A study of the operating characteristics of an experimental absorption cooler using water—lithium bromide—ethylene glycol as a ternary working system

Absorption heat pumps and coolers can be satisfactorily operated using the water—lithium bromide—ethylene glycol ternary system with an ethylene glycol to water mole ratio of 1/15. This gives a high coefficient of performance and a lower risk of crystallization.     

Heat loss reduction from the gas holder/fixed gas dome of a community-size biogas plant

The decrease in the yield of biogas in winter months in the usual systems—fixed dome and floating dome types—can be checked by providing insulation on the inner surface of the gas holder. A mathematical model has been developed to study the effect of putting in such insulation. A novel concept of making a shallow solar pond water heater over the gas holder to reduce the heat losses and simultaneously provide water for hot charging is proposed and analysed. Calculations corresponding to a typical winter day at New Delhi have been made for a numerical appreciation of the developed analysis.     

Effect of using a reflecting sheet in an air gap on the thermal performance of hollow walls and roofs

In this paper, the effect of placing a reflecting sheet in an air gap on the thermal performance of single hollow, double hollow and insulated hollow walls and roofs is studied. One face of the wall or roof is exposed to solar radiation and ambient air and the other is in contact with room air at constant temperature. These results are also compared with the predictions made in the case when a water film is maintained on the roof or wall. Numerical calculations are for a typical hot day (the 26th of May, 1979) in New Delhi. It is seen that the use of a reflecting sheet in single hollow and double hollow walls and roofs is more economical—and gives a better performance—than the water film system.     

Flow pattern maps and transition criteria for flow boiling of binary mixtures in a diverging microchannel

This paper presents a visualization study of flow boiling of binary mixtures (methanol–water and ethanol–water mixtures) in a diverging microchannel. The flow pattern and transition criteria are studied in terms of effects of mass flux, heat flux, and molar fraction of the more volatile component (i.e., methanol or ethanol). Four boiling regimes are identified: bubbly-elongated slug flow, annular flow, liquid film breakup, and dryout. Further, generalized flow pattern maps are constructed using coordinates of nondimensional parameter space (boiling number, Weber number, and Marangoni number), wherein relatively distinct boundaries between the flow patterns are identified. Criteria for transitions between flow patterns are proposed in the form of nondimensional groups and are successfully used to predict the experimental results. More than 92% of the data are correctly located within transition boundaries. The criterion for the onset of nucleate boiling—the boundary between single-phase flow and bubbly-elongated slug flow—is also determined for both methanol–water and ethanol–water mixtures on the basis of the same set of nondimensional parameters.     

Techno-economic assessment of a solar-geothermal multigeneration system for buildings

A techno-economic assessment is conducted for a multigeneration system comprised of two renewable energy subsystems—geothermal and solar—to supply electrical power, cooling, heating, hydrogen and hot water for buildings. The proposed system is evaluated in terms of energy and exergy efficiencies. The simulation results show that the electrolyzer produces 2.7 kg/h hydrogen. A parametric study is carried out to assess the effect of various parameters on the system energy and exergy efficiencies. The economic assessment, performed using the Hybrid Optimization of Multiple Energy Resources (HOMER) software, shows that the net present cost of the optimized electrical power system is $476,000 and the levelized cost of electricity is $0.089/kWh.     

On the burn-up theory of fast soliton reactors

The basic reactor physics of a completely new nuclear fast fission reactor—the Soliton Reactor—is presented. In such a fast reactor, based either on the U/Pu- or the Th/U-233 fuel cycle, an auto-catalytically driven flux-wave, similar to a water wave on shallow water, propagates through initially fertile regions thus burning it up and producing power.Hence, a qualitatively new kind of harnessing nuclear fission energy may become possible: without transports of irradiated fuel elements, reprocessing and—according to Edward Teller—by co-location of the reactor itself and the subterranean final disposal site in a sand bed about 100m underground. Combined with the idea of an “energy island” soliton reactors could form the basis for a practically inexhaustible source of hydrogen for a climate-neutral energy source.     

Status and prospects of local solar heating and cooling systems

In this paper, a state-of-the-art of solar heating and cooling systems is presented. Solar air heaters and different types of solar water collectors are discussed in detail. Storage systems including water, rocks, and heat-of-fusion salts are described as are space heating systems employing solar air heaters, in conjunction with rock or heat-of-fusion salt storage, and the use of water collectors plus hot water storage for space heating and domestic hot water. An indication of the commercialization of various space-heating systems and broad economic projections are presented. The three major solar cooling methods—absorption cooling, solar mechanical systems, and those involving humidification-dehumidification cycles—are also discussed in detail. Finally, an overview of solar heating and cooling activities in Kuwait is also given.     

Solar photocatalysis—a possible step in drinking water treatment

Possibility of the use of solar radiation for reduction of Natural Organic Matter (NOM) content in natural lake water, as a source for drinking water preparation, was the topic of this research. Solar radiation alone does not have enough energy for sufficient degradation of NOM, but in combination with heterogeneous photocatalyst-titanium dioxide (TiO₂), with or without other chemicals, the degradation potential could increase. In specific geographical conditions in Republic of Croatia, e.g. Adriatic islands or Dalmatia, solar radiation could be used for photocatalytic degradation of natural organic matter (NOM) in surface waters and therewith lighten the process of preparing them to the potable water. Specific quality of the geographical locality appears in fact that it is a very attractive tourist destination, especially in period June–September. In this period the drinking water demand is the biggest and, fortunately, the intensity of the solar radiation, too. So, there is a proportion between the drinking water demand and solar radiation available for the use in drinking water treatment.A number of tests with lake water exposed to solar radiation in non-concentrating reactors were performed and photodegradation of NOM for various combinations of doses and crystal forms of TiO₂ with H₂O₂ was studied. Irradiation intensity was estimated from global solar radiation measurements. The best performance for the NOM degradation had combination of 1 g/L TiO₂ both anatase and rutile+solar radiation+H₂O₂, but—economically—it was not the best combination. An estimation of the biodegradation potential of dissolved organic matter after the photocatalytic step is given, too.     

Solar pond ground heat loss to a moving water table

An analytical solution is presented that calculates the heat loss from the bottom of a solar pond (or any heated object) to a soil that contains a moving water table. The water table is treated as a fluid slab moving as a slug flow in one dimension. Edge effects and horizontal heat conduction are ignored. Both steady-state and time-dependent solutions are presented. Results are presented in terms of an effectiveness ratio—the actual heat flux divided by the steady-state heat flux resulting from a constant temperature heat sink at the depth of the water table. The only water-table parameter that strongly affects the effectiveness is the fluid capacity rate. Thus, for any potential solar pond site, a measurement of the mass flow rate of the water table combined with knowledge of the soil thermal properties will allow a good estimation of the ground heat loss expected over the lifetime of the pond.     

Desalination using a parabolic-trough concentrator

There are presented desalination results by using a parabolic-trough concentrator (PTC) device of 5.5 m², 0.7 m of line focal distance and aligned in the East—West direction. The length of the PTC is 2.5 m and its rectangular absorber cavity has 1m length made of black aluminum. The equipment is located in Cocayalta (48 km from Lima, with 700–850 W/m²) and there were made simple modifications on the cavity to increase the fresh water production, from 3250 cm³ (3.25 liters) using the simplest model to 6360 cm³ (6.36 liters) with the thermal insulation and wind protection model, that represents an increase of about 95%. Finally, water analysis showed a good quality of the fresh water obtained.     

Experimental study of thermal performance improvement in a cross-flow heat exchanger by using copper foam

In this study, copper foam was used as a porous medium in place of traditional aluminum fins. A comparison between the two heat exchangers—one with fins and the other with copper foam—was conducted under various conditions. The air inlet velocity ranged from 0.9 to 9.3 m/s, and the water inlet temperature ranged from 10°C to 18°C. Different water flow rates were tested. A comparison was made between the performance of copper foam and aluminum fins by calculating several parameters, including thermal resistance, heat exchanger effectiveness, Colburn factor, Nusselt number, friction factor, and area goodness factor (AG). The experimental results showed that at low air velocities, the heat transfer coefficient for both types of heat exchangers was almost equal. However, at high air velocities, the copper foam exhibited a higher heat transfer coefficient. The Colburn factor was higher for the heat exchanger with copper foam than in the conventional fins, where it was equal to 0.1959 for the copper foam and 0.1186 for the fins. On the other hand, the AG was higher in the case of fins than in the heat exchanger with copper foam.     

建筑节能改造采暖供回水温度的优化

针对既有建筑的节能改造,探讨了建筑改造后采暖热媒参数设定问题。本文主要阐述了供暖系统形式为单管顺流式系统的节能改造建筑,在由于节能改造而导致建筑物热负荷减小的情况下,采暖供回水温度取值的调整问题。从热平衡方程式出发,推导出了节能改造建筑供回水温度的计算公式,为该类建筑的采暖运行提供了理论上的依据。     

The effect of mixed nanoadditive‐blended diesel–water emulsion on the performance,combustion, and emission characteristics of a DI diesel engine

The present paper examines the impact of mixed nanoadditive (Al₂O₃ and ZnO) incorporated diesel–water emulsion on the combustion, performance, and emission of a single‐cylinder diesel engine under varying load conditions. The test fuels consist of constant fuel ratio of 88% diesel, 10% water, and 2% surfactant. Also, different concentrations of mixed nanoadditives—50 ppm, 100 ppm, and 150 ppm—are added to the test fuel. The ultrasonicator bath is employed for agitation or stirring of test fuels. The test results indicate that the mixed nanoadditives in diesel–water emulsion improve combustion characteristics, brake thermal efficiency, and brake‐specific fuel consumption, whereas the maximum improvement is achieved at full load. It is also determined from the test results that the nanoadditive‐blended test fuel showed a noticeable decrement in CO, NO_x, and hydrocarbon emissions as compared with neat diesel. The optimum results are obtained for D88S2W10ZA150 blend. Owing to the higher surface‐to‐volume ratio, enhanced atomization rate, high catalytic behavior, and shortened ignition delay are possible reasons to improve diesel engine working characteristics.     

The flow characteristics of an upward gas‐liquid two‐phase flow in a vertical tube with a wire coil: Part 1. Experimental results of flow pattern,void fraction,and pressure drop

Experiments were carried out to investigate the flow pattern, average void fraction, and pressure drop of an upward air‐water two‐phase flow in vertical tubes of 25‐mm inside diameter with wire coils of varying wire diameter, pitch, and number of coils in cross section. Five kinds of flow patterns—bubble, slug, churn, semiannular, and annular flow—were defined based on the observation of flow behavior in the experiments. At higher water flowrates, the bubble‐to‐slug transition occurred at lower air flowrates in tubes with wire coils than in smooth tubes. The average void fraction was found by using the drift flux model. Further, the experimental results of the friction pressure drop were compared with the Lockhart‐Martinelli correlation. As a result, a correlation with the constant C in Chisholm's equation was obtained as a function of the wire coil pitch‐to‐diameter ratio. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 639–651, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10066     

基于压力容器分析法的凝汽器水室强度计算

以660 MW超超临界两排汽机组凝汽器水室为研究对象,基于JB 4732—1995《钢制压力容器——分析设计标准》,采用弹性应力分析及有限元应力线性化的方法将总应力进行分解,并进行了强度判定。经过水压试验及现场运行的检验可知,强度满足设计要求。     

UNSTEADY THREE-DIMENSIONAL NATURAL CONVECTION OF WATER COOLED INSIDE A CUBIC ENCLOSURE

Three-dimensional unsteady natural convection of cooling water inside a cubical cavity at Ra = 10⁵ is investigated. The finite-volume method with the SIMPLE algorithm is used to solve the nonlinear coupled continuity, momentum, and energy equations. All physical water properties—density, viscosity, thermal conductivity, and specific heat—are allowed to change with temperature. The numerical results for the 3-D geometry show that the side effects are relevant in fluid mechanics and in heat transfer, with larger differences than with the 2-D predictions in the region where the density anomaly of water is important.     

Electrolysis: The important energy transformer in a world of sustainable energy

In a world of sustainable energy supply, the latter will be predominantly generated, distributed and consumed in the form of electric power and hydrogen. In order to balance supply and demand, for storage purposes and to meet the specific requirements of the different end users, we need powerful energy transformers in both directions—fuel cells and electrolyzers.Though based upon a simple electrochemical effect, tough demands on a water splitter, with respect to efficiency, operability, safety and costs make it a modern electrolyzer and a piece of engineering excellence.Furthermore, the general aspects of electrolyzer design and performance will be discussed.     

Experimental Study on Anti-Fouling Performance in a Heat Exchanger with Low Voltage Electrolysis Treatment

An innovative physical method to control fouling in heat transfer equipment—low voltage electrolysis anti-fouling (LVEAF) technology—is introduced. The objective of the present study is to testify the effect of LVEAF treatment in forced convective system and identify the operating mechanism. A series of fouling tests were carried out with and without LVEAF treatment. During the experiments fouling resistance was monitored, and the properties of test liquid were measured, including hardness, alkalinity, electrical conductivity, and pH. The main results were as follows: (1) The fouling was effectively restrained to form on the heat exchanger surface if the circulating water was treated with LVEAF. The scale inhibition ratios exceeded 90% in most cases. (2) The LVEAF technology is an active anti-fouling technology with lower energy consumption. The properties of treated test liquid were changed. (3) Electrochemical reactions occur near the electrode due to the low current existence in the water when the LVEAF device is working. A lot of fouling deposits formed in the test liquid near the cathode or on the inner surface of the treatment unit, but did not deposit on the heat exchanger surface.     

Proton-conducting polymer membrane comprised of a copolymer of 2-acrylamido-2-methylpropanesulfonic acid and 2-hydroxyethyl methacrylate

In order to identify a proton-conducting polymer membrane suitable for replacing Nafion^® 117 in direct methanol fuel cells (DMFC), we prepared a cross-linked copolymer of hydrophilic 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 2-hydroxyethyl methacrylate (HEMA). Fumed silicas were also added in an attempt to increase the amount of water adsorbed by the membrane and to enhance water retention. Hydrated copolymer membranes adsorbed significantly more water than Nafion^® 117, but were no better at retaining water during drying under ambient conditions. Films composed of 4% AMPS—96% HEMA had a room temperature proton conductivity of 0.029 S cm⁻¹, which increased to 0.06 S cm⁻¹ at 80 °C.     

An analysis of energy conservation possibilities in the residential sector in New Zealand

A model which simulates residential energy use in New Zealand until the year 2000 has been developed. This paper describes some of the energy conservation possibilities and their effect on energy use for space and water heating. an engineering analysis made to determine the effect of various factors on energy use for space heating is first described. the information gained from many computer simulations is used to develop a quantitative relationship between space heating energy and major determinants—climatic location, building type and intensity of use. Results from an engineering analysis of a water heating unit are used to establish the energy savings due to improved cylinder insulation and lower storage temperature. A solar space and water heating system is analysed to determine the fraction of total heating load that can be met by harnessing solar energy. the analyses demonstrate that the potential of conservation measures to reduce energy use can be substantial—by raising the insulation level on the building and on the water heating cylinder, by lowering the water storage temperature, and by installing an optimized solar heating system, the energy requirement can be reduced to 0·37 times what it is today for a typical uninsulated home.