Current Heat Flow Research Articles

Local heat current flow in ballistic phonon transport of graphene nanoribbons

Local heat current flow in ballistic phonon transport of graphene nanoribbons

Multi-scale simulation and optimization on a thermal management system of intermediate circuit and experiment validation

In the system-level simulations of heat transfer systems, the characteristics of heat exchangers are often considered constant or used in empirical formulas, which affect the accuracy of the system model. Herein a multi-scale simulation method to analyze the heat transfer characteristics of a thermal management system, including an intermediate loop is proposed. The system model is developed based on the heat current method and flow resistance models. By applying COMSOL LiveLink for MATLAB module, a multi-scale model is obtained, which combines three-dimensional numerical models of the heat exchangers with the system model. Compared to the experimental results, the relative errors associated with the outlet temperatures and heat transfer rate are less than 1.1% and 8.2 %, respectively, thus validating the model. Discussions on the effects of the geometric structure of the heat exchangers on the system show that a plate heat exchanger with 12 plates and a plate spacing of 8 mm is better. For achieving systematic maximum heat dissipation for a certain pumping power consumption, a multi-scale optimization method is proposed by coupling the Lagrange function and numerical model. The results show that the total heat transfer rate improves by 5.89 %, from 8314.81 W to 8804.35 W.

Jan Mayen Microcontinent Composite Tectono-Sedimentary Element and Jan Mayen Prograded Margin Tectono-Sedimentary Element, Greenland Sea

The Jan Mayen Micro-Continent (JMMC) is the result of two Cainozoic phases of continental breakup, and subsequent seafloor spreading. The first established a spreading ridge system consisting of the Reykjanes, Ægir, and Mohn spreading ridges between Norway and Greenland in early Eocene. The second phase established the Kolbeinsey Ridge in Oligocene/Miocene separating the JMMC form Greenland. Two major stratigraphic elements are established accordingly, the Jan Mayen Micro-Continent Composite Tectono-Sedimentary Element (JMMC CTSE) for the Middle Devonian to Miocene succession, and the Jan Mayen Prograded Margin Tectono-Sedimentary Element (JMPM TSE) for the Miocene to Holocene succession. OBS refraction data show that the JMMC is underlain by a generally thickened crust. Plate reconstructions show that this crust most likely is a remnant of continental crust rifted off East Greenland, and thereby, consist of rocks that correlates with the Late Palaeozoic and Mesozoic strata stratigraphy of the conjugate margins of East Greenland and Norway known to be hydrocarbon. The arrival of the Iceland hot spot and the breakup magmatism greatly influenced the historic and current heat flow. Published maturation models and play analysis, show that there is a potential for oil and gas in the Jan Mayen Ridge within the JMMC.

Cenozoic tectono-thermal evolution of the Weihe Basin, Central China

ABSTRACT As a passive rift basin in the Cenozoic, the formation and evolution process of the Weihe Basin has not been well explained. Here we estimate the stretching factor and basal heat flow for each rift period along four geological profiles using a 2D multi-stage finite extension model. The modelling is based on a reconstruction of pre-rift crustal and lithospheric thicknesses, and is calibrated with the current heat flow. The Xi’an Depression had the biggest stretching factor while the Pucheng Uplift had the smallest throughout the Cenozoic period, which saw a range of stretching factors from 1.02 to 2.06. The basal heat flow in the Weihe Basin exhibits a corresponding change. At the end of the Oligocene, Miocene, and Pliocene periods, the basal heat flow varied between 58.5 ~ 64.0 mW·m−2, 59.2 ~ 67.0 mW·m−2, and 59.6 ~ 78.7 mW·m−2, respectively. Increasing stretching factor and basal heat flow indicate that the Weihe Basin is currently in a state of sustained extension. The formation and development of the Weihe Basin are analysed in the context of larger tectonic changes, and it is considered that the Weihe Basin is controlled by pre-existing faults, and formed in a regional tectonic context of sliding and pulling apart first, and tensioning and lifting up later. Since the late Miocene (7.3 Ma), anomalously rapid subsidence has occurred, induced by a new phase of rifting and depth-related lithospheric extension. The thermal genesis of the geothermal system in the Weihe Basin is also thought to be closely related to the latest phase of extension.

Dynamic response of a thermal transistor to time-varying signals

Thermal transistor, the thermal analog of an electronic transistor, is one of the most important thermal devices for microscopic-scale heat manipulating. It is a three-terminal device, and the heat current flowing through two terminals can be largely controlled by the temperature of the third one. Dynamic response plays an important role in the application of electric devices and also thermal devices, which represents the devices’ ability to treat fast varying inputs. In this paper, we systematically study two typical dynamic responses of a thermal transistor, i.e., the response to a step-function input (a switching process) and the response to a square-wave input. The role of the length L of the control segment is carefully studied. It is revealed that when L is increased, the performance of the thermal transistor worsens badly. Both the relaxation time for the former process and the cutoff frequency for the latter one follow the power-law dependence on L quite well, which agrees with our analytical expectation. However, the detailed power exponents deviate from the expected values noticeably. This implies the violation of the conventional assumptions that we adopt.

Experiment and simulation on a thermal management scheme of intermediate circulation based on heat current method

With the increment of Mach number, the heat dissipation load of aeroengine increases significantly. Systematic thermal management has become an urgent problem to be solved. The intermediate cycle system is one of the widely used thermal management solutions. This paper builds an experiment platform of thermal management system of aeroengine including intermediate cycle to explore the influence of working condition on the systematic heat transportation. Water is selected as the working medium in the experiment. The experiment results show all the temperatures of working medium decrease with the flow rate increment of working medium in fuel oil circuit. The temperature of working medium flowing to the afterburner increases with the temperature increment of lube oil circuit1 and 2. But only the temperature of working medium flowing to the main combustor increases while the temperatures of lube oil circuit1 increase. At last, using heat current method and flow resistance model builds the systematic simulation model. The relative errors between the simulation and experimental values are all less than 5%. The simulation results show all the temperatures of working medium increase with the increment of fuel oil circuit temperature. The working medium temperature flowing to the afterburner and lube oil circuit2 increases with the flow rate increment of lube oil circuit3. It reveals the heat transfer principle of the intermediate circulation thermal system under different working states and provides a powerful guidance for the systematic analysis and design.

Superior power generation capacity of GeSn over Si demonstrated in cavity-free thermoelectric device architecture

The performance of a thermoelectric (TE) generator consisting of GeSn wire is experimentally found to be higher than that of a TE generator fabricated by Si wire. The TE generators are developed in a cavity-free architecture, where the wires are directly placed on the substrate without forming a cavity space underneath. In the cavity-free structure, the heat current flows perpendicularly to the substrate and the TE generator is driven by a steep temperature gradient established around the heater inlet. With an identical patterning design, the TE performance of both generators is characterized by varying lengths. The maximum Seebeck coefficient of the generator consisting of GeSn is −277 μV K−1 and that for the Si is −97 μV K−1. The GeSn-TE generator achieves a higher power factor of 31 μW· K−2· cm−1 than that of the Si-TE generator of 12 μW· K−2· cm−1. The maximum areal power density of the GeSn-TE generator is intrinsically higher than that of the Si-TE generator by approximately 2.5 to 6 times considering the wire thickness difference. The obtained results support the superiority of the GeSn-TE generator over the Si-TE generator.

Self-reliant cooling of ultracold atoms

A self-reliant quantum cooler without an external control is proposed. To understand the thermal transport properties of the quantum system interacting with the baths described by the grand canonical ensemble, a two-level system with a single energy transport channel and a two-level coupled system with multi-channels are established. By considering the temperature dependence of the chemical potentials of the ultracold atom baths, the steady-state heat flows, particle currents, and entropy productions of these systems are derived. Results show that a steady heat current flows against the thermal bias for a nonequilibrium system coupled with ultracold quantum gases and the cooling rate can be enhanced by quantum coherence.

Heat current flows across an interface in two-dimensional lattices.

Heat current J that flows through a few typical two-dimensional nonlinear lattices is systematically studied. Each lattice consists of two identical segments that are coupled by an interface with strength k_{int}. It is found that the two-universality-class scenario that is revealed in one-dimensional systems is still valid in the two-dimensional systems. Namely, J may follow k_{int} in two entirely different ways, depending on whether or not the interface potential energy decays to zero. We also study the dependence of J on lattice width N_{Y} and transverse interaction strength k_{Y}. Universal power-law decay or divergence is observed. Finally, we check the equipartition theorem in the systems since it is the basis of all our theoretical analyses. Surprisingly, it holds perfectly even at the interface where there is a finite temperature jump, which makes the system far from equilibrium. However, the equipartition of potential energy, which is observed in one-dimensional systems, is no longer satisfied due to the interaction between different dimensions.

TRANSFER OF HEAT AND HALL CURRENT EFFECTS ON PERISTALTIC FLOW OF A BINGHAM FLUID IN A CHANNEL

TRANSFER OF HEAT AND HALL CURRENT EFFECTS ON PERISTALTIC FLOW OF A BINGHAM FLUID IN A CHANNEL

Thermoelectric Model of the Cutting Process

Thermoelectric modeling is based on the profound physical analogy between heat conduction and current flow in various media. In developing the equivalent circuit, steady machining is assumed (constant spindle speed and cutter feed). That corresponds to a dc circuit. Since the current from a source is constant in any circuit conditions, a current source is used in the circuit, rather than an emf. The integral current source in the equivalent circuit corresponds to a set of thermal components. In this approach, the system consisting of the workpiece, the cutting insert, the tool holder, and the machine-tool housing may be regarded as an element in the block diagram of the thermodynamic control system for the turning of any material.

Dynamic Cooling Load Calculation of Heat Transfer through the Envelope for Cold Storage

The dynamic heat transfer method is adopted, the mathematical model of reaction coefficient method is established and programmed, and a very practical dynamic load engineering algorithm for the wall of cold storage is obtained, which will provide reliable basic data for the continuous automatic regulation and energy saving control of the whole system dynamic real-time load of the cold storage. The calculated heat flow is much smaller than the current heat flow calculated according to the code insulation, and the maximum heat flow is much smaller than the current heat flow calculated according to the code insulation. The method presented in this paper can also be applied to the design and check of the thickness of the insulation layer and the analysis of the wall condensation in the wall system of the cold storage.

Transport and Energetic Properties of a Ring of Interacting Spins Coupled to Heat Baths.

We study the heat and spin transport properties in a ring of interacting spins coupled to heat baths at different temperatures. We show that interactions, by inducing avoided crossings, can be a means to tune both the total heat current flowing between the ring and the baths, and the way it flows through the system. In particular, we recognize three regimes in which the heat current flows clockwise, counterclockwise, and in parallel. The temperature bias between the baths also induces a spin current within the ring, whose direction and magnitude can be tuned by the interaction. Lastly, we show how the ergotropy of the nonequilibrium steady state can increase significantly near the avoided crossings.

Phonon Angular Momentum Induced by the Temperature Gradient.

Phonon modes in crystals can have angular momenta in general. It nevertheless cancels in equilibrium when the time-reversal symmetry is preserved. In this Letter, we show that when a temperature gradient is applied and heat current flows in the crystal, the phonon distribution becomes off equilibrium, and a finite angular momentum is generated by the heat current. This mechanism is analogous to the Edelstein effect in electronic systems. This effect requires crystals with sufficiently low crystallographic symmetries, such as polar or chiral crystal structures. Because of the positive charges of the nuclei, this phonon angular momentum induces magnetization. In addition, when the crystal can freely rotate, this generated phonon angular momentum is converted to a rigid-body rotation of the crystal, due to the conservation of the total angular momentum. Furthermore, in metallic crystals, the phonon angular momentum will be partially converted into spin angular momentum of electrons.

Scaling property of the heat-current flows across a weak interface

We systematically study heat current $J$ that flows through a few one-dimensional nonlinear lattices, each of which consists of two identical segments that are coupled by a weak interface. Existing theoretical analyses expect that $J$ is generally proportional to the square of the interface strength when the temperature drop is fixed and small. However, we observe two completely different classes in our numerical simulations. One follows the original expectation. In the other class, however, $J$ follows a power-law decay with the strength and the detailed power exponent depends on the details of the lattices and the interface interaction. Further theoretical analyses reveal that in the former class the interface potential energy decays with the interface strength linearly, which is commonly observed. In the latter class, the interface potential energy approaches a constant that is independent of the interaction strength. The detailed power exponents are then well explained.

Coherence enhanced quantum metrology in a nonequilibrium optical molecule

We explore the quantum metrology in an optical molecular system coupled to two environments with different temperatures, using a quantum master equation beyond secular approximation. We discover that the steady-state coherence originating from and sustained by the nonequilibrium condition can enhance quantum metrology. We also study the quantitative measures of the nonequilibrium condition in terms of the curl flux, heat current and entropy production at the steady state. They are found to grow with temperature difference. However, an apparent paradox arises considering the contrary behaviors of the steady-state coherence and the nonequilibrium measures in relation to the inter-cavity coupling strength. This paradox is resolved by decomposing the heat current into a population part and a coherence part. Only the latter, the coherence part of the heat current, is tightly connected to the steady-state coherence and behaves similarly with respect to the inter-cavity coupling strength. Interestingly, the coherence part of the heat current flows from the low-temperature reservoir to the high-temperature reservoir, opposite to the direction of the population heat current. Our work offers a viable way to enhance quantum metrology for open quantum systems through steady-state coherence sustained by the nonequilibrium condition, which can be controlled and manipulated to maximize its utility. The potential applications go beyond quantum metrology and extend to areas such as device designing, quantum computation and quantum technology in general.

Crater relaxation on Titan aided by low thermal conductivity sand infill

Titan's few impact craters are currently many hundreds of meters shallower than the depths expected. Assuming these craters initially had depths equal to that of similar-size fresh craters on Ganymede and Callisto (moons of similar size, composition, and target lithology), then some process has shallowed them over time. Since nearly all of Titan's recognized craters are located within the arid equatorial sand seas of organic-rich dunes, where rain is infrequent, and atmospheric sedimentation is expected to be low, it has been suggested that aeolian infill plays a major role in shallowing the craters. Topographic relaxation at Titan's current heat flow was previously assumed to be an unimportant process on Titan due to its low surface temperature (94 K). However, our estimate of the thermal conductivity of Titan's organic-rich sand is remarkably low (0.025 W m−1 K−1), and when in thick deposits, will result in a thermal blanketing effect that can aid relaxation. Here, we simulate the relaxation of Titan's craters Afekan, Soi, and Sinlap including thermal effects of various amounts of sand inside and around Titan's craters. We find that the combination of aeolian infill and subsequent relaxation can produce the current crater depths in a geologically reasonable period of time using Titan's current heat flow. Instead of needing to fill completely the missing volume with 100% sand, only ∼62%, ∼71%, and ∼97%, of the volume need be sand at the current basal heat flux for Afekan, Soi, and Sinlap, respectively. We conclude that both processes are likely at work shallowing these craters, and this finding contributes to why Titan overall lacks impact craters in the arid equatorial regions.

Engineered carbon nanotubes reinforced polymer composites for enhanced thermoelectric performance

Thermoelectric materials have attracted great attention from researchers because of their unique ability to convert thermal energy to electrical energy and vice versa. Based on the coupled theory of transport between heat and electricity in metals, we have carried out finite element simulations on carbon nanotube (CNT)/polyaniline (PANI) composites to compute effective Seebeck coefficients and figures of merit (FOMs). The present study focuses on the effect of interfacial electrical and thermal conductivities, the volume fraction of CNTs and their inclination on the effective electrical and thermal conductivities and thermoelectric performance. It is interesting to report that effective conductivities strongly depend on interfacial conductance in composites where CNTs are transverse to electrical current and heat flow. Interfaces with electrical and thermal conductance less than 103 S m−2 and 107 W m−2 K−1 respectively isolate CNTs from the matrix. This reduces the effective properties, while the conductivities increase with the CNT content if interfacial conductance is more than these specified values. It was also established that the effective Seebeck coefficient and FOM increase with interfacial electrical conductance, while decreasing with an increase in interfacial thermal conductance. Additionally, the effect of inclination on the electrical and thermal conductivities of composites, the effective Seebeck coefficient and the FOM were analysed. It can be concluded from the study that the Seebeck coefficient and FOM of thermoelectric composites are increased if the CNTs are lying perpendicular to the heat and electrical current flow.

Peridynamic Formulation for Coupled Thermoelectric Phenomena

Modeling of heat and electrical current flow simultaneously in thermoelectric convertor using classical theories do not consider the influence of defects in the material. This is because traditional methods are developed based on partial differential equations (PDEs) and lead to infinite fluxes at the discontinuities. The usual way of solving such PDEs is by using numerical technique, like Finite Element Method (FEM). Although FEM is robust and versatile, it is not suitable to model evolving discontinuities. To avoid such shortcomings, we propose the concept of peridynamic theory to derive the balance of energy and charge equations in the coupled thermoelectric phenomena. Therefore, this paper presents the transport of heat and charge in thermoelectric material in the framework of peridynamic (PD) theory. To illustrate the reliability of the PD formulation, numerical examples are presented and results are compared with those from literature, analytical solutions, or finite element solutions.

Bond Based Peridynamic Formulation for Thermoelectric Materials

Modeling of heat and electrical current flow simultaneously in thermoelectric convertor using classical theories do not consider the influence of defects in the material. This is because traditional methods are developed based on partial differential equations (PDEs) and lead to infinite fluxes and stress fields at the crack tips. The usual way of solving such PDEs is by using numerical technique, like Finite Element Method (FEM). Although FEM is robust and versatile, it is not suitable to model evolving discontinuities since discontinuous fields are mathematically singular at the crack tip and required an external criterion for the prediction of crack growth. In this paper, we follow the concept of peridynamic (PD) theory to overcome the shortcomings above. Therefore, the main aim of this paper is to develop the peridynamic equations for the generalized Fourier’s and Ohm’s laws. Furthermore, we derived the peridynamic equations for the conservation of energy and charge for the coupled thermoelectric phenomena.