Magnitude Of Heat Transfer Research Articles

New design concept and thermal performance of a composite wall applied in solar greenhouse

Traditional solar greenhouse wall combines the functions of heat preservation and heating. It cannot accommodate both heat storage and insulation that the heat stored in the wall is uncontrollably lost as the temperature difference between the interior and exterior increases. This study proposed a novel composite wall (NCW) with an independent modular wall made of expanded polystyrene board and reinforced concrete (EPCW), and a solar water heating system (SWHS). The thermal properties of traditional brick walls and novel composite walls were assessed through field tests. Numerical simulations were utilized to analyze the heat transfer processes occurring within the wall, enabling determination of the magnitude of heat transfer towards both the interior and exterior. The thermal resistance of the ECPW with the same thickness is 1.5 times higher than that of clay bricks. Meanwhile, the heat loss from the exterior wall is reduced by 44 % through the EPCW. The SWHS installed on the greenhouse north wall increases heat storage by 89 % and heat release by 256 %. The greenhouse annual input cost for using NCW is 2.5 USD m−2 year−1 in 20-year life. It is 32.4 % lower than that of a conventional clay brick greenhouse, and has some promotional and application value.

Hydro - thermal interactions of a ferrofluid in a non - uniform magnetic field

AbstractA numerical study is performed to examine the influence of a non-uniform magnetic field on the thermo-hydraulic behaviour of a ferrofluid. The analysis is done in the context of a differentially heated semi-circular annulus where a magnetic dipole with its distinct location and dipole strength is used to obtain different configurations. The field variables are computed by solving the coupled set of flow equations, energy equations and the Maxwell’s magneto-statics equations. A detailed description is provided on the flow and thermal response after observing different parameters at both global and local scale. Comparison of streamlines and isotherms with a reference case of natural convection concludes that the recirculation zones are responsible for the increased velocity and heat transfer magnitudes. Another key finding of the present work is about the possibility to locally improve the thermal performance of heat exchangers at any desired position along the circumference.

The various facets of liquid metal convection

Turbulent convection at low Prandtl numbers is in many aspects still terra incognita on the parameter map. One reason for this fact is that laboratory experiments on turbulent convection in this parameter regime are notoriously challenging as they require the use of opaque liquid metals. These working fluids prevent the application of typical optical imaging techniques such as particle image velocimetry. Recent experiments by Grannan et al. (J. Fluid Mech., vol. 939, 2022, R1) shed new light on the variety of regimes in liquid metal flows which include rotating convection, magnetoconvection and rotating magnetoconvection next to the classical Rayleigh–Bénard case. More importantly, the authors manage the seamless crossover from one regime into another. They were thus able to study low-Prandtl-number convection at different levels of complexity in a single experimental set-up. Their work provides new insights into the tight connections between characteristic large-scale flow behaviours and the resulting global heat transfer magnitudes. This has implications for convection in planetary cores and stellar convection zones and connected dynamo action.

Artificial Neural Networking (ANN) Model for Convective Heat Transfer in Thermally Magnetized Multiple Flow Regimes with Temperature Stratification Effects

The convective heat transfer in non-Newtonian fluid flow in the presence of temperature stratification, heat generation, and heat absorption effects is debated by using artificial neural networking. The heat transfer rate is examined for the four different thermal flow regimes namely (I) thermal flow field towards a flat surface along with thermal radiations, (II) thermal flow field towards a flat surface without thermal radiations, (III) thermal flow field over a cylindrical surface with thermal radiations, and (IV) thermal flow field over a cylindrical surface without thermal radiations. For each regime, a Nusselt number is carried out to construct an artificial neural networking model. The model prediction performance is reported by using varied neuron numbers and input parameters, and the results are assessed. The ANN model is designed by using the Bayesian regularization training procedure, and a high-performing MLP network model is used. The data used in the creation of the MLP network was 80 percent for model training and 20 percent for testing. The graph shows the degree of agreement between the ANN model projected values and the goal values. We discovered that an artificial neural network model can provide high-efficiency forecasts for heat transfer rates having engineering standpoints. For both flat and cylindrical surfaces, the heat transfer normal to the surface reflects inciting nature towards the Prandtl number and heat absorption parameter, while the opposite is the case for the temperature stratification parameter and heat generation parameter. It is important to note that the magnitude of heat transfer is significantly larger for Flow Regime-IV in comparison with Flow Regimes-I, -II, and -III.

Temperature Modeling, a Key to Assessing Impact on Rivers Due to Urbanization and Climate Change

With widespread ongoing urbanization and as climate change continues, the importance of protecting the water quality of streams and lakes is intensifying. However, while many water quality constituents in lakes and rivers are of overall interest, water temperature is a ‘key’ variable as temperature influences mixing within a waterbody, influences the acceptability of the habitat for flora and fauna, and serves as a guide to the general health of a stream. To enable the assessment, a physics-based, deterministic hydraulic and heat-balance modeling procedure using the combination of MIKE SHE, MIKE HYDRO and ECO Lab is described to assess heat transfer magnitudes in portions of the Credit River, Ontario. Changes in instream temperature regimes are examined, including both frequency and spatial extent, providing insights into the impacts of urbanization in terms of seasonal temperature shifts arising from land use changes. For flow and temperature regimes, Nash–Sutcliffe model efficiency coefficient (NSE) values of 0.49 and 0.955 were achieved, respectively, for current threshold conditions. Durations of temperature increases from threshold levels indicate that land use changes from current agriculture conditions to urbanization may change stream water temperatures for 9% of the time by 1 °C, and 2% of the time by 2 °C for distances of 1000 m downstream, because of land use change from agriculture to low-density urbanization, and for 20% of the time by 1 °C, and 4% of the time by 2 °C at distances of 1000 m downstream with land use change to high-density urbanization. With climate change RCP 4.5 Scenario in 2050 (Base, for a Wet Year—2017), the continuous amount of time the stream water temperature remains at elevated temperatures of more than 3 °C (from 5000 m to 25,607 m from the most upstream point of Fletchers Creek) for a distance of 20,000 m is more than 13 h. These elevations in temperature may have serious implications for flora and fauna in the creek, particularly impacting the cold-water and mixed-water fish species.

Observation of heat transfer due to variable thermophysical properties of sub-, near- and super- critical fluids in porous media by magnetic resonance imaging

Local velocity and temperature profiles are measured non-invasively using nuclear magnetic resonance (NMR) imaging (MRI) in porous media with a sub-, near-, and supercritical fluid. Heat transfer is driven by natural convection via heating from below. The C2F6 fluid fills the pore spaces in a packed bed of encapsulated phase change material (PCM). As the PCMs melt, 1H signal intensity increases with temperature. Physical properties of C2F6, e.g. thermal diffusivity, vary substantially at the critical point, affecting the rate and magnitude of heat transfer. The changes in bead signal, e.g. temperature, are imaged and measured over time at 27 bar (sub-critical), 32, 34 and 36 bar (near-critical), and 66 bar (supercritical). Despite velocity profile similarities, the temperature in the packed bed varies significantly with thermal diffusivity, the magnitude of which decreases and increases with temperature around the critical point. NMR spatially and temporally captures the resulting dynamic heat transfer processes.

Exact solutions of Stokes' second problem for hybrid nanofluid flow with a heat source

In this study, Stokes' second problem for Cu-Al2O3/water hybrid nanofluid is considered along with the effects of buoyancy force and a heat source. Using Laplace transforms, transient velocity, skin friction coefficient, and local Nusselt number are established in closed forms involving exponentials and error functions. The exact solutions have been compared with the numerical solutions as well as with available exact solutions, which show excellent agreement. It is found that the temperature, skin friction coefficient, and local Nusselt number are strongly affected and increased owing to the increase in the volume fractions of copper and alumina nanoparticles and heat source parameter. On the other hand, the mixed convection parameter noticeably enhances the flow velocity. When the heat source is absent, the skin friction coefficients are oscillating and the heat transfer approaches an asymptotic value. However, for a higher heat source parameter, when time increases, the amplitude of oscillation of the skin friction coefficients gradually increases and the magnitude of heat transfer exponentially increases. Both eventually go to infinity after a long period of time.

Measurement of mid-low order of magnitude of heat transfer rate using infrared thermography in rarefied flow

Based on the analysis of demand for measuring heat transfer of hypersonic vehicle at high attitude, aimed at the characteristic of mid-low order of magnitude of heat transfer rate at ground test for simulating rarefied flow, various factors of the influence on measurement accuracy of mid-low order of magnitude of heat transfer were analyzed. Firstly, the influence of model heating time on heat transfer measurement was analyzed from reducing lateral error of experiment model to controlling temperature rise of model surface, which was based on a steady heat transfer of model surface and one-dimensional and semi-infinite hypothesis. Secondly, model adiabat materials with low thermal diffusivity were put to use. Transient Plane Source Method was introduced so as to calibrate thermal physical parameter(density, specific heat ratio and thermal conductivity) of model material with high accuracy. Kinds of method, such as diffusing compensation and phase-locked method, were adopted to raise measurement accuracy of model surface emittance. Finally, when using thin-wall calorimetry to obtain model surface heat transfer rate, thermocouple was welded on the inner surface of test model to measure heat transfer rate such as MW/m2 order of magnitude, while one was done on the outer surface of model to measure that with several kW/m2 to several hundred kW/m2 by thermocouple or by infrared thermography. In order to compare these results, on the experimental condition of Mach number 12, total pressure 4.2 MPa and total temperature 700 K, heat transfer rate at different points of the double cone thin-wall model was measured by thermocouple and infrared thermography simultaneously. The results indicated that the heat transfer rate measured with infrared thermometry was approaching to that done with thermocouple on the outer surface of model, that heat transfer rate by thermocouple on the outer surface of model was greater than that by thermocouple on the inner surface of test model, and that the influence of model heating time on the measurement of heat transfer rate with different order of magnitude was different.

Numerical and Experimental Analysis of Heat Transfer for Solid Fuels Combustion in Fixed Bed Conditions

The paper concerns the analysis of the heat transfer process that occurred during solid fuel burning in fixed bed conditions. The subject of the analysis is a cylindrical combustion chamber with an output of 12 kW heating power equipped with a retort burner for hard coal and biomass combustion. During the research, a numerical and experimental study is performed. The analysis is prepared for various heat load of the combustion chamber, which allowed for the reconstruction of real working conditions for heating devices working with solid fuels combustion. The temperature distribution obtained by the experimental way is compared with results of the numerical modeling. Local distribution of principal heat transfer magnitudes like a heat flux density and a heat transfer coefficient that occurred on the sidewall of the combustion chamber is analyzed. The analysis showed, that the participation of convection and radiation in the overall heat transfer process has resulted from the heat load of the heating device. Research results may be used for improving an analytical approach of design process taking place for domestic and industrial combustion chambers.

Analysis of heat transfer of spilling fire spread over steady flow of n-butanol fuel

The continuously spilling n-butanol fire is systematically investigated in steady flow state. The influence of thermal conductivity of substrate on spilling fire is revealed. According to the temperature distribution and spreading characteristics, the spilling fire over concurrent steady flow n-butanol is separated into the heat transfer dominant stage in low-discharge rate and the forced flow dominant stage in high-discharge rate with the critical discharge rate Q = 141.5 ml/min. The low-discharge rate spilling fire spread depends on the coupled effects of subsurface flow preheating and intrinsic dragging of flowing fuel, whereas the high-discharge rate spilling fire depends mainly on the dragging effect of non-slip boundary condition on the liquid surface. The temperature distribution of liquid surface proves that the behavior of thermal fluid diffusion occurs in high-discharge rate. The velocity of spilling fire decreases with an increase in thermal conductivity of substrate. The magnitudes of heat transfer involving spilling fire spread over n-butanol inside the subsurface flow namely gas conduction, liquid conduction, liquid convection, sensible heat and heat dissipation from substrate and walls of spilling trench are quantitatively calculated. The sum of sensible heat and convective heat loss accounts for more than 80% of total heat flux.

Thermal performance of a helical shell and tube heat exchanger without fin, with circular fins, and with V-shaped circular fins applying on the coil

This numerical study analyzes the thermal performance of a helical shell and tube heat exchanger without a fin, with circular fins, and with cut (V-shaped) circular fins (with an angle of 15°) applying on the coil. The obtained results showed that in both simple and circular finned heat exchangers when the fluid velocity (both hot and cold) on the shell side is higher than the fluid velocity (both hot and cold) on the tube side, the heat transfer improves. It is also found that flowing the cold water through the shell increases its velocity and flowing the hot fluid through the coil results in higher heat transfer values. Moreover, the results revealed that the highest heat transfer magnitude designates the circular finned heat exchanger with a cold water velocity of 3 m s−1 entering the shell and a hot water velocity of 1 m s−1 entering the tube. Finally, it is found that the cut circular fins effects on the helical shell and tube heat exchanger efficiency and heat transfer are insignificant in comparison with the circular fins.

A numerical study of the ferromagnetic flow of Carreau nanofluid over a wedge, plate and stagnation point with a magnetic dipole

Present communication mainly addresses the fluid transport characteristics of ferromagnetic Carreau nanofluid over a porous wedge, plate, and stagnation point with magnetic dipole effect for shear thinning/shear thickening cases. Suitable self-similarity variables are employed to convert the fluid transport equations into ordinary differential equations which are solved with the use of the Runge-Kutta-Fehlberg (RKF) approach. To check the accuracy of the present model, numerical results for various thermophoretic values for the cases of shear thinning/shear thickening, have been compared with the results obtained by using bvp4c (MATLAB) which divulges good agreement. Influence of active parameters like ferromagnetic-hydrodynamic interaction, thermophoretic, dimensionless distance, Brownian diffusion, suction/injection, Weissenberg number are graphically presented. Computed results manifest that shear thinning and shear thickening fluids express the opposite nature in fluid velocity and temperature for higher values of Weissenberg number. Among the wedge, plate and stagnation point of the plate, the magnitude of heat transfer over the plate is significant for increasing Ferromagnetic-hydrodynamic interaction parameter. Furthermore, it is noticed that higher values of suction/injection parameter decline the fluid temperature over a plate, wedge and stagnation point of a flat plate.

Physical prospective of induction of ferro-constituents in buoyancy-driven magneto-nanofluid under the impact of magnetic dipole

Fulfilment of energy in various sectors of society is the demand of today’s world. Nowadays, researchers are working hard to propose such technologies to eradicate energy losses. Several improvements have been presented by the research community in this regard. After their struggle and hard work, researchers believed that this energy crisis could be overcome with the aid of fluids. So a procedure is executed to subject the fluid flows to a magnetic field. Furthermore, they also disclosed that induction of ferro-elements in a fluid under the existence of magnetic fields, known as ferrofluid, is a remarkable technique to overcome this huge social, economic, and technological problem. So the motto of the current literature is to investigate the elevated thermophysical features of viscous fluid by the inclusion of ferro-particles. To achieve said purpose, nickel zinc ferrite particles (NiZnFe2O4) are added to ethyl alcohol (C2H5OH) in the presence of magnetic dipole. Flow is induced by a two-dimensional linearly elongated sheet. The governing momentum, energy, and thermal transport equations describing the thermomechanical aspects of ferrofluid is modelled in the form of partial differential expressions. Similar variables are needed to transfer the coupled partial expressions into ordinary differential system. Extensive computational interpretation of influencing parameters like ferromagnetic interaction parameter, viscous dissipation, and Curie temperature parameter on associated profiles is accomplished using the shooting method in collaboration with the Runge–Kutta–Fehlberg method. It is found that the primary function of the magnetic dipole is to reduce the velocity within the boundary layer and it tends to enrich the thermal attitude. Diminishing of the momentum distribution of ferro-particles is established in the presence of a magnetic dipole. Inclusion of mixed convection decreases the momentum, whereas an increase is induced in the thermal profile. Decrease of convective heat transfer magnitude is observed in the presence of magnetic dipole.

Numerical analysis of heat removal from gas phase clusters during condensation of Cu nanoparticles under Ar atmosphere

Abstract The statistical analysis of the molecular dynamics modeling for the nucleation of copper (Cu) vapors under argon (Ar) atmosphere in the evaporation-condensation technology was carried out. The model was used to calculate the nucleation in a cell containing 5000 atoms of Cu and 10,000 atoms of Ar. The probabilities of various outcomes in the collision of Ar and Cu atoms with Cu clusters were determined. It was found that pair collisions have a greater probability than the triple collisions. The heat removal from clusters during a collision with Ar and Cu atoms was analyzed to find the probabilities of formation of long-lived small clusters in a variety of conditions, attempting to estimate the magnitude of heat transfer from the clusters of different sizes. It is found that the pair collisions caused a very excited dimer, whereas, the triple collisions formed a more stable dimer.

Lattice Boltzmann simulation of free convection’s hydrothermal aspects in a finned/multi-pipe cavity filled with CuO-water nanofluid

PurposeThis paper aims to investigate the natural convection fluid flow and heat transfer in a finned/multi-pipe cavity.Design/methodology/approachThe cavity is filled with the CuO-water nanofluid. The Koo–Kleinstreuer–Li model is used to estimate the dynamic viscosity and consider Brownian motion. On the other hand, the effect of the shapes of nanoparticles on the thermal conductivity and related heat transfer rate is presented.FindingsIn the present investigation, the governing parameters are Rayleigh number, CuO nanoparticle concentration in pure water and the thermal arrangements of internal active fins and solid bodies. Impacts of these parameters on the nanofluid flow, heat transfer rate, total/local entropy generation and heatlines are presented. It is concluded that adding nanoparticles to the pure fluid has a significant positive influence on the heat transfer performance. In addition, the average Nusselt number and total entropy generation have direct a relationship with the Rayleigh number. The thermal arrangement of the internal bodies and fins is a good controlling tool to determine the desired magnitude of heat transfer rate.Originality/valueThe originality of this paper is to use the lattice Boltzmann method in simulating the nanofluid flow and heat transfer within a cavity included with internal active bodies and fins.

Effects of the magnetic field on the cylindrical Couette flow and heat transfer of a nanofluid

This paper documents the effects of magnetic field on the flow and heat transfer of a nanofluid confined between two cylinders. The inner ring is assumed rotary (representing shaft) while the outer ring was considered fixed (representing the housing). In addition to the single-phase approach, the two-phase model of Buongiorno is used to numerically solve the mass, momentum and energy equations by taking the Brownian and thermophoresis effects into account. The effects of several physical parameters such as the NBT (ratio of Brownian to thermophoretic diffusivities), nanoparticles bulk volume fraction (φb) and the Hartman number on the nanoparticles’ distribution, shear stress and heat transfer at the two rings are reported. It is clearly shown that the magnetic field, changes the linear variation of nanoparticles volume fraction in absence of magnetic field to a non-linear trend in which existence of a minima can be observed. The results indicate that the magnetic field has significant effects on the inner and outer rings’ shear stress and heat transfer such that the Hartman number variations outweighed other parameters’ variations such as NBT and the nanoparticles volume fraction. The results exhibit that increment in the magnetic field drastically reduces the outer ring shear stress and heat transfer magnitude. For example, in the case of Ha = 20, the outer ring shear stress and heat transfer are reduced about 86% and 11 %, respectively in comparison with the case of absent magnetic field (Ha = 0) when NBT=25 and φb=0.05.

Robustness of heat transfer in confined inclined convection at high Prandtl number.

We investigate the dependency of the magnitude of heat transfer in a convection cell as a function of its inclination by means of experiments and simulations. The study is performed with a working fluid of large Prandtl number, Pr≃480, and at Rayleigh numbers Ra≃10^{8} and Ra≃5×10^{8} in a quasi-two-dimensional rectangular cell with unit aspect ratio. By changing the inclination angle (β) of the convection cell, the character of the flow can be changed from moderately turbulent, for β=0^{∘}, to laminar and steady at β=90^{∘}. The global heat transfer is found to be insensitive to the drastic reduction of turbulent intensity, with maximal relative variations of the order of 20% at Ra≃10^{8} and 10% at Ra≃5×10^{8}, while the Reynolds number, based on the global root-mean-square velocity, is strongly affected with a decay of more than 85% occurring in the laminar regime. We show that the intensity of the heat flux in the turbulent regime can be only weakly enhanced by establishing a large-scale circulation flow by means of small inclinations. However, in the laminar regime the heat is transported solely by a slow large-scale circulation flow which exhibits large correlations between the velocity and temperature fields. For inclination angles close to the transition regime in-between the turbulentlike and laminar state, a quasiperiodic heat-flow bursting phenomenon is observed.

Effects of Transient Heat Transfer on Compressor Stability

The effects of heat transfer between the compressor structure and the primary gas path flow on compressor stability are investigated during hot engine re-acceleration transients. A mean line analysis of an advanced, high-pressure ratio compressor is extended to include the effects of heat transfer on both stage matching and blade row flow angle deviation. A lumped capacitance model is used to compute the heat transfer of the compressor blades, hub, and casing to the primary gas path. The inputs to the compressor model with heat transfer are based on a combination of full engine data, compressor test rig measurements, and detailed heat transfer computations. Nonadiabatic transient calculations show a 8.0 point reduction in stall margin from the adiabatic case, with heat transfer predominantly altering the transient stall line. 3.4 points of the total stall margin reduction are attributed to the effect of heat transfer on blade row deviation, with the remainder attributed to stage rematching. Heat transfer increases loading in the front stages and destabilizes the front block. Sensitivity studies show a strong dependence of stall margin to heat transfer magnitude and flow angle deviation at low speed, due to the effects of compressibility. Computations for the same transient using current cycle models with bulk heat transfer effects only capture 1.2 points of the 8.0 point stall margin reduction. Based on this new capability, opportunities exist early in the design process to address potential stability issues due to transient heat transfer.

Flow and Heat Transfer in Nanofluid Flow through a Cylinder Filled with Foam Porous Medium under Radial Injection

The Darcy flow and heat convection in nanofluid through a cylinder filled with a foam porous medium subject to local non-thermal equilibrium (LNTE) condition and uniform radial injection on the outer wall of the cylinder is studied. The momentum and two-energy equations are solved by differential transformation method (DTM) in the form of stream function using similarity variables. The effect on flow and heat transfer of different types of nanofluids and involved physical parameters Prandtl number Pr, Reylond number Re, Darcy number Da, Biot number Bi, Ratio of thermal conductivities Rk, porosity parameter ε, solid volume fraction parameter φ and shape of nanoparticles are analyzed through graphs. The viscous drag force and heat convection at the wall of the cylinder is calculated in terms of non-dimensional skin-friction coefficient and Nusselt number respectively. Decreasing the porosity of foam porous medium causes increment in magnitude of heat transfer rate for both the phases. Spherical shape of nanoparticles transfers more heat in comparison of cylindrical shape nanoparticles. Amongst the nanofluid H2O-Ag, H2O-Cu and H2O-Al2O3 the magnitude of heat transfer for fluid phase Nuf is lowest for nanofluid H2O-Al2O3.

Computational Fluid Dynamics Investigation of Transient Effects of Aircraft Ground Deicing Jets

The present Paper investigates the heat transfer and momentum created by a hot turbulent propylene glycol jet impinging on a horizontal plate at below the freezing-point temperature. A model for the simulation of the initial formation of liquid film at the beginning of an aircraft ground deicing process is proposed. The volume of fluid model coupled with the film formulation is employed using computational fluid dynamics to capture the interface in multiphase flow (liquid propylene glycol/liquid water/air). The three-dimensional Reynolds averaged Navier–Stokes equations are numerically solved using a finite volume discretization under unsteady conditions. The ground deicing case consists of a box and a convergent divergent nozzle installed inside the box. Approximately 512,000 rectangular cells with 0.006 m of thickness are used to refine the mesh of the liquid film on the wall. Flow conditions set are 60°C for the propylene glycol inlet temperature and 0°C for the static ambient temperature. The computed impinged surface skin Nusselt number gives the most noticeable discrepancies at the stagnation point, where the analysis results in a lower skin Nusselt number compared to the experimental results. The magnitudes of heat transfer for the ground deicing case study are found to be in good agreement with experimental hot jet data obtained from the literature.