Desalination Using Low-Grade Heat Sources

This study evaluated the feasibility of utilizing low-grade heat sources such as solar energy or waste heat from industrial processes for desalination. The premise of the approach is that saline waters can be desalinated by evaporation and condensation of fresh water at near-ambient temperatures at low pressures. Low pressures can be achieved naturally in the head space of water columns of height equal to the local barometric head. By connecting the head space of such a saline water column to that of a distilled water column, and by maintaining the temperature of the former about 15–20°C above that of the latter, fresh water can be evaporated from the saline column and condensed in the distilled water column. In this study, it is proposed to use a sensible heat thermal energy storage (TES) system to heat the head space of the saline water column. The TES can be maintained at the desired temperature using solar energy and/or waste heat from thermal power plants, refrigeration plants, or air conditioning units. This paper presents the feasibility of the proposed approach, where the TES is maintained at the design temperature by a solar-powered absorption refrigeration system (ARS) augmented by an electric heater. Results of this feasibility study show that the heat rejected by an ARS of cooling capacity of 3.25?kW (0.975 tons of refrigeration) along with an additional energy input of 208?kJ/kg of desalinated water is adequate to produce desalinated water at an average rate of 4.5?kg/h. The solar panel area required for this application was 25?m2. An integrated process model and performance curves of the proposed approach are presented.     

Double-Pass Photovoltaic-Thermal Solar Air Collector with Compound Parabolic Concentrator and Fins

A solar energy heat collector was combined with photovoltaic cells to form one single hybrid energy generating unit. This system produces both thermal and electrical energies simultaneously. An experimental setup of a double-pass photovoltaic-thermal solar air collector with a compound parabolic concentrator (CPC) and fins was designed and fabricated to study the performance over a range of operating conditions. The collector is designed in such a way that the absorber surface is partially covered by solar cells. A CPC is used to enhance more electrical and thermal energy output from the collector. However, solar cells perform poorly at high operating temperatures. Therefore, fins are attached at the back side of the absorber surface to improve this situation. A circulating air stream passes through an upper channel and then under the absorber plate or lower channel of the collector carrying away the excess heat and thus maintaining the cells at the optimum operating conditions. The performance of the system has been measured. The thermal, electrical, and combined electrical thermal efficiencies of the collector are presented and discussed.     

Unglazed Fiberglass Reinforced Polyester Solar Water Heater with Integrated Storage System

Theoretical and experimental investigations on an unglazed solar hot water heater with integrated storage system were conducted. The system was comprised of a collector and storage tank which was integrated into one unit. All parts of the system have been fabricated from fiberglass reinforced polyester (GFRP). The absorber plate has water tubes of semielliptical shape. The width and length of the absorber plate were 1.4 and 1.8?m, respectively. The absorber plate was fabricated from GFPR using a special resin composition that provides good thermal conductivity and absorptivity. The storage tank has a capacity of 496?L. The storage tank is of sandwich construction with a core material made of polyurethane foam that combines stiffness and lightness of the structure with very good thermal insulation properties. An average tank temperature of 53°C was achieved at an average solar radiation level of 700?W/m2 and ambient temperature of 28°C. The thermal efficiencies of the system were evaluated at 48 and 57% for cloudy and clear days, respectively. Transient performance of the system was predicted by solving the mathematical models consisting of energy balance equations of the system that have been converted to finite difference form and solved by a personal computer. The experimental results were in close agreement as has been found with the theoretical predictions.     

Volatility Diagrams for the Cr-O and Cr-Cl Systems: Application to Removal of Cr2O3-Rich Passive Films on Stainless Steel

Effective diffusional surface treatments of stainless steels require that the naturally forming Cr₂O₃-rich passive layer be removed to ??activate?? or depassivate the surface. Volatility diagrams can be used to understand the possible etching reactions in the Cr-O and Cr-Cl systems and reveal five effective methods for removal of Cr₂O₃-based passivating films: (1) exposure to acetylene (C₂H₂) at 673?K (400?°C) and higher temperatures (providing sooting is avoided); (2) exposure to atomic hydrogen at 10 to 0.001?kPa (0.1 to 0.0001 bar) at 373?K to 673?K (100?°C to 400?°C); (3) exposure to wet oxygen above 573?K (300?°C), forming the volatile species CrO₂(OH)₂; (4) exposure to gaseous HCl at 100?kPa (1 bar) above 473?K (200?°C); and (5) oxidation of Cr₂O₃ to CrO₃ using ozone or atomic oxygen, followed by exposure of CrO₃ to gaseous H₂ or HCl. The last process takes advantage of the fact that CrO₃ is removed more effectively using gaseous H₂ and HCl than is Cr₂O₃.     

Design and Construction of Shielded Lunar Outpost

The construction of an outpost on the Moon in which humans can live and work for periods exceeding six months will require special countermeasures to adapt to the hostile environment present at the lunar surface. Various inherent dangers such as meteoroids, galactic cosmic radiation, solar proton events, and large thermal extremes will drive the design configuration of the outpost. Other considerations such as lunar soil mechanics, equipment performance, mass delivery, risk, reliability, and tele‐operability act strongly as constraints that shape and control the design alternatives. Analysis of these fundamental relationships have resulted in lunar civil engineering guidelines, which are unique to this domain, and these in turn have pointed to research areas needing further attention. A preliminary design is presented for a lunar outpost shelter. Additionally, the design methodology is explored, and early enabling technologies are identified to facilitate an understanding of lunar shelter designs from an integrated system standpoint.     

Heat Flow through Soils and Effects on Thermal Storage Cycle in High-Mass Structures

The solar radiation absorbed in massive building components is stored and later emitted as long-wave thermal radiation into the interior space. Heat storage capacity is directly related to the mass of the building envelope surrounding this space and particularly that of high-mass, homogeneous earthen or cementitious material. A thermal storage cycle is created by the time-lag effect if sufficient mass is available. A similar strategy applied to the lunar and/or Martian regolith would provide a surface structure with micrometeorite and radiation protection, thermal insulation, and natural supplemental heat energy that would significantly reduce the energy requirements met by mechanical equipment. HEAT2 is an energy simulation program that solves heat transfer problems using the partial differential heat conduction equation in two dimensions with the method of explicit finite differences. HEAT2 simulation data suggests that, although thermal mass is most suitable for climates where desired indoor temperatures fall within a large daily external temperature gradient, the heat storage cycle is least effective at the annual extremes occurring in midwinter and in midsummer. A more moderate climate will allow the heat storage cycle to modulate between positive and negative heat flows which are then shifted to align with peak load conditions, reducing energy demand. Also, diurnal and seasonal temperature gradients can initiate a sequence of phase transitions in the soil’s moisture content affecting the overall conductivity. This study will present a more accurate explanation of the heat transfer processes occurring in soils of varying compositions when thermal properties are altered by transient climatic conditions.     

Magnetite Production from Steel Wastes with Concentrated Solar Energy

In order to achieve a balanced development in the application of materials for structural or functional purposes, one of the priority objectives of future work is to achieve the goal of “zero waste” in the different production lines. As would be expected from what was agreed in the Kyoto Protocol and the meetings of Copenhagen 2009 and Cancun 2010, the production of clean energy will be strongly encouraged in the future, and indeed that is already the case now. Taking that into consideration, while the promotion of clean energy production is mainly directed toward electricity, solar thermal is quite interesting because of its direct application to metal mining and the chemical processes used in the sustainable development of materials. The combination of both objectives, “zero waste” and “clean energy,” may pose an interesting challenge in the development of primary iron and steel, as well as in other areas of metal production and even in the field of mining. The help of solar thermal energy, which can be concentrated to reach high temperatures, is a tool that could support both the direct production and the recycling of waste steel, in particular waste which is physically and chemically the worst for the environment. This would mean that the environment itself, solar energy, is in fact the key to environmental protection.     

Solar disinfection of drinking water contained in transparent plastic bottles: characterizing the bacterial inactivation process

A series of experiments is reported to identify and characterize the inactivation process in operation when drinking water, heavily contaminated with a Kenyan isolate of Escherichia coli, is stored in transparent plastic bottles that are then exposed to sunlight. The roles of optical and thermal inactivation mechanisms are studied in detail by simulating conditions of optical irradiance, water turbidity and temperature, which were recorded during a series of solar disinfection measurements carried out in the Kenyan Rift Valley. Optical inactivation effects are observed even in highly turbid water (200 ntu) and at low irradiances of only 10 mW cm-2. Thermal inactivation is found to be important only at water temperatures above 45 degrees C, at which point strong synergy between optical and thermal inactivation processes is observed. The results confirm that, where strong sunshine is available, solar disinfection of drinking water is an effective, low cost method for improving water quality and may be of particular use to refugee camps in disaster areas. Strategies for improving bacterial inactivation are discussed.     

锌铈液流电池研究进展

能源是经济发展和人们生活的重要物质基础.化石燃料的过度消耗加速了能源危机和环境污染的出现.新能源的利用是解决能源问题和环境问题的必然选择.太阳能、风能和潮汐能等新能源发电具有间歇性的特点,给电网的安全稳定运行带来很大的挑战.储能技术是新能源开发的关键技术.在各种储能技术中,电化学储能日益受到重视.液流电池是一种高效大规模储能系统.锌铈液流电池是已知的单电池电压最高的水溶液电解质电池.文中阐述了锌铈液流电池的工作原理,从正半电池反应、负半电池反应和隔膜3个方面综述了当前的研究进展.指出了锌铈液流电池研究中需重点关注的基础问题.     

Low-Temperature Soil Heating Using Renewable Energy

Data from a pilot study, in which renewable energy was used for low-temperature subsurface heating in a northern climate, suggests that such an approach may be useful for remediating low permeable soils. Low-temperature soil heating is expected to enhance remediation effectiveness by increasing contaminant volatility, diffusion, desorption, and microbiological activity. Direct and indirect solar energy was harvested with a hybrid photovoltaic/wind electric system. The electrical energy generated by the hybrid renewable energy system was distributed to the subsurface using a control system and wire, then converted to heat energy using a resistive element emplaced in an unsaturated silty layer 2.3?m below grade. Renewable energy system performance, soil temperature, and environmental data were collected. Ambient soil temperatures fluctuated seasonally within the silt layer from 4?to?15°C. The small renewable energy system performed as predicted and injected 441?kWh of energy into the soil over the eight-month study. This energy input translated to increased soil temperatures ranging from 7.7?to?19.4°C and from 3.3?to?4.3°C above ambient at distances 0.3 and 0.9?m from the heating well, respectively. The system supplied sufficient heat to maintain soil temperatures above ambient even in winter in Vermont, where low direct solar energy was available and sustained low ambient temperatures prevail.