Heat Accumulation Process Research Articles

Characteristics of an antistatic semiconductor bridge based on micro/nano processing techniques

Abstract Regarded as a novel type of igniter, semiconductor bridge (SCB) prove superior in burst time and burst energy (less than 5 mJ). Nevertheless, SCB discharged by strong electrostatic discharge (ESD) inevitably leads to damage. To enhance the electrostatic safety of the semiconductor bridge initiator, an antistatic semiconductor bridge (ASCB) initiator incorporating a transient suppression (TVS) diode was fabricated based on micro/nan processing techniques. Three sizes of polysilicon bridge (10440 µm2, 17020 µm2, and 23760 µm2) and two breakdown voltages of TVS (7.3V and 8.6V) were designed. Then constant discharge test and ESD test were carried out to investigate the effects of bridge area and TVS breakdown voltage on the performance of ASCB. The results showed that, the energy density of polysilicon bridge is a linear function of the ratio of the square of the current to the area of the polysilicon (ISCB2/A). The breakdown voltage will affect the shunt of TVS. During polysilicon heat accumulation process, owing to shunt of TVS, the energy applied to the polysilicon bridge reduced. In addition , the bridge with a larger area were more difficult to reach the explosive limit. Therefore, both the breakdown voltage of the TVS and the area of the polysilicon bridge influenced the explosive characteristics of the ASCB. The antistatic performance of ASCB is obviously stronger than that of SCB, and A2 (ASCB with bridge area of 23760 µm2 and breakdown voltage of 7.3V) is the strongest among the three types of ASCB. Reducing the breakdown voltage of TVS and increasing the bridge area of polysilicon can effectively improve the antistatic performance of ASCB.

Bessel beam fabrication of graphitic micro electrodes in diamond using laser bursts

We present the fabrication of conductive graphitic microelectrodes in diamond by using pulsed Bessel beams in the burst mode laser writing regime. The graphitic wires are created in the bulk of a 500 μm thick monocrystalline HPHT diamond (with (100) orientation) perpendicular to the sample surface, without beam scanning or sample translation. In particular, the role of different burst features in the resistivity of such electrodes is investigated for two very different sub-pulse durations namely 200 fs and 10 ps, together with the role of thermal annealing. Micro-Raman spectroscopy is implemented to investigate the laser-induced crystalline modification, and the results obtained by using two different laser repetition rates, namely 20 Hz and 200 kHz, are compared. A comparison of the micro-Raman spectra and of the resistivity of the electrodes fabricated respectively with 10 ps single pulses and with bursts (of sub-pulses) of similar total duration has also been made, and we show that the burst mode writing regime allows to fabricate more conductive micro electrodes, thanks to the heat accumulation process leading to stronger graphitization. Moreover, the microfabrication of diamond by means of the longest available bursts (~ 46.7 ps duration) featured by 32 sub-pulses of 200 fs duration, with intra-burst time delay of 1.5 ps (sub-THz bursts), leads to graphitic wires with the lowest resistivity values obtained in this work, especially at low repetition rate such as 20 Hz. Indeed, micro electrodes with resistivity on the order of 0.01 Ω cm can be fabricated by Bessel beams in the burst mode regime even when the bursts are constituted by femtosecond laser sub-pulses, in contrast with the results of the standard writing regime with single fs pulses typically leading to less conductive micro electrodes.

The Heat Transfer in Plate Fin Heat Exchanger for Adsorption Energy Storage: Theoretical Estimation and Experimental Verification of the Methodology for Heat Accumulation Process

Adsorption energy storage is a promising resource-saving technology that allows the rational use of alternative heat sources. One of the most important parts of the adsorption heat accumulator is the adsorber heat exchanger. The parameters of heat transfer in this unit determine how fast heat from an alternative energy source, such as the Sun, will be stored. For the design of adsorption heat accumulators, plate fin heat exchangers are mainly used. In this paper, the procedure for the estimation of the global heat transfer coefficient for the adsorber heat exchanger depending on its geometry is considered. The heat transfer coefficient for a LiCl/SiO2 sorbent flat layer under conditions of heat storage stage was measured. Based on these data, the global heat transfer coefficients for a number of industrial heat exchangers were theoretically estimated and experimentally measured for the adsorption cycle of daily heat storage. It was shown that theoretically obtained values are in good agreement with the values of the global heat transfer coefficients measured experimentally. Thus, the considered technique makes it possible to determine the most promising geometry of the plate fin heat exchanger for a given adsorption heat storage cycle without complicated experiments.

Numerical investigation of melting process for phase change material (PCM) embedded in metal foam structures with Kelvin cells at pore scale level

The present numerical study analyzes the melting process of phase change material (PCM) embedded in a metallic foam structure at pore scale level. The computational domain consists of two different sizes of 3D cubic boxes. The analyzed domain is filled with Kelvin cell-structures with different Cell Per Length (CPL) and constant porosity of 0.956. A constant temperature, higher than the melting temperature of PCM, is assigned to one external surface of the enclosure, while the other surfaces are adiabatic. The conjugate problem for the heat transfer between the PCM and the solid structure with Kelvin cells is developed. Enthalpy-porosity method is used to describe the PCM melting process. The finite volume method is used to solve the conjugate heat transfer problem at pore scale level by Ansys-Fluent code. A comparison of different CPL values is reported in terms of liquid fraction, average temperature of the PCM, and energy storage. The comparison is also considered between the two different volumes of the cubic boxes. The presence of the metallic structured Kelvin cells increases the overall heat transfer rate and decreases the melting time. Results for smaller cavity indicates that as the CPL number increases, the time required for the PCM melting process decreases. Furthermore, the total heat accumulation process takes a shorter time to reach the maximum value. The melting time and the duration of heat accumulation are worsened for the large cubic box (L = 4 inch) at CLP>6. This is due to the dominant viscous effect, which decreases the velocity induced by the buoyancy forces because of higher contact surface area. In these cases, heat transfer between liquid and solid phases of the PCM decreases substantially.

Study of the model of the phase transition envelope taking into account the process of thermal storage under natural draft and by air injection

The study proposed mathematical modeling of the enclosing structure of the building, which includes an energy-active panel accumulating solar radiation due to the phase transition of the heat-accumulating material. The mathematical model is based on a two-dimensional non-stationary nonlinear heat conduction equation describing the process of heat transfer in the bearing layer of the enclosing structure and the energy-active panel, taking into account the process of heat accumulation under natural and forced traction by air injection. In comparison of the calculation results, it was found. that the efficiency of the use of forced convection relative to natural was 33–44% in the question of the selection of useful heat, depending on the time (second or first day), and the value of heat accumulation showed almost the same results. Taking into account the research carried out by the authors, it is shown by calculation that enclosing structures in which a heat-accumulating material with a phase transition is used to accumulate solar energy are more energy efficient than simple heat accumulation in the carrier layer. The introduction of highly conductive inclusions into the energy-active panel and the use of forced convection instead of natural traction during heat extraction also significantly increase the energy efficiency of the structure, which can subsequently be used as an option for external fencing under appropriate climatic conditions.

Heat accumulation effects in femtosecond laser-induced subwavelength periodic surface structures on silicon

High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for femtosecond laser-induced subwavelength periodic surface structures on silicon. Femtosecond laser micromachining is no longer a nonthermal process, as long as the repetition rate reaches up to 100 kHz due to heat accumulation. Moreover, a higher repetition rate generates much better defined ripple structures on the silicon surface, based on the fact that accumulated heat raises lattice temperature to the melting point of silicon (1687 K), with more intense surface plasmons excited simultaneously. Comparison of the surface morphology on repetition rate and on the overlapping rate confirms that repetition rate and pulse overlapping rate are two competing factors that are responsible for the period of ripple structures. Ripple period drifts longer because of a higher repetition rate due to increasing electron density; however, the period of laser structured surface is significantly reduced with the pulse overlapping rate. The Maxwell–Garnett effect is confirmed to account for the ripple period-decreasing trend with the pulse overlapping rate.

Experimental and numerical comparison of heat accumulation during laser powder bed fusion of 316L stainless steel

Heat accumulation during laser powder bed fusion (LPBF) of metallic build parts can adversely affect their microstructure and mechanical properties. To study the heat accumulation during 316L steel based parts manufactured by LPBF, a finite element method (FEM) based numerical study is carried out. For the investigation, a computationally efficient FEM based model, where the whole layer is simultaneously exposed to a heat source, is used. The simulation results are compared with experimental results to validate the numerical model. While considering different influencing factors such as volumetric energy density (VED) and inter-layer time (ILT), the FEM model is shown to successfully simulate the process of heat accumulation during LPBF based manufacturing of a cuboidal shaped geometry. It is shown that ILT and VED have a significant effect on heat accumulation. The validated numerical model provides a good basis for the optimization of processing parameters and geometries for a future investigation of a reduction of heat accumulation effects. Furthermore, it can be used to quickly provide preheating boundary conditions for detailed investigations by different model approaches at a finer scale for future studies.

Influence of alternating electric current on the process of heat accumulation in a mixture of Na2SO4·10H2O–Na2S2O3·5H2O

One of the most critical tasks of modern energy is accumulating thermal energy due to the inefficient use of thermal energy during the underloading of power systems in which heat-accumulating materials are used. Therefore the paper studies the effect of alternating electric current on the heat-accumulating properties in a mixture based on Na2SO4·10H2O. It is established that the AC effect leads to an increase in the melt crystallization temperature of Na2SO4·10H2O and Na2S2O3·5H2O and also contributes to the return of heat. The selection of the treatment mode of the Na2SO4·10H2O–Na2S2O3·5H2O (50: 1 wt.) mixture by the AC was carried out. It was shown that the latent heat of melting of 329 kJ/kg is achieved at 500000 Hz frequency.

The Effect of Multiple Thermal Process on Microstructural Evolution and Mechanical Properties of Additive Manufactured Al/Steel Structure

Wire and arc additive manufacturing (WAAM) provides a convenient solution for the integrated design and manufacturing of Al/steel structures. The multiple thermal cycles inherent in WAAM can affect the Al/steel interface and ultimately the overall performance of the Al/steel structure. Herein, the evolution behavior of the Al/steel interface microstructure under different WAAM modes, number of thermal cycles, and interpass temperature is investigated. The results show that the process of heat accumulation plays an important role in the evolution of Al/steel interface. As the number of thermal cycles increases, the intermetallic compounds layer gradually transforms from the mainly τ5‐Al8Fe2Si phase to (Al, Si)13(Fe, Cr)4 phase. The rise of interpass temperature significantly aggravates the microstructural evolution process, but the final interface structure can be manipulated employing temperature control. When the interpass temperature is lower than 250 °C, the formation of the brittle Fe2Al5 phase is avoided. With the increase of thermal cycles, the shear strength of Al/steel additive specimens increases first, then decreases, and finally tends to be stable. The changes in shear strength are closely related to the interface microstructures.

Vibration-Enhanced Heat Transfer of Double-Array Helical Elastic Tube Bundle Heat Exchanger

This paper aims to analyze the heat transfer characteristics of a double-array helical elastic tube bundle heat exchanger with vibration. The characteristics were investigated by using a bidirectional fluid–solid coupling calculation method with different winding numbers and inlet-flow velocities. Results indicate that in the shell-side fluid, the greater the flow velocity, the more the turbulent energy of fluid, the stronger the turbulence characteristics, and the better the heat transfer effect. In the shell-side fluid, the process of heat exchange is a heat accumulation process: the greater the flow velocity, the more heat absorbed by the fluid in a unit of time, and the better the heat transfer effect. The performance evaluation criteria (PEC) have increased by 2.33%, and the average volume heat transfer coefficient (HTC) has increased by 80.80% when the inlet-flow velocity is constant, as the winding number increases. In addition, PEC has increased by 7.84%, and the average volume HTC has increased by 3.6 times when the winding number is constant, as the inlet-flow velocity increases.

CSP clustering in unit commitment for power system production cost modeling

The power system planning requires the simulation of unit commitment (UC) for long time periods up to multiple years or decades which is conducted with production cost modeling (PCM) and usually ends up solving a number of mixed integer programming problems. The development of concentrating solar power (CSP) raises the computational burden of PCM dramatically due to its complex structural and operational characteristics, small unit capacity and large unit number. To improve the PCM efficiency for power systems with large scale CSP generation, a CSP clustering method is proposed based on a novel CSP unit model where the startup and heat accumulation process is considered to simulate CSP operation properly and avoid infeasible operation schemes. In the CSP clustering method, a series of CSP units are modelled in clusters and the numerous binary variables are replaced by integer ones. The number of the variables can be greatly reduced and so is the problem scale. The case studies on the modified IEEE-RTS 1979 have verified the validity and effectiveness of the proposed model and method. The CSP clustering method well outperforms the aggregated unit model which is introduced for comparison. The solution time for the UC with CSP is dramatically reduced (even by 1–2 orders of magnitude) with high accuracy especially the generation cost whose deviation is usually below 0.1%. The proposed method shows great potential in power system planning and operation with large-scale CSP generation.

Long focal length high repetition rate femtosecond laser glass welding.

A long focal length focusing device is proposed for the process of glass welding by femtosecond laser pulses at high repetition rate and we report on the significant advantages. The study is performed using a 100 mm focusing length F-theta lens. The results are compared to those obtained with a high numerical aperture microscope objective. The long focal length with the associated Rayleigh length method allows a robust high process speed: welding at 1000 mm/s has been achieved, several orders of magnitude larger compared to what was reported until now. Moreover, for one pulse, the same energy on a larger laser spot leads to a lower thermic gradient increase. As a result, with the proposed parameters, the heat accumulation process reduces the residual stress in the welding seams, preventing the formation of fractures inside the seams: mechanical resistance at 30 MPa has been measured.

Experimental demonstration of the thermodynamic advantage of modular heat storage system for a variable-temperature input

Storage acts as an inseparable component of the heat accumulation process using an inherently intermittent and variable source such as solar heat. Sensible thermal storage often is chosen over the other options owing to its operational simplicity and lower response time. In the current study we propose a novel method of designing the sensible heat storage system which can provide significantly better energetic and exergetic efficiency particularly under variable temperature profile for the input flow as compared to the conventional single tank storage. Through small scale laboratory experiments, we demonstrate the proof of concept for the proposed modular multi-tank storage against a low temperature input flow having prescribed temperature variations. We observe that for both charging and discharging, the modular storage holds a distinct thermodynamic advantage due the thermal segregation as well as the appropriate sequencing of the use of different tanks based on heat transfer argument. The concept of modular thermal storage can remarkably enhance the flexibility of plant operation and improve the energetic and exergetic efficiencies of the storage.

An experimental and theoretical study of the solidification process of phase change materials in a horizontal annular enclosure

The main purpose of this paper is to examine experimentally and theoretically the process of heat accumulation and heat release for PCM (phase change materials) in an annular space.The theoretical part of this work provides a solution of the problem of liquid solidification in an annular space under the influence of free convection. Here a simplified quasi-steady-state model for solidification has been applied. The new simplified model describes the solidification phenomenon with an imposed boundary condition on the solidification interface by applying a heat transfer coefficient. From the developed model, the influence of various dimensionless parameters on the phase change problem can be seen clearly.Measurements and observation of the thickness of the solidified layer were performed in a newly built apparatus. In addition, this paper is also concerned with the role of the contact layer in the solidification process. Results are showing the thickness of the solidification layer depending on time and the distribution of the local heat transfer coefficient on the surface of the solidification front. The obtained experimental and numerical results show good agreement.The examined solidification process makes it possible to use the results obtained for the design of new heat accumulators. The presented method to analyse heat accumulation is important for power engineering. It opens up the possibility to reduce the size of heat accumulators, thus, possible leading to a reduction in their production costs.

Modelling of the heat accumulation process during short and ultrashort pulsed laser irradiation of bone tissue.

An analytical model is presented that qualitatively describes the cooling of a biological tissue after irradiation with short and ultrashort laser pulses. The assumption that the distribution of temperature at the initial moment of surface cooling repeats the distribution of the absorbed laser energy allowed us to use the thermal conductivity approximation in both cases. The experimental results of irradiation of dry bone with nanosecond and femtosecond laser pulses are compared with the calculated data. The necessity of taking into account the change in the optical parameters of hard tissue in the field of laser irradiation during its treatment by nanosecond and femtosecond laser pulses and the key role of residual heating in its carbonization around the exposure region is shown. The application of the model to a particular biological tissue can significantly simplify the search for optimal parameters of lasers for surgical procedures.

Thermal failure mechanism of fiber ropes when bent over sheaves

Thermal damage is an important failure mechanism that affects the bending failure of fiber ropes. This is relevant because synthetic fibers often have a relatively low melting point and low thermal conductivity. In cyclic bending over sheave (CBOS), the heat generated by friction and deformation is not conducted rapidly to the external environment, and the temperature of the rope core increases quickly. This higher temperature greatly reduces the mechanical properties of the fiber, thus accelerating the final rope failure. In this paper, evidence of thermal damage in the bending process of a braided synthetic fiber rope is given. The test conditions inducing thermal damage are discussed, including stress level, bending frequency and diameter ratio. The reasons for the heat generation and the dynamic process of heat accumulation inside the rope during CBOS are also discussed. This study aims to provide theoretical and experimental guidance for the design and use of fiber rope.

Modelling of heating and photoexcitation of single-crystal silicon under multipulse irradiation by a nanosecond laser at 1.06 μm

We report a theoretical study of heating and photoexcitation of single-crystal silicon by nanosecond laser radiation at a wavelength of 1.06 μm. The proposed physicomathematical model of heating takes into account the complex nonlinear dynamics of the interband absorption coefficient of silicon and the contribution of the radial heat removal to the cooling of silicon between pulses under multipulse irradiation, which allows one to obtain a satisfactory agreement between theoretical predictions of silicon melting thresholds at different nanosecond pulse durations and experimental data (both under single-pulse and multipulse irradiation). It is found that under irradiation by nanosecond pulses at a wavelength of 1.06 μm, the dynamic Burshtein – Moss effect can play an important role in processes of photoexcitation and heating. It is shown that with the regimes typical for laser multipulse microprocessing of silicon (the laser spot diameter is less than 100 μm, and the repetition rate of pulses is about 100 kHz), the radial heat removal cannot be neglected in the analysis of heat accumulation processes.

Integrating two-temperature and classical heat accumulation models to predict femtosecond laser processing of silicon

A robust, computationally efficient modeling method describing multi-pulse femtosecond laser-material interaction is required to determine the optimal laser parameters to control and differentiate non-thermal ablation and heat accumulation processes for surface structuring and laser welding applications. We establish a three-dimensional, two-temperature model (TTM) and a heat-accumulation model based on classical heat generation and conduction equations to evaluate their efficacy and efficiency in simulating non-thermal ablation and heat accumulation during multi-pulse femtosecond laser processing of silicon. Only the TTM is capable of accurately predicting the laser fluences required to achieve non-thermal ablation, which is experimentally validated. Both the TTM and the classical heat accumulation model can predict heat accumulation. The TTM can accurately predict heat accumulation, but requires lengthy simulation times on the order of several hours. The classical heat accumulation model consistently predicts heat accumulation with the TTM and is time efficient, but is case specific to interaction parameters, requiring input of an experimentally-determined absorption coefficient. For the first time to our knowledge, an integrated modeling method is devised to accurately and efficiently simulate laser-processing-induced heat accumulation by using the TTM to determine an absorption coefficient to feed back to the heat accumulation model to extend it to the general case. This integrated modeling method enables the accurate prediction of heat accumulation with simulation times on the order of a minute per pulse, defining a path to determine laser parameters to control heat accumulation for specific processing applications.

Investigation of the efficiency of a high temperature heat storage charging

The article presents the results of the test of a heat storage filled with chamotte brick. The air parameters were used as the basis for determining the heat stream represented by a working medium, which was then compared with the stream accumulated in the material filling the deposit. Additionally, heat streams were shown for individual segments of the deposit. The efficiency of heat accumulation was determined for each of them. They showed that the efficiency of accumulation process was highest in the deposit’s first segments and the lowest in the last segments, where the air was the coldest. The dynamics of the efficiency’s shift was different for each of the observed segments. In the area closest to the inlet of hot air, the dynamics of the process of heat accumulation decreased the fastest and after one hour only a slight increase of efficiency was visible in the function of time. In the accumulation material placed closest to the outlet, the process of absorbing heat was very fast, starting from the 20th minute before the tests were completed. The smallest changes in the process’ character, throughout the whole time of testing, were recorded in the middle layer.

Thermal hazard analysis of cyclohexanone peroxide and its solutions

Cyclohexanone peroxide (CYHPO) is widely used in the chemical industry, but unfortunately, as an organic peroxide, it has been involved in many serious fires and explosions in daily manufacturing, storage, and transportation. We present an advanced methodology of application of thermal analysis for thermal hazard investigation of complex chemical reactions. The applied method is based on a differential isoconversional approach and involves the combination of non-isothermal differential scanning calorimetry (DSC) and adiabatic measurements by accelerating rate calorimeter (ARC) for kinetic analysis and prediction. The kinetic parameters and heat balance were analyzed and used for a simulation of the adiabatic behavior: time to maximum rate under adiabatic conditions (TMRad) and self-accelerating decomposition temperature (SADT). Applications of finite element analysis (FEA) for heat balance and accurate kinetic description allowed us to determine the effect of scale, geometry, heat transfer, thermal conductivity, and ambient temperature on the heat accumulation process. The presented explosion simulations of the thermal behavior of 100kg storage tank at different temperatures, related to the possible storage scenarios, may help in the elucidation of a real accident which occurred in Beijing during CYHPO storage.