A propane water-to-water heat pump booster for sanitary hot water production: Seasonal performance analysis of a new solution optimizing COP

Electrical heat pumps for sanitary hot water production achieve a high performance with a good matching of water and refrigerant temperature profiles during the heat rejection stage, as it happens in CO₂ systems. This work considers the thermodynamic possibility to adapt the condenser pressure of a propane heat pump to maximize the COP, while producing sanitary hot water up to 60 °C from a heat sink equal to 15 or 25 °C. The performance of the heat pump is calculated through specific models which, in combination with a TRNSYS model of the whole system, allowed to assess its seasonal performance for a hotel in Strasbourg, also varying the control logic and the size of the storage tank. Results obtained led to the conclusion that, for achieving a high seasonal performance, the control logic of the tank has the largest influence.     

Delays to Large Construction Projects in Ghana： A Risk Overview

Delay to large scale projects, which is as a result of actions or inactions of some project stakeholders, is becoming a global phenomena and Ghana is no exception. The objective of the research is to identify, rate and rank the most significant risk factors that causes delay on projects and examine the social impact of these delays to recommend modalities to help mitigate these risk factors. The study adopted quantitative methods with the distribution of 144 questionnaires to built environment professionals receiving a response rate of 75.7%. The instrument listed 58 common factors under eight categories that contribute to the causes of delay for respondents to rate. Analysis of data non-parametric test revealed that client, contractor, material and finance category factors significantly resulted in the schedule delay of large infrastructural projects. The survey analysis revealed that micro-factors that result in delays to large construction projects are time constraint, cost overrun, payment problems, dispute and litigation. The research recommended the following modalities to minimize such delays： availability of resources, improved communication and coordination, proper scope definition and feasibilities, utilization of modern technology, appropriate application of technologically based systems and competent project management＇s structures.     

Exergoeconomic evaluation of novel solid oxide fuel cell-integrated solar combined cycle with different solar integration modes

The active use of fuel cells and solar energy in power generation systems can help reduce fossil energy consumption and improve the work capacity of the system, which is an important means to achieve the goal of “carbon neutrality”. In this study, novel solid oxide fuel cell-integrated solar combined cycle systems with different solar integration modes are proposed and investigated. The thermodynamic, environmental and economic performances of new systems with different solar collector integration modes are evaluated using the exergoeconomic theory and environmental performance analysis. The results show that when the new system uses trough solar collectors to replace part of the heating load of the second-stage high-pressure economizer and high-pressure boiler drum, the system has the highest exergy efficiency (52.91%), the lowest unit exergoeconomic cost (0.102109 $/kWh) and the lowest specific CO₂ emission rate (475.27 g/kWh). When the operating conditions of the system remain unchanged, this solar energy integration mode has the highest solar-to-electricity efficiency (26.69%) as well as thermal-to-electricity efficiency (44.22%), and can obtain the best profit in the same operating life. The new system can attain maximum energy efficiency and optimal economic benefits by using this solar energy integration mode.     

Diversity in nutritional composition of wild jack bean (Canavalia ensiformis L. DC) seeds collected from south India

Nine accessions of the wild jack bean (Canavalia ensiformis L. DC) seeds collected from nine different locations of south India were analysed for proximate composition and mineral profiles. The major findings of the study were as follows: crude protein ranged from 28.9 to 35.0%, crude lipid 3.4–4.7%, crude fibre 7.0–10.7%, ash 3.0–5.8%, carbohydrates 46.1–54.5% and energy levels 1469–1574 kJ 100 g⁻¹ DM. Significant (P<0.05) diversity was observed in crude protein and carbohydrate contents among the accessions collected from different locations based on analysis of variance (ANOVA) analysis. Potassium was the most abundant mineral, which ranged from 634 mg 100 g⁻¹ in Dasukuppam accession to 1017 mg 100g⁻¹ in Valacode accession. Sodium and magnesium levels are generally low with mean values of 63 and 250 mg 100 g⁻¹, respectively. In the present study, in all minerals, significant diversity was observed among the accessions collected from different locations.     

大型锅炉水平烟道左右两侧烟温偏差的研究

在我国火电站现用的许多大型４角切圆燃烧锅炉中，存在着水平烟道两侧烟温差的问题，由此产生过热器和再热器超温过热。为了提高其安全可靠性，本文讨论了这种烟温差的影响因素，并对一台１０２５ｔ／ｈ４角切向燃烧锅炉进行了现场试验研究，测定了锅炉水平烟道的两侧速度偏差。并由此计算了两侧的烟温和管壁温度偏差。研究结果表明：该锅炉燃烧器采用３次风反切，对于减少这种烟温差是很有效的。     

NUMERICAL SIMULATION AND ANALYSIS OF PRESSURE PULSATION IN FRANCIS HYDRAULIC TURBINE WITH AIR ADMISSION

In this article, the three-dimensional unsteady multiphase flow is simulated in the whole passage of Francis hydraulic turbine. The pressure pulsation is predicted and compared with experimental data at positions in the draft tube, in front of runner, guide vanes and at the inlet of the spiral case. The relationship between pressure pulsation in the whole passage and air admission is analyzed. The computational results show: air admission from spindle hole decreases the pressure difference in the horizontal section of draft tube, which in turn decreases the amplitude of low-frequency pressure pulsation in the draft tube; the rotor-stator interaction between the air inlet and the runner increases the blade-frequency pressure pulsation in front of the runner.     

Negative bias temperature instability in n-channel power VDMOSFETs

Negative gate bias is used in some applications for faster switching off the n-channel MOS devices. It is shown in this study that NBT stress-related instability in commercial n-channel power VDMOSFETs could be actually more serious than in corresponding p-channel devices. NBT stress is found to create equal V_T shifts in both device types, whereas the subsequent positive bias annealing results in more serious overall V_T instability in n-channel devices. The changes in the densities of stress-induced interface traps in two device types are equal as well, but significant amounts of NBT stress-induced border traps are only found in n-channel devices. All the results are discussed in terms of hydrogen reaction and diffusion model.     

低NOx煤粉燃烧器的试验研究

对低NOx燃烧器从试验和数值模拟两个方面进行了研究,结果表明低NOx燃烧器浓淡两侧的速度比与管道气体速度和分隔板开缝与否均无关,大小为1.14～1.30,速度差为2.37 m/s(管道气体速度U=18 m/s时)～7.90 m/s(管道气体速度U=28 m/s时);低NOx燃烧器分隔板开缝时,相对不开缝结构阻力增加1.3%(180°扭曲分隔板)～10%(平直分隔板);低NOx燃烧器分隔板前布置阻挡锥时,阻力再增加10.1%(180°扭曲分隔板)～12.1%(平直分隔板);低NOx燃烧器浓淡两侧的固气比与分隔板有无开缝无关,浓侧煤粉射流的固气比随气流速度增大而增大,淡侧射流的固气比随气流速度的增大而减小,浓淡两侧的固气比随管道煤粉固气比的增大而增大.常规直流煤粉燃烧器加装不开缝的平直分隔板时,阻力增加17.7%,加装不开缝的180°扭曲分隔板时,阻力增加71.6%.低NOx燃烧器的分隔板开缝时,浓淡两侧的静压平衡,浓淡两侧的湍动能都增加,浓侧湍动能增加大约20%.     

Performance evaluation of a novel CCHP system integrated with MCFC,ISCC and LiBr refrigeration system

This paper proposes a novel combined cooling, heating, and power (CCHP) system integrated with molten carbonate fuel cell (MCFC), integrated solar gas-steam combined cycle (ISCC), and double-effect absorption lithium bromide refrigeration (DEALBR) system. According to the principle of energy cascade utilization, part of the high-temperature waste gas discharged by MCFC is led to the heat recovery steam generator (HRSG) for further waste heat utilization, and the other part of the high-temperature waste gas is led to the MCFC cathode to produce CO₃^2?, and solar energy is used to replace part of the heating load of a high-pressure economizer in HRSG. Aspen Plus software is used for modeling, and the effects of key factors on the system performances are analyzed and evaluated by using the exergy analysis method. The results show that the new CCHP system can produce 494.1 MW of electric power, 7557.09 kW of cooling load and 57,956.25 kW of heating load. Both the exergy efficiency and the energy efficiency of the new system are 61.69% and 61.64%, respectively. Comparing the research results of new system with similar systems, it is found that the new CCHP system has better ability to do work, lower CO₂ emission, and can meet the cooling load, heating load and electric power requirements of the user side at the same time.     

All optical design of binary adders using semiconductor optical amplifier assisted Mach–Zehnder interferometer

With the progress in research in the field of optical computing, architectural designs of various digital components and systems using all-optical technology are being explored. Implementations of basic gates like AND, OR, XOR, etc. and arithmetic components like adder, subtracter, etc. have already been investigated in the all-optical domain. Among the various alternatives, interferometric devices have shown great promise due to their high-speed photonic activity and ease of manufacturing. Many of these works consider semiconductor optical amplifier (SOA) assisted Mach–Zehnder Interferometer (MZI) for the implementation. In this paper we present all-optical implementations of binary adders using MZI switches, which have been validated through numerical simulation of the switch models. Some performance parameters of the design have also been evaluated. Three designs have been explored – a ripple-carry adder, an extension with faster carry propagation, and a carry save adder. The design complexities have been compared with some recently published works, both in terms of optical cost and delay.