Average Heat Transfer Rate Research Articles

Natural convective turbulent heat flow visualization around a vertical plate using low Reynolds number k-ϵ model

The authors of this present paper used the low Reynolds number (LRN) k-ϵ model to introduce the notion of turbulent heat function for visualization of average heat flow direction in a natural convective flow in the vicinity of the vertical plate. The explored problem is two-dimensional and incompressible. Governing equations such as continuity, momentum, energy, turbulent kinetic energy (TKE), dissipation rate of TKE, and also turbulent heat and stream functions are generated based on geometry and turbulent flow assumptions. Owing to the lack of analytical methods for solving the highly nonlinear set of partial differential equations, the Crank–Nicolson scheme (CNS) of finite difference approach is employed to find a numerical approximation of the governing turbulent equations. Further, this approach is unconditionally stable, and it helps in the discretization of governing equations, which are kept in the tridiagonal system of algebraic equations and solved using the Thomas algorithm. The obtained numerical results ensure convergence since the stability and compatibility holds good in CNS. The simulated results are examined using tables and graphs to determine how laminar flow differs from that of turbulent flow in terms of velocity, temperature, heat lines, and streamlines with the help of turbulent Prandtl () and Reynolds () numbers. Also, the authors demonstrated the behavior of average momentum and heat transfer rates of laminar and turbulent flows. Additionally, average velocity, kinetic energy, and dissipation rate contours are plotted and discussed including turbulent isotherms, heat lines, and streamlines. It has been noted that the average momentum rate decreased and the heat transfer rate increased with increasing in laminar flow. However, these rates decreased with increasing values in the turbulent flow. Furthermore, streamlines are denser in laminar and turbulent flow conditions at the top and the leading edge of the plate, respectively. Finally, as a particular instance, the outcomes obtained using the LRN k-ϵ model for turbulent flows are compared to the usual laminar flow and noted to be in excellent agreement.

Pengaruh Variasi Fluida Pendingin Terhadap Laju Pendinginan Engine Yamaha Nmax

Radiator is a cooling system using fluid as a heat exchanger. How the radiator works by channeling the heat released by the motor engine is then absorbed by the radiator coolant fluid. The radiator device consists of a coolant inlet and engine outlet, a cooling fan mounted in front or behind the radiator, and coolant. Coolant in the radiator has a very important role in dissipating engine heat to the environment. In this study, I will analyze the different types of coolant variations, namely water, prestone antifreeze, Seiken, premix coolant DCK, and yamacoolant. on the cooling rate and radiator effectiveness using rotation variations of 1600, 3000,5000 rpm and measurement times of 1, 5, and 10 minutes on the Yamaha Nmax engine. The results of the research that have been carried out are the average heat transfer rate and the highest radiator effectiveness occur in the Yamacoolant type cooling fluid of 1.992kW and 0.726, the second highest occurs in the Prestone cooling fluid where the heat transfer rate value is 1.918kW and the radiator effectiveness is 0.652, then followed by Seiken where the heat transfer rate is 1.901kW and the radiator effectiveness is 0.634, then followed by DCK the heat transfer rate is 1.702kW and the radiator effectiveness is 0.592 and the smallest is experienced by mineral water where the heat transfer rate is 1.542kW and the radiator effectiveness is 0.501.

Numerical simulation and experimental validation on the heat transfer property of vertical buried tube ground heat exchanger

In order to study the effect of the arrangement of buried tubes on heat transfer, a three-dimensional heat transfer model of vertical U-shaped buried tubes is established. The regional thermal efficiency and soil temperature field around the buried tubes arranged in square array and rhombic array are numerically simulated. The numerical simulation results are compared with the experimental data to verify the correctness of the established model and simulation conditions. The results show that the rhombic arrangement form has more advantages than the square arrangement form: with the same number of buried tubes, the land use area of the rhombic arrangement form is smaller and the regional thermal efficiencies of the two forms are almost the same. The experimental validation shows that the experimental value of the average heat transfer rate of a single tube is in good agreement with the simulated value, and the relative error is 5.4%.

Employing spiral fins to improve the thermal performance of phase-change materials in shell-tube latent heat storage units

Adding metal fins to extend the heat transfer area is a viable and effective technology to improve the poor thermal conductivity of Phase-Change Material (PCM). The annular fin is the most common type due to the simple structure, but it weakens the natural convection. Under this condition, the spiral fin is proposed to overcome the poor natural convection. An experimental system was built with three vertical shell-tube latent heat storage units (LHSU), two of which employed annular and spiral fins with the same heat transfer area by taking one without fin as a reference. The melting and solidifying status, temperature distribution and comprehensive efficiency are used to evaluate thermal performance of three LHSUs. Experimental results show adding metal fins contributes to the heat transfer improvement, especially for spiral fins. Employing metal fins can weaken PCM natural convection, but annular fins have a lower weakening efficiency than spiral fins on PCM natural convection. Therefore, the spiral fins provide superior thermal performance with enhanced multi-circulation flows. Compared with annular fins, employing spiral fins can increase the average Nusselt number by 28.6%, the average heat transfer rate by 20.9%–58.2% in charging and discharging processes, and the average heat flux by 17.5%–53.8% in LHSUs.

Parametric investigation of charging and discharging performances of a cascaded packed bed thermal energy storage system

The packed bed thermal energy storage (PBTES) system employing cascaded phase change material (PCM) is useful for low-grade waste heat recovery and utilization. The performance of a cascaded PBTES system is parametrically investigated in the present study. A one-dimensional concentric dispersion model is developed and validated by the experimental results. The average heat transfer rates of a cascaded PBTES system at various volumetric ratios of PCM capsules are numerically investigated, and the cascaded PBTES system of a volumetric ratio of hydroquinone: adipic acid: erythritol = 3:6:1 is found to be the best configuration in the cyclic charging and discharging processes. Furthermore, the comparison of the thermal behaviors of the cascaded and non-cascaded PBTES systems shows that the PCMs in each layer of a cascaded PBTES system complete the phase change at nearly the same time, leading to a larger heat transfer rate compared to the non-cascaded one. The average heat transfer rate of a cascaded PBTES system with the volumetric ratio of 3:6:1 is about 6.96 % higher than that of the non-cascaded one for the cyclic process. In addition, the results show that the average heat transfer rate of the cyclic process of the PBTES system is improved by employing the cascaded PCMs, while the enhancement ratio of average cyclic heat transfer rate is found to decrease from 10.57 % to −1.35 % as the mass flow rate increases from 20 kg·h−1 to 100 kg·h−1 and to decrease from 10.32 % to 0.91 % as the capsule diameter increases from 20 mm to 100 mm.

Enhancement of heat transfer using ultrasonic waves: Experimental investigation and empirical correlations

This work aimed to investigate the effect of ultrasonic waves on heat transfer enhancement under a subcooled pool condition. For this purpose, a cylindrical rod is submerged in distilled water and a 1.7 MHz ultrasonic transducer was utilized to generate ultrasonic waves. Three main parameters were examined including loaded heat flux, water temperature, and heights (distance from ultrasonic transducer). A Particle Image Velocimetry (PIV) is used as a non-intrusive flow visualization system to visualize how ultrasonic waves propagate in a water medium. The results obtained without imposing ultrasonic waves are compared with that of the results where ultrasonic waves are imposed, the average heat transfer rate with imposing ultrasonic waves is increased by 133%, while the increasing in enhancement factor is about 2.4 times at (H = 22 mm). Meanwhile, the increase in water temperature led to decreases in the heat transfer rate, this decreasing in the heat transfer rate is the most with Tw = 50 °C and it's around 46.8%, while it's about 17.2% with Tw = 40 °C under similar conditions. Effect of heated surface height is also investigated and analyzed, the ultrasonic waves are influential in the case of changing height and improved the enhancement factor by 3.52 times at (H = 65 mm). By using the database obtained under test conditions, empirical correlations were proposed to evaluate the real benefits of using ultrasonic waves in heat transfer enhancement.

Structure optimization of tree-shaped fins for improving the thermodynamic performance in latent heat storage

Tree-shaped fins have widely been approved to enhance heat transfer performance in the field of latent heat storage. However, the structure of tree-shaped fins should be optimized to amplify its performance advantages, which are rarely addressed in previous studies. An unsteady numerical model is established to study the thermal performance advantages of tree-shaped fins. A method by coupling a genetic algorithm and a CFD simulation is utilized to optimize the structure of the tree-shaped fins based on the melting and solidification processes of a Phase Change Material (PCM). The results indicate that structural optimization is important and necessary for the application of tree-shaped fins especially in latent heat storage systems. Compared with the radial fins, the optimized tree-shaped fins reduce the phase transition time by 38.83%in the melting process and by 32.71% in the solidification process. Also, the optimized tree-shaped fins increase the average heat transfer rate and average heat transfer coefficient by 65.70% and 65.54% in the melting process while 51.51% and 51.00% respectively in the solidification process. The optimization results also shows that the optimized tree-shaped fins based on different heat transfer processes all show the characteristics of gradually increasing branch length and decreasing branch angle, that is, L0<L1<L2, β1>β2. Interestingly, the optimized structure of the tree-shaped fins based on PCM melting differs from that of the PCM solidification process because of the difference in heat transfer mechanisms. This study provides a method for the structural optimization of tree-shaped fins and increases the application prospect of tree-shaped fins in the field of latent heat storage.

Analysis of temperature distribution over pipe surfaces of air-based cavity linear receiver for cross-linear concentration solar power system.

This analysis is based on the computational fluid dynamics (CFD) of the air-based solar cavity linear receiver (CLR) of the cross-linear concentrated solar power plant. In this study, the temperature distribution along the pipe surface is investigated using a small section of a receiver. To study the variation of temperature over the surface of receiver pipes, a CFD model has been developed in Ansys Fluent. The analysis shows the effect of reflected radiation on the temperature variation over the front and back surfaces of the pipes, as well as the effect of this variation on heat transfer fluid (HTF) outlet temperature. The difference in the HTF outlet temperature and heat transfer rate between experimental data and CFD results has been identified. After rigorous examination, it has been observed that the effective range of length for heat absorbing pipe is from 60 to 600mm (outlet) as HTF continues to absorb heat in this range. The average heat transfer rate was observed to be around 14108W. Finally, the effect of variable mass flow rate over thermal efficiency of the receiver has been examined and it has been observed that once the mass flow rate exceeds 0.06kg/s, further increasing the mass flow rate has little effect on improving the thermal efficiency because after an optimum value of mass flow rate would result in increase in heat loss from the pipe's back wall. In the present study, the results of the CFD analysis have been validated with an experimental test data.

Studi Eksperimental Pengaruh Konfigurasi Penampang Sekat Terhadap Kinerja Novel Cooling Tower Prototype

Cooling towers are widely applied in industries such as power plants and oil refineries, where the equipment produces excess heat that needs to be removed. The effect of baffles configuration on the performance of the novel cooling tower prototype was studied experimentally. The configuration of the baffles used is the baffle section without holes, the baffle section with 15 holes, the baffle section with 25 holes, and the baffle section with 35 holes. The water inlet temperature was varied, namely 55⁰C, 75⁰C, and 90⁰C. water is flowed from the main reservoir to the upper reservoir of the cooling tower using a pump, and water from the upper reservoir falls on the baffles of the cooling tower. Inlet water temperature, outlet water temperature, and water temperature at each baffle were measured using a thermocouple. The results showed that the cooling tower with a baffle of 35 holes produced the most optimal performance. The heat transfer rate produced by the cooling tower with a 35-hole baffle at an inlet temperature of 55⁰C is 624.64 Watts. At the water inlet temperature of 75⁰C, the average heat transfer rate produced by the cooling tower with a 35-hole baffle increased by 42.6%. The average heat transfer rate produced by a cooling tower with a 35-hole baffle at a water inlet temperature of 90⁰C increased by 62.6%. This is because the cooling tower with a baffle of 35 holes causes the water droplets that pass through the baffle to split into more and more so that the heat transfer rate is higher.

Design and Taguchi-based optimization of the latent heat thermal storage in the form of structured porous-coated pipe

In this paper, the solidification and melting processes of phase change material within a Structured Porous-Coated Pipe (SPCP) are investigated, numerically. It is the first time that the applicability of Structured Porous in heat transfer enhancement in PCM is studied. In an SPCP, a pipe is surrounded by a coarse structured porous media and filled with PCM. Since the pore geometry is structured, its behavior is not statistically randomized. Different geometries for SPCP with different materials are designed and simulated. Substantial improvement in heat transfer enhancement, by as much as an order of magnitude, is observed. For example for stainless steel with a relatively low thermal conductivity, the average heat transfer rate increases to 0.61 W from 0.12 W. So, the melting time is reduced to 20% of the required time for simple annuls. For more conductive materials like aluminum and copper, the average heat transfer is 13.5 and 15.25 times a simple annulus, respectively. Finally, Taguchi–based sensitivity analysis and ANOVA are performed. It is shown that the type of material is more important than the thickness of the porous structure. The material contributions percentage for charging and discharging are 51.1% and 40.5%. Also, these values for ΔT are 40.4% and 45.3%, respectively.

Convective heat transfer enhancement in a quarter-circular enclosure utilizing nanofluids under the influence of periodic magnetic field

A coupled one-component numerical model is applied to analyze the transient natural convective hydro-thermal incidents of different nanofluids occupied with a quarter circular vicinity. A sinusoidal magnetic arena is preferred in the transverse direction to examine the magnetization phenomena. The circular arc of the geometry domain is cold and the lowest wall is heated whereas the vertical wall of the arena is kept thermally insulated. During numerical computation, herein considered Water (H 2 O), Kerosene (Ke), Engine Oil (EO) as base fluids and Copper (Cu), Cobalt (Co), and Iron Oxide (Fe 3 O 4 ) as nanoparticles. The dimensionless transports equations are solved numerically by applying the Galerkin weighted residual based finite element method. The outcomes spectacle that heat transfer rate augmented significantly with the increasing values of the Rayleigh number ( Ra ), nanoparticles volume fraction (φ), and period of the magnetic field (λ), whereas an intensification in the Hartmann number ( Ha ) lessens the total heat transfer rate. For nine sorts of nanofluids, the average heat transfer rate is computed along the bottom wall, and found that the heat transfer rate of Co-Kerosene nanofluid is considerably greater than other eight sorts of nanofluids. Finally, it is observed that the Cu-Kerosene nanofluid provides the high heat transfer rate whereas Cu-EO has the low rate of heat transfer for distinct thermal boundary conditions. The numerical results could be useful in assessing heat transfer features of solar collectors, and electronic devices.

MHD influence on convective heat transfer in a semi-circular cavity using nonhomogeneous nanofluid model

A transient free convective heat transfer in a semicircular vicinity occupied with distinct nanofluids has been examined numerically with a periodic magnetic field. The bottom surface of the cavity is heated non-uniformly as parabolic shape whereas the circular surface is kept at constant cold temperature. In the numerical simulation, ZnO, Fe 3 O 4 , Co, Al 2 O 3 , and Ag have been used as nanoparticles and water and kerosene as the base fluid to investigate the flow regimes and thermal fields developed inside the computed vicinity. Effects of various governing parameters are revealed with depictions of isotherms, streamlines and iso-concentrations. The results show that there is found less computational time to reach a steady-state solution for a higher Rayleigh number and the effects of the periodic magnetic field magnifies the strength of the vortices turning in the cavity. The average heat transfer rate at the bottom surface is uppermost for cobalt-kerosene nanofluid compared to other nine sorts of nanofluids. The results also reveal that the periodic magnetic field as well as the Brownian motion have substantial impacts on the heat transfer rate.

Increasing the reliability of biomass solid fuel combustion using a combined regenerative heat exchanger as an indirect burner

In this study, an indirect burner system for solid biomass fuel is designed. The design is motivated by the need to solve the problem related to a direct burner system, such as slagging and high pollutant emissions due to the high-temperature burning process. Therefore, the utilization of an indirect burner is expected to improve the reliability of the solid biomass combustion process. It also can be used to reduce coal consumption by using an indirect burner where the working fluid reaches a relatively higher temperature before entering the boiler. The design used the first principle method for creating the regenerator heat exchanger. The regenerator consists of a mantle and coil heat exchanger. The test used solid biomass fuel for the combustion process where the working fluid first enters the mantle heat exchanger and then the coil heat exchanger. As a result, the mantle absorbs sufficient heat losses from the combustion chamber with the highest temperature increment of 19 °C. The warm water from the mantle then flows to the coil arrangement within the combustion chamber. As a result, the highest temperature of the coil is 84.5 °C. The heat transfer rate for the coil and mantle is 57.2–85.6 and 124.9–141.5 W. The key finding is that the combined regenerative heat exchanger can deliver a higher transfer rate. This can be achieved since the heat exchanger utilizes the same flow distribution, increasing the mean temperature differences at the inlet. Thus, it can produce an average heat transfer rate of 210.5 W. Therefore, energy consumption for coal or other fossil fuels can be reduced significantly. The data can be used for further improvement of the existing boiler system and help to increase the thermal efficiency of the system.

Numerical study on heat transfer enhancement of shell-and-tube thermal energy storage unit using metal foams with non-uniform porosity

ABSTRACT Using metal foams mitigates the low thermal conductivity of phase change materials (PCMs) in latent heat thermal energy storage (LHTES). However, the heat transfer within PCMs is not uniform due to natural convection. In the present study, the effect of the porosity distribution on the heat transfer performance of shell-and-tube thermal energy storage (TES) was analyzed. The results demonstrated that the melting rate and average heat transfer rate both were improved as the porosity gradient increased along positive y-direction. Compared with the uniform porosity (ε = 0.94), the average heat transfer rate was enhanced by 21.6% for ε = 0.94 + 0.267y during the melting process. For the porosity gradient increasing along outer radius direction, the heat transfer rate near the heating wall was improved, while the phase change process of PCM near the outer wall slowed down. The maximum of average heat transfer rate existed for ε = 0.88 + 0.6r.

Computational Fluid Dynamics Simulation on Thermal Performance of Al/Al2O3/SWCNT Nanocoolants for Turning Operations.

The objective of this study is to numerically investigate the thermal performance of cutting fluids dispersed with nanoparticles for effective heat removal during turning operations. The simulations are performed using Ansys Fluent software, and the problem is modelled as a three-dimensional turbulent incompressible single-phase flow. The computational domain consists of a heated cutting tool and work piece, and nanocoolants are sprayed from a nozzle located above the machining zone. The nanocoolants are prepared by mixing mineral oil with nanoparticles of Al2O3 (Aluminium Oxide), Al (Aluminium) and SWCNT (Single Walled Carbon Nanotube). The heat transfer performances of different nanocoolants are compared by varying the nanoparticle volume fraction (φ) and coolant velocity (Uc) in the range of 2% ≤ φ ≤ 8% and 1 m/s ≤ Uc ≤ 15 m/s, respectively. The results indicated a drastic drop in the cutting tool temperature with an increase in the volume fraction of dispersed nanoparticles and coolant velocity. The increase in volume fraction decreases the average cutting tool temperature by 25.65% and also enhances the average heat transfer rate by 25.43%. It is additionally observed that SWCNT nanocoolants exhibited a superior thermal performance and heat removal rate compared with Al and Al2O3 nanocoolants. The analysed numerical results are validated and are in good accordance with the benchmark results validated from literature.

Thermal performance of a hollow cylinder with low conductive materials in a lid-driven square cavity with partially cooled vertical wall

• A hollow cylinder is used to study the thermal performance of different low conductivity materials. • A square chamber is defined as one with a moving top wall and a partly cooled left vertical wall. • Within the lid-driven chamber, a hot hollow cylinder is positioned, which acts as a heat source. • The numerical investigation is obtained by changing the thermal conductivity (K) of the cylinder's solid objects. • The heat absorption rate of all materials decreases significantly over time. Extensive research has focused on mixed convection in a lid-driven cavity. However, the thermal characteristics of a hollow cylinder made of low-conducting materials such as wood, high-density plastic, bricks, and concrete are not explored, even though they have a lot of real-world applications in engineering and technology. Thus the thermal performance of a hollow cylinder with several low conductive materials such as wood, high-density plastic, bricks, and concrete is investigated in this study. A square enclosure with a moving lid and partially cooled right vertical wall is considered. A heated hollow cylinder is placed in the center of the enclosure as a heat source. A set of governing equations with the appropriate initial and boundary conditions of this model is solved using finite element approach based on Galerkin weighted residual method. The numerical study is performed by varying the thermal conductivity ( K ) of the cylinder’s materials with transient conditions, and outcomes are depicted in terms of streamlines, isotherms, and different thermo-hydrodynamic properties such as average shear rate, drag force, average rate of heat transfer and heat absorption rate. The results indicated that the heat transfer rate of wood is initially greatest at the top but gradually decreases to the rock-bottom. Furthermore, the heat absorption rate of all materials decreases significantly over time; on average, wood absorbs 31% more heat than concrete.

Role of obstructing block on enhanced heat transfer in a concentric annulus

The scope of this work is to investigate the influence of an obstruction size and its location on the buoyancy-driven convection in a concentric annulus. The inner cylinder of an annulus is maintained at higher temperature than the outer cylinder. An obstructing adiabatic block is placed in the space between the annulus. To explore the impact of the obstruction on the thermo-fluid flow structure, the block size and its position are varied. The annular region between the cylinders is assumed to be filled with air. The governing differential equations are solved numerically via the finite volume technique-based solver. The simulations are carried out for a controlling range of Rayleigh numbers (Ra = 103–105). The effect of the block size ( = 0–0.8) and its positions (°) on the heat transfer features are extensively examined. It is observed that the heat transfer is maximum for a particular Rayleigh number, block size, and its position. There exist a critical Rayleigh number (Racr) for the enhanced heat transfer. Depending on the block size and its position and Racr, the flow structure exhibits multi-cellular formation, which dictates the heat transfer markedly. The average heat transfer rate improves markedly up to a certain block size and convection regime, after which thermal behavior deteriorates. The local heat transfer attains a peak value near the location, where multi-cells are formed. The heat transfer enhancement parameter is approximately equal to 10% for the optimum block size. The findings of this study will be very helpful for the designing of the thermal system pertaining to efficient heat exchanging devices and other technological applications. Highlights The influence of location and size of an obstructing adiabatic block on buoyant convection in an annulus of the differentially heated concentric cylinder is investigated. Thermo-fluid flow behavior is markedly influenced by the obstructing block size and its position. The optimum block size and position are determined for the maximum heat transfer in an annulus for various Rayleigh numbers. The critical Rayleigh number for the optimum heat transfer is evaluated. The heat transfer parameter is approximately 10% for the optimum block size.

Comparative heat transfer analysis of γ -Al2O3−C2H6O2 and γ -Al2O3−H2O electroconductive nanofluids in a saturated porous square cavity with Joule dissipation and heat source/sink effects

Inspired by the applications in electromagnetic nanomaterials processing in enclosures and hybrid fuel cell technologies, a mathematical model is presented to analyze the mixed convective flow of electrically conducting nanofluids (γ-Al2O3−H2O and γ-Al2O3−C2H6O2) inside a square enclosure saturated with porous medium under an inclined magnetic field. The Tiwari–Das model, along with the viscosity, thermal conductivity, and effective Prandtl number correlations, is considered in this study. The impacts of Joule heating, viscous dissipation, and internal heat absorption/generation are taken into consideration. Strongly nonlinear conservation equations, which govern the heat transfer and momentum inside the cavity with associated initial and boundary conditions, are rendered dimensionless with appropriate transformations. The marker-and-cell technique is deployed to solve the non-dimensional initial-boundary value problem. Validations with a previous study are included. A detailed parametric study is carried out to evaluate the influences of the emerging parameters on the transport phenomena. When 5% γ-Al2O3 nanoparticles are suspended into H2O base-fluid, the average heat transfer rate of γ-Al2O3−H2O nanoliquid is increased by 25.63% compared with the case where nanoparticles are absent. When 5% γ-Al2O3 nanoparticles are suspended into C2H6O2 base-fluid, the average heat transfer rate of γ-Al2O3−C2H6O2 nanofluid is increased by 43.20% compared with the case where nanoparticles are absent. Furthermore, when the heat source is present, the average heat transfer rate of γ-Al2O3−C2H6O2 nanofluid is 194.92% higher than that in the case of γ-Al2O3−H2O nanofluid.

흡수식 냉동기용 유하액막식 증발기의 전열관 형상이 열전달 성능에 미치는 영향

To understand the mechanism and obtain data that can be used for design, an experimental apparatus was constructed to investigate the heat transfer characteristics of a falling film evaporator for an absorption chiller. Evaporators with plain tubes or three enhanced tubes were prepared. The enhanced tubes were designed to improve surface wetting rate with surface protrusions or a floral pattern shape. The performance change of the evaporator was investigated according to the flow rate of chilled water, the inlet temperature of the chilled water, the liquid film Reynolds number, and the evaporation temperature. In the case of using the enhanced tube, the average heat transfer rate was approximately 16.3% higher than that of the plain tube, and the difference in heat transfer rate between the enhanced tubes was as small as approximately 6%. The Nusselt number of end-cross, end-dimple, and end-dimple floral tubes was higher by 13.1%, 26.5%, and 46.9%, respectively, than in the plain tube.

Irreversibility analysis for the natural convection of Casson fluid in an inclined porous cavity under the effects of magnetic field and viscous dissipation

The non-Newtonian fluids are increasingly being employed in various engineering and industrial processes. The Casson fluid model is also used to characterize the non-Newtonian fluid behavior and has great importance in polymer processing industries and biomechanics. Motivated by these developments, the present study explores the entropy generation for the natural convection of Casson fluid in a porous, partially heated square enclosure considering the effects of horizontal magnetic field, cavity inclination and viscous dissipation. The bottom wall of the enclosure is considered partially heated, whereas the left and right walls are taken as cold at constant temperature. The top wall and the remaining portions of the bottom wall are adiabatic. The dimensionless form of the governing conservation laws is simulated via higher order Galerkin finite element method. Particularly, the discretization is performed using biquadratic elements for velocity and temperature components whereas the discontinuous linear elements employed for the pressure. The discretized nonlinear systems are handled by implementing the adaptive Newton-multigrid solver. In order to increase the reliability of the computed results, the designed solver is validated qualitatively and quantitatively for the available numerical and experimental data. The simulated results are analyzed through isotherms, streamlines and two dimensional plots. Moreover, the average entropy generation, kinetic energy and temperature are also computed and analyzed. The controlling parameters are Hartmann number (Ha=0−100), Darcy number (Da=10−4), Prandtl number (Pr=7), Rayleigh number (Ra=105), Casson fluid parameter (γ=0.1−10), cavity inclination (ϕ=0°−90°) and Eckert number (Ec=10−6−10−4). It is concluded that the average heat transfer rate decreases whereas the total entropy generation increases by increasing the cavity inclination (ϕ) for each value of Ha. Further, the irreversibilities due to heat transfer and magnetic field both are increasing for function of ϕ.