Helical Exchanger Research Articles

Helicity-resolved Raman scattering of MoS2 bulk crystal.

Helicity-resolved Raman spectroscopy (HRRS) can effectively distinguish the Raman modes of two-dimensional (2D) layered materials by phonon symmetry. In this paper, we systematically investigated the phonon helicity selection of basal and edge planes of MoS2 bulk by HRRS. We find that the symmetry of the crystal structure changes the helicity selection of the E1g, E1 2g, and A1g modes in the edge plane. The theoretical calculation results confirm that the E1 2g and A1g modes of the basal plane exhibit a perfect helicity exchange, and the helicity selections of the E1 2g and A1g modes of the edge plane are eliminated or weakened. Our study provides references for phonon helicity selection of 2D layered materials represented by MoS2.

Helicity exchange and symmetry breaking of in-plane phonon scattering of h-BN probed by polarized Raman spectroscopy

Due to its atomic thickness and insulating nature, hexagonal boron nitride (h-BN) is considered to be one of the most promising substrates and gate insulating materials for two-dimensional electronic devices. In this study, polarized Raman spectroscopy was employed to uncover the effects of polarized incident light on the optical properties of h-BN phonon modes. Our measured polarization-resolved Raman spectra indicate that the symmetrical nature and the broken symmetry of degenerate phonon modes from h-BN are induced by linearly and elliptically polarized light, respectively. Moreover, a helicity exchange was observed between the excitation of circularly polarized light and the resulting opposite circular polarization of scattered light from h-BN. The measured phenomena were modeled on the basis of Raman tensors and Jones calculus to eventually calculate the amplitude coefficients of two orthogonal in-plane phonon modes. Hence, our experimental study provides a holistic understanding of the vibrational modes in h-BN, which is expected to enhance the knowledge of physical mechanisms such as heat capacity and thermal and electrical conductivities of this layered material.

Investigation of thermal performance and entropy generation in a helical heat exchanger with multiple rib profiles using Al2O3-water nanofluid

This research aims to assess the in detail thermal performance and entropy generation of a helical heat exchanger with multiple rib profiles and coil revolutions using water-based Al2O3 nanofluid with 5% concentration. A steady-state computational fluid dynamic model was used in determining the thermal and hydraulic parameters. The numerical model was validated with a numerical study and an experimental study. Three multiple rib profiles (2 rib, 3 rib and 4 rib) and three different coil revolutions (10, 20 and 30) were considered to design nine cases of heat helical exchangers. The geometrical effect was assessed and further represented as the streamlines, isotherms, overall Nusselt number, friction factor, thermal enhancement factor, and entropy generation. It is found that with the growth of coil revolutions the overall heat transfer rate and friction factor rise. The most efficient heat exchanger found in terms of thermal enhancement factor is 3 rib 10 revolutions with the value of 1.34. The entropy generation increases with the rise of the coil revolution. The maximum entropy generation increased by 19.5% for varying the coil revolution with a constant rib profile. Finally, this study is a guide of choosing an efficient heat transfer in terms of thermo-hydraulic performance.

Analysis of heat transfer in a helical exchanger using different correlations

This research focuses on the evaporation process carried out in a helical exchanger where the R134a refrigerant passes through the internal diameter as primary fluid, the saturation temperatures are in the range of 10-20 oC with mass flows of 0.022 to 0.043 kg/s. Water-Ethylene Glycol 50% as secondary fluid that passes through the external diameter. Different correlations are applied to determine the convective coefficients, later the theoretical results will be compared with experimental results shown in the literature. It was observed that the coefficients increase when the quality of the coolant increases, increases

UTILIZING WASTE HEAT FROM THE REFRIGERATION CYCLE BY USING A TWO-STAGE HEAT EXCHANGER

Refrigeration, and air conditioning systems are designed to transport heat from internal spaces or products and discard it into the surrounding. Refutation of heat might happen in a straight line to the air, as in the case of most conventional units of air-source, or to water flowing from a cooling tower. This heat is of a "low-grade diversity", it still signifies wasted energy. According to the viewpoint of energy conservation, it would be necessary to regain this heat in a serviceable form. In this research, a practical study aims to collect the heat emitted from the cooling condenser by 35% and exploit it in heating hot water for domestic purposes, in addition to other uses, including reducing the consumption of electrical energy as a result of exploiting and collecting waste heat, from cooling devices using a system consisting of two types of helical heat exchangers and two stages. The first stage consists of a tube-in-tube helical exchanger and the second stage includes a tube-in-shell heat exchanger using R410A refrigerant. The EES engineering equation solving program was used to solve the numerical equations that are used to solve problems related to thermodynamics, due to its high accuracy in solving equations, extracting values and graphs, and calculating the performance coefficient of the COP to obtain better efficiency for the work of the system, as it was found that the higher the temperature. As a result of increasing the flow rate of deionized water, the percentage of performance coefficient of COP has increased.

Effects of Kaplan-Shekhtman-Entin-Wohlman-Aharony interaction on quantum discord of non-markovian dynamics under different magnetic fields

Since the discovery of symmetric helical interactions in the spin-orbit coupled single-band Hubbard model by Moriya and Kaplan, Shekhtman, Entin, Aharony et al. have successfully used this non-negligible symmetric helical exchange interaction to explain the weak ferromagnetism of La<sub>2</sub>CuO<sub>4</sub>. By using the non-Markovian quantum state diffusion method, the quantum discord of non-Markovian dynamics in the spin chain system that has Kaplan–Shekhtman–Entin-Wohlman–Aharony interactions and Dzyaloshinskii-Moriya interactions is studied. The effects of Kaplan–Shekhtman–Entin-Wohlman–Aharony interaction on the quantum discord under different external magnetic fields at zero and finite temperatures are discussed. The results show that the quantum discord in the system can be increased via the increasing of Kaplan–Shekhtman–Entin-Wohlman–Aharony interaction in the case of zero or uniform magnetic field, while the case is opposite under the nonuniform magnetic field. More importantly, the ideal discord state can be obtained by modulating the uniform magnetic field and Kaplan–Shekhtman–Entin-Wohlman–Aharony interaction. Moreover, the Markovian case and the effect of temperature on the quantum discord are also discussed, respectively.

How thermally efficient are chaotic advection mixers? An experimental assessment

Chaotic Laminar Mixers (CLMs) are static mixers whose concept uses chaotic advection based on the baker's transformation. The present work is an attempt to study CLMs from the viewpoint of heat transfer efficiency and global energy efficiency, and to compare them with helical heat exchangers with the same exchange surface. In the present work, we propose two new CLM geometries alongside two classical geometries. The influence of the number of bends and of the orientation of curvature planes was studied to detect the role of regular and alternate Dean flow. An experimental investigation using water as the inner hot fluid was carried out. It is shown that for the studied range of Reynolds numbers (100–2000), CLMs have a heat transfer efficiency two-times better than helical heat exchangers. However taking into account pressure losses, helical exchangers have global energy efficiency comparable to CLMs. For laminar flows, CLMs might be good heat exchangers when only mixing and heat transfer are required.

Nonkinematic solar dynamo models with double-cell meridional circulation

Employing the standard solar interior model as input we construct a dynamically-consistent nonlinear dynamo model that takes into account the detailed description of the Λ- effect, turbulent pumping, magnetic helicity balance, and magnetic feedback on the differential rotation and meridional circulation. The background mean-field hydrodynamic model of the solar convection zone accounts the solar-like angular velocity profile and the double-cell meridional circulation. We investigate an impact of the nonlinear magnetic field generation effects on the long-term variability and properties of the magnetic cycle. The nonlinear dynamo solutions are studied in the wide interval of the α effect parameter from a slightly subcritical to supercritical values. It is found that the magnetic cycle period decreases with the increasing cycle's magnitude. The periodic long-term variations of the magnetic cycle are excited in case of the overcritical α effect. These variations result from the hemispheric magnetic helicity exchange. It depends on the magnetic diffusivity parameter and the magnetic helicity production rate. The large-scale magnetic activity modifies the distribution of the differential rotation and meridional circulation inside convection zone. It is found that the magnetic feedback on the global flow affects the properties of the long-term magnetic cycles. We confront our findings with solar and stellar magnetic activity observations.

Spin-Orbital Momentum Decomposition and Helicity Exchange in a Set of Non-Null Knotted Electromagnetic Fields

We calculate analytically the spin-orbital decomposition of the angular momentum using completely nonparaxial fields that have a certain degree of linkage of electric and magnetic lines. The split of the angular momentum into spin-orbital components is worked out for non-null knotted electromagnetic fields. The relation between magnetic and electric helicities and spin-orbital decomposition of the angular momentum is considered. We demonstrate that even if the total angular momentum and the values of the spin and orbital momentum are the same, the behavior of the local angular momentum density is rather different. By taking cases with constant and non-constant electric and magnetic helicities, we show that the total angular momentum density presents different characteristics during time evolution.

Electrodynamics of dual superconducting chiral medium

We study the electrodynamics of the chiral medium with electric and magnetic charges using the effective Maxwell–Chern–Simons theory extended to include the magnetic current. The exchange of helicity between the chiral medium and the magnetic field, known as the inverse cascade, is controlled by the chiral anomaly equation. In the presence of the magnetic current, the magnetic helicity is dissipated, so that the inverse cascade stops when the magnetic helicity vanishes while the chiral conductivity reaches a non-vanishing stationary value satisfying σχ2<4σeσm, where σe, σm and σχ are the electric, magnetic and chiral conductivities respectively. We argue that this state is superconducting and exhibits the Meissner effect for both electric and magnetic fields. Moreover, this state is stable with respect to small magnetic helicity fluctuations; the magnetic helicity becomes unstable only when the inequality mentioned above is violated.

The Effect of Geometrical Parameters on Heat Transfer and Hydro Dynamical Characteristics of Helical Exchanger

Compact size and high heat transfer coefficient of helical coil heat exchangers causes them to have an important role in various industrial applications. This paper investigate numerically on the influence of different parameters such as coil radius, coil pitch and diameter of tube on the hydrodynamic and heat transfer characteristics of helical double tube heat exchangers using the CFD software which is based on the principles of heat transfer, fluid mechanics and thermodynamics. The results indicated that heat transfer augmentation occurs by increasing of the inner Dean Number, inner tube diameter, curvature ratio and by the reduction of the pitch of heat exchanger coil. By increasing the radius of coils, the secondary flow effects due to centrifugal forces diminishes and flow of fluid through the coils tends to flow in a straight path and as a result, the friction coefficient decreases consequently.

Structural Basis for the Assembly of Kinesin-5 into Bipolar Anti-Parallel Tetramers

Cell division is driven by organized mitotic spindles and requires diverse groups of molecular microtubule-based kinesin motor proteins. Kinesin-5 motors form a unique and conserved class of tetrameric bipolar motor proteins, consisting of dual motor domain sets oriented at opposite ends of a central rod-like structure. The bipolar organization is critical for kinesin-5 to crosslink and slide adjacent anti-parallel microtubules in opposite directions required for spindle elongation in anaphase. Here we present the atomic structure of Drosphila kinesin-5, KLF61F, bipolar assembly (BASS) domain, which explains how four molecules assemble to form a bipolar functional motor. Instead of the predicted dual traversing parallel coiled-coils, the BASS structure reveals a novel 26nm long antiparallel 4-helical bundle filament, where the basic assembly unit is an anti-parallel coiled-coil that originate from opposite ends of the bipolar structure, and folds onto a second unit in an anti-parallel manner. A striated pattern of hydrophobic and hydrophilic pockets precisely oriented monomers within the BASS tetramer to form this bipolar arrangement. Strikingly, the BASS N-termini undergo a helical exchange from anti-parallel bundle in the center to form homo-dimeric parallel helical coiled-coils at the poles. These parallel BASS N-termini are 100 degrees rotated compared to N-termini emerging from the opposite pole, providing a physical explanation for the known kinesin-5 preference for sliding anti-parallel versus parallel microtubules. We have generated a structural model for the kinesin-5 tetramer using the BASS structures and all electron microscopy that explains key features of the kinesin-5-driven sliding filament mechanism.

Heat transfer of dilute viscoelastic solutions in helical exchangers

The study examined heat transfer of two dilute viscoelastic solutions in helical exchangers of circular cross-section. Ten helical coil heat exchangers with diameter ratios ranging from 4 to 50 were constructed. Results showed doubling the concentrations of polymer increased heat transfer performance by 12 %. The results were expressed in forms of some existing equations and were found to be in fair agreement to previous results.

Relaxation-time measurement via a time-dependent helicity balance model

A time-dependent helicity balance model applied to a spheromak helicity-injection experiment enables the measurement of the relaxation time during the sustainment phase of the spheromak. The experiment, the Helicity Injected Torus with Steady Inductive helicity injection (HIT-SI), studies spheromak formation and sustainment through inductive helicity injection. The model captures the dominant plasma behavior seen during helicity injection in HIT-SI by using an empirical helicity-decay rate, a time-dependent helicity-injection rate, and a composite Taylor state to model both the helicity content of the system and to calculate the resulting spheromak current. During single-injector operations, both the amplitude and the phase of the periodic rise and fall of the toroidal current are predicted by this model, with an exchange of helicity between the injector states and the spheromak state proposed as the causal mechanism. This phenomenon allows for the comparison of the delay between the current rises in the experiment and the numerical model, enabling a measurement of the relaxation time. The measured relaxation time of 4.8 μs ± 2.8 μs is shorter than the toroidal Alfvén timescale. These results validate Hall MHD calculations of the Geospace Environmental Modeling challenge.

Case study of heat transfer behavior of helical ground heat exchanger

This paper presents an experimental and numerical case study of the heat transfer around the helical ground heat exchanger. With varying helical pitch, indoor thermal response tests were conducted in a dry sand. The tests were analyzed based on axisymmetric finite element analyses and recently published heat source models for spiral coil heat exchanger including our modifications of them by adding finite-length line source solution to consider vertical return pipe at center of helical heat exchanger. In addition to reasonable agreements in soil temperature rises at exteriors the helical heat exchanger, existence of return pipe was found to be important for estimation of heat transfer inside helical exchanger. Besides, the heat source models were found to be applicable to approximate mean fluid temperature during TRTs. The numerical and analytical models were applied to field thermal response test for an energy pile reported in literature. Compared with numerically estimations, the analytical solutions considerably overestimated temperature rise at the exterior of the energy pile. The results reveal that reasonable considerations in estimation of effective thermal properties may be needed when applying the heat source models for energy pile, even though they would evaluate reliable heat transfer behavior of helical heat exchanger embedded in a homogeneous ground.

Exchange of helicity in a knotted electromagnetic field

AbstractThere are solutions of Maxwell equations in vacuum in which the magnetic and the electric lines have a nontrivial topology. This behaviour has physical consequences since it is related to classical expressions indicating aspects of the photon content of the electromagnetic field. In this work we present for the first time an exact solution of Maxwell equations in vacuum, having non trivial topology, in which there is an exchange of helicity between the electric and magnetic part of such field. We calculate the temporal evolution of the magnetic and electric helicities, and explain the exchange of helicity making use of the Chern‐Simon form. We also have found and explained that, as time goes to infinity, both helicities reach the same value and the exchange between the magnetic and electric part of the field stops.

Consolidation of heat transfer coefficients of viscoelastic simulated food solutions in helical exchangers

Heat transfer of viscoelastic liquids in helical exchangers attracted limited work in the past. Most heat transfer equations proposed do not reduce to the Graetz–Leveque equation for the straight tubes. Heat transfer coefficients were obtained for seven copper helical coil heat exchangers with different diameters and diameter ratios. Hot water was used as the heating medium; and dilute polyacrylamide solutions were used to simulate the food solutions. Results showed increased heat transfer coefficients but the magnitudes were lower than those obtained by previous workers. A unified form of the Graetz–Leveque equation obtained was:Nu=1.75 Gz1/3[1+0.5421Dn0.45(d/D)0.54] for water. The heat transfer equation for the 250ppm solution is represented by, Nu=1.75 Gz1/3[1+0.3515Dn0.45(d/D)0.54]; and for the 500ppm solution the results can be represented by Nu=1.75 Gz1/3[1+0.3615Dn0.45(d/D)0.54]. Viscoelasticity reduces heat transfer performance.

MAGNETIC HELICITY EXCHANGE BETWEEN NEIGHBORING ACTIVE REGIONS

Addressing the long-lasting problem of the magnetic helicity distribution in the solar corona, a proof for magnetic helicity exchange between two neighboring emerging active regions (ARs) was found: when AR 9188 emerged, it first started to accumulate positive helicity, while the later neighboring emerging AR 9192 accumulated negative helicity. At a later time, after the bright connecting loops became visible between the two ARs, AR 9188 also suddenly started to gain negative helicity. At the same time AR 9192 started to loose negative helicity. It was found that the magnetic helicity fluxes of the two ARs changed simultaneously by almost the same amount. At one instant it was even possible to determine that the connecting loop between the two ARs carried negative helicity. We excluded the possibility that magnetic flux emergence was causing the observed variation of the magnetic helicity. Hence, magnetic helicity was indeed transferred from the late emerging AR 9192 to AR 9188 via an unbalanced magnetic torque along the loop. Such kinds of helicity transfer might be a common mechanism of redistribution of magnetic helicity in the solar atmosphere, which has just not been widely observed yet.