The Roadmap to Realize Memristive Three-Dimensional Neuromorphic Computing System

Neuromorphic computing, an emerging non-von Neumann computing mimicking the physical structure and signal processing technique of mammalian brains, potentially achieves the same level of computing and power efficiencies of mammalian brains. This chapter will discuss the state-of-the-art research trend on neuromorphic computing with memristors as electronic synapses. Furthermore, a novel three-dimensional (3D) neuromorphic computing architecture combining memristor and monolithic 3D integration technology would be introduced; such computing architecture has capabilities to reduce the system power consumption, provide high connectivity, resolve the routing congestion issues, and offer the massively parallel data processing. Moreover, the design methodology of applying the capacitance formed by the through-silicon vias (TSVs) to generate a membrane potential in 3D neuromorphic computing system would be discussed in this chapter

Enhanced Fabrication of Microdroplet Generator Nozzle Arrays: Optimizing KOH Etching for Microfluidic Applications

Ultrasonic microdroplet generators are useful devices with broad applications ranging from aerosolized drug delivery to three-dimensional (3D) printing-based additive manufacturing. One such technology comprises a microfabricated array of nozzles with droplet production driven by a piezoelectric transducer. The present study focuses on refining a critical fabrication step, anisotropic wet etching of pyramidal nozzles using a basic potassium hydroxide (KOH) solution. Given the integral role of nozzle geometry in device operation, high-precision techniques including Reactive Ion Etching (RIE), Deep Reactive Ion Etching (DRIE), and KOH wet etching were employed. A tapering geometry is preferred for acoustic wave focusing and efficient droplet generation, and KOH etching naturally yields pyramids due to preferential removal of the (100) plane versus the (111) plane of single-crystal silicon. Though wet etching is less precise than dry etching, it is difficult to form these 3D shapes using dry etching alone. Thus, this work focused on realizing the highest possible level of control over KOH etching. Challenges were encountered in using a conventional etching setup to achieve uniform etching and good surface smoothness, which are crucial to definition of the pyramidal tip geometry. These aspects are also important for use of KOH etching to define microstructures in a range of microfluidic systems. Here, we introduce an ultrasonic-assisted etching method to enhance the KOH etching process, addressing issues like non-uniform etching rates and surface roughness. This research not only provides insight into the microfabrication of ultrasonic microdroplet generators but also contributes to further improvements in microfluidic device manufacturing

Evaluation of frost prevention strategies for membrane energy exchangers

In cold climates, the application of heat recovery is restricted by the issue of frost, which causes potential damage to heat exchangers and degrades their effectiveness. Membrane energy exchangers (MEEs), which enable simultaneous heat and moisture transfer, can reduce and delay frost formation and accumulation in cold climates. MEEs are recognized as the essential component for the new generation of Heating, Ventilation, and Air Conditioning (HVAC) systems. Despite of extensive studies on heat and mass transfer characterising and increased use of MEEs, the evaluation of suitable frost control strategies for the emerging MEEs in cold climates are still missing. This study presents numerical models of a quasi-counter-flow membrane energy exchanger (QCFMEE) and a quasi-counter-flow heat exchanger (QCFHE). Three different frost prevention strategies are examined: preheating outdoor air, heating room air and bypassing outdoor air. These strategies’ threshold values to prevent frost are calculated numerically and validated against experimental measurements. The results show that QCFMEE has lower threshold values and thus better frost tolerance ability compared with QCFHE because of mass transfer through the membranes. Moreover, the frost prevention strategies are evaluated based on annual energy consumption, energy saving ratio (ESR), and complexity of control for real-life applications. The simulated results show that among the discussed frost prevention strategies, preheating outdoor air has the advantage of the lowest energy consumption and highest ESR. Meanwhile, heating room air consumes the most energy and faces the problem of overheating outdoor air. Finally, concerning the bypassing outdoor air strategy, the significant fluctuation of its threshold values increases the complexity of control for real-life applications.publishedVersio

Theoretical analysis of a membrane-based cross-flow liquid desiccant system

Liquid desiccant air dehumidification has become one of the most widely used dehumidification technologies with advantages of high efficiency, no liquid condensate droplets and capability of energy storage. In this paper a cross-flow mathematical model is developed for a single layer membrane unit. The governing equations are solved iteratively by finite difference method. The performance analysis is carried out for a small-scale membrane-based dehumidification module consisting of 8 air channels and 8 solution channels. The influences of main design parameters on system effectiveness are evaluated. These include air flow rate (NTU), solution to air mass flow rate ration (m*) and solution inlet temperature and concentration. It is revealed that higher sensible and latent effectiveness can be achieved with larger NTU and m*. Increasing solution concentration can also improve the dehumidification effect

Theoretical analysis of a membrane-based cross-flow liquid desiccant system

Liquid desiccant air dehumidification has become one of the most widely used dehumidification technologies with advantages of high efficiency, no liquid condensate droplets and capability of energy storage. In this paper a cross-flow mathematical model is developed for a single layer membrane unit. The governing equations are solved iteratively by finite difference method. The performance analysis is carried out for a small-scale membrane-based dehumidification module consisting of 8 air channels and 8 solution channels. The influences of main design parameters on system effectiveness are evaluated. These include air flow rate (NTU), solution to air mass flow rate ration (m*) and solution inlet temperature and concentration. It is revealed that higher sensible and latent effectiveness can be achieved with larger NTU and m*. Increasing solution concentration can also improve the dehumidification effect

Experimental study of a membrane-based dehumidification cooling system

Membrane-based liquid desiccant dehumidification has attracted increasing interests with elimination of solution droplets carryover problem. A membrane-based hybrid liquid desiccant dehumidification cooling system is developed in this study, which has the ability to remove latent load by a liquid desiccant dehumidification unit and simultaneously to handle sensible load by an evaporative cooling unit. The hybrid system mainly consists of a dehumidifier, a regenerator and an evaporative cooler, calcium chloride is used as liquid desiccant in the system. This paper presents a performance evaluation study of the hybrid system based on experimental data. Series of tests have been conducted to clarify the influences of operating variables and conditions (i.e. desiccant solution concentration ratio, regeneration temperature, inlet air condition, etc.) on the system performance. The experimental results indicate that the system is viable for dehumidification cooling purpose, with which the supply air is provided at temperature of 20.4°C for the inlet air condition at temperature of 34°C and relative humidity of 73%. At desiccant solution concentration ratio of 36%, the thermal COPth of 0.70 and electrical COPel of 2.62 are achieved respectively under steady operating condition

A membrane-based flat-plate liquid desiccant dehumidification air-conditioning system

The enormous increase of energy consumption for building indoor environment, specifically for indoor thermal comfort has brought numerous state-of-art technologies as alternatives to the traditional vapour compression air-conditioning system. The membrane-based liquid desiccant dehumidification has gain wide attention for good feasibility, high energy efficiency and no desiccant carry-over problem. As a matter of fact, the membrane-based liquid desiccant system is still under research and development stage with limited number of literatures. The main aim of this thesis is to develop and evaluate a novel membrane-based liquid desiccant dehumidification air-conditioning system. The research scope mainly covers system design, numerical modelling, simulation programme development, experimental testing and system performance evaluation. The first step in the study is to develop a numerical model for a cross flow flat-plate type membrane-based dehumidifier and validate model by experimental data. Following this, a single regenerator with the similar structure as the dehumidifier is investigated numerically and experimentally. With models for single dehumidifier and regenerator, a numerical model for a more realistic complete membrane-based dehumidification system, which consists of two membrane-based heat and mass contractors, three heat exchangers, cooling water and hot water supply units is developed and validated experimentally. Finally, influences of using mixed LiCl-CaCl2 solution with different mixing ratios on the system performance are analysed. The results show that the number of heat transfer unit NTU and mass flow rate ratio m^* have the most significant effects on the performance of the dehumidifier and regenerator, and their effects are interacted with each other. The increasing gradients of dehumidifier and regenerator effectiveness hardly change when NTU and m^* exceed their critical values 〖NTU〗_crit and m_crit^*, which are 4 and 1 for the dehumidifier, and 4 and 2 for the regenerator. The dehumidifier sensible effectiveness is insensitive to both solution inlet temperature T_sol and concentration C_sol, while the latent effectiveness increases significantly with C_sol at a high solution temperature. The dehumidifier shows broad adaptability in different weather conditions by providing relative stable state supply air, in particular at high NTU, while neither T_(air,in) nor W_(air,in) has remarkable influence on the regenerator performance, though the solution re-concentration ability can be enhanced slightly by applying drier and warmer air. Regenerator can benefit from increased solution temperature as enhanced re-concentration (0.8% increase of moisture flux rate MFR) and cooling effects (13.7% increase of temperature decrease rate TDR). However this means more cooling energy is required for the high temperature desiccant solution. For the complete system, 〖NTU〗_de and m^* have the most considerable impact on the overall system effectiveness. The critical values of m^* vary under different NTUs, and it is preferable to keep m^* at or below the critical values as further increasing solution flow rate would reduce the system coefficient of performance COP. The latent cooling output Q_lat is normally two times higher than the sensible cooling output Q_sen under all circumstances meaning further cooling, such as indirect evaporative cooling is required after the dehumidification. Compared with the pure LiCl solution system, the mixed solution system COP can be raised up to 30.23% by increasing CaCl2 content. The optimum mixing ratio varies with the solution concentration. For the LiCl-CaCl2 solution, the highest COPs appear at the mixing ratios of 3:1, 2:1 and 1:1 for 20%, 30% and 40% concentrations respectively

ab-plane tilt angles in REBCO conductors

Critical current (Ic) of REBCO tapes is strongly aniso-tropic with respect to the orientation of the magnetic field. Usually, Ic is at maximum when the ab-plane of the REBCO crystal is parallel to the magnetic field. In commercial REBCO tapes, it is commonly assumed that the ab-plane is coincide with the tape plane. While in fact, the ab-plane is near but slightly tilted from the tape plane in the transverse direction. To accurately measure Ic as a function of the field angle {\theta} , which is defined as the angle between ab-plane and the magnetic field direction, and to design and fabricate REBCO mag-net coils based on the measured Ic(angle), it is important to measure the tilt angle. In this work, we used x-ray diffraction (XRD) to measure the tilt angles at room temperature for a large number of REBCO conductors made by SuperPower Inc. Transmission electron mi-croscopy (TEM) was also used to investigate the origin of this tilt. The measured data are presented, and the measurement uncer-tainty is discussed.Comment: 4 pages, 7 figure

Experimental study of liquid to air membrane energy exchanger (LAMEE) performance by measuring its temperature fields

Many studies have already been conducted to assess liquid to air membrane energy exchanger (LAMEE) performance by numerical and experimental methods. However, the LAMEE temperature field is still an unknown area due to the operation difficult. In this study, an experimental method is adopted to investigate the performance of LAMEE by measuring its temperature fields. The effects of main parameters such as the solution temperature, solution concentration and air relative humidity, are investigated. The results show that the air relative humidity and solution temperature have negative influences on the LAMEE efficiency. It is found that the total effectiveness reduces 2.7% and 7.7% when the air relative humidity increases from 62% to 74%, and the solution temperature changes from 18℃ to 26℃, respectively. Increasing the solution concentration decreases the sensible effectiveness while enhancing the latent and total effectiveness. The total effectiveness increases 3.5% as the solution concentration increase from 30% by 39%. These results are useful to optimize the LAMEE in the future

Experimental study of a membrane-based liquid desiccant dehumidifier based on internal air temperature variation

A membrane-based liquid desiccant dehumidifier with the separated air stream and liquid desiccant channels has the ability to solve its working fluid carryover problem in the traditional direct contact system. The sensible, latent, total effectiveness and air moisture removal rate are adopted for the dehumidifier performance evaluation in this paper, and the dehumidifier main operating parameters are investigated experimentally to identify their influences and internal air temperature variations, including inlet air relative humidity (RH), inlet solution concentration and temperature, heat capacity rate ratio (Cr*) and number of heat transfer units (NTU). It is found that both the inlet air RH and solution temperature have the negative influences on the dehumidifier effectiveness, while the desiccant solution concentration has little positive influence; the air moisture removal rate rises sharply with the inlet air RH and solution concentration. The highest sensible, latent and total effectiveness achieved in this study are 0.823, 0.802 and 0.810 respectively when both Cr* and NTU are equal to 12. However the operating condition with NTU=8 and Cr*=6 is recommended with the corresponding sensible, latent and total effectiveness of 0.758, 0.71 and 0.728 respectively