Performance Evaluation Criteria Research Articles

EXPERIMENTAL AND NUMERICAL CONVECTIVE HEAT TRANSFER INVESTIGATION IN LAMINAR RECTANGULAR-CHANNEL FLOW ACROSS V-SHAPED GROOVES

The influence of staggered V-grooves on the hydrothermal performance of a rectangular-channel flow is systematically investigated through a combination of numerical and experimental approaches. The 3-D numerical simulation is developed adopting computational fluid dynamics (CFD) (ANSYS FLUENT) for a range of Reynolds numbers (Re) from 100 to 1000. The experiments are conducted on straight and V-grooved channels (with pitch-to-height and height-to-hydraulic diameter ratios of 2 and 0.75) for distilled water under constant wall heat flux conditions to validate the computational model. Additionally, the impact of V-shaped groove arrangements, forward V-grooved channel (FVGCH) and backward V-grooved channel (B-VGCH), on the flow and heat fields, as well as the effect of groove depths (<i>d</i> = 1.5, 2.5, and 3.5 mm), are also studied. In both experimental and numerical results, the performance evaluation criterion (PEC) grows with rising Reynolds numbers. The highest PEC values of the numerical and experimental findings for the F-VGCH are 2.18 and 2.29, respectively, at Re = 1000. Whereas the highest PEC values of the numerical and experimental results for the B-VGCH are 1.81 and 1.96, respectively, at the same Re (Re = 1000). In addition, the values of PEC for F-VGCH are greater than the PEC values of B-VGCH for all examined groove depths over the entire range of Reynolds numbers. Thus, the F-VGCH offers the best performance evaluation criterion in comparison with B-VGCH.

HEAT TRANSFER ENHANCEMENT IN A CHANNEL WITH INCLINED BAFFLES UNDER PULSATING FLOW: A CFD STUDY

This study numerically investigated hydraulic and thermal performance in a channel with inclined baffles under pulsating flow conditions. The baffles were placed in a staggered arrangement. The governing equations were discretized with the finite volume method (FVM), and the pressure-velocity coupling was handled by the SIMPLE algorithm. The Strouhal number (St: 0.5,1, 2, 3, and 4), pulsation amplitude (A: 0.2, 0.5, and 0.8), and Reynolds number (200 ≤ Re ≤ 1000) were changed. The top and bottom surfaces of the channel were kept at <i>T</i><sub>ω</sub> = 350 K, and thermal improvement and friction factor were calculated for a pulsating cycle. The results were given in terms of thermal enhancement (η), relative friction factor (<i>f</i><sub>rel</sub>), and performance evaluation criteria (PEC). The flow and temperature contours were presented to determine the impacts of the pulsation frequency, the pulsation amplitude, and the Reynolds number. The results showed that the pulsation amplitude and the pulsation frequency contributed remarkably to thermal enhancement with increasing Reynolds numbers, while the heat transfer improved significantly depending on pulsation parameters together with a slight rise in friction factor. The highest thermal enhancement achieved was about 1.47 at <i>Re</i> = 1000, <i>A</i> = 0.8, and <i>St</i> = 4. The highest PEC obtained was approximately 1.12 at <i>Re</i> = 1000, <i>A</i> = 0.2, and <i>St</i> = 4.

Investigation of the Thermo-hydraulic performance of a roughened Parabolic trough collector

Parabolic trough collectors (PTC) are an already established technology set to prove its competitiveness. Recently, a lot of research is ongoing to further enhance the thermal performance of PTC systems. Computational Fluid Dynamics (CFD) can help in the design and development of PTCs with optimized thermal efficiency. In the current work, a combined enhancement in the performance of a PTC is evaluated, involving modifications to the geometry of the absorber tube and the use of a heat transfer fluid (HTF) (Syltherm800). Absorber tube geometries involving dimpled protrusions (d-PTC) and circumferential inclined ribs (IR-PTC) are used. The performance of PTC with and without turbulators is compared with that of a smooth absorber tube by calculating the Nusselt number (Nu), friction factor (f) and performance evaluation criterion (PEC). PEC values of 1.46 and 1.18 are observed by using inclined ribs and dimpled protrusions, respectively at an absorber tube inlet temperature (Tin) of 500 K and mass flow rate (ṁ) of 0.5 kg s−1. Thus, a significant enhancement in thermo-hydraulic performance of PTC is observed with inclined rib turbulators.

Ensemble Machine Learning Paradigms in Software Defect Prediction

Predicting faults in software aims to detect defects before the testing phase, allowing for better resource allocation and high-quality software development, which is a requisite for any organization. Machine learning techniques aid in the resolution of such issues and a variety of predictive models are being developed to categorize the software into defective modules and the one which is non-defective ones. Though applying these advanced machine learning techniques results in better utilization of time and other resources, there is still poor prediction as reported in many studies. This is because of several challenges that block defective software data, including redundancy, correlation, feature irrelevance, missing samples, and an imbalanced distribution between the faulty and non-faulty classes. Ensemble Machine learning has been adopted by practitioners and researchers globally to deal with such problems, and it is proven to demonstrate some improvement in defect prediction performance. In this review paper, all ensemble-based machine learning techniques developed for software defect prediction from 2018 to 2021 have been critically analyzed. The nucleus of this paper is to get a deep insight into why the various hybrid models still suffer from poor performance on the available datasets. A detailed review with a focus on multiple perspectives viz. faulty and non-defective datasets, performance evaluation criteria, and machine learning techniques have revealed certain gaps that can be addressed by developing more robust hyperparameter optimization algorithms, feature engineering, developing stacking and averaging models.

HEAT-TRANSFER ENHANCEMENT OF A SOLAR PARABOLIC TROUGH COLLECTOR USING TURBULATORS AND NANOPARTICLES: A NUMERICAL STUDY

Solar energy harnessing devices exhibit promising potential for providing a significant portion of the energy requirement. Among these devices, the solar parabolic trough collector (PTC) is a well-renowned and effective technology. In recent times, a great deal of research has been done further improving the thermal performance of PTC systems. The current numerical study investigates the effect of modifications to the geometry of the absorber tube and the effect of nanoparticles on the thermal performance of PTC. A corrugated tube (CT), sinusoidal corrugated tube (SCT), the corrugated tube having a cylindrical insert (CI), star insert (SI), and increasing diameter rod insert (IDRI) are used to modify the geometry of the absorber tube. The corrugated tube is also analyzed with water-Al<sub>2</sub>O<sub>3</sub> and water-TiO<sub>2</sub> nanofluids at volume concentrations of 2%, 4%, and 6%. The results showed that the sinusoidal corrugated tube produced the best results with a value of Nusselt number (Nu) being 15.2% greater than simple corrugated absorber tube without incurring any significant increase in pressure. Moreover, the performance evaluation criterion (PEC) value is also found to be greater than that of simple corrugated geometry. The use of nanofluids as the heat-transfer fluid (HTF) led to an overall enhancement in the heat transfer coefficient h by as much as 20%.

A comparison of multivariate statistical methods to detect risk factors for Type 2 diabetes mellitus

Aim: The goal of this study is to compare the performances of Logistic Regression (LR), Artificial Neural Networks (ANN) and Decision Tree models, which are machine learning classification methods, in the diagnosis of Type 2 Diabetes Mellitus (DM) and to determine the most successful method. It is also the examination of risk factors affecting Type 2 DM using these models. Method: The study's data was collected from patients who visited the Diabetes and Thyroid polyclinic at the Inonu University Faculty of Medicine Turgut Ozal Medical Center, Department of Internal Medicine. The k-Nearest Neighbor algorithm, which is one of the missing value assignment methods, was used to eliminate the problems related to missing values. Sensitivity, accuracy, precision, specificity, AUC F1-score, and classification error were used as performance evaluation criteria. Evolutionary algorithm parameter optimization method was used to optimize the parameters of the ANN model. Missing value assignment, modeling and parameter optimization were done with Rapidminer Studio Free version 8.1. Results: Among the three methods applied in the diagnosis of Type 2 DM, the ANN gave the best classification performance. The accuracy, sensitivity, selectivity, precision, F1-score, AUC and classification error values obtained from this method are respectively; 98.94%, 100%, 97.73%, 98.04%, 99.01%, 0.978 and 1.06. For the ANN method, the importance values of the gender, long-term drug use, family history, concomitant disease, cortisone use, stress factor, high blood pressure, smoking, high cholesterol, heart disease, exercise status, carbohydrate use, alcohol consumption, vegetable use, meat use, age, weight, height, starting age, daily bread consumption, LDL, HDL, Total Cholesterol, Triglyceride, Fasting blood sugar the importance values of independent variables are respectively; 0.017, 0.009, 0.013, 0.017, 0.008, 0.016, 0.008, 0.006, 0.053, 0.024, 0.023, 0.040, 0.007, 0.020, 0.007, 0.046, 0.083, 0.049, 0.024, 0.066, 0.084, 0.083, 0.020, 0.031, 0.244. Conclusion: According to the performance criteria obtained from the three classification models used to predict Type 2 DM; it has been found that the best classification performance belongs to the ANN model. According to the ANN method, the three most important risk factors that may cause Type 2 DM were found to be fasting blood glucose, LDL, and HDL, respectively.

EFFECTS OF NANOPARTICLE SIZE ON PROPERTIES OF NANOFLUID AND HEAT TRANSFER ENHANCEMENT IN SPIRAL EXCHANGER USING TURBULATORS

In energy systems that use nanofluids as heat transfer fluid, the physical properties of nanofluids are important parameters in the efficiency of various heat exchangers, including small-scale micro channels or large-scale heat exchangers. In the present work, a comprehensive study is conducted to evaluate the thermal performance of a spiral heat exchanger with ball-type turbulators using nanofluid Al<sub>2</sub>O<sub>3</sub>/water. To investigate the effect of particle dimensions on nanofluid properties, nanoparticles with sizes of 20 nm and 50 nm at a volume concentration of 2% were examined. Heat transfer rate in the heat exchanger, performance evaluation criteria, heat transfer coefficient value, pressure drop, friction factor, Reynolds-Nusselt numbers relationship and pump power for fluid circulation have been calculated. ANSYS Fluent software as a computational fluid dynamic method was utilized to analyze the spiral heat exchanger under different working conditions. It was observed that both thermal conductivity and viscosity values increased as the nanoparticle size decreased. Heat transfer coefficient analyses showed that nanofluids with 20 and 50 nm particles exhibited a maximum improvement of 30.59% and 21.53%, respectively, when compared to pure water at an inlet velocity of 0.1 m/s. Additionally, the heat exchanger with turbulator showed a maximum increase of 24.87% at an inlet velocity of 0.5 m/s compared to the heat exchanger without turbulator. Moreover, maximum heat transfer rate enhancement was found to be 14.07% when the exchanger was equipped with turbulators.

Heat transfer performance of liquid lead–bismuth eutectic and supercritical carbon dioxide in double D-type straight channel

• The thermal and hydraulic performance for LBE and SCO 2 in PCHE is simulated. • Effects of operational and structural parameters are analyzed in detail. • The heat transfer performance is evaluated based on PEC and GRA. The printed circuit heat exchanger is currently the most recommended heat exchanger type for the lead-bismuth eutectic fast reactor coupled Brayton cycle system. Here, the flow and conjugate heat transfer for lead-bismuth eutectic and supercritical carbon dioxide in a double D-type straight channel printed circuit heat exchanger was investigated using numerical simulations. The results indicated that the overall heat transfer coefficient was positively correlated with the mass flux of both lead-bismuth eutectic and supercritical carbon dioxide, with the latter having a greater effect. Moreover, increasing the temperature difference between the two fluids inhibited the heat transfer effect on the supercritical carbon dioxide side, while increasing the pressure reduced the overall heat transfer coefficient. Further, a reduction in the tube diameter and wall thickness strengthens the overall heat transfer efficiency through enhancing the turbulent kinetic energy of the fluid and reducing the heat transfer thermal resistance, respectively. A performance evaluation criterion and Grey relational analysis were combined to evaluate the heat transfer performance of the printed circuit heat exchanger, and the results showed that a smaller diameter and wall thickness, an increased inlet mass flow rate of supercritical carbon dioxide, and an appropriate reduction in the temperature difference would improve the heat transfer performance.

A study on the evaluation criteria of sports performance in a Chinese university based on Internet technology

The physical education performance of contemporary college students is crucial to every college student's physical health as well as credit grades. And the good or bad sports performance is closely related to the sports evaluation criteria. Relying on Internet technology, this paper takes undergraduates of a domestic university as the research object, adopts a variety of research methods, carries out in-depth research on the evaluation criteria of several items, and develops a more appropriate quantitative evaluation sports scoring standard through analysis and comparison. The experiment shows that the graduation quantitative evaluation sports scoring standards proposed in this paper can meet the graduation assessment needs and better respond to the differences of students' sports quality.

Implementation and Analysis of a Fuzzy Logic and Sliding Mode Controller on a Boost DC/DC Converter in a PV Array

The DC/DC converters are primarily and practically used for switch-mode regulated power source and renewable energies such as photovoltaic or wind turbine. the principal purpose of these converters is to adapt the input with the output in other words, to preserve a consistent output voltage no matter the variations of the internal and external parameters of the converter. Different control techniques are commonly used to adapt and regulate the output voltage of these converters and make them more efficient and more robust in the event of unwanted disturbances, such as classic linear controllers for instance (proportional integrator and derivator controller PIDC ) and nonlinear controllers as (fuzzy logic FLC, sliding mode controller SMC). This article presents a comparative performance of Fuzzy Logic Control (FLC) and Sliding Mode Control (SMC) on a DC/DC Boost converter submitted to different type of variations. The performance evaluation criteria depend on speed and precision of the transient response. The two proposed controllers are modeled, designed and simulated using MATLAB/SIMULINK. The results of the comparison between the two controllers confirm the effectiveness of sliding mode control in terms of rapidity and precision compared with FLC.

Field PMU Test and Calibration Method—PartII: Test Signal Identification Methods and FieldTest Applications

Synchrophasor measurement units (PMUs) provide synchronized measurement data for wide-area applications. To improve the effectiveness of synchrophasor-based applications, field PMUs must be tested to ensure their performance and data quality. In the companion paper (Part I), we proposed a field PMU test and calibration framework consisting of a PMU calibrator and analysis center. Part I presents the development and test of the PMU calibrator. This paper focuses on the analysis center and field test applications. First, the critical component of the analysis center is the signal identification module, for which the step and oscillation signal identification methods are proposed. Here, the performance evaluation criteria of PMU in these two cases are different from others. The methods include a step signal detection method based on singular value decomposition (SVD), which has the capability of weak step detection to account for energy leakage of the signal during the step process, and an oscillation signal identification method based on SVD and fast Fourier transform, which can accurately extract oscillation components that benefit from the adaptive threshold setting method. Second, the analysis center software is implemented based on identification results. By integrating the PMU calibrator in Part I with the analysis center in Part II, we can examine in depth the field PMU test applications in three test scenarios, including standard, playback, and field signal test. Results demonstrate the effectiveness and applicability of the proposed field PMU test methods from both Parts I and II.

VIBRATION AND HEAT TRANSFER STUDY ON IMPROVED ELASTIC BUNDLE HEAT EXCHANGER

The comprehensive performance of an improved elastic tube bundle heat exchanger (IETB) was studied by varying its structural parameters (diameter and wall thickness). The influence of the structural parameters on the vibration and heat transfer properties of IETBs at different inlet velocities (u<sub>in</sub>) was studied. The results show that the average amplitude of IETBs maximum increase was 41.67% and the average heat transfer coefficient (HTC) maximum increase was 46.47% as the u<sub>in</sub> value increased from 0.3 m/s to 0.5 m/s. As the diameter increased from 8 mm to 12 mm and the wall thickness increased from 1.2 mm to 1.8 mm, the average amplitude of IETBs maximum decreased by 98.18% and 11.73%, respectively, and the heat transfer intensity of vibration enhancement decreased by 10.69% and 15.83%, respectively. According to the performance evaluation criteria analysis, when the wall thickness was constant at 1.5 mm, the comprehensive performance of the IETB heat exchanger with a diameter of 8 mm was better than that at other diameters. When the diameter was constant at 10 mm, the IETB heat exchanger with a wall thickness of 1.2 mm had a better comprehensive performance than those with other wall thicknesses.

Numerical Study on Heat Transfer Characteristics of Dielectric Fluid Immersion Cooling with Fin Structures for Lithium-Ion Batteries

Electric vehicles (EVs) are incorporated with higher energy density batteries to improve the driving range and performance. The lithium-ion batteries with higher energy density generate a larger amount of heat which deteriorates their efficiency and operating life. The currently commercially employed cooling techniques are not able to achieve the effective thermal management of batteries with increasing energy density. Direct liquid cooling offers enhanced thermal management of battery packs at high discharging rates compared to all other cooling techniques. However, the flow distribution of coolant around the battery module needs to be maintained to achieve the superior performance of direct liquid cooling. The objective of the present work is to investigate the heat transfer characteristics of the lithium-ion battery pack with dielectric fluid immersion cooling for different fin structures. The base structure without fins, circular, rectangular and triangular fin structures are compared for heat transfer characteristics of maximum temperature, temperature difference, average temperature, Nusselt number, pressure drop and performance evaluation criteria (PEC). Furthermore, the heat transfer characteristics are evaluated for various fin dimensions of the best fin structure. The heat transfer characteristics of the battery pack with dielectric fluid immersion cooling according to considered fin structures and dimensions are simulated using ANSYS Fluent commercial code. The results reveal that the symmetrical temperature distribution and temperature uniformity of the battery pack are achieved in the case of all fin structures. The maximum temperature of the battery pack is lower by 2.41%, 2.57% and 4.45% for circular, rectangular, and triangular fin structures, respectively, compared to the base structure. The triangular fin structure shows higher values of Nusselt number and pressure drop with a maximum value of PEC compared to other fin structures. The triangular fin structure is the best fin structure with optimum heat transfer characteristics of the battery pack with dielectric fluid immersion cooling. The heat transfer characteristics of a battery pack with dielectric fluid immersion cooling are further improved for triangular fin structures with a base length -to -height ratio (A/B) of 4.304. The research outputs from the present work could be referred to as a database to commercialize the dielectric fluid immersion cooling for the efficient battery thermal management system at fast and higher charging/discharging rates.

Thermo-convective behavior and entropy generation studies on Alumina and Titania nanofluids flowing through polygonal ducts

The current study emphasizes the thermal performance of 0.05, 0.1, and 0.2% volume concentrated Al2O3/DI water and TiO2/DI water nanofluids flowing through three different ducts (equilateral triangle, square, and hexagonal shaped) were compared with circular tubes. The thermo-convective experiments were carried out in the turbulent regime (5000≤ Re ≤ 10,000) at iso-heat flux conditions. The experimental outcome reveals that the maximum Nusselt number of 78, 74, and 71 were achieved when 0.2% Al2O3/DI water flowed through hexagonal, square, and triangular ducts, respectively. Similarly, the desired lowest friction factor of 0.03692, 0.03688, and 0.03686 was achieved by the same nanofluid through those orientations, which ensured that the Al2O3/DI water outperformed TiO2/DI water. The maximum Performance Evaluation Criteria (PEC) was 1.102 when comparing the 0.2% Al2O3/DI water nanofluid flow through a hexagonal duct with water through a circular tube, and 1.169 when the flow through the duct is compared with DI water flow through the same hexagonal duct. When evaluating the performance of all these augmented flow orientations by Entropy Performance Evaluation Factor (EPEF), the maximum values of 665, 572, 635, and 654 were achieved by 0.2% Al2O3/DI water and 660, 531, 561, and 628 by 0.2% TiO2/DI water while flowing through the circular tube, triangular, square, and hexagonal ducts, respectively. Correlations for Nusselt number and friction factor employable to these orientations were derived based on the dominant dependant parameters.

Multi-objective optimization of single-phase flow heat transfer characteristics in corrugated tubes

In this study, the use of corrugated surfaces as one of the passive heat transfer improvement methods on straight tubes is numerically investigated related to the determination of Nusselt number, friction factor, and performance evaluation criteria. With the same diameter of 5.75 mm and length of 390 mm, 9 corrugated tubes having corrugation pitches of 6, 12 and 18 mm, and depths of 0.6, 0.8 and 1.0 mm are considered for the parametric studies. Water is employed as a operating fluid with Reynolds number values from 480 to 6100 covering different flow regimes. Sensitivity analyses by Genetic Aggregation Response Surface Methodology and multi-objective optimization analyses by NSGA-II are performed in order to maximize heat transfer and minimize pressure drops. It is determined that the thermal-flow augmentation created by the use of corrugated surfaces in laminar flow conditions is quite higher than those in the turbulent region of the smooth tube. According to the obtained optimum parameters and flow conditions, the maximum value of the performance evaluation criteria is 2.48 in comparison to the use of equivalent smooth and corrugated tubes. In addition, Nusselt number and friction factor equations are suggested by using 220 data points within deviation bands of ±10% and ±15%, respectively.

Forward osmosis, reverse osmosis, and distillation membranes evaluation for ethanol extraction in osmotic and thermic equilibrium

One of the significant challenges of the industry is the economic extraction of ethanol from aqueous solutions of interest to the food industry. Specifically, in the alcoholic beverages industry, the non-alcoholic beverage market has gained importance, demanding more non-alcoholic drinks with higher organoleptic quality. In this context, the technology related to the use of membranes has shown great potential. Our research aims to determine the performance of forward osmosis using FO, RO, and MD membranes as an option in the extraction of alcohol in an osmotic (Δπ = 0) and thermal (ΔT° = 0) equilibrium process. The results showed that all the membranes have the potential to dealcoholize a 12% v.v. synthetic ethanol solution. The results showed that Membrane Distillation is a viable strategy as a complement in a hybrid FO-MD approach, achieving ethanol flux values close to those offered by FO membranes and much higher than those shown by RO membranes. We also proposed other technical criteria for membrane performance evaluation, such as maintaining a low reverse salt flux and a low or no water flux to keep the organoleptic properties of a hypothetical alcoholic beverage subjected to the FO-MD hybrid process. For a high Ethanol/Salt flux ratio, the RO-82V and FO-CTA membranes presented the best performance. Furthermore, in an Ethanol/Water flux ratio, RO membranes perform best when working in an osmotic equilibrium process with a water flux equal to zero. Regarding the FO membranes, in an Ethanol/Water flux ratio, the FO-TFC membrane presented the best performance.

Multi structural parameter analysis based on the labyrinth valve design with high pressure drop and low noise

Labyrinth channel design is a key for achieving high pressure loss for the labyrinth valve in a thermal power plant. However, the labyrinth channel structures are relatively complex, with many influencing parameters. An unreasonable design generates high noise, adversely affecting personnel and equipment. In this paper, pressure drop is used as a typical parameter for evaluating pressure loss performance, while cavitation, flow velocity, and transmission loss are used as characteristic parameters for assessing noise performance. A comprehensive evaluation criteria of noise performance is constructed. The numerical models with various stage numbers, entrance widths, channel depths, transition part parameters, and expansion coefficients are established, the effects of different structural parameters on the labyrinth channel pressure loss and noise performance are systematically studied to achieve a labyrinth valve design with high pressure loss and low noise. The results show that the influence of different structural parameters on the labyrinth channel pressure loss and noise performance is not the same. The parameter selection of multi-stage, small entrance width, medium channel depth, large transition part parameters, and high expansion coefficient is important way for realizing the design of high pressure loss and low noise labyrinth valve.

Intensification of thermal efficiency of a cross-flow heat exchanger under turbulent flow conditions using CuFe2O4/water nanofluid

The use of nanofluids has opened new intellectual horizons in improving the performance of heat exchangers. Therefore, in this work an experimental study was conducted for investigating the effect of CuFe2O4/water nanofluid on the heat transfer rate enhancement in a cross-flow type heat exchanger under turbulent flow conditions. Heat transfer rate were examined at different volume percentages of CuFe2O4 nanoparticle (0≤ φ ≤ 0.9% vol.) with a nominal diameter of 28 nm at three inlet fluid temperatures of 72, 80 and 88 °C, water pump rotational speeds of 2000 rpm and 3000 rpm, and cross-flow fan speeds of 1500, 2000 and 2500 rpm. According to the results, the heat transfer rate in the case of using nanofluids with a volume percentage of 0.1% was significantly higher than that of distilled water in all test conditions. The highest relative increase in the universal heat transfer coefficient (U) equal to 92.3%, compared to the use of water (φ = 0) was obtained at 0.1% vol% of nanoparticles, the lowest temperature of fluid entering the heat exchanger (72 °C), medium pump speed (2000 rpm) and low fan speed (1500 rpm). The maximum Performance Evaluation Criterion (PEC) improvement of 44.46% also occurred at this working condition.

Thermal-hydraulic characteristics of FLiBe in annuli with helical wire

A fully tight-fitting triangular wire coil is used to enhance heat transfer of FLiBe in the annular channel for the first time. The numerical simulations of annular channels with triangular wire coil were performed with three helical pitches, three annular widths, and one equilateral triangle corresponding to Reynolds number of 4000–10000. It is found that adding triangular wire coil generates a vortex and reduces significantly the lengths of flow and thermal entrance regions of the annular channel. The local Nusselt number for peripheral point is extremely non-uniform. The Nusselt number decreases with annular width and helical pitch increase. The Nusselt number of enhanced annular channel is 1.45–1.98 times that of smooth annular channel. The overall performance of annular channel with helical pitch of 15 mm and annular width of 10 mm is best by using the principle of entropy generation. However, by using the performance evaluation criteria, the annular channel with helical pitch of 15 mm and annular width of 19.4 mm is best when the Reynolds number is less than or equal to 5500. And the annular channel with helical pitch of 20 mm and annular width of 19.4 mm is best at the high Reynolds number.

Research and optimization of new wavy fin geometry parameters in positive temperature coefficient heaters for electric vehicles

The positive temperature coefficient (PTC) heater is an automotive heating device widely used in electric vehicles to ensure the conversion efficiency of the battery in winter, but the heater consumes a large amount of battery capacity. Therefore, it is necessary to improve the performance of PTC heaters to meet the maximum mileage of electric vehicles in winter. We propose to replace plate fin heating with wavy fins and develop PTC heaters with 7 kW class and higher heating performance. In the flow rate range of 100–500 kg/h, this study investigates the effects of four parameters, including fin pitch (Fp), fin amplitude (Fa), fin thickness (Ft) and ripple number (Rn) on the heat transfer performance and resistance performance of the heater by numerical simulation. The area goodness factor is chosen as the performance evaluation criterion for heat transfer and flow. Based on the multi-response Taguchi design method, the influence factors are Fp, Fa, Ft and Rn, with four levels of each factor. Heating capacity, AGF and pressure drop is used as three response, and the comprehensive weighted score is taken as the overall performance criterion. The results of the range analysis and analysis of variance (ANOVA) using Minitab software show that reducing Fp and choosing a smaller Rn can improve the overall performance, the best overall performance when Ft = 0.3 mm, Fa is a secondary factor and it reflects the volatility. The optimal combination of Fp = 2 mm, Fa = 0.8 mm, Ft = 0.3 mm and Rn = 2 was obtained by discussing the design parameters. The new wavy fin heater has a heating performance of 7.19 kW and a pressure drop of 18.3 Pa. At the standard flow rate, the wavy fin heater has 16.91 % higher heating capacity, 7.95 % higher pressure drop and 33.40 % higher AGF than the plate fin heater. The comparison of results shows that the numerical simulation and analysis method based on Taguchi's design proposed in this paper can achieve the optimal design of PTC heaters, this method provides a reference for the performance prediction and parameter design of early products.