Synergy Angle Research Articles

Analysis of light field and flow field of vortex rods tube photobioreactor based on field synergy principle

A new static mixer called the vortex rod static mixer was introduced into the photobioreactor. This study focused on the vortex rod tubular reactor as the subject of investigation. The effects of different incident light field intensities (I0 = 375 μmol/(m2·s), 800 μmol/(m2·s), and 1200 μmol/(m2·s)) on reactor efficiency were simulated using the CFD simulation method, considering variations in vortex rod arrangement (60°, 90°, and 120°) and tilt angle (α = 27°, 36°, 45°, 54°, and 63°). In the SST turbulence simulation flow field results, the movement process of algae cells in the tube was simulated using the particle tracking module. By taking into account the average frequency of the light-dark cycle, the enhancement efficiency of the light-dark cycle, and the synergy angle of the light gradient and velocity field, the following results were obtained: the optimum tilt angle for the vortex rod is α = 45°. For incident light field intensities of I0 = 375 μmol/(m2·s) and 800 μmol/(m2·s), the 60° arrangement yielded the best results, resulting in a 54.491 % and 66.258 % increase in cycle frequency, an 18.747 % and 22.795 % enhancement in efficiency, and an average |cosβ| = 0.68055. For an incident light field intensity of I0 = 1200 μmol/(m2·s), the 90° arrangement proved to be the most effective, resulting in a 57.580 % increase in cycle frequency, an 18.058 % enhancement in efficiency, and an average |cosβ| = 0.68975.

Heat transfer performance and entropy generation analysis of Taylor–Couette flow with helical slit wall

The turbulent flow between concentric cylinders and its heat transfer performance is studied by the large eddy simulation. The models with longitudinal slit and helical slit spacing in the range from 168 to 672 mm on the outer cylinder are investigated to compare their heat transfer ability. Further, the notion of field synergy and entropy formation serves as the foundation for evaluating heat transfer qualities. According to the results, the enhancement effect of helical slits on heat transfer is better than that of longitudinal slits. Helical slits are more effective in promoting fluid mixing at different temperatures within the annulus. In terms of field synergy, the helical slit models exhibit a smaller field synergy angle compared to the longitudinal slit model at various Reynolds numbers from 3061 to 4592. Results of using helical slits indicate an improved coordination between the velocity and temperature fields. Thermodynamic analysis reveals that the helical slit models have lower entropy generation as compared to the longitudinal slit models. Higher efficiency in energy utilization and superior heat transfer properties of the helical slit models are noticed. Findings of this study provide valuable insights for the optimal design of various rotating machinery applications.

Experimental and numerical study of the enhancement effects on the performance of PEMFC with side blockage in straight flow-field

Flow channel design is a hot research topic of proton exchange membrane fuel cells (PEMFCs). An innovation straight with side blockage flow channel is proposed to investigate the enhancement effects on mass transportation and performance of PEMFCs by combing the numerical simulation and experimental study. Compared to traditional channel, cathode flow channel with double-side blockage shows the best performance with up to 10% improvement at 1800 mA cm−2. Electrochemical impedance spectroscopy (EIS) measurements are carried out to analyze the mechanism of the performance improvement during experimental tests. The equivalent resistance of activation and concentration losses decreases due to the enhancement of charge and mass transfer with the increase of temperature and the arrangement of side blockages, leading to the performance improvement. Along with the output performance improvement, the pressure drops of flow channels with blockages are higher than traditional channel. Thus synergy angle and cost-benefit ratio are used to evaluate the superiority of the flow field design through numerical simulation. The double-side blockage flow channel exhibits greater capacity of mass transfer and larger cost-benefit ratio, consisting with the cell performance variation characteristics.

Synergy principle and its application of endwall loss analyses in the turbine stator

The endwall flow significantly impacts the turbine performance behavior, and it is necessary to investigate the development of endwall secondary vortices and relevant losses. Inspired by the field synergy principle, the synergy between the velocity and the pressure gradient established by the three-dimensional mechanical energy conservation equation is innovatively applied to the endwall loss analysis in the stator of an axial-inflow turbine. In terms of the synergy equation, the loss is not only related to the viscous dissipation, but also the included angle (or the synergy angle) between the velocity vector and the pressure gradient vector. The physical content of the synergy angle suggests that the larger synergy angle is (i.e., the worse synergy), the higher losses should be. This conclusion has been validated by present numerical results, and an apparent positive correlation between the synergy angle and the losses could be perceived under time-averaged and transient conditions. The worse synergy could be observed at the passage rear part and the wake, where complex passage vortices and local separation exist. In these regions, the local velocity vector is not aligned with the bulk pressure gradient of the mainstream. Hence, the synergy angle has a marked rise, corresponding to the local high losses.

Analysis of vortex combustion flow in a chamber of guide ring coupling with swirl flow

To investigate the impact of different vortex structure on the combustion stability in a chamber, this paper evaluates the performance of a vortex combustion chamber coupled with a swirler and a guide ring. The simulated cases include different guide ring angles of 95°, 105°, 115°, 125° and 135°, in addition to a control case without coupling the guide ring. The distributions of velocity, vorticity, temperature, outlet temperature distribution factor ( OTDF), reaction rate, turbulent kinetic energy ( k), synergy angle ( β), and NO emission are numerically analyzed. Results show that the coupling of the swirler and guide ring changes the vortex structure and significantly influences the chamber performance. The increase of the guide ring angles ( α) enhances the interaction between the swirl flow and the direct jet, which intensifies heat and mass transfer, as well as turbulence. The application of the guide ring induces external entrainment of the jet, leading to the formation of a large central recirculation zone compared to that without a guide ring. With increasing the α from 95° to 135°, both average outlet velocity and tangential velocity ( Vt) at the coaxial line position decrease, while the flame length decreases by 286 mm. And the OTDF variation among all cases is less than 0.065. The β of the central section decreases from 76.18° to 70.17°. Furthermore, combustion chamber without the guide ring exhibits higher temperature and OTDF.

Study on the competition effects between thermal conductivity and viscosity of graphene reinforced octadecane phase change material

In this study, a combination of microscale molecular dynamics (MD)-based and macroscale computational fluid dynamics (CFD)-based simulations are employed to investigate the effects of graphene with varying mass ratios on the thermal conductivity and viscosity of octadecane, revealing the nature of the competition effects of thermal conductivity and viscosity in the heat transfer process. The results show that graphene can significantly increase the average thermal conductivity of octadecane. But when its synergy angle in the direction of heat flux is close to 90°, the thermal conductivity of nanocomposite phase change materials (NCPCMs) is only 0.125 W·(m·K)−1, which is lower than that of pure octadecane by 18.83 %. The viscosity of NCPCMs decreased significantly with the decrease of graphene weight ratio and the increase of temperature, and the viscosity of NCPCMs with 9.15 wt% and 28.71 wt% at different temperatures was 812.65 % (max) and 313.75 % (min), respectively. Finally, the equilibrium point between the thermal conductivity and viscosity competition effects favors the viscosity side as the graphene mass ratio increases. Accordingly, natural convection became more crucial in the heat transfer process as the graphene mass ratio increased. Consequently, NCPCMs with the best heat transfer performance should possess a low graphene mass ratio, which results in a high Rayleigh number, providing them with high synergistic efficiency.

Heat and mass transfer efficiency in the T-Shaped geometry: Entropy generation analysis

Thermodynamic analysis of energy efficiency, especially those utilizing the second law ofthermodynamics, is focus of scientific inquiry, particularly given the interest in the efficient use of heatedenergy sources. In this work, we characterize the geometry in terms of entropy generation witch due tothe heat transfer and fluid friction as function of generalized Reynolds number under the effects ofdifferent inlet temperatures.This work has been performed for the important parameters in the following ranges: generalizedReynolds number (Reg = 1 to 60). As generalized Reynolds number increases, the entropy generation dueto heat transfers decreases, which reveal that the effect of the generalized Reynolds number on heattransfer performance is substantial. These results verify that the T-shaped channel can effectively enhancethe heat transfer performance for all cases. Overall, the entropy generation and synergy angle aresignificant characteristics to consider when building micromixers for thermal efficiency and misciblefluid mixing.

Effect of tubular heater structures on the thermal behaviors of waxy crude oil

In this paper, we research the temperature field, flow field and melting law of gelled crude oil with different diameters, locations and inclination angles of heating tube by numerical simulation method. Using the synergy angle, temperature variance and effective heating ratio as evaluation indices, the effect of the heating tube and distribution homogeneity of the temperature field were examined. The simulation results show that the temperature field and velocity field of waxy crude oil and the melting law of gelled crude oil are basically the same under different conditions. The most important factor affecting average temperature and temperature variance is the location of heating tube, which can increase the average temperature by 1.252 °C and decrease the temperature variance by 9.019°C2. The most important factor affecting the synergy angle is the inclination angle of heating tube, which can be reduced by 4.104°. In the 8 cases, when the inclination angle of the heating tube is 45°, the temperature maintaining effect of tubular heating is the best, and the synergy angle is the smallest. The least temperature variance is the uniform arrangement of heating tube. The results of this study will provide theoretical guidance for the optimization design of tubular heater structure.

Improvement of flow field uniformity and temperature field in gasoline engine catalytic converter

The uneven temperature field, flow field, and internal low temperature of the catalytic converter can cause substrate thermal deformation and catalytic ability decrease, which is not conducive to the service life of catalytic converter and control of automotive pollutants emission. A novel substrate structure with uniformly changes cell density and a new heater of three layers diffuser with optimized flow field uniformity are proposed. Their application in catalytic converter can effectively improve the above problems. Firstly, physical and mathematical models of the new catalytic converter were established, and the accuracy was verified by experiments. Next, the flow characteristics and catalytic performance was analyzed. Finally, the effects of different parameters on catalytic performance and temperature were analyzed. The results show that: (1) Compared with traditional catalytic converter, gas uniformity and NO conversion efficiency of the new catalytic converter are increased by 0.0885% and 13.66%, respectively, improving flow field uniformity and NO conversion. (2) The NO conversion efficiency increases and then decreases with adding of electric power, exhaust inlet temperature and exhaust inlet velocity; substrate temperature increases with adding of electric power and exhaust inlet temperature, but decreases with increase of exhaust velocity. During heating time, the NO conversion efficiency and substrate temperature first increase and then tend to stabilize. After heating is stopped, the NO conversion efficiency and substrate temperature will decrease. (3) The field synergy theory shows that synergy angle cosβ tends to − 1 with increase of electric power, which means convective heat transfer effect inside substrate becomes worse. (4) The grey relational analysis shows that exhaust inlet temperature is a key factor affecting the new catalytic converter performance.

Multiple field synergy mechanism of the desulfurization process in the intensified spouted beds

The semi-dry flue gas desulfurization process in the conventional spouted bed (CSB), integral multi-jet spouted bed (IMJSFB), spouted bed with longitudinal vortex generator (SB with LVG) and swirl blade nozzle (SB with SBN) was simulated using the multi fluid model. Meanwhile, the multiphase reaction system of intensified spouted beds was explored based on the field synergy theory. The analysis of the synergy angle among three fields of the gas phase velocity, temperature, and pressure in the spouted bed shows that adding intensification structures can effectively enhance the gas heat transfer and reduce the gas drag and pressure drop. The intensified spouted beds also had better synergy among the multiphase field of velocity, velocity gradient, and temperature gradient. The desulfurization efficiencies in the CSB, SB with LVG, IMJSFB, and SB with SBN were 77.75 %, 80.85 %, 87.97 %, and 88.81 %, respectively, and the promotion effects in descending order of SBN > multi-jets > LVG.

Field synergy and thermodynamic evaluation of a mini-duct with several protrusions utilizing the cross-flow method: A numerical exercise

The field synergy and entropy generation analysis of turbulent flow in a mini rectangular duct featuring surface protrusions has been numerically explored in a finite volume approach. The governing differential is solved iteratively using adequate numerical boundary conditions and a second-order upwind technique. In the post-processing, entropy generation, and irreversibilities are measured. The duct Reynolds number (ReDh, duct) has been varied from 17,831 to 53,492 at a fixed nozzle Reynolds number (ReDh, nz) of 5104. The effects of the duct Reynolds number on the thermal and frictional irreversibility have been quantified. Thermal, frictional, and total irreversibilities have been reported to rise with ReDh, duct. Furthermore, it is discovered that thermal irreversibility dominates over frictional irreversibility. It has been found that conducting triangular protrusions creates more entropy than conducting rectangular protrusions. Filed synergy analysis has also been carried out by integrating the energy equation. Heat transfer rate has been seen to increase with synergy angle (α). Triangular protrusions have a greater field synergy angle (α) than rectangular protrusions.

Investigations of flow structures and performances of heat transfer in semi-circular grooved ducts by applying field synergy principal analysis: An experimental and numerical study

The present study aimed at investigating the flow structure and heat transfer mechanism through the corrugated channel experimentally and numerically. Particle imaging velocimetry (PIV), which can give detailed information about the wake and shear flow regions, was used for the experiments. The experimental and numerical works were performed considering Reynolds numbers in the range of 6 × 103 ≤ Re ≤ 12 × 103 and 3 × 103 ≤ Re ≤ 2 × 104, respectively. In the numerical part, aspect ratios (R/hp) of examined grooves have been chosen as 0.1, 0.2, and 0.3, and for the experiment, only one aspect ratio was chosen which was 0.3. The experimental studies were conducted regarding different Reynolds numbers as well as the distributions of instantaneous and time-averaged velocity contours, Turbulence Kinetic Energy, Reynolds shear stress, and vorticity. The standard SST k-ω turbulent method was employed for the case of numerical study to predict the thermal performance (η) along with Nusselt numbers (Nu) the friction factors (f) and local field synergy angles (α, β) were calculated. As a result, the Nusselt number (Nu) values of the corrugated channels were higher than the parallel plate, and the increment in the Nusselt number initially increased and later decreased with Reynolds numbers for all aspect ratios considered.

Numerical investigation on combustion flow characteristics of a micro gas turbine swirl combustor with different protruded bluff body structures

A micro gas turbine swirl combustor with protruded bluff body is proposed. Compared with no bluff body, the protruded bluff body can significantly improve the combustion performance. When the bluff body height is 40 mm and the length is 30 mm, the average outlet NO emission is reduced by 14.43%, the pressure loss is decreased by 5.96%, and the outlet temperature distribution factor (OTDF) is dropped by 31.93%. The influence of different bluff body lengths (15–30 mm) and heights (10–50 mm) on the combustion flow are numerically analyzed further. The results show that the change of bluff body structure will affect the performance of combustor. In the range of 15–25 mm, with the increase of the bluff body length, the scope of central recirculation zone becomes narrower, velocity near the inlet and pressure loss decrease, the OTDF and field synergy angle β both become larger. When the bluff body length grows from 15 mm to 30 mm, the average outlet NO emission increases by 36.74%. The range of the central recirculation zone is gradually widen, and the average reaction rate grows up with the increase of bluff body height. The synergistic effect becomes better, and the heat transfer capacity is enhanced. When the bluff body height grows from 30 mm to 50 mm, the average outlet NO emission reduces from 35.84 ppm to 25.65 ppm.

Investigation of field synergy principle for convective heat transfer with temperature-dependent fluid properties

The field synergy principle is widely used in the analyses and optimizations of convective heat transfer, but its original derivations are based on fluids with constant thermal properties. The applicability of the principle for fluids with temperature-dependent properties needs clarification. A theoretical analysis of the problem is conducted. It is found that a synergy principle of mass flux vector and specific enthalpy gradient is more fundamental. Because temperature gradients are parallel to specific enthalpy gradients, the original field synergy principle of velocity and temperature fields is still valid. Heat transfer of supercritical CO2 and molten salt in different finned channels is numerically studied, and different mean synergy angles are compared. It is found that the domain integration mean synergy angles calculated with specific enthalpy gradient or temperature gradient have the same trends. For the volume-weighted mean angles, the absolute value of dot product of velocity and temperature gradient should be used in calculating the local synergy angles. Otherwise, the trend of the volume-weighted mean angles can be contrary to the field synergy principle. Meanwhile, the accuracy of the mesh and the temperature gradient near the heat transfer surfaces is important for the numerical applications of the field synergy principle.

Heat transfer characteristics and deformation effects of compressor air-cooled cylinder based on heat-flow-solid coupling

In order to ensure the safe and stable operation of compressor air-cooled cylinder, grasp the influence of heat transfer on deformation of air-cooled cylinder and suppress the deformation effect of air-cooled cylinder, a study on the heat transfer characteristics and deformation effect of compressor air-cooled cylinders based on heat-flow-solid coupling was carried out. Based on the field synergy theory, four heat transfer-deformation evaluation indexes were established: the percentage of the hot zones, the average temperature gradient, the percentage of the high-speed zones and the average field synergy angle. And the accuracy of the simulation model was verified by using the field temperature test of the air-cooled cylinder. The results show that the overall volume of the hot zones of the air-cooled cylinder is 44.1%, which are concentrated in the exhaust chamber and the working chamber area, consistent with the “drum-shaped” deformation characteristics of the air-cooled cylinder, and the maximum deformation is 0.451 mm; The average radial temperature gradient of the cylinder working chamber is 73.4 ℃/m, the radial temperature distribution is more uneven, resulting in the radial deformation of the working chamber showing an “eccentric circle-like” out-of-circle shape, the maximum effective deformation is 0.133 mm; the volume of the overall high-speed zones of the air-cooled cylinder are 8.4%, the average field synergy angle of each characteristic section are larger, which are not conducive to the heat transfer between the solid wall and the fluid, thus increasing the deformation of the air-cooled cylinder. The heat transfer-deformation process forms a correspondence relationship. This study provides theoretical guidance to improve the heat transfer characteristics of air-cooled cylinder and reduce the deformation effect of air-cooled cylinder.

Study on Optimization of Copper to Aluminum for Locomotive Finned Tube Radiator

The influence of the improvement of the finned tube radiator unit structure on the fluid flow and heat transfer effect of the locomotive was studied. A saw-toothed fin structure with aluminum instead of copper was proposed to keep the position and size of the flat copper hot water pipe unchanged. CFD simulation analysis was carried out by ICEPAK17.0, under the conditions of an ambient temperature of 24.6 °C, atmospheric pressure of 85,040 Pa and air density ρ = 0.94 kg/m3, to compare the changes of velocity field, temperature field, turbulence field and field synergy angle. The sawtooth structure of the new heat sink increases the turbulence effect of the fluid, reduces the thickness of the outer boundary layer of the water pipe, and strengthens the heat transfer effect of the radiator. Finally, the baffle height, wing window width and sawtooth angle of the sawtooth structure were selected, and the heat transfer coefficient and pressure under three conditions of low, medium and high were used as indexes to analyze the influence of each parameter on the performance of the radiator. The results show that the heat dissipation effect of the serrated aluminum sheet is higher than that of the copper sheet, the heat transfer coefficient is increased by about 1.3%, the average pressure is reduced, the turbulence performance is improved, the synergy angle is reduced by about 2.3°, and the new radiator has better performance. The fin factor has the greatest influence on the heat transfer coefficient and the least influence on the pressure. When the baffle is about 0.15 mm high, the heat transfer coefficient is the largest, and the height change has the highest effect on the pressure. The included Angle factor has the least influence on the heat transfer effect, and the influence on the pressure is higher. By changing the fin window structure, the thermal performance of the finned tube radiator can be improved.

Heat transfer and flow resistance performance of nonuniform distributed serrated fins

This article numerically investigates the behavior of nonuniform distributed serrated fins including equaled, shortened, lengthened, short on both sides, and long on both sides. In outputs, not only the temperature field and velocity contour but also the synergy field were examined. The results show significant advantages of nonuniform fins, having certain characteristics, in improving the overall heat transfer performance. At the near entrance of nonuniform fin type, heat transfer can be improved by increasing fin length gradually, while it becomes worsened by decreasing fin length. The length of the first fin in the near inlet region has a great influence on the distribution of the temperature field. For the best array compared with the uniform case, the Colburn j factor increased by 9.1 − 16.8%. Either uniform or nonuniform fin type deteriorates the flow resistance while heat transfer capability is enhanced. From the perspective of synergy between temperature gradient and velocity, the local field synergy angle at the near inlet region, and the windward side of the fin has a decisive effect on the heat transfer performance.

Experimental and numerical investigation of flow and heat transfer characteristics of Chinese ink nanofluid in built-in rotor tube

For increasing the heat transfer efficiency of the tubular heat exchanger, Chinese ink (CI) nanofluid was applied in the built-rotor tube, and the effects of the mass fraction of CI and structures of the rotors were investigated through experiments and numerical simulations. The experimental results indicated that the heat transfer performance improved with an increase in the nanofluid mass fraction and that the nanofluid in the built-in rotor tube produced a better heat transfer enhancement effect than that in a plain tube (PT). The Nu of 0.1% CI nanofluid in the PT increased by 11.12%–13.69%, whereas that in the built-in rotor tube increased by 17.57%–18.94%. The flow pattern and temperature distribution in the tube were studied via numerical simulations. The addition of rotors can make the flow pattern change from an axial flow to a three-dimensional spiral flow. This flow pattern reduces the thickness of the laminar sublayer and the temperature of the medium near the wall, as well as the synergy angle in the tube, which makes nanofluid with good thermophysical properties have a better heat transfer enhancement effect in the built-in rotor tube than in the PT.

Numerical analysis on hydrogen swirl combustion and flow characteristics of a micro gas turbine combustor with axial air/fuel staged technology

• 1 Axial air staging, axial fuel staging and jet stabilized technology are combined with swirl combustion. • 2 Outlet NO emission decreases from 20.2 ppm to 2.28 ppm as secondary air ratio grows from 0% to 40%. • 3 Fuel staging has a more significant effect on reducing NO emission than air staging. To analyze the effects of the two staging techniques on combustion characteristics and emissions, the influence of different secondary oxygen ratios (0-40%) and secondary fuel ratios (0-10%) on the combustion flow, emission characteristics, field synergy and other parameters of the micro gas turbine combustor are investigated by numerical simulation based on computational fluid dynamics (CFD) method. The realizable k-epsilon model is adopted for turbulence simulation, the combustion model is general finite rate model. The results show that with the increase of secondary oxygen ratio from 0% to 40%, scope of central recirculation zone becomes smaller, outlet velocity grows, OTDF becomes larger and pressure loss rises, the average outlet NO emission decreases from 20.2 ppm to 2.28 ppm, synergy angle β of the central plane becomes larger, and the change mainly occurs in the recirculation zone and the rear of the combustion chamber. As the secondary fuel ratio grows, outlet velocity decreases, pressure loss drops, and the outlet temperature distribution becomes more and more uniform. The synergy between velocity and temperature gradient of the central plane becomes better. When the secondary fuel ratio is 10%, the maximum NO emission on the central axis is 9.27 ppm, which is only 8.51% of the fuel unstaged value. The outlet NO emission does not drop monotonously with more secondary fuel. Fuel staging has a more significant effect on reducing NO emission than air staging.

Numerical analysis of heat transfer characteristics in a flywheel energy storage system using jet cooling

A flywheel energy storage system (FESS), with its high efficiency, long life, and transient response characteristics, has a variety of applications, including for uninterrupted power supplies and renewable energy grids. The heat produced by the system as a result of power loss has a significant negative impact on the long-term stability in a vacuum environment. This paper proposes an impingement jet cooling structure with rotating axis to facilitate the heat dissipation of FESS. The implications of the cooling medium, nozzle length, cavity zone diameter, and nozzle diameter of the impingement jet cooling structure on flow and heat transfer performance are studied by field synergy theory. Additionally, the structural parameters are optimized using the response surface method. The Nusselt number, friction coefficient, field synergy angle, comprehensive coefficient of heat transfer, and temperature field are analyzed. Heat transfer can be improved by decreasing the diameter of the cavity zone, lengthening the nozzle, and increasing the nozzle diameter. The pressure drop of the optimized structure is at least 62.48% less than that of the unmodified structure, while the temperature increase of the cooling medium is nearly 3.5 times higher.