Increase In Nusselt Number Research Articles

Joule heating and heat generation/absorption effects on the heat transfer mechanism in ternary nanofluid containing different shape factors in stretchable converging/diverging Channel

The analysis of an advanced ternary nanofluid with different nanoparticle shapes in stretchable convergent/divergent channels with the same slope of equal magnitude is a topic of paramount significance at the current time. Therefore, a new heat transport model of a ternary nanofluid is developed under innovative effects of the magnetic field (), thermal radiation (), heat absorption/generation () and stretching/shrinking () effects developed. To acquire the fine heat transfer results, an efficient numerical scheme, the Galerkin Finite Element Method is implemented and the heat transfer results are furnished under the physical ranges of the aforementioned parameters. It is analyzed that heat generation , and stronger dissipation effects contributed potentially to thermal enhancement in the ternary nanofluid for convergent/divergent walls with stretchable effects. The absorption and Joule heating effects are good to control the heat and also a significant increase in Nusselt number is observed for the ternary nanofluid containing blade nanoparticles.

Optimization of response function on hydromagnetic buoyancy-driven rotating flow considering particle diameter and interfacial layer effects: Homotopy and sensitivity analysis

Alumina is one of the modern era and most utilized ceramic materials. One example of an electrical insulating substance is alumina. It has an enhanced temperature, chemical stability and higher thermal conductivity. It is mostly used in medical, industry, household items, military purposes, production of batteries and electrical parts. Therefore, the authors have formulated a mathematical model of the three-dimensional magnetohydrodynamic mixed convective flow of a nanofluid containing Alumina nanoparticles past a stretching surface. Preliminary assumptions bound the nanofluid flow to be rotational, electrically conducting, dissipative, buoyancy driven, thermally heated and convective. An important investigation based on the effects of nanoparticle diameter and nanolayer of the nanofluid makes the novelty of this investigation. The modeled problem is solved with a homotopic approach, which is suitable for the solution of the highly nonlinear differential equations and has quick convergence. The outcomes of the present analysis are shown with the help of Tables and Figures. The outcomes showed that the higher resistive force at the sheet surface caused by the higher solid volume fraction (varies from 1% to 4%), diminishes the primary velocity, while escalates the secondary velocity. Additionally, the greater solid volume fraction (which ranges from 1% to 4%) raises the thermal conductivity of the nanofluid flow, resulting in an increasing conduct in the thermal function. The enhancing nanolayer to base fluid conductivity ratio (which ranges from 1.1 to 65.25), results in an increase in both velocities and thermal functions, gives the nanofluid flow a higher thermal conductivity. Additionally, the local Nusselt number and skin friction increase as a result of the higher thermal conductivity. The primary velocity and temperature are reduced due to the decrease in thermal and momentum boundary layer thicknesses brought on by the rising nanoparticle diameter (which ranges from 1 nm to 50 nm). The rate of heat transfer is significantly achieved at the higher levels of the volume fraction and radiation factor while heat source is at lower level. The friction rate at the surface is dominant at higher level values of magnetic and volume fraction factor and medium level of rotation factor. The transport of heat has highest sentivity at the middle level of thermla radaition and volume fraction of the nanoparticle and low level of heat source, while the highest sensitivity of friction factor is observed at the middle level of thermal rotation and high level nanoparticle volume fraction and magnetic factor.

Multiphysics coupling investigation of interphase heat transfer in gas-particle coaxial-jet swirling flow via CFD-DEM-CHT

The swirling particulate flows with heat transfer are widely encountered in the industry, yet the internal multiphysics coupling characteristics resulting from fluid, particle, and structure interactions are not well-understood. In present employment, a coupled method of computational fluid dynamics-discrete element method and conjugated heat transfer is constructed to provide insights into the thermal analysis in the industrial-scale annular pipe. The heat transfer behaviors between gas-pipe wall, gas-particle, particle-particle and particle-pipe walls are taken into account for the gas-particle coaxial-jet swirling flow. After verifying the mathematical model, the heat and momentum transfer behavior is analyzed, followed by a comprehensive exploration of fluid hydrodynamics, heat transfer characteristics, and particle properties under diverse swirler geometries. The results demonstrate that the presence of the swirler reinforces the forced convection between the jet and the high-temperature pipe wall. The heat exchange performance between the jet and the Wallcp-ann-cas enhances with the increase of vane angle and diameter of the swirler but decreases with the increase of swirler height. The impact of the swirler installing position on the thermophysical field can be neglected. An excessive number of swirler vanes adversely impacts the heat transfer process between the gas phase and pipe walls. The particle temperature increases with decreasing height, while the particle Nusselt number increases and then decreases with the decrease in height.

Numerical investigation of mixed convection from rectangular cylinders subjected to upper cross flow

Unsteady combined natural and forced convection heat transfer from a rectangular cylinder subjected to upward cross flow is investigated numerically. The working fluids are air (Pr = 0.7) and water (Pr = 7), and the flow is laminar. The governing flow and energy equations are solved using a fractional step finite-difference scheme. The effects of the cylinder aspect ratio (a = L/D), Reynolds and Richardson numbers on the flow and heat transfer characteristics are investigated. Numerical simulations were carried out for the cylinders with aspect ratios of a = 0.5, 1, and 2, while the Richardson and Reynolds numbers varied between 0 to 10, and 100 to 200, respectively. The mean drag, mean rms lift coefficients, as well as the Strouhal number and the mean Nusselt number were computed for each simulation to determine the quantitative effects on flow and heat transfer. Steady flow is observed for Pr = 0.7, Ri = 0.5, and a = 0.5 or for Re ≥ 150 and Ri ≥ 1. For Ri = 10 and Re = 200, the flow becomes unsteady in the downstream region and trigger vortex street formation for a = 0.5, 1, and 2. Decreasing the aspect ratio, as well as increasing Reynolds number, increases the heat transfer from the cylinder. The rms lift coefficient decreases sharply at Ri < 1 for Pr = 0.7, Ri < 2 for Pr = 7 due to vortex breakdown. Further increase in the Richardson leads to a slight increase in rms lift coefficient except for Re = 200 where the sharp increase is observed due to triggered vortex formation again. For air, the increase in the mean Nusselt number in Ri = 10 case with respect to the forced convection case (Ri = 0) was 54–65% and 80–98%, respectively, for a = 0.5 and 2, while these values for water were realized as 50–68% and 53–63%, respectively. Using the computed data and nonlinear regression, the mean Nusselt number and the drag coefficients were developed.

Study on enhanced heat transfer of a phase change material slurry in transverse corrugated tubes

Enhancing the heat transfer of ice slurry is a key to improving its application. The outward transverse corrugated tube (OTCT) presents a better heat transfer enhancement as an effective passive flow control method. In this paper, the thermo-fluidic performance and enhanced heat transfer mechanism of ice slurry in OTCT are numerically studied using Euler-Euler multiphase model. The results indicated that turbulent vortex of ice slurry in OTCT is enhanced with the rise in the ratio of corrugation height to diameter (H/D), and declined with rising the of ratio corrugation pitch to diameter (P/D), and ratio of corrugation pitch to width (W/D). The ice concentration presents a periodic fluctuation along the flow direction. The values of H/D, W/D, and P/D have a significant influence on the mass transfer for ice slurry. And the ice particle concentration displays more even distribution as increasing H/D, and decreasing W/D and the P/D. The average flow resistance (fave) and Nusselt number (Nuave) increase with the increasing H/D and decreasing P/D, and decrease with increasing W/D. Nuave presents a linear increase with Re. For the inlet ice volume fraction of αin = 10%, Nuave enlarges significantly by increasing the Re from 4950 to 9540 for different H/D, P/D, and W/D values. The performance evaluation criterion (PEC) reaches a maximum value for different H/D and P/D at Re = 9540 when W/D = 0.4, αin = 10%. For bigger inlet ice particle concentration, the increment of Nuave of ice slurry in OTCT is more significant at higher Re compared with the smooth tube. Meanwhile, under higher ice concentration, the overall heat transfer performance is more prominent at large Re. Finally, the empirical correlations of the fave and Nuave are established to predict the thermal–hydraulic performance of ice slurry flowing through OTCT.

Experimental and numerical study on the heat transfer enhancement over scalene and curved‐side triangular ribs

AbstractThe present study examines the turbulent flow of mixed convection heat transfer enhancement within a rectangular channel considering three different novel shapes of ribs (smooth, scalene, and curved‐side triangular). The investigations were conducted experimentally by developing a new test facility, while the numerical computations were carried out using the finite volume method. The experimental work involves constructing of the channel, ribs, and all equipment and measurement instruments. The numerical work is based on ANSYS FLUENT considering the k–ε turbulent model. The results are presented and compared in terms of Nusselt number, friction factor, and performance factors for Reynolds numbers ranging between 3000 and 12,000. By comparing the average values of the numerically obtained Nusselt number with experimental measurements, the data showed a close agreement with a maximum difference of 5%. It also found that scalene triangular ribs (STRs) provide better performance in terms of heat transfer, although introducing a slight increase in friction losses. STRs showed (20%) increase in Nusselt number compared with smooth channel, and 3%–6% increase in Nusselt number compared with curved‐side triangular ribs (CTRs). In contrast, CTRs have a lower friction factor value of 5% compared with STRs at a low value of a Reynolds number of 3000. Furthermore, the Nusselt number changes significantly (250% increase) by increasing the value of the Reynolds number from 3000 to 12,000. A thermal performance factor of up to 1.28 was achieved for the STRs at the lowest range of Reynolds' number of 3000. The findings from the present study are of practical importance for industries requiring heat transfer enhancement techniques to improve heat transfer equipment performance.

Magnetic SWCNT–Ag/H2O nanofluid flow over cone with volumetric heat generation

The theme of this model is to examine the characteristics of heat and mass transfer flow through cone along with volumetric heat generation, variable viscosity, magnetic field and higher-order chemical reaction utilizing SWCNT–Ag/H2O hybrid nanofluid. The transformed partial differential equations are solved by shooting scheme. The numerical outcomes of physical quantities are revealed by graphs and tables. The local Nusselt number and Sherwood number are displayed with the support of bar diagram. The study depicted that an increase in temperature-dependent viscosity parameter for a particular magnetic field induced an increase in the local Nusselt number and Sherwood number. Furthermore, there was a rise in the data of internal heat generation, temperature outlines of hybrid nanofluid escalated while concentration profiles of working fluid depreciated.

Numerical simulation of flow and heat transfer of n-decane in sub-millimeter spiral tube at supercritical pressure

The flow and heat transfer characteristics of n-decane in the sub-millimeter spiral tube (SMST) at supercritical pressure (p = 3 MPa) are studied by the RNG k − ε numerical model in this paper. The effects of various Reynolds numbers (Re) and structural parameters pitch (s) and spiral diameter (D) are analyzed. Results indicate that the average Nusselt number (Nu¯) and friction factor (f¯) increase with an increase in Re, and decrease with an increase in D/d (tube diameter). In terms of the structural parameter s/d, it is found that as s/d increases, the Nu¯ and f¯ first increase, and then decrease. and the critical structural parameter is s/d = 4. Compared with the straight tube, the SMST can improve Nu¯ by 34.8% at best, while it can improve f¯ by 102.1% at most. In addition, a comprehensive heat transfer coefficient is applied to analyze the thermodynamic properties of SMST. With the optimal structural parameters of D/d = 6 and s/d = 4, the comprehensive heat transfer factor of supercritical pressure hydrocarbon fuel in the SMST can reach 1.074. At last, correlations of the average Nusselt number and friction factor are developed to predict the flow and heat transfer of n-decane at supercritical pressure.

Computational Heat Transfer Fluid Flow Analysis in a Diamond Hole Microchannel

— This report is based on a numerical analysis of a three-dimensional analysis of diamond-hole cooling channels in laminar forced convection of a solid body experiencing heat on one side. A diamond hole configuration was studied with different aspect ratios that give a minimum peak temperature at every point in the structure. The solid body volume is fixed and the channel aspect ratio is allowed to change in this direction. The solid body experiences heat flux ( ) on one side and the coolant is allowed to enter into the channels from the opposite side at a given Reynolds number ( ) such that 100 ≤ ≤ 500, and channel aspect ratio ( ) from 1 to 4. The results show that as the and increase, the maximum temperature and thermal resistance ( ) decrease while the Nusselt number increases. Also, the and increase, friction factor decreases and increases, respectively. Comparatively, for a given range of 100 ≤ ≤ 500, and channel aspect ratio ( ) from 1 to 4, about 4%-12% and 37%-44% reduction in the maximum wall temperature and thermal resistance respectively, were reported, while about 55.6%-75% and 50%-68% improvement in Nusselt number and pumping power respectively, were observed. The results establish that heat transfer is improved in the diamond hole channel at various Re and AR. Also, the results reveal that the Colburn j-factor decreases when rises and the aspect ratio decreases due to the heat transfer characteristic increases. Again, pumping power increase rapidly as and increase, which causes a higher pressure drop across the channel and leads to higher energy consumption.

Performance improvement of shell and tube heat exchanger by using Fe3O4/water nanofluid

The objective of this paper is to study the effect of nanofluid on the performance of the heat exchanger, as well as the heat transfer rate, coefficient of total heat transfer, friction influence and average Nusselt number, and thermal efficiency factor and has been investigated and discussed. In this work, the output heat transfer of Fe3O4/water nanofluid through shell and tube heat exchanger has been numerically investigated under laminar flow. CFD simulations with ANSYS FLUENT 2020R1 were used adopting finite volume approach to solve the governing equations. Numerical calculations were carried out for Reynolds numbers ranging from 200 to 1400, with nanoparticles as the volume fraction (0.2% and 0.35%). The results show that the augmentation in increase Nusselt number and amount of heat transfer rate and the efficiency of nanofluid at the concentration of 0.35% are approximately 19%, 25% and 12% respectively. It was observed through the results that the friction decreases as the Reynolds number increase.

Experimental investigation of natural convection of Fe3O4-water nanofluid in a cubic cavity

Convective heat transfer of nanofluids has been an active research topic in recent times. But the relative amount of research in natural convection of nanofluids is scarce in comparison with forced convection. In this study the effect of Fe3O4/water nanofluid on the natural convection behavior in a differentially heated cubic cavity of characteristic length 30 mm has been investigated. The nanofluids are synthesized using a two-step approach and their thermophysical properties like thermal conductivity and viscosity are measured in the temperature ranging from 20 to 60 ° C . The effect of nanoparticle volume fraction on heat transfer performance is studied with concentration ranging from 0–0.8% by volume. The cavity is made up of Poly-lactic acid (PLA) with two sides covered with copper plates. One of the copper plates is kept in contact with ambient atmosphere while variable heat flux using silica gel heater is applied on the other copper plate. All previous results have shown either monotonous deterioration or an increment followed by a continuous decrease in heat transfer coefficient and Nusselt number with increase in concentration. The results of this study have shown that for constant input heat flux the Nusselt number decreases monotonously. Further it is observed that for constant Rayleigh number there is an increase in Nusselt number with increase in concentration.

Thermal efficiency improvement of parabolic trough solar collector using different kinds of hybrid nanofluids

In this paper, the use of eight hybrid nanofluids to improve the thermal efficiency of a parabolic trough solar collector (PTSC) is investigated. The analysis is performed with the thermal model developed and validated with Sandia National Laboratory’s experimental data using pure Syltherm 800. The developed model results prove a good agreement with the experimental study with an average error of 1.92% and 2.34% to calculate the outlet temperature and thermal efficiency. The simulation results showed that PTSC thermal efficiency could achieve its maximum improvement of 2.8% using hybrid nanofluids evaluated and an average improvement of PTSC thermal efficiency of 1.6% under the operating conditions of the examined tests compared to Syltherm 800. All hybrid nanofluids achieve a better PTSC’s thermal efficiency than the base fluid, and the difference between them is insignificant due to keeping the total concentration constant (ϕ=3%) for all of them. This improvement of PTSC’s thermal efficiency using hybrid nanofluid is explained by the most significant increase and improvement of heat transfer coefficient and Nusselt number compared to pure Syltherm 800. This paper is beneficial to researchers focused on applying and improving the PTSC’s thermal performance based on the improvement of heat transfer fluids.

Control of the melting process in a rectangular energy storage chamber filled with phase change material in the presence of an oscillating and rotating cylinder

In the present research, the efficacy of rotating and oscillating cylinders on the melting process in a rectangular chamber has been investigated numerically. Porosity-enthalpy model has been used to model the melting process. The effect of the radius, location, rotational and oscillating speed (amplitude and frequency) of the cylinder, the presence of different arrangements of the cylinder and the temperature changes of the active boundary on the liquifying process have been investigated. As the cylinder has an oscillating motion, the dynamic mesh is employed. The phase change material (PCM) is Lauric acid. The consequences reveal that the existence of the cylinder betters the rate of the melting process, and the best melting process occurs at R = 0.3, and the time required for the complete liquifying of the PCM for this state is lessened by 12.84 % compared to the state with R = 0.01. The rotating cylinder reduces the PCM liquifying rate, so that by selecting the rotational speed of −3 and + 10 rad/s, the average melting fraction of PCM has decreased by 7.96 and 8.67 %, respectively, compared to the fixed cylinder state. The oscillating movement of the cylinder improves the liquifying rate. Increasing the oscillation range and frequency will decrease and increase the liquifying rate, respectively. The temperature changes of the active boundary with time have improved the melting process compared to the constant temperature state. In the cases where the average Nusselt number increases, the melting rate has decreased. Among the arrangements considered for the cylinder arrangement, the best melting performance has been observed when two cylinders are placed horizontally in the chamber.

HOW THE ESTIMATION OF ENTROPY GENERATION AND EXERGY LOSS OF HYBRID NANOFLUIDS GOVERNS THE THERMAL PERFORMANCE OF HEAT EXCHANGER

The present study reports heat-transfer performance, exergy analysis, entropy generation, and pressure drop of shell and helically coiled heat exchanger (SHCHE) with Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-CuO/water hybrid nanofluid (HYNF) as a working fluid. Helical coil is made of copper material with 54 turns and pitch ratio is 31.35 mm. Hot oil streams at the shell with 75&amp;deg; C, and the working fluid streams at the helical coil with 30&amp;deg; C. The volume fraction of the nanoparticles is considered as 0.1 vol.&amp;#37;. Reynolds number of the oil is fixed as 900 and the Reynolds number of the working fluid varies from 6000 to 15,000. The numerical code is validated with the earlier experimental work. Highest thermal performance is obtained by using 0.1 vol.&amp;#37; HYNF than nanofluids and base fluid. Role of mass flow rate, and Reynolds number on heat-transfer rate, effectiveness, total entropy generation, exergetic efficiency, exergy loss, and dimensionless exergy loss are investigated. An &amp;#126; 20&amp;#37; increase in Nusselt number and &amp;#126; 48&amp;#37; increment in exergetic efficiency are noted with the usage of HYNF. Entropy generation of SHCHE is lower by adding nanoparticles. This study enables the readers to understand the irreversibility of heat transfer in shell and helically coiled heat exchanger.

Heat transfer enhancement in a helically coiled convergent and divergent tube heat exchanger with Al2O3 nanofluid

In this investigation, the analysis of the heat transfer coefficient of a shell, helically coiled convergent-divergent tube heat exchanger has been carried out by utilizing Al2O3-water nanofluid. The nanofluid was prepared using a two-stage technique with proportions of 0.1 vol.%, 0.3 vol.%, and 0.5 vol.%. The inner heat transfer coefficient, overall heat transfer coefficient, and Nusselt number were analyzed and it found that the heat transfer coefficient is increased, with increase of inner dean number and particle volume concentration. The experimental tests were carried out in the range of Dean number, 1100 &lt; De &lt; 4200. When compared to base fluid, the overall heat transfer coefficient improved by 27%, 55%, and 78% at 0.1%, 0.3% and 0.5% with Al2O3-water nanofluid, respectively. When compared to base fluid at a fixed dean number, the increase in Nusselt number was viewed as 27%, 51%, and 72% at 0.1%, 0.3%, and 0.5% of Al2O3- water nanofluid, respectively. The investigations of enhancement were increased due to increased nanofluid thermal conductivity while increasing the vol.% concentration and Brownian movement of the nanoparticles. The viscosity of nanofluid is increased with increase of particle volume which increase the pressure drop. It is concluded the convergent-divergent helically coiled tube heat exchangers along with nanofluid is able to enhance the heat transfer with considerable pressure drop. There is no adverse effect on the development of optional streams or the blending of liquids.

Heat transfer studies in a plate heat exchanger using Fe2O3-water-engine oil nanofluid

Improving the heat transfer performance of conventional fluid creates significant energy savings in process Industries. In this aspect, an experimental study was performed to evaluate the heat transfer performance of Fe2O3-water (W)-engine oil (EO) nanofluid at different concentrations and hot fluid inlet temperatures in a plate heat exchanger. Experiments were conducted by mixing Fe2O3 nanoparticles (45 nm) in a W-EO mixture base fluid with volume fractions of 5% EO + 95% W and 10% EO +90% W. The main aim of the present study was to assess the impacts of nanoparticle volume fraction and hot fluid inlet temperature variations on the heat transfer performance of the prepared nanofluid. The convective heat transfer coefficient, Reynolds, Prandtl, and Nusselt numbers were determined based on the experimental results. The result shows that at the hot fluid inlet temperature of 75 ?C, the increase in Nusselt number and convective heat transfer coefficient are optimum at 0.9 vol. % nanoparticle for both the base fluid mixtures. The increase in heat transfer coefficient is because of the Brownian motion (increasing thermal conductivity) effect, motion caused by the temperature gradient (Thermo-phoretic), and motion due to concentration gradient (Osmophoretic). If the volume fraction of the nanoparticle increases, then the Reynolds number increment is higher than the Prandtl number decrement, which augments the Nusselt number and convective heat transfer coefficient.

Influences of electrical conductivity of the cylindrical walls on heat transfer enhancement of nanofluid swirling flow

The swirling nanofluid flow driven by a revolving bottom disk of a cylindrical container under magnetic field effect and temperature gradient is examined in this study. The effects of the electrical conductivity of cylindrical walls’ on heat transfer enhancement are quantitatively investigated. The finite volume approach is used to solve the governing equations under the appropriate assumptions. This study considers four cases of combined electric conducting and insulating walls. The solid nanoparticle (copper) with volume fraction (ϕ = 0.1) is added to water. Calculations were done for fixed Reynolds number (Re=1000), Richardson number (0≤Ri ≤2), and various Hartmann numbers. The mean Nusselt number decreased as the Richardson number increased owing to stratification layers. These latter restrict heat exchanges between the cylinder’s hot and cold zones. The results show that within a particular range of Hartmann numbers, the Nusselt number increases, especially when the revolving lid is electrically conducting. The best heat transfer occurs when all of the walls are electrically conductive, which results in a 100% improvement at low Richardson values. Finally, the electrical conductivity of the revolving lid was a key factor in enhancing heat transfer.

Computation of Stagnation Point Convection Flow of Carbon Nanotube Nanofluids From a Stretching Sheet With Melting: Dual Solutions

Abstract A theoretical study in stagnation point flow is presented where melting heat transfer effects of carbon nanotube (CNT) from a stretching surface is appeared. Both carbon nanotubes like single-wall CNT (SWCNT) and multiwall CNT (MWCNT) are homogeneously dispersed in the base fluid. As the ordinary (or base) fluids, water and kerosene oil are employed. A set of nonlinear ordinary differential equations with appropriate boundary conditions is formed by transforming the governing equations via similarity transformations. The transformed nonlinear ordinary differential equations are then solved numerically using the bvp4c solver in matlab, an efficient numerical finite difference method. The impact of nanoparticle volume fraction, velocity, melting, stretching parameter, and CNT type on transport characteristics are explored and visualized graphically and in tabular forms. Verification of the matlab computations with available data in certain limiting cases is included showing excellent agreement. Existence of dual (upper and lower branch) solution is shown for a certain range of stretching sheet parameter. The obtained dual solutions are examined for velocity and temperature in detail. A stability analysis demonstrates that the first solution is a stable solution, and the second solution is an unstable solution. Local skin friction and local Nusselt number are also computed in order to determine critical values that can permit dual solutions. It is observed that when a dimensionless melting parameter is greater than 1, SWCNT nanofluids attain greater velocities than MWCNT nanofluids for water as well as kerosene oil base fluids. Moreover, the flow is accelerated for SWCNT compared with MWCNT for both water and kerosene oil. With increasing stretching parameter, the heat transfer rate (Nusselt number) increases, whereas skin friction coefficients decrease. Higher skin friction and Nusselt number are obtained for SWCNTs compared to MWCNTs due to their greater density and thermal conductivity. The study is relevant to phase change manufacturing fluid dynamics of nanomaterials.

CFD analysis of heat transfer enhancement in a concentric tube counter flow heat exchanger using nanofluids (SiO2/H2O, Al2O3/H2O, CNTs/H2O) and twisted tape turbulators

A concentric tube, counter flow heat exchanger with nanofluids under turbulent flow conditions has been examined using a computational fluid dynamics model. The proposed model consists of Twisted Tape Turbulators (TTT) on the annular side and inside the tube along with different nanofluids. Twisted Tape Turbulators produce a swirl motion within the fluids to increase heat transfer. Al2O3/H2O, SiO2/ H2O, and CNTS/ H2O nanofluids (with varying volume concentrations of 1 %, 2 %, and 3 %) with the turbulent flow (Reynold number Re = 2000 to 10000) were considered to determine three major parameters i.e., heat transfer rate (Q), overall heat transfer coefficient (U) and Nusselt number (Nu). This study resulted in 6.03 %, 16.74 %, and 6.74 % enhancement of overall heat transfer coefficient (U) with a 3 % volume concentration of CNTS/H2O nanofluid, Al2O3/H2O nanofluid, and SiO2/H2O nanofluid, respectively, when equated to without twisted tape tabulators. This analysis shows the maximum value of Nusselt number as 143,136.68 and 140.12 for CNTS/H2O, Al2O3/H2O, and SiO2/H2O, respectively, for the twisted tape tubular arrangement. It is concluded that when using twisted tape turbulator, the heat transfer rate (Q), overall heat transfer coefficient (U), and Nusselt Number (Nu) increase with increasing Reynolds number (turbulent flow conditions) and volume concentrations of nanofluid.Novelty statement: Twisted Tape Turbulators (TTT) arrangement with different concentrations and types of nanofluids combined are infrequent in the study of concentric tube heat exchanger with turbulent flow to obtain enhanced heat transfer.

Effect of baffle angles on flow and heat transfer in a circular duct with nanofluids

This work numerically analyzes the hydraulic and thermal performance of CuO-water nanofluid in a circular duct with different baffle angles. In the numerical work, governing equations are discretized with the finite volume method, and the simulations are solved with SIMPLE algorithm. The surfaces of the duct containing baffles are kept at 340 K. In the analysis, the effects of different Reynolds numbers (200 ≤ Re ≤ 1000), nanoparticle volume fractions (1% ≤ ϕ ≤ 3%), and baffle angles (30º ≤ α ≤ 150º) on the thermal enhancement factor (η) and the friction factor are investigated. In addition, the flow and temperature contours are presented for different parameters within the duct. From those contours, it is observed that the baffles cause flow oscillation and recirculation zones are formed. The numerical results show that baffles and nanofluid flow contribute significantly to the thermal enhancement. The Nusselt number (Nu) and relative friction factor (r) increase as the Reynolds number and nanoparticle volume fraction increase. While the highest thermal enhancement factor and relative friction factor are obtained at α = 90º baffle angle, the best performance evaluation criterion (PEC) value is found at α = 150º baffle angle.