Multipass System Research Articles

Performance prediction of single-pass and multi-pass low-cost solar air heater

This study introduces a mathematical model and experimental evaluation of solar air heating utilising an absorber surface constructed from low-cost upcycled materials. The research presents a solar air heater prototype, suitable for applications such as space heating and agricultural drying. The solar heating system was modelled using upcycled beverage aluminium cans, considering both single and multi-pass flow configurations. Performance in terms of useful heat was determined through both mathematical model simulations and experimental methods. The multi-pass system demonstrated superior performance, delivering increased usable heat at elevated temperatures compared to the single-pass system. A comparative analysis and validation were conducted between numerical investigations with natural and forced convection on the five-pass solar air heater and experimental test outcomes. This research highlights the potential of utilising waste materials to develop cost-effective, solar heating solutions, contributing to energy management and waste reduction strategies. The findings can be explored for future explorations into sustainable and renewable energy solutions, particularly beneficial in regions with constrained economic resources.

A white cell based broadband transient UV-vis absorption spectroscopy with pulsed laser photolysis reactors for chemical kinetics under variable temperatures and pressures

UV-vis spectroscopy is widely used for kinetic studies in physical chemistry, as species’ absolute cross-sections are usually less sensitive to experimental conditions (i.e., temperature and pressure). Here, we present the design and characterization of a multipass UV-vis absorption spectroscopy white cell coupled to a pulsed-laser photolysis flow reactor. The glass reactor was designed to facilitate studies of gas phase chemical reactions over a range of conditions (239–293 K and 10–550 Torr). Purged windows mitigate contamination from chemical precursors and photolysis products. We report the measured impact of this purging on temperature uniformity and the absorption length and present some supporting flow calculations. The combined optical setup is unique and enables the photolysis laser to be coaligned with a well-defined absorption pathlength probe beam. This alignment leverages the use of one long-pass filter to increase the spectrum flatness and increase the light intensity vs other systems that use two dichroic mirrors. The probe beam is analyzed with a dual exit spectrograph, customized to split the light between an intensified CCD and photomultiplier tube, enabling simultaneous spectrum and single wavelength detection. This multipass system yields a pathlength of ∼450 cm and minimum observable concentrations of ∼3.7 × 1011 molecule cm−3 (assuming cross-sections ∼1.2 × 10−17 cm2). The temperature profile across the reaction region is ±2 K, defined by the worst-case temperature of 239 K, validated by measurements of the N2O4 equilibrium constant. Finally, the system is implemented to study the simplest Criegee intermediate, demonstrating the instrument performance and advantages of simultaneous spectrum and temporal profile measurements.

Development of dual-path multi-pass Thomson scattering system in GAMMA 10/PDX

A dual-path Thomson scattering (DPTS) system was developed to measure electron temperature and density in a GAMMA 10/PDX central cell (CC) and an end cell (EC). The DPTS comprises CC Thomson scattering system (CC-TS) and an EC Thomson scattering system (EC-TS). In the CC-TS, we developed a multipass system to improve the signal intensities and time resolution. In the EC-TS, a double-pass system was developed as a preliminary step in developing a multipass system. In a previous EC-TS, the optical components for the double-pass configuration were placed in a vacuum vessel. To reduce the influence of stray light and facilitate alignment, a hole for the double-pass laser path was made on the partition wall in the vacuum chamber such that the probe laser could be extracted into the atmosphere and the double-path configuration could be easily adjusted. We applied DPTS to detached plasma experiments and successfully measured the core and edge electron temperatures and densities with the detached plasma experiments with the additional application of supersonic molecular beam injection and central electron cyclotron heating in the core plasma to simultaneously introduce intermittent particle flux.

Propagation and amplification law of undetermined stray light and influence of signal-to-noise ratio in a multipass amplifier system

Multipass amplifier systems in areas such as high-energy-density physics and astrophysics play an important role, but the undetermined stray light caused by defects seriously influencing the output signal-to-noise ratio (SNR) and even resulting in the failure of the main pulse bombardment. In this study, the modulation of nondeterministic stray light caused by the defects in the optical paths of different components in a multipass amplifier system was examined, and a Mie scattering model of multi-crack defects established. Using ray-tracing simulation, the spatial and temporal distribution of stray light was analysed, and experimental verification was conducted. The law of energy amplification for nondeterministic stray light caused by component defect modulation and an empirical formula for the signal to noise ratio of the pre-pulse system were established. This study provides a reference for the accurate troubleshooting of components, optical path defects and an important theoretical basis for the processing and correction of system components.

Modelling of washboard effect on unpaved roads experimental evidence on non-cohesive materials

Washboard or corrugation is a common phenomenon in unpaved roads. The washboard effect can be very uncomfortable for the driver, but it can also be very dangerous due to the loss of contact between the wheels and the road. There are few pieces of research about this topic, but undulations seem to emerge due to the caŕs velocity and mass. This work aims to identify the main physical variables controlling the appearance of the washboard effect. For this purpose, an experimental set-up of a multi-pass system was developed. This apparatus consists of a rotating wheel rolling over a sandy path. This model allows evaluation of the evolution of the undulations resulting from the washboard phenomenon and allows relating it to variables such as the dynamic forces and track profile. Different scenarios were evaluated, including wheel velocity, wheel mass, and soil density.

Upgraded TV Thomson scattering system on the T-10 tokamak

The Thomson scattering system on the tokamak T-10 was upgraded in 2016. The new system is based on previous diagnostic with replacement of main components: laser, fiber bundle and camera. It is the first TS system combining Nd:YAG laser with a TV registration. Previous laser was replaced by a new 100 Hz Nd:YAG laser working during the whole plasma discharge on the second harmonic (λ = 532 nm) with pulse energy of 2,5 J and a duration of 10 ns. A multi-pass system with 5 passes of the beam through the plasma volume is used to inject laser light into the vacuum chamber. The scattered light is transported to the spectrometer by means of a new fiber-optic bundle providing a high spatial resolution of 5 mm over the full plasma diameter of 600 mm. An image intensifier with a GaAs photocathode and a P43 phosphor is used for detection. Fast CMOS camera Vision Research Phantom V7.3 captures images and allows to measure background plasma light between laser pulses. The diagnostic worked during three experimental campaigns and demonstrated the operability in various plasma regimes.

A novel approach for the improvement of the sensitivity of the flow visualization system on supersonic molecular beam of tokamak fuelling

Supersonic molecular beam injection is a robust alternative to control the particles in fusion plasma devices. It is widely used in many experimental studies on the plasma physics. Direct visualization of beam makes it possible for precise optimization of the beam characteristics. However, a normal visualization system does not fully meet the requirements of the measurement of the beam distribution in the low gas density vacuum environment. This paper reports a newly designed multi-pass visualization system without changing the schlieren mirrors. This multi-pass system is designed to make the light passing the testing area several times, where the deflection angle of the light would simultaneously increase. Thus, the sensitivity of the schlieren image is enhanced. The testing result proves the improvement of the sensitivity, which makes it possible to optimized the beam structure in low gas density working conditions.

Improvement in multipass Thomson scattering system comprising laser amplification system developed in GAMMA 10/PDX.

The multipass Thomson scattering (MPTS) technique is one of the most useful methods for measuring low-electron-density plasmas. The MPTS system increases Thomson scattering (TS) signal intensities by integrating all multipass (MP) signals and improving the TS time resolution by analyzing each pass signal. The fully coaxial MPTS system developed in GAMMA 10/potential-control and diverter-simulator experiments has a polarization-based configuration with image-relaying optics. The MPTS system can enhance Thomson scattered signals for improving the measurement accuracy and megahertz-order time resolution. In this study, we develop a new MPTS system comprising a laser amplification system to obtain continuous MP signals. The laser amplification system can improve degraded laser power and return an amplified laser to the MP system. We obtain continuous MP signals from the laser amplification system by improving the laser beam profile adjuster in gas scattering experiments. Moreover, we demonstrate that more MP signals and stronger amplified MP signals can be achieved via multiple laser injections to the laser amplification system in the developed MP system comprising a laser amplification system.

Thin-disk laser system operating above 10 kW at near fundamental mode beam quality.

We report on a thin-disk laser system with more than 10 kW of output power and a beam quality of M2=1.76 at an overall optical-to-optical efficiency of 51%. The system consists of two thin-disk laser oscillators and a thin-disk multi-pass amplifier system. To reach high output powers while maintaining good beam quality, the output beams of two identical laser oscillators are polarization-combined. Subsequently, the beam is amplified in a multi-pass system. To the best of our knowledge, this is the highest output power achieved for a thin-disk laser system with a beam quality close to fundamental mode.

Saturation Time Characteristics of RO Membrane Skid to Clean Water Supply with Pressure Stage in Rejection

Reverse osmosis (RO) is one major water treatment process used to filter out the water pollution due to the Tsunami disaster in Pandeglang. This technology is applied where highly purified water is essential, including sea/groundwater desalination, boiler feed water filtering, product rinsing, laboratory testing, and biotechnology. However, RO requires advanced research to ascertain the method and optimum pressure of the multi-pass system needed to produce clean water through a membrane with a long saturation time. Therefore, this study employs RO multi-pass by varying pressure 6-3, 6-4, and 7-4 on the first and second stage to observe the effects of decreasing flux and TDS enhancement for 72 hours in Tanjung Lame village. The results showed more performance in producing potable water at pressure P1 = 6 bar/P2 = 3 bar compared to P1 = 6/P2 = 3, and P1 = 7/P2 = 4. Moreover, the total dissolved solids (TDS) known to satisfy clean water provision was estimated at 20 ppm, after the permeate in the first stage is used as feedstock in the second. Furthermore, applying P1 = 6 bar and P2 = 3 bar for the first and second stage produced the membrane saturation time in hours ranging between 72-80 and 72-131, respectively.

Evaluation of bend curvature of superheater tube using CFD analysis

PurposeThe heat transfer within a heat exchanger is highly influenced by geometry of the components especially those with hollow structures like tubes. This paper aims to intend toward the study of efficient and optimized heat transfer in the bends of superheater tubes, with different curvature ratio at constant Reynolds Number.Design/methodology/approachThe effect of changing curvature ratio on enthalpy of the fluid passing through the superheater tubes for multi-pass system has been studied with the aid of computational fluid dynamics (CFD) using ANSYS 14.0. Initially a superheater tube with two pass system has been examined with different curvature ratios of 1.425, 1.56, 1.71, 1.85 and 1.99. An industry specified curvature ratio of 1.71 with two pass is investigated, and a comparative assessment has been carried out. This is intended toward obtaining an optimized radius of curvature of the bend for enhancement of heat transfer.FindingsThe results obtained from software simulation revealed that the curvature ratio of 1.85 provides maximum heat transfer to the fluid flowing through the tube with two pass. This result has been found to be consistent with higher number of passes as well. The effect of secondary flow in bends of curvature has also been illustrated in the present work.Research limitations/implicationsThe study of heat transfer in thermodynamic systems is a never-ending process and has to be continued for the upliftment of power plant performances. This study has been conducted on steady flow behavior of the fluid which may be upgraded by carrying out the same in transient mode. The impact of different curvature ratios on some important parameters such as heat transfer coefficients will certainly upgrade the value of research.Originality/valueThis computational study provided comprehensive information on fluid flow behavior and its effect on heat transfer in bends of curvature of superheater tubes inside the boiler. It also provides information on optimized bend of curvature for efficient heat transfer process.

Modified ray transfer matrix method for accurate non-sequential ray tracing between arbitrary reflective mirrors.

The ray transfer matrix method is widely used for analyzing beam-transmission properties and designing multi-pass systems. In this paper, a modified ray transfer matrix method is proposed for tracing an accurate non-sequential ray in three-dimensional space based on a vector reflection theory. The modified ray transfer matrix method can be utilized to analyze a ray transmitting between arbitrary surfaces, which is not confined to rotational symmetrical structures. There is no need to project rays onto two perpendicular planes, nor to introduce a paraxial approximation in our calculation. Since the length and angle of every ray can be calculated accurately, almost no deviation is accumulated in multi-pass system. The modified ray transfer matrix method can be applied in optical design, especially in the design of multi-pass cavities and multi-pass cells.

Adaptive Very Deep Convolutional Residual Network for Noise Robust Speech Recognition

Although great progress has been made in automatic speech recognition, significant performance degradation still exists in noisy environments. Our previous work has demonstrated the superior noise robustness of very deep convolutional neural networks (VDCNN). Based on our work on VDCNNs, this paper proposes a more advanced model referred to as the very deep convolutional residual network (VDCRN). This new model incorporates batch normalization and residual learning, showing more robustness than previous VDCNNs.Then, to alleviate the mismatch between the training and testing conditions, model adaptation and adaptive training are developed and compared for the new VDCRN. This paper focuses on factor aware training (FAT) and cluster adaptive training (CAT). For FAT, a unified framework is explored. For CAT, two schemes are first explored to construct the bases in the canonical model; furthermore, a factorized version of CAT is designed to address multiple nonspeech variabilities in one model. Finally, a complete multipass system is proposed to achieve the best system performance in the noisy scenarios. The proposed new approaches are evaluated on three different tasks: Aurora4 (simulated data with additive noise and channel distortion), CHiME4 (both simulated and real data with additive noise and reverberation), and the AMI meeting transcription task (real data with significant reverberation).The evaluation not only includes different noisy conditions, but also covers both simulated and real noisy data. The experiments show that the new VDCRN is more robust, and the adaptation on this model can further significantly reduce the word error rate (WER). The proposed best architecture obtains consistent and very large improvements on all tasks compared to the baseline VDCNN or long short-term memory. Particularly, on Aurora4 a new milestone 5.67% WER is achieved by only improving acoustic modeling.

Development of a laser amplification system for the multi-pass Thomson scattering system for GAMMA 10/PDX.

The multi-pass Thomson scattering (MPTS) system is a useful technique for increasing the Thomson scattering (TS) signal intensities and improving the TS diagnostic time resolution. The MPTS system developed in GAMMA 10/PDX has a polarization-based configuration with an image relaying system. The MPTS system has been constructed for enhancing the Thomson scattered signals for the improvement of measurement accuracy and the megahertz sampling time resolution. However, in the normal MPTS system, the MPTS signal intensities decrease with the pass number because of the damping due to the optical components. Subsequently, we have developed a new MPTS system with the laser amplification system. The laser amplification system can improve the degraded laser power after six passes in the multi-pass system to the initial laser power. For the first time worldwide, we successfully obtained the continued multi-pass signals after the laser amplification system in the gas scattering experiments.

Compact optical multipass matrix system design based on slicer mirrors.

High path-to-volume ratio (PVR) and low-aberration-output beams are the two main criteria to assess the performance of multipass absorption cells. However, no substantial progress has been reported for large-numerical-aperture-coupled multipass cells, which is due to the accumulated aberrations caused by a large number of off-axis reflections. Based on Chernin's design, in this study, we modified Chernin's four-objective multipass matrix cell by using slicer mirrors to eliminate alignment difficulty and decrease the system volume. A generalized design routine based on user requirements is also proposed. Based on the automatic modeling tool package (Pyzdde) connected with Zemax and boundary conditions of the parameters selection proposed, a low-aberration-output beam and a high PVR are easily obtained compared with other multipass cells schemes. In one demo design, 108 passes (5×7 matrix spots) in a base length of 300mm are presented. The PVR and peak-to-valley value wavefront errors are 67.5m/L and 0.92μm, respectively. Finally, a tolerance analysis of this optical multipass system is also presented. This work may provide better broadband optical absorption cells in terms of response time and a better detection sensitivity in versatile applications.

Effect of Single‐Pass and Multipass Milling Systems on Whole Wheat Durum Flour and Whole Wheat Pasta Quality

Single‐pass and multipass milling systems were evaluated for the quality of whole wheat durum flour (WWF) and the subsequent whole wheat (WW) spaghetti they produced. The multipass system used a roller mill with two purifiers to produce semolina and bran/germ and shorts (bran fraction). The single‐pass system used an ultracentrifugal mill with two configurations (fine grind, 15,000 rpm with 250 μm mill screen aperture; and coarse grind, 12,000 rpm with 1,000 μm mill screen aperture) to direct grind durum wheat grain into WWF or to regrind the bran fraction, which was blended with semolina to produce a reconstituted WWF. Particle size, starch damage, and pasting properties were similar for direct finely ground WWF and multipass reconstituted durum flour/fine bran blend and for direct coarsely ground WWF and multipass reconstituted semolina/coarse bran blend. The semolina/fine bran blend had low starch damage and had desirable pasting properties for pasta cooking. WW spaghetti was better when made with WWF produced using the multipass than single‐pass milling system. Mechanical strength was greatest with spaghetti made from the semolina/fine bran or durum flour/fine bran blends. The semolina/fine bran and semolina/coarse bran blends made spaghetti with high cooked firmness and low cooking loss.

Multi-pass solar air heating collector system for drying of screw-pine leaf (Pandanus tectorius)

An experimental investigation of solar drying of screw-pine leaf has been conducted in the open space of the solar research site, Universiti Teknologi PETRONAS Malaysia (4.385693° N, 100.979203° E). Screw-pine leaf has been used for handcraft in many villages in Asia and Africa. A transient state lumped element analysis was developed to determine the thermal performance of the multi-pass solar collector system (MSCS) in accordance with ASHRAE standards. The facility was assessed under the average daily solar irradiance of 412.6 Wm−2 and ambient temperature of 30 °C over an air mass flow rate range from 0.010 kgs−1 to 0.032 kgs−1. Drying kinetics profiles of screw-pine have been obtained and an improved range from 22% to 26% of instantaneous thermal collector efficiency has been recorded over the double pass collector system (DPCS) while thermal energy storage has contributed 5–8% to system performance. MSCS performance has been determined and achieved the thermal collector, pickup, drying and exergy efficiencies of 58.73%, 66.95%, 36.04% and 27.23–86.82%, respectively. The level of risk on the investment in MSCS has been measured using economic indices to obtain a payback period of 0.75 year. The thermal loss through conventional collector back plate has been prevented by integration of collector unit and the drying cabinet of the system. There is still need to further improve the system performance efficiency through enhanced energy saving innovation technique.

Optical Axis Perturbation Analysis for the Unit-Magnification Multipass System

The optical axis sensitivity for the unit-magnification multipass system (UMS) is presented by using a general misaligned optical element transfer model. The generalized sensitivity factors SD1, SD2, ST1, and ST2 influenced by both the axial and angular misalignments of the objective mirrors in a UMS have been calculated for the first time. The Bernstein-Herzberg White Cells are used as an example, and their alignment tolerance and stability properties are found when their configurations change. The analysis in this paper is helpful for the design of other kinds of multipass gas cells (MGC) with high robustness and avoiding the violent vibration of the optical axis when the misalignment of each mirror is controlled within the tolerance range. Among the five possible perturbations sources, the misaligned factors δix,δiy,θix have more effects on the output beam’s position and the perturbed sources from δix,θix and δiy,θiy have more impacts on the output beam’s slope referred to as x-axis and y-axis, respectively. Higher reflection times mean smaller tolerance range. The results benefit the multipass cell design and the precise alignment of the mirrors within the cell with the purpose of long-term stability in measurements.

Multipass optical system for a Raman gas spectrometer.

In the present work, a multipass optical system intended for increasing the sensitivity of a Raman gas spectrometer based on the 90° geometry of scattered light collection is described. The system is characterized by an adjustment stability and an increased number of laser beams that pass through a small scattering volume, thus allowing the intensities of Raman signals from components of the gas medium in this volume to be increased. It is demonstrated that the application of this multipass optical system allows the sensitivity of the Raman gas spectrometer to be increased practically by 20 times (to several ppm for the 30-s registration time).

Multipass relativistic high-order-harmonic generation for intense attosecond pulses

We demonstrate that the total reflected field produced by the interaction of a moderately relativistic laser with dense plasma is itself an efficient driver of high-order-harmonic generation. A system of two or more successive interactions of an incident laser beam on solid targets may therefore be an experimentally realizable method of optimizing conversion of laser energy to high-order harmonics. Particle-in-cell simulations suggest that attosecond pulse intensity may be increased by up to four orders of magnitude in a multipass system, with decreased duration of the attosecond pulse train. We discuss high-order-harmonic wave-form engineering for enhanced attosecond pulse generation with an electron trajectory model, present the behavior of multipass systems over a range of parameters, and offer possible routes towards experimental implementation of a two-pass system.