Decrease In Heat Transfer Rate Research Articles

Flow of a biomagnetic fluid embedded by magnetic dipole over a continuously moving sheet

AbstractThis paper is concerned with the investigation of steady, two‐dimensional, and laminar boundary layer flow of a biomagnetic fluid over a continuously moving sheet in the presence of a magnetic dipole. The magnetic field resulting from the dipole is contemplated to be strong enough to saturate the biofluid. The magnetization of the fluid is regarded to be a linear function of temperature. The solution procedure involves the reduction of a nonlinear system of coupled PDEs into ODEs that comprise five parameters. The transformed ODEs along with the boundary conditions are then solved numerically by introducing an efficient numerical technique based on the finite difference algorithm. The velocity, as well as temperature profiles within the boundary layer, are illustrated at specified values of free stream velocity (), wall velocity () and ferrohydrodynamic interaction parameter (). The demonstration of the Nusselt number and friction factor are achieved for various governing parameters. Considering a specified Prandtl number () and normalized velocity difference , higher values of the friction factor are obtained for increasing and than that of . Whereas for the Nusselt number, we attain higher values for decreasing and . Moreover, an increase in the velocity ratio results in a decrease in both heat transfer rate as well as friction factor. Furthermore, as increases, the heat transfer rate decreases yet we get higher values for higher and . In the case of friction factor, it increases with increasing and gives higher values for lower and higher . We have also depicted the streamlines for the 2‐D boundary layer flow of the biomagnetic fluid for different . The graphical results manifest that the flow field is greatly impacted by the ferrohydrodynamic field, which could be of interest in medical as well as bioengineering implementations, like, magnetic drug delivery in blood cells, separating RBCs as well as controlling the flow of blood during surgical procedures.

Thermally radiative flow of MHD Powell-Eyring nanofluid over an exponential stretching sheet with swimming microorganisms and viscous dissipation: A numerical computation

This work deals with the study of mass and heat transmission in nanofluid flow in the Powell-Eyring model over a sheet that is exponentially stretched with motile microorganisms. Additionally, viscous dissipation and radiation sources are considered. The governing flow expressions are remodeled into nonlinear ordinary differential equations by implementing the appropriate transformations. The remodeled equations are numerically computed by using the bvp4c technique via MATLAB. The various flow parameters are used to investigate and explain in depth the nanofluid velocity, thermal, nanoparticle volume fraction, and motile microbe density profiles. It is noted that the nanofluid velocity decreases with enlarging the values of the magnetic field parameter. The fluid thermal profile develops for greater quantities of radiation thermophoresis and Brownian motion parameters. The nanoparticle concentration decays when the Prandtl number and Lewis number are increased. The motile microbe density profiles suppress when heightening the values of the Peclet number, bioconvection Lewis number, and bioconvection parameter. The magnetic field parameter leads to a decrease in local skin friction, heat, and mass transfer rates.

Effects of vibration on natural convection in a square inclined porous enclosure filled with Cu-water nanofluid

PurposeThe purpose of this paper is to investigate the effects of gravitational modulation on natural convection in a square inclined porous cavity filled by a fluid containing copper nanoparticles.Design/methodology/approachThe present study uses a system of equations that couple hydrodynamics to heat transfer, representing the governing equations of fluid flow in a square domain. The Boussinesq–Darcy flow with Cu-water nanofluid is considered. The dimensionless partial differential equations are solved numerically using finite difference method based on alternating direction implicit scheme. The cavity is differentially heated by constant heat flux, while the top and bottom walls are insulated. The authors examined the effects of gravity amplitude (λ), vibration frequency (σ), tilt angle (α) and Rayleigh number (Ra) on flow and temperature.FindingsThe numerical simulations, in the form of streamlines, isotherms, Nusselt number and maximum stream function for different values of amplitude, frequency, tilt angle and Rayleigh number, have revealed an oscillatory behavior in the development of flow and temperature under gravity modulation. An increase of amplitude from 0.5 to 1 intensifies the flow stream (from |ψmax| = 21.415 to |ψmax| = 25.262) and improves heat transfer (from Nu¯ = 17.592 to Nu¯ = 20.421). Low-frequency vibration below 50 has a significant impact on the flow and thermal distributions. However, once this threshold is exceeded, the flow weakens, leading to a gradual decrease in heat transfer rate. The inclination angle is an effective parameter for controlling the flow and temperature characteristics. Thus, transitioning the tilt angle from 30° to 60° can increase the flow velocity (from 22.283 to 23.288) while reducing the Nusselt number (from 16.603 to 13.874). Therefore, by manipulating the combination of vibration and inclination, it is founded that for a fixed frequency value of σ = 100 and for increased amplitude (from 0.5 to 1), the flow intensity at inclination of 60° is boosted, and an increase of the heat transfer rate at inclination of 30° is also observed. Convective thermal instabilities may arise depending on the different key factors.Originality/valueTo the best of the authors’ knowledge, this study is original in its examination of the combined effects of modulated gravity and cavity inclination on free convection in nanofluid porous media. It highlights the crucial roles of these two important factors in influencing flow and heat transfer properties.

Turbulent mixed convection in a horizontal cylindrical cavity with the off-lattice Boltzmann method

Large-eddy simulations (LES) of turbulent mixed convection in a horizontal concentric cylindrical cavity when cylinders are subjected to rotations are investigated in the present study. A characteristic-based finite-difference off-lattice Boltzmann method solver is employed to investigate whether rotation enhances heat transfer in a horizontal concentric cylindrical cavity configuration where buoyancy acts perpendicular to the cylinder axis. The study focuses on assessing heat transfer characteristics for different rotation intensities in both counter-rotating-cylinders (CRC) and outer-rotating-cylinder (ORC) configurations. The LES simulations are performed for Rayleigh number, Ra=106, and Reynolds numbers, Re=0,500,1000, and 5000 for air (Pr=0.71), employing a classical Smagorinsky sub-grid-scale (SGS) model. The numerical solver is verified using two benchmark problems, namely (i) Buoyancy-driven flow in a differentially heated air-filled cubic enclosure and (ii) turbulent Taylor-Couette flow. The CRC and ORC configurations are chosen for the three-dimensional simulations in this study, prompted by the notable improvement in heat transfer observed in their respective two-dimensional simulations. A thorough comparison between two- and three-dimensional mixed convection results reveals substantial influence from secondary flow in the axial direction. While three-dimensional CRC simulations exhibit a modest increase in heat transfer at Re=500, the ORC configuration experiences a decrease in heat transfer rate as the Reynolds number increases, contrasting with two-dimensional simulation trends. The CRC configuration enhances the axial motion of the flow with Reynolds number, and its magnitude is larger than that of the ORC configuration and natural convection. A significant difference between two-dimensional and three-dimensional mixed convection simulation results is observed because of considerable secondary flow. Furthermore, the flow and thermal characteristics of turbulent mixed convection are investigated using streamlines, isotherms, Q-criterion, Nusselt number variation along the cylinders, anisotropy analysis, turbulent kinetic energy (TKE), dissipation, contours of radial and axial components of velocity.

Simulation investigation of the oscillatory motion of two elliptic obstacles located within a quarter-circle cavity filled with Cu-Al2O3/water hybrid nanofluid

This study investigates the consequences of introducing a pair of oscillating elliptical obstacles on the natural convection and entropy generation within a quarter-circle cavity that is filled with a water-based hybrid nanofluid. The Galerkin Finite Element Method was utilized to perform numerical simulations on a 2-dimensional cavity, where the outer wall was set to a low temperature and the inner wall was kept at a high temperature, while the other walls were adiabatic. The hybrid nanofluid containing Cu-Al2O3 nanoparticles was used. The impact of changes in the values of dimensionless parameters, such as the Rayleigh number, heated wall length, oscillation frequency, oscillation amplitude, and oscillation period, on the flow and heat transfer within the cavity was examined. Results showed that an increase in the length of the hot source resulted in a decrease in heat transfer rate and that increasing the Rayleigh number led to a significant increase in total entropy generation and heat transfer irreversibility. A drop in the average Bejan number was noted as the Rayleigh number increased, demonstrating the prevalence of entropy caused by fluid friction. The effect of changing the amplitude had a higher impact on the average Nusselt number compared to the frequency value. At low Rayleigh numbers, the average Nusselt number was higher when the elliptical obstacles oscillated in the same direction, while the opposite trend was observed at higher Rayleigh numbers.

Comparative analysis of nanofluid flows in the dilating squeezing porous channel with thermal jump and slip conditions

This study investigates the behavior of the mono and hybrid nanofluid flows in an absorbent dilating/squeezing channel influenced by a magnetic field. The mono nanofluid is molded by inserting iron oxide (Fe3O4) nanoparticles into the blood (base fluid) and the targeted hybrid magnetic nanofluid is formed when the Cobalt iron oxide (CoFe2O4) nanoparticles are added into Fe3O4/blood nanofluid mixture. For a permeable channel, the slip boundary along with the thermal jump condition is imposed. The process for heat transfer is examined considering the Cattaneo-Christov heat flux. Throughout the analysis, platelet-shaped nanoparticles are used. The Tiwari and Das (single phase) nanoliquid flow model is adopted here. The ordinary differential equations (ODEs) are accomplished via similarity transformations and are numerically assessed using the bvp4c software. Moreover, the consequences of the resulting pertinent parameters on the streamlines, temperature, and velocity distributions are scrutinized using graphical representations. It is observed that the surface drag on the wall is weaker for the dilating/injection case as compared to the squeezing/suction scenario. Streamlines show how a suitable magnetic field may be used to regulate medicine distribution in the blood flow. An innovative mass-based model comprising mono and hybrid nanofluid flow models is discussed. A comparison of heat transfer between both is undertaken. The results indicate that increasing the magnetic parameter leads to an enhancement in heat transfer rate when the upper and lower walls are dilated with wall injection Conversely, if the upper and lower walls are squeezed with wall suction the heat transfer rate decreases. The novelty lies in the consideration of both types of models and making a comparison of these.

Designing mould fluxes to prevent longitudinal cracking for peritectic steel slab casting

ABSTRACT During continuous casting of hypo-peritectic steel slabs, control of horizontal heat transfer rate in mould is important to avoid longitudinal cracks. This rate can be manipulated by mould slag crystallization. From an industrial situation where the longitudinal cracking index was too high, a new mould flux was designed with appropriate crystallization kinetics. The mould flux crystallization process was analysed in laboratory through differential scanning calorimetry. The Friedman isoconversional method was applied to determine the activation energy of crystallization from melt. Besides, a new quick test was developed to evaluate crystallization kinetics. The industrial tests have shown that the new mould flux decreases the longitudinal cracking index, and this is related to the decrease of horizontal heat transfer rate during the continuous casting process, which in turn is related to crystallization from mould slag.

Synergistic enhancement strategy on the heat charging process of a shell-and-tube thermal storage device based on close-contact melting mechanism and nano-enhanced phase change material

Nano-enhanced phase change materials (NePCM) exhibit immense potential for thermal energy storage (TES) applications, due to its improved thermal conductivity. However, its high viscosity can cause a significant deterioration in natural convection. In some cases, even a decrease in the total heat transfer rate can occur in shell-and-tube TES devices after nano-additives loading. Close-contact melting (CCM), featuring heat conduction through micro-liquid film, is regarded as a viable pathway to maximize the advantage of NePCM's high thermal conductivity and weaken the adverse effect of high viscosity on convection. To reveal the synergistic impacts of CCM and NePCM on the charging process of TES device, this study achieved the regulation of CCM by changing the fin configuration, and further analyzed the charging process of NePCM samples with three nano-additives loadings (0 wt%, 1 wt%, and 3 wt%) in TES devices with three different fin configurations. It was shown that expanding the CCM surface can significantly enhance CCM and weaken the contribution ratio of natural convection to the total heat transfer process. Under the experimental conditions established in this study, the best enhancement effect based on the synergistic strategy of NePCM and CCM was achieved, with a remarkable boost of >100 % in power density and a significant shortening of the total melting time to only 52.7 % of the original case. The introduction of CCM in LHTES through reasonable fin configuration is thus regarded as a highly applicable improvement method to enhance the power density, especially used in conjunction with NePCM, exhibiting great potential in the field of high-power-density latent heat storage and thermal management.

Experimental study of non-condensable gas effects on sonic limit of sodium heat pipe

Due to unexpected gas leakage and long-term operation, the non-condensable gas (NCG) inevitably exists in high-temperature alkali metal heat pipe. Previous studies have mainly focused on its influences on startup and steady state operation characteristics of heat pipes. However, few of them conducted experiments to study the effects of NCG on sonic limit, which usually occurs during heat pipe startup or during steady state operation when the heat transfer coefficient at condenser section is high. In present work, experimental and analytical studies are conducted to the explore the effects of NCG on sonic limit of sodium heat pipes. With the heating power ranging from 500 to 1400 W, the sonic limit of 1 m-long sodium heat pipes with artery wick and axial groove wick are obtained based on oil-cooling system, which can widely adjust the cooling capacity at condenser section. The amount of NCG in heat pipe is estimated by Heat Pipe Transient Analysis Code (HPTRAN) and verified by experimental data. It is found that the existence of NCG in heat pipe leads to the decrease of maximum heat transfer rate under sonic limit. The mechanism of NCG effects on sonic limit is discussed based on phenomenological analysis. By introducing the added back pressure, a modified model to predict sonic limit considering NCG effect is proposed and the comparison with experimental data shows good agreements.

Effects of discharge angle of jet from a slot orifice on cooling performance for a perforated air ducting system in dairy cattle barn

By employing a type of ventilation system that relies on perforated air ducting (PAD) and slot orifices, dairy farmers can help their cows avoid heat stress and in so doing increase milk production. However, the air jets from the orifices would be delivered at an angle, namely the discharge angle, which is the angle between the outflowing jet direction and the axis of the air duct. The discharge angle can affect the system’s efficiency and the jet will fail to deliver a sufficient amount of air if the angle is such that the jet does not properly target the cow. Consequently, by means of computational fluid dynamic simulation, this study sought to optimize the discharge angle on the cooling efficiency of PAD system, first by examining the factors (such as airflow rate and duct diameter) that affect the discharge angle and then by evaluating two types of air jet deflector (rectangular duct and rectangular plate) and also the effects produced by varying the spacing between the slot orifices. Results showed that the first orifice (counting from the inlet to the end of the duct) was mostly affected by the two investigated factors. Increasing the airflow rate from 376.3 to 564.5 m3 h−1 and the duct diameter from 0.8 m to 1.0 m had a limited effect on the discharge angle (around a 2° difference in the discharge angle). Also, as the number of sequential orifices increased, the discharge angle increased gradually, and the discharge angle of the last orifice remained at a constant 90°. Of all the discharge-angle mitigation tested, the rectangular-duct deflector produced the highest mean-convection heat transfer rate of the skin surface (98.37 W m−2) and the lowest standard deviation (±1.25 W m−2). The convection heat transfer rate registered by the cow positioned under the first orifice would increase by as much as 27.5% after the spacing between the orifices was modified (in comparison with the original case), while both an increase and a decrease in the convective heat transfer rate were observed to occur among the other cows. Given these findings, it was concluded that the PAD system’s performance could best be improved by adding a deflector with a rectangular duct to adjust the discharge angle.

Numerical study of reverse jet for mitigating shock/shock interaction heating

A numerical study is carried out to investigate the mechanism and assess the parameters of a reverse jet in heat reduction of type IV shock/shock interactions. A hypersonic flow at a Mach number of 8 with a fixed 18.1-deg incident shock is considered. A type IV shock/shock interaction occurs in the front of the blunt leading edge. Compressed air is supersonically injected into the freestream at various jet parameters. The results indicate that a 77% decrease in the peak heat transfer rates can be obtained with a reverse jet placed at the centerline of the blunt body. This study corroborates that the primary physical mechanism of heat reduction of a reverse jet is the transformation of shock interaction from type IV to type III. Moreover, the change of jet parameters, including angle, Mach number, and width, produces different heat reduction effects by influencing the angle between the shear layer of type III interference and the wall tangent.

Performance analysis of backpropagated networks for entropy optimized mixed convection nanofluid with second-order slip over a stretching surface

Due to their excellent generalization performance, artificial neural networks (ANN) are becoming more and more popular for solving difficult nonlinear real-world scientific and engineering challenges. The article in hand addressed the comparative study of artificial intelligence-based backpropagated neural networks (ABPNN) with Levenberg Marquardt scheme (LMS) and Bayesian Regulation scheme (BRS) for mixed convection-based nanofluid flow model (MCNM) optimized with entropy and second-order slip past a stretching sheet. The system is converted into an ordinary differential system and then solved with the Homotopy analysis method (HAM) to generate datasets by varying different parameters. The datasets are divided into training, testing, and validation to find the solution through LMS and BRS and further compared with reference technique i.e Homotopy analysis. The proficiency of the proposed ABPNN is proved by error histogram, mean squared error (MSE), and regression fitness analysis of LMS and BRS. Furthermore, flow field, concentration, thermal gradient, heat transfer rate, Sherwood number, Bejan number, skin friction, and entropy generation are found graphically and numerically. The results indicate that for higher values of slip parameters the velocity decays. Ec and Nt behave as a growing function of temperature. The fluid’s concentration is increased by an increase in E, whereas K shows an opposite trend. As the slip parameters rise, the system’s overall entropy reduces. Bejan number indicates a rising trend against slip parameters. For higher Nt and E, heat and mass transfer rates decrease. The solution is accurate up to 3–7 decimal places for all scenarios which are considered to fulfill the consistency standards.

Simulation model of boiling heat transfer and flow maldistribution in parallel mini-channels heated unequally

• Focus on boiling flow in parallel mini-channels heated unequally. • Developed model predicts boiling heat transfer and flow maldistribution. • Unequal heating among channels causes deterioration of heat transfer rate. • Considering the wall temperature distribution across the channels is important. Heat exchangers using parallel refrigerant mini-channels have been developed recently to improve the performance of air conditioning systems. Due to the unequal heat loads among channels, the boiling flow is unevenly distributed across parallel mini-channels in evaporators. Because this phenomenon sometimes causes deterioration of the heat exchange performance and difficulty in performance prediction, thus, it is essential to understand the characteristics of boiling heat transfer under unequally heated conditions. In this study, a novel simulation model was developed to predict the heat transfer characteristics and flow maldistribution of refrigerants flowing in parallel mini-channels with different heat fluxes or wall temperatures among channels. The model predicted well the flow maldistribution and the local quality, heat transfer coefficient, and dryout region of the two parallel mini-channels heated unequally. The mean heat transfer rate of the channels decreased remarkably with the increasing difference in wall temperature between the channels. The validity of the model was confirmed by comparing the predicted heat transfer rate with the experimental results. Furthermore, for ten parallel mini-channels, the decrease in the channel-mean heat transfer rate was indicated by the model, and the rate of decline varied significantly depending on the wall temperature distribution across the channels.

Lattice Boltzmann-based numerical analysis of nanofluid natural convection in an inclined cavity subject to multiphysics fields

This research conducts a study of natural convection heat transfer (NCHT) in a nanofluid under a magnetic field (MF). The nanofluid is in a cavity inclined at an angle of 45°. The MF can take different angles between 0° and 90°. Radiative heat transfer is present in the cavity in volumetric form. There are two hot semicircles, similar to two half-pipes, on the bottom wall. The top wall is kept cold. The side walls and parts of the bottom wall, except the pipes, have been insulated. The lattice Boltzmann method has been used for the simulation. The studied parameters are the Rayleigh number (in the range 103–106), magnetic field angle, radiation parameter (in the range 0–2), and nanoparticle volume fraction (in the range 0–5%). The generated entropy has been studied as the NCHT. The results indicate that adding nanoparticles improves heat transfer rate (HTR). Moreover, the addition of volumetric radiation to the cavity enhances the Nusselt number by 54% and the generated entropy by 12.5%. With an augmentation in the MF angle from 0° to 90°, HTR decreases and this decrease is observed mostly at higher Rayleigh numbers. An augmentation in the Ra increases NCHT and entropy generation. Indeed, a rise in the Ra from 103 to 106 increases HTR by almost sixfold.

MHD mixed convection and irreversibility analysis of hybrid nanofluids in a partially heated lid-driven cavity chamfered from the bottom side

In this research, magneto-convection flow in the cavity problem driven by the lid is examined using computational fluid dynamics (CFD) techniques. To this effect, the cavity considered in this numerical study has two rounded corners and is partially heated from the bottom side and filled with Al2O3-Cu/water hybrid nanofluid (HBNF). Accordingly, a solver based on C++ object-oriented language has been developed under OpenFOAM® libraries to solve the mathematical governing equations. The numerical findings are thoroughly validated with other studies. To this end, different parameters analysis is adopted, which consists of Richardson numbers (0.1 ≤ Ri ≤ 10), Hartmann numbers (0 ≤ Ha ≤ 100), magnetic field angle (0° ≤ γ ≤ 90°), solid volume fraction (0 ≤ ϕ ≤ 0.04), composition ratio (25 % ≤ Cu,Al2O3 ≤ 75%), corners radius (0.01 ≤ R ≤ 0.3). This analysis is achieved by exploring streamlines, isotherms, total entropy generation, local and average Nusselt numbers. After the data analyses, the findings indicated that the magnetic field orientation strongly affects the hybrid nanofluid flow and temperature distribution. In other words, at Ri = 10, Applying a magnetic field perpendicular to the gravity force leads to better heat transfer. Furthermore, decreasing corners radius enhances heat transmission and reduces irreversibility. The composition ratio (Al2O3 75%, Cu 25%) gave the highest values of the mean Nusselt Number (Num) and the total entropy production (Sg). Moreover, the heat transfer rate and irreversibility decrease with increasing Ha and decreasing Ri. Finally, suspending nanoparticles (NPs) in the base fluid improves heat transfer and increases irreversibility except for Ri = 10 at Ha = 100 and Ri = 1 at Ha = 50, where the opposite behavior has been observed.

EFFECT OF HEAT AND MASS TRANSFER AND THERMAL RADIATION ON A STEADY MHD CONVECTIVE FLOW WITH VISCOUS DISSIPATION AND SUCTION/INJECTION

Our motive is to examine the impact of thermal radiation and suction or injection with viscous dissipation on an MHD boundary layer flow past a vertical porous stretched sheet immersed in a porous medium. The set of the flow equations is converted into a set of non-linear ordinary differential equations by using similarity transformation. We use Runge Kutta method and shooting technique in MATLAB Package to solve the set of equations. The impact of non-dimensional physical parameters on flow profiles is analysed and depicted in graphs. We observe the influence of non-dimensional physical quantities on the Nusselt number, the Sherwood number, and skin friction and presented in tables. A comparison of the obtained numerical results with existing results in a limiting sense is also presented. We enhance radiation to observe the deceleration of fluid velocity and temperature profile for both suction and injection. While enhancing porosity parameter accelerates velocity whereas decelerates temperature profile. As the heat source parameter increases, the temperature of the fluid decreases for both suction and injection, it has been found. With the increasing values of the radiation parameter, the skin friction and heat transfer rate decreases. Increasing magnetic parameter decelerates the skin friction, Nusselt number, and Sherwood number.

온실가스 저감을 위한 암모니아 혼소가 초임계 화력 발전시스템 보일러에 미치는 열성능 영향성 평가

Co-firing ammonia with coal is emerging as a transitional technology in the power industry for the major reduction of greenhouse gas emissions. Although ammonia has the disadvantages of low combustion reactivity and the generation of nitrogen oxides, it can effectively reduce greenhouse gas due to the generation of only moisture and nitrogen after the combustion. Therefore, for the efficient co-firing of the coal and ammonia in the power plant system, it is essential to evaluate the effect of co-firing ammonia on the boiler system. We selected the 870 MWe supercritical coal-fired boiler system and developed the process simulation model of the target boiler system. In this study, process simulation of the target boiler system was performed according to the ammonia co-firing ratio of 0, 5, 10, 20, and 30%. In addition, the effect of ammonia co-firing on the boiler thermal performance was evaluated according to the load condition and the quality of coal. As the ammonia co-firing ratio increases, the flue gas flow rate and the radiation and convective heat transfer rate decrease. Accordingly, the main and reheat steam temperatures decrease. Although the reduction of carbon dioxide is quantitatively confirmed according to the co-firing ammonia, the boiler thermal efficiency decreases due to the increase in the amount of moisture in the flue gas.

Theoretical analysis of modified eyring powell fluid flow

Background: Applications of Eyring-Powell fluid is found in paint industries, pharmaceutical companies and armour construction. Eyring-Powell fluid models are able to model Newtonian and shear-thinning fluids under different conditions, but researchers have reported seemingly contradicting results based on the effects of Eyring-Powell parameter on flow velocity. Methods: This paper shows that Eyring Powell fluid can also exhibit shear-thickening properties when certain conditions are imposed. By introducing this condition on Eyring-Powell model, a new class of Modified Eyring-Powell fluid is presented in this study, which clearly shows why different results are obtained by different researchers. A theoretical analysis of the heat transfer is carried out on the flow of MEP on a linearly stretching flat plate and the results are depicted as graphs and tables. Significant Findings: It is found that increasing Prandtl number causes a decrease in the temperature. Under shear-thinning condition, increasing the Eyring-Powell parameters leads to a decrease in both skin-friction coefficient and heat transfer rate. Under shear-thickening condition, increasing the Eyring-Powell parameters leads to an increase in both skin-friction coefficient and heat transfer rate.

Experimental study on the influence of airflow velocity on frosting and defrosting performance of compact precooler under actual air humidity condition

Due to the precooler of hypersonic vehicle is frosted during the process of operation, the flow channel is blocked and the performance of engine is affected, which resulting in the decline of thrust and specific impulse. Therefore, for the purpose of maintain the performance of aero-engine, it is necessary to defrost the precooler. In order to study the influence of the airflow velocity on the frosting and defrosting performance of the compact precooler under actual air humidity condition, the frosting and defrosting performance of the microtubule precooler are experimentally studied in the wind tunnel under the conditions of air humidity of 1.8 g/kg and main flow velocities are 10 m/s, 20 m/s and 30 m/s, respectively. Methanol is utilized as the defrosting solvent, the mass ratio of methanol ranges from 0.8 to 1.2. The experimental results reveal that under the frosting experimental conditions, frost layer quickly condenses on the outside of tube bank, the wall surface temperature and heat transfer rate decrease dramatically, but the pressure drop coefficient increases sharply. It indicates that the frosting has an adverse effect on throughflow characteristics and heat transfer performance of the precooler. However, for the defrosting experiments, the wall temperature increases significantly, the defrosting effect and heat transfer rate are improved obviously and the pressure loss coefficient drops distinctly. In addition, with the increase of airflow velocity, the pressure drop coefficient increases sharply, but the coverage area of the frost layer gradually decreases, it manifests that increasing the main flow velocity is beneficial to suppress the formation of the frost layer. Through the analysis of experimental results, it can be found that within the range of experimental study parameters, the optimal defrosting performance can be obtained when the mass ratio of methanol is about 1.1. Moreover, with the increase of mass ratio of methanol, although the amount of condensation decreases, the condensation gradually evolves from the fluffy frost layer to the mixture layer of frost and ice, and eventually develops to whole ice layer.

Multi-Objective Constructal Optimization for Marine Condensers

A marine condenser with exhausted steam as the working fluid is researched in this paper. Constructal designs of the condenser are numerically conducted based on single and multi-objective optimizations, respectively. In the single objective optimization, there is an optimal dimensionless tube diameter leading to the minimum total pumping power required by the condenser. After constructal optimization, the total pumping power is decreased by 42.3%. In addition, with the increase in mass flow rate of the steam and heat transfer area and the decrease in total heat transfer rate, the minimum total pumping power required by the condenser decreases. In the multi-objective optimization, the Pareto optimal set of the entropy generation rate and total pumping power is gained. The optimal results gained by three decision methods in the Pareto optimal set and single objective optimizations are compared by the deviation index. The optimal construct gained by the TOPSIS decision method corresponding to the smallest deviation index is recommended in the optimal design of the condenser. These research ideas can also be used to design other heat transfer devices.