In-line Arrangement Research Articles

Optimization of Thermal and Pressure Drop Performance in Circular Pin Fin Heat Sinks Using the TOPSIS Method

This study aims to optimize the thermal performance of pin fin heat sinks by minimizing the maximum temperature of the heat source. Using ANSYS ICEPAK, simulations were conducted for various design parameters, including the number of fins, inlet flow rate, and fin thickness, across circular fins in both inline and staggered arrangements. The circular staggered configuration with 36 fins (3 mm thick) and a flow rate of 6 CFM (Cubic Feet per Minute) achieved the lowest temperature of 34.96 °C, outperforming the inline arrangement. The Taguchi method helped strike a balance between heat transfer and pressure drop, revealing that flow rate has a greater influence when varied compared to the number of fins and fin thickness. An optimal configuration was identified with 36 fins and a flow rate of 4 CFM, which was less sensitive to operational variations. Analysis of Variance (ANOVA) revealed that inlet flow rate significantly impacts heat sink performance, while polynomial regression models demonstrated strong generalization capabilities, with Root mean square error (RMSE) of 8.92%. These findings provide reliable predictive tools and practical insights for optimizing heat sink designs in electronics cooling applications. By utilizing the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method, the coefficient of relative closeness (Cn*) is plotted as a main effect. Referring to the multi-objective optimization-based TOPSIS method, it is found that the attributes are partly from the inlet flow rate (Q) are 63.4% of the number of fins (Nf) (25.05%).

Alignment impact of three unequal-sized square cylinders on the wake flow pattern and fluid forces

A finite volume method and a full multi-grid technique are implemented to analyze the influence of alignment type of three unequal-sized square cylinders on the characteristics of wake flow pattern and fluid forces of the flow. Three-square cylinders with different dimensions C1, C2, and C3 are arranged for three main combinations, namely, in-line arrangement, side-by-side arrangement, and staggered arrangement. Analysis of flow patterns in different regimes is performed for the different arrangement type and for Reynolds number (Re) varied in range (1, 200). The second parameter is the arrangement type. The wake flow patterns including vortex shedding and the evolution of vortices, and force coefficients are predicted and analyzed for the three unequal-sized square arrangements in terms of streamlines, iso-vortices, and drag (CD) and lift (CL) coefficient evolutions for steady and unsteady regimes. Of great interest is the analysis of the combined effect of the Reynolds number and the adopted arrangements on the bifurcation emergence phenomenon and the CL and CD evolutions profiles while predicting the critical Reynolds number for each configuration. The numerical outcomes demonstrate that Re values and the different three-square cylinders arrangements have a prominent influence on the flow characteristics. The study reveals that the unsteady regime of the flow appears in the side-by-side arrangement at (Rec = 63), in the staggered arrangement (Rec = 76), and finally in the in-line arrangement for the specific value (Rec = 146). Furthermore, the effect of different arrangements on time averaged drag and lift is explored and discussed. It is found that the in-line alignment causes a strong reduction in drag values, while highest values are obtained for the side-by-side combination.

Film Superposition Characteristics With Laidback Fan-Shaped Holes Under the Influence of Internal Crossflow

Abstract In the serpentine passage of actual rotor blades, the coolant at the inlet of the film hole has an internal crossflow. The internal crossflow significantly influences the film cooling effectiveness of multi-row film holes. This paper presents a numerical investigation of the superposition characteristics of multiple rows of laidback fan-shaped holes under the influence of internal crossflow. The numerical simulations utilize the RANS method considering the effects of blowing ratio, crossflow velocity ratio, arrangement patterns, and row-to-row spacing of the internal crossflow on the superposition characteristics of film holes. The results indicate that film cooling effectiveness exhibits a distinctly asymmetric distribution under crossflow conditions. At different blowing ratios, there exists an optimal crossflow velocity ratio, at which the laterally averaged film cooling effectiveness is maximized. The crossflow-to-jet velocity ratio (VRi) is utilized to comprehensively evaluate the impact of blowing ratios and crossflow velocity ratios, and the range of high area-averaged film cooling effectiveness is accurately captured. Regarding the study of arrangement patterns and row-to-row spacings, it has been found that under identical coolant mass flowrates, the staggered arrangement is better than the inline arrangement in both laterally averaged film cooling effectiveness and cooling uniformity. Meanwhile, reducing the row-to-row spacing leads to an improvement in laterally averaged film cooling effectiveness. Finally, an assessment of the Sellers model's applicability under crossflow conditions revealed that it demonstrates good applicability in cases of staggered arrangement with lower blowing ratios.

Direct numerical simulation of skin friction drag reduction on supersonic turbulent boundary layers with micro-blowing

The flow control mechanism and skin friction drag reduction characteristics of micro-blowing on a Ma2.25 supersonic turbulent boundary layers are investigated through direct numerical simulations, and the effects of blowing intensity and micro-hole arrangement on turbulent structure and skin friction drag in the local control region and downstream region are considered. The results show that the skin friction drag decreases remarkably in the control region under the influence of micro-blowing, and a certain drag reduction can still be maintained in the downstream region. The drag reduction performance in the control region is jointly determined by blowing intensity and micro-hole arrangement. The drag reduction performance of the staggered arrangement is 5.7% and 11.1% higher than that of the inline arrangement at blowing intensities of 0.2% and 0.5%, respectively. However, it is found that the drag reduction in the downstream region is only determined by the blowing intensity and almost independent of the micro-hole arrangement. The effect of micro-blowing on turbulent structures is quantitatively characterized by energy spectrum analysis, and it shows that the streamwise scales of the near-wall streaks are significantly reduced under the influence of micro-blowing. In addition, the compressibility of fluids and the local reverse transfer in the strong expansion region are significantly improved under the influence of micro-blowing. These effects should be considered when performing Large Eddy Simulation modeling of supersonic turbulent boundary layers with micro-blowing.

Numerical study on heat transfer characteristics of LBE cross flow tube bundle under rolling conditions

Combined with the neutron economy and good heat transfer performance, lead–bismuth fast reactor (LFR) has a larger prospect for marine applications. Helical coiled once-through tube steam generator (HCOTSG) is also a typical heat exchanger option for LFR. It is widely adopted in a variety of energy utilization fields, such as petrochemical industry. Study on Lead-bismuth eutectic (LBE) cross flow of tube bundle under moving conditions is necessary for obtaining the flow and heat transfer characteristics of LBE HCOTSG in marine conditions. A numerical method to simulate the heat transfer characteristic of LBE cross tube bundle flow under rolling conditions is proposed. The influence of the rolling conditions on the models with different tube arrangements are investigated. The temperature fluctuation curves with time and the time-averaged heat transfer characteristics are compared and analyzed. The results of the influence of rolling conditions under different working conditions and different tube bundle arrangements are obtained. The improvement ratio under inclined arrangement and staggered arrangement is more than 20 %, but the improvement under inline arrangement can only reach 10–15 %. Among the calculated models under different rolling conditions, the maximum heat transfer improvement reached 27.3 %. Besides, the circumferential temperature results under different conditions were also compared to analyze the influence of rolling conditions. This study may contribute to the application of LBE HCOTSG under marine conditions.

دراسة عددية لتعزيز انتقال الحرارة للتدفق المضطرب في ال نابيب المدملة

The importance of heat transfer enhancement has gained greater significance in many engineering applications, and a great amount of effort has been devoted to the use different techniques to improve the thermal performance of flowing fluids in pipes. Dimpled tubes were used for this purpose in this study. In this investigation, the heat transfer-flow characteristics of turbulent flow in dimpled tubes subjected to uniform heat flux are numerically investigated. The rate of heat transfer, friction factor, and performance evaluation criterion were determined for various designs of dimpled tubes and compared with smooth tubes. The considered cases are conducted in the Reynolds number range of 3000 to 12,000. The ANSYS Fluent R19 is used for this purpose. The Reynolds-averaged Navier-Stokes equations(RANS) are used to model the governing flow equations. The realizable k-ε turbulence model is used with enhanced wall conditionsto simulate turbulent flow adjacent to the inner wall surface. The results revealed that the rate of heat exchange in dimpled tubes higher than that of smooth ones. but with additional pressure loss. Moreover, the heat transfer performance of the staggered arrangement is higher than the inline arrangement by 17 %. Also, the performance evaluation criteria (PEC) increases with the increasing in dimples diameter, and decreases with increasing in relative pitch spacing, the maximum enhancement reaches 31% for d = 5 mm, and relative pitch spacing S/D = 2 at Re = 4000.

Off-axis digital lensless holographic microscopy based on spatially multiplexed interferometry.

Digital holographic microscopy (DHM) is a label-free microscopy technique that provides time-resolved quantitative phase imaging (QPI) by measuring the optical path delay of light induced by transparent biological samples. DHM has been utilized for various biomedical applications, such as cancer research and sperm cell assessment, as well as for in vitro drug or toxicity testing. Its lensless version, digital lensless holographic microscopy (DLHM), is an emerging technology that offers size-reduced, lightweight, and cost-effective imaging systems. These features make DLHM applicable, for example, in limited resource laboratories, remote areas, and point-of-care applications. In addition to the abovementioned advantages, in-line arrangements for DLHM also include the limitation of the twin-image presence, which can restrict accurate QPI. We therefore propose a compact lensless common-path interferometric off-axis approach that is capable of quantitative imaging of fast-moving biological specimens, such as living cells in flow. We suggest lensless spatially multiplexed interferometric microscopy (LESSMIM) as a lens-free variant of the previously reported spatially multiplexed interferometric microscopy (SMIM) concept. LESSMIM comprises a common-path interferometric architecture that is based on a single diffraction grating to achieve digital off-axis holography. From a series of single-shot off-axis holograms, twin-image free and time-resolved QPI is achieved by commonly used methods for Fourier filtering-based reconstruction, aberration compensation, and numerical propagation. Initially, the LESSMIM concept is experimentally demonstrated by results from a resolution test chart and investigations on temporal stability. Then, the accuracy of QPI and capabilities for imaging of living adherent cell cultures is characterized. Finally, utilizing a microfluidic channel, the cytometry of suspended cells in flow is evaluated. LESSMIM overcomes several limitations of in-line DLHM and provides fast time-resolved QPI in a compact optical arrangement. In summary, LESSMIM represents a promising technique with potential biomedical applications for fast imaging such as in imaging flow cytometry or sperm cell analysis.

Analyze the influence of nozzle shape and orientation on inline arrangement of multiple jets impingement on a concave surface

ABSTRACT The present study reports the thermal behavior of multiple jets on a hot concave surface with different nozzle geometries such as circular and elliptical and different orientation. Tests are performed with five different nozzles at different values of nondimensional nozzle to surface distance (z/d = 2–10) and Reynolds number (5000–28,000). Here, the parameter coefficient of variation (COV) is used to estimate the non-uniformity in the local Nu variation. For N-2, the value of CO V y , non − dim is found to be 50–60% higher compared to N-3 at z/d = 2; while at z/d ≥ 8, for N-3, the value of CO V y , non − dim is found to be 10–15% higher compared to N-2. The higher temperature uniformity ( CO V x , non − dim ) is noted in the fountain region compared to impingement region for the circular and elliptical nozzles. The thermal performance of elliptical jets is found to be sensitive toward the jet orientation at lower z/d values. The magnitude of temperature non-uniformity decreases with the increase in the z/d values. Among the tested nozzles, Nozzle N-2 consistently demonstrates superior performance across all nozzle-to-plate distances and with an increase in the z/d value improvement with nozzle N-2 reduces.

In-line PIV Using a Schlieren System

"The article describes recent tests and developments of PIV recording and evaluation techniques that take advantage of strong forward scattering of tracer particles by in-line recording set ups. By collimating the light of a low-power light source between a pair of schlieren mirrors the observation area is increased to more than 350 mm. The same setup allows for schlieren recording of density gradients. The in-line imaging arrangements have a relatively high background intensity level on which brighter particle images can be detected. Ideally this background is constant in time such that it can be removed through subtraction. The use of forward scattering has a significant influence on the required pulse energy of the light source used. Typically, sufficient illumination is achieved with about 1% of the pulse energy that would normally be used for a conventional orthogonal PIV arrangement employing a laser light sheet. "

Numerical study on heat transfer characteristics of multiple air jet impinging at lower jet to plate spacing

For multi-nozzle jet impinging, the effects of impinging distance (Z/D), streamwise spacing (X/D) and spanwise spacing (Y/D) on heat transfer characteristics should be considered. The heat transfer characteristics for multi-nozzle jet impinging structure with different nozzle spacings were investigated by numerical method. When the impinging distance is constant (Z/D = 0.2), the effects of Reynolds number (Re = 12,000–28,000), streamwise spacing (X/D = 3, 4, 6, 8, 10), spanwise spacing (Y/D = 3, 4, 6, 8, 10) and impinging nozzle arrangement (in-line structure and staggered structure) are considered. The Standard k-ε model was chosen for simulating after comparison to the relevant experimental values. The influences of nozzle spacing and the Reynolds number on the heat transfer characteristics were examined. The Colburn factor j and friction factor f were investigated in relation to Re. The performance criteria η of the Reynolds number ranging from 12,000–28,000 was calculated. The calculations indicated that the jet impinging heat transfer coefficient is highest under the structure of X/D = 3 and Y/D = 3. Compared to the in-line arrangement, the staggered arrangement has a higher average Nusselt number. This is because the turbulent kinetic energy of the staggered structure on the impinging target surface is larger and the heat exchange efficiency is higher. However, the gap between the average Nusselt numbers of the staggered and in-line nozzle arrangements decreases with an increase in Reynolds number. Given the same heat exchange surface, the average Nusselt number is highest under the X/D = 8 and Y/D = 8 arrangements. This is because the larger the impinging nozzle spacing, the fewer the number of nozzles. Therefore, the greater the speed of the gas reaching the nozzle outlet, the greater the average Nu of the target surface.

Numerical investigation and comparison on thermal-hydraulic performance of H-type finned tube heat exchanger

H-type finned tube heat exchangers have been widely used in boilers and waste heat recovery devices due to their advantages of wear resistance and anti-fouling. In order to improve the energy-saving effect, the flow and heat transfer characteristics of H-type finned tube heat exchangers with different tube bundle arrangements were studied. It was found that, at the same Re number, the column staggered arrangement can compensate for the limited heat transfer performance of the in-line arrangement and reduce the high pressure drop associated with the row staggered arrangement. Honeycomb arrangement was proposed based on the column staggered arrangement. Then, the effects of Re and tube pitches thermal-hydraulic performance of tube bundles with in-line and honeycomb arrangements were examined. The critical tube pitch or velocity at which the honeycomb tube bundle achieves the same thermal performance as the in-line tube bundle are determined. The results provide valuable insights for the practical application of flue gas heat exchangers with honeycomb arrangement.

Local Heat Transfer of a Smooth Flat Plate Impinged by Multiple Jets

A smooth flat plate impinged by multiple jets is investigated for the local heat transfer using a thermal imaging technique. An inline arrangement of circular jets with all side exit scheme is implemented. Jets are introduced from a 4 mm thick orifice plate. The jet diameter is 3 mm. Reynolds numbers (based on the jet diameter) range covered in this study are from 500 to 15,000. The variation of the local, spanwise average, and overall average Nusselt numbers is investigated for nozzle exit to targeted plate spacing of 0.5 d–6 d, where d is the jet diameter. A periodic pattern is witnessed in the local Nusselt number with a drop in its amplitude in the spanwise direction. For a given Reynolds number, the local and average Nusselt numbers are influenced by nozzle exit to targeted plate spacing. The influence of Reynolds number on the local and average Nusselt number is captured using Re n . The value of n is found to be 0.5 and 0.6 depending on the Reynolds number range. In comparison with a single jet, multiple jet impingement on a smooth flat plate deteriorates the local Nusselt number. A semi-empirical correlation that captures the periodic nature of local and average Nusselt numbers is suggested.

Fluid structure interaction problem for flow past three unequal sized square cylinders at different Reynolds numbers

The flow past three square cylinders of unequal size placed in an inline arrangement is studied using the lattice Boltzmann method at different Reynolds numbers [Re = (u∞ d)/ν] within the range of Re = 120, 150, 160, 175, and 200 for various gap spacings (g = s/d), ranging from 1 to 6. This study focused on the symmetric examination of flow behavior for various gap spacing within the three unequal-sized square cylinders. The main objective of this study was to investigate the effects of Reynolds numbers and gap spacing for flow structure mechanism and vortex shedding suppression in between the gap and down-stream position of all three cylinders. Results are obtained in terms of vorticity contours visualization, drag and lift coefficients, Strouhal number, and physical parameters. In vorticity contour visualization, different flow behaviors are observed, known as flow regimes, and are named according to their characteristics, and they are (i) steady flow regime, (ii) shear layer reattachment flow regime (SLR), (iii) fully developed vortex shedding flow regime, (iv) two-row fully developed vortex shedding flow regime, and (v) fully developed irregular vortex shedding flow regime. The present study also includes a discussion on aerodynamic forces, namely the mean drag coefficient (Cdmean), root mean square of the lift coefficient (Clrms), and Strouhal numbers (St) for three cylinders with sizes d = 20, d1 = 15, and d2 = 10, respectively. The maximum value of Cdmean for the first cylinder (C1) is obtained at (Re, g) = (200, 3) that is, 1.5156, where the existing flow regime is the SLR flow regime, while for C2 and C3, the maximum Cdmean values are examined at critical flow behaviors, where the existing flow regime is a fully developed irregular vortex shedding flow regime. Negative values of Cdmean are also examined for cylinders C2 and C3 at some combinations of (Re, g), attributed to the effect of thrust. Furthermore, it is noticed that the values of Strouhal number are increased with an increment in values of gap spacing. The highest value of the Strouhal number for all three cylinders is observed for C1 at (Re, g) = (120, 5), reaching 0.1556 along with a two-row fully developed flow regime. Furthermore, it is investigated from the present problem that the position of unequal sized square cylinders strongly influenced the flow structure mechanism. The information found and discussed in this study could be effective for structure designing arrangement in the case of three square cylinders of unequal size placed in a horizontal arrangement.

Heat Transfer and Flow Resistance in Crossflow over Corrugated Tube Banks

The engineering of tubes with surface corrugations is recognized as an effective method for enhancing heat transfer within the tube. Yet the impact of surface corrugation on the flow and heat transfer around the tube’s exterior remains inadequately explored. This study investigates the crossflow and heat transfer characteristics in banks of periodically inward-corrugated tubes using computational fluid dynamics. Numerical simulations were performed for both in-line and staggered tube arrangements, covering Reynolds numbers from 1000 to 10,000. The aim was to examine how various corrugation parameters affect heat transfer and flow dynamics in tube banks configured in both in-line and staggered layouts. The results show that the heat transfer and the pressure drop in crossflow across tube banks are substantially influenced by changes in corrugation parameters. Specifically, in the in-line arrangement, both the Nusselt number and Euler number decrease significantly as the corrugation height increases. In contrast, in the staggered arrangement, the Nusselt number and Euler number exhibit less variation in response to surface corrugation. A comparative analysis of performance criteria suggests that a staggered arrangement is more advantageous for improving thermal–hydraulic efficiency in crossflow through corrugated tube banks.

Effects of Flow Pulsation and Surface Geometry On Heat Transfer Performance in a Channel with Teardrop-Shaped Dimples Measured by Transient Technique

Abstract This study focuses on the heat transfer performance of a pulsating flow over a channel surface with teardrop-shaped dimples. Heat transfer measurements were performed by a transient technique with compensation of three-dimensional heat conduction under a bulk Reynolds number of 25,000. Seven types of surfaces with the teardrop-shaped dimples were examined, where dimple arrangement (in-line/staggered) and inclination angle (0-60 deg) were varied. A pulsating flow with the Strouhal number of 0.15 was generated by vibrating a rubber film section on the channel wall using a vibration generator. The pulsation amplitude was evaluated by calculating the root-mean-square value of the phase averaged velocity. Two conditions of the pulsation amplitudes were examined (0.09 and 0.12 of mean velocity). The results showed that the surface-averaged Nusselt number and friction factor for the pulsating flow increased from those for the steady flow. The highest increases of the surface-averaged Nusselt number and heat transfer efficiency index appeared in the 30deg in-line arrangement, and those were 16.1% and 9.8%, respectively, at most as compared with the steady case. Due to the flow pulsation, the local Nusselt number was enhanced at the leading-edge region of the dimples, and supplementary RANS/URANS results showed that the flow separation size was shrunk by the flow pulsation there.

Experimental Study of Reverse Flow Solar Air Heater Having Perforation and Delta Wing on Absorber Plate

fThe traditional solar air heater (SAH) has poor thermal performance due to low heat transfer coefficient. Artificial roughness, flow passage alteration, absorber modification, etc. can enhance it. Thus, an experimental investigation is performed to study the thermohydraulic characteristics of a reverse flow SAH with perforated absorber and delta wing (DW) structure. The present study investigates the effect of attack angle (15°–75°) at constant streamwise pitch (35 mm), transverse pitch (70 mm), height (h), and width (w) of DW 20 mm, under Reynolds number (Re) ranging from 4000 to 20 000. The perforation index (PI = ADW/Aap) for inline and staggered arrangements are 9.52 and 4.76, respectively. The results indicate that the concept of perforated absorber and DW leads to enhanced heat transfer, reduced pressure drops, and enhanced utilization of solar energy. The Nusselt number (Nu), friction factor (f), and thermohydraulic performance enhance about 6.6, 9.4, and 3.06 times, respectively, at attack angle 75o for inline arrangement of DW over the smooth duct. Thermohydraulic performance of reversed‐flow SAH is compared with previously published works, and it highlights that the full‐length inline and staggered arrangement of the DW offers the most significant improvements in heat transfer and friction factor.

The impact of tube bundle layout on the thermal and fluidic behaviour of liquid lead–bismuth eutectic in a helical-coiled once-through steam generator

This study introduces a numerical model to assess the thermal and frictional properties of LBE crossflow over tube bundles on the shell side of a Helical-coiled Once-Through Steam Generator (H-OTSG) considering different arrangements, including inline, obliquely staggered, triangular, and rotated square configurations. The k-ω SST turbulence model combined with Kays turbulent Prandtl number model is utilized to develop the numerical model. The simulation results have been validated against experimental data and empirical correlations. The layouts of the tube bundles significantly influence the generation of transverse flow, vortical structures and rate of heat transfer in the flow domain. The maximum Nusselt number of 8.2 is observed for the triangular layout as significant crossflow is induced, which is a 10% increase compared to the inline arrangement where the Nusselt number is 7.45. Triangle layouts also exhibit a higher friction factor of 0.45, marking a 20% increase compared to the 0.45 friction factor observed in the inline arrangement. Increasing the oblique angle usually reduces the heat transfer rate and friction factor. Yet, at a 45-degree layout, higher turbulence intensity results in a Nu of 7.05, surpassing 6.93 observed at 30° but falling short of 7.15 at 15°. Nu decreases for rotated square arrangements, but a friction factor greater than the inline arrangement is observed at higher diagonal pitches. The Thermal Enhancement Factor (THEF) is employed to assess the thermal effectiveness of the different tube bundle layouts, and the maximum THEF of 1.1 is observed for the layout with an oblique angle of 45°. Favorable THEF values of 1.06 and 1.05 are recorded for the triangular layout and 30-degree oblique angle, respectively. This numerical study will assist the design and development of LBE H-OTSG.

Numerical study on flow and heat transfer characteristics in structured packed bed

The ANSYS software is introduced to reproduce the in-line and staggered sphere packed bed model. To investigate the influence of model on the heat transfer and flow characteristics in the high temperature packed bed, numerical simulations of pore-level was used to numerically appreciate the changes of pressure drop, temperature and velocity. The simulation values qualitatively agree with the experimental result. The results show that the pressure drop in high temperature packed bed increases significantly. The pressure drop increases about 3200 Pa when the inlet velocity is 0.33-0.73 m/s. The model has significant influence on the average temperature of solid and gas phases. Compared with the in-line arrangement, the heat wave transfer is slower and the temperature is slightly higher by 20 K in the staggered model. The average velocity in the structured packed bed increases and decreases periodically. In staggered model, the velocity disturbance is more significant. These findings are helpful for understanding transport phenomena in packed beds as well as the design of high efficiency reactors.

On the reductions of airfoil broadband noise through circular dimples

This paper presents systematic and comprehensive experimental investigations into the use of circular dimples to reduce broadband noise on airfoils. The dimples are introduced on the suction surface of symmetric NACA airfoils with different thickness ratios for the control of broadband noise over a wide range of frequencies. The effects of dimple arrangements (inline and staggered) and their locations (1/3rd and 1/5th of the chord from the leading edge) on the noise characteristics are studied in detail to determine the best dimple arrangement, location, and airfoil geometry for low noise. Results indicate that the inline arrangement of dimples positioned at 1/3rdof the chord from the leading edge provides significant noise reductions of about 6–8 dB, particularly from mid to high frequencies. When the dimples are shifted to 1/5thof the chord from the leading edge, the degree of noise reduction decreases, which indicates that the noise reduction performance of airfoils decreases when the dimples are introduced near the leading edge. Further, it reveals that the inline arrangement of dimples on thicker airfoils provides superior noise reductions (6–8 dB) as compared to thinner airfoils (4–6 dB). Flow visualization reveals that the flow field is inconsistent throughout the span of the dimpled surface due to the evolution of small vortices from the dimple corner. It enhances mixing and accelerates flow structures passing over the dimpled surface, which is indicated by the presence of a high degree of spanwise decoherence/phase lag in the hotwire measurements. The presence of higher spanwise decoherence/phase lag due to the presence of the inconsistent flow field leads to significant reductions of far-field noise in dimpled airfoils. Further, the inline arrangement of dimples exhibits much higher levels of noise reduction as compared to staggered ones, due to the presence of a greater degree of spanwise decoherence/phase lag resulting from the substantial disruption of the flow field in the spanwise direction.

Experimental investigation of pressure drop and heat transfer in minichannel with smooth and pin fin surfaces

This study investigates pressure drop and heat transfer characteristics in a minichannel heat exchanger experimentally. The experimental testing was carried out on a minichannel with a hydraulic diameter of about 2.5 mm, with smooth and embedded with circular pin-fins. The testing was conducted with different hot fluids, air and water, over different Reynolds numbers ranges, and over different heat capacity ratios (0.25, 0.5, 0.75, and 1). The experimental study of the pressure drop covers a Reynolds number range between 100-1900 for the hot water, and Reynolds number range between 500-10,000 for the hot air. The hot fluid flows through a channel with an inline arrangement with a 1750 pin fin, while the cold fluid flows through a smooth channel. Increasing flow rates resulted in an increase in pressure drop and heat transfer coefficients. When using pin-fins surface instead of smooth surface, the overall heat transfer coefficient (U) increased by 190% when water is used as the heat transfer fluid (HTF), and the same coefficient increased by 42% when air is used as the heat transfer fluid. Similarly, the difference in pressure drop is low in the case of water-water, while in the case of air-water, the difference in pressure drop is more substantial as Reynolds number increases.