Experiment and numerical simulation on flow and heat transfer in all-glass evacuated tube solar collectors

The experimental study of natural convection in allglass evacuated tube solar collectors is performed through the experimental platform of the solar-assisted fuel cell system.The experimental facility includes solar collectors with different length and diameter tubes, different coating materials, and with / without guide plates, respectively. Threedimensional mathematical models on natural and forced convections in the solar collectors are established and the experimental data is validated by field synergy and entransy principles. The results of natural convection show that the water temperature increases and thermal efficiency decreases gradually with the evacuated tube length. The thermal efficiency increases when absorption rates increase from 0. 95 to 1. 0 and emission rates decrease from 0. 16 to 0. 06. The thermal efficiency of solar collectors is increased after being equipped with the guide plate, which is attributed to the disappearance of the mixed flowand the enhancement of the heat transfer at the bottom of the evacuated tube. The results of forced convertion indicate that the Reynolds, Nusselt and entransy increments of the horizontal double collectors are higher than those of the vertical single collector while the entransy dissipation is lower than that of the vertical single collector. It is concluded that the solar collectors with guide plates are suitable for natural convection while the double horizontal collectors are suitable for forced convection in the thermal field of solar-assisted fuel cell systems with lowand medium temperatures.

Evacuated tube transport technologies (ET3)^(tm):a maximum value global transportation network for passengers and cargo

Evacuated Tube Transport Technologies （ET3） offers the potential for more than an order of magnitude improvement in transportation efficiency, speed, cost, and effectiveness. An ET3 network may be optimized to sustainably displace most global transportation by car, ship, truck, train, and jet aircraft. To do this, ET3 standards should adhere to certain key principals： maximum value through efficiency, reliability, and simplicity; equal consideration for passenger and cargo loads; optimum size; high speed/high frequency operation; demand oriented; random accessibility; scalability; high granularity; automated control; full speed passive switching; open standards of implementation; and maximum use of existing capacities, materials, and processes.

Effect of Streamlined Nose Length on the Aerodynamic Performance of a 800 km/h Evacuated Tube Train

The aerodynamic resistance of a train running in the open air limits the maximum speed that can be attained by the train.For this reason,evacuated tube trains(ETT)are being considered as valid alternatives to be implemented in the future.The atmosphere in the tube,the so-called blocking ratio and the length of the streamlined nose are the key factors affecting the aerodynamic performances of these trains.In the present work,we investigate evacuated tube trains with different lengths of the streamline nose on the basis of computational fluid dynamics(CFD).The three-dimensional steady compressible Navier-Stokes equations are solved.The running speed of the ETT is 800 km/h and the blocking ratio is 0.2.Results show that with the increase of the streamlined nose length,the aerodynamic drag and lift forces of the head car decrease gradually,and the drag and lift forces of the middle car change slightly.For the tail car,the drag force decreases,whereas the absolute value of the lift force increases.At a speed of 800 km/h,a slight shock wave appears at the rear of the tail car,which affects the aerodynamic forces acting on the train.

Key vacuum technology issues to be solved in evacuated tube transportation

Evacuated tube transportation （ETT） will be one of the ultra-large-scale vacuum application areas. This paper lists some key vacuum technology issues in ETT： （1） how to construct ultra-large-scale vacuum chamber with lower cost and high reliability, （2） how to evacuate gas out of the ETT tube in short time, （3） how to release heat or reduce temperature in the vacuum tube, （4） how to avoid vacuum discharge, （5） how to make vehicles with airproof shells and life support system, and （6） how to detect leaks and find leak positions efficiently. At the same time, some solutions are proposed.

Aerodynamic Design of a Subsonic Evacuated Tube Train System

The so-called Evacuated Tube Train(ETT)is currently being proposed as a high-speed transportation system potentially competitive with airplane transportation.Aerodynamic resistance is one of the most crucial factors for the successful design of an ETT.In the present work,a three-dimensional concept ETT model has been elaborated.The aerodynamic characteristics of the subsonic ETT have been numerically simulated under different conditions.The train’s running speed varies from 600 km/h up to 1200 km/h,and the blockage ratio is in the range between 0.1 and 0.3.As the blocking ratio and running speed increase,the resistance of the head car increases greatly,while the resistance of the middle car changes slightly.The aerodynamic resistance of the tail car is affected by the shock wave emerging in the wake flow.Two different design criteria for the maximum allowed aerodynamic resistance are proposed for aerodynamic parameter matching.With an increase in the blockage ratio and running speed,the atmospheric pressure in the tube should be decreased to achieve a balance.

Numerical simulation and analysis of aerodynamic drag on a subsonic train in evacuated tube transportation

The aerodynamic drag on a train running in an evacuated tube varies with tube air pressure, train speed and shape, as well as blockage ratio. This paper uses numerical simulations to study the effects of different factors on the aerodynamic drag of a train running at subsonic speed in an evacuated tube. Firstly, we present the assumption of a steady state, two dimensional, incompressible viscous flow with lubricity wall conditions. Subsequently, based on the Navier-Stokes equation and the k-c turbulent models, we calculate the aerodynamic drag imposed on the column train with a 3-meter diameter running under different pressure and blockage ratio conditions in an evacuated tube transporta- tion （ETT） system. The simulation is performed with FLUENT 6.3 software package. An analyses of the simulation re- sults suggest that the blockage ratio for ETT should be in the range of 0.25-0.7, and the tube internal diameter in the range of 2-4 m, with the feasible vacuum pressure in the range of 1-10 000 Pa for the future subsonic ETT trains.

Aerodynamic simulation of evacuated tube maglev trains with different streamlined designs

Based on the Navier-Stokes （N-S） equations of incompressible viscous fluids and the standard k-ε turbu- lence model with assumptions of steady state and two dimensional conditions, a simulation of the aerodynamic drag on a maglev train in an evacuated tube was made with ANSYS/FLOTRAN software under different vacuum pressures, blockage ratios, and shapes of train head and tail. The pressure flow fields of the evacuated tube maglev train under different vacuum pressures were analyzed, and then compared under the same blockage ratio condition. The results show that the environmental pressure of 1 000 Pa in the tube is the best to achieve the effect of aerodynamic drag reduction, and there are no obvious differences in the aerodynamic drag reduction among different streamline head shapes. Overall, the blunt-shape tail and the blockage ratio of 0.25 are more efficient for drag reduction of the train at the tube pressure of 1 000 Pa.

The approach to calculate the aerodynamic drag of maglev train in the evacuated tube

In order to study the relationships between the aerodynamic drag of maglev and other factors in the evacuated tube, the formula of aerodynamic drag was deduced based on the basic equations of aerodynamics and then the calculated result was confirmed at a low speed on an experimental system developed by Superconductivity and New Energy R＆D Center of South Jiaotong University. With regard to this system a high temperature superconducting magnetic levitation vehicle was motivated by a linear induction motor （LIM） fixed on the permanent magnetic guideway. When the vehicle reached an expected speed, the LIM was stopped. Then the damped speed was recorded and used to calculate the experimental drag. The two results show the approximately same relationship between the aerodynamic drag on the maglev and the other factors such as the pressure in the tube, the velocity of the maglev and the blockage ratio. Thus, the pressure, the velocity, and the blockage ratio are viewed as the three important factors that contribute to the energy loss in the evacuated tube transportation.

Design consideration of a super-high speed high temperature superconductor maglev evacuated tube transport (I)

The super-high speed high temperature superconductor （HTS） maglev evacuated tube transport （ETT） is a promising transport mode for the future. As a key component of the HTS maglev vehicle, the permanent magnet guide- ways （PMGs） with different geometrical configurations and iron yoke widths are analyzed by finite element method （FEM）. The levitation force of a single onboard HTS maglev device over the designed PMG at different field cooling heights （FCH） is measured by magnetic levitation measurement system. Based on the designed PMG and experimental results, a preliminary scheme of subterranean super-high speed HTS maglev ETT is described in this paper. The HTS maglev ETT is mainly composed of an evacuated tube, HTS maglev vehicle, PMG, propulsion system, station, emergency rescue system, etc. In addition, a subterranean tube that consists of foundation tube and vacuum airproof layer is introduced. In order to convert the stress caused by the air pressure difference between inside and outside of the vehicle, a multi-circular vehicle body is designed. The vehicle is driven by a linear motor propulsion system under the control of a ground controlling system. The scheme of long-distance super-high speed passenger transportation is accomplished by the connection of different vehicles.

Performance enhancement of filled-type solar collector with U-tube

In order to increase the efficiency of solar collector, a methodology is proposed based on the analysis of its influencing factors, such as thermal conductivity of filled layer, structure forms of filled layer and heat loss coefficient. The results of analysis show that the heat transfer between pipes in evacuated tube is one of the most important factors, which can lead to the decrease of the outlet temperature of working fluid. In order to eliminate the negative influence of the heat transfer between pipes, the hollow filled-type evacuated tube with U-tube(HUFET) was developed, and the heat transfer characteristics of HUFET were analyzed by theoretical and experimental studies. The results show that the thermal resistances decrease with the increase of the thermal conductivity of filled layer. When the thermal conductivity is over 10 W/(m·K), the change of thermal resistances is very little.Furthermore, the larger the thermal conductivity of filled layer, the less the rate of the energy transfer between the two pipes to the total energy transfer, which is between the absorber tube and the working fluid. There is a little difference between the efficiencies of HUFET and UFET, with the efficiency of HUFET 2.4% higher than that of UFET. Meanwhile, the validation of the model developed was confirmed by the experiment.

Wireless Network Architecture for Evacuated Tube Transportation System

Evacuated Tube Transportation(ETT)systems have been claimed to have considerable strengths,including ultra-highspeed,safety,and environmentally-friendly.However,the frequent handover caused by the high-speed brings a challenge for ETT mobile wireless communication to preserve steady link performance.Moreover,in such a special scenario,the wireless link between the base station and the passengers on the train needs to experience fading from both metal pipe and train,thus the free-wave coverage with antennas in traditional high-speed rail wireless communication systems is not suitable for ETT.Based on the characteristics of ETT,an improved architecture of wireless communication network is proposed,using distributed base stations with remote radio units(RRUs)and baseband units(BBUs)and leaky waveguides to form stable coverage.And a redundant BBUs or RRUs structure is designed for coverage enhancement.Based on this redundant architecture,a fast handover scheme is proposed to resolve the handover problem.The analytical and simulation results show that the proposed scheme is capable of reducing communication outage probability and handover failure probability remarkably.

Some possible station layouts and characteristics of evacuated tube transportation

Since Maglev vehicles will run in a closed vacuum tube,the layout of the terminal stations of evacuated tube transportation（ETT） will differ from the traditional railway stations.This paper deals with some possible station layouts of ETT,e.g.,a station with an airlock,a station without an airlock,above ground and underground stations,and stations with either level arrayed or rotation platforms.Then different station layouts are compared,and characteristics of each are analyzed.Finally,a more secure mode for ETT station layouts is suggested,which can be the basis for future ETT station layout and designs.

An Evaluation to the Performance of Evacuated Tube Solar Heaters for Arid and Hot Areas

Solar energy applications could be the best alternative to the conventional fuels for the purposes of domestic,water and space heating and some industries in the sunny,arid,and hot areas.In the present study,the performance of an evacuated tube solar heater for water heating for months of February and March was experimentally investigated.This was performed in a hot and arid area(Nasiriya City,South of Iraq).A solar heater with ten evacuated tube solar collectors with a capacity of 100 liter was used in the experiments.Each evacuated tube had a length of 1.8m with an outside diameter of 8 cm.It was observed that for the two selected months,water temperature of the solar heater reached a maximum more than 70°C during sunny days with no heat extraction from the tank of the solar heater.Moreover,heat was extracted from the solar collector with four different flowrates 0.5,0.75,1,and 1.25 l/min,respectively.The results showed that temperature of the solar heater behaved differently from the static situation.When the heat extraction begun,there was a gradual and noticeable decrease in the water temperature of the heater.The observed decrease was slight with the lowest flowrate(0.25 l/m)and becomes sharp with the highest flowrate(1.25 l/min).However,water temperature of the solar heater remained higher than 40°C for the investigated flowrates except the case of 1.25 l/min.The results showed that evacuated tube solar heater can work efficiently in arid and hot areas in winter and spring seasons when the conditions of solar radiation are suitable.

Performance of Water in Glass Evacuated Tube Solar Water Heater under Kenya Climatic Condition

Solar water heaters which provide a cost-effective and environmental friendly approach to hot water generation are in widespread application. Evacuated tube solar water heaters perform better than flat plate solar water heaters as a result of their greater surface area exposed for sunlight absorption. Water-in-glass evacuated tube solar water heaters are widely used as compared to heat-pipe solar water heaters due to their short payback periods. In this study, the performance of water-in-glass evacuated tube solar water heater is investigated through experiments under the climatic conditions in Kenya. The results revealed a daily efficiency range of 0.58 - 0.65 and a daily final outlet temperature greater than 55°C given an initial temperature of 25°C.

MEASUREMENT OF THE EFFICIENCY OF EVACUATED TUBE SOLAR COLLECTORS UNDER VARIOUS OPERATING CONDITIONS

The operating efficiency of evacuated tubes themselves under varying environmental conditions and installation scenarios,independent of water and space heating auxiliary equipment,are not readily available values.Further,Manitoba specific data has not been established.The purpose of this research program was to measure the efficiency of evacuated tube solar collectors under various operating conditions including:the angle of inclination towards the incident solar radiation,heat transfer fluid flow rate,glazing installation,and number of evacuated tubes.The operating conditions and configurations were chosen to represent realistic or probable installation scenarios and environmental conditions.Furthermore,the research aimed to identify the suitability of evacuated tube solar collectors to each of the scenarios.These design values are of use for appropriate sizing of water or space heating systems,system configuration and optimization,and calculation of return on investment.The scope of the research project was limited to the efficiency of various configurations of a 32-tube panel,not the entire solar domestic hot water or space heating system.Thus,factors such as heat loss in the tubing,solar storage tank,and heat exchanger efficiency were not investigated.The findings indicated that efficiency varied by approximately 5%between the different collector configurations,as observed from the overlay graph of results.When the efficiency of a collector is considered within a system it is proposed that effectiveness may be a better measure of overall performance.

Performance of U-tube Solar Water Heaters Facing Different Directions

System performance of solar water heaters depends upon collector and storage tank designs, solar radiation intensity and ambient temperature, amongst others. Evacuated glass tube collectors with U-tubes inside are less prone to leakages than the all-glass or the heat pipe types. U-tube solar water heaters suspended on walls and balconies could help overcome present day roof space restriction and increasing apartment-style housing. As such, their performance would depend upon its orientation when mounted in a vertical position. This paper reports the results of outdoor tests conducted on natural convection U-tube solar water heaters oriented towards different directions. Long and short term test procedures were employed to allow us to compare their performances as if they were tested simultaneously side-by-side.

Developments of solar collectors in China

China has abundant solar energy resource. Solar thermal collectors, particularly all-glass evacuated tubular collectors, have been studied and developed for 30 years, and solar thermal industry has developed rapidly for 15 years. There are various solar thermal systems, with an operation area of around 108 million m2 in 2007. These systems mainly provide domestic hot water, but some other applications are under extensive study and development as well.

Modelling, Transient Simulation and Economic Analysis of Solar Thermal Based Air Conditioning System in Gujarat

Commercial building sector accounts for 8% of the total electricity consumption in India. Cooling activities (HVAC) in commercial buildings consume 55% of the total energy utilized. Consequently, CO2 emissions from conventional buildings in India were estimated to be 98 metric tonnes of CO2 per million ft2 in 2014. Solar thermal air conditioning can be the solution to these demands and can contribute to about 15% to 20% of India’s total oil consumption thereby reducing the dependence on fossil fuels. Hence, the main objective of the work is to model and simulate a solar absorption cooling system for GERMI office building located in Gandhinagar, Gujarat, India, using the transient simulation software ‘TRNSYS’. Cooling load estimation and comfort conditions required for the building were determined based on ASHRAE standards. Evacuated tube collectors were selected because of its market availability, ease of manufacturing and proven technology. Single effect absorption chiller was used because of its commercial availability. The effects of storage tank volume, collector area and collector slope were also investigated for parametric optimization. The results of the simulation and parametric analysis are analyzed and presented in the paper.

A CARBON CLOUD WITH PLATINUM LINING

Picture this.On a freezing December day,a few days before Christmas,2008 an electrical fire started in the basement utility room.The burn damage was so severe at the origin site that the exact cause could not be determined,but the theory is that a transfer switch connected to an emergency power generator started the fire when an auto test series was initiated.The fire quickly spread to the ceiling of the basement utility room,which was not fire rated,and burned the floor out of the kitchen above,at the center of the two-story home.In a very short time,the kitchen collapsed into the basement.The fire began shortly after the five family members left for work and school and was discovered by a worker who arrived to complete a bathroom remodel.Thick black smoke poured through every vent to the outside.By the time firefighters gained control of the blaze,the 3,000-sq-ft house and everything in it was ruined.If this image conjures a big black carbon cloud for you,imagine what the family was going through.Everything they owned was burned or covered with black soot and ice.It was a devastating blow to a smart young family going about their daily lives.It was the epitome of a dark cloud,and a silver lining seemed only like a myth.About the same time,a group of local tradesmen called the Hamptons Green Alliance(HGA),who organized a few months earlier,were busy soliciting local architects.Through the AIA Peconic,the HGA sent an e-mail blast to all members in order to find a project they could initiate in order to exercise their old and new sustainable building skills.Their goals were to apply their cumulative knowledge and expertise in sustainable practices and integrate them into a sum greater than the parts.Each individual company had experience,but never before had they consciously collaborated on a design that integrated all their systems at once.All would share the benefit and help the HGA raise the bar on sustainable building so they could offer experience,expertise,and specific energy usage and production data,including life cycle analysis,to future clients.They offered their services at their cost,to any architect’s client interested in a new house or remodel that would be rebuilt with the highest and best sustainable practices possible.At the peak of the financial panic,AIA members found no takers.Richard(Ric)Stott,AIA LEED AP,architect,was a friend of the fire-struck family and of course offered help.After the first meeting with another family friend and architect Craig Lee,AIA,it struck Ric that this would be the perfect project for the Hamptons Green Alliance.The owner agreed,a meeting was scheduled,and a project involving all major trades,the architects,owners,and even the insurance adjusters was born.It was not hard for Ric to convince the team that the LEED for Homes program would be appropriate for this project and soon the team began meeting once a week to focus on goals,discuss strategy,and learn about the requirements of the LEED for Homes system.By default,it was an“Integrated Project Delivery”(IPD).All the team members were in play from the beginning,the budget was fixed at what the insurance claim paid,plus the owners’out-of-pocket expense to add a family room and bedroom.The commitment was made by the HGA members to work for no profit,which allowed the family to make the additions and improvements.At weekly meetings,the team decided to pursue LEED Platinum status,to incorporate all renewable technologies that were economically feasible,but first and foremost we would incorporate high performance building science as our basic energy conservation methodology.Besides aiming for LEED Platinum status,the team also established the goal to rebuild this project as carbon neutral.A major decision had to be made with respect to the existing structure.To demolish the house or salvage the frame was a dilemma.Building from scratch would be easier,faster,and probably cheaper,but was it the most sustainable?Does saving the remains of a charred wood frame add or subtract from the overall carbon footprint?Certainly,bringing the framing and sheathing to the landfill is not a carbon friendly concept.The family was concerned that if we saved the structure,it would retain the smoky smell and wanted a guarantee that no odors would be perceived,even on the hottest summer days.We contacted a number of fire renovation companies and they all agreed that full encapsulation would have to be performed on the structure after we cleared the burned and structurally compromised framing away.The majority of the frame was structurally sound and it would be difficult to recycle it,so the decision was made to re-use the frame and most of the exterior sheathing including a good portion of the existing cedar shingles.

Solar Heater Technologies Selection Using Multi-criteria Analysis

Regarding sun＇s potential in Middle East and North Africa zone and particularly in Morocco, we focus our work on the development of the knowledge and information concerning the solar heaters for domestic applications, in order to help the industrial and the consumer to select an adaptive technology. As a result, a Moroccan mapping of solar water heating systems is presented in this work. This mapping concerns two technologies commonly used： the FPC （flat plate collectors） and the ETC （evacuated tubes ones）. It is based on three criteria： firstly, the efficiency of the STC （solar thermal collectors）; secondly, the economic aspect and at last, the reliability requirements. Based on these information, the multi-criteria outranking methodology PROMETHEE （preference ranking organization method for the enrichment evaluations） allows us to define an adequate solar heater technology linked with the climatic zoning of Morocco.