Friction Factor Research Articles

Performance investigation of a supergravity CO2 refrigeration cycle under off-design conditions

The transcritical CO2 refrigeration cycle is a research hotspot in CO2 refrigeration technology, but it suffers from significant throttling, compression, and gas cooling losses. The recently proposed supergravity CO2 refrigeration cycle, which utilizes centrifugal potential energy-pressure energy conversion in the rotating heat exchanger, provides a new approach to address these issues. However, the flow efficiency of the serpentine rotating channels requires further validation, and the operating characteristics of the system under off-design conditions need exploration. To this end, we first conducted a study on the pressure drop characteristics of a serpentine rotating channel using experimental and numerical simulation methods. We found a strong linear relationship between the friction factor and the rotation number, with the flow efficiency approaching 1.0 beyond a certain threshold, providing critical support for the cycle. Additionally, we established a distributed parameter model for the cycle and theoretically analyzed its operational performance. The results show that the COP of this cycle reaches 6.91 under air conditioning conditions. This is primarily because the local isentropic compression/expansion efficiency of CO2 in the rotating channel exceeds 99 %. Additionally, the temperature slip during the gas cooling process is only 1.2 °C, demonstrating the feasibility of achieving nearly isothermal compression through the rotating heat exchanger. Furthermore, the results showed that changes in boundary conditions resulted in minimal changes in system pressure differential, not exceeding 2 %. However, increases in CO2 charge and rotational speed led to substantial changes in system pressure differential, increasing by 39 % and 51 %, respectively. These trends reflect the effect of the centrifugal potential energy-pressure energy conversion on the operating characteristics of the system. In addition, there exists a maximum charge limit to prevent the cycle from entering the two-phase region. There is also an optimal combination of rotating heat exchanger and compressor speeds that ensures maximum COP while guaranteeing the cooling capacity. The main novelty of this paper lies in elucidating the coupling mechanism between operational parameters and the thermodynamic parameters of the supergravity CO2 refrigeration cycle.

Radiation, absorption, and Joule heating Influence on MHD Casson fluid flow over an exponentially stretching surface

This work investigates the MHD convective flow through the boundary layer of a Casson nanofluid over an exponentially inclined porous stretched surface in the occurrence of radiation, absorption, and Joule heating. The proper conversions transform the PDEs that specify flow into a series of nonlinear ODEs. The MATLAB in-built solver bvp4c helps one to solve the problem. Graphical findings also show for non-dimensional profiles. For various values of parameters controlling the flow system, the numerical values of the Sherwood number and Nusselt number, friction factor are shown in tabular form. A comparison table is used to confirm the acquired findings.

Establishment of Colburn ‘j’ factor and Fanning friction factor ‘f’ correlations for a compact heat exchanger having perforated wavy fins using Computational Fluid Dynamics

Wavy fins find widespread application in compact heat exchangers, due to their ability to achieve high heat transfer coefficients and lower friction factors, resulting in reduced pumping power requirements and improved overall efficiency. Despite the extensive literature available on these fins, no previous study has explored the influence of perforations on wavy fins. This study aims to establish accurate correlations for evaluating the Colburn ‘j’ factor and Fanning friction factor ‘f’ in wavy fins incorporating perforations, specifically tailored for compact heat exchangers. The Colburn ‘j’ factor guides the determination of the heat transfer coefficient, while the Fanning friction factor ‘f’ is instrumental in assessing pressure drop across the fin, both essential considerations in the rating and sizing of compact heat exchangers. The numerical model involves a perforated wavy fin constructed from ‘aluminum’ with ‘air’ as the fluid medium. To derive correlations, 1458 cases were simulated using ANSYS Fluent, systematically varying geometric parameters such as fin height (h), fin spacing (s), fin thickness (t), hole diameter (d), and fin pitch (p). The study spans Reynolds numbers from laminar (200≤Re≤1500) to turbulent (2000≤Re≤10000). ‘j’ &‘f’ factor values were validated using experimental data for wavy fins without perforations, followed by additional analysis incorporating perforations. The analysis showed a 19%–35% increase in the ‘j’ factor and a 21%–33% increase in the ‘f’ factor for perforated wavy fins compared to plain wavy fins. New ‘j’ and ‘f’ factor correlations were established, with over 96.3% and 95.0% of the points within ±16% and ±18% bounds, respectively. These innovative correlations applicable across the entire spectrum of operating and design conditions are expected to facilitate a more streamlined design process for compact heat exchangers featuring this unique fin geometry, enabling designers to reduce iterations during the design phase.

In-situ manipulating nanochannel wettability to evaluate fluid transport under nanoconfinement

Understanding the transport of nanoconfined fluid and its underlying mechanism is essential for manipulating fluid transport in nanochannels and nanoporous media. The wettability of the channel wall is one of the most important factors that determine the property and transport of nanoconfined fluid. However, the experimental studies of wettability adjustment for manipulating nanofluid transport were rarely reported. In this work, the wettability of nanochannels in nanofluidic chips was tuned in situ to investigate the transport of water and alkane. The surface hydrophobicity of the channel wall was adjusted through hydroxylation and silanization. The friction factor of water increased with the hydroxylation time of the channel wall, and decreased after surface hydrophobization with octadecyltrichlorosilane (OTS) and trimethylchlorosilane (TMCS), indicating surface hydrophobization had a significant effect on friction reduction. The linear correlation between the transport distance ΔX2 and time t could be theoretically described based on the Lucas-Washburn equation for fully developed flow. With the same channel depth, the fitted apparent contact angle θapp for nanochannels of different hydrophobicity followed the trend of OTS > TMCS > pristine > hydroxylation. The transport of water in hydrophobized nanochannels was faster than that in pristine and hydroxylated nanochannels, which coincided with the friction factor results. The transport of n-hexane was significantly faster than that of water, which could be explained by the differences in the fluid viscosity, surface tension and wettability. This work provides experimental evidence and useful insights into the understanding of the wettability effect of nanochannel on the transport of different fluids, which has implications for the transportation characteristics of nanoconfined fluids in the applications, such as advanced batteries, separation membranes, unconventional reservoirs, etc.

Machine learning analysis of thermophysical and thermohydraulic properties in ethylene glycol- and glycerol-based SiO2 nanofluids

The study investigates the heat transfer and friction factor properties of ethylene glycol and glycerol-based silicon dioxide nanofluids flowing in a circular tube under continuous heat flux circumstances. This study tackles the important requirement for effective thermal management in areas such as electronics cooling, the automobile industry, and renewable energy systems. Previous research has encountered difficulties in enhancing thermal performance while handling the increased friction factor associated with nanofluids. This study conducted experiments in the Reynolds number range of 1300 to 21,000 with particle volume concentrations of up to 1.0%. Nanofluids exhibited superior heat transfer coefficients and friction factor values than the base liquid values. The highest enhancement in heat transfer was 5.4% and 8.3% for glycerol and ethylene glycol -based silicon dioxide Nanofluid with a relative friction factor penalty of ∼30% and 75%, respectively. To model and predict the complicated, nonlinear experimental data, five machine learning approaches were used: linear regression, random forest, extreme gradient boosting, adaptive boosting, and decision tree. Among them, the decision tree-based model performed well with few errors, while the random forest and extreme gradient boosting models were also highly accurate. The findings indicate that these advanced machine learning models can accurately anticipate the thermal performance of nanofluids, providing a dependable tool for improving their use in a variety of thermal systems. This study's findings help to design more effective cooling solutions and improve the sustainability of energy systems.

Response surface-based optimization of thermal characteristics for frustum roughened solar air heater: An experimental and numerical study

Artificial roughness on the absorber plate of the solar air heater increases its thermal characteristics, thermohydraulic performance, and overall performance of the solar air heater. The roughness and flow parameters selected for artificial roughness play a vital role. Along with selection of geometry, range of roughness parameter at optimum values creates keen interest in research field. The present investigation is in line with the previous work of the authors in which an experimental and numerical simulation was carried out to explore the thermal characteristics of a frustum roughness solar air heater. Roughness configuration such as the relative height of the roughness (e/Dh), the relative diametral ratio(d1/d2), and the roughness to the diameter of the base diameter (e/d1) was calculated to optimize the thermal characteristic. To optimize thermal characteristics (Nusselt number and friction factor) a response surface optimization (RSM) was applied. The suggested design of the experiment (DOE) was performed experimentally and numerically. Data collected from experiment and simulation are used to develop mathematical model using analysis of variance (ANOVA) approach. Nusselt number achieves its maximum optimum value of 256.78 at e/Dh = 0.043, d1/d2 = 2.33, e/d1 = 0.98 and Re = 12500. Friction factor achieves its minimum optimum value of 0.009 at e/Dh = 0.014, d1/d2 = 2.06, e/d1 = 1.44 and Re = 12158.

Numerical modeling and parametric optimization of a dual media tank thermal energy storage system for enhanced industrial heat processes

ABSTRACT In this study, a 1-D numerical model is developed to investigate the Dual Media Tank (DMT) thermal energy storage (TES) system. A physical model of 29 kWTH DMT is designed to evaluate the effect of parameters such as inlet velocity, pebble diameter and void fraction on discharging efficiency, friction factor and thermocline thickness. In addition, a Response Surface Methodology (RSM) is also used to optimize the design and operating parameters for maximum discharging efficiency and minimum pressure drop. The analysis result indicates a 41% increase in discharging efficiency and a 53% drop in friction factor for Reynolds number ranging from 16–23. However, a sharp increase in thermocline thickness (0.25–0.75 m) is found for Reynolds numbers ranging from 16–18; thereafter, the growth of thermocline thickness is slower. This shows that thermal degradation is higher for low Reynolds numbers. In this analysis, the effect of pebble diameter is also studied, and the result shows a 22% drop in discharging efficiency for pebble diameter varying from 0.03–0.09 m. In addition, the pebble diameter also affects the discharging time, and the result indicates a maximum discharging time of 40 minutes for smaller pebble diameters. Accordingly, parametric optimization has also been done to optimize the mass flow rate and pebbles diameter for maximum efficiency and minimum friction factor. The optimization result shows that a mass flow rate of 0.10 kg/s and pebbles diameter of 0.07 m is the optimum value for both minimal pressure drop and maximum discharging efficiency.

Development and calibration of a fast flow model for solid oxide cell stack internal manifolds

Due to the commercialization of solid oxide cells (SOC) progressing at an accelerated pace, computationally inexpensive SOC models adapted to the iterative nature of the engineering process are in increasing demand. Flow simulation in the stack is especially challenging in this regard because detailed computational fluid mechanic models are computationally demanding, while simplified models rely on pressure loss coefficients and friction factors not readily available in the literature. In this study, a computationally inexpensive algebraic model of an SOC stack internal manifold is developed and calibrated for laminar flow conditions. Thereby, pressure loss coefficients and Darcy friction factors are determined for a broad range of operating conditions through symbolic regression of Navier–Stokes flow simulation results of stacks of 20 to 40 cells. The derived Darcy friction factors for the inlet and outlet manifolds prove to be of particular importance, as they deviate strongly from the expressions assumed in similar modeling studies. The predictive power of the developed model is demonstrated by providing accurate predictions of the flow distribution in the stack, even outside of the calibration window.

Analysis of nanofluid and nano-enhanced phase change material (NEPCM) in a heat exchanger for thermal management of electronic devices

Thermal management of high-power electronic devices is essential to control their enormous heat generation, which is usually the cause of their damage. Scientists have found several solutions for cooling electronic devices, but a counter-current heat exchanger has never been used. In the same context, numerical research on the thermal performance of a proposed new cooling system based on a counterflow heat exchanger combined with a heat sink is conducted in this article. Cu-H2O nanofluid, n-Docosane nano-enhanced phase change material, and water were selected as coolants, and they are compared in terms of temperatures, Nusselt number, heat transfer coefficient, pressure drop, friction factor, and performance enhancement coefficient using a two-phase mixture transient model based on Finite Volume method. Two cases of the proposed system are studied to find the optimal distance between heat exchanger pipes and the hot surface. Results are compared with previous experimental data to demonstrate that the system under study is accurate. They revealed that integrating the heat exchanger with the heat sink using Cu-H2O nf as a coolant maintained the hot surface temperature below 308 K with improved heat transfer by 31.22% compared to water. 0.25 mm is the optimum distance to find the highest thermal performance of the cooling system.

Heat transfer enhancement characteristics of sinusoidal corrugated tubes fabricated via laser powder bed fusion

Laser powder bed fusion (LPBF) has emerged as a powerful tool to develop heat transfer devices with higher efficiency. Corrugated tubes are commonly used components to achieve enhanced heat transfer in these devices. However, there still lacks a comprehensive study on the thermal-hydraulic performance of LPBF-fabricated corrugated tubes. In this work, we investigated the heat transfer enhancement characteristics of sinusoidal corrugated tubes (SCTs) fabricated via LPBF. SCTs with different amplitude-to-diameter ratios (A/D ratio) and wavelength-to-diameter ratios (S/D ratio) were designed and fabricated. The geometrical morphologies and surface roughness of LPBF-fabricated SCTs were characterized. Numerical simulations were performed to investigate the effects of A/D ratio and S/D ratio on the flow patterns and flow dynamics. A test system was developed to measure the pressure loss and thermal performance. Performance Evaluation Criterion were calculated to characterize the heat transfer enhancement. A/D ratio was found to have more significant impacts on the friction factor and Nusselt numbers than S/D ratio. Correlation models were developed to predict friction factors and Nusselt numbers based on the least square method. Mean prediction errors of ±3.3 % and ±5.3 % and maximum prediction errors of ±11.6 % and ±18.1 % were achieved for Nusselt numbers and friction factor, respectively.

Multi-Objective Optimization towards Heat Dissipation Performance of the New Tesla Valve Channels with Partitions in a Liquid-Cooled Plate

The utilization of liquid-cooled plates has been increasingly prevalent within the thermal management of batteries for new energy vehicles. Using Tesla valves as internal flow channels of liquid-cooled plates can improve heat dissipation characteristics. However, conventional Tesla valve flow channels frequently experience challenges such as inconsistencies in heat dissipations and unacceptably high levels of pressure loss. In light of this, this paper proposes a new type of Tesla valve with partitions, which is used as internal channel for liquid-cooled plate. Its purpose is to solve the shortcomings of existing flow channels. Under the working conditions of Reynolds number equal to 1000, the neural network prediction-NSGA-II multi-objective optimization method is used to optimize the channel structural parameters. The objective is to identify the optimal structural configuration that exhibits the greatest Nusselt number while simultaneously exhibiting the lowest Fanning friction factor. The variables to consider are the half of partition thickness H, partition length L, and the fillet radius R. The study result revealed that the optimal parameter combination consisted of H = 0.25 mm, R = 1.253 mm, L = 0.768 mm, which demonstrated the best performance. The Fanning friction factor of the optimized flow channel is substantially reduced compared to the reference channel, reducing by approximately 16.4%. However, the Nusselt number is not noticeably increased, increasing by only 0.9%. This indicates that the optimized structure can notably reduce the fluid’s friction resistance and pressure loss and slightly enhance the heat dissipation characteristics.

Thermal case exploration of electromagnetic radiative tri-hybrid nanofluid flow in Bi-directional stretching device in absorbent medium: SQLM analysis

Ternary hybrid nanofluids offer promising roles in biomedical engineering, solar energy, atomic reactors, automobiles, and heat pipes. Through these facts and influenced by recent work in nanotechnology and their rich utilization, this particular research emphasizes the MWCNT (Multi wall carbon nano tube)-Au-Ag/blood ternary nanofluid flow through a bidirectional stretching sheet. The coupled non-linear partial differential equations (PDEs) for the developed model are altered into dimensionless ordinary differential equations (ODEs) via similarity transformations, also subsequently undertaken computationally via the spectral linearization methodology. The physical description of parameters is presented against the flow parameters graphically, also related physical quantities such as the Sherwood quantity and surface frictional force are exhibited. Furthermore, surface plots are presented to examine the boundary layer effect. The study reveals that increasing the stretchable ratio of the surface upsurges the y− velocity as a result of the thinning of the surface in this same direction, which reduces the resistance to fluid movement. Trihybrid nanofluid rapidity is less than the rapidity of hybrid nanofluid due to the increment of the number of molecules in the fluid which reduces the interspace between these molecules. Enhancing the Lorentz force and surface pores numbers reduces the surface frictional force factors of the ternary hybrid nanofluid.

Comparative analysis of tube designs in heat exchangers: A numerical simulation study for enhanced thermal-flow efficiency, "optimizing wavy tubes bundle geometries for enhanced heat transfer in underwater applications"

With the growing challenges of heat transfer in marine vehicles and underwater power stations, the demand for an effective tube heat exchanger has surged. Numerical simulations were conducted on the constant, laminar flow of an incompressible viscous fluid inside a wavy tube while keeping the wall temperature consistent. The laminar flow was modeled in two dimensions using ANSYS FLUENT 19.2. For the water fluid model, an integrated algorithm was used to link the pressure and velocity fields. Primarily examined were circular tube banks organized in a staggered arrangement. The primary equations were approached via a finite volume method based on a combined technique. This study aimed to evaluate and contrast the heat exchange and flow traits of four distinct tube designs: asteroid (ASTB), hypotrochoid (HTB), Wavy edge circle (WCTB), and mixed bundle (MBT). The influence of tube design on a heat exchanger’s thermal-flow efficiency was measured across Reynolds numbers ranging from 100 to 400. The results indicated an improved Colburn factor and a decrease in both the friction factor and tube performance for all scenarios examined. Three key metrics determined the optimal tube design: the performance evaluation criterion (PEC), the global performance criterion (GPC), and the average Nusselt number (Nu). Regardless of the Reynolds number, the conventional HC had the least efficient PEC, while the STB registered the peak PEC value. The highest GPC was attained with the STB. Nu values remained relatively consistent for ASTB, HTB, WCTB, and MBT. In evaluating the average Nusselt number, the ASTB outperformed the STB (92–106% higher), HTB (36–48% higher), WCTB (21–32% higher), and MBT (57–64% higher).

Multi-objective optimization study of airfoil fin printed circuit heat exchanger with tip gap based on machine learning

The printed circuit heat exchanger (PCHE), a compact and highly efficient device, is capable of operating effectively under demanding conditions, which makes it ideal for supercritical CO2 Brayton cycles. In this study, we present a novel airfoil fin PCHE with tip gap, and conduct multi-objective optimization on the tip gap and arrangement of airfoil fins based on the analysis of the supercritical CO2 flow and heat transfer characteristics. We conduct a parameter design using Design of Experiment to examine the impact of the dimensionless design parameters, including the horizontal number (ζh), staggered number (ζs), vertical number (ζv), and gap number (ζg). To forecast the flow and heat transfer performance, we utilize a neural network model called Particle Swarm Optimization-Back Propagation (PSO-BP). We employ the non-dominated sorting genetic algorithm II to obtain the Pareto optimal front by utilizing ζh, ζs, ζv, and ζg as variables for optimization, and the volumetric heat transfer coefficient (hv) and Fanning friction factor (f) as objectives for optimization. The results find that the utilization of tip gap can enhance heat transfer while reducing flow resistance. The PSO-BPNN model exhibits higher prediction accuracy and excellent generalization ability compared with traditional BPNN model. The VIKOR and TOPSIS methods identify compromise schemes with excellent thermal-hydraulic performance. The mechanism of heat transfer enhancement can be elucidated using the principle of field synergy.

Heat transfer and hydrodynamic performance of ZrO2 geothermal nanofluids through tubular and plate heat exchangers

The improvement in heat transfer equipment plays a significant role to enhance the overall performance of many systems and a wide variety of industrial processes. Heat exchangers are widely used in many of these applications and, with the aim of limiting the growing of energy demand, further improvement is needed. A low-enthalpy geothermal system is commonly constituted by a ground heat exchanger, a heat pump unit, and indoor heating/cooling units. In the ground heat exchanger circuit, the heat exchange occurs between the fluid of the wellbore and the ground through a tubular section similar to that of the inner tube of a Double-Tube Heat Exchanger (DTHE), and between the fluid of the wellbore and the refrigerant of the heat pump in the evaporator/condenser, which is typically a Plate Heat Exchanger (PHE). The use of new nano-enhanced heat transfer fluids featuring improved properties, known as nanofluids, has been proposed as a potential solution for energy efficiency improvement. This study aims to analyse the feasibility of ZrO2 nanofluids based on a propylene glycol:water 10:90 vol% mixture as working fluids in heat transfer applications, focusing on renewable energy systems such as low-enthalpy geothermal installations. The heat transfer performance and hydrodynamic behaviour of four new ZrO2-based nanofluids at nanoparticle mass concentrations of 0.25, 0.50, 0.75, and 1.0 wt% are analysed and compared with the base fluid. Tests through a PHE and a DTHE were performed, and convective heat transfer coefficients and pressure drops were obtained in laminar and turbulent regimes. Increases of the convective heat transfer coefficients up to 123 % and 8.8 % were found for the nanofluids in comparison to the base fluid for laminar flow in the PHE and for turbulent flow in the DTHE, respectively. Finally, a dimensionless analysis was carried out through Nusselt and Reynolds numbers and Darcy friction factor.

Nonlinear radiative thermal analysis of magneto-micropolar fluid over a bidirectionally extending sheet with varied thermal conditions

Thermal fluid flow analysis occasioned by stretching surfaces offers practical industrial and engineering applications, such as extrusion and drawing processes and materials experiencing heating and cooling conditions. Thus, this study explores magnetohydrodynamic micropolar fluid flow under varied thermal conditions and nonlinear thermal radiation over a dually stretched sheet subject to surface mass flux and an internal heat source. The study thus provides insight into the dynamics of heat transfer mechanisms for improving material processing techniques in many engineering processes. The flow dynamics with the thermal analysis are evaluated by applying two thermal conditions in the heat equation: the prescribed surface temperature (PST) and the prescribed heat flux (PHF). The formulated partial derivative equations that describe the current problem are changed into ordinary derivatives using some similarity quantities, while the converted equations are tackled with the combined techniques of shooting and Runge–Kutta Fehlberg. Consequently, diverse tables and figures are displayed to deliberate on the impacts of the physical terms on the dynamics of flow and heat transmission processes. The consequence of the analysis reveals a higher heat gradient in the prescribed surface temperature case than the uniform temperature distribution, as the Prandtl number magnifies. The micropolar material term reduces the surface frictional factor and depletes heat transmission, but the magnetic field term raises the skin friction coefficient.

Experimental Investigations of Heat Transfer in Simultaneously Developing Transitional Regime of Mixed Convection Flows in a Vertical Tube

Abstract The study of flow behavior in the simultaneously developing transitional regime of mixed convection flows is rare. It has been believed that the transitional regime will give a good compromise between pressure drop and heat transfer compared to laminar and turbulent flow regime. In this experimental study, the friction factor (f) and Nusselt number (Nu) characteristics for buoyancy-assisted and opposed flows of water in concurrently developing transitional regime of mixed convection through a vertical tube are studied. Experiments were done for Reynolds numbers (Re) varying from 500 to 15,000, Grashof numbers (Gr) from 1.25 × 104 to 5 × 106, Prandtl numbers (Pr) from 3 to 7, and Richardson numbers (Ri) from 0 to 0.1 subjected to uniform heat flux boundary conditions. A flow visualization provision after the test section which confirms an early transition in buoyancy-opposing flow (Rec = 2264) compared to buoyancy-aiding flow (Rec = 2468) at a fixed Ri of 0.1. Further, with the increase in Ri from 0 to 0.1, the average f decreases, and the average Nu increases in both aiding and opposing flows. It confirms that the onset of transition gets delayed with the increase of heat flux supplied in both the flows. Based on the present outcomes, an efficient heat exchanging device can be operated either to delay or advance the transition in a vertical pipe flow for optimum heat transfer.

Experimental and numerical analysis of heat sink using various patterns of cylindrical pin-fins

The increasing heat generated by electronic devices requires effective dissipation methods. This research proposes a unique pin-fin (PF) design inspired by cylindrical pin-fins, including three patterns: cross-pin-fins (CPFs), parallel-pin-fins (PPFs) and double-cross-pin-fins (DCPFs). The study examines the hydrothermal performance of these designs within Reynolds numbers of 4500 to 18,000 and heat fluxes of 445 W/m² to 2281 W/m². The PF design aims to maximise performance by increasing surface area and airflow turbulence. Experimental data confirmed the computational results for the PF and CPF heat sinks, exhibiting significant agreement. A numerical study evaluated the hydrothermal performance, revealing that DCPFs deliver a superior performance. As the diameter expands, the Nusselt number (Nu) rises significantly across each design, with increases of 100 %, 162 % and 328 % for the PPFs, CPFs and DCPFs, respectively. Each configuration achieved a Heat Transfer Performance Factor (HTPF) exceeding 1, indicating improved heat transfer efficiency over the friction factor. The heat sink comprising the DCPFs achieved a high HTPF of approximately 2, irrespective of the Reynolds numbers and heat fluxes, demonstrating its effectiveness in heat dissipation compared to other designs.

Synergistic effects of a swirl generator and MXene/water nanofluids used in a heat exchanger pipe of a negative CO2 emission gas power plant

The focus on optimizing heat exchangers contributes to improved temperature control mechanisms, ensuring the sustainable operation of innovative power plants working toward negative CO2 emissions. In the realm of oxy-combustion within Negative CO2 Emission Power Plants (nCO2PP), the temperature of combustion products surpasses 3000 ( K ) . Addressing this challenge, the imperative arises to reduce these elevated temperatures to a manageable 1100 ( ° C ) . This critical cooling process is achieved through the injection of water, facilitated by the implementation of heat exchangers. The study delves into the optimization of heat transfer within the heat exchanger pipe, specifically tailored for the context of a nCO2PP. Employing a numerical simulation, the investigation explores the impact of vortex generator geometry, vane angles, single and dual propeller-type swirl generators, and the integration of a novel class of fluid, MXene/water nanofluid. Initially, the study scrutinizes propeller-type geometry at vane angles spanning from 15° to 60°. The enhanced swirl flow associated with lower vane angles leads to improved fluid mixing, fostering more effective heat transfer. Results showed that the 15-degree vane angle, with a wider circumferential coverage, may result in increased wall contact, influencing heat transfer efficiency. Subsequently, at Re = 6000, incremental rates of the Nusselt number ( Nu n − Nu s Nu s %), for θ = 15°, 30°, 45°, and 60° are 175.1, 108.8, 90.7, and 40.3%, respectively. Also, the increment rates of Friction Factor ( f n f s ) for aforementioned vane angle are 38.48, 9.26, 4.08, and 2.42%, respectively. In addition, for ∅ MXene = 0.5 % , the Nusselt number experiences considerable increments of 22.94, 24.17, 24.70, and 24.707% at Reynolds numbers of 6000, 12,000, 18,000, and 24,000, respectively, compared to pure water, emphasizing the potential of MXene to enhance heat transfer efficiency.

Effect of trapezoidal louvered winglets on increased heat transfer and exergy in tubular heat exchanger

The effect of inserting a trapezoidal louvered winglet tape (TLWT) into a uniformly heat-fluxed tube on its thermal effectiveness was studied experimentally. The exergy and entropy analyses for turbulent flows, as well as frictional loss and thermal features, were highlighted as key aspects of the experimental finding for the Reynolds number which measured between about 4700 and 30,000. Because fixing baffles to the curved shape of tube wall presented a challenge, the baffles were consequently positioned on double surfaces of a flat tape. Six values of the louver angle (θ1 = 0°, 25°, 30°, 45°, 60°, and 90°) and three values of the relative pitch of winglet (PR = 1.0, 1.5, and 2.0) were employed in the arrangement of TLWTs, with the V-apex oriented upstream (V-up). Each of these had only a fixed height (BR = 0.25) and angle of attack (α = 30°). The winglets were utilized to induce streamwise vortices which can hinder the boundary layer formation, while the louvered openings were adopted to lessen pressure drop without significantly impacting the primary vortices. The experiment results disclosed that the smallest θ1 and PR produced the largest relative friction factor (fR) and NuR, which were about 13.57 and 4.04 times higher, while PR = 1 and θ1 = 45° provide the greatest TEF of about 2.27. The greatest exergy efficiency (ηEx) resulting from the TLWT was reached at θ1 = 0°, but the generation of entropy (S˙g′) dropped with lowering θ1 and Re. A further examination, however, showed that the best scenario with α = 60° and staggered arrays is more desirable since it yields the largest TEF of 2.45 at θ1 = 45° and PR = 1. For the range of parameters under consideration, the Nu and f correlations were additionally established.