Asymmetric Heating Research Articles

Investigation of asymmetric heating in Poiseuille-Rayleigh-Bénard water flow: A numerical study

In this paper, a numerical investigation of the impact of asymmetric heating on laminar mixed convection in Poiseuille-Rayleigh-Bénard water flow within parallel horizontal channels is presented. The study has been carried out in a rectangular channel with a transverse aspect ratio of 10, and considered both low (Ra = 1.28 × 104) and high (Ra = 1.4 × 105) Rayleigh numbers, with Reynolds numbers of 50 and 100. A uniform heat flux was applied to the top and bottom walls of the heated region to assess its effect on the system's thermoconvective behavior and heat transfer efficiency. Two flux ratio scenarios were considered: qt/qb = 1 and qt/qb = 2.The results indicate that increasing the flux ratio intensifies the destabilizing temperature gradient and significantly enhances buoyancy-induced flow, thereby influencing the patterns of thermoconvective structures. Specifically, flux ratios lead to an increased number of plumes originating from the bottom of the channel, while reducing their height and confining them between the bottom wall and the upper thermal boundary layer. It is also observed that flux ratios do not affect the mechanisms involved in the formation of longitudinal rolls. Furthermore, at low Rayleigh numbers, asymmetric heating has a pronounced impact on the establishment length. In contrast, this effect diminishes and becomes negligible at higher Rayleigh numbers. Numerical computations further reveal that near the bottom wall, the Nusselt number exhibits singular behavior, approaching infinity. Regardless of Reynolds and Rayleigh numbers, flux ratios significantly enhance heat transfer within the system. Additionally, near the top wall, the buoyancy effects from the bottom wall have negligible impact on heat transfer, except in the case where qt/qb = 2, Re = 50 and Ra = 1.4 × 105, where instability in the upper thermal layer was observed.

A GTC spectroscopic study of three spider pulsar companions: Line-based temperatures, a new face-on redback, and improved mass constraints

Abstract We present GTC-OSIRIS phase-resolved optical spectroscopy of three compact binary MSPs, or ‘spiders’: PSR J1048+2339, PSR J1810+1744, and (for the first time) PSR J1908+2105. For the companion in each system, the temperature is traced throughout its orbit, and radial velocities are measured. The radial velocities are found to vary with the absorption features used when measuring them, resulting in different radial velocity curve semi-amplitudes: for J1048 (Kmetals, red = 344 ± 4 km s−1, Kmetals, blue = 372 ± 3 km s−1) and, tentatively, for J1810 (KBalmer = 448 ± 19 km s−1, Kmetals = 491 ± 32 km s−1). With existing inclination constraints, this gives the neutron star (NS) and companion masses MNS = 1.50–2.04 M⊙ and M2 = 0.32–0.40 M⊙ for J1048, and MNS > 1.7 M⊙ and M2 = 0.05–0.08 M⊙ for J1810. For J1908, we find an upper limit of K2 < 32 km s−1, which constrains its mass ratio q = M2/MNS > 0.55 and inclination i < 6.0○, revealing the previously misunderstood system to be the highest mass ratio, lowest inclination redback yet. This raises questions for the origins of its substantial radio eclipses. Additionally, we find evidence of asymmetric heating in J1048 and J1810, and signs of metal enrichment in J1908. We also explore the impact of inclination on spectroscopic temperatures, and demonstrate that the temperature measured at quadrature (φ = 0.25, 0.75) is essentially independent of inclination, and thus can provide additional constraints on photometric modelling.

Rectifiable Conductive Thermal Diodes Enabling Thermal Circuits with Selectable Operations for Thermal Logic Applications

AbstractThermal logic paves the way to replace electric logic in scenarios where electronic signals are susceptible to interference or traditional electronics cannot be used, however, is still considered a theoretical and numerical stage. Emerging thermal metalmaterials (TMMs) have the potential to enhance thermal information processes. Compared to TMMs with single‐and‐fixed heat transfer capabilities, rectifiable‐TMMs enable thermal circuits to perform selectable operations, but they are also limited by low operating temperatures and narrow temperature biases. Here, macro‐ and experimental thermal diodes with tree‐like eutectic gallium‐indium/printed polylactic‐acid (EGaIn/PPLA) interface, are demonstrated to be capable of extending asymmetric heat transfer difference to 5.81 times in ambient operation, compared with basic EGaIn/PPLA interface with an input temperature bias of 63.7 °C. Given this, basic thermal gates can be constructed through the incorporation of resistors and a pair of diodes working in the same or opposite directions, with the propagation delay time td within 18 min. Compound logic gates can be cascaded by basic gates in the same way as composed Boolean functions, with td within 4 min. Such thermal circuits prove to perform reliably under dynamic ambient conditions, advancing the engineering of devices designed to manipulate thermal energy and process abundant thermal information.

Identifying Three‐Dimensional Radiative Patterns Associated With Early Tropical Cyclone Intensification

AbstractCloud radiative feedback impacts early tropical cyclone (TC) intensification, but limitations in existing diagnostic frameworks make them unsuitable for studying asymmetric or transient radiative heating. We propose a linear Variational Encoder‐Decoder (VED) framework to learn the hidden relationship between radiative anomalies and the surface intensification of realistic simulated TCs. The uncertainty of the VED model identifies periods when radiation has more importance for intensification. A close examination of the radiative pattern extracted by the VED model from a 20‐member ensemble simulation on Typhoon Haiyan shows that longwave forcing from inner core deep convection and shallow clouds downshear contribute to intensification, with deep convection in the downshear‐left quadrant having the most impact overall on the intensification of that TC. Our work demonstrates that machine learning can aid the discovery of thermodynamic‐kinematic relationships without relying on axisymmetric or deterministic assumptions, paving the way for the objective discovery of processes leading to TC intensification in realistic conditions.

A novel method for introducing asymmetry in pulsating heat pipes to enhance performance

The primary objective of this study is to improve the performance of a pulsating heat pipe (PHP) by introducing a novel method of incorporating asymmetry into the PHP design. This asymmetry is achieved by inserting a copper wire into one column of a single-loop PHP. Five different configurations of single-loop PHPs were created for this study: one with a uniform internal diameter (ID) of 2.5 mm (UPHP), one with dual diameters (2.5 mm and 1.8 mm ID) (DPHP), and three with a uniform ID of 2.5 mm but with varying wire diameters (0.7 mm, 1.2 mm, and 1.7 mm) inserted into one column (WAPHP). The PHPs were constructed using borosilicate glass. The performance of these PHPs was evaluated through visualization techniques and by calculating equivalent thermal resistance. A comprehensive study was conducted by varying filling ratios, inclination angles, and heat loads to understand their influence on PHP performance. The results indicate that at a 60% filling ratio, the wired asymmetric pulsating heat pipe (WAPHP) with a 1.2 mm diameter wire exhibited superior performance compared to all other tested configurations achieving a thermal resistance of 1.27 K/W. The WAPHP performed effectively up to an inclination angle of 15°. Additionally, the WAPHP with a 1.7 mm wire diameter demonstrated the earliest startup, taking just 35 s, and showed the maximum heat load capacity at a 50% filling ratio in a vertical orientation. Furthermore, dry-out did not occur in the 1.2 mm and 1.7 mm diameter WAPHPs at 50% and 60% filling ratios up to the tested heat load.

Analytical Investigation on Flow Reversal in a Fully Developed Steady Mixed Convection Flow With Boundary Condition of the Third Kind

ABSTRACTThis work presents exact solutions to analyze the effect of the Biot number on mixed convection flow in a vertical channel with asymmetric heating and flow reversal. The equations governing flow formation and temperature distributions are offered with convective boundary conditions. Closed‐form solutions for temperature, velocity, and skin friction are found and simulated graphically.

Vertical instability prediction and its direction control using a support vector machine in integrated commissioning of JT-60SA solely based on magnetics

Abstract We developed a redundant logic for predicting Vertical Displacement Events (VDEs) using only magnetic diagnostics with a Support Vector Machine (Inoue et al 2022 Nucl. Fusion 62 086007). This logic was experimentally validated in the integrated commissioning of JT-60SA. Triggering of VDEs results in significant asymmetric heat loads on first walls and electromagnetic loads on conducting materials. These concerns are mitigated by a newly proposed direction control for VDEs. We successfully detected VDEs in experiments and controlled their direction by setting the control voltage to zero upon detection, thus guiding VDEs in an intended direction and reducing the risk to the device from unmitigated VDEs in either direction, although completely avoiding VDEs remains the ideal. In the developed predictor, VDEs are predicted using proxies to monitor the controller’s performance with an adaptive voltage allocation scheme (Inoue et al 2021 Nucl. Fusion 61 096009). For future experiments, we plan to extend our approach to monitor more detailed information from the equilibrium controller, including control values of each PID component, which has been shown to enhance the prediction accuracy of VDEs.

Numerical investigation and optimization of an asymmetric elliptical-cylindrical pin fin heat sink

A 3D numerical simulation was performed to analyse the heat transfer characteristics of an asymmetric elliptical-cylindrical pin fin heat sink (AECPFHS) in a turbulent flow scenario and to determine the optimum asymmetric elliptical-cylindrical pin fin (AECPF) structure. The investigation is performed in three stages. The numerical procedure and the software tool used in the current research are first validated with another work in which the performance enhancement of a heat sink with staggered cylindrical pin fins (CPFs) was studied. A cylindrical pin fin heat sink (CPFHS) with staggered fins was considered as the reference case. In the next stage, the heat sink with staggered solid-AECPFs (SAECPFs) was simulated, and its performance was compared with the reference case. The highest fin effectiveness obtained was 1.43 for the fin radius (r) to channel height (H) ratio (r/H) = 0.9. This structure was chosen as the base case, and in the third stage, its performance is improved by adding perforation on AECPFs. The influence of nine distinct perforation patterns of three different hole size were selected, and their thermal performance was analysed in detail. The highest fin effectiveness noted for the fins with 8 holes of 3 mm diameter is 2.25 at Re 3111. Furthermore, with the proposed perforated-AECPFHS (PAECPFHS) structure, in comparison to the reference case, the volume of the fins was lowered by as much as 60 %.

Evaluation of the Heat Transfer Performance of a Device Utilizing an Asymmetric Pulsating Heat Pipe Structure Based on Global and Local Analysis

PHPs (pulsating heat pipes) are widely used as an efficient heat transfer element in equipment thermal management and waste heat recovery due to their flexibility. The purpose of this study was to design a heat transfer device that utilizes an asymmetric pulsating heat pipe structure by adjusting the lengths of selected pipes within the entire circulation pipeline. In the experiment, a constant temperature water bath was used as the heat source, with heat dissipated in the condensing section via natural convection. An infrared thermal imager was used to record the temperature of the condensing section, and the local wall temperature distribution was measured in different channels of the condensing section. Based on an in-depth analysis of the wavelet frequency, the following research conclusions are drawn: Firstly, as the heat source temperature increases, the start-up time of the pulsating heat pipe is shortened, the operating state changes from start–stop–start to stable and continuous oscillation, and the oscillation mode changes from high amplitude and low frequency to low amplitude and high frequency. These changes are especially pronounced when the heat source temperature is 80 °C, which is when the thermal resistance reaches its lowest value of 0.0074 K/W, and the equivalent thermal conductivity reaches its highest value of 666.29 W/(m·K). Secondly, the flow and oscillation of the working fluid can be effectively promoted by appropriately shortening the length of the condensing section of the pulsating heat pipes or the heat transfer distance between the evaporation and condensing sections. Third, under a low-temperature heat source, the oscillation frequency of each channel of a pulsating heat pipe is found to be low based on wavelet analysis. However, as the heat source temperature increases, the energy content of the temperature signal of the working fluid in each channel changes from a low- to a high-frequency value, gradually converging to the same characteristic frequency. At this point, the working fluid in the pipes no longer flows randomly in multiple directions but rather in a single direction. Finally, we determined that the maximum oscillation frequency of working fluid in a PHP is around 0.7 HZ when using the water bath heating method.

Numerical and analytical investigation of vapor flows in a flat plate heat pipe: Effects of length ratio and Reynolds number

Heat pipes are crucial in a wide range of applications, ranging from space satellites and industrial systems to electronic cooling and X-ray tube thermal management. This study introduces a method investigation into vapor flows within a flat plate heat pipe, utilizing the collocation method (CM) and the fourth-order Runge-Kutta-Fehlberg (RKF45) method. Building on previous efforts, this work explores the effects of the evaporator-to-condenser length ratio and Reynolds number on velocity and pressure distributions along the entire heat pipe. The significance of this research lies in its ability to elucidate critical parameters that directly influence heat pipe performance, offering deeper insights that are vital for optimizing design and efficiency. The primary motivation of this study is to fill existing gaps in the literature by developing a comprehensive analytical model that accurately characterizes vapor and liquid flow in asymmetrical flat plate heat pipes. The model's validity is confirmed through a satisfactory agreement with numerical results, underscoring the reliability of the methods used. Notably, the findings reveal that higher Reynolds numbers reduce pressure drop and shift the maximum velocity toward the bottom wick in the evaporation section, providing valuable guidance for future design improvements. Additionally, this research presents a powerful method for solving non-linear ordinary differential equations, offering significant time savings and enabling predictive functions. These contributions are poised to enhance the performance of thermal management systems across various engineering disciplines.

Reconfigurable, zero-energy, and wide-temperature loss-assisted thermal nonreciprocal metamaterials

Thermal nonreciprocity plays a vital role in chip heat dissipation, energy-saving design, and high-temperature hyperthermia, typically realized through the use of advanced metamaterials with nonlinear, advective, spatiotemporal, or gradient properties. However, challenges such as fixed structural designs with limited adjustability, high energy consumption, and a narrow operational temperature range remain prevalent. Here, a systematic framework is introduced to achieve reconfigurable, zero-energy, and wide-temperature thermal nonreciprocity by transforming wasteful heat loss into a valuable regulatory tool. Vertical slabs composed of natural bulk materials enable asymmetric heat loss through natural convection, disrupting the inversion symmetry of thermal conduction. The reconfigurability of this system stems from the ability to modify heat loss by adjusting thermal conductivity, size, placement, and quantity of the slabs. Moreover, this structure allows for precise control of zero-energy thermal nonreciprocity across a broad temperature spectrum, utilizing solely environmental temperature gradients without additional energy consumption. This research presents a different approach to achieving nonreciprocity, broadening the potential for nonreciprocal devices such as thermal diodes and topological edge states, and inspiring further exploration of nonreciprocity in other loss-based systems.

Spectral characteristics of a rotating solar prominence in multiple wavelengths

We present synthetic spectra corresponding to a 2.5D magnetohydrodynamic simulation of a rotating prominence in the k Ly alpha , and Ly beta lines. The prominence rotation resulted from angular momentum conservation within a flux rope where asymmetric heating imposed a net rotation prior to the thermal-instability-driven condensation phase. The spectra were created using a library built on the framework called which provides boundary conditions for incorporating the limb-darkened irradiation of the solar disk on isolated structures such as prominences. Our spectra show distinctive rotational signatures for the k Ly alpha , and Ly beta lines, even in the presence of complex, turbulent solar atmospheric conditions. However, these signals are barely detectable for the and spectral lines. Most notably, we find only a very faint rotational signal in the line, thus reigniting the discussion on the existence of sustained rotation in prominences.

Design and experimental analysis of a novel thermal diode with asymmetric heat transfer inspired by feather

To overcome the limitation of isotropic heat transfer of traditional heat pipes, a novel thermal diode with asymmetric flow resistance vapor channel inspired by the goose feather fibers is proposed in this study. The thermal performance of novel thermal diode is experimentally investigated. Results show that under the wide range of operating conditions, the thermal resistance of one end surpasses the thermal resistance of the other end, indicating its excellent thermal rectification capability. Under the filling ratio of 10 % and heating power of 7.5 W, the maximum thermal resistance of the thermal diode is 5.23 times the minimum thermal resistance, demonstrating excellent asymmetric heat transfer performance. Experimental results demonstrate that the novel thermal diode proposed in this study can easily change its unidirectional heat transfer direction by simply adjusting the internal filling ratio, showing significant application potential in the fields of thermal control system.

Investigating asymmetric mass and heat transfer in the calendering of modified double-base propellants

To improve the plasticization quality and process safety of Modified Double-Base (MDB) propellants during the calendering process. This study, using actual physical parameters of MDB propellant, a three-dimensional thermo-fluid coupled model was developed to investigate the effects of process parameters on the heat and mass transfer behavior of MDB materials during the calendering process. By comparing the effects of different roller speed ratios, roller gaps, and roller speeds on the material's velocity, temperature, and viscosity distribution during the calendering process, it was found that the material forms an asymmetric vortex reflux movement during the calendering process. This unique flow characteristic is the primary reason for the material's asymmetric mass and heat transfer properties. Changes in the rotational speed ratio have a minor impact on the reflux movement but significantly affect process safety. A rotational speed ratio of 1.25 can effectively reduce the temperature of the material at the vortex center, thereby decreasing the risk of combustion. The smaller the roll gap, the higher the starting position of the material reflux. By selecting a roll gap of 0.8 mm, it's possible to effectively reduce the viscosity gradient while simultaneously decreasing the material's residence time. Increasing the rotation speed enhances the intensity of reflux. A speed setting of 20:15 not only reduces heat generated from shearing but also controls the temperature distribution range of the material, thereby enhancing the efficiency of the calendering production process. These adjustments in process parameters enhanced the safety and production efficiency of the MDB propellant calendering process, providing valuable insights for the safe production of MDB propellant calendering technology.

A Chimera method for thermal part-scale metal additive manufacturing simulation

This paper presents a Chimera approach for the thermal problems in welding and metallic Additive Manufacturing (AM). In particular, a moving mesh is attached to the moving heat source while a fixed background mesh covers the rest of the computational domain. The thermal field of the moving mesh is solved in the heat source reference frame. The chosen framework to couple the solutions on both meshes is a non-overlapping Domain Decomposition (DD) with Neumann–Dirichlet transmission conditions.Increased steadiness and accuracy within the vicinity of the Heat Affected Zone (HAZ) are the main advantages of this approach. The steadiness gain allows for the use of larger time steps, which is vital in AM applications and, in particular, Laser Powder Bed Fusion (LPBF), where the disparity of time scales represents a major hurdle. Moreover, enhanced accuracy can be observed in the resulting morphology of the melt pool. It will be shown that the method addresses classical shortcomings pointed out by Goldak without requiring the use of an asymmetrical heat source profile.

Flow and heat transfer characteristics and comprehensive evaluation of asymmetric plate heat exchangers for centralized heat supply

The structure of flow channel on both sides of the conventional plate heat exchanger(CPHE) is symmetrical. CPHEs are struggle to perform efficiently when subjected to asymmetric working conditions in district heating system. In order to improve the performance of plate heat exchangers under asymmetric conditions, asymmetric plate heat exchangers(APHEs) was designed. In this paper, APHEs were parameterized by asymmetric factor a. An evaluation index η for APHE is introduced to quantitatively analyze APHE’s suitability in district heating system. Numerical simulations were performed to investigate the heat transfer characteristics and resistance characteristics of the APHEs with 11 asymmetric factors a. Through using η, APHEs with the best comprehensive performance were found, when the flow ratio is 1.50, 1.75, 2.00, 2.25, 2.50 and 2.75. In flow ratio, APHEs provide the comprehensive performances with an improvements of 28 %, 39 %, 54 %, 65 %, 72 % and 83 % compared with CPHEs. Correlations equation for the average Nu and f on both hot and cold sides of the APHEs were established. There exists a correlation between Nu and f for the APHEs with respect to asymmetry factor a and flow ratio.

A Study of Asymmetric Hyperbolic Heat Storage Unit

ABSTRACTDue to the advantages of high energy density and constant temperature, phase change energy storage technology has attracted much attention in energy saving and efficient utilization of energy. In this paper, Fluent software is used to simulate and analyze the heat storage characteristics of six new thermal storage units: corrugated tube, hyperbolic‐shape, non‐hyperbolic‐shape, symmetric frustum‐shape, non‐frustum‐shape, and bow‐shape. The results show that the melting rate of the non‐hyperbolic‐shape phase change unit is significantly higher than that of the circular tube, the heat storage time is shortened by 22.52%, and Ra* reaches 0.0086. Second, the effects of the radius difference (δ) between the inlet and outlet of the non‐hyperbolic‐shape phase change unit and the asymmetric position (s) on the heat storage process are studied. The results show that when δ increases from 2 to 10 mm, the melting time of phase change material (PCM) is shortened by 22.89%, that is, the average heat transfer rate between PCM and heat transfer fluid increases with the increase of δ. On the other hand, the average heat storage rate of the heat storage unit decreases first and then increases with the increase of s. When δ = 10 mm, s = 35 mm is the best working condition, the average heat storage rate of the non‐hyperbolic‐shape thermal storage unit reaches 34.3 J/s. This study can provide new ideas and references for the optimization design of latent heat storage units and the progress of experiments.

China coasts facing more tropical cyclone risks during the second decaying summer of double-year La Niña events

Long-lasting La Niña events (including double-year and triple-year La Niña events) have become more frequent in recent years. How the multi-year La Niña events affect tropical cyclone (TC) activities in the western North Pacific (WNP) and whether they differ from single-year La Niña events are unknown. Here we show that TCs are more active over the far-WNP (FWNP, 110°–150°E), leading to marked high risks at China coasts during the second decaying summer of double-year La Niña events. The anomalous TC activities are directly related to the enhanced cyclonic anomaly over the FWNP, possibly a result of large-scale remote forcing initiated by the tropical North Atlantic (TNA) cooling. The persistent TNA cooling from the decaying winter to summer of double-year La Niña events drives westerlies over the Indo-western Pacific through Kelvin waves, which induce the cooling over the north Indian Ocean via the wind-evaporation-sea surface temperature effect, favoring the asymmetric heat distribution pattern and stimulating an anomalous vertical circulation over the eastern Indian Ocean to FWNP. The cooling over the north Indian Ocean also excites Gill responses, magnifying the TNA-induced westerlies and boosting the anomalous vertical circulation, and thus gives rise to the strong cyclonic circulation anomaly over the FWNP in summer. We suggest that the key point of the process is the strong TNA cooling related to the persistent negative Pacific-North American pattern (PNA) and positive North Atlantic Oscillation (NAO) while double-year La Niña events decay, distinct from the rapid decline of PNA and NAO during single-year La Niña events. The work provides a unique perspective on understanding TC activities over the WNP related to the El Niño-Southern Oscillation.

Thermal entrance solution for parallel plates with asymmetric arbitrary wall heat flux

Thermal entrance solution for parallel plates with asymmetric arbitrary wall heat flux

Heat transfer and entropy generation in viscous-joule heating MHD microchannels flow under asymmetric heating

PurposeThis paper aims to present a numerical investigation into heat transfer and entropy generation resulting from magnetohydrodynamic laminar flow through a microchannel under asymmetric boundary conditions. Furthermore, the authors consider the effects of viscous dissipation and Joule heating.Design/methodology/approachThe finite difference method is used to obtain the numerical solution. Simulations are conducted across a broad range of Hartmann (Ha = 0 ∼ 40) and Brinkman (Br = 0.01 ∼ 1) numbers, along with various asymmetric isothermal boundaries characterized by a heating ratio denoted as ϕ.FindingsThe findings indicate a significant increase in the Nusselt number with increasing Hartmann number, regardless of whether Br equals zero or not. In addition, it is demonstrated that temperature differences between the microchannel walls can lead to substantial distortions in fluid temperature distribution and heat transfer. The results reveal that the maximum entropy generation occurs at the highest values of Ha and η (a dimensionless parameter emerging from the formulation) obtained for ϕ = −1. Moreover, it is observed that local entropy generation rates are highest near the channel wall at the entrance region.Originality/valueThe study provides valuable insights into the complex interactions between magnetic fields, viscous dissipation and Joule heating in microchannel flows, particularly under asymmetric heating conditions. This contributes to a better understanding of heat transfer and entropy generation in advanced microfluidic systems, which is essential for optimizing their design and performance.