Prediction Of Friction Factor Research Articles

Improving the Heat Transfer using Fe3O4 Nanoparticles Suspended in Water Flow through Circular Tube

The new class of pressure drop and heat transfer enhancement through pipes and heat exchangers is defined a nano-fluid. The applications of this process are the cooling of oil inside heat exchanger and the flow of oil into the pipe line. In this work, the prediction of heat transfers and friction factor in a heated tube is studied. ANSYS software of CFD simulation through the geometrical problem undertaken was utilized. The Fe3O4 nanoparticles suspended in pure water has been adopted to flow through the test rig under ranges of nanoparticles mass concentrations and Reynolds number 1% to 4% and 4000 to 10000 respectively. The numerical results show that the friction factor and heat transfer enhancement increase as increase of nanoparticles mass concentrations 23% and 4% respectively. Additionally, the heat transfer is increased and the friction factor is decreased as increase of Reynolds number. It was concluded that Nusselt number increases due to add the solid nanoparticles to the water but slightly increases of pumping power. This obtained results are validated with the available data in the literature.

Analysis, prediction, and optimization of heat transfer coefficient and friction factor of water-$${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$$ nanofluid flow in shell-and-tube heat exchanger with helical baffles (using RSM)

Analysis, prediction, and optimization of heat transfer coefficient and friction factor of water-$${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$$ nanofluid flow in shell-and-tube heat exchanger with helical baffles (using RSM)

Pressure Drop in Seven-Pin Wire-Wrapped Rod Bundle for the Sodium Cartridge Loop in Versatile Test Reactor

This work studies the hydrodynamics of the seven-pin wire-wrapped rod bundle in the sodium cartridge loop for the Versatile Test Reactor (VTR) through scaled water experiments and computational fluid dynamics (CFD) simulations. The scaling analysis is first performed to demonstrate the hydrodynamic similarity between water and sodium flows at the same Reynolds number . A separate-effects test facility is designed and constructed based on the scaling analysis. Detailed experimental data on the pressure drop covering a wide range of values (1165 to 27 689) are obtained, which are used to evaluate existing correlations for friction factor and to benchmark CFD simulations. The experimentally determined friction factors agree well with the Upgraded Cheng and Todreas Detailed Correlation and Pacio-Chen-Todreas Detailed Model within but are significantly underpredicted by Rehme’s correlation by 25%. Various CFD near-wall treatment methods are tested using ANSYS Fluent and evaluated by experimental data. It is found that when the recommended wall values are met, most of the near-wall treatment methods can give accurate friction factor predictions. The resolved near-wall method () with the Shear Stress Transport turbulence model and the scalable wall functions () with the realizable turbulence model can predict within . The standard wall functions () and nonequilibrium wall functions () with the realizable model can predict within ± 10%.

Artificial neural networks application on friction factor and heat transfer coefficients prediction in tubes with inner helical-finning

A study presents new model of the artificial neural network to predict friction factor and heat transfer coefficients for the turbulent flow in tubes with inner helical-finning. A fin geometry differs in its form, shape and fabrication method. The generalized equations, correlating thermal performance in such tube, available in earlier works by other authors primarily apply to a single type of inner helical-finning. In present work, we compile experimental results of other authors to an extended database that has been used further for artificial neural network training procedure. The presented model of artificial neural network applies to all types of inner helical tube finning. The mean average percent error values of 11.8% for friction factor and 16.3% for Nusselt number values for the ANN model over the whole database have been achieved. The performance validation of the obtained model was based on a comparison of predicted data with the independent experimental results obtained by authors, yielding excellent accuracy. • Extended database of Nusselt number and friction factor in helicallyfinned tubes. • Novel generalization model of artificial neural network. • Systematic analysis and validation of obtained artificial neural network model.

Thermo-fluid performance enhancement of a fin-and-tube heat exchanger by rectangular winglets

In this study, numerical simulations have been performed to investigate the influence of rectangular winglets as Vortex generators for enhancement of thermo-fluid performance in a fin-and-tube type heat exchanger having five staggered rows of tubes. The influence of placement of winglets over different pair of tubes, attack angles of the winglet pair, and their location has been examined under laminar flow conditions for Re ranging 400–1500. For the present analysis rectangular winglet pairs having “common-flow-up” orientation were employed for vortex generation. The effect of placement of different number of rectangular winglet pairs (1–5) has been investigated and the maximum enhancement in thermo-fluid performance was obtained as 27.4% compared to the baseline model (without winglet model). The winglets attack angle (5°, 10°, 15°, 20°, and 25°) were also investigated for best thermo-fluid performance and the optimum attack angle resulted in enhancement up to 33% over the baseline model. The optimum stream-wise and span-wise locations were identified which resulted in enhancement up to 29% and 25%, respectively, over the baseline model. Correlations for the prediction of Nusselt number, friction factor, and enhancement factor have been developed for stream-wise distance, span-wise distance, and attack angle of the winglets.

Analysis of pressure losses and flow distribution in wire-wrapped hexagonal rod bundles for licensing. Part I: The Pacio-Chen-Todreas Detailed model (PCTD)

This two-part paper presents an updated version of the long term MIT-NTHU modeling effort on the hydraulics of hexagonal arrays of wire wrapped fuel pins. It has been stimulated by the emergence of technical licensing considerations from the current development efforts for MYRRHA, the accelerator-driven system cooled by lead–bismuth eutectic being conducted at SCK CEN in Belgium. This added licensing perspective has been introduced into this hexagonal array modeling effort through the recent collaboration of this paper’s lead author with the MIT-NTHU team resulting in the creation of the new model called the Pacio-Chen-Todreas Detailed model (PCTD).Models used for licensing calculations must be able to predict pin bundle hydraulic and thermal behavior within a prescribed upper bound of uncertainty. This must be done for all postulated scenarios with sufficient accuracy to maintain required safety margins. This capability requires a predictive model of sufficient detail to represent the bundle friction and flow distribution behavior. The Upgraded Cheng and Todreas (UCTD) model from 2018 is unique in this ability and was selected as the basis for this effort.The major improvement needed was correction of the consistent over-prediction of flow velocity in the edge subchannels. This was addressed by recognizing and adding an additional physical mechanism of momentum exchange due to the flow mixing effect resulting from the wire rod spacers. While this added momentum exchange has also slightly improved the UCTD bulk friction factor prediction, most importantly it has provided for corrected prediction of subchannel axial velocity. Since the velocities in the corner, edge and interior subchannels differ, this velocity distribution has been characterized as the bundle flow split. Its accurate prediction is essential for prediction of maximum rod cladding temperature the key bundle safety parameter.Part I, here following, summarizes the existing UCTD and then presents the new PCTD model including the governing equations, the constitutive models, the empirical parameters, an example calculation and an associated statistical evaluation. Part II, published separately in this issue, presents the experimental data base from which the empirical parameters in the new model are calibrated. Based on the analysis of these data, it is suggested that future experimental efforts focus on the laminar flow regime (relevant in accidental conditions) and flow-split data. Moreover, numerical simulations are expected to play an increasing role in the safety assessment, and the database collected in this work can be used for a benchmarking exercise to evaluate further model developments.

Interfacial Friction Prediction in a Vertical Annular Two-Phase Flow Based on Support Vector Regression Machine

Accurate prediction of interfacial friction factor is critical for calculation of pressure drop and investigation of flow mechanism of vertical annular two-phase flows. Theoretical models of interfacial friction factor based on physical insight have been developed; however, these are inconvenient in engineering practice as too many parameters need to be measured. Although many researchers have proposed various empirical correlations to improve computation efficiency, there is no generally accepted simple formula. In this study, an efficient prediction model based on support vector regression machine (SVR) is proposed. Through sensitivity analysis, five factors are determined as the input parameters to train the SVR model, relative liquid film thickness, liquid Reynolds number, gas Reynolds number, liquid Froude number and gas Froude number. The interfacial friction factor is chosen as the output parameter to check the overall performance of the model. With the help of particle swarm algorithm, the optimization process is accelerated considerably, and the optimal model is obtained through iterations. Compared with other correlations, the optimal model shows the lowest average absolute error (AAE of 0.0004), lowest maximum absolute error (MAE of 0.006), lowest root mean square error (RMSE of 0.00076) and highest correlation factor (r of 0.995). The analysis using various data in the literature demonstrates its accuracy and stability in interfacial friction prediction. In summary, the proposed machine learning model is effective and can be applied to a wider range of conditions for vertical annular two-phase flows.

Analysis of pressure losses and flow distribution in wire-wrapped hexagonal rod bundles for licensing. Part II: Evaluation of public experimental data

This two-part paper presents an updated version of the long term MIT-NTHU modeling effort on the hydraulics of hexagonal arrays of wire wrapped fuel pins. It has been stimulated by the emergence of technical licensing considerations from the current development efforts for MYRRHA, the accelerator-driven system cooled by lead–bismuth eutectic being conducted at SCK CEN in Belgium. This added licensing perspective has been introduced into this hexagonal array modeling effort through the recent collaboration of this paper’s lead author with the MIT-NTHU team resulting in the creation of the new model called the PCTL model (PCT). Models used for licensing calculations must be able to predict pin bundle hydraulic and thermal behavior within a prescribed upper bound of uncertainty. This must be done for all postulated scenarios with sufficient accuracy to maintain required safety margins. This capability requires a predictive model of sufficient detail to represent the bundle friction and flow distribution behavior. The Upgraded Cheng and Todreas (UCTD) model from 2018 is unique in this ability and was selected as the basis for this effort. The major improvement needed was correction of the consistent over-prediction of flow velocity in the edge subchannels. This was addressed by recognizing and adding an additional physical mechanism of momentum exchange due to the flow mixing effect resulting from the wire rod spacers. While this added momentum exchange has also slightly improved the UCTD bulk friction factor prediction, most importantly it has provided for corrected prediction of subchannel axial velocity. Since the velocities in the corner, edge and interior subchannels differ, this velocity distribution has been characterized as the bundle flow split. Its accurate prediction is essential for prediction of maximum rod cladding temperature the key bundle safety parameter. Part I, published separately in this issue, summarizes the existing UCTD and then presents the new PCT model including the governing equations, the constitutive models, the empirical parameters, an example calculation and an associated statistical evaluation. Part II, here following, presents the experimental data base from which the empirical parameters in the new model are calibrated. Based on the analysis of these data, it is suggested that future experimental efforts focus on the laminar flow regime (relevant in accidental conditions) and flow-split data. Moreover, numerical simulations are expected to play an increasing role in the safety assessment, and the database collected in this work can be used for a benchmarking exercise to evaluate further model developments.

A comprehensive model to predict friction factors of fluid channels fabricated using laser powder bed fusion additive manufacturing

Laser powder bed fusion (L-PBF), or selective laser melting, can be used to significantly reduce the size and weight of hydraulic components. However, the current design approach still greatly depends on the technician’s experience. The friction loss of the L-PBF fabricated fluid channels is greatly affected by the fabrication quality but remains unknown, which is essential for the design approach. In this study, circular 316L SS fluid channels with various diameters (4–10 mm) and build angles (0–90°) were fabricated using L-PBF. Fabrication quality was characterized, and the friction factors were measured and analyzed. The results indicate that the geometric tolerance and surface roughness are closely related to the build angle. The friction factor of the L-PBF fabricated channels, which is higher than the classical theory in the turbulent flow, is influenced by both channel diameters and build angles. A comprehensive model is developed to predict friction factors of the L-PBF fabricated fluid channels. Design guidelines of fluid channels are proposed, for the first time, by considering both fabrication quality and friction factors. • The influence of build angle on channel forming quality is studied. • The relationship between forming quality and friction factor is developed. • A comprehensive friction factor prediction model for 316L SS L-PBF channel is developed. • Design guidelines of L-PBF fabricated fluid channels are proposed.

Hydrothermal characteristics of a double flow parabolic trough solar collector equipped with sinusoidal-wavy grooved absorber tube and twisted tape insert

PurposePresent investigation conducts a study on the hydrothermal features of a double flow Parabolic Trough Solar Collector (PTSC) equipped with sinusoidal-wavy grooved absorber tube and twisted tape insert filled with nanofluid. This paper aims to present an effectual PTSC which is comprised by nanofluid numerically by means of finite volume method.Design/methodology/approachThe beneficial results such as pressure drop inside the absorber tube, mean predicted friction factor, predicted average Nusselt number and hydrothermal Performance Evaluation Criteria (PEC) are evaluated and reported to present the influences of numerous factors on studied interest outcomes. Effects of different Reynolds numbers and environmental conditions are also determined in this investigation.FindingsIt is found that using the absorber roof (canopy) can enhance the heat transfer ratio of PTSCs significantly during all studied Reynolds numbers. Also, it is realized that the combination of inner grooved surface, outer corrugated surface and inserting turbulator can improve the thermal-hydraulic characteristics of PTSCs sharply.Originality/valueNovel PTSC (N.PTSC) filling with two Heat Transfer Fluids (HTFs), inner and outer surface corrugated absorber tube, absorber roof and inserting twisted tape (N.PTSC.f) has the highest PEC values among all novel configurations along all investigated Reynolds numbers which is followed by configurations N.PTSC with two HTFs and inserting twisted tape (N.PTSC.e), N.PTSC with two HTFs and outer surface corrugated absorber tube (N.PTSC.b) and N.PTSC with two HTFs and inner surface corrugated absorber tube (N.PTSC.c), respectively. N.PTSC.f Nusselt number values can overcome the high values of friction factor, and therefore is introduced as the most efficient model in the current study.

Silver-Water Nanofluid for Heat Transfer Applications

Introduction: Nanoscale materials have attracted a great deal of attention of many researchers and academician in mechanical engineering because of their size and shape dependent thermal properties. The attractiveness of its superior thermal properties compared to its base materials is the main reason for the effective utilization of nanomaterials for the energy systems. The rapid development and researches in nanotechnology led to the development of new class of heat transfer fluid called nanofluid for heat transfer enhancement. The nanoparticles dispersed in the fluid increase the surface area, heat capacity and thermal conductivity of the fluid making it very suitable for heat transfer enhancement (1). Methods: Silver being a safe material with higher thermal conductivity of 429 W/mK can be extensively used for the heat transfer applications. Silver-water nanofluid was prepared by dispersing silver nanoparticles of sizes 20, 30-50 and 50-80 nm in the volume concentrations of 0.01, 0.05 and 0.1%. Polyvinyl pyrrolidone (PVP) has been used as surfactant to stabilize the nanofluid. Thermal conductivity of nanofluid was measured by kD2 Pro thermal analyzer. The stability of nanofluid was analyzed by sedimentation technique, pH measurement, zeta potential and particle size distribution. The effect of surfactant on the thermal conductivity enhancement and stability of nanofluid was studied (1,2). Then the investigations on the heat transfer and pressure drop of silver-water nanofluid in a circular tube under constant wall heat flux condition were carried out in laminar and turbulent flow regimes. Results & Discussions: Among the three sizes of silver nanoparticles used in the investigation, nanofluid with 20 nm exhibited better thermal conductivity enhancement and stability due to lower size. The addition of surfactant improved the stability of nanofluid but caused reduction in thermal conductivity enhancement slightly. Increase of concentration of nanoparticles from 0.01 to 0.1% improved the thermal conductivity of nanofluid up to 50% (1). Experimental study on use of silver-water nanofluid for heat transfer applications showed enhancement in heat transfer coefficient of nanofluid up to 36% and 74% respectively for laminar and turbulent flow conditions. However, the addition of nanoparticles increases the pressure drop slightly. But the higher enhancement of heat transfer overcomes the increase of pressure drop of nanofluid. The proposed correlations for the prediction of Nusselt number and friction factor showed good agreement with the experimental results (3.4). Conclusions: Lower size and lower concentrations of silver water showed better hydrothermal performance of heat transfer systems. The effect of pressure drop and erosion problem due to the addition of nanoparticles will be minimized with low concentrations and lower size of silver nanoparticles. It can be a suitable nanofluid for the thermal energy systems requiring improvement in their performance. Keywords: Silver Nanoparticles, Nanofluid, Thermal conductivity, Heat transfer

Prediction of heat transfer coefficient and friction factor of mini channel shell and tube heat exchanger using numerical analysis and experimental validation

Minichannels are a key technology that results in energy, space, material, and cost savings in shell and tube heat exchangers (STHEs) because they improve performance by increasing compactness and reducing the dimensions, volume, and mass, as well as the amount of working fluids used. This paper employed the Computational Fluid Dynamics (CFD) method to investigate the effect of minichannels on the thermal and hydrodynamic performance of a STHE. The reliability and accuracy of numerical results were corroborated with experimental results. Numerical solutions were performed under constant heat flux conditions at 2650 < Re < 9500, the range in which internal flows are considered transition and turbulent flows. The results showed that the higher the Reynolds (Re) number, the higher the convective heat transfer coefficient (CHTC) and pressure drop. The performance benchmark (ψ) is defined as the variations in CHTC per unit of pressure drop. The results showed that the higher the Re number, the lower the ψ. Based on numerical solutions regarding ψ, the flow in the minichannel tube reached optimal conditions both thermally and hydrodynamically at Re ≅ 5900. The deviation between the numerical and experimental CHTCs ranged from −15 % to +15 %, while that between the numerical and experimental friction factors ranged from −13 % to +13 %. These results can be used for engineering designs and applications.

RANS simulations for transition and turbulent flow regimes in wire-wrapped rod bundles

Internal flows through rod assemblies are commonly found in heat exchangers, steam generators, and nuclear reactors. One of the fuel assembly designs considered for liquid metal-cooled reactors utilizes wires helically wrapped around each fuel rod as spacers. The wires keep the fuel pins separated, enhancing the turbulent mixing, and heat transfer, but also affecting the pressure drop. It is of interest the understanding of the fluid flow phenomena in the sodium-cooled fast reactor as it is one of the Generation IV advanced reactor designs and it has been a motivating topic of research for the last decade. A wire-wrapped fuel assembly replica with 61-pins has been in operation at the Thermal-Hydraulic Research Laboratory of Texas A&M University. This facility produced high-fidelity velocity and pressure drop data for validation of computational fluid dynamics codes. This study investigates the effects of geometrical features and operating conditions on the flow behavior of the 61-pin wire wrapped bundle using Reynolds-Averaged Navier-Stokes (RANS) models to predict the axial and transverse pressure drops for a range of Reynolds numbers from 1,270 to 100,000. The friction factor predictions were in satisfactory agreement with the experimental data and the Upgraded Chen and Todreas correlation. The internal subchannel velocity results were compared with experimental data and Large Eddy Simulations (LES) and found in reasonable agreement. This study demonstrates that RANS is a suitable approach in predicting velocity and pressure fields in wire-wrapped rod bundles, with a relatively low computational effort.

The effect of linearly increasing/decreasing pitch ratio twisted tape with various progression rate and nanofluid towards the system performance

The overall enhancement ratio decreases with increasing Reynolds number for most of the existing modification of twisted tape. Hence, in this study, a new innovative twisted tape with linearly increasing/decreasing pitch ratio at various progression rate of 0.2, 0.25 and 0.3 (LIPR/LDPR) combined with three different nanofluid (Al2O3/water, SiC/water and CuO/water) are designed and analyzed. The analysis is conducted at Reynolds number ranges from 4000 to 16,000 and volume fraction ranges from 1% to 3% by using numerical and experimental approaches. ANSYS FLUENT software is selected for simulation analysis by adopting RNG K-ε turbulent model using enhanced wall treatment method. Five different geometries of twisted tape including standard twisted tape with constant PR of 2 (TT PR 2), linearly-increasing-progression-rate of 0.2 twisted tape (TT LIPR 0,2), linearly-increasing-progression-rate of 0.25 twisted tape (TT LIPR 0.25), linearly-increasing-progression-rate of 0.3 twisted tape (TT LIPR 0.3) and linearly-decreasing-progression-rate of 0.25 twisted tape (TT LDPR 0.25) are used for analysis. Among all geometries of twisted tapes, TT LIPR 0.25 creates the highest turbulent kinetic energy value at the cross-sectional area. TT LIPR is the best choice to be utilized under turbulent flow regime where Reynolds number >10,000 as it creates higher overall enhancement ratio compared to TT PR 2 and TT DPR. The simultaneous use of 1% SiC/water nanofluid and TT LIPR 0.25 at 10,000 Reynolds number has increased overall enhancement ratio up to 2.985. The empirical correlation is generated for future prediction of Nusselt number, friction factor and overall enhancement ratio with wide range of nanofluid type, fluid flow range and Reynolds number of twisted tapes.

Influence of Broken Twisted Tape on Heat Transfer Performance in Novel Axial Corrugated Tubes: Experimental and Numerical Study

The insertion of a broken twisted tape (BTT) in tube is a novel passive heat transfer augmentation method, which constitutes the subject of the present investigation. Effect of BTT on heat transfer performance in novel triangular axial corrugated tubes is investigated experimentally and numerically. In order to augment the thermohydraulic performance, a corrugated tube with inserts is offered. The analyses are conducted for Reynolds number extending from 10,000 to 80,000 within the turbulent regime. The shear stress transport model is applied as the turbulence model. Air is used as the working fluid. The typical full-length twisted tapes with two different twist ratios and the broken twisted tape with two different twist ratios, and three gap ratios are used for the comparative analysis. The angular pitch between the two neighboring corrugations and the angle of the corrugation are kept constant through the experiments at 120° and 60°, respectively, while three different corrugations heights are analyzed. Eventually, correlations for predicting friction factor and Nusselt number are developed. The thermohydraulic performance is also calculated. The results show a good correspondence with the measurements and the published correlations of other researchers. For all examined cases, the performance factors are always larger than unity.

Experimental study of thermohydraulic characteristics and irreversibility analysis of novel axial corrugated tube with spring tape inserts

The current study experimentally investigates the heat transfer augmentation on the novel axial corrugated heat exchanger tube in which the spring tape is introduced. Air (Pr = 0.707) is used as a working fluid. In order to augment the thermohydraulic performance, a corrugated tube with inserts is offered. The experimental study is further extended by varying the important parameters like spring ratio (y = 1.5, 2.0, 2.5) and Reynolds number (Re = 10 000–52 000). The angular pitch between the two neighboring corrugations and the angle of the corrugation is kept constant through the experiments at β = 1200 and α = 600 respectively, while two different corrugations heights (h) are analyzed. While increasing the corrugation height and decreasing the spring ratio, the impact of the swirling effect improves the thermal performance of the system. The maximum thermal performance is obtained when the corrugation height is h = 0.2 and spring ratio y = 1.5. Eventually, correlations for predicting friction factor (f) and Nusselt number (Nu) are developed.

Numerical Analysis of FLiBe Laminar Convective Heat Transfer Characteristics in Tubes Fitted With Coaxial Cross Twisted Tape Inserts

Molten salts are now widely used as heat transfer fluids in solar thermal plants and molten salt nuclear reactors. In order to explore its heat transfer enhancement method, new coaxial cross twisted tapes (CCTTs) are applied to plain tube with molten salt FLiBe as working fluid, and the characteristics of pressure drop and heat transfer are numerically investigated by the CFD software STAR-CCM+. Simulations are performed in a laminar flow regime where Reynolds number ranges from 100 to 1100, and the velocity, temperature profiles, and enhanced performance evaluation criteria (PEC) are analyzed to investigate the heat transfer performance of FLiBe in the tube fitted with CCTTs and typical twisted tape (TT). Water and lubricating oil are also researched to investigate the effects of fluid thermal-physical properties on the performance of CCTTs. The results show that CCTTs can produce stronger swirl flow and greatly enhance heat transfer. For overall heat transfer performance, the maximum PEC of FLiBe with CCTTs reaches 2.37. The comparison of three different fluids also indicates that CCTTs have better heat transfer performance for higher Prandtl number fluids such as molten salt. The correlations of CCTTs and TT are developed into a unified form for the prediction of friction factors and Nusselt numbers for various Prandtl number fluids.

Experimental study and CFD modelling on the thermal and flow behavior of EG/water ZnO nanofluid in multiport mini channels

Nanofluid and mini channel are two promising approaches to enhance the heat transfer performance. The present study combined these two techniques together and investigated the heat transfer and flow behavior of ZnO ethylene glycol (EG)/water nanofluid inside two multiport mini channels with the hydraulic diameters of 1.22 mm and 1.42 mm. ZnO nanoparticles with an average diameter of 30 nm were dispersed into 40%/60% EG/water solution to get nanofluids with 0.75% and 1.5% volume concentration. The heat transfer and flow performance under various operational conditions were identified by both experiments and CFD simulation. Experimentally, it reveals that the Nusselt numbers are averagely improved by 6.7% and 9.8% for nanofluids with 0.75% and 1.5% concentration respectively. However, the friction factors are also enlarged by 4.6% and 8.6% correspondingly, which results to a various thermal performance factor ranging from 0.94 to 1.31 with the average values of 1.05 and 1.07. The decrement of channel diameter leads to greater heat transfer coefficients, pressure drop, friction factor but nearly the same Nusselt number. A new correlation is developed to predict the Nusselt number for ZnO nanofluid flow in multiport mini channels with a MARD of 9.2%. Numerically, single-phase model gives better predictions for both Nusselt number and friction factor with the average relative deviations of nearly 16% and 19.1% correspondingly. Mixture model severely overestimates the Nusselt number but shows a reasonable friction factor prediction. The present study is expected to give some guidance for the study of nanofluid in mini channels.

Heat transfer and exergy analysis of solar air heater tube with helical corrugation and perforated circular disc inserts

The effects of perforated circular disc swirl generator on heat transfer (HT) and flow fields in a solar air heater helical corrugated tube have been investigated experimentally. Thermal energy transport coefficient at different values of the corrugation angle (θ), the corrugation pitch ratio (y), the perforation ratio (k), and the perforation disc pitch ratio (s) is studied for Reynolds numbers (Re) ranging from 10,000 to 52,000. Isothermal pressure drop tests and heat transfer experiments under a uniform heat flux conditions have been carried out. The results indicate that in the presence of a perforated circular disc inside the helically corrugated tube, heat transfer is augmented by around 50–60%. Entropy generation in the form of irreversibility is reported. Exergy analysis, in terms of exergy efficiency, is presented. The corrugated tube with swirl generator inserts augments the thermal energy transport coefficient mostly, which is accompanied by a minimum pressure penalty. The combined geometry augments more thermal energy transport coefficient than those of acting alone. A predictive Nusselt number and friction factor correlation are also developed. A large data set has been created for thermal energy transport coefficient and thermal–hydraulic performance, which is beneficial for the design of solar thermal air heaters and heat exchangers.

A new joint friction model for parameter identification and sensor-less hand guiding in industrial robots

PurposeThe purpose of this paper is to propose a new joint friction model, which can accurately model the real friction, especially in cases with sudden changes in the motion direction. The identification and sensor-less control algorithm are investigated to verify the validity of this model.Design/methodology/approachThe proposed friction model is nonlinear and it considers the angular displacement and angular velocity of the joint as a secondary compensation for identification. In the present study, the authors design a pipeline – including a manually designed excitation trajectory, a weighted least squares algorithm for identifying the dynamic parameters and a hand guiding controller for the arm’s direct teaching.FindingsCompared with the conventional joint friction model, the proposed method can effectively predict friction factors during the dynamic motion of the arm. Then friction parameters are quantitatively obtained and compared with the proposed friction model and the conventional friction model indirectly. It is found that the average root mean square error of predicted six joints in the proposed method decreases by more than 54%. The arm’s force control with the full torque using the estimated dynamic parameters is qualitatively studied. It is concluded that a light-weight industrial robot can be dragged smoothly by the hand guiding.Practical implicationsIn the present study, a systematic pipeline is proposed for identifying and controlling an industrial arm. The whole procedure has been verified in a commercial six DOF industrial arm. Based on the conducted experiment, it is found that the proposed approach is more accurate in comparison with conventional methods. A hand-guiding demo also illustrates that the proposed approach can provide the industrial arm with the full torque compensation. This essential functionality is widely required in many industrial arms such as kinaesthetic teaching.Originality/valueFirst, a new friction model is proposed. Based on this model, identifying the dynamic parameter is carried out to obtain a set of model parameters of an industrial arm. Finally, a smooth hand guiding control is demonstrated based on the proposed dynamic model.