equations, which are further analytically derived, and then employing MATLAB codes to compute the illustrations for the interpretation of the results. The effects of key parameters like plug flow region, pore size and diameter of membranes on the velocity field, wall shear stress, pressure gradient, fanning friction factor, head loss and particle trajectories, are analysed in the microchannel. Results of the present model conclude that the geometrical properties of membranes, rheological properties of fluids and porosity of the medium significantly alter the flow and pumping characteristics which give valuable insights for the design of micro-valve less pumping actuators to be aimed at controlling microscale transport processes in various medical diagnoses and treatments.

Heat and mass transfer analysis of Casson-based hybrid nanofluid flow in the presence of an aligned magnetic field: An application toward mechanical engineering

This examination explores the flow of a hybridized nanofluid (HyNf) containing silica and tin oxide nanoparticles mixed with engine oil (EO/SnO2-SiO2). The flowing occurs via a permeable material constrained by a semi-infinite flat plate. The study takes into account various factors such as convective heat and mass transference, chemical reactions, the Dufour effect, the Lorentz force, thermal radiative fluxing, and radiative absorbing. The research involves converting the managing formulas of the flowing model into a dimensionless form and applying the regular perturbation procedure to find solutions for the rate of fluid flow, temperature, and species diffusion. The surface frictional factor, Nusselt quantity, and Sherwood quantity reflect the shearing stress, rates of heat transference, and rates of mass transport at the plate, respectively. An analysis is conducted on the impact of several factors, including the suction variable, magnetic variable, radiation-absorbing factor, Casson parameter, and Dufour number, on the flow and related quantities. This analysis is based on an examination of graphs and tables. The findings suggest that the heat transference rate in the Casson hybridized nanofluid is better than that in the mono nanofluid. It is exposed that the temperature reduces at the plate having improved frequency of oscillation and also fluid velocity declines for improving values of aligned magnetized field [Formula: see text], but it shows the reverse phenomenon with Gr1 and Gc1.

Two-phase numerical simulation of thermal and solutal transport of zero mass flux conditions over a porous deformable disc: The extension of Jeffrey-Hamel model

In recent times, numerous assertions on the thermophysical properties of nanoliquids in various flow regimes, particularly the laminar flow regimes have been documented in the literature. With this focus, this theoretical investigation is to explore multiple solutions of the laminar two-dimensional Jeffrey fluid describing the Buongiorno nanofluid model and features of heat transport near a stagnation point across a movable radial disc. Also, the study seeks to explore the effects of zero mass flux and velocity of mass transpiration embedded within a Jeffrey fluid. With the help of the ansatz similarity transformations, the study simplifies complex partial differential equations into a set of ordinary differential equations, facilitating numerical dual solutions employing the bvp4c solver. The multiple solutions become apparent in a specific range of the shrinkable parameter. The results of the present study show that the suction parameter intensifies the phenomena of friction factor in the upper solution, whereas an annulment trend is observed in the lower solution. In addition, the shear stress and heat transfer rate decline with higher impacts of the Deborah number for the first solution while a monotonical behaviour is seen for the second solution. Besides, the absolute critical value decreases owing to the change value of the Deborah number, as a result, the separation of the boundary layer accelerates. Moreover, the heat transfer rate declined by about 0.29%, 0.37%, and 0.28% for the FBS and 0.30%, 0.32%, and 0.28% for the SBS with larger values of Nta, Nba and Sca, respectively. Lastly, the outcomes of the present examination with existing data are an excellent match for the limiting cases.

Enhancing heat transfer in various grooved annular for Taylor-Couette-Poiseuille flow

The present study investigated the impact of various parameters on pressure drop, Nusselt number, and friction factor in grooved annular channels, which have practical applications in cooling electric motors and generators. The parameters studied include the effective Reynolds number, Taylor number, groove aspect ratio, number of grooves, and groove angle. The k-ω SST turbulence model was employed in CFD simulations for various parameter ranges. These ranges include an effective Reynolds number spanning from 4.42 × 103to 1.6 × 104, Taylor number of 0–2.24 ×106, the groove aspect ratio of 0 to 2, the number of grooves ranging from 5 to 20, and the groove angle ranging from 70° to 130°. As the effective Reynolds and Taylor numbers increase within the ranges noted above, the Nusselt number exhibits a corresponding increase of 9.16 % and 1.77 %, respectively. However, the effective Reynolds number plays a more significant role. Various design factors, including the number of grooves, the aspect ratio, and the groove angle, also influenced the heat transfer enhancement. As any of these factors increase within the specified ranges, the corresponding Nusselt number values increase by 2.35 %, 3.62 %, and 6.09 %, respectively.

Thermo-fluid performance for helical coils inserted in a tube using hybrid CFD-ANN approach

This paper presents a numerical investigation into the thermal performance of helical coils, assessing the impact of spacing, wire diameter ratio, and coil pitch ratio on the pressure drop and heat transfer characteristics. Heat flux was maintained at 1000 W/m2, while Reynolds numbers ranged from 5000 to 30,000. Coil configurations encompassed pitch ratios within 1 ≤ p/d ≤ 3, wire diameter ratios spanning 0.044 ≤ e/d ≤ 0.133, and spacing intervals of 0.5, 1, and 2 mm. The finite volume method was employed to solve the energy, Navier-Stokes, and 3D continuity equations. Results indicate substantial influences of wire diameter, coil pitch ratios, and spacing on Nusselt number friction factors within the coiled tube. Notably, Nusselt number enhancements within the studied intervals ranged from 16 % to 102 %, with an overall performance criteria improvement reaching 43 %. Furthermore, a machine learning approach utilizing artificial neural networks (ANN) was employed, with comparisons drawn between results obtained from the ANN and computational fluid dynamics (CFD). The congruence between experimental, CFD, and ANN findings underscores the reliability of the study outcomes.

Forecasting particle Froude number in non-deposition scenarios within sewer pipes through hybrid machine learning approaches

Sediment deposition has a substantial effect on the hydraulic capacity of channels in urban drainage and sewer systems. In this sense, the self-cleaning concept has been extensively used in the construction of urban drainage and sewer systems. In this regard, the design of the sewer system heavily depends on the accurate forecasting of the particle Froude number (Fr). This study is conducted on experimental data sets collected from existing studies, including a wide range of dimensionless grain size of particles (Dgr), sediment median size (d), hydraulic radius (R), volumetric sediment concentration (Cv), and pipe friction factor (λ) for the condition of clear bed. We forecasted the particle Froude number using four different input combinations. We employed the Random Tree (RT) and Reduced Error Pruning Tree (REPT) methods as standalone methods, as well as Random Committee (RC) and Bagging (BA) methods as hybrid machine learning (ML) methods in particle Froude number forecasting. Hybrid machine learning methods demonstrate enhanced performance compared to both standalone machine learning methods and empirical equations. In the context of sewer system design under non-deposited bed conditions, there is a need to accurately forecast the particle Froude number, RC-RT (IA = 0.96, R = 0.928, MSE = 0.718, RRMSE = 0.197, NSE = 0.86, and PBias = −0.284) performed the best, followed by BA-RT, RC-REPT, BA-REPT, RT, and REPT. In our research, it was found that, in forecasting the particle Froude number under non-deposited bed conditions, Cv emerges as the most responsive input parameter among others.

The thermal and hydrodynamic analysis in a heat sink with different configurations of shark scales-based fins

The development of efficient thermal management techniques in cooling systems will lead to achieving a higher power capacity for electronic devices. Extended surfaces such as fins and riblets effectively improve the heat transfer rate in heat sinks, but they can cause increasing the friction factor. In this numerical study, a novel configuration of fins is introduced according to the shark scales’ geometry to provide a trade-off between heat transfer rate and friction losses compared to simple fins in a microchannel cooling system. Also, the cooling effect of concentrations of graphene oxide (GO)+ silver (Ag)/water (H2O) and molybdenum disulfide (MoS2) + cobalt oxide Co3O4/water (H2O) nanofluids (1, 3, and 5 wt%) are investigated for the Reynolds number ranging from 130 to 525. The geometrical parameters and different materials such as copper, nickel, and silver are evaluated by ANSYS-FLUENT under steady-state conditions. The comparison of outlet temperature, pressure drop, and temperature difference by experimental results verifies the accuracy of the numerical model. The results indicate that increasing arc width from 1 mm to 1.5 mm reduces the maximum CPU (central processing unit) temperature by 5 K while the temperature uniformity index decreased by 9.96 % at 0.3 m/s of inlet flow rate. The novel configuration of fins results in a performance evaluation criterion (PEC) greater than 1 for GO+Ag/water nanofluids in all cases compared to simple circular fins.

A Review of Pressure Drop and Mixing Characteristics in Passive Mixers Involving Miscible Liquids.

The present review focuses on the recent studies carried out in passive micromixers for understanding the hydrodynamics and transport phenomena of miscible liquid-liquid (LL) systems in terms of pressure drop and mixing indices. First, the passive micromixers have been categorized based on the type of complexity in shape, size, and configuration. It is observed that the use of different aspect ratios of the microchannel width, presence of obstructions, flow and operating conditions, and fluid properties majorly affect the mixing characteristics and pressure drop in passive micromixers. A regime map for the micromixer selection based on optimization of mixing index (MI) and pressure drop has been identified based on the literature data for the Reynolds number (Re) range (1 ≤ Re ≤ 100). The map comprehensively summarizes the favorable, moderately favorable, or non-operable regimes of a micromixer. Further, regions for special applications of complex micromixer shapes and micromixers operating at low Re have been identified. Similarly, the operable limits for a micromixer based on pressure drop for Re range 0.1 < Re < 100,000 have been identified. A comparison of measured pressure drop with fundamentally derived analytical expressions show that Category 3 and 4 micromixers mostly have higher pressure drops, except for a few efficient ones. An MI regime map comprising diffusion, chaotic advection, and mixed advection-dominated zones has also been devised. An empirical correlation for pressure drop as a function of Reynolds number has been developed and a corresponding friction factor has been obtained. Predictions on heat and mass transfer based on analogies in micromixers have also been proposed.

Experimental Heat Transfer Analysis of a New Turbulator in a Concentric Heat Exchanger Tube: A Full Factorial Design Approach

Abstract People have been looking for alternative energy sources because current sources may be depleted. Furthermore, it is critical to utilize available energy sources as effectively as possible. Turbulators are among the topics to consider when it comes to energy efficiency. In practice, turbulators are often used in exchangers to enhance heat transfer. Putting newly constructed turbulators in determined locations of the constant surface temperature heat exchanger, velocity, temperatures, pressure, and flow measurements have been performed in the inlet and outlet. In the case of using different numbers of turbulators, their placement in different locations, their arrangement at different distances, and their use at different Reynolds, the changes in pressure drop, Nusselt number, friction factor, efficiency, exergy loss rate, and NTU were determined with the full-factor experimental design. When the test data were evaluated, it was seen that as the number of turbulators increased, the thermal efficiency, friction factor, and pressure loss also increased. Using turbulators in different numbers, at different positions, at different distances, and with different Reynolds numbers, the effect ratio on the pressure loss, Nusselt number, and friction factor parameters was detected. In the analyses made, the most efficient parameters on heat transfer were determined, respectively, as Reynolds number (64.55%), the position of turbulators (19.73%), the distance between turbulators (6.09%), and the number of turbulators (5.94%).