Parallel Heat Research Articles

Numerical study of divertor detachment in TCV H-mode scenarios

The effect of divertor closure and nitrogen seeding on the detachment process has been studied by performing 2D numerical simulations of tokamak à configuration variable (TCV) H-mode divertor scenarios with the SOLEDGE3X-EIRENE edge plasma transport code. The simulations reveal that, in the cases with only deuterium gas fuelling, detachment occurs at a similar level of divertor neutral pressure (0.76 Pa), despite the difference in divertor closure achieved by changing the length of the outer baffle. Nitrogen reduces the target temperature with little effect on the upstream density and momentum loss but drops the upstream pressure, leading to a decrease in the target particle flux and divertor neutral pressure. Furthermore, when the radiation front starts to move up from the outer target, the peak parallel heat flux level at the outer target remains approximately the same ( MW m−2), regardless of whether it is a deuterium fuelling scan, a nitrogen seeding scan at a fixed fuelling rate, or a change in the length of the outer baffle. An empirical partial detachment qualifier calibrated on AUG experimental data was compared with the TCV simulations. The results show good agreement in detachment state prediction, indicating the potential of this detachment qualifier to be applied in devices of different sizes, emphasizing the combined influence of input power entering the divertor, neutral pressure, and the concentration and species of impurity in achieving divertor detachment.

A study on how efficient measures for secondary district heating system performance can be encouraged by motivational tariffs

BackgroundDistrict Heating (DH) is a technology that provides heating and domestic hot water to buildings and is an important technology for supporting the European energy transition. As such the heating systems increasingly resort to renewable heat sources and waste heat, it is even more important that they operate in the most efficient way possible. DH companies have access to the primary network of which they can impact system performance. To maximize the efficiency of the system, however, it is important that the system at the building level, known as the secondary system, is also efficient; otherwise, overall system efficiency is reduced. To increase system efficiency, return temperatures from the secondary system into the primary system have been targeted through motivational tariffs. There is limited information on how to establish a motivational tariff that motivates the customer to improve both the primary and secondary systems, which is a gap that this paper aims to fill.ResultsIn this paper, the impacts of retrofit actions in secondary systems are assessed through simulations. The identified relevant refurbishment measures to lower the return temperature to the primary system are variable flow pumps, low-temperature radiators, parallel heat exchangers, and a pass-through DHW system. Apart from simulated refurbishments, we also identify that the secondary system sometimes generates excess heat, which is valuable to recover, especially during peak load periods for the primary system. Hence, motivational tariffs targeting secondary system efficiency should also encompass an incentive for the customer to make use of waste heat in the secondary circuit to lower peak demand for the DH system.ConclusionsTo date, the most commonly used parameters introduced to customers are linked to the flow of water through the customer’s asset and the bonus malus principle. The results from simulations show that DH companies can introduce additional parameters to support customers in guiding their secondary system to perform more efficiently. Increased overall system efficiency has a positive impact on both costs and emissions.

Infrared detection of tungsten cracking on actively cooled ITER-like component during high power experiment in WEST

The consequences of tungsten (W) damaging processes, such as cracking and melting, on divertor lifetime and plasma operation are high priority issues for ITER. A sustained melting experiment was conducted in WEST using a 2 mm deep groove geometry on the upstream mono-block (MB) to overexpose the sharp leading edge (LE) of the downstream MB. W-cracking has been evidenced for the first time with a very high spatial resolution infrared camera before tungsten melting was reached. These cracks develop when the monoblock temperature is about 2600 °C, thus higher than both ductile to brittle transition and softening threshold of tungsten, suggesting that these cracks are different from the ones observed in previous campaigns where brittle failure was involved, because of transient events on cold monoblock. Post-exposure analyses have been performed on the damaged monoblock, highlighting 12 main cracks on the LE, with a width varying from 33 µm to 77 µm, and an average spacing of 0.45 mm. Parallel heat flux about 90 MW/m2 has been derived from infrared temperature measurements, with a heat flux decay length on the target of 4 mm. The T-REX modelling code suggest here that with these thermal inputs, a crack can initiates due to thermal cycling without disruption, with a ductile failure, under 1 to 5 cycles for a tungsten DBTT varying from 400 °C to 500 °C.

Optimization of Natural Cooled Heat Sinks for Panel Mounted Solid State Relays

A solid state relay mounted at a cabinet wall dissipating 30 W heat is considered in this analysis. A parallel plate mid-finned heat sink is designed for the relay to accommodate within 100 × 60 × 100 mm3 volume. A heatsink of 100 mm × 56 mm base size, 6 mm trunk thickness, 3 mm fin thickness, 6 mm fin spacing, and 102 mm length is attained by optimization. Further, it is optimized by trimming off the inefficient portion of the fin height, thereby attaining a taper heat sink without compromising the thermal performance. The appraisement of this trimming is characterized by the taper angle formed between the base of the heat sink and the line connecting all fin tips. The temperature profiles for heatsinks with 90°, 85° and 80° taper angle are presented in this paper for various power levels. The heat sink with 85° taper angle is optimum and the same is fabricated and tested experimentally. Thus, the parallel plate heat sink is optimized to improve the overall fin effectiveness and a 13% reduction in weight is achieved at 85° taper angle with a notional increment in temperature.

Coupld thermo-hydraulic modelling of heat storage in an embankment

Coupld thermo-hydraulic modelling of heat storage in an embankment

Potenential for thermal energy from Tunnels beneath Manchester and Crewe: a case study

potenential for thermal energy from Tunnels beneath Manchester and Crewe: a case study

A Thermal Conductivity Model for Grey Iron

Thermal conductivity is an important property for many iron cast components, and the lack of widely accepted thermal conductivity model for cast iron, especially grey cast iron, motivates the efforts in this research area. The present study contributes to understanding the effects alloy microstructure has on thermal conductivity. A thermal conductivity model for a pearlitic cast iron has been proposed, based on the as-cast alloy composition and microstructural parameters obtained at different solidification rates. According to the model, available parallel heat transfer paths formed by connected graphite flakes across eutectic cells are determined by the space between dendrite arms. The uncertainties both for model inputs and for validation measurements have been estimated. Sensitivity analysis has been conducted to result in better understanding of the model behaviour. The agreement between modelled and measured thermal conductivities has been achieved within 5% on the average for the investigated samples.

Development of high-throughput rapid heat-treatment and characterization process

Heat treatment plays an important part in materials development, but traditional heat treatment methods can only develop one target temperature/cycle at a time, which impairs the experimental efficiency in the development of new materials. We have therefore introduced the use of high-throughput experiments, changed the traditional sequential iterative method to parallel processing, and developed an efficient multi-temperature-field heat-treatment method. Microwave radiation is used as the heating source, and the method takes advantage of the selective heating ability of microwaves to generate 100 temperature zones that can heat treat 100 individual sheet samples simultaneously. The method incorporates various rapid characterization techniques, which enables a large amount of characterization data to be obtained in a short time. The obtained data can be uploaded to a high-throughput materials database to provide data to support subsequent studies. In this study, high-carbon, high-chromium steel was subjected to parallel tempering heat treatment at 109–786 °C. The relationship between the tempering temperature and the material microstructure and properties was derived from the changes in the microstructure and properties after parallel tempering, and used to verify the feasibility of this method.

Electron Heating and Associated Electrostatic Waves in Magnetic Flux Rope Embedded Within Super‐Alfvén Plasma Flow

AbstractMagnetic flux ropes (MFRs) are significant regions for the production of energetic electrons in space and astrophysical plasmas. However, the research on electron heating and acceleration driven by turbulence in MFRs is still quite rare. Utilizing in‐situ measurements from MMS satellite, we study electron heating and associated electrostatic waves in an ion‐scale MFR within terrestrial super‐Alfvén plasma flow. Lower‐hybrid drift waves, generated locally in this MFR, can contribute to the perpendicular heating through their electrostatic potential accelerating electrons. The parallel heating is attributed to antiparallel propagating electron beams. These beams excite the broadband electrostatic waves that can interact with electrons and thermalize electrons. Our study promotes understanding of electron energization driven by plasma waves and wave‐particle interaction in MFRs.

Topology optimization of laminated-sheet microchannel heat sinks based on a pseudo-three-dimensional method

Laminated-sheet microchannel heat sinks (LS-MHSs) have shown enormous potential in the thermal management of integrated chips due to their advantages of easy integration, high surface-to-volume ratio and high heat transfer efficiency. In this paper, a five-layer pseudo-3D (P3D) conjugated heat transfer model of the double-layer microchannel heat sink (DL-MHS) was established, and topology optimization (TO) was applied for optimal design of the DL-MHS. The effects of different inlet pressures and lamination methods on the optimal design were discussed, and then, the optimization results were compared with those obtained for a single-layer microchannel heat sink (SL-MHS) and conventional parallel microchannel heat sink (CP-MHS). A full-scale 3D conjugate heat transfer numerical model was also built to investigate the heat transfer and fluid flow performance of the topology optimized microchannel heat sink. The results showed that the topology optimized microchannel heat sink can enhance heat transfer and show a higher heat transfer and comprehensive performance compared to the conventional parallel microchannel heat sink. Under the same pumping power consumption, the topology optimization of the DL-MHS with parallel flow obtains the best heat transfer performance, which is 2.04 times that of the CP-MHSs and 1.09 times that of the SL-MHS. Under the same pumping power consumption, the topology optimization of the DL-MHS with counter flow achieves the best temperature uniformity and its maximum temperature difference is 5.0–16.9 K lower than that of the CP-MHSs and 1.6–3.4 K lower than that of the SL-MHS.

Electron heat flux and propagating fronts in plasma thermal quench via ambipolar transport

The thermal collapse of a nearly collisionless plasma interacting with a cooling spot, in which the electron parallel heat flux plays an essential role, is both theoretically and numerically investigated. We show that such thermal collapse, which is known as thermal quench in tokamaks, comes about in the form of propagating fronts, originating from the cooling spot, along magnetic field lines. The slow fronts, propagating with local ion sound speed, limit the aggressive cooling of plasma, which is accompanied by a plasma cooling flow toward the cooling spot. The extraordinary physics underlying such a cooling flow is that the fundamental constraint of ambipolar transport along the field line limits the spatial gradient of electron thermal conduction flux to the much weaker convective scaling, as opposed to the free-streaming scaling, so that a large electron temperature and, hence, pressure gradient can be sustained. The last ion front for a radiative cooling spot is a shock front where cold but flowing ions meet hot ions.

Saturated flow boiling heat transfer of R1233zd(E) in parallel mini-channels: Experimental study and flow-pattern-based prediction

The parallel channel is widely used in the two-phase flow boiling heat transfer due to its simple structure, but the existence of multiple flow patterns causes a complex and non-unified explanation of the heat transfer mechanisms. In this study, a saturated flow boiling experiment was designed in a parallel mini channel heat sink with R1233zd(E) as the working fluid. By controlling the vapor quality difference at the inlet and outlet to around 0.1–0.2, each single flow pattern was isolated and presented in the test section, and the corresponding variations of heat transfer coefficient (HTC) were discussed. The results showed that the flow pattern during the saturated flow boiling included bubbly flow, slug flow, wavy-annular flow and local dry-out. The transition boundaries between bubbly flow, slug flow and wavy-annular flow showed good agreement with the present criteria, while a modification was made on the transition from wavy-annular flow to local dry-out. The HTC showed a fast increase under low vapor qualities, then became stable and decreased with the increase of vapor quality. In addition, 6 correlations were selected to compare with the measured HTC classified according to the flow patterns. The comparison showed that the present correlations had different prediction accuracies on the HTC data under each flow pattern. The best prediction on the heat transfer during bubbly and slug flow was achieved by Liu and Winterton's model with the MAE of 16.4% and 12.9%, while Li and Wu's model showed the best agreement with the HTC data during wavy-annular flow with the MAE of 9.1%.

Microscopic thermal characteristics of parallelly arranged nanowires in a liquid: the role of interface thermal resistance, solid-like liquid layer, and the restricted phonon transport

Nanofluids based on extended nanostructures, such as nanowires, have been demonstrated improved thermal conductivities (κ). However, the lack of a complete understanding at the microscopic level hinders the development of such nanofluids towards practical applications. We aim to provide it by investigating how the interface thermal resistance (R b ), ballistic phonon transport, and the solid-like liquid layer affect the heat conduction in nanowire-based nanofluids. By employing Non-Equilibrium Molecular Dynamics (NEMD), it is found that the heat conduction in the parallelly arranged liquid and the nanowires exhibit a coupled thermal behavior owing to the R b . This contradicts the predictions of the classical parallel heat conduction model, therefore, a novel model is proposed taking this coupled behavior into account. Using this model, it is shown that the high κ of the solid phase has a limited contribution to the effective κ of nanofluids having short nanowires due to the dominant R b effect. For the case of long nanowires, however, the individual nanowire κ becomes a vital parameter defining the effective κ. Further, NEMD calculations reveal that the κ of suspended nanowires in a liquid is markedly reduced, questioning the validity of classical effective medium theories which use the bulk parameters. This reduction is attributed to surface atoms’ restricted vibrational freedom and the nanowire’s phonon-boundary scattering. By substituting this reduced κ of the solid phase into the new mathematical model, the theoretical predictions align closely with the NEMD calculations, exhibiting deviations below 10%. The sole contribution from the solid-like liquid layer to the κ enhancement lies between 20%–30% in the nanofluids presently considered. Therefore, the findings of this study highlight the important roles play by the identified microscopic thermal characteristics in defining the effective κ of nanofluids based on nanowires.

Modelling of Floor Heating and Cooling in Residential Districts

In this study, a method is proposed to expand the utilization of an existing calculation model for a floor heat exchanger (HX) from room scale to small district scale. The model, namely Trnsys Type 653, is typically employed for the simulation of single or simultaneously controlled parallel heating circuits. It uses a simplified approach to calculate the heat exchange between fluid and screed, taking the HX effectiveness as an input. In order to calculate the effectiveness based on the HX design, fluid properties and mass flow rate, a Python model is developed to be coupled with Type 653. The results are compared to a reference finite element model set up in COMSOL® and depend on the HX design. The highest deviations range from over 1 K for 35 min to over 2 K for 175 min, while the lowest deviations range from below 0.5 K to below 1 K. Furthermore, the simplification of the floor HX model is analyzed by summarizing heating circuits from single rooms to a whole flat and from single flats to a whole floor. This approach results in deviations of approximately 2 and 4%, respectively, in the overall transferred heat over longer periods of time, while the switch-on frequency of the controller in an exemplary day is halved. While further analysis is required, the described simplifications seem promising for detailed district simulations with relatively low computational effort.

Statistical Study of Anisotropic Proton Heating in Interplanetary Magnetic Switchbacks Measured by Parker Solar Probe

Magnetic switchbacks, which are large angular deflections of the interplanetary magnetic field, are frequently observed by Parker Solar Probe (PSP) in the inner heliosphere. Magnetic switchbacks are believed to play an important role in the heating of the solar corona and the solar wind as well as the acceleration of the solar wind in the inner heliosphere. Here, we analyze magnetic field data and plasma data measured by PSP during its second and fourth encounters, and select 71 switchback events with reversals of the radial component of the magnetic field at times of unchanged electron-strahl pitch angles. We investigate the anisotropic thermal kinetic properties of plasma during switchbacks in a statistical study of the measured proton temperatures in the parallel and perpendicular directions as well as proton density and specific proton fluid entropy. We apply the “genetic algorithm” method to directly fit the measured velocity distribution functions in field-aligned coordinates using a two-component bi-Maxwellian distribution function. We find that the protons in most switchback events are hotter than the ambient plasma outside the switchbacks, with characteristics of parallel and perpendicular heating. Specifically, significant parallel and perpendicular temperature increases are seen for 45 and 62 of the 71 events, respectively. We find that the density of most switchback events decreases rather than increases, which indicates that proton heating inside the switchbacks is not caused by adiabatic compression, but is probably generated by nonadiabatic heating caused by field–particle interactions. Accordingly, the proton fluid entropy is greater inside the switchbacks than in the ambient solar wind.

Efficient optimization of parallel micro-channel heat sinks based on flow resistance network model

Electronics cooling is a critical issue affecting technological development. Parallel micro-channel heat sink (PMCHS) is widely applied for electronics cooling. However, the existing optimization methods are incapable to perform efficient design of three-dimensional liquid-cooled PMCHSs, impeding the thermal management of high power and volume-shrinking electronics. In this study, a flow resistance network (FRN) model is developed for structural optimization of three-dimensional liquid-cooled PMCHSs. Based on the uniform flow rate distribution, the FRN model is used to determine the optimized parallel channel widths and the optimized inlet deflector shape of the PMCHS. With the optimized parallel channel widths, the maximum temperature (Tmax) of the PMCHS is decreased by 4.0 K and the temperature standard deviation (σT) is decreased by 20%. With the optimized inlet deflector shape, Tmax and σT are reduced by 4.8 K and 14% respectively. The optimization method based on the developed FRN model for structural design of PMCHSs avoids multiple iterations of system parameters in existing optimization methods, showing its potential in high efficient thermal management of electronics.

Improving the Quality of Environmentally Friendly Liquid Smoke Distillation Process to Increase Artisan Income

The problems the Smoke-liquid Craftsman Group often faces are production capacity, product quality, and low selling prices. Low production capacity due to the limited ability distillation machine. The low quality of smoke-liquid products is due to the absence of standard quality. The smoke produced from the coconut shell charcoal production process has the potential to disturb the environment, so it has been carried out the process of melting smoke into liquid, which is then called smoke-liquid. However, the resulting smoke-liquid is still mixed with ash, brown colour, and intense aroma, and still contains much tar, so it does not meet the standard quality for food preservatives the price is low. The objective of this activity is to apply appropriate technology is carried out by enforcing standard product quality and repairing distillation machines to produce high-quality smoke liquid. This one is to support renewable and environmentally friendly energy programs while being able to increase revenue. Appropriate Technology (TTG) is in the form of improvements in distillation technology, which was previously a distiller using annular pipes, where the inner pipe is 1/2 inch. The outer pipe diameter is 1.5 inches and is changed with parallel heat pipe exchanger technology using an inner pipe with a diameter of 1 inch and an outer pipe with a diameter of 4 inches. The result of this service is prototyping a new distillation machine that can increase the production capacity and quality of liquid smoke that meets the specified standard quality and increase the selling price four times.

Influence of system pressure on flow boiling in microchannels

The effect of pressure on the flow boiling characteristics of HFE-7200 between 1.0 to 2.0 bar was investigated in a parallel microchannel heat sink (Dh = 0.48 mm, 44 channels). The mass flux and subcooling degree were kept constant at 200 kg/m2 s and 10 K respectively, while heat flux ranged from 26.1 – 160.7 kW/m2. Increasing system pressure decreased the vapour density ratio, thus leading to reduced pressure drop, increased bubble generation frequency and two-phase heat transfer coefficients in the system, though this may not be apparent at low superheat degrees at higher pressures. Smaller bubble diameters were observed at higher pressures and resulted in a delay in flow regime transition to slug flow, which is prone to flow reversal. The experimental work showed promising means to manage flow instabilities and enhance heat transfer performance in two-phase microchannel systems for HFE-7200.

Simulation and 4E analysis of a novel trigeneration process using a gas turbine cycle combined with a geothermal-driven multi-waste heat recovery method

A novel hybrid system using geothermal energy and fuel gas in a co-feed structure is proposed. The main objectives include improving the sustainability of a gas turbine cycle associated with a geothermal power plant and reducing carbon emissions. To this end, a novel multi-waste heat recovery process was developed in which the heated airflow in the gas turbine cycle was directed to the geothermal flash cycle to increase the viability of the flash process in this unit. A parallel heat recovery structure then used part of the waste heat from the gas turbine cycle to start a supercritical carbon dioxide cycle and also improve the performance of the geothermal flash cycle. Hence, two organic Rankine cycles were used in the geothermal flash cycle. The other part of the waste heat from the gas turbine cycle was consumed in a cascade framework in a steam Rankine cycle and a desalination plant in combination with a domestic water heater. The defined structure was simulated and a comprehensive study was done from the viewpoints of energy, exergy, environment, and thermoeconomics. This structure reduced the total irreversibility as well as the carbon dioxide emissions compared to the existing literature data.

Comparative experimental study on series–parallel heat transfer characteristics of flat heat pipes

In this study, a thermal performance test rig for heatpipes with different connection modes is independently designed to explore the steady-state and transient thermal performance of series–parallel flat heat pipes under different heat source powers. The dynamic thermal performance changes of three parallel modules, 1A2,2A1,3A2, and three series modules, 12A,21A,23A, under different power conditions are compared and analysed. The experimental results show that the total thermal resistance of the parallel modules is the lowest, followed by the total thermal resistance of the traditional module, and the total thermal resistance of the series modules is the highest. The minimum total thermal resistance of the parallel module is 0.02 K/W. At the 23.6 W input power, the parallel heat dissipation has the lowest heat source temperature of 74 °C and the slowest heat source heating rate of 3.2 °C/min in comparison with other heat dissipation methods. Further, under the parallel connection condition, the standard deviation of condenser and evaporator of the No. 2 heat pipe is reduced by 0.45 and 6 respectively, indicating that the sintered flat heat pipe has better temperature equalization than the grooved flat heat pipe. Different from the other two dissipation methods, the maximum temperature of the heat pipe in parallel heat dissipation is only 57.2 °C, which can satisfy the heat dissipation requirements of the heat source. It is important to mention that the parallel heat dissipation method of the flat heat pipe proposed in this investigation can realize the double-sided arrangement of heat sources of multiple components and accomplish the rapid heat transfer process while increasing the heat flux exponentially, which provides technical support for solving the problem of high heat flux concentration of multi-chip components.