Space Debris can be both magnetic and non-magnetic. The Electromagnetic-net Carrier system is a result of combining electromagnetic properties with a Dyneema net to capture space debris present in the lower Earth orbit. The system works on the principle of electromagnetism and uses the net to capture both varieties of debris, ones that exhibit magnetic properties and those that don't. This allows for an efficient capture and opens room for using debris for experiential learning and studying aerospace technologies.

The combustion characteristics of oxygen-enriched air-methane (i.e., O-2/N-2/CH4) flames in a premixed mode are investigated using both experimentally and numerically under atmospheric conditions for emissions reduction purposes. The investigation is carried out using a gas turbine model combustor equipped with a multihole burner that mimics gas turbine micromixer burners. The resulting flame is of jet type, and the velocity of the jet is kept at 5.2 m/s for all the considered flames. Models used in the numerical study include large eddy simulation, discrete ordinate, and partially premixed combustion for turbulence, radiation, and species models, respectively. The numerical results are validated, and a suitable agreement is achieved with experimental data. The results indicated that the temperature distribution, shape, and size of O-2/N-2/CH4 flames are predominantly controlled by adiabatic flame temperature (T-ad). However, the oxygen fraction, rather than T-ad, is responsible for the reaction progress. The emission of NO, CO, and CO2 increases with an increase in oxygen fraction, and the product formation in O-2/N-2/CH4 flames is less compared to their oxy-fuel (i.e., O-2/CO2/CH4) counterparts, because N-2 is mostly inert, compared to CO2. The latter participates significantly in flame reactions, which increases the rate of product formation in O-2/CO2/CH4 flames.

An experimental study was performed to investigate the effects of flow swirl on flow/flame characteristics and stability of atmospheric premixed oxy-methane (CH4/O-2/CO2) flames. The flames generated by two swirlers of 55(degrees) and 45(degrees)swirl angles were tested on a test stand for a dry low emission (DLE) model gas turbine combustor at constant inlet flow velocity of 5.2 m/s and over ranges of operating oxygen fraction (OF: 21% to 70% - by volume in the O-2/CO2 mixture) and equivalence ratio (phi: 0.2 to 1.0). Combustor static stability limits (flashback and blow-out) were determined experimentally in the phi-OF domain to identify the operational ranges of the combustor while varying inlet flow swirl. To understand the mechanisms for flashback and blow-out, the lines representing the stability limits were displayed in the phi-OF domain against the contours of combustor power density (PD: MW/m(3)/atm), adiabatic flame temperature (AFT), and inlet flow Reynolds (Re). Comparison of flame macrostructure and measurements of local flame temperatures were performed for the two swirlers over ranges of phi, OF, and AFT to determine the effects of such operational parameters on flow/flame interactions and flame stability and to serve as a database for validating numerical models for such flames. The results show that, for both swirlers, the flames blow-out at a very similar AFT of similar to 1600 K indicating the dominant role of AFT in controlling premixed oxy-flame stability near the blow-out limit. Compared to the same combustor with a 55(degrees) swirler, the 45(degrees) swirler has a wider stable combustion zone. Comparing the flames of the same AFT, at fixed inlet flow velocity, shows almost identical flame macrostructure whatever the operating inlet flow swirl, OF and phi.

In this study a comparison between the premixed methane oxygen-enriched-air (CH4/O2/N2) and oxy-methane (CH4/O2/CO2) in a gas-turbine model combustor that imitates pre-mixers in operational air-fuel dry low emissions gas turbines is presented. The comparison and analyses that follow in this study are based on the results of experiments conducted. The combustion stability maps were obtained through the estimation of acoustic limits and measurement of blowout limits within the space of equivalence ratio (φ) – oxygen fraction (OF). The stability maps obtained were superimposed on the contour plots of constant adiabatic temperature (Tad), Reynolds number (Re), and power density (PD) of the combustor. Effects of Tad on flame macrostructure, flame stability, flame speed, and blowout mechanism were investigated. The temperature distributions were also measured. The study results indicated that blowout of CO2 as well as N2 flames occur at constant Tad. These results are more pronounced in the case of the multi-hole burner because, such burner is not characterized with sporadic nature of flame lifting and reattachment that dominate the occurrence of a blowout in swirl burner; for a given OF, φ at which CO2 flames blowout is higher than that of N2 flames due to the poorer resistance of oxy-flames to blowout as compared to air flames; the stable combustion zone of CO2 flames is larger than that of N2 flames.

A B S T R A C TAll the previously reported research based on the performance assessment of both absorption (abs) and adsorption (ads) chillers clearly reveal that the coefficient of performance ( COP ) as well as specific cooling power ( SCP ) measured for either of these systems still lag far behind the value typically measured for vapor compression (VC) systems. The commercial utility of both the abs and ads systems has thus still not been able to replace their VC counterpart for domestic cooling applications. However, for excessively large-scale cooling as observed in the case of on-site refrigeration/air-conditioning of post-harvest storage houses, electrically powered VC systems generally prove to be unaffordably expensive while solar-powered VC systems result in values of COP even below either of their abs or ads counterparts. In this work, an integrated abs/ads refrigeration system has been designed and numerically evaluated for its performance with the aim of combining the intrinsically low driving temperature of the ads component with the intrinsically higher COP value of the abs component. Five integrated solar-powered designs constituting a single-effect LiBr/water abs chiller with a double-bed silica gel/water adsorption chiller have been proposed and numerically evaluated for theoretical values of both COP and SCP . The results have been compared with stand-alone single-effect abs and double-bed solar powered ads chillers for realizing improvements in performance if any by virtue of design integration.

The study presents an experimental and numerical investigation to determine the role of adiabatic lame temperature on controlling the operability of a micromixer-based gas turbine model combustor holding premixed CH4/CO2/O2 non-swirl jet flame for carbon capture. The experimental test rig consists of a mixing pipe and multihole/micromixer-like burner of 61 tubes. The numerical aspect of the study is achieved using the computational fluid dynamic (CFD) approach. Models of the Ansys Fluent are used to solve elliptical governing equations involved in the combustion system. Since flames under consideration are jet premixed releasing into a quiescent atmosphere, the partially premixed combustion of species model is used. Large eddy simulation (LES) is used as the turbulence model while radiative transfer equation (RTE) is solved using discrete ordinate (DO). A good agreement between experimental and numerical results is achieved. Results indicated that; adiabatic flame temperature (Tad) controls the flame macrostructure, oxygen fraction (OF) controls the peak of the product formation rate rather than Tad, positions of OH radical reaffirmed that Tad controls the flame macrostructure and increasing the OF leads to reaction rate dominancy and, hence, increases the Damkohler number.

The previously published literature based on the performance prediction of solar-powered adsorption chillers generally incorporates fixed heat/mass recovery (HR/MR) cycle times which remain unchanged during the entire course of operation of the adsorption chiller. In reality, the dynamics of the HR/MR processes are continuously subject to change due to temporal variations in the solar radiation intensity, and thus fixed HR/MR cycle times might not prove to be compatible with the actual dynamics of a transient solar-powered chiller operation. The current study proposes a numerical scheme for performance modeling of a commercial-scale adsorption chiller with adaptive HR/MR cycle times following the adsorption/desorption (ads/des) cycle. A novel model of the MR cycle has been proposed which, in accordance with the best knowledge of the authors, cannot be find anywhere else in the previously published literature. The ads/des -> HR -> MR -> des/ads half cycle has been predicted to yield an almost 52% higher cycle-averaged value of coefficient of performance (COP), an almost 16% higher value of specific cooling power (SCP), and a roughly 146% higher value of solarCOP (COPsc) than the ads/des -> MR -> HR -> des/ads half cycle over the entire course of operation of the adsorption chiller till sunset.

The combustion, exhaust-gas concentrations, and stability characteristics of premixed CO2-diluted oxy-propane (C3H8/O-2/CO2) flames were investigated computationally using large eddy simulations (LES) in a swirl-stabilized model gas-turbine combustor. The simulations were carried out for ranges of equivalence ratio (phi: 0.26-0.80) and oxygen fraction (OF: 35%-60%) at a fixed bulk inlet velocity of 5.2 m/s. The results indicate that the reaction rates increase with the increase of phi and OF. Flames of the same adiabatic flame temperature (T-ad) show similar macro-and flowfield-structures, in terms of flame shape, flow circulation, and temperature, and species distributions, irrespective of the values of phi and OF. At higher T-ad, the flames were observed to be more compact with reduced flame thickness and higher Damkohler number (Da). In all cases, Da > 1 were observed, indicating the dominance of reaction rate in oxy-propane flames than the diffusion rate. A secondary IRZ was also observed near the outlet of the combustor. Mixture composition and combustion temperature influence the CO concentration at the combustor exit. The highest CO emission was observed at 0.17 ppm for the flame with highest phi and T-ad, meanwhile no CO emission was seen for flames with high OF and low phi among the studied cases. Highlights Adiabatic flame temperature is a quantifying parameter for flame characterization. The outer recirculation zone plays a vital role in flame anchoring/stabilization. Primary inner recirculation zone has several eddies controlled by the equivalence ratio. Secondary inner recirculation zone was also observed near the combustor outlet. Elevated CO emission was observed at high equivalence ratio and low oxygen fraction.

This paper presents the performance of a single effect absorption cooling system under three different climates in Saudi Arabia. The considered system capacity is 10.5kW and uses LiBr/water pair. The study results indicated that considering the dynamic response of the cooling cycle significantly increases (close to 30%) the time taken to reach steady-state operations and that the sensitivity of the system to form precipitation of LiBr also increases. Also, the dynamic performance was investigated under different heat inputs and resulted in shorter transient period with increasing the heat input. In addition, the performance of the solar absorption system was investigated for a representative summer day in different climatic regions in Saudi Arabia. The results indicated the requirement of different areas of collectors to meet the absorber heating demand from 09:00 a.m. to 04:00 p.m. if there is no auxiliary heating. Auxiliary heating is required from 04:00 p.m. to 09:00 a.m. Finally, the results indicated that the system performs better in Riyadh city than in Dhahran and Jeddah. This study emphasizes the importance of taking into consideration the thermal inertia of the system components when analyzing the performance of such systems.

The published literature on natural circulation in package boilers lacks a model that performs calculations for each circuit and determines circulation parameters for all circuits. This study presents a developed computational procedure capable of sizing and analyzing the performance of natural circulation package boilers to meet a specific load. Also; the study identifies the most critical circuit of a package boiler and determines the impact of heat flux, friction factor and tube plugging on the circulation ratio and wall temperature. The model was validated by comparing its results with experimental data. The results revealed that the Circuit 3 (The D-Tubes) is the most critical circuit. Plugging some of these tubes reduces the circulation ratio and increases the tube wall temperature significantly. The results indicate that the circulation ratio decreased by 20% and the wall temperature increased by 9.6% as a result of increase in the heat flux by 24%.

This paper presents the thermodynamics (energy and exergy) analysis of a power plant using the design data. The plant is a triple pressure combined cycle power plant (CCPP) equipped with reheat facilities. The temperature gradient as well as the exergy destruction were determined across each components of the heat recovery steam generator (HRSG). Among the components of the HRSG high-pressure evaporator experienced a large temperature gradient which accounted for high irreversibility while intermediate-pressure superheater experienced low-temperature change and therefore low irreversibility. Exergy analysis showed that the major source of irreversibility (exergy destruction) in the steam turbine cycle (STC) of the CCPP is the stack followed by the HRSG, turbine, and condenser. The exergetic efficiency of the turbine is the highest in the STC with more than 92% while the exergetic efficiency of the condenser was the lowest one with less than 63%. Parametric analyses were conducted where the effects of some operating parameters on the turbine output, efficiencies, and exergy destruction were investigated. The results indicated that superheat pressure, reheat pressure, and steam quality at the exit of the low-pressure steam turbine significantly affect the output of the turbine and efficiencies.

The previously published studies based on the performance prediction of solar-powered adsorption chillers incorporate a fixed cycle time which is either prespecified, or determined as a result of a numerical optimization procedure. However, the cycle time of a solar-powered commercial adsorption chiller cannot be expected to remain constant with the number of cycles owing to the continuously varying intensity of solar radiation from sunrise till sunset. This paper presents the first attempt of comparing the numerically predicted performance of a solar-powered two-bed silica gel/water adsorption chiller based on adaptive and fixed cycle time conditions using a two-stage iterative optimization. The adsorption/desorption (ads/des) stage for the adaptive cycle time condition is terminated as soon as the ads/des uptakes reach their corresponding equilibrium values, while the preheating/precooling (PH/PC) stage is ended as soon as the vapor pressure gradient inside either of the two beds becomes negligibly small. The optimal ads/des as well as the PH/PC times for the adaptive cycle time condition have been used as a baseline for maximizing system performance for the fixed cycle time condition using a two-stage iterative optimization, and the two optimized cycle time conditions have been compared in the context of commercial applications.

This paper presents the results of an experimental investigation of combustion characteristics of nonswirl CH4/CO2/O-2 flames under atmospheric pressure in a lean-premixed multihole burner's gas-turbine model combustor. The CO2 and O-2 are well premixed and then channeled to a test rig, which is made up of a 2 in. diameter 1 m long pipe to premix the fuel and oxidizers before getting to the multihole burner. The burner consists of main holes and subholes that prevent flashbacks that may lead to rig explosion. The burner imparts jet to the premixed measured composition of CH4/CO2/O-2. The results indicated that the adiabatic flame temperature (T-ad) is a strong controlling parameter in quantifying the stability map and combustor flame shape; variation in oxygen fraction and equivalence ratio influence the flame shape, whereas the equivalence ratio (phi) is the major controlling parameter of temperature distribution within the combustor. The results also indicated that the stability map does not follow the lines of constant power density, mass flow rate of the mixture (m(mix))over dot, and Reynolds number (Re).

High temperature that reaches to 50 °C in summer, high humidity, and dust storms are considered as the main characteristics of the climate of many countries around the world such as those in the Gulf States, Asia, and Africa. According to the latest studies, air conditioning (A/C) systems in the residential areas used around 65% of the generated energy. This paper is aimed at presenting a new residential thermal model that can be used to estimate the energy consumption of A/C units used to achieve comfort in houses. The results of the newly developed residential thermal model will be compared with exiting residential thermal models using simscape in matlab program and data measurements. Different physical properties of the house that affect the heat gains through the house envelop at different weather conditions, and the internal heat gains are taken into account in this study. Hourly, daily, monthly, and annually energy consumption and coefficient of performance (COP) are calculated, based on actual hourly outdoor temperature measurements and indoor generation heat for the year 2017, using the three thermal models and compared with the pertinent actual measurements. The total measured energy consumption for nine months' work in 2017 was 14488.09 kWh, and the total energy consumption predicted by the simulation for the simple model, intermediate model, and comprehensive model were 8438.40 kWh, 12656.10 kWh, and 13900.61 kWh, respectively, with deviations of 41.75%, 12.65%, and 4.05%, respectively, from the actual measurements.

The simulation studies of conventional small-scale adsorption chillers reported so far in literature incorporate a pre-determined user-defined cycle time which remains constant with the increasing number of cycles. This study presents the first attempt of the numerical simulation of a two-bed solar adsorption chiller with “adaptive” cycle time based on the temporal variations of temperatures and pressures existing inside the beds, the evaporator and the condenser. A water-stable metal organic framework (MOF), MIL-100(Fe), has been selected as the adsorbent while water has been chosen as the refrigerant. A flat-plate solar collector with three different glaze configurations, namely single-glazed (S-G), double-glazed (D-G) and single-glazed with transparent insulation material (TIM), has been employed. The performance of the two-bed adsorption chiller has been evaluated in terms of the variations of the specific cooling power (SCP), the coefficient of performance (COP) and the solar coefficient of performance (COPsc) with increasing number of cycles.

The mitigation of environmental effects on clean-energy technology is an area of increasing interest. Photovoltaic (PV) modules have been widely used in small and large-scale applications for many years. However, they are not yet competitive with other electrical energy-generation technologies, especially in environments that suffer from dust, airborne particles, humidity and high ambient temperatures. This paper presents a review of the effect of climatic conditions on PV module performance, in particular, the effect of dust fouling. Research to date indicates that dust deposition has a considerable effect on PV module performance as it reduces the light transmissivity of the PV module surface cover. Studies on the ways in which dust is deposited on PV module surfaces are reviewed, as understanding this process is essential to develop effective mitigation approaches. Module performance is also adversely affected by high ambient temperature, humidity and lack of rainfall. The current review summarizes the past, current and promising future approaches towards mitigating environmental effects, in particular dust fouling. Electrostatic cleaning methods and micro/nanoscale surface functionalization methods both have the potential to counteract the negative effects of dust deposition, with the combination of the two methods showing special efficacy, particularly in arid regions.

The stability of a turbulent diffusion flame temperature in an atmospheric gas-turbine combustor is investigated experimentally over a range of operating conditions to study the combined effect of hydrogen-enriched- methane (as fuel) and oxygen with carbon dioxide (oxy-fuel, as the oxidizer) on the combustion flame stability. These conditions included varying fuel and oxidizer mixture compositions, swirl angles, and equivalence ratios. The fuel (i.e. methane) is enriched with hydrogen (H2) in a ratio that ranged from zero to 50%; where the oxidizer (pure oxygen) is mixed with carbon dioxide (CO2) in a ratio that ranged from zero up to the value of flame blow-off. Different swirl vane angles corresponding to different swirl numbers were considered. The results indicated that stable regime (flame) is achieved close to stoichiometric conditions at high oxygen (O2) to CO2 ratio and high H2 (50%) enriched fuel; while the flame blow-off occurred at low O2 to CO2 ratios (20% or less). High-level flame stability with moderate flame length and temperature were observed at the highest swirl vane angle.

This paper presents development of a dynamic model of a 3 TR single-effect absorption cooling cycle that employs LiBr-water as an absorbent/refrigerant pair coupled with solar collectors. Due to the frequently changeable cooling load, and the freckle nature of the solar radiation which indirectly provides the heat input; the system performance is highly transient. Even if, the input power from the solar field is controlled, there will be an unsteady period that precede the steady operation period of the cooling system. Throughout this transient period, most parameters keep fluctuating and do not stabilize at particular values, and some of them may go away from their allowed ranges in a manner that affects the system performance severely. This phenomena is considered as a prime motivation and fundamental concern of this study. The dynamic model is based on mass, energy balances and heat transfer equations while taking into account the dynamic response of the cycle. The results indicate that it takes an average of fourteen minutes before most parameters stabilize at their operating values and the dynamic terms almost diminish in what could be considered steady-state period. In addition, the performance of a solar absorption system was investigated under meteorological conditions of Dhahran - Saudi Arabia for a representative summer day. The results indicated that; a 60 m 2 of evacuated tube solar collectors is needed to meet the 3 TR cooling load without auxiliary heating during the period 8:00 a.m. to 3:00 p.m. an auxiliary heating is required outside this period to meet the cooling load. The developed dynamic model is able to predict the transient performance of a 3 TR single-effect LiBr-Water solar absorption cooling system which in turn helps in designing appropriate integrated systems for various sustainable applications.

Diesel-powered pumps are widely employed in farming and grassland irrigation. However, there can be problems of reliability and availability where fuel supply is erratic and expensive, high maintenance cost, and short life expectancy. These and recent concerns for the environment associated with the diesel engines call for a viable alternative source of power for irrigational water pumping. Renewable energy sources have gained a lot of attention as a replacement for fossil fuels or as a supplement in hybrid systems. Solar-powered (photovoltaic) systems are one of the viable alternatives that have attracted considerable attention in this regard. They have been deployed in many remote regions for various applications, ranging from rural electrification and community water supplies to irrigation and livestock water supplies. Although photovoltaic (PV) systems generally have a high investment cost, it has many features which make it attractive as an alternative source of power for water pumping. It is clean, as it produces no carbon emission, it generates no noise, and it has low operational and maintenance cost. This manuscript presents a detailed intensive review of solar-powered water pumping systems as reported in the literature to serve as a quick reference to researchers and engineers who are working or interested in the subject.

The increased level of emissions of carbon dioxide into the atmosphere due to burning of fossil fuels represents one of the main barriers toward the reduction of greenhouse gases and the control of global warming. In the last decades, the use of renewable and clean sources of energies such as solar and wind energies has been increased extensively. However, due to the tremendously increasing world energy demand, fossil fuels would continue in use for decades which necessitates the integration of carbon capture technologies (CCTs) in power plants. These technologies include oxycombustion, pre-combustion, and post-combustion carbon capture. Oxycombustion technology is one of the most promising carbon capture technologies as it can be applied with slight modifications to existing power plants or to new power plants. In this technology, fuel is burned using an oxidizer mixture of pure oxygen plus recycled exhaust gases (consists mainly of CO2). The oxycombustion process results in highly CO2-concentrated exhaust gases, which facilitates the capture process of CO2 after H2O condensation. The captured CO2 can be used for industrial applications or can be sequestrated. The current work reviews the current status of oxycombustion technology and its applications in existing conventional combustion systems (including gas turbines and boilers) and novel oxygen transport reactors (OTRs). The review starts with an introduction to the available CCTs with emphasis on their different applications and limitations of use, followed by a review on oxycombustion applications in different combustion systems utilizing gaseous, liquid, and coal fuels. The current status and technology readiness level of oxycombustion technology is discussed. The novel application of oxycombustion technology in OTRs is analyzed in some details. The analyses of OTRs include oxygen permeation technique, fabrication of oxygen transport membranes (OTMs), calculation of oxygen permeation flux, and coupling between oxygen separation and oxycombustion of fuel within the same unit called OTR. The oxycombustion process inside OTR is analyzed considering coal and gaseous fuels. The future trends of oxycombustion technology are itemized and discussed in details in the present study including: (i) ITMs for syngas production; (ii) combustion utilizing liquid fuels in OTRs; (iii) oxy-combustion integrated power plants and (iv) third generation technologies for CO2 capture. Techno-economic analysis of oxycombustion integrated systems is also discussed trying to assess the future prospects of this technology. Copyright (c) 2017 John Wiley & Sons, Ltd.