Low Thermal Load Research Articles

Solid State Joining of a Cold Rolled Zr-Based Bulk Metallic Glass to a Wrought Aluminum Alloy by Power Ultrasonics.

Ultrasonic metal welding (UMW) enables joining in the solid state at relative low temperatures with short cycle times. This technique is of particular interest for joining metallic glasses to each other or to other materials, because crystallization of the amorphous structure can be prevented due to the low thermal loading and the rapidity of the process. In this work, UMW is applied to join one 1 mm thick sheet of a commercial wrought aluminum alloy (AA5754) and one 0.4 mm thick strip of a commercial Zr-based bulk metallic glass (AMZ4). The introduced heat of the welding process is detected with thermocouples and thermal imaging. To investigate the strength of the joint and the influence on the microstructure, mechanical tensile tests are carried out in combination with scanning electron microscopy and differential scanning calorimetry. The results show that ultrasonic metal welding is a suitable technique to join amorphous bulk metallic glasses to crystalline aluminum alloys. The metallic glass component retains its amorphous structure in the joint, and the joint strength is higher than the strength of the Al sheet. These findings will help to develop future applications of BMG-based multi-material components, including medical tools.

Approaches to tailor the cooling supply to the grinding process

This study presents original research of the investigation of the coolant supply to the contact area with two different approaches. The cooling and lubrication are key aspects of manufacturing processes such as grinding to achieve a high surface quality at high productivity. The coolant supply to the contact area has a high impact on the performance of the coolant. This paper presents the results from two approaches to tailoring the coolant supply for conventional and high-performance processes. An analytical approach is established to determine the coolant outlet velocity. Afterward, a sensor is developed to measure the coolant velocity at the nozzle. Conclusively, the influence of the coolant velocity on the volume flow through the contact zone is investigated. The results of this study highlight the importance of coolant outlet velocities of at least 60% of the cutting speed. The two approaches outline low impact possibilities to ensure optimal coolant outlet velocities and thus low thermal loads during the grinding process.Article HighlightsAnalytical approach to calculate outlet velocities for varying noozles in high-performance grinding with cutting speeds of up to 100 m/sUtilization of a high-speed camera to determine the outlet nozzle velocities in a conventional deep grinding processValidation of the impact of the coolant outlet velocity on the volume flow through the contact area by means of a coolant collection box

Effect of flame retardants on side-wall quenching of partially premixed laminar flames

A combined experimental and numerical investigation of partially premixed laminar methane-air flames undergoing side-wall quenching (SWQ) is performed. A well-established SWQ burner is adapted to allow the seeding of the main flow with additional gaseous products issued from a (secondary) wall inlet close to the flame’s quenching point. First, the characteristics of the partially premixed flame that quenches at the wall are assessed using planar laser-induced fluorescence measurements of the OH radical, and a corresponding numerical simulation with fully-resolved transport and chemistry is conducted. A boundary layer of enriched mixture is formed at the wall, leading to a reaction zone parallel to the wall for high injection rates from the wall inlet. Subsequently, in a numerical study, the wall inflow is mixed with dimethylmethylphosphonat (DMMP), a phosphor-based flame retardant. The DMMP addition allows the assessment of the combined effects of heat loss and flame retardants on the flame structure during flame-wall interaction. With an increasing amount of DMMP in the injected mixture, the flame stabilizes further away from the wall and shows a decrease in the local heat-release rate. Thereby, the maximum wall heat flux is significantly reduced. That results in a lower thermal load on the quenching wall. The flame structure analysis shows an accumulation of the intermediate species HOPO at the wall similar to the CO accumulation during the quenching of premixed flames without flame retardant addition. The study shows how the structure of a partially premixed flame is influenced by a wall that releases either additional fuel or a mixture of fuel and flame retardant. The insights gained from the canonical configuration can lead to a better understanding of the combined effects of flame retardants and heat losses in near-wall flames.

Optimization of the gain layer design of ultra-fast silicon detectors

In the past few years, the need of measuring accurately the spatial and temporal coordinates of the particles generated in high-energy physics experiments has spurred a strong R&D in the field of silicon sensors. Within these research activities, the so-called Ultra-Fast Silicon Detectors (UFSDs), silicon sensors optimized for timing based on the Low-Gain Avalanche Diode (LGAD) design, have been proposed and adopted by the CMS and ATLAS collaborations for their respective timing layers. The defining feature of the Ultra-Fast Silicon Detectors (UFSDs) is the internal multiplication mechanism, determined by the gain layer design. In this paper, the performances of several types of gain layers, measured with a telescope instrumented with a 90Sr β-source, are reported and compared. The measured sensors are produced by Fondazione Bruno Kessler (FBK) and Hamamatsu Photonics (HPK).The sensor yielding the best performance, both when new and irradiated, is an FBK 45 μm-thick sensor with a carbonated deep gain implant, where the carbon and the boron implants are annealed concurrently with a low thermal load. This sensor is able to achieve a time resolution of 40 ps up to a radiation fluence of 2.5⋅1015 neq/cm2, delivering at least 5 fC of charge.

Development of 3-D numerical methodology to investigate transient characteristics of fuel temperature and hydrated residual water during drying process of dry storage system

The dry storage system (DSS) is the most popular method for the interim storage of spent nuclear fuels (SNFs). The internal environment with high humidity and radiation would induce radiolysis and recombination, degrading the internal components and SNFs within the DSS during the storage period. A three-dimensional (3-D) transient heat transfer methodology is developed to model the hydrated residual water in drying process for the DSS. Effects of thermal loading and fuel burnup on SNF temperature and residual water are also considered. Based on the comparison, effects of burnup on the SNF temperature and the drying ratio are insignificant. More hydrated water is retained on the fuel surface for the lower thermal loading. Present simulation results strongly recommend that the lower thermal loading should be used to evaluate the drying process in order to avoid the unexpected residual water retained on the fuel surface in any one DSS.

A study on the effect of qualitative control coupling variable engine speed on the hydrogen-fueled Wankel rotary engine at wide-open throttle

Hydrogen-fueled Wankel rotary engine, with few available research currently, has excellent power and emission characteristics, however, with lower efficiency. With increasing attention to low-carbon emission, it is of great significance to explore methods to improve the efficiency of hydrogen-fueled Wankel rotary engines. This work aims to study the effect of qualitative control coupling variable engine speeds at the wide-open throttle on the power control. The comparative effect of qualitative control coupling engine speeds from 1000 r/min to 1500 r/min under the wide-open throttle and quantitative control at 1500 r/min on the combustion and emission characteristic of hydrogen-fueled Wankel rotary engine is investigated. The results show that compared with quantitative control, qualitative control coupling variable engine speed can achieve excellent performance. The brake thermal efficiency can be maximally increased by 43.5%, an absolute increase of 6.22%, as well the volumetric efficiency with a maximal 105% improvement. The thermal load and risk of knock can be greatly reduced. Moreover, NO emission also can be reduced by more than an order of magnitude or even by zero. Although there is an increase in cyclic variation, the value is no more than 4%. In addition, qualitative control coupling variable engine speed allows flexible matching of appropriate engine speed and excess air ratio based on the actual requirements of efficiency, stability, durability and emission. • The power control method of the hydrogen Wankel rotary engine is investigated. • Qualitative control achieves better engine performance than quantitative control. • Qualitative control coupling engine speed meets the power and high-efficiency demand. • Lower thermal load, knock tendency and NO emission can be obtained. • Much high excess air ratio isn't recommended due to high cyclic variation.

Thermal load distributions on the large-scale turbine blade tip with a rounded inlet edge

Thermal load and near-wall flow characteristics on the flat tip with a rounded inlet edge are investigated in a large-scale aeroengine turbine cascade with the change of tip gap-to-span ratio (h/s), using the naphthalene sublimation and oil film methods. When h/s ≤ 1.5%, there exists no distinct flow separation at the tip gap inlet. For h/s = 0.5% and 1.0%, the tip surface near the inlet has high local thermal load, whereas that near the exit has low local thermal load. When h/s ≥ 1.75%, however, there is a strong flow reattachment after the inlet flow separation, and severe thermal load is found at the reattachment site. Thus, the critical value of h/s, at which the inlet flow separation is triggered, is about 1.75%. The increments of h/s from 0.5% to 1.5%, from 1.5% to 1.75%, and from 1.75% to 2.5% result in a little decrease, a substantial increase, and a relatively small increase in the average tip thermal load, respectively. The rounded flat tip has much lower average thermal load than the simple flat tip especially when 0.5% ≤ h/s ≤ 1.5%. In this study, qualitative tip gap flow models over the rounded flat tip are suggested for the wide range of h/s.

Energy burden and air conditioning adoption in New York City under a warming climate

• Adaptation to summer heat can place uneven economic burden across households • Climate change intensifies relative energy costs of air conditioning use • Low income homes see large burden increase in spite of lower thermal load rise Global climate change has increased the need for cooling indoor spaces, leading to a rise in adoption of air conditioning. This adoption, while decreasing health risks, can increase energy use and pose economic burdens in low income households. Here, we estimate the burden associated with cooling, as well as potential extreme heat exposure without it in the largest city in the US, New York using a coupled weather and building energy model, utility pay scales, and household income data from the US Census.Results show uneven distribution of AC economic burden, with lower income neighborhoods experiencing the largest relative costs. High-burden neighborhoods see the largest climate-driven increases in spite of lower enthalpy increases. These neighborhoods also have the most exposure to indoor extreme heat, which may triple by end of century. Energy burden may pose a barrier to AC operation, with estimated cost in the lowest income households reaching up to 6.1% of income for a 100 m 2 dwelling, which could increase to 8% by end of century. We also explore adaptation strategies and quantify their impacts, finding that modifying traditional set points and reflective roofs can reduce energy burden significantly, by up to 20% in the highest burden neighborhoods.

Development of 4kA Current Leads Using Stacked REBCO Tapes for BESIII Detector Magnet

For the Beijing Spectrometer III (BESIII) superconducting solenoid magnet (SSM) backup valve box upgrade project, a pair of 4kA HTS current leads was designed, manufactured and tested. The baseline design of the current leads adopted a stacked REBCO (Rare-Earth Barium-Copper-Oxide) conductor solution to achieve a lower thermal load at 4 K, improve the stability of the magnet, and meet the requirements in the upgrade project such as leaving the existing cryogenic system and the internal space of the valve box unchanged. Owing to the adoption of REBCO conductor, the heat leakage was effectively controlled.Construction of offline test platform and a preliminary test result are discussed, verified the current capacity of the current lead prototype. The development of a novel soldered stacked REBCO conductor is also described.

Experimental Study on Preparation and Heat Transfer of Nickel-Based Ammonia Loop Heat Pipe

Abstract The loop heat pipe (LHP) is a passive heat sink used in aerospace and electronic devices. As the core component of the LHP, the physical property parameters of porous wick directly affect the overall performance of the LHP. In this paper, the performance of the porous wick is improved by adjusting the pore size, thereby improving the performance of the LHP. The nickel-based double-pore porous wicks are prepared by T225 nickel powder and NaCl particles, and the pore size of the porous wicks can be changed by different cold pressing force (30 kN, 40 kN, 50 kN, and 60 kN). The effects of different cold pressing force on the porosity, permeability, and other physical property parameters are studied when the ratio of pore former is 20 wt.%. In the end, we select the cold pressing force of 30 kN to prepare the porous wick of the LHP. Then the effects of constant load and variable load of the heat transfer performance under different placement elevations are studied. The results show that the heat load range is 10 W–100 W, the minimum evaporator thermal resistance is 0.424 K/W, and the minimum LHP thermal resistance is 0.598 K/W. When β = 0 deg, there is a “backflow” phenomenon at the initial stage of low thermal load. With the increase of thermal load, the “backflow” duration decreases until it disappears, and the startup time becomes shorter. The thermal resistances of the evaporator and LHP decrease rapidly and then slowly increase. When β = –90 deg, the LHP appears to demonstrate “reverse startup” phenomenon.

Laser ablation of silicon with THz bursts of femtosecond pulses

In this work, we performed an experimental investigation supported by a theoretical analysis, to improve knowledge on the laser ablation of silicon with THz bursts of femtosecond laser pulses. Laser ablated craters have been created using 200 fs pulses at a wavelength of 1030 nm on silicon samples systematically varying the burst features and comparing to the normal pulse mode (NPM). Using bursts in general allowed reducing the thermal load to the material, however, at the expense of the ablation rate. The higher the number of pulses in the bursts and the lower the intra-burst frequency, the lower is the specific ablation rate. However, bursts at 2 THz led to a higher specific ablation rate compared to NPM, in a narrow window of parameters. Theoretical investigations based on the numerical solution of the density-dependent two temperature model revealed that lower lattice temperatures are reached with more pulses and lower intra-burst frequencies, thus supporting the experimental evidence of the lower thermal load in burst mode (BM). This is ascribed to the weaker transient drop of reflectivity, which suggests that with bursts less energy is transferred from the laser to the material. This also explains the trends of the specific ablation rates. Moreover, we found that two-photon absorption plays a fundamental role during BM processing in the THz frequency range.

Repetitive tip convective transport and its flow physics in a large-scale turbine cascade

In order to understand repetitive convective transport and its flow physics over the flat tip of a turbine blade, high-spatial resolution measurements of thermal load and aerodynamic loss are performed in a large-scale cascade. The thermal load distributions measured with the naphthalene sublimation technique show that for two tip gaps of h/s = 1.0% and 2.0%, there is a repetitive change of thermal load upstream of the mid-chord, and wider tip gap makes thermal load change more severe but less repetitive. The mean distance between the neighboring peaks of thermal load in the direction normal to local flow for h/s = 2.0% is twice the one for h/s = 1.0%. Present total pressure measurements show that in the area of repetitive thermal load change for h/s = 2.0%, there exists a distinct repetitive loss change only near the tip surface. A qualitative flow model in the area of repetitive change is proposed for h/s = 2.0%. According to the flow model, the separation bubble undergoes a wave-like repetitive change in its thickness and length. Just behind the ridge of the wave-like separation bubble, low thermal load coexists with high loss, whereas just behind its valley, high thermal load coexists with low loss.

High pressure thermal sterilization of barramundi ( Lates calcarifer ) muscles in brine: Effects on selected physicochemical properties

Barramundi (Lates calcarifer) muscle with brine 2% in Stand-up-retort pouches was treated at different temperatures from 90°C to 120°C at 600 MPa, 5 min. Samples retorted with Fo = 3.38 min were used as control. Texture attributes such as hardness and springiness of the high pressure thermal sterilized (HPTS) barramundi samples were increased compared to the retorted samples. Color, TBA, and pH values were similar for all treatments, except for a significant increase in pH of samples treated at 90°C, 600 MPa, 5 min after 3 months of storage, indicating microbial spoilage. Textural sensory quality of HPTS products was also better than retorted products. High pressure thermal sterilization (HPTS) at 600 MPa and 110°C or 120°C for 5 min resulted in shelf-stable barramundi products. Overall, HTPS could be a feasible option for the production of sterilized fish product with better texture compared to conventional retorted fish product. Practical applications High pressure and thermal sterilization (HPTS) of food products is emerging as an innovative method with many advantages. HPTS could result in better nutrition and sensory quality of sterilized food products as lower thermal load applied to the product and less unwanted food processing contaminants such as furan are also produced in food products. However, the application of HPTS on food products, especially, seafood products is still in early stage and limited. The result of this study could be used to develop a scale-up process for sterilized barramundi products in the food industry.

Investigating the dearating hotwell working regimes of the PT-60-130/13 steam turbine

THE PURPOSE. To consider the problems of the increasing dissolved oxygen concentration in feedwater, especially after the condensate pumps. To estimate the opportunity of the vacuum thermic deaeration intensification inside the PT-60-130/13 LMZ steam turbine condenser to reduce the feedwater system rate of corrosion. Perform a thermal test of the external deaerating hotwell, which provides reducing dissolved oxygen concentration by the hot drains and recirculating feedwater. To evaluate the march of the dissolved oxygen concentration in feedwater after the inclusion of the deaerating hotwell. METHODS. The thermal test of the external deaerating hotwell was chosen for evaluating water deaeration. RESULTS. In this paper, the results of the thermal tests are given. The relation of the dissolved oxygen concentration from heating fluid flow is also presented. CONCLUSION. The use of the external deaerating hotwell allows achieving dissolved oxygen concentration below the norms established by the сode of operation for electrical power plants and grids to ensure the maintenance of an acceptable water-chemical regime of the feedwater. During the tests, the dissolved oxygen concentration decreased by 70% and reached a value of 8 mcg/dm3. The deaerating hotwell of the considered type can be recommended for the operation, especially during start-up modes and modes with the low thermal load on the condenser cooling surface.

Thermomechanical fatigue resistance of low temperature solder for multiwire interconnects in photovoltaic modules

Novel interconnect technologies leveraging low melting temperature solders, such as multiwire interconnects, are being deployed in photovoltaic (PV) modules for improved reliability through interconnect redundancy and lower thermal loads during interconnection and lamination. However, the equivalency of standardized accelerated testing to field conditions has not yet been established for these emerging technologies. In this study, the thermomechanical fatigue resistance of low temperature solder alloys is investigated and compared to that of conventional SnPb to assess the acceleration behavior of these alloys. While InSn is shown to have sufficient thermomechanical fatigue resistance on the order of that of SnPb, these results indicate Sn–Bi alloys may have poor thermomechanical fatigue resistance at field conditions. The results also show that Sn–Bi alloys have thermal cycling acceleration factors of less than one. This indicates that the standardized accelerated thermal cycling test, such as that in IEC 61215, will produce misleading results for Sn–Bi alloys and that unique testing is required for this PV module architecture. Though accelerated thermal cycling may be a meaningful qualification test for SnPb solder joints, these results suggest that mechanical loading may be a more appropriate test for Sn–Bi multiwire interconnects. This is due to the distinct processing and geometry of multiwire interconnects which may allow for mechanical, rather than strictly metallurgical interconnections.

An accurate calorimeter-based method for the thermal characterization of heat pipes

This study presents a method that can be used to accurately determine the thermal performance of a cylindrical heat pipe. In the method, the heat pipe is placed between two stainless steel 304 cylindrical blocks, configured as radial calorimeters that achieve thermal contact with the evaporator and condenser sections of the pipe. A flexible isothermal electrical heater mat surrounds the evaporator block, and a liquid-cooled copper pipe wrapped around the condenser block is used to remove heat. High precision thermistors (±0.01 K) positioned at fixed radial locations within the calorimeters are used to measure the heat supplied to the evaporator and the heat extracted from the condenser. One-dimensional radial conduction is assumed to occur within each calorimeter, and this enables the quantification of heat flows from the temperature readings. This assumption is verified by a steady-state analysis of the radial, axial and circumferential temperature differences within the evaporator calorimeter, based on data recorded for the lowest and highest heat inputs. Furthermore, a numerical model is used to confirm that end effects have a negligible influence on radial conduction within each calorimeter. This study concludes that the most commonly used characterization techniques for heat pipes can greatly overestimate thermal performance (15–32% for input powers of 7.5–25 W respectively) due to inaccurate quantification of heat flows into the evaporator and from the condenser. The calorimetric technique reported here achieves uncertainties in thermal resistance of <7.5% for low thermal loads (<12.5 W) and <6% for higher loads (>12.5 W). Moreover, the method achieves a significant improvement in the experimental thermal efficiency, with values of >75% recorded for all heat inputs in this study. The use of radial calorimeters in the current study obviates the requirement for calculating the losses from the heater to ambient, hence achieving low uncertainties in thermal resistance and effective thermal conductivity for a range of heat inputs.

Mechanical and Thermal Load Effects of Novel MWFs Delivery Method in Milling of Ti–6Al–4V

This work mainly focuses on the effectiveness of both rake and flank face application of the different metal working fluid (MWF) strategies such as liquid CO2, minimal quantity lubrication (MQL), and emulsion in face milling of Ti–6Al–4V alloy. Modified CoroMill 600 cutter via internal channels to both rake and flank faces of the inserts with PVD coated inserts were used for the studies. This novel approach of delivery of MWFs has been investigated on effective thermo-mechanical loads; in terms of the evolution of cutting temperature, cutting forces, and residual stresses. The hardness of the machined surfaces and chip microstructure analysis were also conducted to understand more about the mechanical and thermal load effects in machined material and observed parameters. It has been found that the effectiveness of both rake and flank application of the liquid CO2 machining is a better alternative for the emulsion and MQL strategies. Low thermal deformation of the material, higher magnitude of compressive residual stresses, and lower thermal load throughout the machining cycle have been observed. However, an increase in the mechanical load was observed because of the cold strength hardening of the Ti–6Al–4V workpiece at the liquid CO2 environment. These effects are negligible at room temperature after machining. Overall results show that the cryogenic machining offers best and lower thermal load effects over MQL and emulsion strategies for both rake and flank applications.

Low load performance of tangentially-fired boiler with annularly combined multiple airflows

A novel burner arrangement scheme with annularly combined multiple airflows (ACMA) was previously proposed for wall-tangentially fired boiler (WTFB), and its superiority over traditional WTFB had been proved. However, coal-fired boilers are often required to play the role of peak-shaving. To this, low load performances of ACMA boiler were investigated in this work to test whether ACMA can still work well under low boiler thermal load (BTL) conditions. Results show that ACMA boiler performance is still better than that of traditional WTFB under low BTL condition, with smaller airflow deflection, improved coal combustion behavior and alleviated thermal deviation on suspended heating surfaces. Besides, NOx emission characteristic of ACMA boiler under low BTL is more desirable. Furthermore, the location of non-service burners has significant effects on coal combustion and heat transfer processes under 440 MW load conditions, and closing the upper burner group is the optimal choice in terms of the comprehensive boiler performance. These findings deepen the understanding of ACMA boiler and provide theoretical and practical guidance in its application in power plants.

Thermomechanical behaviour of an energy pile–raft foundation under intermittent cooling operation

This paper presents two in situ experimental investigations of the influence of intermittent and continuous cooling operation on thermal and mechanical responses of a foundation. The experiment was conducted with 16 h of cooling operation and 8 h of rest (C-16 mode) for 46 days and with 24 h of cooling operation (C-24 mode) for 32 days. A lower number of daily operating hours promoted natural ground thermal recovery and led to higher heat exchange rates with lower thermal loads on the foundation. The constant heat exchange rate in C-16 was approximately 115 W/m, which was 53.3% higher than the constant heat exchange rate at the same time in C-24. The pile temperatures at all depths in C-16 were decreased by 29.0–36.8% compared to those in C-24. Thermally induced stresses of the pile and raft in C-16 were 25.8–35.7% and 85.9% lower than the thermally induced stresses of the pile and raft in C-24. The mechanical responses of the energy pile in C-16 were reversible. During the cyclic cooling and recovery of C-16, stable changes in axial strain and stress with pile temperature were observed over further cycles, without significant variations in pile end displacement and the vertical stress at the pile toe.

Methodological investigation into the noise influence on nanolasers' large signal modulation.

Nanolasers are considered ideal candidates for communications and data processing at the chip-level thanks to their extremely reduced footprint, low thermal load and potentially outstanding modulation bandwidth, which in some cases has been numerically estimated to exceed hundreds of GHz. The few experimental implementations reported to date, however, have so-far fallen very short of such predictions, whether because of technical difficulties or of overoptimistic numerical results. We propose a methodology to study the physical characteristics which determine the system's robustness and apply it to a general model, using numerical simulations of large-signal modulation. Changing the DC pump values and modulation frequencies, we further investigate the influence of intrinsic noise, considering, in addition, the role of cavity losses. Our results confirm that significant modulation bandwidths can be achieved, at the expense of large pump values, while the often targeted low bias operation is strongly noise- and bandwidth-limited. This fundamental investigation suggests that technological efforts should be oriented towards enabling large pump rates in nanolasers, whose performance promises to surpass microdevices in the same range of photon flux and input energy.