Helical Duct Research Articles

Thermal performance of a hybrid thermal management system based on the half helical coil coupled with air jet cooling for cylindrical Lithium-ion battery

The Battery Thermal Management System (BTMS) is crucial for the efficient and safe operation of Lithium-ion batteries (LIBs). It is challenging for liquid cooling to apply to areas of battery modules with complex surface forms, such as the positive and negative cell terminals, cell holders, etc. Herein, the thermal management scheme integrated with the half helical coil and air jet impingement is proposed for cylindrical LIBs. Heat is transferred from the LIBs' sides by helical flow and dissipated from the LIBs' ends by air jet impingement. The three-dimensional computational fluid dynamics model of battery modules with cell holders is developed. The thermal performance of the LIBs at various BTMS strategies, the number of turns of the helical coil, airflow inlet velocity, inlet temperature, and contact resistance are investigated. When the impinging air jets are arranged on both ends of the cylindrical form, the maximum values of temperature difference (ΔT) of the LIBs fall from 5.7°C to 4.0°C compared with that of liquid-based BTMS. The arrangement of the half helical duct divided into two separate sections reduces the coolant flow path length, which decreases the maximum temperature (Tmax) and ΔT to 28.9°C and 3.6°C. The proposed BTMS exhibits an enhanced heat dissipation performance and provides a design guideline for developing the hybrid BTMS.

Numerical and experimental study of a novel GER fluid damper based on helical duct flow

The benefits of giant electrorheological fluids (GER fluids) have been harnessed to enhance their effect in damping force generation. However, few results have been reported on the issue of taking advantage of a helical duct flow in improving the performance of a GER-based damper in generating and tuning damping effects. In this study, an innovative GER fluid-based damper with helical flow ducts is proposed. The proposed flow mode can achieve a greater pressure gradient during operation, and, thus, improve the damping performance by enlargement of the length of the active region with more compact dimensions. A mathematical model aiming to explain the mechanical properties of the damper is investigated based on the continuity equation and Navier–Stokes equations. Then, simulation studies based on computational fluid dynamics (CFD) solvers are conducted to verify the effectiveness of the mathematical model. Additionally, an experimental prototype of the GER fluid damper is fabricated, and damping force measurements under different excitations are carried out. The experimental results agree well with the results obtained from theoretical analysis and CFD solvers. The regulation coefficient that illustrates the tunable range of the damping force is found to reach a value of eight times under an electric field ranging from 0 to 1 kV mm−1.

Thermal management of cylindrical lithium-ion battery based on a liquid cooling method with half-helical duct

To maintain the maximum temperature within the optimum range and to improve the temperature uniformity of cylindrical lithium-ion battery, a liquid cooling method based on the half-helical duct was proposed. The effects of inlet mass flow rate, pitch and number of helical duct, fluid flow direction and diameter of helical duct on the thermal performance of battery at 5 C discharge rate were analyzed numerically. The results showed that the maximum temperature and temperature difference decreased with an increase in the inlet mass flow rate. When the pitch and the number of helical duct changed at the optimal inlet mass flow rate of 3 × 10−4 kg/s, there was no obvious improvement in the cooling performance. If the flow direction was varied according to six kinds of cases, the maximum temperature and the temperature difference for the Case4 all displayed the lowest values. If the diameter of half-helical duct varied from 2.0 mm to 3.8 mm, the temperature difference would retain within 4.3 °C, but the maximum temperature would approach to 30.9 °C, slightly higher than 30.5 °C. In comparison to the thermal management with jacket liquid cooling method, the thermal management with half-helical duct liquid cooling method might be better and more effective owing to the low fluid volume and no stagnant zone.

Bending Behavior of HTS Stacked Tapes in a Cable-in-Conduit Conductor With Twisted Al-Slotted Core

In this paper, we report on the experimental study of the bending behavior, at 77 K, of a cable-in-conduit conductor composed of a stack of REBa 2 Cu 3 O 7-x (REBCO) tapes inserted into a helical duct formed in the extruded aluminum cylindrical core. The investigation was carried out by powering each single tape individually. By the analysis of the single tape I c dependence as a function of the bending radius, R b , the effect of bending strain as a function of tape position inside the stack was investigated for each tape. The results evidence the good bending strain tolerance of all the tapes, showing the onset of degradation at R b ≈ 0.25 m, ascribed to the slippage occurring among tapes within the stack. Interestingly, the decrease in the intertape contact resistance between neighboring tapes with respect to the straight cable condition reveals that the bending stress results in a beneficial additional transverse load on the stacks, which leads to a more uniform compaction of tape stack. The experimental I c behavior with R b has been explained considering that the current transfer mechanism among tapes might mitigate the degradation of the tape I c due to the bending strain. The identification of the mechanisms acting on individual tapes under cable bending conditions is a relevant achievement in perspective of the interpretation of the electromechanical behavior of the conductor with all tapes powered in parallel.

Flow Analysis of Multiple Injectors in High-Power-Density HSDI CR Diesel Engines

The primary task in DI (Direct Injection) diesel engines design is the fulfilment of the required emission limits. This result should be achieved with acceptable power-to-rpm diagrams, acceptable fuel consumption, acceptable power density and affordable purchase and maintenance expenses. The most common approach to fulfil these requirements is the downsizing. In this case a significant increase in the crankshaft speed and boost pressure is unavoidable. In this way, an improvement in airflow through the redesign of the intake and exhaust geometry is obtained. Unfortunately, duct design is extremely difficult due to “Mach lock”. A further important boundary condition is due the injector inertia. The dynamic response improves with small injectors due to the Newton’s second law. Small injectors designed for unitary power of 15 to 70 HP are extremely common. Therefore, most of the research is centered on these injectors. Furthermore, their small inertia favors better opening and closing time. Nozzles number and position is also greatly influential on combustion performance. The larger surface of the spray reduces the gasification time of the droplets. For these reasons, multiple injectors systems may be used in large high pressure HSDI-CR (High Speed Direct Injection – Common Rail) diesels. Multi injection was commonplace in relatively large old diesels. This paper proposes new intake duct geometries for modern two-injectors-per-cylinder truck-size engines. For this purpose a new promising, patented concept is introduced. The study includes flow simulations during the intake phase. This patented geometry induces the presence of two extremely strong swirls approximately centered to the injectors, with excellent swirl coefficient and high flow rate. The use of swirl generators on the manifolds avoids the necessity to design helical intake ducts. This patented approach simplifies head design. Moreover, using a VG (Variable Geometry) arrangement for the volutes (swirl generators) it is possible to tune the swirl index at the optimum for every crankshaft velocity and every load. In this way, the vehicle fuel consumption is also reduced.

Comparison and analysis of the arrangement of delta winglet pair vortex generators in a half coiled jacket for heat transfer enhancement

In this paper, multiple delta winglet pairs (DWP) vortex generators were periodically mounted on the heated wall of the half coiled jacket to reinforce heat transfer capability. The jacket is approximated as a helical duct with semicircular cross section. The height of DWP is half the jacket pipe and the circumferential spacing angle between the adjacent DWPs is fixed as θ1 = 90°. Numerical investigations were performed to compare fluid flow and heat transfer performance in jackets (Re = 4000–18,000) under four types of DWP arrangement. Results according to the present study show that the common-flow-up (CFU) configuration of DWP has more advantages in heat transfer enhancement than the common-flow-down (CFD) one. The DWP with CFU-V arrangement provides best overall heat transfer performance when the attack angle β of DWP is between 25° and 30°. This is due to stronger vortices produced by it, slower dissipation of the coupled vortices and subsequently emerged additional vortices. Its comprehensive evaluation factors JF range is from 1.005 to 1.082. The comprehensive heat transfer enhancement effect of CFU-V DWP decreases with the reducing of the jacket curvature ε.

Experimental and Numerical Investigation of the Outer Ring Cooling Concept in a Hybrid and in an All-Steel Ball Bearing Used in Aero-Engines by the Introduction of a Helical Duct

Rolling element bearings for aero engine applications have to withstand very challenging operating conditions because of the high thermal impact due to elevated rotational speeds and loads. The high rate of heat generation in the bearing has to be sustained by the materials, and in the absence of lubrication these will fail within seconds. For this reason, aero engine bearings have to be lubricated and cooled by a continuous oil stream. When the oil has reached the outer ring it has already been heated up, thus its capability to remove extra heat from the outer ring is considerably reduced. Increasing the mass flow of oil to the bearing is not a solution since excess oil quantity would cause high parasitic losses (churning) in the bearing chamber and also increase the demands in the oil system for oil storage, scavenging, cooling, hardware weight, etc. A method has been developed for actively cooling the outer ring of the bearing. The idea behind the outer ring cooling concept was adopted from fins that are used for cooling electronic devices. A spiral groove engraved in the outer ring material of the bearing would function as a fin body with oil instead of air as the cooling medium. The method was first evaluated in an all steel ball bearing and the results were a 50% reduction in the lubricating oil flow with an additional reduction in heat generation by more than 25%. It was then applied on a Hybrid ball bearing of the same size and the former results were reconfirmed. Hybrid bearings are a combination of steel made parts, like the outer ring, the inner ring, and the cage and of ceramic rolling elements. This paper describes the work done to-date as a follow up of the work described in, and demonstrates the potential of the outer ring cooling for a bearing. Friction loss coefficient, Nusselt number, and efficiency correlations have been developed on the basis of the test results and have been compared to correlations from other authors. Computational Fluid Dynamics (CFD) analysis with ANSYS CFX has been used to verify test results and also for parametric studies.

Experimental and numerical study of the laminar flow in helically coiled pipes

The problem of steady incompressible laminar flow in helically coiled pipes is addressed from an experimental and numerical point of view. At first a brief review of published works on the subject presents some of the main steps made toward the comprehension of the considered phenomenon. An experimental campaign performed in a facility simulating a helical tube of the Steam Generator of a Small-medium Modular Reactor (SMR) is presented and discussed. In particular, the measured values of the Darcy friction factor are analyzed and then compared with numerous empirical correlations for laminar flow in helical pipes available in literature, in order to compare their predictions of friction pressure losses. Moreover, different numerical codes are applied. In particular the hydraulic problem of laminar flow in helical ducts is solved making use of commercial software, namely FLUENT, OpenFOAM fluid dynamic codes and COMSOL Multiphysics. The numerical simulation allows to describe the effect of geometry on the flow through the onset of a secondary motion and the deformation of the axial velocity profile, which affects in turn the friction factor. The prediction capabilities of the adopted codes are assessed comparing numerical friction factor values with experimental data and literature correlations. Maximum deviations result of the order of few percent.

Field synergy analysis for helical ducts with rectangular cross section

This paper proposes a new approach based on VSP method (Vorticity–Stream function–Poisson equation method), to study numerically fully developed laminar flow characteristics and heat transfer behaviors of helical ducts with rectangular cross section. The aim is to guide heat transfer enhancement for helical rectangular ducts. Based on the numerical results, synergies between velocity field and temperature field have been investigated through field synergy principle. The effects of curvature, torsion, aspect ratio, Reynolds number, and Prandlt number on velocity field, temperature field and field synergy have been examined. The results show that the secondary flow of the central regions is weaker than that in other locations of the cross section. With reference to the entire cross section, the best values of synergy between velocity field and temperature field can be found in the center of the section. Increasing the curvature, Reynolds number and Prandtl number causes the mean synergy angles of the cross section to increase. This result indicates that it is more important to improve the field synergy for high Prandlt number fluid, especially at high Reynolds number. As the torsion increases, the average synergy angles decreases. The mean synergy angles reach the maximum value when the aspect ratio is equal to one; therefore, one can conclude that the field synergy of helical ducts with square cross section is the worst. To enhance heat transfer performance of helical rectangular ducts, for small aspect ratio, the main important aspect is to improve the secondary flow in the center of the cross section. On the contrary, for moderate values of the aspect ratio, the most important aspect is to improve the field synergy of the region near the upper and the lower wall. The correlations of friction factor and Nusselt number have been also developed for helical ducts with rectangular cross section.

Numerical Investigation of the Transient Hydrothermal Behavior of a Ferrofluid Flowing Through a Helical Duct in the Presence of Nonuniform Magnetic Field

This paper investigates numerically the time dependent hydrothermal behavior of a ferrofluid (water and 4 vol. % Fe3O4) flowing in a helical channel, which is exposed to a nonuniform transverse magnetic field and its walls are subjected to uniform heat flux. The two phase mixture model and control volume technique have been used to study the flow. The results show that applying the nonuniform transverse magnetic field considerably increases the velocity and flow rate in the vicinity of the channel walls while it significantly decreases the velocity at the center of the channel. Applying magnetic field also decreases considerably the temperature of the inner wall of the helical channel. Furthermore, the average Nusselt number is increased by applying the nonuniform transverse magnetic field and it is more enhanced by increasing the magnetic field intensity.

Investigation of Semi-Solid Slurries Prepared by Helical Curve Duct

A new method of helical curve duct (HCD) to prepare semi-solid slurry was investigated. The semi-solid slurry of A356, AZ91, Cu-2.21wt%Ca (0.45wt%Ce) alloys were prepared through this method of HCD. Comparison of the microstructures of slurry prepared through the helical curve duct with different structure parameters and process parameters are made and the effects of structure and process parameters on microstructures are analyzed. The results show that the melt is stirred effectively by flowing through the helical curve duct and the semi-solid slurry of alloys could be prepared through the helical curve duct process; Spherical microstructures of alloy slurry were obtained through controlling or adjusting the process parameters to control solidification conditions.

Modeling fully developed laminar flow in a helical duct with rectangular cross section and finite pitch

The mass and momentum transport equations are written in an orthogonal coordinate system using Germano’s transformation to model a laminar flow in a helical duct with a rectangular cross section and finite pitch. The system of governing equations are discretized and solved by the finite-volume numerical method. The three dimensional domain is reduced to a two dimensional slab of cells, orthogonal to the main flow direction, enforcing the fully developed state for 2π/(τ·dh)>>1 where τ and dh representing the duct’s centerline torsion and its hydraulic diameter. This approximation and the use of an orthogonal grid allow a great simplification on the numerical procedure. Comparisons of the numerical solution against experimental data are drawn to assess the accuracy of the approximation.

Heat transfer and pressure drop through rectangular helical ducts

Optimization of heat transfer and flow in a helical duct of rectangular cross-section used to cool the stators of electric machines is studied using computational fluid dynamics (CFD) techniques. Realizable turbulent model is used with water and oil as working fluids for two different designs (helical continuous (HC) and helical reverse annulus (HRA) designs) and total of five configurations of the helical duct at small pitch size of 0.00254 m. The HRA is a new design proposed by the author. Due to the curvature of the ducts, as fluid flows through curved tubes, a centrifugal force is generated. A secondary flow induced by the centrifugal force has significant ability to enhance the heat transfer rate. Results showed that the HC design provides better heat transfer in terms of lower surface temperatures at the expense of higher pressure drop for the same flow rate of fluid.

Effects of geometrical parameters and internal wall velocity on turbulent flow and heat transfer in helical square duct with moving wall

In this study the effect of geometrical dimensions and the internal wall velocity on turbulent flow and heat transfer in a helical square duct with movable wall are numerically analyzed. RNG k-e turbulent model and finite volume method are used in the numerical solutions. The validity of the numerical solutions are tested by previous experimental studies with different boundary conditions and it has been determined that the helical duct curvature ratio and the internal wall velocity have significant effects but the dimensionless helical pitch has not on the internal wall Nusselt number. Key words: Helical square duct, RNG k-e turbulent model, finite volume method, curvature ratio, internal wall velocity, dimensionless pitch.

Numerical Procedure for the Laminar Developed Flow in a Helical Square Duct

The incompressible fully developed laminar flow in a helically duct of square cross section is studied expressing the governing equations in terms of an orthogonal coordinate system. Numerical results are obtained with the described continuity, vorticity, and pressure (CVP) numerical method using a colocation grid for all variables. Since there are not approximations, the interaction effects of curvature, torsion and axial pressure gradient on the velocity components and the friction factor are presented. The results show that the torsion deforms substantially the symmetry of the two centrifugal vortices of the secondary flow, which for large values of torsion combined with small curvature tend to one vortex covering the whole cross section. The friction factor decreases for torsion in the range 0 to 0.1 and increases as the torsion increases further, a behavior which is more profound as the Dean number increases. Our results are stable for the calculated Dean numbers.

Efficient Equipment with Special Heat Exchanger for Thermal Treatment of Polluted Air—Experiments, Computations, Applications

A quite new and unique piece of equipment for the thermal treatment of gas wastes (i.e., the incineration of volatile organic compounds contained in polluted air) has been developed. This compact equipment is characterized by a cylindrical combustion chamber placed inside a heat exchanger—a polluted air preheater. This cylindrical preheater consists of several concentric stainless sheets. Both flue gas from the combustion chamber and polluted air heated by flue gas flow in the spaces between the cylindrical sheets. Narrow distance strips placed between the sheets form helical rectangular ducts, through which we can achieve a counter-current flow of process fluids.A mathematical model for the calculation and/or simulation of the equipment consists of submodels of a heat exchanger and combustion chamber and the annular space between them. Based on the results of measurements on an industrial scale experimental facility, new correlations for the thermal and hydraulic calculations of the heat exchanger were developed. Some industrial applications are briefly mentioned.

913 長方形断面を有するら旋管内における周期流れについて

913 長方形断面を有するら旋管内における周期流れについて

712 長方形断面を有するら旋管内の発達した層流について

712 長方形断面を有するら旋管内の発達した層流について

Series solution of low Dean and Germano number flows in helical rectangular ducts

The flow in a helical duct with rectangular cross-section is analyzed. A series solution based on curvature and torsion is introduced. The components of the series are determined analytically using appropriate eigenfunction expansions. The resulting solution is limited to flows in the low Dean number, low Germano number regime. An analytical friction factor relation is established and compared with previous numerically determined correlations.

Laminar flow of four gases through a helical rectangular duct

AbstractMeasurements and a model of gas flow through a helical duct of rectangular cross section are reported. Observations of the rate of rise of pressure in a known volume located downstream from the duct yielded molar flow rates of helium, nitrogen, argon and sulfur hexafluoride. The model predicts flow rates from the duct's entrance pressure, exit pressure, and temperature. It accounts for the gas's nonideal equation of state, gas expansion along the duct's length, the increase of kinetic energy near duct's entrance, and slip. After adjusting only one parameter (the duct's height), the model agrees with the data to within 0.2% in the range of Reynolds number 0.08<Re<40. To extend the model to Re = 1,000, the centrifugal effects were accounted for by rescaling Targett et al.'s (1995) numerical calculations. The extended model agrees with the data to within 0.2% in the range 40 < Re < 400 and to within 1% in the range 400 < Re < 1,000.