Hot Cylinder Research Articles

Simulation of mixed-convection of water and nano-encapsulated phase change material inside a square cavity with a rotating hot cylinder

Nano-encapsulated PCM consists of a solid shell and a phase change material (PCM) in the core that improves the thermal properties of base fluids. The heat capacity of the nanofluid increases due to the latent heat of the NEPCM core and the heat transfer rate increases dramatically. Also, a phase change occurs in a certain range of temperature. In the present study, the core and shell of NEPCM are n-nonadecane and polyurethane, respectively. Mixed convection of water-NEPCM is simulated inside a square chamber with cold walls and a hot rotating cylinder in the center. Coupled PDE equations are solved by the SIMPLE algorithm and developing C++ code. The parameters of Grashof number, Reynolds number, intensity of stored energy in the core of NEPCM (χ), and fusion temperature (θf) have been studied on the flow pattern, temperature contour, heat capacity ratio (Cr) contour, and Nusselt number. Based on this study it can be concluded that in general the optimal state of θf is in moderate values or especially numbers close to 0.5 and at this range of θf, χ reduction can enhance Nusselt number more. Also, at high Gr number by increasing Re number, heat transfer rate reduces. The results also show that adding NEPCM can increase the Nusselt number by more than 13%.

Effects of radius ratio on annular centrifugal Rayleigh–Bénard convection

We report on a three-dimensional direct numerical simulation study of flow structure and heat transport in the annular centrifugal Rayleigh–Bénard convection (ACRBC) system, with cold inner and hot outer cylinders corotating axially, for the Rayleigh number range $Ra \in [{10^6},{10^8}]$ and radius ratio range $\eta = {R_i}/{R_o} \in [0.3,0.9]$ ( $R_i$ and $R_o$ are the radius of the inner and outer cylinders, respectively). This study focuses on the dependence of flow dynamics, heat transport and asymmetric mean temperature fields on the radius ratio $\eta$ . For the inverse Rossby number $Ro^{-1} = 1$ , as the Coriolis force balances inertial force, the flow is in the inertial regime. The mechanisms of zonal flow revolving in the prograde direction in this regime are attributed to the asymmetric movements of plumes and the different curvatures of the cylinders. The number of roll pairs is smaller than the circular roll hypothesis as the convection rolls are probably elongated by zonal flow. The physical mechanism of zonal flow is verified by the dependence of the drift frequency of the large-scale circulation (LSC) rolls and the space- and time-averaged azimuthal velocity on $\eta$ . The larger $\eta$ is, the weaker the zonal flow becomes. We show that the heat transport efficiency increases with $\eta$ . It is also found that the bulk temperature deviates from the arithmetic mean temperature and the deviation increases as $\eta$ decreases. This effect can be explained by a simple model that accounts for the curvature effects and the radially dependent centrifugal force in ACRBC.

Jet Impingement Cooling of a Rotating Hot Circular Cylinder with Hybrid Nanofluid under Multiple Magnetic Field Effects

The cooling performance of jet impinging hybrid nanofluid on a rotating hot circular cylinder was numerically assessed under the effects of multiple magnetic fields via finite element method. The numerical study was conducted for different values of Reynolds number (100≤Re≤300), rotational Reynolds number (0≤Rew≤800), lower and upper domain magnetic field strength (0≤Ha≤20), size of the rotating cylinder (2 w ≤r≤ 6 w) and distance between the jets (6 w ≤ H ≤ 16 w). In the presence of rotation at the highest speed, the Nu value was increased by about 5% when Re was increased from Re = 100 to Re = 300. This value was 48.5% for the configuration with the motionless cylinder. However, the rotations of the cylinder resulted in significant heat transfer enhancements in the absence or presence of magnetic field effects in the upper domain. At Ha1 = 0, the average Nu rose by about 175%, and the value was 249% at Ha1 = 20 when cases with the cylinder rotating at the highest speed were compared to the motionless cylinder case. When magnetic field strengths of the upper and lower domains are reduced, the average Nu decreases. The size of the cylinder is influential on the flow dynamics and heat transfer when the cylinder is rotating. An optimum value of the distance between the jets was obtained at H = 14 w, where the Nu value was highest for the rotating cylinder case. A modal analysis of the heat transfer dynamics was performed with the POD technique. As diverse applications of energy system technologies with impinging jets are available, considering the rotations of the cooled surface under the combined effects of using magnetic field and nanoparticle loading in heat transfer fluid is a novel contribution. The outcomes of the present work will be helpful in the initial design and optimization studies in applications from electronic cooling to convective drying, solar power and many other systems.

Types and Composition of Biomass in Biocoke Synthesis with the Coal Blending Method

The steelmaking industry requires coke as a reducing agent, as an energy source, and for its ability to hold slag in a blast furnace. Coking coal as raw coke material is very limited. Studying the use of biomass as a mixture of coking coal in the synthesis of biocoke is necessary to reduce greenhouse gas coal emissions. This research focuses on biomass and heating temperature through the coal blending method to produce biocoke with optimal mechanical properties for the blast-furnace standard. The heating temperature of biomass to biochar was evaluated at 400, 500, and 600 °C. The blending of coking coal with biochar was in the compositions of 95:5, 85:15, and 75:25 wt.%. A compacting force of 20 MPa was employed to produce biocoke that was 50 mm in diameter and 27 mm thick using a hot cylinder dye. The green sample was heated at 1100 °C for 4 h, followed by quenching with a water medium, resulting in dense samples. Increasing heating temperature is generally directly proportional to an increase in fixed carbon and calorific value. Biocoke that meets several blast-furnace criteria is a coal mixture with coconut-shell charcoal of 85:15 wt.%. Carbonization at 500 °C, yielding fixed carbon, calorific value, and compressive strength, was achieved at 89.02 ± 0.11%; 29.681 ± 0.46 MJ/kg, and 6.53 ± 0.4 MPa, respectively. This product meets several criteria for blast-furnace applications, with CRI 29.8 and CSR 55.1.

Numerical study on square enclosure with a hot cylinder accompanied by circular bluff bodies

Numerical study on square enclosure with a hot cylinder accompanied by circular bluff bodies

MHD natural convection nanofluid flow in a heat exchanger: Effects of Brownian motion and thermophoresis for nanoparticles distribution

The free convection of Cu-water nanofluid is simulated and investigated inside a square heat exchanger chamber in the presence of MHD magnetic field. The Buongiorno model with the effects of Brownian and thermophoresis motion is considered to nanoparticles distribution inside the chamber. The geometry consists of a square chamber with two cylinders on the right and left sides as heater and cooler in order to create the buoyancy force, respectively. These cylinders represent hot and cold pipes, and the walls of the chamber are heat and mass insulation. the FVM with SIMPLE algorithm are used for velocity and pressure coupling. In current two-phase simulation, the effects of Rayleigh number, Hartmann number, inclination angle of chamber and volume fraction on streamline contours, isothermal lines, Lorentz force lines, nanoparticle distribution and Nusselt number are investigated. By modeling the motion of nanoparticles and evaluating it, a nanoparticle transport zone was observed. The diffusion effects of thermophoresis were significant in this zone. The nanoparticles were thrown from the hot cylinder to the cold cylinder. The application of a magnetic field enlarged the nanoparticle transport zone. However, increasing the Rayleigh number and decreasing the inclination angle of the enclosure caused the nanoparticles to disperse evenly.

Magnetohydrodynamic natural convection of a hybrid nanofluid from a sinusoidal wavy cylinder placed in a curve-shaped cavity

A numerical investigation has been executed in a curve-shaped enclosure crammed with a hybrid nanofluid containing a wavy-shaped inner cylinder with the existence of a magnetic field. A mixture of copper and alumina nanoparticles in a normal water-based solution is used to create the hybrid nanofluid. The natural convective flow in the enclosure is generated as a result of the temperature difference between a cold outer curve-shaped enclosure and a hot inner wavy cylinder. A numerical parametric examination is performed for several values of the Rayleigh number, volume concentration of nanoparticles, Hartmann number, and wave number of the inner cylinder. Outcomes are explained in terms of velocity field, isotherms, and local and average Nusselt numbers with changes in physically significant parameters. The outcomes reveal that the rate of thermal transmission is considerably augmented for rising the concentration of the hybrid nanofluid and Rayleigh number; however, with a higher Hartmann number, opposite tendency is exhibited. In addition, the intensity of the fluid flow and the heat transfer inside the enclosure are controlled by the number of waves in the internal cylinder.

Study on the effect of flow velocity and thermal buoyancy on the dynamic behaviour of flow inside a two-hole chamber

This work aims to study the behaviour of the fluid inside a square chamber that has two openings at the top of vertical walls for the entry and exit of the fluid. Also, the chamber is arranged around two hot cylinders located vertically. The fact that the fluid is cold and the walls of the cylinders are hot, a vertical transfer of the fluid is shown due to thermal buoyancy force. The study was accomplished numerically. The pertinent parameters examined are as follows: the number of Reynolds (= 1-40) and the number of Richardson (= 0-1). The value of Prandtl number of the working fluid is (Pr = 1). The values of Nu number for the two cylinders are calculated and expressed in terms of the values of Re and Ri. The results showed that the effect of the fluid on the cylinders differs from the lower cylinder to the upper cylinder. Also, the presence of counter-flows in some cases creates hydrodynamic force in the opposite direction. For example, for Re = 40 increasing the Ri value from 0 to 1 increases Nu by an average of 3.84% for the upper obstacle and 81% for the lower one.

Galerkin finite element analysis of thermal aspects of Fe3O4-MWCNT/water hybrid nanofluid filled in wavy enclosure with uniform magnetic field effect

In this contribution, a numerical investigation was made for heat transfer and steady magneto-hydrodynamic natural convection in a fined cold wavy-walled porous enclosure with a hot elliptic inner cylinder occupied by hybrid Fe3O4-MWCNT /water nanofluid. The enclosure is also placed in a uniform magnetic field. The governing equations are verified by using the Galerkin Finite Element Method (GFEM). Our numerical conclusions are expressed in terms of distributions of isotherms, Nusselt number, and streamlines, which are important, control parameters for the heat convection, and flow in the enclosure. The findings elucidate that the Nuavg rises with the growth of Ra, porosity ratio, and Da ratio increase, though it reduces with the growth of Hartmann number.

Research on Selection of Heating Extraction Point for H Class Gas-Steam Combined Cycle Unit in Zengcheng， Guangzhou

Introduction To find out the best extraction heating scheme according to the medium pressure heating steam parameters of large capacity combined cycle unit. Method Combined with the heat load characteristics of Zengcheng project， this paper discussed and analyzed in detail the system configuration， initial investment， load adaptability， unit efficiency and power output of various extraction heating schemes applied to gas steam combined cycle units. Result The analysis results showed that， compared with hot section extraction and IP cylinder extraction， cold section extraction has higher unit power generation output， power generation efficiency and comprehensive energy utilization， and the initial investment was the lowest. Conclusion Cold section steam extraction is a kind of medium pressure steam extraction heating scheme with better parameter matching adaptability， stronger ability to adapt to variable operating conditions of units， better thermal economy and initial investment， and more suitable for large capacity combined cycle units. This scheme can be used for reference for similar engineering designs.

Buoyant Convective Flow and Heat Dissipation of Cu–H2O Nanoliquids in an Annulus Through a Thin Baffle

This article numerically investigates the buoyant convective flow and thermal transport enhancement of Cu–H2O nanoliquid in a differentially heated upright annulus having a thin baffle. For the analysis, the outer and inner cylinders are cooled and heated respectively through insulated top and lower boundaries. Also, the baffle temperature is assumed to be that of the hot cylinder. The finite difference based numerical technique is used to solve the system of equations governing the physical processes. The findings are accessible in terms isotherms, streamlines and Nu number for wider ranges of baffle positions and lengths, Rayleigh numbers, and by considering different nanofluid (NF) volume fractions. The average Nu number is enhanced in addition of the Cu nanoparticle to the base liquid and it is also found the liquid flow and heat transport can be successfully controlled via the appropriate selection of baffle location and length. Principally, the baffle length having 20% of annular width placed at 80% of the annular height has been found to produce higher thermal transport rates as compared to other choices of baffle lengths and positions.

Mixed Convection in Square Enclosure by Considering the Thermal Effect on Cylinder

This study deals with the influence of a rotating cylinder inside the square cavity and multiwalled carbon nanotube–iron oxide () hybrid nanofluid with water. A two-dimensional system of partial differential equations has been discretized by employing Galerkin finite element method. A finite element method involving the cubic polynomials has been implemented to compute for velocity, temperature, and concentration fields, while the pressure is approximated by quadratic finite element space of functions. The adaptive Newton method is implemented to solve the discrete system of nonlinear equations. Numerical simulations are performed for different ranges of pertinent parameters such as the nanoparticles volume fraction (between 0 and 0.3%), angular velocity (between and ), Richardson number (between 0.01 and 3), and rotating cylinder sizes (between 0.2 and 0.4), and three different thermal conditions on the cylinder are investigated: namely, the adiabatic cylinder, cold cylinder, and hot cylinder. It is inferred that the average Nusselt number increases, when the cylinder rotates clockwise. On the contrary, the average Nusselt temperature increases, when the cylinder rotates counterclockwise. Moreover, the local Nusselt number increasing instead of enhancing the rotational speed of the circular cylinder toward the clockwise rotation. The flow philosophy is presented in the form of isotherms, streamlines, and some appropriate plots.

Natural Convection from Two Hot Semi-Circular Cylinder Confined in Cold Circular Cylinder

Numerical simulations were performed to study the pertinent parameters of natural convection in annular space. The studied geometry consists of two semi-circular cylinders of hot walls confined in cold cavity of circular cross-sectional form. The simulations were done by solving numerically the governing equations via the commercial software ANSYS-CFX. The results showed that this new form of inner cylinders is suitable for insulating applications. The pertinent parameters were selected for this work were: Prandtl number (Pr = 0.71 to 1000) and Rayleigh number (Ra = 103, 104 and 105).

Thermo-economic and entropy generation analyses of magnetic natural convective flow in a nanofluid-filled annular enclosure fitted with fins

A numerical analysis on the thermo-natural convection as well as entropy generation of Al2O3-H2O nanofluid enclosed by two circular cylinders in the presence of magnetic fields was performed. The internal hot cylinder is fitted with rectangular fins of different lengths. Irreversibilities related to the thermal effects, friction effects, magnetic effects were considered. FEM was selected as solving method. Results described the impact of active parameters on the thermo-natural convective flow and heat transfer behaviour as well as entropy generation characteristics. In addition, a basic economic analysis has been proposed to consider the cost of nanofluids in comparison to their contribution in enhancing heat transfer rate. Results show that significant effects of pertinent parameters e.g. Rayleigh, Hartmann, and fins' size on flow, heat transfer, and irreversibilities within annulus. It is also found that for low Rayleigh, irreversibility related to thermo-effects is predominant within the annulus, and by augmenting Rayleigh values, the irreversibility due to the thermo-effects is no longer the key contributor to overall entropy production. The magnetic forces help to increase thermo-effects irreversibility contribution to overall irreversibilities. Finally, thermal transfer enhancement in case of the presence of magnetic forces is found to be more costly in terms of nanofluid utilization.

Classification of Flow Modes for Natural Convection in a Square Enclosure with an Eccentric Circular Cylinder

The present study investigated the natural convection for a hot circular cylinder embedded in a cold square enclosure. The numerical simulations are performed to solve a two-dimensional steady natural convection for three Rayleigh numbers of 103, 104 and 105 at a fixed Prandtl number of 0.7. This study considered the wide range of the inner cylinder positions to identify the eccentric effect of the cylinder on flow and thermal structures. The present study classifies the flow structures according to the cylinder position. Finally, the present study provides the map for the flow structures at each Rayleigh number (Ra). The Ra = 103 and 104 form the four modes of the flow structures. These modes are classified by mainly the large circulation and inner vortices. When Ra = 105, one mode that existed at Ra = 103 and 104, disappears in the map of the flow structures. The new three modes appear, resulting in total six modes of flow structures at Ra = 105. New modes at Ra = 105 are characterized by the top side secondary vortices. The corresponding isotherms are presented to explain the bifurcation of the flow structure.

Thermal-natural convection and entropy production behavior of hybrid nanoliquid flow under the effects of magnetic field through a porous wavy cavity embodies three circular cylinders

In this numerical contribution, hybrid nanofluid flow behavior, thermal characteristics, and entropy generation analysis through a porous enclosure containing three circular cylinders with magnetic field effects were investigated using finite element approach. The cylinders are arranged in horizontal arrangement in the middle of cavity height, and the active hot central cylinder can move along the vertical central axis while other cold cylinders are considered fixed. The cylinders are enclosed by an adiabatic wavy cavity loaded with Cu-Al2O3-water. The results are discussed for the scrutinized parameters e.g., Rayleigh number (Ra), Darcy number (Da), Hartmann number (Ha), relative position of the hot cylinder (δ), and concentration in volume of nanoparticles (ϕ). It was inferred that the thermal-natural convective flow and overall heat transmission were reinforced by boosting Ra and Da, and lowering Ha. Changing the relative position of the hot cylinder has a remarkable effect on nanoliquid flow patterns, convective heat transfer and entropy generation characteristics.

Effect of wall-slip on natural convection in a circular annulus

Two-dimensional natural convection in an annulus enclosed by a hot inner cylinder and cold outer cylinder with air (Prandtl number, Pr=0.71) as the fluid is numerically investigated for Rayleigh number (Ra)= 5 × 104 using OpenFOAM. For a gap width to radius ratio (L/Ri ) of 1.6, the slip configurations are imposed by varying the Slip factor (SF) from 0 (no-slip) to 1 (full-slip) in steps of 0.2. The flow patterns and thermal fields for each slip factor are visualised using streamlines and isotherms and heat transfer is quantified by Nusselt number (Nu). It is observed that the natural convection patterns at full-slip boundary condition (SF=1) exhibit unique phenomena like vortex splitting, shrinkage in the thermally stagnant regions, and reduction in thermal boundary layer thickness. The heat transfer characteristics, in general, get enhanced with the increase in SF.

Effect of wall-slip on natural convection in the annulus between a circular cylinder and square enclosure

Two-dimensional natural convection in the annulus between a hot circular cylinder and cold square enclosure is numerically investigated for Rayleigh number (Ra)=106 using OpenFOAM. The Prandtl number (Pr) and radius to length (R/L) ratio are fixed at 0.71 and 0.2 respectively and slip condition is imposed by varying the Slipfactor (SF) from 0 (no-slip) to 1 (full-slip) in steps of 0.2. For each value of SF, the flow patterns are visualised using streamlines and heat transfer behaviour is examined using isotherms. The full-slip boundary condition (SF=1) witnesses significant phenomena like vortex splitting, shrinkage in thermally stagnant region and reduction in thermal boundary layer thickness. The heat transfer rate is found to increase with an increase in SF and results are quantified using local Nusselt number (Nui) and average Nusselt number (Nu avg) along the hot wall. It is noticed that for full-slip (SF=1) configuration, the natural convection patterns and heat transfer characteristics undergo notable changes.

Natural convection of nanoliquid from elliptic cylinder in wavy enclosure under the effect of uniform magnetic field: numerical investigation

In the current article, a three-dimensional numerical simulation is conducted to scrutinize the steady laminar natural convective flow and transfer of heat between a cold wavy porous enclosure and a hot elliptic cylinder. Alumina nanoparticles are dispersed in the water to enhance the heat exchange process. The nanofluid flow is taken as laminar and incompressible, while the advection inertia effect in the porous layer is taken into account by adopting the Darcy–Forchheimer model. The problem is explained in the dimensionless form of the governing equations and solved by the finite element method. The influences of different governing parameters such as nanoparticles volume fraction (ϕ), angle of rotation (α), Darcy number (Da), Hartmann number (Ha), and Rayleigh number (Ra) on the fluid flow, temperature (T) filed and average Nusselt number are presented. The results exhibit that the heat transfer is enhanced when either of Ra, Da and ϕ is raised. The permeability increment achieved a 12.73% enhancement in the heat transfer rate. Also, when $$\mathrm{Ha}$$ is altered from 0 to 100, a reduction in values of the Nusselt number is given up to 22.22%. Furthermore, the optimal inclination angle for the convective process is α = 45°.

α-Stirling hydrogen engines for concentrated solar power

α-Stirling engines are receiving more and more attention for applications of concentrated solar power in small power installations (15–30 kW). The design of these engines has not experienced in recent years the breakthrough needed to deliver close to the Carnot Cycle energy conversion efficiencies. The delivered efficiencies are limited to mid-to-high 20% in the typical installations “Dish Stirling”. Here we review the latest studies made on α-Stirling engines, unfortunately mostly based on theoretical models of limited reliability, but also including very few examples of Computer-Aided Engineering (CAE) modeling followed by prototyping and testing. Finally, we present in detail one CAE model of an α-Stirling engine delivering energy conversion efficiencies of 42% with hydrogen as working fluid and adopting one hot cylinder, one cold cylinder, and one regenerator, with the hot fluid temperature of 800 °C. This efficiency is much higher than current air microturbines, which may deliver efficiencies of only about 20% working at much lower temperatures.