Thermally Coupled Research Articles

Very high-order accurate polygonal mesh finite volume scheme for conjugate heat transfer problems with curved interfaces and imperfect contacts

The conjugate heat transfer problem is found in non-isothermal physical systems that involve thermodynamic processes between materials that are thermally coupled through non-adiabatic contacts. A very high-order accurate finite volume scheme in general polygonal meshes is proposed to solve conjugate heat transfer problems with arbitrary curved interfaces and imperfect thermal contacts. Besides the discontinuous thermal properties, imperfect thermal contacts are challenging to address since the obtained temperature is also discontinuous on the interface as a consequence of the interfacial thermal resistance. Moreover, the arbitrary curved interfaces are discretized with polygonal meshes to avoid the shortcomings of classical curved mesh approaches, but a specific treatment is required to overcome the geometrical mismatch and properly fulfill the prescribed interface conditions. The proposed method is based on a partitioned formulation of the conjugate heat transfer problem with the appropriate thermal coupling. A generic polynomial reconstruction method is used to provide local approximations of the temperature complemented with the reconstruction for off-site data method to properly fulfill the prescribed interface conditions. A comprehensive numerical benchmark is provided to verify the proposed method and assess its capability in terms of accuracy, convergence order, stability, and robustness. The results provide the optimal very high-order of convergence and prove the capability of the method to handle arbitrary curved interfaces and imperfect thermal contacts. This contribution represents a significant step towards more efficient and versatile numerical methods for complex conjugate heat transfer problems in engineering applications.

Thermally coupled SHS processes in layered (Fe2O3 + 2Al)/(Ti + Al)/(Fe2O3 + 2Al) structures: An experimental study

TiAl intermetallic was prepared through thermal coupling of highly exothermic Fe2O3–Al reaction (donor) and low-caloric Ti–Al reaction (acceptor). Green compacts represented three-layer ‘donor–acceptor–donor’ sandwich-type structures. The combustion process was video taped and combustion temperatures in the bulk of donor and acceptor layers and at the interfaces were monitored with a set of thermocouples. The results of video filming and thermocouple measurements allowed us to establish which mode of thermally coupled SHS reaction took place in our conditions. The combustion product was found to contain the TiAl intermetallic with small admixture of Ti3Al and unreacted Al.

Synthesis of simultaneously heat integrated and thermally coupled nonsharp distillation sequences based on stochastic optimization

Synthesizing simultaneously heat integrated and thermally coupled distillation sequences (HITCDSs) is a complex combinatorial optimization problem and it is difficult to solve this problem, especially when considering nonsharp splits. Based on stochastic optimization, we propose an efficient approach to synthesize nonsharp HITCDSs. First, an implicit mathematical formulation for the HITCDS optimization is presented. Next, encoding strategies are used tactfully to represent HITCDS structures and evolving rules are developed to generate neighboring HITCDS structures. Finally, simultaneously optimizing the distillation sequences, thermal coupling structures, heat integrated networks, and operating parameters of the columns is easily attained through an improved simulated annealing algorithm. Three cases are studied to validate the high solution efficiency of the approach. The optimization results show that nonsharp HITCDSs are more energy efficient than the sharp ones. Besides, HITCDSs have lower total annual cost than conventional distillation configurations, configurations only employing heat integration, and configurations only employing thermal coupling.

Thermal coupling opportunities for floating natural gas liquefaction plants

In order to meet current carbon dioxide emissions reduction challenges, natural gas processing and refining industries have to find new ways to minimize energy requirements. Building on foundations laid down in a preceding effort, this paper shows that this could be achieved in a cost-effective way for the distillation section in natural gas liquids fractionation plants. A conventional demethanizer column, combined with either a thermally coupled direct sequence of deethanizer and propane–butane recovery columns or a dividing wall column, produces significant savings in capital and hot utilities costs as compared to conventional distillation with a direct sequence, without any temperature penalty on cold utilities side. The choice between available options will largely depend on important process considerations that may differ for offshore and onshore plants and specific site requirements.

Exergy valorization of a water electrolyzer and CO2 hydrogenation tandem system for hydrogen and methane production

In this work, we introduce a water electrolysis and CO2 hydrogenation tandem system which focuses on methane generation. The concept consists of a water electrolyzer thermally coupled to a CO2 hydrogenation reactor, where the power required to generate hydrogen comes from renewable energy. A thermodynamic analysis of the tandem system was carried out. Our analysis exposes that it is possible to increase the exergy efficiency of the water electrolyzer and CO2 hydrogenation system by thermal coupling, where the thermal energy required to split water into H2 and O2 during the electrolysis process is compensated by the heat generated during the CO2 hydrogenation reaction. Here, the conditions at which high exergy efficiency can be achieved were identified.

Process intensification in multicomponent distillation: A review of recent advancements

Process intensification (PI) is an emerging concept in chemical engineering that describes the design innovations that lead to significant shrinkage in size and boost in efficiency of a process plant. Distillation, the most commonly used separation technique in the chemical industry, is a crucial component of PI. Here, we systematically discuss the following aspects of PI in non-azeotropic multicomponent distillation: (1) Introducing thermal couplings to eliminate intermediate reboilers and condensers to save energy and capital cost; (2) Improving operability of thermally coupled columns by means of eliminating vapor streams in thermal couplings with only liquid transfers or column section rearrangement; (3) Enabling double and multi-effect distillation of thermally coupled configurations to further reduce heat duty; (4) Performing simultaneous heat and mass integration among thermally coupled columns to reduce the number of columns and heat duty; and (5) Conducting any thermally coupled distillation in n-product streams using 1 to n−2 column shells with operable novel dividing wall columns. We demonstrate these aspects of PI through examples to illustrate how they lead to compact, easy-to-operate, energy efficient and cost effective multicomponent distillation system designs.

Anti-parity-time symmetry in diffusive systems.

Various concepts related to parity-time symmetry, including anti-parity-time symmetry, have found broad applications in wave physics. Wave systems are fundamentally described by Hermitian operators, whereas their unusual properties are introduced by incorporation of gain and loss. We propose that the related physics need not be restricted to wave dynamics, and we consider systems described by diffusive dynamics. We study the heat transfer in two countermoving media and show that this system exhibits anti-parity-time symmetry. The spontaneous symmetry breaking results in a phase transition from motionless temperature profiles, despite the mechanical motion of the background, to moving temperature profiles. Our results extend the concepts of parity-time symmetry beyond wave physics and may offer opportunities to manipulate heat and mass transport.

Making heat stand still

Physics Dissipative oscillating systems (waves) can be described mathematically in terms of non-Hermitian physics. When parity-time symmetric systems have dissipative components, the interplay between gain and loss can lead to unusual and exotic behavior. Li et al. show theoretically and demonstrate experimentally that such behavior need not be limited to wave systems. Looking at the diffusion of heat, they devised an experimental setup comprising two thermally coupled disks rotating in opposite directions. The thermal energy transported by each disk is strongly coupled to the disk rotating in the opposite direction, providing a return path for the heat wave. For a particular rotation rate, there is an exceptional point where thermal coupling and counterrotating motion balance, resulting in the thermal energy profile being stationary over time. Science , this issue p. [170][1] [1]: /lookup/doi/10.1126/science.aaw6259

Conceptual comparison of four configurations in the thermal coupling of ammonia synthesis and 2-butanol dehydrogenation

In this study, simultaneous production of ammonia and methyl ethyl ketone (MEK) based on thermal coupling idea is analyzed in four different configurations by considering various feeding modes. Ammonia synthesis, as the exothermic reaction, performs in the inner tube of the proposed thermally coupled reactor, while MEK and hydrogen are produced by the endothermic dehydrogenation reaction of 2-butanol in the outer tube. As a result of heat transfer between tubes, inter-stage coolers and furnace which were required for the ammonia synthesis and 2-butanol dehydrogenation plants are eliminated, respectively. Besides, the produced hydrogen is employed to supply 60.91%, 62.89%, 63.49%, and 64.19% of the required hydrogen for ammonia synthesis in each configuration. Therefore, a significant decrease in capital and operational costs as well as energy saving and removing furnace emissions like CO, CO2, and NOx are achieved. Based on the simulation results, series feeding on the ammonia synthesis and parallel feeding on the 2-butanol dehydrogenation showed the maximum nitrogen conversion, ammonia production and yield, while series-series feeding resulted in the best performance from the 2-butanol conversion, MEK production, and yield viewpoint. Finally, the two aforementioned configurations were optimized by applying the multi-objective optimization method.

Hydraulic Design of Thermally Coupled Columns and a DWC for NGL Fractionation Plants

Combining a conventional demethanizer with thermally coupled deethanizer and propane-butane recovery columns or a three-product dividing wall column (DWC) provides a realistic opportunity for natural gas liquids (NGL) fractionation complexes as encountered in floating, as well as on-land natural gas liquefaction plants, to minimize energy requirements and reduce carbon dioxide emissions accordingly, in a cost-effective way. The present paper addresses and discusses hydraulic design aspects of these two thermal coupling arrangements, including the choice of the most appropriate column internals that largely depends on important design, construction, and operating considerations that differ for floating and on-land plants.

Comparison of co-current and counter-current flow in a bifunctional reactor containing ammonia synthesis and 2-butanol dehydrogenation to MEK

In this study, a multi-tubular thermally coupled packed bed reactor in which simultaneous production of ammonia and methyl ethyl ketone (MEK) takes place is simulated. The simulation results are presented in two co-current and counter-current flow modes. Based on this new configuration, the released heat from the ammonia synthesis reaction as an extremely exothermic reaction in the inner tube is employed to supply the required heat for the endothermic 2-butanol dehydrogenation reaction in the outer tube. On the other hand, MEK and hydrogen are produced by the dehydrogenation reaction of 2-butanol in the endothermic side, and the produced hydrogen is used to supply a part of the ammonia synthesis feed in the exothermic side. Thus, 30.72% and 31.88% of the required hydrogen for the ammonia synthesis are provided by the dehydrogenation reaction in the co-current and counter-current configurations, respectively. Also, according to the thermal coupling, the required cooler and furnace for the ammonia synthesis and 2-butanol dehydrogenation conventional plants are eliminated, respectively. As a result, operational costs, energy consumption and furnace emissions are considerably decreased. Finally, a sensitivity analysis and optimization are applied to study the effect of the main process parameters variation on the system performance and obtain the minimum hydrogen make-up flow rate, respectively.

Optical thermometry based on cooperation of temperature-induced shift of charge transfer band edge and thermal coupling.

A novel optical thermometry is put forward, based on the cooperation of temperature-induced red shift of the charge transfer band (CTB) edge of the vanadates and thermal population of the thermally coupled energy levels (TCELs). Particularly, temperature-dependent CTB of Sm3+ (Er3+) doped LuVO4 was investigated from 300 to 480 K. Then, under the excitation of 360 nm at which the excitation efficiency enhances with temperature due to the temperature induced red shift of the CTB edge, temperature-dependent emissions of the TCELs of Sm3+ and Er3+ were investigated. The results indicate that the emission from the upper-level in the TCELs exhibits a dramatic increase, along with the increase of temperature. High relative sensitivity of 4304/T2 was obtained, which is remarkably superior to the previous reported sensors, using the temperature-dependent fluorescence intensity ratio of TCELs. This suggests that the proposed strategy is a promising candidate for highly sensitive optical thermometry.

Chebyshev Spectral Collocation Method Approximation to Thermally Coupled MHD Equations

In this study, a Chebyshev spectral collocation method (CSCM) approximation is proposed for solving the full magnetohydrodynamics (MHD) equations coupled with energy equation. The MHD flow is two-dimensional, unsteady, laminar and incompressible, and the heat transfer is considered using the Boussinesq approximation for thermal coupling. The flow takes place in a square cavity which is subjected to a vertically applied external magnetic field, and the presence of the induced magnetic field is also taken into account due to the electrical conductivity of the fluid. The governing equations given in terms of stream function, vorticity, temperature, magnetic stream function, and current density, are solved iteratively using CSCM for the spatial discretisation, and an unconditionally stable backward difference scheme for the time integration. The induced magnetic field is obtained by means of its relation to the magnetic stream function. The behaviours of the flow and the heat transfer are investigated for varying values of Reynolds ($Re$), magnetic Reynolds ($Rem$), Rayleigh ($Ra$) and Hartmann ($Ha$) numbers.

Minimum energy of multicomponent distillation systems using minimum additional heat and mass integration sections

Heat and mass integration to consolidate distillation columns in a multicomponent distillation configuration can lead to a number of new energy efficient and cost‐effective configurations. In this work, a powerful and simple‐to‐use fact about heat and mass integration is identified. The newly developed heat and mass integrated configurations, which we call as HMP configurations, involve first introducing thermal couplings to all intermediate transfer streams, followed by consolidating columns associated with a lighter pure product reboiler and a heavier pure product condenser. A systematic method of enumerating all HMP configurations is introduced. The energy savings of HMP configurations is compared with the well‐known fully thermally coupled (FTC) configurations. HMP configurations can have very similar and sometimes even the same minimum total vapor duty requirement as the FTC configuration is demonstrated, while using far less number of column sections, intermediate transfer streams, and thermal couplings than the FTC configurations. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3410–3418, 2018

The effect of lateral thermal coupling between parallel microchannels on two-phase flow distribution

Evaporating flows in parallel channels occurring in a variety of industrial heat exchange processes can encounter non-uniform flow distribution between channels as a result of two-phase flow instabilities. Such flow maldistribution can have a negative impact on the performance, robustness and predictability of these systems. Two-phase flow modeling can assist in understanding the mechanistic behavior of this flow maldistribution, as well as determine parametric trends and identify safe operating conditions.The work described in this paper expands on prior two-phase flow distribution modeling efforts by including and assessing the effect of thermal conduction in the walls surrounding the parallel channels. This thermal conduction has a critical dampening effect on wall temperature gradients. In particular when a channel is significantly starved of flow rate and risks dryout, channel-to-channel thermal coupling can redistribute the heat load from the flow-starved channel to neighboring channels. The model is used to simulate the two-phase flow distribution in a system of two parallel channels driven by a constant flow rate pump. A comparison between thermally isolated and coupled channels indicates that thermally coupled channels are significantly less susceptible to maldistribution. Furthermore, a parametric study reveals that flow maldistribution is only possible in thermally coupled systems beyond a certain critical heat flux threshold. This threshold heat flux increases as the lateral wall conductance is increased, converging to a constant value in the limit of very high lateral conductance.

Thermal coupling and effect of subharmonic synchronization in a system of two VO2 based oscillators

We explore a prototype of an oscillatory neural network (ONN) based on vanadium dioxide switching devices. The model system under study represents two oscillators based on thermally coupled VO2 switches. Numerical simulation shows that the effective action radius RTC of coupling depends both on the total energy released during switching and on the average power. It is experimentally and numerically proved that the temperature change ΔT commences almost synchronously with the released power peak and T-coupling reveals itself up to a frequency of about 10 kHz. For the studied switching structure configuration, the RTC value varies over a wide range from 4 to 45 μm, depending on the external circuit capacitance C and resistance Ri, but the variation of Ri is more promising from the practical viewpoint. In the case of a “weak” coupling, synchronization is accompanied by attraction effect and decrease of the main spectra harmonics width. In the case of a “strong” coupling, the number of effects increases, synchronization can occur on subharmonics resulting in multilevel stable synchronization of two oscillators. An advanced algorithm for synchronization efficiency and subharmonic ratio calculation is proposed. It is shown that of the two oscillators the leading one is that with a higher main frequency, and, in addition, the frequency stabilization effect is observed. Also, in the case of a strong thermal coupling, the limit of the supply current parameters, for which the oscillations exist, expands by ∼10%. The obtained results have a universal character and open up a new kind of coupling in ONNs, namely, T-coupling, which allows for easy transition from 2D to 3D integration. The effect of subharmonic synchronization hold promise for application in classification and pattern recognition.

Towards ultra-high sensitive colorimetric nanothermometry: Constructing thermal coupling channel for electronically independent levels

Accurate intracellular thermal reading calls for luminescent nanothermometer with high temperature sensitivity in biological temperature region. Fluorescence intensity ratio method based on the conventional thermally coupled levels pair has been widely applied to thermal sensing. However, the narrow energy spacing between the thermally coupled levels, which is subject to the Boltzmann population distribution rule, leads to low relative temperature sensitivity in biological temperature region as well as inferior signal discriminability. By constructing thermal coupling channel for electronically independent levels, the restriction for narrow energy spacing could be broken by applying thermal coupling mechanisms unbound to Boltzmann population distribution rule. Herein, we show for the first time that the green 2H11/2 and 4S3/2 emitting states of Er3+ can be thermally coupled with the red 4F9/2 emitting one via the 4T1 state of Mn2+, through a distance-sensitive exchange interaction between Er3+ and Mn2+ in KMnF3 where lattice thermal expansion plays a vital role. As a consequence, a promising colorimetric up-conversion luminescent nanothermometer working in the biological temperature region (303K–343K) with ultra-high sensitivity and excellent signal discriminability is achieved. This work provides a novel route for designing delicate luminescent nanothermometer applicable in intracellular thermal sensing and imaging.

Active thermal-electronic devices based on heat-sensitive metal-insulator-transition resistor elements

New active thermal-electronic device family is proposed. These devices operate by means of thermal (or hot electron) coupling between adjacent domains containing heating (input) and thermally sensitive (output) elements. The theoretical background, basic equations and comparison with the conventional electron devices are the main subject of this work. According to the theoretical assumptions the realization of the thermal-electronic device needs a very sensitive output element i.e. temperature sensor. Among others, the metal-insulator transition (MIT) based resistor fulfills this requirement. The MIT resistor itself has got thyristor-like I–V characteristics due to solely the high electric field, or Joule heating induced extremely strong step-like resistance drop at a given temperature. Using thermally coupled MIT and/or other resistors it is possible to build a special device, namely phonsistor (=phonon transistor). This device consists of only bulk type intrinsic domains, containing significantly fewer regions, junctions, depleted layers, surfaces and interfaces compared to conventional electron devices. Thus, these devices can be integrated together with each other and with conventional CMOS, forming, for example, thermal-electronic logic circuit (TELC) for the More-Than-Moore concept devices.

Parallel plates reactor simulation: Ethanol steam reforming thermally coupled with ethanol combustion

This work presents a theoretical study on the thermal coupling of ethanol steam reforming with ethanol combustion in a parallel plates reactor. A one-dimensional, heterogeneous, mathematical model is used and the effects of the main operative and constructive variables on the performance of the system are analyzed. Thermal coupling between combustion and reforming of ethanol is plausible and an adequate behavior of the reactor in terms of hydrogen yield and conversion of ethanol is predicted. The importance of distributing the source of heat is evidenced since high molar fractions of ethanol in the combustion stream can lead to excessive hot spots.

Note: A wide temperature range MOKE system with annealing capability.

A novel sample stage integrated with a longitudinal MOKE system has been developed for wide temperature range measurements and annealing capabilities in the temperature range 65 K < T < 760 K. The sample stage incorporates a removable platen and copper block with inserted cartridge heater and two thermocouple sensors. It is supported and thermally coupled to a cold finger with two sapphire bars. The sapphire based thermal coupling enables the system to perform at higher temperatures without adversely affecting the cryostat and minimizes thermal drift in position. In this system the hysteresis loops of magnetic samples can be measured simultaneously while annealing the sample in a magnetic field.