Convective Heat Transfer Process Research Articles

The Role of Heater Size and Location in Modulating Natural Convection Behavior in Cu-Water Nanofluid-Loaded Square Enclosures

Enhancing the energy efficiency of thermal systems reduces their consumption, lowers costs, and reduces undesired environmental impact, thus making these systems more sustainable. The current work introduces a passive method for heat transfer enhancement that is carried out using natural convection by nanofluid. This work introduces a computational study of the process of natural convection within a square cavity containing Cu/H2O nanofluid. The cavity wall on the left side undergoes partial isothermal heating, while the opposing side is fully cooled isothermally, with all other boundaries maintained adiabatic. A mathematical model formulated based on a 2-D model was used to provide the solution for the system of governing equations of mass, momentum, and energy conservation, employing the finite element technique. A commercial CFD package is utilized to perform the computational simulation. The present investigation delves into the impact of the Rayleigh number, nanoparticle concentration, heater length, and heater location on the flow field and heat transfer characteristics. The model outcomes were displayed for a wide range of the pertinent parameters as 103 ≤ Ra ≤ 106, 0.25 ≤ lh ≤ 1.0, 0.125 ≤ hc ≤ 0.875, and 0.02 ≤ ϕ ≤ 0.10. Also, correlation equations relating the average Nusselt number to these crucial parameters are derived. These equations are simple and can be applied in practice easily in many fields, such as electric and electronic equipment cooling and thermal management of heat sources. Also, these equations gather all the parameters that affect the heat transfer process. They are shedding light on the intricate interplay between these parameters in the natural convection heat transfer process.

Investigation of the melting and solidification processes of a phase change material in cylindrical annular enclosures: A parametric study for energy densification in hot water tanks

The present study focuses on the analysis of the effect of the phase change material (PCM) cavity size on the melting and solidification processes for application to thermal energy densification in a hot water tank through latent heat thermal energy storage in cylindrical annular cavities. A 2D axisymmetric composite geometrical pattern is considered, formed by a phase change material surrounded by a conductive and an insulating material. A parametric study is conducted on the phase change material cavity size, and the results are presented using non-dimensional numbers: Fourier number, Rayleigh number, and aspect ratio. Two approaches have been developed based on local and global analyses. The local one showed the predominance of the conductive or convective heat transfer process concerning the influence of the phase change material size, and thus the Rayleigh number, on the evolution of the solid/liquid interface and streamline shapes. The global one allowed correlations for melting and solidification Fourier numbers with respect to the Rayleigh number and aspect ratio to be built from simulation data. Two parameters for each process have been identified and defined from the present study: the critical Fourier number and the aspect ratio constant. The critical Fourier number corresponds to the maximum Fourier number that the phase change material needs to achieve for a melting or solidification process. The aspect ratio constant provides information on the phase change material aspect ratio value where the Rayleigh number no longer influences the process. In the case of the melting process, this parameter is an indication that convection has reached a maximum intensity and no longer influences the process. Finally, this study proposes a suitable aspect ratio for optimizing the melting process: 19.32, and another for optimizing the solidification process: 16.29.

Finite element analysis of Cu-water nanofluid flow and heat transfer in a dynamically bulging enclosure

PurposeThe main purpose of this study is to analyze the heat transfer phenomena in a dynamically bulging enclosure filled with Cu-water nanofluid. This study examines the convective heat transfer process induced by a bulging area considered a heat source, with the enclosure's side walls having a low temperature and top and bottom walls being treated as adiabatic. Various factors, such as the Rayleigh number (Ra), nanoparticle volume fraction, Darcy effects, Hartmann number (Ha) and effects of magnetic inclination, are analyzed for their impact on the flow behavior and temperature distribution.Design/methodology/approachThe finite element method (FEM) is employed for simulating variations in flow and temperature after validating the results. Solving the non-linear partial differential equations while incorporating the modified Darcy number (10−3 ≤ Da ≤ 10−1), Ra (103 ≤ Ra ≤ 105) and Ha (0 ≤ Ha ≤ 100) as the dimensionless operational parameters.FindingsThis study demonstrates that in enclosures with dynamically positioned bulges filled with Cu-water nanofluid, heat transfer is significantly influenced by the bulge location and nanoparticle volume fraction, which alter flow and heat patterns. The varying impact of magnetic fields on heat transfer depends on the Rayleigh and Has.Practical implicationsThe geometry configurations employed in this research have broad applications in various engineering disciplines, including heat exchangers, energy storage, biomedical systems and food processing.Originality/valueThis research provides insights into how different shapes of the heated bulging area impact the hydromagnetic convection of Cu-water nanofluid flow in a dynamically bulging-shaped porous system, encompassing curved surfaces and various multi-physical conditions.

Infrared radiation characteristics simulation of exhaust suppression type ships

An equivalent calculation method for the infrared-suppressed ship’s infrared radiation is carried out, which couples thermal characteristics of the ship surface and the exhaust system. Firstly, a refined physical model for the infrared suppressed exhaust system is proposed, which considers the processes of convective heat transfer and radiative heat transfer. The model generates the equivalent heat flow boundary conditions of the internal heat source through the numerical calculation of Computational Fluid Dynamics (CFD), and combines with the energy balance physical model. The energy balance model on the ship surface is developed, which considers external thermal environment conditions including itself radiation, solar radiation, atmospheric radiation, and reflective radiation among surface elements. The temperature calculation model for the ship with a jet exhaust system is formed. Subsequently, an exhaust-suppressed ship infrared radiation calculation model is formed based on the infrared radiation rendering of solid targets and the narrow spectral principle of exhaust plumes, which considers the spontaneous radiation and environmental radiation of ships. Finally, the infrared simulation results are compared and verified based on experimental data. The results indicate that the infrared radiation error on the ship’s typical parts is less than 30 %. Additionally, 90.1 % of the cabin walls using exhaust suppression systems have a temperature difference of less than 3 K under different operating conditions. It suggests that the exhaust suppression system is effective in reducing the temperature of the cabin wall. The calculation method for ship infrared characteristics constructed in this paper has reasonable results, and it can be used for infrared characteristic analysis of exhaust suppression ships.

Geothermal energy appraisal and subsurface structural mapping of the Rafin Rewa warm spring region, Precambrian basement complex of Nigeria

This research work aims at evaluating the geothermal energy potentials of the Rafin Rewa warm spring (RRWS) of the Precambrian Basement Complex in Nigeria as an alternative energy source using integrated aeromagnetic geophysical techniques. Four aeromagnetic dataset were acquired, assemblage, analyzed, and interpreted using integrated geophysical processing techniques of spectral analysis and Euler deconvolution. Qualitative interpretation of the residual anomalous map reveals a distribution of positive anomalies (> 53 nT) majorly in the central and southeastern regions, which are traced to the granitic rocks, while the low anomalies (< − 1.5 nT) have been traced to the RRWS location emanating from the coastal plain sands of the Pliocene, Pleistocene, Oligocene, and Miocene ages. Quantitatively, the depth to the top (DTT) of the anomalous bodies reveals a depression that is almost intersecting with the Curie point depth (CPD) plot at the RRWS location, which indicates high heat flow in the RRWS region. The Spectral Analysis results reveal that the DTT and the CPD in this area ranges from 0.512 to 0.761 km and 6.504 to 10.582 km, respectively while the average CPD is 8.543 ± 0.325 km. It is observed that the DTT and CPD decrease as one move away from the RRWS region. The computed heat flow average was 160.76 ± 19.09 mW/m2 within the RRWS region. The Euler deconvolution result reveals the presence of geological structures, which were interpreted as faults and fractures. The major fractures trend in the east–west (E-W) directions, while the minor fractures trend northeast-southwest (NE-SW) directions. The geochemical result presented shows that iconic compositions impact the convective heat transfer processes associated with geothermal systems. It was conclusively believed that regions with comparable shallow CPDs could be viable for further geothermal energy investigations.

The flow and heat transfer characteristics of supercritical mixed-phase CO2 and N2 in a 3D self-affine rough fracture

Utilizing a three-dimensional self-affine function, we constructed the fracture morphology and established a numerical model considering the thermal-hydraulic coupling (TH) mechanism to simulate the flow and heat transfer processes of CO2 and N2 in a single fracture under supercritical mixed-phase conditions in dry hot rock. The fractal dimension of the fracture was set to 2.5, and the Joint Roughness Coefficient (JRC) roughness coefficient was 13.71. The model accurately simulated the flow and heat transfer processes of supercritical mixed-phase CO2 and N2 fluids within the fracture under the conditions of 50 MPa underground pressure, 200 °C rock exterior temperature, initial temperature of 32 °C for the heat transfer fluid, and inlet velocities ranging from 0.005 to 0.03 m/s. The results revealed that the output thermal power curves for nine different ratios of CO2 and N2 could be classified into three categories.Among the four conventional thermodynamic parameters, specific heat capacity and density significantly impacted output thermal power. The convective heat transfer process between the fluid and the rock wall resulted in temperature fluctuations, primarily influenced by the sharp edges of the fracture wall. As the inlet velocity increased, the outlet-inlet temperature difference monotonically decreased. The fluid with a composition of 45 % N₂ and 55 % CO₂ exhibited the smallest reduction in temperature, with a value of 50.52 °C. Meanwhile, the output thermal power monotonically increased, with the fluid composition of 5 % N2 and 95 % CO2 experiencing the most significant increase, reaching 122.22 W.

Experimental investigation on the stability and heat transfer enhancement of phase change materials composited with nanoparticles and metal foams

Conventional phase change materials (PCMs) possess the challenge of low thermal conductivity, which hinders the energy exchange rate and storage efficiency. PCMs composited nanoparticles and metal foams have been a proven solution to enhance the thermal characteristics of PCMs. In this work, three enhanced PCM composites including nanoparticle/paraffin, metal-foam/paraffin and nanoparticle/metal-foam/paraffin were prepared using fusion blending and vacuum impregnation method. The effects of different nanoparticles with different mass fractions on the stability and heat storage and release characteristics of nanoparticle/paraffin were investigated. Compared with paraffin, the melting time and solidification time of nano-metal/paraffin are reduced by a maximum of 30.18 % and 43.15 %, respectively. In addition, the effect of pore density of metal foam on natural convective heat transfer process was evaluated. The results showed that the stability in descending order is as follows: nano‑aluminum, nano‑copper and nano‑silver. The optimal mass fraction of nanoparticles with good stability was 1.5 wt% (copper), 1.0 wt% (silver), 1.5 wt% (aluminum), respectively. The metal foam makes the internal temperature distribution of PCMs more uniform in the heat transfer process, while inhibiting the convective heat transfer process. With the increase of pore density, the effect on natural convection heat transfer process rises. When the PPI (pores per linear inch) of foamed metal is greater than 40, the natural convection process can be inhibited, obviously. The foam metal has a more significant effect on the heat transfer performance of nanoparticle/metal-foam/paraffin than that of the nanoparticles. The economic benefits of nanoparticle/paraffin, metal-foam/paraffin and nanoparticle and metal foam composite phase change materials are progressively decrease, with MFP being suitable for applications with high economic budgets.

Thermal Performance of Hybrid PV/T-TEC Air Collector with Perforated-Finned Absorber Plate

PV/T-TEC collector is a device that can produce thermal energy and electrical energy at the same time. The electrical performance may be increased by absorbing residual heat from the PV surface. Due to the temperature difference available between the hot and cold sides of this collector, additional electrical energy can be also generated by using the TEC to increase the total efficiency. The purpose of this study is to evaluate the thermal effect of using both fins and TECs acting as a heatsink. Thus, the perforated zone with a dimension of 100 x 50 x 2 mm was manufactured by lancing and bending processes. Furthermore, 44 pieces of TECs were placed inside the perforated-finned zone and were attached underneath the PV surface to allow a convection heat transfer process. The model collector was then tested by using a solar simulator under 1100 W/m2 with different fluid mass flow rates ranging from 0 to 0.339 kg/s. To meet the test requirements, environmental fluid flow was also implemented and simulated by a fan with an air velocity of 1 m/s. The results showed that increasing the air mass flow rate as a working fluid by five times can reach the operating temperature of the model collector by about 64 °C (24% decrease) and 74 °C (26% decrease) for both with and without environmental fluid flow, respectively. Meanwhile, under the same test conditions, the maximum value for the temperature difference of TEC sides is found to be 5.6 °C for both with and without ambient fluid flow.

Study on the convective heat exchange coefficient of concrete surface considering the surface roughness

A heat exchange experiment of concrete surface under different roughness conditions was conducted, and the convective heat exchange coefficient model of concrete surface influenced by many factors was deduced and developed. The model comprehensively considers the effects of concrete surface roughness, wind speed, air humidity and thermal conductivity on the surface heat exchange performance. We obtained the model parameters from experimental data, which captured the convection heat transfer process under controlled laboratory conditions. The comparison between the calculation result and the measurement data is good enough, and prove the selection value of the model parameters are very good. The new convective heat exchange model can better reflect the heat exchange of the concrete structure surface under complex boundary conditions, provide support for more accurate simulation analysis of concrete temperature field, and provide the possibility for better calculation of concrete temperature stress and control of temperature cracks.

Numerical Investigation of Double-Diffusive Convection in an Irregular Porous Cavity Subjected to Inclined Magnetic Field Using Finite Element Method

Purpose—This study aims to perform an in-depth analysis of double-diffusive natural convection (DDNC) in an irregularly shaped porous cavity. We investigate the convective heat transfer process induced by the lower wall treated as a heat source while the side walls of the enclosure are maintained at a lower temperature and concentration, and the remaining wall is adiabatic. Various factors, such as the Rayleigh number, Darcy effects, Hartmann number, Lewis number and effects of magnetic inclination are evaluated for their influence on flow dynamics and heat distribution. Design/methodology/approach—After validating the results, the FEM (finite element method) is used to simulate the flow pattern, temperature variations, and concentration by solving the nonlinear partial differential equations with the modified Rayleigh number (104 ≤ Ra ≤ 107), Darcy number (10−4 ≤ Da ≤ 10−1), Lewis number (0.1≤Le≤10), and Hartmann number 0≤Ha≤40 as the dimensionless operating parameters. Findings—The finding shows that the patterns of convection and the shape of the isotherms within porous enclosures are notably affected by the angle of the applied magnetic field. This study enhances our understanding of how double-diffusive natural convection (DDNC) operates in these enclosures, which helps improve heating and cooling technologies in various engineering fields. Research limitations/implications—Numerical and experimental extensions of the present study make it possible to investigate differences in thermal performance as a result of various curvatures, orientations, boundary conditions, and the use of three-dimensional analysis and other working fluids. Practical implications—The geometry configurations used in this study have wide-ranging applications in engineering fields, such as in heat exchangers, crystallization, microelectronics, energy storage, mixing, food processing, and biomedical systems. Originality/value—This study shows how an inclined magnetic field affects double-diffusive natural convection (DDNC) within a porous system featuring an irregularly shaped cavity, considering various multiphysical conditions.

Numerical investigation of three-dimensional natural convection heat transfer on corrugated plates of variable height

PurposeThe purpose of this study is to numerically investigate the geometric influence of different corrugation profiles (rectangular, trapezoidal and triangular) of varying heights on the flow and the natural convection heat transfer process over isothermal plates.Design/methodology/approachThis work is an extension and finalization of previous studies of the leading author. The numerical methodology was proposed and experimentally validated in previous studies. Using OpenFOAM® and other free and open-source numerical-computational tools, three-dimensional numerical models were built to simulate the flow and the natural convection heat transfer process over isothermal corrugation plates with variable and constant heights.FindingsThe influence of different geometric arrangements of corrugated plates on the flow and natural convection heat transfer over isothermal plates is investigated. The influence of the height ratio parameter, as well as the resulting concave and convex profiles, on the parameters average Nusselt number, corrected average Nusselt number and convective thermal efficiency gain, is analyzed. It is shown that the total convective heat transfer and the convective thermal efficiency gain increase with the increase of the height ratio. The numerical results confirm previous findings about the predominant effects on the predominant impact of increasing the heat transfer area on the thermal efficiency gain in corrugated surfaces, in contrast to the adverse effects caused on the flow. In corrugations with heights resulting in concave profiles, the geometry with triangular corrugations presented the highest total convection heat transfer, followed by trapezoidal and rectangular. For arrangements with the same area, it was demonstrated that corrugations of constant and variable height are approximately equivalent in terms of natural convection heat transfer.Practical implicationsThe results allowed a better understanding of the flow characteristics and the natural convection heat transfer process over isothermal plates with corrugations of variable height. The advantages of the surfaces studied in terms of increasing convective thermal efficiency were demonstrated, with the potential to be used in cooling systems exclusively by natural convection (or with reduced dependence on forced convection cooling systems), including in technological applications of microelectronics, robotics, internet of things (IoT), artificial intelligence, information technology, industry 4.0, etc.Originality/valueTo the best of the authors’ knowledge, the results presented are new in the scientific literature. Unlike previous studies conducted by the leading author, this analysis specifically analyzed the natural convection phenomenon over plates with variable-height corrugations. The obtained results will contribute to projects to improve and optimize natural convection cooling systems.

Climatology of Synoptic Non-Gaussian Meteorological Anomalies in the Northern Hemisphere during 1979–2018

The analysis of spatial and temporal variability in the number of non-Gaussian extreme anomalies of climatic parameters was carried out for both the initial time series and synoptic variability in the troposphere of the Northern Hemisphere over the period 1979–2018, based on ERA-Interim reanalysis data. There are predominantly three types of empirical distribution densities at 850 hPa, each characterizing the processes of advective and convective heat transfer. At the beginning of the 21st century, compared to the end of the 20th century, there was an increase in the number of anomalies in vertical wind speed and specific humidity for the Northern Hemisphere. Additionally, there is an increase in the number of zonal wind speed anomalies in the low and middle latitudes. Regions with the maximum number of anomalies are primarily located over the continents, while for vertical wind speed anomalies, they are predominantly over the oceans. The application of R/S analysis and multifractal analysis has established that the identified tendencies (which are persistent processes) will continue in the identified regions. The time series of non-Gaussian anomalies (both initial and synoptic scales) exhibit a long-term memory of approximately four years, and synoptic extreme anomalies were found to be more predictable.

Optimization analysis of nuclear thermal coupling for a small nuclear thermal propulsion (SNTP) reactor

As a main structure, tie-tube elements are used both in the traditional and modern LEU nuclear thermal propulsion reactors. This complex structure and its corresponding complex convective heat transfer process have been studied, including CFD calculations. But these studies did not effectively evaluate the applicability of the models and typical problems. In this study, a general small nuclear thermal propulsion (SNTP) reactor model is established by using three-dimensional Monte Carlo code and commercial CFD program Fluent. The applicabilities of material properties, turbulence models and grids are clarified by analyzing various influencing factors. The calculation results show that due to the small enthalpy difference and heat transfer, the convection effect of inner flow based on hydrogen can be ignored. There is no factor that can significantly reduce the maximum fuel temperature, but the porosity of the insulator can significantly improve the heat transfer ratio. In terms of thermal safety and overall performance, 2:1 support ratio is still the best choice. Based on the simulation results, the phenomenon of steep temperature rise of outer tie-tubes is found, and the SST k-omega model with Y + <3 is recommended for simulation of similar problems.

Numerical Simulation of Heat Transfer of Porous Rock Layers in Cold Sandy Regions

The heat transfer characteristics of porous rock layers (PRLs) have significant seasonal differences. This feature has been used to protect the permafrost subgrade under highways and railways from degeneration. However, in cold sandy environments, the transformation law of heat transfer characteristics of PRLs on account of climate warming and aeolian sand filling needs to be solved. This work developed a coupled heat transfer model for the soil–PRL system aimed at analyzing the convective heat transfer process and mechanism of a closed PRL. Furthermore, the impact of climate warming and sand filling on the cooling performance of the PRL under different mean annual air temperatures (MAATs) of −3.5, −4.5, and −5.5 °C was quantified. The numerical results indicated that the natural convection of the closed PRL occurred only in winter, and the effective convective height of the rock layer decreased with the sand-filling thickness. As the thickness of sand filling increased, the critical temperature difference for the occurrence of natural convection increased, accompanied by decreases in the Rayleigh number, the duration, and intensity of natural convection. When the sand-filling thickness exceeded 80 cm, natural convection would not occur in the PRL. Under a warming scenario of 0.052 °C·a−1, the cooling performance of the PRL could offset the adverse impact of climate warming and raise the permafrost table in the first 20 years. Moreover, the closed PRL can be more effective in permafrost regions with colder MAATs. For cold sandy permafrost zones, sand-control measures should be taken to maintain the long-term cooling performance of the PRL. This study is of great significance in guiding porous rock embankment design and road maintenance along the Qinghai–Tibetan Railway.

Computational fluid dynamics analysis of PCM-based ocean thermal engine with external rib turbulators

The concept of extracting energy from ocean thermal gradients for the long-term deployment of underwater profiling vehicles is promising. One potential method to capture ocean thermal energy is leveraging the volume change of phase-change materials (PCMs). However, the low thermal conductivity of PCMs and the low heat transfer coefficient between heat exchangers and seawater limit the performance of PCM-based ocean thermal engines (OTEngs). In this paper, a new type of heat exchanger structure with external rib turbulators is proposed. Detailed computational fluid dynamics analysis is conducted for the external forced convection heat transfer process of the heat exchanger with Reynolds number in the range of 240,000 to 600,000. In addition, a solver for calculating the phase-change process of the PCM inside the heat exchanger was developed based on OpenFOAM. The influence of the ribs on the heat transfer and energy conversion processes of the OTEng was analyzed. Results show that (i) the heat transfer coefficient of the ribbed heat-exchanger wall significantly improves, especially at low Reynolds numbers; (ii) 2.5–5 mm high ribs can effectively enhance heat transfer through the wall. When rib weight exceeds 5 mm, the heat transfer coefficient does not increase with the height; (iii) increasing the rib spacing reduces the water resistance and heat transfer coefficient of the wall; and (iv) the ribbed OTEng has a higher net power output compared with the conventional engine.

Modeling of convective heat transfer processes between inhomogeneous gas mixtures and surfaces of a small-caliber artillery barrel

Modern models of aviation artillery weapons are pulsed heat engines that convert the energy of a powder charge into the energy of highly compressed and heated powder gases (hereinafter referred to as gases), which, when expanding, perform work on communicating kinetic energy to the projectile. In the context of artillery science, aviation artillery weapons and ammunition are structured as a system that interacts with heat sources and the environment, sequentially completing thermodynamic cycles. The main element that is most intensively subjected to thermophysical loads and has a significant impact on the combat qualities and cost of aviation artillery weapons is a small-caliber artillery barrel (hereinafter referred to as the barrel). As a result, the problem of determining the temperature field of the barrel is one of the central problems of designing aviation artillery weapons and optimizing firing modes. The successful solution of this problem largely depends on the accuracy of modeling the processes of heat transfer to the channel and from the outer wall of the barrel during firing. At the same time, an adequate synthesis and calculation of the relations describing the phenomenon of convection accompanying the shot is difficult, which is due to the presence of phase transformations in the state of gases; the simultaneous presence of supersonic and subsonic zones in the solution regions; the existence of laminar, turbulent flows and other non-linear formations. The aim of the work is to develop a relatively simple and acceptable for engineering practice mathematical model of heat transfer inside and around the wellbore with near-wall coolant flows (hereinafter referred to as the model). Achieving the goal of the work is carried out by a concentrated choice of criterial equations of the apparatus of thermodynamic similarity, corresponding to the geometric and physical conditions for the uniqueness of the processes of loading the shaft. The introduction of functions that take into account the dependence of the thermophysical properties of gases on temperature made it possible to increase the accuracy of determining the parameters of heat transfer during a shot by 19% in comparison with the known results. The developed model can be used in applied calculations related to determining the thermal state of the wellbore. The specialization of the object of study does not exclude the possibility of refining the model for the purpose of mathematical representation of thermal effects in thermally stressed structures of complex shape.

Studying Alumina–Water Nanofluid Two-Phase Heat Transfer in a Novel E-Shaped Porous Cavity via Introducing New Thermal Conductivity Correlation

Investigating natural convection heat transfer of nanofluids in various geometries has garnered significant attention due to its potential applications across several disciplines. This study presents a numerical simulation of the natural convection heat transfer and entropy generation process in an E-shaped porous cavity filled with nanofluids, implementing Buongiorno’s simulation model. Analyzing the behavior of individual nanoparticles, or even the entire nanofluid system at the molecular level, can be extremely computationally intensive. Symmetry is a fundamental concept in science that can help reduce this computational burden considerably. In this study, nanofluids are frequently conceived of as a combination of water and Al2O3 nanoparticles at a concentration of up to 4% by volume. A unique correlation was proposed to model the effective thermal conductivity of nanofluids. The average Nusselt number, entropy production, and Rayleigh number have been illustrated to exhibit a decreasing trend when the volume concentration of nanoparticles inside the porous cavity rises; the 4% vol. water–alumina NFs yield 17.35% less average Nu number compared to the base water.

Study on unsteady natural convection heat transfer of crude oil storage tank based on fractional-order Maxwell model

When considering the natural flow processes in crude oil in static storage tanks, researchers usually treat the nonlinear heat and mass transfer and flow using integer-order models. However, this ignores the nonlinear convection and heat-transfer phenomena that occur; these are dependent on time and space due to the viscoelasticity of crude oil, which is a non-Newtonian fluid. In this work, we examined the time and space dependence of the nonlinear natural convective heat-transfer processes in crude-oil storage tanks. Fractional-order Maxwell and Cattaneo–Vernotte models were applied to the traditional momentum and temperature equations considering the Boussinesq approximation. Based on the L1 discrete format, the fractional-order pressure-correction equation was derived, and an associated solver, CaputoTemporalFractionalFoam (CTfracFoam), was developed to simulate the convection processes in static crude-oil storage tanks. The results show that when α equals 0.1, the maximum velocity in monitoring area 2 is 0.1404 m/s, and the velocity gradually increases as α increases with a maximum value of 1.1468 m/s at 0.9. When the β is 0.1 and 0.2, the temperature changes in the transition region are −5.204 and −0.165 °C, respectively, while when β is greater than 0.2, the temperature changes are all positive values with a maximum value of 1.924 °C at 0.9. Compared with integer-order Fourier heat-transfer and Newtonian fluid-flow models, the developed fractional-order model can describe the natural convection phenomena of non-Newtonian fluids such as crude oil more flexible and accurately.

INFLUENCE OF THE DIAMETER OF CYLINDRICAL SAMPLES MADE OF DIFFERENT GRADES OF ALUMINUM ON THE COOLING KINETICS

The influence of the diameter of cylindrical samples from various grades of technical aluminum (A0, A5, A6), aviation AB98 and high-purity aluminum A5N on their characteristic cooling times and rates, as well as on heat transfer processes in a wide temperature range, was studied. It was revealed that cooling of the samples occurs due to convective heat transfer and radiation, which have characteristic times. An assessment of the magnitude of characteristic cooling times due to convective heat transfer and radiation has been carried out. It is shown that the characteristic cooling time due to radiation is less than the characteristic cooling time due to convection. Using experimental data on the cooling rate of the studied samples and theoretically calculated values of their heat capacity according to the Neumann-Kopp rule, heat transfer coefficients for the processes of convective heat transfer and radiation depending on temperature were determined. It has been established that with increasing temperature, the contribution of radiation to the total heat transfer coefficient increases, and the coefficient of convective heat transfer with increasing temperature first increases, then after passing a maximum it decreases. The contribution to the overall heat transfer coefficient from radiation is noticeable at high temperatures. It was revealed that the characteristic cooling times due to radiation and convection increase nonlinearly with increasing sample diameter (V/S). This dependence is explained by a decrease in the heat transfer coefficient with increasing sample diameter. Compared with the patterns of influence of sample size on the thermophysical properties of spherical samples. It was revealed that spherical samples cool faster than cylindrical samples of the same mass, and the heat transfer coefficients are higher.

Quadratic Thermal Convection in Magneto-Casson Fluid Flow Induced by Stretchy Material with Tiny Particles and Viscous Dissipation Effects

This investigation is based on the phenomenon of quadratic thermal convection in Magneto-Casson fluid flow induced by stretchy material with tiny particles and viscous dissipation effects. The study aims to understand and optimize the complex behaviour of fluid flow and heat transfer in this system, which has significant implications for engineering and industrial applications. The Magneto-Casson fluid, characterized by its non-Newtonian behaviour and yield stress, interacts with stretchy material and tiny particles, introducing unique flow characteristics and thermal properties. Viscous dissipation, resulting from internal friction, further influences the convective heat transfer process. Mathematical models are developed and solved by employing a numerical technique through the Runge-Kutta Fehlberg scheme coupled with the shooting method to investigate these phenomena comprehensively. The results are deliberated using several graphs on the dimensionless profiles. The results showed that there is a decline in the momentum boundary film as the magnetic field improves due to the effect of the Lorentz force. Also, an increase in the Casson fluid term raises the viscosity and thereby resists the fluid motion.