Homogeneous Temperature Distribution Research Articles

Thermal Protection Performances of the Macro and/or Nano Enhanced PCM in a Representative Battery Pack

ABSTRACT This experimental study focused on the comparison of thermal protection performances of macro and/or nano enhanced organic PCM in a representative battery pack from low to high discharge rates. The macro/nano enhanced RT-44 provides the desired battery thermal protection requirements in terms of criteria such as maximum temperature and maximum temperature difference restriction and uniform temperature distribution throughout the battery pack. It increases the effective battery thermal protection time by 117%-32% depending on the discharge rates. While PCM thermal protection provides a more homogeneous temperature distribution throughout the battery pack, nano and/or macro enhanced one provides it throughout the cell. The macro enhancement essentially makes a major contribution to shortening the cooling time for the next use.

Improved performance of polyimide Cirlex‐based dielectric barrier discharge plasma actuators for flow control

AbstractDielectric barrier discharge (DBD) plasma actuators are simple electrohydrodynamic devices, which are able to provide effective aerodynamic control. One of the main components of these devices is the thin dielectric layer, which allows to separate and prevent the arc between the high‐voltage electrodes. Different materials can be used as dielectric layer to reduce the power consumption or boost the flow controlling effect of the actuators. In this context, this report presents a comparative study of two commercial polyimides, Kapton and Cirlex, used as dielectric layer of surface DBD plasma actuators. The electrical, dielectric, mechanical, electromechanical, and thermal properties were obtained to evaluate overall performance. It was verified that Cirlex (8.3 W) consumes less power than Kapton (21.3 W) to generate higher induced flow velocity of ≈3.4 m/s for an input voltage of 11 kVpp and 24 kHz. During one AC cycle at 11 kVpp the charge transferred for Cirlex (70 nC) is lower than for Kapton (100 nC), as well as the dielectric breakdown voltage to ignite the plasma discharge, 1.5 and 2.2 kVpp, respectively. The Cirlex DBD presents a higher voltage operation limit (at least 14 kVpp) and a more regular plasma discharge, which results in a more homogenous thermal profile and temperature distribution during its operation. The Cirlex actuator delivered higher mechanical power (6.2 mW) and achieved higher electromechanical efficiency (0.004%). The polyimide Cirlex proved to be a suitable alternative for Kapton to fabricate DBD plasma actuators for flow control with improved performance.

Effects of Temperature (In)homogeneity during Hot Stamping on Deformation Behavior, Structure, and Properties of Brass Valves

Herein, assessing the effects of initial temperature (in)homogeneity on a hot‐stamped CuZn40Pb2 medical gas valve (fitting) via numerically and experimentally defining mutual relations of selected deformation parameters and optimizing temperature distribution within the original semi‐product heated via induction are focused. For these purposes, three preheating regimes are simulated, and deformation behaviors are evaluated. The predicted results are validated by experimental stamping and subsequent evaluation of the structure and properties of stamped fittings. The results show that preheating the semi‐product with a certain temperature gradient occurring between the axial and (sub)surface regions is favorable, as homogeneous initial temperature distribution results in rapid surface cooling by the effect of heat transfer from semi‐product to die, which imparts inhomogeneous stress distribution, local changes in structural phases, and possible occurrence of oxides. Too low (sub)surface temperature of the semi‐product can result in a significant (local) increase in flow stress, which consequently results in the danger of occurrence of forming defects. The brass fitting stamped with the optimized preheating procedure features an average grain size of 5.8 μm, uniform grains’ orientations with maximum texture intensity of two times random, and ultimate tensile strength of almost 400 MPa, while maintaining elongation to failure of more than 35%.

What causes the absence of pulsations in Central Compact Objects in supernova remnants?

Most young neutron stars belonging to the class of Central Compact Objects (CCOs) in supernova remnants do not have known periodicities. We investigated seven such CCOs to understand the common reasons for the absence of detected pulsations. Making use of XMM-Newton, Chandra, and NICER observations, we perform a systematic timing and spectral analysis to derive updated sensitivity limits for both periodic signals and multi-temperature spectral components that could be associated with radiation from hotspots on the neutron star surface. Based on these limits, we then investigated for each target the allowed viewing geometry that could explain the lack of pulsations. We find that it is unlikely (< 10−6) to attribute that we do not see pulsations to an unfavorable viewing geometry for five considered sources. Alternatively, the carbon atmosphere model, which assumes homogeneous temperature distribution on the surface, describes the spectra equally well and provides a reasonable interpretation for the absence of detected periodicities within current limits. The unusual properties of CCOs with respect to other young neutron stars could suggest a different evolutionary path, as that proposed for sources experiencing episodes of significant fallback accretion after the supernova event.

Performance evaluation of a 4-stack solid oxide module in electrolysis mode

To support the current trend of testing bigger reversible Solid Oxide Cell (rSOC) modules, CEA has built the 120 kWDC Multistack platform. It was used to test SOLIDpower recently developed-Large Stack Module (LSM) in electrolysis mode.Results show high thermal performance of the LSM, with homogeneous temperature distribution and losses in the kilowatt range above 700 °C. A performance map was recorded between 712 and 744 °C over 22.4-to-29.6 kg h−1 steam flowrates using a fast control strategy to avoid endothermic operation. A peak power of 74 kWDC was converted into more than 50 kg day−1 of H2 (35.5 kWhDC kgH2−1). In addition, fuel utilization of more than 90% and steam conversion above 80% were demonstrated at the module level. In the end, the modular design of the LSM seems well suited for system scale up, paving the way for mutualization of auxiliaries and CAPEX reduction.

Plasma-assisted rapid sintering of nanotitania powders

In this work, Plasma-Assisted Rapid Sintering (PARS), a pulsed DC plasma system in a hollow cathode regime, is presented as a novel technology to sinter nanoceramics. Nano-TiO2 powders are used as proof of concept and submitted to thermal treatment using several PARS conditions and sintering schedules. PARS heating process induced solely by the hollow cathode effect is consistent and affordable, providing a homogeneous temperature distribution to the compact. Furthermore, the heating rate and the maximum temperature are easily tunable by the discharge current applied in the plasma source and can go safely from room to maximum temperature in a matter of seconds with heating speed comparable with other reported rapid sintering techniques. Using 1-min of non-isothermal PARS cycles up to 1000 °C, porous nanostructured samples were obtained; reaching 80 % relative density while the grains remained at the nanoscale. Adding dwell times, the relative density was increased up to 96 % using a temperature plateau for up to 10 min, but the TiO2 grains grow intensively when temperatures exceeded 1000 °C. The results indicate that the developed process is a promising new alternative technology for sintering nanoceramics.

Numerical investigations on the optimal tool temperature distribution for the integrated manufacturing of hybrid structures

The combination of hot-stamped steels and fibre-reinforced thermoplastics (FRTP) offers great potential for lightweight design. The process steps of hot stamping and thermoforming for the manufacturing of such hybrid structures are usually carried out in two separate steps. After hot stamping, the blank has to be reheated for the application of FRTP in order to enable the bonding of FRTP to the blank. Process integration of the individual processes means that reheating of the blank during thermoforming is no longer necessary. Due to non-uniform contact conditions during hot stamping between blank and tool, an inhomogeneous temperature distribution in the blank occurs, which would lead to non-uniform bonding properties between blank and FRTP after thermoforming. The aim of this work is to determine this non-uniform contact and the resulting heat transfer by a numerical model. By segmenting the tool in the model, a possibility is shown to control the non-uniform contact and to achieve a homogeneous temperature distribution in the blank after hot stamping. Furthermore, the temperature adaptability of the used tool and the resulting temperature distribution in the blank is investigated. Finally, the manufactured structures are tested in a numerical three-point bending test in order to be able to make a statement about their performances.

Numerical Analysis of Friction Effects on Temperature and Phases within Forged Ti-6Al-4V Alloy Aeroengine Drum

Friction conditions significantly impact the temperature and phases of titanium forged parts, further directly affecting the microstructures and mechanical properties of final parts. In this paper, a 2D simplified finite element (FE) model combined with phase transition equations is developed to simulate a Ti-6Al-4V drum forging procedure. Then, friction effects on the temperature and phases of the forged drum are numerically analyzed and verified by experiments. The simulated results indicate that a reasonable range of friction factor is needed to obtain a relatively homogenous temperature distribution within the forged drum. Moreover, unlike its small influence on the α + β phase, improving friction obviously decreases the general levels of temperature and β phase and increases the homogeneities of α and β phases within the forged drum, which are associated with cooling rates and the heating effects of friction and deformation.

Numerical and Experimental Study of Inverse Diffusion LPG-Air Flames Pulsation

This study uses Ansys 16 commercial package to investigate an accurate numerical model that can trace the flame shape from inverse diffusion combustion of LPG with a focus on the effect of air pulsation on the combustion characteristics. The simulation is based on solving the energy, mass and momentum equations. The large eddy simulation turbulence model and the non-premixed combustion model are used to simulate the pulsating combustion reaction flows in a cylindrical chamber with an air frequency of 10,20,50,100 and 200 rad/sec. The numerical results are in great agreement with the experimental results in the flame shape and the temperature distribution along the combustion chamber in both pulsating and non-pulsating combustion. Diffusion combustion responds positively to pulsating combustion and increases mixing in the reaction zone. Increasing the air frequency increases the temperature fluctuations, the peak turbulent kinetic energy and maximum velocity magnitude, respectively, by 27.3%, 300%, and 200%. Increasing the Strouhal number to 0.23 shortens the flame by 40% and reduces nitric oxide and carbon monoxide by 12% and 40%, respectively, including an environmentally friendly combustion product. The maximum average temperature dropped from 1800 K to 1582 K with a very homogeneous temperature distribution along the combustion chamber which is very important for furnaces.

Enhanced airflow by additional axial fans for produce cooling in a cold room: A numerical study on the trade-off between cooling performance and irreversibility

Enhanced airflow by axial fans is widely applied for efficient convective heat transfer and thermal management. The authors previously proposed the use of additional axial fans to enhance the airflow in a cold room and obtained improved cooling performance as well as increasing irreversibility through experimental thermodynamic analysis. In this study, the proposed strategy is numerically investigated via a validated computational model to evaluate distribution characteristics of airflow, temperature and entropy generation. The trade-off between cooling performance and irreversibility was analyzed under different operating conditions of additional axial fans. Numerical results indicated more homogeneous airflow and temperature distribution with increasing entropy generation caused by additional axial fans between produce bins. Additional axial fans with an operating angular velocity of 55 rad•s−1 at five positions between produce bins resulted in 18 to 37% improvement of cooling performance and 47% higher irreversibility when compared to the case without additional axial fans. An improved trade-off between improved cooling performance and increasing irreversibility could be achieved with lowering the operating angular velocity and reduced number of additional axial fans.

Comparative study of deposition patterns for DED-Arc additive manufacturing of Al-4046

Quality assurance is one of the largest challenges to the widespread adoption of metal additive manufacturing technology. Deposition pattern can significantly impact the temperature distribution during manufacturing process and thus the overall quality and residual stress formation of the manufactured components. In order to explore the intricate relationship, three different deposition patterns in DED-Arc additive manufacturing, the meander pattern, the spiral pattern and the newly developed S pattern, were experimentally and numerically scrutinized in terms of the resulting temperature distribution, grain size, porosity as well as residual stress formation. The study reveals that the variation of the deposition paths results in characteristic temperature fields and gradients with distinct local peak temperatures that determine the deposition quality, and simultaneously offers great degrees of freedom for optimal pattern design. Comparing the results with different deposition patterns, the S pattern leads to a more homogeneous temperature distribution, showing beneficial effects on the microstructure, porosity and residual stress formation in the deposited Al-4046 material, and is thus regarded as a promising alternative for improving additively manufactured parts quality.

Development and Evaluation of an Improved Apparatus for Measuring the Emissivity at High Temperatures.

An improved apparatus for measuring the spectral directional emissivity in the wavelength range between 1 µm and 20 µm at temperatures up to 2400 K is presented in this paper. As a heating unit an inductor is used to warm up the specimen, as well as the blackbody reference to the specified temperatures. The heating unit is placed in a double-walled vacuum vessel. A defined temperature, as well as a homogenous temperature distribution of the whole surrounding is ensured by a heat transfer fluid flowing through the gap of the double-walled vessel. Additionally, the surrounding is coated with a high-emitting paint and serves as blackbody-like surrounding to ensure defined boundary conditions. For measuring the spectral directional emissivity at different emission angles, a movable mirror is installed in front of the specimen, which can be adjusted by a rotatable arrangement guiding the emitted radiation into the attached FTIR-spectrometer. The setup of the emissivity measurement apparatus (EMMA) and the measurement procedure are introduced, and the derived measurement results are presented. For evaluating the apparatus, measurements were performed on different materials. The determined emissivities agree well with values published in literature within the derived relative uncertainties below 4% for most wavelengths.

Thermal conditions in households and assessment of building's flexibility potential. Variations in time, space and between dwellings

There is little specific knowledge of actual temperature conditions in buildings. This paper contributes with results from a detailed long-term monitoring campaign of temperature conditions in 17 households. Furthermore, these measurements are combined with qualitative interviews with 22 occupants in 16 households, on their heating practices. Implications for the assessment of the heat demand flexibility potential are discussed, and it is suggested that including occupants in future experiments can be a way to reach the full potential of buildings flexibility potential to a renewable energy sources dependent energy system. Quantitative data show that temperature conditions vary with time and space within each dwelling and between dwellings. In the same apartment, the temperature difference between spaces can be 7 K. The living rooms have the most homogeneous temperature distribution during 24 h period and the bedrooms most significant variations. Qualitative data indicate that aspects of: Activities performed by occupants; Caring for things, others and oneself; Comfort; Convenience; Natural and material surroundings affect occupants’ heating practices.

A novel pressure-controlled joule-heat forge welding method to fabricate sound carbon steel joints below the A1 point

A novel solid-state joining method, that we called Pressure-controlled Joule-heat Forge Welding (PJFW), in which electric resistance heat is utilized as the heat source, was successfully developed. Medium carbon steel, S45C, rods were joined using this PJFW method under various conditions. The welding temperature can be determined uniquely by the applied pressure in the PJFW. The fabricated joints show homogeneous temperature distribution and hence hardness distribution along the weld interfaces. A sound S45C joint showing superior tensile properties comparable with the base material was successfully fabricated by providing an appropriate high pressure to lower the welding temperature below the A 1 point in order to prevent the brittle martensitic transformation, and applying a sufficiently large faying-surface deformation, not only to introduce significant microstructural refinement and large strains to prevent the softening, but to also sufficiently fragment the oxide layers, generate fresh surfaces, promote their atomic bonding and eliminate weld interface defects. • A novel “Pressure-controlled Joule-heat Forge Welding (PJFW)” method was developed. • The welding temperature is determined uniquely by the applied pressure in PJFW. • Uniform temperature and hardness distributions are achieved over weld interfaces. • A sound S45C steel joint was successfully fabricated by PJFW under the A 1 point. • This method shows potential to well join carbon steel regardless of carbon content.

Error analysis of contactless optical temperature probing methods for cryogenic Yb:YAG

In this work, we have investigated six different in situ optical contactless temperature probing methods for cryogenic Yb:YAG systems. All the methods are based on variation of fluorescence spectra with temperature, and they either look at the width of the emission line, the ratio of the emission intensity at different wavelengths and to the overall spectral change at selected wavelength intervals. We have shown that, for Yb:YAG crystal with homogeneous temperature distribution, one can perform real-time contactless optical temperature measurements with a ± 1 K accuracy in the 78–300 K range. We have further tested the methods in measuring the average temperature of Yb:YAG rods at up to 500 W absorbed pump power level. We have seen that, a real-time temperature measurement accuracy of ± 5 K is feasible in both lasing and non-lasing situations for estimating the average temperature of crystals under nonhomogeneous thermal load. The techniques are quite valuable in evaluating the bonding quality of Yb:YAG crystals in cryogenic systems. Moreover, the real-time temperature information provides feedback on parameters like cavity alignment status and extraction efficiency to the laser engineers while optimizing the system.

Numerical investigation of thermal hydraulic behaviors in wire-wrapped bundle with smaller wire diameter of peripheral rods

In this paper, a new pattern bundle with a smaller wire diameter of peripheral rods was proposed. By decreasing the wire diameter of peripheral rods, the flow area of peripheral sub-channels is reduced diverting more coolant towards the central sub-channels. This would lead to a more uniform sub-channel temperatures distribution. To analyze the flow and heat transfer performance of the new bundle, the comparative study between the new bundle and conventional one was carried out by RANS-based CFD simulation. It was found that decreasing the partial wire diameters, the uniformity of coolant flow distribution is improved, resulting in a more homogeneous temperature distribution. The local transverse pressure difference characterizing global swirl motion is smaller, resulting in a weaker sweeping flow in peripheral sub-channels. Moreover, the obvious sweeping flow also could be observed in inter-connected sub-channels due to the smaller wire diameter of peripheral rods. At last, Nusselt number and friction factor are the parameters targeted for the investigation, and the results show that the thermal-hydraulics performance of the new bundle has been significantly improved. Through the research of this paper, the qualitative understanding of fuel assembly structure optimization could be provided for the core design in future.

PYROLYSIS OF SOLID WASTE AND ITS COMPONENTS IN A LAB SCALE INDUCTION-HEATING REACTOR

The present study investigates the thermochemical conversion of Solid Recovered Fuel (SRF), represented by selected “model materials”. A laboratory-scale induction heated device was specifically developed to achieve fast pyrolysis conditions close to those encountered in a fluidized bed reactor. The novel device can handle up to 5 grams of solid, allowing fast heating rates (near 70°C/s) and a homogeneous distribution of temperature all along the reactor. Pyrolysis tests of a SRF sample and four model materials (Polyethylene, Polyethylene Terephthalate, beech wood, cardboard) were performed at 800°C. The yield and composition of the produced gas for each sample were determined. Experimental results will help to elucidate the relation between the initial components of waste derived fuels and the obtained reaction products.

Heat transfer intensification with packed open-cell foams in TSA processes for CO[formula omitted] capture

Packed open-cell foams are proposed as an alternative to standard packed bed configuration commonly adopted for the adsorption columns of a temperature swing adsorption process. In this contribution, heat transfer in an adsorption column with a packed foam configuration is investigated by experimental and modeling analysis, in comparison to a standard packed bed. The introduction of the packed foam allows for more rapid temperature transitions and substantial reduction of temperature gradients within the adsorption bed. The impact of this heat transfer enhancement on the separation performance of a temperature swing adsorption process is evaluated by modeling an example post-combustion CO2 capture application. Although the presence of the foam implies a loss of sorbent inventory (-26.5%), higher process productivity (+80%) is achieved thanks to faster temperature swings and more homogeneous temperature distribution within the adsorption columns.

Towards Enhancing the Potential of Injection Molding Tools through Optimized Close-Contour Cooling and Additive Manufacturing.

This work deals with the parametric optimization of the position and form of a conformal cooling used in the injection molding industry. Based on a literature survey, an optimization routine concerning the parameter optimization of cooling system designs was developed and implemented with the help of the software package Moldflow. The main objective of the optimization is to reduce the cooling time; the second is to obtain an optimized homogeneous temperature distribution over the complete tool surface. To enable a comparison of the new close-contour solution with a classical manufacturing process, an optimized cooling system simulation, based on a conventional manufacturing solution, was established. It can be shown that the optimized close-contour cooling design offers significant advantages that cannot be exploited using classical manufacturing. Finally, the additive manufacturing of a prototype in the framework of powder bed fusion is documented as a proof of concept.

Design and Simulation of Ethylene Cooled Microchannel Heat Exchanger for Micro Processors

In this study, a microchannel heat exchanger with operating with ethylene was proposed instead of air-cooled microprocessor heat sinks and flow and heat transfer simulations were made using Flo-EFD software. First, the temperature distribution of the air domain and the microprocessor in the computer case was obtained for air-cooled heat sink, and then the flow paths of the air coming from the outside with the help of the fan were observed. Afterwards, the system with the proposed micro channel heat exchanger was subjected to the same processes and the results were compared. As a result of the study, it was revealed that the micro channel heat exchanger reduced the processor temperature between 54-55°C and 18-19°C. It has also been observed that removing the heat sink allows the air drawn from the outside environment to circulate more efficiently around other heat generating elements in the computer case. Hence more homogeneous and lower temperature distribution within the computer case was obtained.