Pitch Ratio Research Articles

Experimental Investigations on Single-Phase Heat Transfer Enhancement in an Air-To-Water Heat Exchanger with Rectangular Perforated Flow Deflector Baffle Plate

Experimental analysis was conducted to investigate the turbulent heat transfer behaviors within a tubular heat exchanger, incorporating a novel baffle plate design. The new design includes a perforated circular baffle plate with a rectangular flow deflector that can be adjusted to different inclination angles. The baffle plate is strategically positioned at the entrance of the heat exchanger, resulting in a swirling flow downstream. To assess the impact of the baffle plate design, three baffle plates were placed longitudinally along the flow, with varying pitch ratios (l/D). The effects of pitch ratio (ranging from 0.6 to 1.2), deflector inclination angle (ranging between 30⁰ to 50⁰), and Reynolds numbers (ranging between 16000 to 29000) were examined. The outcomes highlighted the substantial impact of pitch ratio and inclination angle on the thermal enhancement factor. In particular, compared to single segmental baffle plates working under similar operating conditions. The result indicates that an inclination angle of 30° and a pitch ratio of 1 exhibited an average 41.49% augmentation in thermal-fluidic performance compared with an exchanger with a segmental baffle plate.

Preparation of Silicon Oxide-Carbon Composite with Tailored Electrochemical Properties for Anode in Lithium-Ion Batteries

For high-efficiency and high-stability lithium ion batteries, a silicon oxide-based carbon composite has been developed as an anode material. To minimize structural defects (cracking and pulverization) due to volumetric contraction/expansion during charge/discharge, silicon oxide (SiOx) is adopted. A pitch—a carbon precursor—is introduced to the surface of SiOx using the mechanofusion method. The introduced pitch precursor can be readily transformed into a carbon layer through stabilization and carbonization processes, resulting in SiOx@C. This carbon layer plays a crucial role in buffering the volume expansion of SiOx during lithiation/delithiation processes, enhancing electrical conductivity, and preventing direct contact with the electrolyte. In order to improve the capacity and cycle stability of SiOx, the electrochemical performances of SiOx@C composites are comparatively analyzed according to the mixing ratio of SiOx and pitch, as well as the loading amount in the anode material. Compared to pristine SiOx, the SiOx@C composite prepared through the optimization of the experimental conditions exhibits approximately 1.6 and 1.8 times higher discharge capacity and initial coulombic efficiency, respectively. In addition, it shows excellent capacity retention and cycle stability, even after more than 300 charge and discharge tests.

Influence of fluidelastic vibration frequency on predicting damping controlled instability using a quasi-steady model in a normal triangular tube array

Researchers have applied theoretical and CFD models for years to analyze the fluidelastic instability (FEI) of tube arrays in steam generators and other heat exchangers. The accuracy of each approach has typically been evaluated using the discrepancy between the experimental critical flow velocity and the predicted value. In the best cases, the predicted critical flow velocity was within an order of magnitude comparable to the measured one. This paper revisits the quasi-steady approach for damping controlled FEI in a normal triangular array with a pitch ratio of P/d=1.375. The method addresses the fluidelastic frequency at the stability threshold as an input parameter for the approach. The excellent agreement between the estimated stability thresholds and the equivalent experimental results suggests that the fluidelastic frequency must be included in the quasi-steady analysis, which requires minimal computing time and experimental data. In addition, the model allows a simple time delay analysis regarding flow convective and viscous effects.

Reduction of Aerodynamic Noise radiated from Rectangular Cylinders in Cross Flow

In the present paper the attention is focused on reduction of noise generated from rectangular cylinders in cross flow. The width-to-height ratios of was 3.0. The tube pitch ratio in the transverse direction was 8.0. We measured the aerodynamic sound radiated from the rectangular cylinders in the range of Reynolds numbers from about 10^3 to 10^4. The several high peaks were formed at the spectrum of SPL. The sound power of vortex shedding noise was proportional to the freestream velocity to the power of six. On the other hand, the strange noise occurred at five times the vortex shedding frequency. We have discussed how to counteract the noise generated by rectangular cylinders.

Power consumption and thermal performance of tube employing punched delta winglets

The method of enhancing heat transfer (HT) by combining jets and main longitudinal vortex (MLV) had been proposed and proven effective. Based on this method, this article further explored the interference effect of VG structure on jets, MLVs, and other forms of vortices, as well as the corresponding HT mechanism. The punched delta winglet vortex generators (PDWVGs) applied in this work had three inclined angles (α=30°,60°,90°), three numbers (N=2,4,6), and three pitch ratios (PR=4.89,3.27,1.63). The secondary vortices number (Se values were used to measure the strength and position of different vortices, and the field synergy number (Fc) was also applied to measure the underlying causes of HT rate. The results confirmed that MLVs (induced by PDWVGs in core-flow region) were created, which improved the mixing rate of the air. It was worth mentioning that the structure of MLVs and jets was different at different α values, specifically when α>30°, the jets would carry away heat from the wall surface and would also collide with the reflux MLVs, suppressing the further formation of the reflux region. The Se values of different cases clearly demonstrate the morphology and intensity of mixed vortices. Within the studied parameter range, the biggest TEFof 1.29 was observed at N = 2, PR = 1.63, α = 30° at Re=9090.

Numerical modeling and optimization of perforated twisted tape insert based on hybrid ANSYS‐RSM approach

AbstractHeat exchangers have a wider scope in numerous applications, such as space heating, chemical industries, power stations, and so on. Due to heat loss and the thermal properties of the materials involved, the overall performance of a heat exchanger is questionable. Therefore, studies related to heat transfer techniques are appreciated in the research community. Thus, the present study numerically investigates the heat transfer performance of a horizontal heat pipe equipped with hexagonal perforated twisted tape inserts. Further, the numerical solutions of Nusselt number (Nu), friction factor (f), and thermal performance factor (TPF) are optimized with the help of response surface methodology (RSM). The parameters investigated in this study are Reynolds number (Re), which varies between 500 and 1500, input heat supply (Q) between 100 and 1000 W, and pitch ratio (3.2, 4, and 5.2). ANSYS fluid flow fluent was used to perform flow simulations for three different twisted tape inserts: horizontal, vertical, and alternate hexagon perforations. Optimum solutions are obtained at 1000 W heat supply, 1500 Re, and p/di = 4 from alternatively perforated twisted tape inserts. The optimum Nu, f, and TPF achieved are 119.545, 0.437, and 1.82, respectively. Also, the proposed RSM optimization method is evidenced with a maximum of 2.673% error during the confirmatory test.

A weather optimal heading-based incremental feedback control for dynamic positioning of ships

In this brief, the weather optimal heading-based incremental feedback control algorithm is built for dynamic positioning (DP) of ships in the presence of model uncertainties and unknown environmental disturbances induced by wind, waves and currents. The proposed control algorithm has two parts, i.e., the weather optimal heading portion and the control portion. An improved ZPC-W approach with the deviation of the lateral control force is designed in order to enhance the convergence rate of the desired weather optimal heading and avoid overshoot as well. In addition, based on the iterative sliding mode function, a concise incremental feedback control scheme is designed with the pitch ratio of the thruster as the control input. It is measurable in the practical plant and has nothing to do with ship models with good stability and strong robustness. Lastly, simulation studies are performed to illustrate the performance and the superiorities of the proposed control algorithm.

Heat transfer enhancement through pitch ratio optimization of butterfly inserts in minichannel heat sinks

Thermohydraulic characteristics of square minichannel heat sinks (MHS) with butterfly inserts are computationally studied for Reynolds numbers between 200–900 for two hydraulic diameters (Dh) of 2mm and 2.6mm and varied pitch distances (P). The present investigation examines the effect of pitch ratio (P∗=P/Dh) of butterfly inserts on overall thermal performance of MHS to discern its optimal value for the best possible overall performance. Since inserts result in a concurrent rise in both pressure drop and heat transfer rate, this overall thermohydraulic performance is measured using Performance Evaluation Criteria (PEC), which incorporates the simultaneous effects of change in hydraulic and thermal performance. In the present study, PEC values for all analyzed configurations are found to be above unity, which indicates the adequacy and efficacy of the employed butterfly inserts. The study also corroborates the literature-reported finding that the pitch ratio of butterfly inserts significantly alters the thermohydraulics of MHS. Heat transfer performance is found to improve drastically when pitch ratio is reduced from 5 to 1.5, showing a Nusselt number enhancement of 29.57% to 78.47% for Dh=2mm and 27.73% to 63.47% for Dh=2.6mm for the tested range of Reynolds numbers. However, further reduction in pitch ratio is found to deteriorate the thermohydraulic performance of these inserts. The highest PEC value is obtained for P∗=1.5 for both the studied hydraulic diameters, leading to the conclusion that P∗=1.5 is the optimal pitch ratio of butterfly inserts when employed within rectangular MHS.

The interaction between cross-flow induced vibration and convection heat transfer in tube bundle at subcritical Reynolds number

This work numerically investigates the interaction between flow-induced vibration (FIV) and forced convection heat transfer in tube bundle with a pitch ratio of 1.5 at subcritical Reynolds number (Re = 5 × 103-3 × 104). The range of reduced velocity is 0.53 ≤ Vr ≤ 2.71. The mass-damping parameter of coupling system is 0.07. The three-dimensional refined FIV simulation considering fluid viscous damping has been validated by the literature experiment to capture three continuous FIV mechanisms, namely turbulence-induced vibration, vortex-induced resonance and fluidelastic instability. The heat transfer and pressure drop in tube bundle are validated by the experiment. The coupling of Navier-Stokes equations, energy equations and vibration equations is solved by under-relaxation algorithm. The results of vibration response, the change of damping for the coupling system, flow field and temperature field, heat transfer and pressure drop are presented and delineated in this paper. The results show that for the low velocity turbulence-induced vibration, the interaction between FIV and flow heat transfer is negligible due to the weak fluid–solid interaction. In vortex-induced resonance region, the wall heating makes each row tube be out of phase by affecting the vortex shedding and reduces the positive feedback of resonance, which reduces the amplitude. The wall heating reduces the damping of coupling system, which causes an earlier transition from vortex-induced resonance to fluidelastic instability and a faster increase of amplitude in fluidelastic instability. In both vortex-induced resonance and fluidelastic instability, the vibration of tube bundle dominates the vortex shedding by the natural frequency, and further dominates the change of heat transfer. The best performance of enhanced heat transfer induced by FIV is located in vortex-induced resonance region, in which the time–space averaged Nusselt number is increased by 8.83%. Due to the redistribution of flow field and the elimination of deflective flow pattern, compared with vortex-induced resonance, the increasing ratio of heat transfer induced by FIV is lower and the increasing ratio of pressure drop induced by FIV is higher in the fluidelastic instability.

Effect of triangular perforated flat cone-shaped inserts on performance of double-tube heat exchanger

This study investigated the effect of triangular perforations with flat conical inserts in a double-tube heat exchanger. Triangular perforations with flat cone-shaped inserts were placed inside the inner tube to enhance the heat transfer coefficient. The experiments were conducted for a number of flat conical strips (m) and pitch ratios (P = p/di) for flows varying from Re = 3000 to 9000 at a constant attack angle (α = 20°). The results showed that a triangular perforation with flat cone-shaped inserts remarkably increases the heat transfer factor, in contrast to flat conical inserts. The rise in the coefficient of heat was attributed to the creation of turbulence and disturbance of the boundary layer caused by perforated inserts. Furthermore, it was observed that the heat transfer coefficient increased with the Reynolds number, indicating that the effect of the inserts was more significant at higher fluid velocities. Correlations were developed to compare and analyze the results of the Nusselt number and friction factor. The developed correlation results are in good agreement with the experimental results. The findings obtained from this study can be implemented to enhance the performance and optimize the design parameters of industrial heat exchangers.

Experimental and numerical analysis of intermetallics in Al–Mg friction stir welds

In this research work, it was aimed to analyse the thermal behaviour during FSW in order to understand the diffusion behaviour of Al (AA6061)-Mg (AZ31B) dissimilar joints. Three heat input levels at different weld pitch ratios (WPR) of 0.087, 0.068 and 0.051 are accounted for the analysis. Finite element modelling (FEM) is employed to predict temperature evolutions. From the FEM results and fundamental diffusion equations, the intermetallic thickness and the diffusion behaviour between the Al and Mg material were analyzed and found that the Al-rich intermetallic phases Al3Mg2 grow faster and wider than the Mg-rich phase Al12Mg17. Tensile test demonstrates that a lower welding pitch ratio (WPR) leads to the formation of thicker intermetallic layers, resulting in reduced tensile strength and joint efficiency. In contrast, a higher WPR (0.087) minimizes intermetallic thickness, yielding superior tensile properties (138mpa). Microhardness measurements at the stir zone reveal a broad range from 70 to 164 HV, signifying mechanical heterogeneity. Microstructural reveals that a complex interplay between Al and Mg materials, resulting in fine equiaxed grains, intermetallic compounds, and distinct flow patterns in the stir zone.

Air Bubble Effect on Heat Transfer Enhancement in 90° Ribbed Parallel Channels Based on Photovoltaic-Thermal Collector Cooling

The effect of entrained air bubbles on heat transfer enhancement inside 90° ribbed parallel channels has been experimentally studied to improve electrical efficiency inside future solar panels. In this work, the Reynolds number was measured from 200 to 600. The essential ratios of channel aspect, rib height, and rib pitch were all set to 0.4, 0.18, and 10, respectively. The volumetric flow fraction for all test conditions varied from 0.0 to 0.5. The overall heat transfer distributions on the surface were captured using an infrared thermography camera. The main finding showed that the average heat transfer rate and the thermal performance gained beyond 25–81% and 7–82% compared with the smooth wall. In addition, the volumetric flow fraction of 0.5 at the Reynolds number of 200 became the best.

Optimized geometric designs of desiccant wheels with metal-organic frameworks considering dehumidification capacity and energy

With the increasing demand for handling dehumidification loads and energy savings in air-conditioning systems, solid-desiccant dehumidification systems have been implemented in passive and zero-energy buildings. Although novel metal-organic frameworks (MOFs) have been introduced to improve the performance of desiccant wheels, previous studies have mainly focused on silica gel-based desiccant rotors (DRs). This study aimed to optimize the geometric design of MOF DRs to achieve enhanced dehumidification and energy performance. A numerical model for estimating the performance characteristics of MOF DRs was developed using the adsorption isotherm curves measured in this study. The numerical model was validated by comparing the predictions with the experimental data. The dehumidification and energy performance of the MOF DRs were analyzed in terms of the coating amount, channel pitch, rotor thickness, and process-regeneration area ratio. Accordingly, the optimized geometric designs of the MOF DRs were determined to achieve the maximum dehumidification capacity and minimum energy consumption. Compared to the baseline MOF DR, the capacity-optimized MOF DR exhibited a 47.4 % higher moisture removal capacity, whereas the energy-optimized MOF DR exhibited a 48.6 % lower sensible energy ratio.

The influence of geometrical and operational parameters on thermofluid performance of discontinuous colonial self‐swirl‐inducing baffle plate in a tubular heat exchanger

AbstractAn exploratory investigation was conducted to analyze a tubular heat exchanger's turbulent heat transfer characteristics using an innovative baffle plate design. The design incorporated a perforated conical baffle plate and an adjustable rectangular deflector. The strategic placement of this baffle plate at the heat exchanger inlet facilitated a swirling flow downstream. To assess the impact of this design, three baffle plates with varying pitch ratios (l/D) were positioned in the direction of the flow. The study examined the effects of pitch ratio (ranging from 0.6 to 1.2), deflector inclination angle (ranging from 30° to 50°), and Reynolds numbers (ranging from 16,500 to 29,500). Moreover, the size of the conical baffle plate (H/D) was altered (from 0.25 to 0.15). The findings highlighted the substantial influence of pitch ratio, inclination angle, and height ratio on the heat exchanger's performance. Notably, the configuration featuring an inclination angle of 50° and height ratio of 0.15 exhibited an average performance improvement of 22% compared to other height ratios, inclination angles, and pitch ratios.

The effect of swallow-shaped bionic ribs on the thermal-hydraulic performance of heat exchanger tubes

This paper combines the bionic structure and multi-vortex longitudinal swirl to enhance the heat transfer in the heat exchanger tube while reducing the increase in flow resistance. The design of the enhanced tube with swallow-shaped bionic ribs is inspired by the aerodynamic profile of the swallow flight process to improve the comprehensive performance. The SST k-ω model is selected for numerical simulation. The study of the effect of TCR (triangular concave rib) bionic rib and TVR (triangular convex rib) bionic rib on the flow field characteristics and thermal–hydraulic performance, and the analysis of the effect of pitch ratio (P*) on the thermal–hydraulic performance of TCR tube. The results show that both types of bionic ribs promote the formation and development of multi-vortex longitudinal swirl and transverse swirl in the tube, strengthening the mixing of hot and cold fluids in the tube, improving the synergy of velocity and temperature fields, and making the temperature distribution in the tube more uniform. When P* = 0.75, Nusselt number of the TCR and TVR enhanced tubes is increased by 52.3 %–65.8 % and 43.3 %–57.9 %, respectively, and friction factor is increased by 92.7 %–202.3 % and 78.7 %–263.9 %, respectively, over the smooth tubes. The effect of P* on the thermal–hydraulic performance of the TCR tube is studied, and the PEC value increases as P* decreases. Compared to smooth tubes, TCR enhanced tubes have improved Nusselt number by 26.4 %–95.6 %, friction factor by 50.4 %-345.8 %, and PEC can reach 1.335 when the pitch ratio P* = 0.5. Consequently, the enhanced tube obtains the good comprehensive performance.

Impact of vortex generator, magnetic field, and magnetic two-phase hybrid nanofluid on the performance of a dual-tube heat exchanger: Hydrodynamic and exergy analyses

In this study, a three-dimensional model of a counter-flow dual-tube heat exchanger is developed. The heat exchanger is equipped with a vortex generator, and the working fluid used is a hybrid nanofluid consisting of water and iron-copper oxide. The effects of using the hybrid nanofluid and pure water are investigated. Turbulent flow conditions are assumed within a Reynolds number (Re) range of 30,000 to 48,000, employing the realizable k-ε turbulence model. The coupled algorithm is employed to solve the velocity and pressure equations, and the equations are discretized using the least square method. The vortex generator is utilized with various pitch ratios (Ω). Furthermore, the magnetic field affects the middle section of the inner tube, with Hartmann numbers (Ha) of 35, 65, 95, and 125. The study reveals that an increase in the volume fraction (φ) positively impacts the exergy of the heat exchanger, while an enhancement in Ω negatively influences it. Furthermore, the energy efficiency improves with increasing Re. By applying the magnetic field, the maximum power of the system in producing work corresponds to Re = 36,000 because ηex is reduced when Re > 36,000. At all values of Re, the increase in Ha improves ηex.

A case study on thermal performance of solar air heater with down apex position of open trapezoidal ribs with gaps

This study aims to experimentally explore the impact of multiple open trapezoidal ribs with gaps (MOTRG) on the thermal efficiency of a rectangular duct in a solar air heater (SAH). The designed parameters of ribs i.e. relative limb length (L/w), relative pitch ratio (p/e), relative gap ratio (g/e) and relative rib height (e/Dh) are varied as 0.2–1.0, 6–12, 1–5 and 0.023–0.056, respectively. The experiments have been conducted for Reynolds number (Re) span of 2000–16000. Since then, open trapezoidal rib designs have made significant improvements to SAH performance. A highest value of 78.86% of thermal efficiency has been observed corresponding to α = 60°, g/e = 1, L/w = 0.8, p/e = 10, W/w = 6, and e/Dh = 0.043. The global best values of enhancement factors of 3.032, 2.726 and 2.496 have been found for insolation values of 1000 W/m2, 800 W/m2 and 600 W/m2. The findings demonstrate that, when compared to other roughened SAH ducts, the MOTRG roughened duct provides superior thermal performance.

Experimental investigation on jet impingement heat transfer analysis in a channel flow embedded with V-shaped patterned surface

ABSTRACT Heating and cooling systems benefit from jet impingement as it increases efficiency while reducing operating costs. The combined methodology, integrating jet impingement and passive heat transfer through the use of roughened surfaces, offers significant potential for improving heat transfer. This research presents the results of an experimental study on a channel flow commonly used for air heating, known as a solar air heater (SAH), with impinging air on the heated surface. The surface is embedded with V-shaped ribs as turbulence promoters, and it receives a continuous heat flow of 1,000 W/m2. Various design combinations were tested experimentally, including streamwise pitch ratio X/Dh = 0.866, spanwise pitch ratio Y/Dh = 0.866, jet diameter to hydraulic diameter ratio Dj/Dh = 0.065, and an angle of attack (α) ranging from 45° to 90°. During these experiments, the Re varied from 3,500 to 18,000. The optimal improvement was observed at values of X/Dh = Y/Dh = 0.866, Dj/Dh = 0.065, and α = 60°. This paper presents novel findings demonstrating that incorporating V-shaped rib patterns in SAHs can yield Nusselt numbers up to 5.2 times higher than those in smooth duct SAHs, offering substantial potential for enhanced energy efficiency. When the entering jet impacts and flows along the ribs of the absorber, the findings suggest that the V-shaped ribs accelerate the flow, resulting in enhanced heat transfer. All datasets were also analyzed for their thermo-hydraulic performance, with the maximum value recorded as 3.301 within the constraint range used in this analysis.

The time-averaged aerodynamic performance of three circular columns arranged inline at a subcritical Reynolds number

This study conducted a series of wind tunnel tests to present the time-averaged aerodynamic performance of three equidistant circular columns arranged inline at various incidence angles and center-to-center pitch ratios under a subcritical Reynolds number of 6.4 × 104. The incidence angle α and pitch ratio L/D change in the range of 0°–90° and 1.2–4.0, respectively. The results show that the time-averaged aerodynamic performance of the three columns varies significantly with α as well as L/D. Based on the pitch ratio, the time-averaged aerodynamic coefficients can be approximately classified into four types: minimum pitch ratios (1.2≤L/D < 1.4), small pitch ratios (1.4≤L/D < 2.5), medium pitch ratios (2.5≤L/D < 3.5), and large pitch ratios (3.5≤L/D ≤ 4.0). The aerodynamic interference of the time-averaged aerodynamic coefficients under these four types is discussed by comparing the results obtained for the three columns with those for a single one. The time-averaged drag coefficient mainly experiences a reducing effect at the minimum and small pitch ratios and a certain extent of amplifying effect at the medium pitch ratios. The time-averaged lift coefficient appears non-zero values at some incidence angles, the range of which depends on the pitch ratio. The mechanism of the aerodynamic interference is also discussed by analyzing the time-averaged wind pressure distribution.

Effectiveness of a tubular heat exchanger and a novel perforated rectangular flow-deflector type baffle plate with opposing orientation

Purpose The purpose of this experimental research was to examine a novel axial heat exchanger featuring swirling air movement over heated tubes. This apparatus is designed with perforated circular baffle plates complemented by rectangular air deflectors operating at different inclination angles. The tubes were arranged in a consistent layout parallel to the longitudinal airflow. The deflector’s heightened air-side turbulence initiates the frenzied motion, escalating the surface heat transfer rate. Design/methodology/approach The tubes maintained a constant heat flux condition over the surface. In each baffle plate, eight deflectors with identical inclination angles were devised in a reverse position, forming a rotation of air inside a circular duct that held tubes (carrying hot water) which elevated air-side turbulence, thereby enhancing the rate of heat transference on the surface. The baffle plates were equally situated from each other at changing pitch ratios. The Reynolds quantity was preserved in the scope of 16,000–30,000. The performance of the heat exchanger considering pitch ratios and inclination angles was examined. Findings The research indicates that when examined under similar conditions, an exchanger with a deflector baffle plate shows a strong dependence on the pitch ratio and inclination angle with a mean rise of 0.19 times in thermal enhancement factor at an inclination angle of 30° and a pitch ratio of 1.2 contrasted with an exchanger with segmental baffle plates. Originality/value The result shows the dependence of pitch ratio, Reynolds number and inclination on the heat transfer and friction factor rate.