Constant Heat Flux Conditions Research Articles

Artificial intelligence approach for energy and entropy analyses of NiFe2O4/H2O nanofluid flow in a tube with vortex generator

The base purpose of the study is to examine the influence of vortex generator geometry and nanofluid on thermo-hydraulic and irreversibility behavior by using a numerical and predictable approach under a laminar flow regime. The selection of an original magnetic nanofluid, the handling of forced convection in a tube including a vortex generator with the artificial neural network approach, and the 2nd law analysis of thermodynamics reflect the novelty of the study. In this context, it was explored numerically for heat transfer and flow profiles of NiFe2O4/H2O flowing with 1% volume fraction in a tube with different vortex generator geometries. This study has been carried out with the solutions under constant heat flux conditions of 2000 W/m2 along the tube. The analyzes have been applied in the range of 500≤Re≤2000. The Laminar model and single-phase approach in all analyses have been taken into account. Heat convection coefficient, pressure drop, and entropy generation were analyzed for the smooth tube and tube with wave ratio (WR=h/w) of 2, 3, and 4. Levenberg-Marquardt as train algorithm and Learngdm and Tansig as transfer function was used as the MLP network model in the present study. As a result, The highest heat transfer ratio, pressure drop, frictional entropy, and total entropy values are obtained for the tube with a wave ratio of 2. The highest deviation rates between the predicted and numerical results for WT1 and WT2 cases (the supreme among all cases) have been seen as 4.67% and 1.73% for the heat convection coefficient and pressure drop values, respectively.

Melting process of RT-25 as a phase change material by placing innovative rectangular and parallelogram fins: Effect of shape and angle of fins

This numerical research used innovative fins that mix parallelogram and rectangular fins to look at the melting of the phase change material (PCM). This paper analyzed, in 2D and using a numerical solution, the melting behavior of several fin models with various angles under constant flux circumstances in a rectangular cavity. The left wall of the storage was subjected to a heat flux of 2500 W/m2. The major objective of the current research was to introduce fins with novel models, which are a mix of rectangular and parallelogram fins, in order to further enhance the melting performance of PCM. For this purpose, the effect of different fin models (with different angles:15°, 30°, 45°, 60°, 75°, and 90°) in the condition of constant heat flux in a rectangular cavity was studied. The results show that among various geometries studied by fin, proposed geometry of model E was selected among the models. Changing the fin model reduces the melting time, which led to a higher energy charging rate. Moreover, by examining different melting angles, the maximum and minimum melting times occurred at 0° and 60°, respectively. The heat flux had an inverse relationship with the melting time; the higher the heat flux, the shorter the melting time. E model with an angle of 60° had the best performance. Because it had reached complete melting in the shortest time, in this model, after 52.25 min, the PCM completely melts. The stored energy for PCM at 60° was less than other angles, and equal to 236.04 MJ. The average power for angles from 15° to 90° was almost equal, and at angle 0°, it was less than other angles.

Arbitrary temperature gradient in thermal-postbuckling behavior of polymer nanocomposites reinforced by boron nitride nanotubes

Polymer nanocomposites reinforced by boron nitride nanotubes (BNNTs) have great potential for use in a wide variety of thermal environments. A closed-form solution for nonlinear bending and thermal-postbuckling behavior of BNNT-reinforced nanocomposite beams under arbitrary temperature gradient in the thickness and length directions is presented for the first time. The uniform and functionally graded (FG) distributions of BNNTs through the thickness of macro-or micro-sized beams are considered. For constant temperature or constant heat flux conditions at two ends of the beam, thermal analysis is carried out to obtain temperature field ΔTx,z using the two-dimensional heat conduction equation and the assumption of arbitrary variation in the z direction. The governing equations of modified couple stress Timoshenko beam theory with von Kármán geometric nonlinearity are derived for BNNT-RC beams subjected to thermomechanical loads. Applying change of variable technique, the governing equations are exactly solved to develop closed-form expression for nonlinear transverse deflection. Finally, parametric study is performed to investigate the effects of length scale parameter, aspect ratio (L/h), distribution of BNNTs, and temperature gradient on the nonlinear bending and postbuckling equilibrium paths. It is shown that the thermal-buckling behavior of clamped and cantilever beams is completely different. Under thermomechanical loading, an initial snap-through buckling behavior is observed in the cantilever beam, while there exist both stable and unstable configurations in the static equilibrium path of clamped beam. Moreover, it is found that the assumption of parabolic variation of temperature through thickness is not compatible with real situations, since the temperature field is obtained as harmonic functions with very short wavelengths in the length direction.

Multiparameter optimization of the thermoelectric module under the constant heat flux condition

Thermoelectric (TE) technology enables direct heat-to-electricity conversion and offers an alternative way to carbon neutralization. Conventional TE device design is usually conducted under the constant temperature difference (CTD) condition. However, the constant heat flux (CHF) condition dominates in realistic applications. Here, using finite element simulation, we investigate the relationship between the geometric parameter and the TE performance under the CHF condition. Our results reveal that the thermal properties are the governing factors under the CHF condition. The simulations suggest that both the maximum output power and conversion efficiency increase with the height, decrease with the fill factor, and share a parabolic tendency as the cross-sectional area ratio changes. Instead of using the module parameters optimized under the CTD condition, the TE performance can be enhanced by 43% after geometric optimization under the CHF condition, suggesting that the optimization under the CHF condition is of significance for realistic applications.

Effect of aspect ratio on PCM melting behavior in a square cavity

For latent heat thermal energy storage applications with phase change material (PCM) in restricted space, the factors such as container shape and heating surface must be considered. In this paper, a 2D square cavity PCM is taken as the research object, and the melting process of PCM with different square cavity aspect ratio (AR) was simulated under the condition of constant heat flux (60 W) at the left wall/bottom wall. An innovative and effective indicator, i.e., differential liquid fraction curve along with solid-liquid interface evolution is proposed to reveal the melting rate and typical phase change characteristics. The results show that the complete melting time increases with the increase of AR for both left wall and bottom wall heating conditions. For general applications, the bottom wall heating has a higher melting rate compared with left wall, especially for the cavity with AR >1. During the phase change process, the melting rate can reach its maximum value at the peak of differential liquid fraction curve with an observation of the longest solid-liquid interface. In addition, the melting pattern of high AR cavity during the latter part of the left wall heating process would become similar to the low AR case under the “scouring effect” of natural convection on the solid-liquid interface. For bottom wall cases, the natural convection waveform presents Rayleigh-Benard convection cells, and with the increase of AR, the irregularity of the vortex structure becomes more obvious. The results can provide useful guidance for accurately evaluating phase change characteristics and designing thermal energy storage system.

Experimental Evaluation of Thermoelectric Generator Performance under Different Heat Conduction Boundary Conditions

Heat conduction boundary conditions play a crucial role in the performance of thermoelectric generators (TEG). The TEG output voltage and power were measured under constant temperature boundary and heat flux conditions to evaluate the TEG performance under different heat conduction boundary conditions. External loading pressure and thermal interface material (TIM) were applied to reduce the interfacial thermal contact resistance. In our measurement setup, a fast-response electronic load was used for the rapid current-voltage scan, which can eliminate the thermal drift caused by the Peltier effect. A guard heater arrangement is used to minimize heat loss. In constant temperature boundary conditions, reducing the thermal contact resistance can increase the effective temperature drop across the TEG module and significantly improve the output voltage and power. But in the constant heat flux conditions, since the heat flux flow through the TEG is unchanged, the temperature drop across the TEG was unaffected by the thermal contact resistance. As a result, the TEG performance was lightly influenced by the thermal contact resistance.

Entropy Optimization and Slant MHD Mixed Convection Hybrid Nanofluid Flow Within an Oblique Irregular Lid-Driven Enclosure Contains Baffles: Local Thermal Non-equilibrium Model

This paper explores the heat transfer by mixed convection within double lid-driven enclosures filled with Cu–Al_2O_3 hybrid nanofluids. The domain contains T-shaped baffles and is filled with local thermal non-equilibrium (LTNE) porous medium. The wavy boundaries are partially cooled, while the inner baffles have constant heat flux conditions. Mathematical formulations for the system irreversibility in cases of LTNE, constant heat flux conditions and double diffusive are presented and analyzed. The solution methodology is depending on the finite volume scheme in case of non-orthogonal grids. The major results revealed that the alteration of the undulation number lambda from 1 to 5 gives an augmentation in values of theta _text {f,max} up to 4.57%. Also, the increase in the lengths of the baffles causes a reduction in the flow, while theta _text {f,max} is rising. Furthermore, the alteration in Ri from 0.5 to 10 gives an augmentation in theta _text {f,max} up to 12.97%.

Particle-resolved simulations for nanofluid thermal enhancement in channel flows

Nanofluids have been studied extensively for improved heat transfer performances in various thermal systems. In this article, we adopt the particle-resolved method to study the thermal enhancement of nanofluids in channel flows under constant wall temperature (CWT) and constant heat flux (CHF) conditions. The smoothed profile method is employed to describe the nanoparticles suspending in the base fluid and the lattice Boltzmann method is utilized to solve the flow and temperature fields. Unlike the continuum representation of nanofluids, this particle-resolved approach can incorporate the thermophysical properties of the base fluid and nanoparticles directly in simulation, and flow and temperature distributions around nanoparticles are available. Our simulations reveal detailed information on the nanoparticle influence on the wall thermal distributions, and illustrate the enhancement mechanism for heat transfer between the boundary wall and fluid flow: The nanoparticles near the wall increase the local heat flux under CWT and decreases the local wall temperature under CHF condition. The heat transfer coefficient is utilized to characterize the thermal performance for nanofluids, and it increases 6–16% for the nanofluid systems considered in our simulations. The effects of key system parameters, such as the nanoparticle volume fraction, thermal conductivity, and Reynolds number, are also investigated. Our results show that, for both CWT and CHF systems, the particle volume fraction and thermal conductivity can both increase the heat transfer coefficient; however, the particle conductivity effect becomes less significant or even negligible when it is greatly larger than the base fluid conductivity. For the limited range and relatively low values of Reynolds numbers considered in this work, it appears that the Reynolds number has no obvious influence on the system thermal performance. These finding could be beneficial for a better understanding of the complexity of nanofluid systems and for future nanofluid development and applications.

Numerical Study of Convective Heat Transfer Performance, Entropy Generation and Energy Efficiency of Al and Al2O3 Nanofluids in Minichannel

Due to their enhanced thermophysical properties, nanofluids are considered a promising cooling solution in many applications including energy systems and electronics. The convective heat transfer (CHT) characteristics and entropy generation of ethylene glycol (EG)/water-based Al and Al2O3 nanofluids are numerically investigated for five nanoparticles concentrations (from 1.0 to 3.0 vol.%) and Reynolds number ranges between 400 and 2000 (laminar flow) under constant heat flux conditions in a minichannel. CFD tools are used to develop the numerical approach which is validated using experimental data of the base fluid. The results show good enhancement in CHT for both nanofluids in comparison with the base fluid and the CHT rises with increasing nanoparticles concentration and reaches the maximum enhancements of 20.3% for Al nanoparticles and 25.1% for Al2O3 nanoparticles at 3.0 vol.% concentration. The pressure drop also increases with increasing nanoparticles concentration and Re for both nanofluids, while friction factor is increased with increasing concentration of nanoparticles and reduced with the increase of Reynolds number. The results of entropy generation showed a decrease with increasing the nanoparticles’ concentration with lower values for Al nanofluids than Al2O3 nanofluids. In another hand, the energy efficiency evaluation of the nanofluids performance flow through the heat transfer system shows that there is no considerable change in the used energy of the overall system with nanofluids due to the increase in the pumping power.

Effect of surfactants on the convective heat transfer and pressure drop characteristics of ZnO/DIW nanofluids: An experimental study

The advancement of nanotechnology has demonstrated the ability of metal-oxide-based nanofluids (NFs) to produce high heat flux in microscale thermal applications. Convective heat transfer (HTC) and flow characteristics (pressure drop (ΔP) and friction factor (f)) of aqueous ZnO NFs' within a circular mini tube (Di = 1.0 mm, L = 330 mm) were analyzed. Experiments were carried out under steady-state and varying flow rates using 0.012–0.048 wt % of NFs and sodium hexametaphosphate (SHMP) and acetylacetone (ACAC) as surfactants (SFs). Laminar flow and constant wall heat flux conditions were used to assess NFs heat transfer properties, ΔP and f. The viscosity (VC) and thermal conductivity (TC) of NFs exhibited a strong dependence on the operating temperature and NFs concentration. VC and TC increased by increasing the NFs concentration and decreased by increasing the operating temperature. Maximum VC and TC enhancement of 16.75% and 23.70% were achieved for SHMP-stabilised NFs, respectively. The average HTC increased by increasing NFs loading and flow rate, with HTCmax of 17.0% noticed for ACAC-stabilised NFs. The ΔPmax and fmax were 16.0% and 12.0%, respectively. Experimental and theoretical results showed a maximum deviation of ±7.0% and ±4.0%, respectively.

Experimental and numerical study of drag reduction and heat transfer enhancement in a vertical pipe using water/polyisobutylene/nano-SiO2 polynanofluids

Poly-nanofluids (PNFs) are a new type of material that is manufactured by dispersing nanoparticles in dilute polymer solutions. This study looked at heat transfer and drag reduction using a water/polyisobutylene/nano-SiO2 PNF through a vertical copper pipe under conditions of constant heat flux. The effects of ploy-isobutylene (PIB) polymer solution, water/nano-SiO2 nanofluid, and aqueous PNF on heat transfer and drag reduction in a vertical pipe have been studied, separately. All prepared solutions had Reynolds numbers ranging from 7000 to 22000. Nano-SiO2 particles with an average size 20 nm and concentration ranges of 0.1–1 wt.% have been dispersed in aqueous PIB solutions as base fluids with 10–50 ppm concentration of the polymer. The optimal nanoparticle and polymer concentrations for the prepared nanofluid, polymer solution, and PNFs were 0.75 wt.% and 50 ppm, respectively. The friction factor of PNFs at optimal concentrations was 75% less than pure water. Ansys Fluent software was employed to verify the findings of the experiment and simulate the heat transfer and drag reduction phenomena at optimal conditions. Based on the results, the experimental and numerical data were in reasonable agreement, with a deviation of less than 5%.

EXPERIMENTAL INVESTIGATION ON TWO-PHASE HEAT AND FLUID FLOW IN POROUS HEAT SINKS

The current paper presents a novel experimental study on flow boiling in heat sinks with rectangular cross-section parallel microchannels fabricated by conventional powder metallurgy process. The dimensions of microchannel heat sinks are 20 mm × 20 mm. Porosities of heat sinks produced by sintering vary between 13.9% and 21.3%. A pure (nonporous) copper heat sink was also produced to compare the experimental data with each other. Channel sizes and numbers of all heat sinks used in the tests are identical. Flow boiling tests were carried out with deionized water at a flow rate of 238.2 kg/m<sup>2</sup> s and 430.32 kg/m<sup>2</sup> s. The fluid enters the heat sink at 80°C, completely liquid. The tests were carried out under constant heat flux conditions and the heat fluxes are 46.5 W/cm<sup>2</sup> and 61.5 W/cm<sup>2</sup>. Experimental studies have shown that the heat transfer coefficients in the heat sink with the highest porosity are from 28% to 33.3% higher than in the pure copper heat sink. Experimental heat transfer coefficients increase with increasing flow rate and decrease with increasing heat flux and vapor quality. On the other hand, the pressure drop values of the heat sink sample with the highest porosity were measured to be one and half times more than that of the pure copper heat sink. The imaging technique was used during the experiments. With the imaging technique, it was determined that the fluctuations in the pressure values were caused by the reverse steam flow. Additionally, the heat transfer coefficient values obtained experimentally were compared with the existing correlations in the literature. Experimental results showed that pure heat sinks are more compatible with the results given in the literature than porous heat sinks.

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

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

Influence of sawtooth twisted tape on thermal enhancement of heat exchanger tube

This article employs sawtooth twisted tapes to generate swirling flow and interrupted flowing disturbance in order to increase the level of heat transfer rate. The influences of the sawtooth twisted tape (S-TT) on enhanced heat transfer rate, friction factor and aerothermal performance index (API) behaviors are analyzed. The sawtooth twisted tapes (S-TTs) possessing constant pitch/twist ratio (y//W) of 3.0 and six sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° are assessed. Considering turbulent flow using air as the testing fluid, experiments were investigated at 6,000 <Re < 20,000 under boundary conditions of constant heat flux. According to the experimental findings, sawtooth twisted tape (S-TT) improves heat transfer rate and raises pressure loss with varying rates based on sawtooth angles (α). With the sawtooth twisted tape (S-TT) and 70° sawtooth angles, the optimum API of 1.33 is attained, while Nusselt number and friction factor are 32 and 0.135 at Re = 6,000. The recommended sawtooth twisted tape (S-TT) yields a highest Nusselt number of 78, which is 1.6 times greater than the typical twisted tape (TT) and 1.1 times greater than the plain tube. The combination of the TT and sawtooth patterns can be beneficial in terms of boosting heat transfer rate and API relating coupling of swirling flow and interrupted flowing disruption effects since the sawtooth twisted tape (S-TT) offers superior performance than the TT. Additionally, the heat exchanger tubes fitted with sawtooth twisted tape (S-TT) at sawtooth angles (α) of 20°, 30°, 40°, 50°, 60°, and 70° gain greater Nusselt number than the plain tube up to 158.3%, 162.2%, 166.1%, 171.7%, 179.7% and 186.2%, respectively.

Entropy generation analysis and simulation of turbulent forced convection around tube with integral wake splitter using artificial neural network approach

This paper deals with the investigations on entropy generation around a circular plain tube with integral downstream splitter plates with cross flow of air in a rectangular duct. This study is carried out in the Reynolds number range 49 × 103 to 227 × 103 on single plain cylinder and single cylinder of various splitter length-to-tube diameter ratios, L/D = 0, 1/3, 2/3, 1, 3/2, 2 and 5/2. Entropy generation characteristics are studied under constant heat flux and temperature conditions and simulated using the artificial neural network (ANN) algorithm. The analysis of the second law of thermodynamics, which considers both the heat transfer and pressure drop effects, indicated the addition of the plate decreases the entropy generation with increased plate length, the entropy generation number being more sensitive to the Reynolds number as plate length increases. entropy generation reduction was, in general, also evident with increased plate length. Results point towards tube with wake splitter being more efficient than plain tube based on entropy generation. The predicted values of the entropy generation number of augmented design, NS,a, using the ANN algorithm are compared with the calculated results. The results showed that the ANN model has good expectation performances with error approaches zero without conducting extra experiments consuming time, money and effort or solving nonlinear mathematical models. Owing to its performance, ANN is a good choice for modeling the entropy generation around a circular plain tube with integral downstream splitter plates.

Role of additives in influencing heating and melting of polymers during thermoforming

AbstractThe heating stage in thermoforming of amorphous and semi‐crystalline polymers was analyzed for constant heat flux conditions using an energy balance model; candidate polymers were high impact polystyrene and isotactic polypropylene. Using an analytical solution, temperature differences as large as 100°C were predicted to arise between the surface and the interior of the sheet being thermoformed for conditions chosen in this work, and these can limit the heat flux being used. A Matlab program was used to compute temperature and crystallinity profiles for crystal melting. Melting took almost as much time as required to heat the surface of the film to the crystal melting point. High thermal conductivity additives, such as calcium carbonate and graphene, can provide temperature uniformity, and the additive uniformity can be verified using thermogravimetric analysis. The ability of these additives to provide temperature uniformity and to reduce energy consumption and heating time is determined in a quantitative manner. Both additives improve heat transfer, and, at the same added volume fraction, graphene is more effective. However, calcium carbonate has a lower cost. The role of density, specific heat, thermal conductivity, and amount of the polymers and additives in influencing temperature and crystallinity profiles was explored, and methods of carrying out thermoforming in an energy efficient manner are proposed.

Heat transfer enhancement of nanofluid flow at the entry region of microtubes

A numerical investigation on laminar nanofluid flow and convective heat transfer at the entry region of microtubes subjected to constant wall temperature and constant heat flux boundary conditions has been carried out employing a multiphase Eulerian–Lagrangian method. The impacts of the Peclet number (175 ≤ Pe ≤ 3500), nanoparticle volume fraction (0.1 ≤ φ ≤ 1.0%), and nanoparticle diameter (40 ≤ dp ≤ 130 nm) on thermal characteristics of Al2O3-water nanofluid flow through a microtube are analyzed in detail. The results indicate that the influence of the Reynolds number on apparent friction factor and the impact of the axial heat conduction on the Nusselt number for the nanofluids have to take into account in the entry region. Compared with the influences of particle concentration and particle size, the entrance effect dominates pressure drop and thermal performance of the nanofluids near the entrance of the channel. As the dimensionless axial distance increases, the entrance effect is weakened, and the influences of particle concentration and particle size are gradually reflected in flow and heat transfer results. Besides, the particle effects on thermal performance of the nanofluids are earlier and higher than that on flow resistance. Performance evaluation demonstrates that the nanofluids in the entrance region have not only heat transfer enhancement but also a good economy. When Pe = 175, the PEC of Al2O3-water nanofluids with particle concentrations of 0.1, 0.2, 0.5, and 1% increased by 104.0, 103.1, 113.8, and 128.5% under constant heat flux condition, respectively, at the dimensionless axial distance x* = 0.01 compared with deionized water; the PEC improved by 74.6, 77.2, 85.6, and 102.5% under constant wall temperature condition compared with deionized water, respectively.

The Impacts of Wind Shear on Spatial Variation of the Meteorological Element Field in the Atmospheric Convective Boundary Layer Based on Large Eddy Simulation

As wind shear increases, the quasi-two-dimensional structure of flows becomes more significant in the convective boundary layer (CBL), indicating that wind shear plays an essential role in the variation of the field of atmospheric flow. Therefore, sensitive numerical experiments based on Large Eddy Simulation (LES) techniques were conducted to comprehensively investigate the effects of wind shear on the spatial variations in the velocity and potential temperature (θ) horizontal fields. Under the constant surface heat flux condition, the main findings are summarized. Firstly, in the CBL, the variances of the streamwise velocity (u), cross-stream velocity (v), and θ enhance as wind shear increases, whereas the variance of vertical velocity (w) is insensitive to wind shear. Secondly, in the CBL, with increasing wind shear, low-wavenumber Power Spectrum Densities (PSDs) of u, v, w, and θ increase significantly, suggesting that the increasing wind shear always enhances the large-scale motions of the atmosphere (i.e., low-wavenumber PSD). Therefore, it is more likely that some mesoscale weather processes will be triggered. Thirdly, generally, in the high-wavenumber range, with increasing wind shear, the PSDs of u, v, and θ increase slightly, whereas the PSD of w decreases slightly. This study provides a new perspective for understanding the role of wind shear in the spatial variations of the horizontal fields of meteorological elements under the same conditions of surface heat flux.

Thermal radiation effect on Viscoelastic Walters’-B nanofluid flow through a circular cylinder in convective and constant heat flux

The investigation on flow of nanofluid are well known amongst researchers due to its utilization in the industrial and engineering sector. It is useful for cooling purposes in the electronic devices, which has shown good results in energy saving. Thus, this study focusses on the analysis of radiation effects on mixed convection of Walters’-B nanofluid flow through a circular cylinder in the constant heat flux (CHF) and convective boundary conditions (CBC) horizontally. The sodium carboxymethyl cellulose (CMC-water) nanofluid is considered as conventional fluid containing copper nanoparticles. The numerical method of Keller-box is conducted to simplify the partial differential equations. Graphical profiles are plotted and discussed to examine the impacts of various physicals terms on velocity, skin friction, temperature and thermal transfer. The results discover the fluid velocity and temperature boost for increasing radiation and Biot number caused by the raise of energy supply in the fluid flow. The velocity profile decreases when nanoparticles volume fraction increases as the increment of fluid concentration slowing down the fluid flow. The convective heat transfers and skin friction increases as mixed convection parameter rises by varying the thermal boundary region. Furthermore, the temperature and velocity in CHF condition are comparatively higher than CBC condition.

Study of Baffles Arrangement Influence on the Natural Convection into a Heated Square Channel

The present experimental paper is officiated to study the heat characteristics and performance of air flow through a square cross-sectional heated channel under natural heat convection conditions. The influence of baffles arrangement and perforated baffles on the rate of heat transfer through a channel are studied. Four cases of a heated channels are studied, one is a plain channel and other three channels with a baffle namely, three inline baffles, three staggered baffles and three staggered perforated baffles arrangements. The outer tested channels surfaces are electrically heated with a constant surface heat flux condition. All tested channels are fabricated by cold forming with constant dimensions using aluminum plate has thickness of 1.0 mm. The heat performance is assessed for all tested channels. The results of present paper are approved than the available data in the previous paper and a good convergence are noticed. Obtained experimental results appear that a three staggered perforated baffles arrangement is a best selection as it improves heat transfer rate in expression of Nusselt number, it higher about 22% to 27% than that the plain channel for same conditions.