Increase In Friction Factor Research Articles

Effect of splitter angles and orientations attached to pin fin on heat transfer and hydraulic characteristics in a jet impingement rectangular channel

Heat transfer improvement of heat sinks is very interesting in many applications including electronic devices cooling. In this study, the influence of rotational angle of splitters attached to pin fins for two cases of identical and opposite directions is investigated. Five angles including 0, 30, 45, 60 and 90 are considered in the analysis conducted for the rectangular channel. Air as the heat transfer fluid at 302 K and 35,000 Reynolds number enters the channel. The temperature of the bottom of the channel is assumed to be constant. 18 rows of circular pin fins on which splitters are attached for enhancement of heat transfer are examined. In the numerical analysis, Nusselt number, turbulent kinetic energy, friction factor and pressure drop are analyzed parameters. The simulation of the models presented in the current study is endeavored using ANSYS Fluent software, which employs finite volume method. Results revealed that, for the identical-direction case, as the angle rises, the average Nusselt number, turbulent kinetic energy, friction factor and pressure drop increase, in a way that for the case of 90 degree, Nusselt number is 9 % and turbulent kinetic energy is 96 % higher than the base case of zero angle. Moreover, friction factor and pressure drop of the vertical-splitter case are 4.8 and 4.6 times more than those of the base case. It is also concluded that increasing angle from 0 to 45° for the opposite-direction case, Nusselt number diminishes. However, extra increase in the angle from 45 to 90 degree results in Nusselt number enhancement. Similar trend of variation is also reported for turbulent kinetic energy. Results also indicated that for the opposite-direction case, friction factor and pressure drop rise; for the case of 90 degree, friction factor and pressure drop increase 4.4 and 4.32 times, respectively.

Thermo-fluidic performance of SiO2–ZnO/water hybrid nanofluid on enhancement of heat transport in a tube: Experimental results

This paper reports an experimental investigation on the convective heat transfer and flow performance of silica-zinc oxide (SiO2–ZnO)/water hybrid nanofluid (HNF) flowing inside a tube with constant heat flux at different Reynolds number (Re) from 7743 to 23,228. A well-stabilized SiO2–ZnO/water HNF with 0.025–0.10weight fractions(φ) was produced via two-step method. Thermal conductivity and viscosity of HNF were measured. The convective heat transfer and flow characteristics of the HNF were determined. Thermal conductivity and viscosity of HNF showed notable enhancements as compared to water. The convective heat transfer coefficient (CHTC) of HNF enhanced with increasing φ and Re. A maximum of 29.44% enhancement in CHTC was obtained with φof 0.10 at Re = 20,131 when compared to water. Further, the friction factor and pressure drop of HNF increased with increasingφ. A maximum of 17.45% increase in friction factor and a maximum increase of 24% in pressure drop were recorded withφ of 0.10 at Re = 23,228 as compared to water. New CHTC and friction factor correlations of high accuracies (R2>90%) have been proposed. A Figure of Merit (FOM) was drawn to describe the thermal performance of HNF. Based on the analysis, the optimum thermal performance was achieved with φ of 0.10 at Re = 20,131.

CFD of roughness effects on laminar heat transfer applied to additive manufactured minichannels

AbstractAdditive manufacturing has received significant interest in the fabrication of functional channels for heat transfer; however, the inherent rough surface finish of the additively manufactured channels can influence thermal performance. This study investigates the impact of roughness on the thermo-fluid characteristics of laminar forced convection in rough minichannels. A numerical model was developed to create 3D Gaussian roughness with specified root-mean-square height. The finite volume method was used to solve the conjugate heat transfer of developed laminar flow in square minichannels. For Reynolds numbers ranging from 200 to 1600, the simulation results indicated enhanced heat transfer and increased flow resistance as Reynolds number increases, compared to a smooth minichannel, where effects on heat transfer and flow friction were negligible. For channels with relative roughness (root-mean-square height to channel hydraulic diameter) of 0.0068, 0.0113, and 0.0167, increasing the Reynolds number led to increased friction factor by 1.56, 1.71, and 2.91%, while the Nusselt number was enhanced up to 0.03%, 32.74%, and 46.05%, respectively. Heat transfer reduced in roughness valleys due to the presence of local low-velocity fluid in these regions; however, recirculation regions can occur in deep valleys of high roughness, increasing heat transfer and flow friction. Heat transfer was enhanced over roughness peaks due to flow impingement on the windward face of roughness as well as intensified energy transfer to the channel wall from roughness. Moreover, surfaces with higher roughness have a greater number of high peaks providing a thermal-flow path of a larger area and a thermal conductivity greater than that of the fluid.

Heat transfer augmentation in a solar air heater with conical roughness elements on the absorber

Adding flow-disturbing components to the absorber plate's effective heat transfer zone is the most efficient Thermo-hydraulic performance enhancement approach for a solar air heater (SAH). Researchers are attempting to decide the best geometrical parameters for a SAH when the turbulent flow has fully established with fabricated roughness protrusions on the absorber surface plate in a cone-shaped contour. The Thermo-hydraulic performance of the proposed SAH design is taken into account throughout the optimization process. Air flow rate and geometrical variables such as the Reynolds number R e = 3000 to 8000 , relative rib pitch p / e = 10 to 20 , and relative rib gap w / e = 4 to 8 are varied in a series of experiments to assess the SAH's performance. Flow angle of attack ( α = 90°), relative roughness height ( e / D h = 0.08), and rectangular flow passage aspect ratio ( W / H = 5) are maintained constant in all the trials for inline and staggered configurations. Series of tests are carried out to establish statistical correlations between the average Nusselt number and the average friction factor. Thermo-hydraulic performance is affected by the Reynolds number (Re) as well as relative roughness gaps ( w / e ) and relative roughness pitch ( p / e ) of the conical protrusions. There was a 64.5% increase in Nusselt number and a 153.3% increase in friction factor at Re = 8000, p / e = 10 and w / e = 4. Cone-shaped roughness, as suggested, has a Thermo-hydraulic efficiency index of 0.8233, which ocuurs at p / e = 20 and w / e = 8 at Re = 3000.

Numerical investigations on the difference between aiding and opposing flows in the developing regime of laminar mixed convection in vertical tubes

The present article discusses the numerical simulation results of laminar mixed convection flow in vertical tubes. A comparative analysis of the thermal and hydrodynamic features of both buoyancy-assisted and opposed flows was performed for Reynolds number (), Grashof number () and Richardson number () with uniform heat flux boundary condition. 2-D axisymmetric steady state simulations were carried out for a length-to-diameter () ratio of with water as the working fluid. Numerical simulations were performed by employing SIMPLE scheme for pressure–velocity coupling in momentum equations and second order UPWIND scheme for solving energy equations. In case of assisting flow (), at fully developed state the centerline velocity decreases, and velocity is increased near the tube wall due to heat flux induced free convection. With increasing heat flux, the decrement in centerline velocity compared to the no-heat flux condition increases. Further, with increasing heat flux, the increase in friction factor and Nusselt number was observed. Therefore, at the same the variation of heat flux led to unique velocity profiles and temperature gradients. The variation of centerline velocity and temperature in developing region was also studied. While centerline temperature was monotonically increasing with length, the centerline velocity increased up to a maximum in the developing region and then attained the steady state at a lower value in the fully developed state. Subsequently we studied the dependence of on the hydrodynamic and thermal features. For constant friction factor and Nusselt number was observed to increase with increase in from 0.1 to 1.5 range. At fixed variation of heat flux leads to variation of or Hence, the buoyancy effect has a significant role in the entrance length development. The hydrodynamic entry length after an initial increase, attained an almost constant value with increasing On the other hand, the thermal entry length exhibited a decreasing trend with increasing Similarly, at constant Nusselt number increased with increasing for a range of 100–1000. It was evident that for a given and the heat transfer in the developing flow is always higher as that of the fully developed flow. Contrasting observations were observed for buoyancy-opposed flow. Velocity is accelerated at the center as compared to the tube wall in case of opposing flow for same and For a fixed the friction factor and Nusselt number decreased with increasing the Both the hydrodynamic and thermal entry length increases for opposing flows. Finally, we have developed correlations for fully developed friction factor () with as well as and Nusselt number () with for buoyancy-assisting and buoyancy-opposing flows. Two independent correlations are also produced for with Graetz number () for developing and fully developed regimes in both assisting as well as opposing flows.

Convective flow of a Williamson hybrid nanofluid in a porous medium through a cone and wedge with the effect of the shape of nanoparticles

AbstractThe performance of nanofluid in the heat transport phenomena showed satisfactory results, which have been considered by scientists and researchers. The dispersion of two nanoparticles to form a mixture which named as hybrid nanofluid. It has been proved experimentally that hybrid nanofluid has good thermal performance compared to unitary nanofluid. The present study inspected the convective flow of a Williamson hybrid nanofluid through a cone and wedge in a porous medium of different shapes of nanoparticles (cylindrical‐, spherical‐, blades‐, platelets‐, bricks‐) under the influence of a magnetic field. The partial differential equations were converted to an ordinary differential equation and the resulting equations were solved using the bvp4c MATLAB code. The effect of some important physical parameters on both the velocity and temperature profile was graphically plotted and the effect of the shape and size of nanoparticles was discussed, the numerical values of the friction coefficient and Nusselt number were obtained. As observed, the friction factor of Ag–TiO2–H2O hybrid nanofluid was more than that of TiO2–H2O nanofluid. A significant enhancement in bulk temperature is seen for the Ag–TiO2 hybrid and nanofluid formed by blade‐shaped nanoparticles followed by cylindrical, platelet, brick, and spherical nanoparticles. In addition, for a 5% volume fraction of using blade nanoparticles shape givean increase in skin friction factor about 4.8% compared tobrick hybrid nanoparticles. A comparative study of different forms for Ag‐TiO2was presented graphically.

Evaluation of Thermal Performance of Conically Shaped Micro Helical Tubes Using Non-Newtonian Nanofluids–A Numerical Study

Abstract Nowadays, the cooling and heating of micro-thermal devices have received a growing interest. To improve the thermal management of these micro-thermal devices, various efforts are being made by the researchers. In the present study, conically shaped micro helical tubes are used to investigate the coil side heat transfer rate and friction factor of non-Newtonian nanofluids under laminar flow conditions. For the numerical analysis, single-phase approach with commercial software ansys-fluent-19 has been utilized. Investigations encompass generalized Reynold numbers ranging from 306 to 2159 and four different curvature ratios (0.066, 0.076, 0.088, and 0.1) of conically shaped micro helical tubes. The inner diameter of the helical tube is 2 mm and contains 20 turns. Al2O3-based non-Newtonian nanofluids with volume concentrations of 0.0%, 0.1%, and 0.2% having base fluid of aqueous solution of carboxymethyl-cellulose (CMC) are used as the working fluid (hot) for the coil side, while in the shell side cold water is used. The results from numerical investigation are validated and found in good agreement with earlier experimental results. The results show that with the increase in the curvature ratio of conically coiled tubes both heat transfer rate and friction factor increase by 46% and 98% respectively, for base fluid at a curvature ratio of 0.1. Also, the present study reveals that adding nanoparticles to the base fluid enhances the heat transfer rate to a maximum value of 40%. Moreover, the maximum value of thermal performance factor (TPF) is found to be 1.52.

Experimental investigation of the effect of a novel curved winglet vortex generator on heat transfer with a designed controller circuit

In the presented experimental study, twelve different double-sided curved blade vortex generators were produced at two blade angles (15° and 30°) based on the turbulator blade angle, blade direction, and the placement of the turbulators in the pipe. After conducting smooth pipe studies, the curved structure's winglet components were mounted on the pipe at various angles and locations, and the effects on heat transfer and pressure drop were determined for Reynolds Numbers ranging from 16,210 to 41,470. The smooth pipe results obtained were compared with the results obtained from the numerical Gnielinski, Dittus-Boelter, Blasius, and Petukhov equations. In addition, a control circuit has been developed to ensure the precision and recording reliability of the results. The root mean square error (RMSE) and mean absolute percent error (MAPE) results obtained by the controller circuit were found to be in good agreement with the results of the experimental study. Considering the results obtained with the elements placed in the pipe, the highest increases in Nusselt number and friction factor compared to the smooth pipe were 173% and 592%, respectively. The most notable Nusselt number (Nua/Nuo) and friction factor (fa/fo) increases were seen in the values of 3.41 and 6.92, respectively. The highest PEC value for the heat transfer improvement effect was approximately 1.79 for the low Reynolds Number value of 16,214. Among all the turbulators, the highest heat transfer increase was achieved with the double-sided opened blade (UD-30) type turbulator, while the lowest heat transfer increase effect was achieved with the one-bladed opened type (OC-15) turbulator. In terms of PEC, eight turbulators had a significant effect on all Reynolds values, but the remaining four had no effect.

Energy absorption and vibration of smart auxetic FG porous curved conical panels resting on the frictional viscoelastic torsional substrate

In recent years, the utilization of various methods to absorb vibration in widely-used structures has gained significant attention to control and reduce the destructive effect of the resonance phenomenon. The increased useful lifetime and reduced maintenance and repair costs are the advantages of vibration absorption. Besides, utilization of energy absorbers is one of the most effective strategies for reducing energy supply costs for different parts of the structure, such as sensors. In this regard, a numerical study is performed in this research to evaluate the energy absorption by vibrations' absorption in a conical three-layered panel located on a viscoelastic substrate. This three-layered panel is composed of three parts: piezoelectric upper layer reinforced with Graphene nanoplatelets (GPLs), auxetic core, and functionally graded material (FGM) porous lower layer. The substrate includes spring element, shear, torsion, and substrate-structure friction factor. Hamilton's principle and energy method have been used to extract the governing equations to model the first-order shear deformation theory (FSDT) for the presented structure. The Differential Cubature Method (DCM) and the Newmark method have been used to solve the governing equations. Results show that by applying the negative voltage to the sandwich conical panel, the in-plane compression forces and natural frequency are increased, while the maximum dynamic deflection is decreased. Furthermore, increasing the inherent damping coefficient increases the damping decrement. Meanwhile, the nonlinear scattering and increased dispersion concentration of GPLs near the upper and lower surfaces of the piezoelectric layer will increase the frequency and energy absorption. Besides, the increased friction factor of the viscoelastic substrate and sandwich cone leads to more absorption energy.

Numerical study on thermal-hydraulic characteristics of flattened microfin tubes

Abstract The thermal-hydraulic characteristics and performance of the circular and flattened straight tubes with longitudinal inward microfins are studied with isothermal wall condition and Reynold numbers (Re) between 10,000 and 30,000. The geometric models with fins (8, 12, and 16 fins) and three flattening ratios (1.4, 2, and 3.4) are considered for the simulation. The results indicate that the longitudinal microfins have a limited effect on the improvement of heat transfer, but the application of microfins increases the pressure drop significantly. Furthermore, an increase in Reynolds number increases the heat transfer characteristics. Therefore, a discriminative use of longitudinal microfins for circular tubes to improve thermal performance is advised. Flattening the microfin tubes has shown a significant increase in heat transfer coefficient and friction factor compared to circular cross-section tubes with microfins. The percentage gain in heat transfer with the flattening ratio of 3.4 is about 52% compared to the circular fin tube at Re = 30,000. A 61% increase in centreline velocity is observed at Re = 10,000. Area-based Enhancement Factor (AEF) and performance evolution factor (PEF) are more than 1 for flattened tubes with microfins. It shows an improvement in the overall thermal-hydraulic characteristics of tubes.

Numerical analysis of heat transfer improvement for pulsating flow in a periodic corrugated channel with discrete V-type winglets

In the present study, the effects on the hydraulic and thermal performance of pulsating flow in a periodic corrugated channel with discrete V-type winglets were numerically investigated. Three different channel flows were considered with non-winglet, solid winglet, and perforated winglet configurations. The winglets were placed in the center of the channel in a discrete V-shape downstream. Numerical analyses were carried out with the finite volume approach. The effects of pulsation amplitude (A), Strouhal number (St), and Reynolds number (Re) on the flow and heat transfer were examined. The upper and lower surfaces of the corrugated channel were protected at Tw = 350 K and thermal performance and pressure drop were acquired for a pulsating cycle across the channel. The numerical results were presented in terms of thermal performance (η), dimensionless friction factor (Γ), and thermal performance factor (TPF). To observe the effects of the pulsation parameters and Reynolds number, time-averaged velocity and temperature distributions in the channels were obtained. The findings showed that the flow and heat transfer characteristics were highly affected by the channel and winglet geometry. The pulsation parameters significantly contributed to heat transfer improvement, especially at high Reynolds numbers. Thermal performance increased considerably with increasing pulsation amplitude and frequency with a slight increase in friction factor. Also, it was observed that the perforated winglets reduced the friction factor compared to the solid winglets. The highest TPF values for non-winglet, solid winglet, and perforated winglet configurations were respectively found as 5.71, 4.68, and 5.17 at Re = 1000, A = 1.5, and St = 8.

Heterogeneous and homogeneous reactive flow of magnetite-water nanofluid over a magnetized moving plate

This model is dedicated to visualizing the nature of magnetite-water nanoliquid induced by a permeable plate having variable magnetic effect, non-linear radiation, heterogeneous and homogeneous chemically reactive species. The system of momentum, thermal and concentration expressions is formulated and transformed from the partial to ordinary differential systems by using the adequate transforms. This highly non-linear system is solved through RKF (Runge-Kutta-Fehlberg) numerical method. Important parameters such as suction/injection, magnetic, and radiation effects as well as other relevant parameters are investigated. The graphs show that the rise in radiation parameter numerically improves the thermal distribution, implying a faster heat transfer rate. Non-linear radiation has greater effect on temperature than the linear radiation. While the volume concentration effect reveals that the friction factor increase with the enhancement of nanoparticle concentration. It is also observed that, plate velocity decreases the skin-friction but increases the wall heat transfer for both suction and blowing cases. The results indicate that the current research has a strong agreement with the relevant data in a limiting approach.

Heat transfer characteristics and flow features of nanofluids in parallel flat minichannels

Nanofluid in a mini/microchannel heat sink is an effective technique that combines advantages of micro/minichannels and nanofluids to obtain high single-phase enhancement of heat transfer. Experiment comparison and numerical analysis of irreversibility are used to analyze features of Al2O3-H2O nanofluid in minichannels. Results showed that transition point of the nanofluid from laminar flow to turbulent flow is 1300. Nusselt number of the Al2O3-H2O nanofluid presents the maximum increment in the concentration of 0.01% when Re ≈ 5200, with a maximum increase of 47.5%. The increase of friction factor of the nanofluid is 15.1%. Nu and f value indicated the efficient heat transfer of low-concentration nanofluids under low flow resistance compared with the results of previous studies. Thermal entropy generation rates of the nanofluid are the main irreversible loss and the frictional entropy generation rate is the main part before Re = 5000.

Scattering of oblique water waves by thick porous structure and thin elastic plate

The present study deals with the usefulness of the partial porous structure of finite width placed at a finite distance from the elastic plate to mitigate the hydrodynamic response of the elastic plate. Two different configurations of the porous structure namely bottom-standing and surface-piercing structures are analyzed. The elastic plate is modeled using thin plate theory, and the wave past the thick porous structure is based on Sollitt and Cross model, the problems are investigated based on the small-amplitude water wave theory in water of finite depth. With the aid of the eigenfunction expansion method, the associated boundary value problem is reduced to a system of linear algebraic equations, which is solved numerically. For both configurations, the effects of various system parameters such as wavenumber and angle of incidence are analyzed. The impacts of structural parameters such as length, width of the porous structure, porosity are investigated from the graphs plotted on the reflection coefficient, transmission coefficient and dissipation coefficient and hydrodynamic forces. Further, detailed analysis on free surface elevation, elastic plate deflection, shear force and strain is presented. The study reveals that with an increase in length, width, porosity, and friction factor of the porous structure the dissipation of wave energy increases which helps in diminishing the wave impact on the elastic plate.

Comparative Study of Numerical Analysis of Compacted Strand and Round Strand under Axial Tensile Load

Using differential geometry theory, geometric modeling and finite element modeling of round strand and compacted strand before and after the rolling process are carried out. Using Costello theory, the rationality of the model is verified. The effects of five different friction factors on the mechanical properties of both were simulated and analyzed under the same axial tensile load. The results show that under the same axial tensile load and friction factor, the maximum equivalent stress and displacement of the compacted strand is smaller than those of round strand. When the axial load is 5 kN and the friction factor is 0, the maximum equivalent stress of the compacted strand relative to the round strand is reduced by 38.1%, and the displacement is reduced by 19.3%. Under the same axial tensile load and different friction factors, the maximum equivalent stress of the round strand increases approximately linearly with the friction factor; while the maximum equivalent stress of the compacted strand has a small increase between the friction factor of 0 and 0.05, and after 0.05 the maximum equivalent stress almost does not change. The displacement of both decreases as the friction factor increases. Under the same strain, the reaction force of the compacted strand is greater than that of the round strand, which proves that the compacted strand has higher tensile strength than the round strand.

Frictional resistance of supercritical pressure RP-3 flowing in a vertically downward tube at constant heat fluxes

Based on the demands of compact heat exchangers and micro cooling channels applied for aviation thermal protection, the flow resistance characteristics of aviation kerosene RP-3 were experimentally studied in a vertically downward circular miniature tube with an inner diameter of 1.86 mm at supercritical pressures and constant heat fluxes. A long and short tube method was used to accurately calculate the frictional pressure drop, and experimental conditions are supercritical pressures of 4 MPa, mass flow rates of 2–4 g/s (i.e., mass fluxes of 736–1472 kg/(m2∙s)), heat fluxes of 100–500 kW/m2, and inlet temperatures of 373–673 K. Results show that the sharp variations of thermophysical properties, especially density, have significant influences on frictional resistances. Generally, the frictional pressure drop and the friction factor increase with increasing inlet temperatures, and this trend speeds up in the relatively high-temperature region. However, the friction factor has a sudden decline when the fuel outlet temperature exceeds the pseudo-critical temperature. The frictional pressure drop and the friction factor basically remain unchanged with increasing heat flux when the inlet temperature is relatively low, but increase quickly when the inlet temperature is relatively high. Besides, a larger mass flux yields a higher pressure drop but does not necessarily yield a higher friction factor. Finally, an empirical friction factor correlation is proposed and shows better predictive performance than those of previous models.

AN EXPERIMENTAL INVESTIGATION FOR THE USE OF MULTI-WALL CARBON NANOTUBES BASED ON WATER NANOFLUID IN A PLATE HEAT EXCHANGER

An experimental study has been conducted to investigate the performance of an Armfield plate heat exchanger (HT32) with an Armfield heat exchange service unit (HT30X) using multi-wall carbon nanotubes (MWCNTs) based on distilled water with different volume concentrations. There are five volume concentrations used in this study (0.22%, 0.33%, 1.66%, 1.1%, 1.53%). The Reynolds number of the hot fluid (distilled water &nanofluids) range 100 ˂ Re ˂ 700. The overall heat transfer coefficient, pressure drop, friction factor, the mean Nusselt number, and the effectiveness were calculated by measuring the variables. The experimental results obtained showed that Nanofluids have a significant effect on the heat transfer process depending on the concentration of nanoparticles in the base fluid. Overall heat coefficient and Nusselt number increase with the increase of volume concentration. The enhancement in the value of the overall heat coefficient depends on the volume concentration of nanoparticles compared with pure distilled water. The pressure drop and the friction factor increase with the increase of the volume concentrations of nanoparticles. The enhancement in the value of Nusselt number reaches 32% in case of use nano-fluid with a volume concentration of 1.53% in comparing of distilled water. The effectiveness increases with the increase of the volume concentrations and Reynolds number. An empirical correlation to calculate the Nusselt number is obtained. By the comparison between the results in the current study and the literature, one can find an acceptable agreement.

Numerical analysis on heat transfer and flow resistance performances of a heat exchanger with novel perforated wavy fins

The experimental and numerical studies of thermo-hydraulic characteristics of perforated wavy fin heat exchanger and unperforated wavy fin heat exchanger were conducted. Firstly, the two kinds of fins were studied under different air in?let velocity and constant inlet temperature. The results show that Nusselt number increases with Reynolds number and friction factor decreases with Reynolds number. Then, the performance of the two kinds of fins is numerically analyzed, and the simulation results are in good agreement with the experimental data. On this basis, the influence of different perforated fin parameters (fin height, H, fin pitch, s, wave amplitude, wa, perforation number, n, perforation diameter, d) on the thermal performance of wavy fin heat exchanger is discussed. It is indicated that friction factor and Nusselt number increase with increasing aperture, wave amplitude, fin pitch and perforation number or decreasing fin height under constant Reynolds number condition. Finally, the performance evaluation of heat exchangers with different parameters is carried out to obtain the best performance heat exchanger parameters, which can provide a reference for the design of the new wavy fin heat exchanger.

Experimental analysis to study the effect of perforated louvered strip‐coiled spring insert on heat transfer performance in a double pipe heat exchanger

AbstractExperiments have been conducted to study the effect of louvered strip‐coiled spring (PLSCS) turbulators having different pitches and the same angle of attack on thermal performance and pressure drop of a concentric tube heat exchanger. Two inserts in combined form were used for experimentation under turbulent flow at different Reynolds numbers (Re) ranging between 5000 and 20,000. Two pitches (40 mm and 50 mm) of elliptical‐shaped perforated louvered strips (PLS) having the same angles of attack have been taken that were welded on the central core rod. Spring inserts have the same coil diameter of 12 mm with two varying pitches to achieve pitch ratios of 0.5 and 1. Both heat transfer and pressure drop increase with a decrease in pitches of both LS and spring inserts. Nusselt number has the maximum value with spring of pitch 6 mm in combination with a PLS of 40 mm pitch at which is 130.75% higher than the plain tube at the lowest Re among the PLSCS inserts. With perforation, a slight increase in both Nusselt number and friction factor was observed. The maximum thermal performance efficiency value is 1.105 for the lowest Re value.

Thermal–hydraulic analysis of a solar air heater fitted with a wire-roughened absorber plate

This study is to evaluate heat transmission and friction in a rectangular solar air heater with a V-shaped wire rib roughness on the absorber plate that operates in fully formed turbulent flow. Additionally, studies are performed to generate prediction equations for the average friction factor, Stanton number, and efficiency index. The Reynolds number [Formula: see text]–[Formula: see text], angle of attack [Formula: see text]20[Formula: see text]–90[Formula: see text]), relative roughness pitch [Formula: see text]–[Formula: see text], relative roughness height [Formula: see text]–[Formula: see text], and the aspect ratio [Formula: see text]–[Formula: see text] was varied. The efficiency index [Formula: see text] is commonly employed as a thermo-hydraulic performance metric. It is computed as [Formula: see text]. The wire roughness and airflow parameters [Formula: see text] are optimized to maximize heat transfer while retaining minimal friction losses. On the basis of resemblance criteria, average Stanton numbers, average Nusselt numbers, and even average friction factors are derived. The results are compared to those obtained with a smooth absorber duct under similar airflow circumstances in order to assess the increase in heat transfer coefficient and friction factor. The [Formula: see text], and [Formula: see text] have a significant influence on thermo–hydraulic performance, according to these studies. With [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text], the optimal configuration geometry for wire roughness and solar air heater duct is identified.