Investigations of heat powered ejector cooling systems

In this thesis, heat powered ejector cooling systems was investigated in two ways: to store the cold energy with energy storage system and to utilize low grade energy to provide both electricity and cooling effect. A basic ejector prototype was constructed and tested in the laboratory. Water was selected as the working fluid due to its suitable physical properties, environmental friendly and economically available features. The computer simulations based on a 1-0 ejector model was carried out to investigate the effects of various working conditions on the ejector performance. The coefficients of performance from experimental results were above 0.25 for generator temperature of lI5°C-130 °C, showing good agreements with theoretical analysis. Experimental investigations on the operating characteristics of PCM cold storage system integrated with ejector cooling system were conducted. The experimental results demonstrated that the PCM cold storage combined with ejector cooling system was practically applicable. The effectiveness-NTU method was applied for characterizing the tube-in-container PCM storage system. The correlation of effectiveness as the function of mass flow rate was derived from experimental data, and was used as a design parameter for the PCM cold storage system. In order to explore the possibility of providing cooling effect and electricity simultaneously, various configurations of combined power and ejector cooling system were studied experimentally and theoretically. The thermal performance of the combined system in the range of 0.15-0.25 and the turbine output between 1200W -1400W were obtained under various heat source temperatures, turbine expansion ratios and condenser temperatures. Such combined system was further simulated with solar energy as driving force under Shanghai climates, achieving a predicted maximum thermal efficiency of 0.2. By using the methods of Life Saving Analysis, the optimized solar collector area was 30m2 and 90m2 respectively for the system without and with power generation. The environmental impacts and the carbon reductions of these two systems were discussed

Investigations of heat powered ejector cooling systems

In this thesis, heat powered ejector cooling systems was investigated in two ways: to store the cold energy with energy storage system and to utilize low grade energy to provide both electricity and cooling effect. A basic ejector prototype was constructed and tested in the laboratory. Water was selected as the working fluid due to its suitable physical properties, environmental friendly and economically available features. The computer simulations based on a 1-0 ejector model was carried out to investigate the effects of various working conditions on the ejector performance. The coefficients of performance from experimental results were above 0.25 for generator temperature of lI5°C-130 °C, showing good agreements with theoretical analysis. Experimental investigations on the operating characteristics of PCM cold storage system integrated with ejector cooling system were conducted. The experimental results demonstrated that the PCM cold storage combined with ejector cooling system was practically applicable. The effectiveness-NTU method was applied for characterizing the tube-in-container PCM storage system. The correlation of effectiveness as the function of mass flow rate was derived from experimental data, and was used as a design parameter for the PCM cold storage system. In order to explore the possibility of providing cooling effect and electricity simultaneously, various configurations of combined power and ejector cooling system were studied experimentally and theoretically. The thermal performance of the combined system in the range of 0.15-0.25 and the turbine output between 1200W -1400W were obtained under various heat source temperatures, turbine expansion ratios and condenser temperatures. Such combined system was further simulated with solar energy as driving force under Shanghai climates, achieving a predicted maximum thermal efficiency of 0.2. By using the methods of Life Saving Analysis, the optimized solar collector area was 30m2 and 90m2 respectively for the system without and with power generation. The environmental impacts and the carbon reductions of these two systems were discussed

Recent research developments in polymer heat exchangers: a review

Due to their low cost, light weight and corrosive resistant features, polymer heat exchangers have been intensively studied by researchers with the aim to replace metallic heat exchangers in a wide range of applications. This paper reviews the development of polymer heat exchangers in the last decade, including cutting edge materials characteristics, heat transfer enhancement methods of polymer materials and a wide range of polymer heat exchanger applications. Theoretical modelling and experimental testing results have been reviewed and compared with literature. A recent development, the polymer micro-hollow fibre heat exchanger, is introduced and described. It is shown that polymer materials do hold promise for use in the construction of heat exchangers in many applications, but that a considerable amount of research is still required into material properties, thermal performance and life-time behaviour

Evidence of decoupling consumption-based CO₂ emissions from economic growth

Decoupling economic growth from resource use and emissions is a precondition to stay within planetary boundaries. A number of countries have achieved a reduction in their production-based emissions in the past decade. However, the decline in PBE has often been achieved via outsourcing of emissions to other countries, which may even lead to higher emissions globally. Therefore, a consumption-based perspective that accounts for a country's emissions along global supply chains should also be employed when investigating progress in decoupling. Here we investigate the progress countries made in reducing their production-based and consumption-based emissions despite growth in gross domestic product (GDP). We found that 32 out of 116 countries (mainly developed ones) achieved absolute decoupling between GDP and production-based emissions in recent years (2015–2018), and 23 countries achieved absolute decoupling between GDP and consumption-based emissions. 14 countries have decoupled GDP growth from both production- and consumption-based emissions. Even countries that have achieved absolute decoupling are still adding emissions to the atmosphere thus showing the limits of ‘green growth’ and the growth paradigm. We also observed that decoupling can be temporary, and decoupled countries may switch back to increasing emissions, which means that continuous efforts are needed to maintain decoupling. An analysis of driving factors shows that whether a country can achieve decoupling mainly depends on reducing emission intensity along domestic and import supply chains. This highlights the importance of decarbonizing supply chains and international collaboration in controlling emissions

Evidence of decoupling consumption-based CO₂ emissions from economic growth

Decoupling economic growth from resource use and emissions is a precondition to stay within planetary boundaries. A number of countries have achieved a reduction in their production-based emissions in the past decade. However, the decline in PBE has often been achieved via outsourcing of emissions to other countries, which may even lead to higher emissions globally. Therefore, a consumption-based perspective that accounts for a country's emissions along global supply chains should also be employed when investigating progress in decoupling. Here we investigate the progress countries made in reducing their production-based and consumption-based emissions despite growth in gross domestic product (GDP). We found that 32 out of 116 countries (mainly developed ones) achieved absolute decoupling between GDP and production-based emissions in recent years (2015–2018), and 23 countries achieved absolute decoupling between GDP and consumption-based emissions. 14 countries have decoupled GDP growth from both production- and consumption-based emissions. Even countries that have achieved absolute decoupling are still adding emissions to the atmosphere thus showing the limits of ‘green growth’ and the growth paradigm. We also observed that decoupling can be temporary, and decoupled countries may switch back to increasing emissions, which means that continuous efforts are needed to maintain decoupling. An analysis of driving factors shows that whether a country can achieve decoupling mainly depends on reducing emission intensity along domestic and import supply chains. This highlights the importance of decarbonizing supply chains and international collaboration in controlling emissions.</p

Influences of the mixed LiCl-CaCl 2 liquid desiccant solution on a membrane-based dehumidification system: parametric analysis and mixing ratio selection

The membrane-based liquid desiccant dehumidification system has high energy efficiency without the traditional liquid system carry-over problem. The performance of such a system strongly depends on solution's temperature and concentration, which have direct relationship to the solution surface vapour pressure. Compared with the pure liquid desiccant solution, the mixed liquid desiccant solution has lower surface vapour pressure, better system performance and lower material cost. In this paper, the performance of a flat-plate membrane-based liquid desiccant dehumidification system with the mixed solution (LiCl and CaCl2) is investigated through theoretical and experimental approaches. A mathematical model is established to predict the system performance, while the electrolyte non-random two-liquid (NRTL) method is applied to calculate the mixed solution properties. The influences of the solution mixing ratio, temperature Tsol and concentration Csol are evaluated, and it is found that the regeneration heat Qreg can be dramatically reduced by either applying a high concentration solution or increasing CaCl2 content in the mixed solution. Compared with the pure LiCl solution system, the mixed solution system COP can be improved up to 30.23% by increasing CaCl2 content for a 30% concentration solution. The optimum mixing ratio varies with the solution concentration. For the mixed LiCl-CaCl2 solution, the system highest COPs appear at the mixing ratios of 3:1, 2:1 and 1:1 for 20%, 30% and 40% concentrations respectively

A SYSTEM-ON-CHIP 1.5 GHz PHASE LOCKED LOOP REALIZED USING 40 nm CMOS TECHNOLOGY

This work presents the design and realization of a fully-integrated 1.5 GHz sigma-delta fractional-N ring-based PLL for system-on-chip (SoC) applications. Some design optimizations were conducted to improve the performance of each functional block such as phase frequency detector (PFD), voltage-controlled oscillator (VCO), filter and charge pump (CP) and so as for the whole system. In particular, a time delay circuit is designed for overcoming the blind zone in the PFD; an operational amplifierfeedback structure was used to eliminate the current mismatch in the CP, a 3rd LPF is used for suppressing noises and a current overdrive structure is used in VCO design. The design was realized with a commercial 40 nm CMOS process. The core die sized about 0.041 mm2. Measurement results indicated that the circuit functions well for the locked range between 500 MHz to 1.5 GHz

CenGCN : centralized convolutional networks with vertex imbalance for scale-free graphs

Graph Convolutional Networks (GCNs) have achieved impressive performance in a wide variety of areas, attracting considerable attention. The core step of GCNs is the information-passing framework that considers all information from neighbors to the central vertex to be equally important. Such equal importance, however, is inadequate for scale-free networks, where hub vertices propagate more dominant information due to vertex imbalance. In this paper, we propose a novel centrality-based framework named CenGCN to address the inequality of information. This framework first quantifies the similarity between hub vertices and their neighbors by label propagation with hub vertices. Based on this similarity and centrality indices, the framework transforms the graph by increasing or decreasing the weights of edges connecting hub vertices and adding self-connections to vertices. In each non-output layer of the GCN, this framework uses a hub attention mechanism to assign new weights to connected non-hub vertices based on their common information with hub vertices. We present two variants CenGCN_D and CenGCN_E, based on degree centrality and eigenvector centrality, respectively. We also conduct comprehensive experiments, including vertex classification, link prediction, vertex clustering, and network visualization. The results demonstrate that the two variants significantly outperform state-of-the-art baselines. © 1989-2012 IEEE

A novel evaporative cooling system with a polymer hollow fibre spindle

A polymer hollow fibre evaporative cooling system with a novel configuration of fibre bundle is proposed. With the aim to avoid the flow channelling or shielding of adjacent fibres the fibres inside each bundle were made into a spindle shape to maximize contact between the air stream and the fibres. For the porous wall of hollow fibre, the vapour of evaporated water can permeate through it effectively, while the liquid water droplets can be prevented from mixing with the processed air. For various dry bulb temperatures (27 °C, 30 °C, 33 °C, 36 °C and 39 °C) and relative humidity (23%, 32% and 40%) of the inlet air, the cooling performances of the proposed novel evaporative cooling system were experimentally investigated. The variations of outlet air dry bulb temperature, wet bulb effectiveness, dew point effectiveness and cooling capacity with respect to different incoming air dry bulb temperature were studied. The effects of various incoming air Reynolds number on the heat and mass transfer coefficients, heat flux and mass flux across the polymer hollow fibre module were analysed. Experimentally derived non-dimensional heat and mass transfer correlations were compared with other correlations from literature. Due to the proposed spindle shape of hollow fibre bundle, the shielding between adjacent fibres could be mitigated greatly, therefore the heat and mass transfer performance of the proposed system demonstrated significant improvement compared with other designs reported in literature

State-of-the-art review of 3DPV technology: structures and models

© 2019 Elsevier Ltd Increasing energy conversion efficiency from sunlight to power is one of the key solutions for the world's energy shortage and greenhouse gas reduction, but the conventional flat photovoltaic module without sun tracking mechanism has the low sunlight energy collection ability. This paper presents the state-of-the-art three-dimensional photovoltaic (3DPV) technology with high photovoltaic energy conversion efficiency, which is able to absorb off-peak sunlight and reflected light more effectively, thereby it can generate more power. At first, this paper is to catalogue and critique different 3DPV structures and models, as well as assess their characteristics. Afterwards, the main influence factors on the 3DPV structures and models including shape, height and spacing of the solar cells, latitude of the installation, optimal device design and shadow cast, are reviewed. Finally, the challenges and future technological developments of 3DPV structures and models are highlighted. This study demonstrated that the 3DPV technology can increase the captured sunlight approximately 15–30% in comparison with the conventional flat PV technology