Increment Of Coefficient Research Articles

An Analysis on the Increment of Coefficient of Performance of an On-Farm Direct Expansion Bulk Milk Cooler (DXBMC) Through the Use of a Raw Milk Pre-Cooler

The performance of a direct expansion bulk milk cooler is influenced by various factors on the farm. This study presents an analysis on the increment of the coefficient of performance of an on-farm direct expansion bulk milk cooler (DXBMC) through the use of a raw milk pre-cooler during the milk cooling process. Accordingly, a data acquisition system (DAS) was designed and deployed to accurately measure the power consumption of the BMC and temperature of raw milk. The volume of milk produced per day was extracted from the daily records on the farm. Empirical models were used together with the experimental data to simulate the operation of the DXBMC if a pre-cooler was being used. The findings from the experimental study showed that through the use of raw milk pre-cooler, the average raw milk temperature delivered to the DXBMC will be 20.43°C. This leads to the COP of the DXBMC increasing by an average of 25% from 2.15 to 2.67. Increase in the milk volume led to an increase in the COP such that the peak period with higher milk volumes recorded a high COP increase of 16.21%. The use of a pre-cooler would lead to an average energy saving of 17,667.67 kWh in a year as well as 17.83 tCO2 will be avoided.

Thermal elastohydrodynamic lubrication of modified gear system considering vibration

The thermal elastohydrodynamic lubrication characteristics of a modified gear system under a dynamic load were investigated, including the influence of the modification coefficient and vibrations. Based on the dynamic theory of gear systems, a six-degree-of-freedom tribo-dynamics model was established. Thermal elastohydrodynamic lubrication characteristics of a modified gear system under vibrations and a static load were analyzed. The results showed that the positive transmission gear system exhibited the better lubrication effect compared with other transmission types. A thick lubricating oil film could be formed, and the friction coefficient between the teeth and the oil film flash temperature was the smallest. As the modification coefficient increased, the lubrication condition was continuously improved, and the scuffing load capacity was enhanced. The increment of the modification coefficient increased the meshing stiffness of the gear system but reduced the stiffness of the oil film.

Laminar flow instabilities of a grooved circular cylinder

This paper represents a numerical study on the flow past a grooved circular cylinder with a diameter of D. The study aims to investigate the instabilities of the flow at laminar flow regimes when Reynolds number varies from 50 to 200. Three different geometrical grooves are examined, including square, triangular, and dimple. The grooves are located at $$ \theta $$ = 0°, 30°, 45°, 60° and 90°, separately relative to the front stagnation point. The effects of the groove on the flow control and imposed forces on the cylinder are studied at different Re. It is found that the presence of the groove affects the dynamic behaviour of the streamwise vortices. This behaviour leads to alteration of the pressure coefficient and a significant increment in lift coefficient, in particular for the triangular grooved cylinder. At Re = 200, the results show that the magnitude of the lift coefficient of the triangular grooved cylinder with $$ \theta $$ = 45° is 200% more than that of the square grooved cylinder. The results also reveal that the drag coefficient reduces up to 100% by employing a triangular groove shape at $$ \theta $$ = 45°. These variation in lift and drag coefficients leads to maximising the aerodynamic efficiency factor (lift-to-drag ratio) of the triangular grooved cylinder up to 200%.

Direct numerical simulation of subsonic, transonic and supersonic flow over an isolated sphere up to a Reynolds number of 1000

In the present study, compressible low-Reynolds-number flow past a stationary isolated sphere was investigated by direct numerical simulations of the Navier–Stokes equations using a body-fitted grid with high-order schemes. The Reynolds number based on free-stream quantities and the diameter of the sphere was set to be between 250 and 1000, and the free-stream Mach number was set to be between 0.3 and 2.0. As a result, it was clarified that the wake of the sphere is significantly stabilized as the Mach number increases, particularly at the Mach number greater than or equal to 0.95, but turbulent kinetic energy at the higher Mach numbers conditions is higher than that at the lower Mach numbers conditions of similar flow regimes. A rapid extension of the length of the recirculation region was observed under the transitional condition between the steady and unsteady flows. The drag coefficient increases as the Mach number increases mainly in the transonic regime and its increment is almost due to the increment in the pressure component. In addition, the increment in the drag coefficient is approximately a function of the Mach number and independent of the Reynolds number in the continuum regime. Moreover, the effect of the Mach and Reynolds numbers on the flow properties such as the drag coefficient and flow regime can approximately be characterized by the position of the separation point.

Heat Transfer Enhancement of Supercritical Nitrogen Flowing Downward in a Small Vertical Tube: Evaluation of System Parameter Effects

In this paper, the heat transfer enhancement (HTE) of supercritical nitrogen flowing downward in a vertical small tube (diameter 2 mm) is studied using the commercial software CFX of Ansys16.1, to provide theoretical guidance on the design of high-performance heat transfer systems. An effective numerical simulation method, which employs the SSG Reynolds stress model with enhanced wall treatment, is applied to study the heat transfer of supercritical nitrogen under typical working conditions. The objective is to evaluate the effect of the main parameters taking into account the buoyancy and flow acceleration effects. Simulation results are compared with results calculated from three well-known empirical correlations and the applicability of empirical correlation is discussed in detail. It is discovered that the Watts and Chou correlation accurately fits the simulation results of supercritical nitrogen and the Dittus-Boelter and Jackson correlations can only be used for high-pressure conditions. The HTE of supercritical nitrogen is closely related to the laminar sub-layer and buffer layer of a boundary layer. The buoyancy effect on the HTE should be considered at low mass flux conditions, and thermal acceleration can be completely ignored for the cases studied. The special HTE featured by the increment in heat transfer coefficient with increasing heat flux is discovered at low pressure, and simulation results proved that this HTE is caused by the combined actions of buoyancy as well as significant variations in specific heat and viscosity.

CONVECTIVE HEAT TRANSFER AND POWER SAVING APPLICATION OF SI BASED NANOPARTICLES IN A CIRCULAR PIPE

A numerical study of laminar forced convection heat transfer for the fully developed region inside a circular pipe filled with Si based nanoparticle is presented for investigating the parameters of heat transfer. Four Si based nanoparticles Si, SiC, SiO2, Si3N4 with 1-5% volume fraction have been mixed with water to prepare nanofluids which is used for working fluid to flow over a circular pipe with 5mm diameter and 700mm length. Heat transfer characteristics and pumping power have been calculated at fully developed region with constant heat flux condition on pipe wall to identify the heat transfer enhancement ratio and pumping power reduction ratio among base fluid water and each nanofluids. It is worth mentioning that utilizing SiC nanoparticle shows not only the highest increment of Nusselt number and convective heat transfer coefficient but also the highest decrement of pumping power requirement and FOM in comparison to the base fluid.

A comparative study on utilizing hybrid-type nanofluid in plate heat exchangers with different number of plates

Different methods have been utilized to enhance the thermal efficiency of the heat exchangers (HEs). A widely used method to upgrade the thermal efficiency of HEs is upgrading the thermal properties of working fluid by utilizing nanoparticles. In this study, Al2O3 and CuO have been utilized to prepare Al2O3–CuO/water hybrid nanofluid. Accordingly, Al2O3 and CuO nanoparticles have been mixed into the water with 1% (50:50) weight concentration. The main objective of this work is testing the prepared hybrid nanofluid in plate-type HEs (PHEs) with 8, 12 and 16 plates to determine the influence of number of plates on heat transfer improvement by hybrid nanofluid. Experimental findings of the present study demonstrated that utilizing Al2O3–CuO/water hybrid-type nanofluid in the PHE enhanced thermal efficiency notably in comparison with single-type nanofluids. Using this hybrid nanofluid increased the thermal performance in all PHEs with different number of plates. However, it is observed that increasing number of plates led to more increment in thermal performance by utilizing hybrid nanofluid. The highest increment in overall heat transfer coefficient was obtained as 12%, 19% and 20% in PHEs with eight, 12 and 16 plates, respectively. In addition, the highest enhancement in effectiveness was achieved as 10%, 11.7% and 16% in PHEs with eight, 12 and 16 plates, respectively.

Two-phase permeable non-Newtonian cross-nanomaterial flow with Arrhenius energy and entropy generation: Darcy-Forchheimer model

The present work concentrates on two-dimensional steady incompressible flow of a non-Newtonian cross nanofluid past a linear stretching/shrinking sheet with a magnetic field in Darcy-Forchheimer porous regime. The entropy theory with Arrhenius energy is incorporated into the study. The shooting method is employed to obtain numerical solutions of the transformed system of non-linear equations. The influence of the governing parameters on the non-dimensional velocity, temperature, micro-rotation, drag force, heat and mass transfer rates, rate of entropy generation, Bejan number, streamlines and finally isotherms are incorporated. The significant outcomes of the current investigation are that increment in suction parameter uplifts flow velocity, temperature and concentration while injection is petered out them. Bejan number augments due to increment in inertia coefficient while reduces due to magnetic strength and Eckert number.

Utilization of CFD for the Aerodynamic Analysis of a Subsonic Rocket

Nowadays, every single country aims to have a domestic and national defense industry. In accordance with this purpose, the design of missile structures has become more important than ever. In this study, the design and analyses of a subsonic rocket was carried out with the utilization of Computational Fluid Dynamics (CFD) tools. Also, the effects of several critical parameters; i.e. Mach number, turbulence intensity, turbulence model, on the rocket performance were investigated. It was found out that a variation in Mach number has a substantial effect on the drag coefficient; i.e. an increment in Mach number at approximately 30% results in an increment of drag coefficient nearly 68%. Contrarily, changing the turbulence intensity does not make any significant difference on drag coefficient. Although the appropriate turbulence intensity should be used for every unique problem, in this case, this parameter is not a critical variable to ponder upon. Finally, the implementation of the appropriate turbulence model is critical in the design process as expected. Utilization of k-ω and k-ω SST models differs approximately 12% in terms of drag coefficient; the drag coefficient obtained from k-ω is higher than that of obtained from k-ω SST.

Aspect ratio effects on hydrodynamic characteristics of Magnus stabilizers

Magnus stabilizer is a novel device for anti-rolling of ships which generates lift through a high-speed rotating rotor (rotor wing) based on Magnus effect. The present work aims to investigate the influence of aspect ratios, AS (ratio of the length and the diameter) on hydrodynamic characteristics with particular attention paid to the AS at maximum hydrodynamics (lift/drag, hydrodynamics coefficients and lift-drag ratio). The simulation experiments were carried out on two different conditions: rotor wings in flow with ship speed and rotary speed not changed and with ship speed or rotary speed changed. For the first condition, hydrodynamics on rotor wings with the length 1 m–4 m and diameters from 0.05 m to 0.8 m were investigated. The relationships between the aspect ratios at the maximum hydrodynamics and the length of rotor wing were summarized. For the second condition, hydrodynamics on rotor wings with the same length but different diameters from 0.05 m to 0.8 m were investigated. How the AS at maximum hydrodynamics affected by ship speed or rotary speed were analyzed. Finally, for practical purposes, the aspect ratio was optimized considered about AS at maximum lift coefficient, lift-drag ratio and lift increment for a 2.5-m rotor wing.

High performance heat sink with counter flow diverging microchannels

Effective thermal management of high-power electronics is urgently demanded for the further development of electric vehicles. Two-phase flow boiling in microchannels is well recognized as a prominent approach for high density heat dissipation. This study develops a novel high performance heat sink with counter flow diverging microchannels to further enhance the flow boiling performance. A unique and significant heat exchange between the neighboring channels is demonstrated to dramatically alter the flow pattern transition in the counter-flow microchannel manifold. In particular, as the flowing bubbles in the microchannels can shrink or even disappear before exiting, no back flow or partial dry-out is observed throughout all the tested conditions. Therefore, this additional heat transfer mechanism in the present design enables significant enhancement of temperature uniformity, up to a heat flux of 2677 kW·m−2 with 45.1% increment of heat transfer coefficient, 73.8% reduction of pressure drop and 123.1% increment of coefficient of performance when compared with those of traditional co-current flow design. Overall, with the excellent flow boiling performance, the present study offers a highly promising microchannel design for a variety of applications requiring high heat flux dissipation.

Testing of High-Lift Common Research Model with Integrated Active Flow Control

A 10%-scale high-lift version of the Common Research Model and an active flow control (AFC) version of the model equipped with a simple-hinged flap were successfully tested. The main objective of the test was to develop an AFC system that can provide the necessary lift recovery on a simple-hinged flap high-lift system while minimizing its pneumatic power requirement. The tests were performed in the 14- by 22-Foot Subsonic Tunnel at the NASA Langley Research Center. Three types of AFC devices were examined: the double-row sweeping jets (DRSWJ), the alternating pulsed jets (APJ), and the high-efficiency low-power (HELP) actuators. The DRSWJ and the APJ actuators used two rows of unsteady jets, whereas the HELP actuators used a combination of unsteady and steady jets, to overcome strong adverse pressure gradients while minimizing the mass flow usage. Nozzle pressure ratio, mass flow consumption, and the power coefficient were used for judging the performance efficiency of the AFC devices. The current data are presented with the Transonic Wall Interference Correction System method applied. The HELP actuation concept was effective in controlling flow separation in the linear region of the curves comparing lift coefficient to mass flow rate. The HELP actuation achieved a targeted lift coefficient increment of 0.5, thus meeting the lift performance goal of the NASA Advanced Air Transport Technology project.

Heat transfer performance of U-tube molten salt steam generator

Heat transfer and thermal performance of U-tube molten salt steam generator was experimentally reported with inlet water flow rate of 22.4-89.6 L/h, water temperature of 20-100°C, salt flow rate of 1-2.2 m3/h and salt temperature of 306.5-395.3°C. The heat transfer mechanism of U-tube molten salt steam generator was experimentally revealed, and overall heat transfer coefficient was influenced by salt convection and water boiling, while thermal efficiency was determined by heat absorption and heat loss. As inlet water flow rate rose, overall heat transfer coefficient and thermal efficiency rose initially and decreased afterwards, while they dropped with inlet water temperature rising as subcooling boiling changed to saturation boiling. As salt temperature increased, salt convection was enhanced, while boiling heat transfer coefficient rose initially and dropped afterwards with superheat rising, so overall heat transfer coefficient and thermal efficiency rose initially and dropped afterwards. As salt flow rate rose, overall heat transfer coefficient under low salt temperature rose for boiling heat transfer coefficient increment, and that under high salt temperature first rose and then dropped as boiling curve had maximum heat flux, while thermal efficiency dropped as heat loss and wall temperature increasing. Molten salt heat transfer outside U-tube bundle was remarkably higher than that inside tube, while it was lower than that outside straight tube bundle. Heat transfer correlation of salt outside U-tube bundle was first proposed, and that had good agreement with experiment data with maximum deviation 7.8%. The heat transfer mechanism and correlation in present work can provide reliable basis for design and application of U-tube molten salt steam generator.

Effect of Gurney flap on the aerodynamic behavior of an airfoil in mutational ground effect

In this research, the effect of Gurney flap on the aerodynamic behavior of an airfoil in mutational ground effect is investigated. To perform this, lift and drag coefficients of NACA 4412 airfoil section in the presence and absence of Gurney flap in mutational ground effect are evaluated and compared. To provide a better illustration of the effect of Gurney flap on the aerodynamic behavior of the airfoil section in the mutational ground effect, results are obtained during the takeoff and landing processes. Validation of the used numerical model is also performed by comparison of the obtained results with those of other works and reasonable agreements were seen. Results show that inclusion of Gurney flap to the airfoil leads to higher variations of lift and drag coefficients during takeoff and landing process. During the takeoff process, the flapped airfoil results in a higher lift decrement and drag increment although an increase in distance of airfoil from the ground or angle of attack causes the lift decrement of the flapped airfoil to get close to that of clean airfoil. It is shown that during takeoff process, downwash is generated around the airfoil as the airfoil leaves the step and as the airfoil gets away from the step, the generated downwash decreases. During the landing process, at each distance of airfoil form the ground and angle of attack, the lift decrement and drag increment of the flapped airfoil are significant compared to that of the clean airfoil. Results exhibit that during landing process, upwash is generated around the airfoil as the airfoil reaches the step and further airfoil move on the step leads to the decrease in the upwash. The decrement in lift coefficient and also the increment in drag coefficient during landing process are more remarkable than those in takeoff process.

Rheology of Pastes Containing High-Volume Fly Ash and Their Permeability Because of Calcium Leaching Procedure in Ammonium Chloride Solution

Abstract This article presents the findings of a research program that concern the rheology of fresh paste containing high-volume fly ash and its permeability because of calcium leaching procedure after 90 days’ curing. In a fresh state, the combined influence of fly ash content and water addition time on Herschel–Bulkley parameters was investigated. The critical value of fly ash content and water addition time was defined. In a hardened state, ammonium chloride (NH4Cl) was chosen as the accelerate leachant based on the comparison of microscale effect of ammonium nitrate (NH4NO3) and NH4Cl solution as well as leaching mechanism establishment. At specified leaching durations, the leached depth and porosity and permeability coefficient of both sound and deteriorated paste specimens were tested. It was indicated that both the porosity increment and permeability coefficient increment have a linear relation to the square root of leached ratio. Additionally, the velocity of the porosity increment declines with fly ash content, whereas the velocity of permeability coefficient increment declines with fly ash content at first and increases slightly when the fly ash dosage ranges from 40 % to 60 %. It can be concluded that fly ash was effective in improving leaching resistance. Finally, the relevance of fresh and hardened behavior was proposed.

Molecular Dynamic Simulations of Diethyl Ether and its Mixture with Cellulose Dinitrate Tripolymer Molecules for their Thermal Diffusion Behaviors

In this paper, thermal diffusion states of pure diethyl ether and its mixture with cellulose dinitrate tripolymer were uncovered by LAMMPS-based Molecular Dynamic (MD) simulations. Those MD simulations were generally performed through specified ReaxFF reactive force field to obtain the properties of the chemical system such as molecular energy, density, mean square displacement (MSD) and molecular coordinate. The result of MD simulations presented the clear superheating phenomenon of pure liquid diethyl ether system in the studied environment. The obtained phase transition point was much higher than the reported one. The deviation between two temperatures was about 132.369[Formula: see text]K. It was also demonstrated that the transition process was associated with the sharp increment of potential energy, volume, diffusion coefficient and cohesive energy. However, the split of these diethyl ether molecules was not uniform. The cluster-like transition state was observed before the end of the vaporing process (460[Formula: see text]K). As for the addition of cellulose dinitrate tripolymer, these molecules were not agglomerated in the simulated organic mixture. However, the diffusion of cellulose dinitrate tripolymer was much weaker than those diethyl ether molecules. While the concentration of cellulose dinitrate tripolymer was higher, molecular interactions of this organic mixture were consequently improved, and this further limited the diffusion behavior of the entire chemical system. It could be concluded that the diffusion behavior of the entire organic system was decreased with more amount of cellulose dinitrate tripolymer molecules.

Understanding the effect of transverse vibration on hollow fiber membranes for submerged forward osmosis processes

External concentration polarization (ECP) remains a pervasive challenge for submerged forward osmosis (FO) systems, as it critically reduces the water flux of membranes. In this study, we propose to use transverse vibration on hollow fiber membranes to effectively reduce the ECP and increase the FO water flux performance. The effects of different vibrating amplitude and frequency were investigated. Also, the vibration effect was evaluated under different draw solution concentrations, membrane orientations and draw solute types. Our results show increased water flux with increasing vibrating intensity (i.e., amplitude and frequency) while maintaining a constant specific reverse solute flux (Js/Jw). At the highest amplitude (1.2 cm) and frequency (3 Hz) used, the mass transfer coefficient is increased from 0.7 × 10−5 m s−1 (at no vibration) to 1.8 × 10−5 m s−1, which falls within the optimal flux range as determined from our FO modelling results. The increment in mass transfer coefficient is found to be closely related to the improved hydrodynamic conditions due to vibration, and less dependent on the membrane orientation and draw solution concentration. In addition, both modelling and experimental results show that maintaining a reasonably high mass transfer coefficient is especially important for FO process with severe ECP conditions, such as when dilutive ECP is present (i.e., active-layer-facing-feed-solution orientation) or when a high water flux is applied (usually in the active-layer-facing-draw-solution orientation). However, the severe ECP arising from large draw solutes (e.g., larger sized polymer with low diffusivity and high viscosity) might not gain greater benefits from the vibration or improved hydrodynamic conditions.

Experimental and numerical investigation of convection heat transfer in a circular copper tube using graphene oxide nanofluid

To able to employ nanofluids in engineering applications, it is essential to investigate heat transfer properties in addition to thermophysical characteristics. In this work, the convection heat transfer coefficient of graphene oxide-distilled water nanofluid along a circular copper tube having a constant heat flux at the outside surface has been investigated both numerically and experimentally under turbulent flow regime. While the nanofluid convection heat transfer and head loss of pressure have been evaluated in the experimental section, the tube wall surface temperature, the convection heat transfer coefficient and friction factor have been obtained by using finite volume method in the numerical part with a three-dimensional domain by assuming single-phase flow. Surface and fluid temperatures and pressure drop of the distilled water have been acquired and compared with the related output from the correlation. Besides, the variations of the tube surface temperatures and the convection heat transfer coefficients of the nanofluids have been examined as numerical and experimental comparisons. The contours of the temperatures, convection heat transfer coefficients and pressure distributions for fluids have been presented. The convection heat transfer performances of the nanofluids according to the different volumetric flow rates, concentrations and the heat flux values have been exhibited in this study. The heat transfer coefficient increment value for the nanofluid of 0.02 vol% concentration and with a flow rate of 1.5 l/min (Re = 5032) has been obtained as about 48% for 5073.244 W/m2 (350 W) heat flux according to the distilled water.

Theoretical method to calculate pipeline thermal transient-induced walking rate considering nonlinear time-dependent soil resistance

Submarine pipeline was widely used to transport oil and gas in offshore petroleum exploitation. In practice, deep-water pipeline experiences several times of maintenance every year. This periodic open-up and shut-down operation causes cyclic rise and fall in the temperature of a pipeline, resulting in the periodic expansion and contraction of the pipeline. Due to the characteristics of heating-up operation, the expansion and contraction movement are symmetrical about different points, and it leads to the pipeline walking phenomenon. As a key factor, the axial soil resistance affects the walking displacement heavily. The shearing generated by expansion and contraction of a pipeline section causes intermitted consolidation of soil and cyclic increment in the equivalent soil resistance coefficient. This paper analysed pipeline walking of a free-end pipeline laid on even seabed with consideration of cyclic soil strength hardening. New driving mechanism for pipeline walking caused by thermal transient due to the influence of time-dependent soil resistance was proposed. A common theoretical method to calculate walking displacement was also established.

Effects of circular trailing edge with the dimple on flow separation of NACA S1210 hydrofoil

Flow separation over a hydrofoil affects its hydrodynamic performance and ultimately reduces the power production of a turbine. Therefore, the different flow control methods have been proposed by the researchers to overcome these challenges. In this study, the combined effects of circular trailing edge with dimple have been investigated numerically on NACA S1210 hydrofoil to control the flow separation of the hydrofoil. The results showed that the coupled effects of the dimple and circular trailing edge modification appeared effective compared to baseline hydrofoil at a wide range of angles of attack. Maximum lift coefficient increments are 9 and 12% at an angle of attack of 10° and 12°, respectively, for circular trailing edge hydrofoil. The maximum increase of glide ratio for the coupled effect (circular trailing edge with outward dimple) is approximately 114% at an angle of attack of 12°. The outcome will be advantageous to design a proper blade profile for horizontal axis current turbines.