Thermal analysis and measurement of a solar pond prototype to study the non-convective zone salt gradient stability

Solar ponds combine solar energy collection with long-term storage and can provide reliable thermal energy at temperature ranges from 50 to 90 °C. A solar pond consists of three distinct zones. The first zone, which is located at the top of the pond and contains the less dense saltwater mixture, is the absorption and transmission region, also known as the upper convective zone (UCZ). The second zone, which contains a variation of saltwater densities increasing with depth, is the gradient zone or non-convective zone (NCZ). The last zone is the storage zone or lower convective zone (LCZ). In this region, the density is uniform and near saturation. The stability of a solar pond prototype was experimentally performed. The setup is composed of an acrylic tube with a hot plate emulating the solar thermal energy input. A study of various salinity gradients was performed based on the Stability Margin Number (SMN) criterion, which is used to satisfy the dynamic stability criterion. It was observed that erosion of the NCZ was accelerated due to mass diffusion and convection in the LCZ. It can be determined that for this prototype the density of the NCZ is greatly affected as the SMN reaches 1.5.     

全饱和型太阳池的热稳定性条件

对太阳池的一般特征及共工作原理、双扩散系统所遵循的流体力学普遍方程组、具有非恒定的温度和盐浓度梯度的双扩散系统进行介绍，并对全饱和型太阳池的热稳定性条件进行讨论。     

Theoretical and experimental comparison of conventional and advanced solar pond performance

Numerical and physical experiments were carried out to compare the performance of two solar pond systems: (a) a conventional salt gradient solar pond (CSP) and (b) a salt gradient pond operated as an “advanced solar pond” (ASP). The main differences in the ASP, as originally proposed by Osdor[1], are an increase in overall salinity and the introduction of a stratified flowing layer near the bottom of the gradient zone. The increased salinity is meant to reduce evaporative heat loss and make up water requirements, while the additional flowing layer allows extra heat extraction and possibly higher temperatures to develop in the lower convective zone. A numerical study was performed to evaluate the salinity effect and the results show only a minor effect of increased salinity on heat collection efficiency. However, slightly higher collection temperatures are obtained, which may provide some benefit for heat engine efficiency. Physical experiments were performed to test the feasibility of constructing and maintaining the necessary flow system for the ASP and also to compare the performance of the ASP and the CSP under similar laboratory conditions. These tests showed that a stable stratified flowing layer could be maintained and that the ASP configuration produced higher efficiencies.     

Fertilizer solar ponds as a clean source of energy: Some observations from small scale experiments

Commercially available NH₂CONH₂ is used to establish a salinity gradient solar pond in a small 1 m² outdoor tank. With a salinity difference of 35% between the upper and lower zone, a temperature difference of 23°C was obtained without any instabilities in the gradient zone. The difference in concentration of solution required to sustain a temperature difference of 40°C across the gradient zone is 520 kg/m³. By economically using runoff into the fertilizer cycle of an agricultural system the estimated cost of fertilizer solar pond generated heat is Rs. 1.10/kWh.     

超声波在煤粉中的衰减特性的仿真

基于随机介质的衰减理论 ,分析超声波在煤中的传输特性 ,采用了漫射近似方法建立了超声波传输过程中由衰减规律的理论模型。在理论模型的基础上建立了对象的仿真模型 ,用以研究衰减特性和传播距离、超声波频率湿度 ,以及煤粉颗粒浓度的关系。通过对仿真试验的分析和比较 ,证明了模型的正确性 ,该仿真模型能用于超声波在煤粉中的传输特性的分析。     

Transient natural convection in an enclosure with vertical solutal gradients

Transient natural convection in an enclosure with vertical solutal gradients has been studied in this paper. Transfers in a rectangular cavity configuration translating hydrodynamic and thermal phenomena are numerically predicted by means of computational fluid dynamics (CFD) in transient regime.The objective of this numerical study is to give a fine knowledge of the hydrodynamic and thermal characteristics during energy storage in an enclosure filled with water stratified by downward salinity gradient. The enclosure is divided into three zones with different salinity level such as salt gradient pond (SGP). Water is heated by a heating device at the bottom of the cavity.The Navier–Stokes, energy and mass equations are discretized using finite-volume method, and a two-dimensional analysis of the hydrodynamic and thermal behaviors generated in transient regime in the cavity are performed. The mathematical modelling has allowed the prediction of the storage performances by developing parametrical study in view to search the convective heat transfer coefficient at the bottom of the enclosure. Velocity vector fields show the presence of recirculation zones caused only in the lower region and permit to explain the increase of the temperature in the lower convective zone (LCZ).This study shows also the importance of the salinity in the preservation of the high temperature in the bottom of the cavity, and the important reduction of the phenomenon of thermal transfer across the non-convective zone (NCZ).     

Modeling the dynamics of the mixed layer in solar ponds

A new model is proposed to explain the Nielsen's equilibrium condition. This model takes into account the effects of both turbulent entrainment and diffusion on the growth/erosion of the gradient zone. The existing turbulent entrainment model is modified to make it applicable near the equilibrium condition. The new model predictions indicate the dependence of the equilibrium condition on the mixed layer depth, apart from the salinity and temperature gradients in the gradient zone.     

Comparison of open-air and semi-enclosed cultivation system for massive microalgae production in sub-tropical and temperate latitudes

This study compared open-air and semi-enclosed production system of the marine microalgae Nannochloropsis oculata in a sub-tropical region (32°S; 52°W) under uncontrolled environmental conditions. The semi-enclosed system was composed of 1.2 m³ circular tanks installed inside of a greenhouse. Water temperature was 4 °C higher in the indoor treatment than in the outdoor, mainly in winter although no difference was observed in warmer seasons. Moreover, variation in salinity was observed in the outdoor treatment due to rainfall (winter) and evaporation (spring), whereas indoor treatment experienced an increase (up to 100 PSU) due to evaporation only in warmer seasons. Light transmission was approximately 20% lower in the indoor treatment although cell densities and biomass yields were higher indoor during winter. As the temperature increased (spring) no differences were observed among treatments. In summary, partial control of temperature and salinity in the semi-enclosed system, especially during the colder and rainy season, allowed higher microalgae biomass production. Further experiments must be conducted with CO₂ addition, larger pH range and salinity control.     

Dynamic effects in a salinity-gradient solar-pond heating system

Numerical computer models have been developed to study the dynamics of a salt-gradient solar-pond heating system in a northern cold climate. The models are applicable for predicting the temperature and salinity profiles in a pond. Special emphasis is laid on the behaviour of the upper convective layer. In the calculations, the solar pond is considered as a part of a community-scale residential heating system and the effects of the pond's dynamics on the overall system performance are assessed. All calculations were made with 1-h time steps for a hypothetical pond in Helsinki (60° N). The results indicate that the consideration of the dynamics of the salinity profile may reduce the pond's bottom temperature by 10°C in comparison with a static salt distribution. The maintenance of the salinity gradient would allow a maximum surface washing interval of 5 weeks without severely affecting the pond's performance. Then the daily salt consumption would be about 40 g per square metre. For regions with cold winters, the surface should be washed with fresh water, just before surface freezing takes place, to prevent shrinking of the non-convective stabilizing gradient zone. It was also observed that a solar-pond heating system may reach considerable solar fractions in a northern climate.     

Control of a solar pond

Solar ponds hold the promise of providing an alternative to diesel generation of electricity at remote locations in Australia where fuel costs are high. However, to reliably generate electricity with a solar pond requires high temperatures to be maintained throughout the year; this goal had eluded the Alice Springs solar pond prior to 1989 because of double-diffusive convection within the gradient zone. This paper presents control strategies designed to provide successful high temperature operation of a solar pond year-round. The strategies, which consist mainly of manipulating upper surface layer salinity and extracting heat from the storage zone are well suited to automation. They were tested at the Alice Springs solar pond during the summer of 1989 and maintained temperatures in excess of 85°C for several months without any gradient stability problems.     

PES Digital Library

This paper introduces a traveling wave-based relaying approach dedicated to sophisticated protection of six-phase transmission lines. In this ultra-high-speed (UHS) approach fault detection, classification, and faulted phase selection can be achieved within a quarter of a cycle. Two discriminants are used to differentiate between transients due to faults in the protected zone from other transients or faults occurring outside the protected zone.     

基于SYSNOISE软件的穿孔管消声器声学性能分析

为减小穿孔管消声器模型的复杂性,通过在SYSNOISE软件中定义阻尼传递矩阵对穿孔管进行模拟,仿真结果与Sullivan和Crocker预测和试验测量结果吻合良好,验证了方法的可行性与正确性。通过对不同穿孔率和不同尺寸的穿孔管消声器的消声特性的比较,得出结论:穿孔管消声器的消声特性在k₀l值较小时与共振腔消声器的消声特性类似,在k₀l值较大时与扩张室消声器的消声特性类似。     

Double diffusive zone-boundary migration in solar ponds

The problem of gradient zone-boundary migration in solar ponds has been investigated. Models based on thermal burst stability theory and microconvection theory of boundary undulation and temperature modulation have been considered. Computational results of solutions for stability problem of the double diffusive interface are presented for an extended range of salinity gradient (1-10000 kg m⁻⁴) and examined with empirical correlations as well as experimental data. The results indicate that the erosion or growth of the gradient zone at the interface is a strong function of the ratio of diffusivities τ and density stability ratio R_ρ.     

Gradient maintenance using discrete brine injections in a salt gradient solar pond

A method for the maintenance of the stratification in the gradient zone of a salt gradient solar pond is presented. The method is unique for solar ponds in that it involves the injection of highly turbulent colummar jets into homogeneous convective zones. This contrasts with the more common practice of traversing the gradient zone with a disk-shaped diffuser while injecting fluid at low exit Froude numbers. Using turbulent jet theory which is well understood for columnar buoyant jets, the method allows a priori determination of the resulting salinity gradient with a reasonable level of confidence. The simple injector is easily constructed and deployed. Field data collected at the Alice Springs solar pond show that the technique can quickly remove internal convective zones as well as extend the top of the gradient into the surface layer, providing a valuable tool for the operators of solar ponds.     

High salinity fluid handling in Milos geothermal field

On Milos island, where a high enthalpy gecthermal field capable:of producing high salinity fluids has been discovered a 2MW Pilot plant was installed. Systematic production tests have been carried out at the production well, with emphasis on geothermal fluid chemistry and behaviour. During successive long term operation trials of the Unit (turbogenerator, steam gathering and brine transmission system), problems arose in both steam and brine cycles due to severe scaling phenomena encountered. The sequence of events in identifying the scaling problems and the technical approaches applied to remedy them, are reported in this paper together with data concerning the plant's operational problems and with the direct hot reinjection used as brine disposal method.     

The influence of the heat extraction mode on the performance and stability of a mini solar pond

The performance and stability of a 0.64 m² mini solar pond were experimentally and numerically studied. The experimental results showed that the daily average temperatures of the mini pond increased quickly to reach 54 °C in the lower convective zone after only 20 days. A 1 D numerical model to predict the temperature and the salinity in the mini pond was developed. The results obtained from the numerical calculation were compared with our experimental results and good agreement was found. Therefore a new method of heat extraction from the non convective zone was numerically investigated in order to enhance the mini pond performance. Using this new method of heat extraction, the numerical results showed that the mini pond efficiency could be considerably improved. However, the method was found to reduce the stability of the lower interface.     

Geology and fluid chemistry of the Fushime geothermal field, Kyushu, Japan

The Fushime geothermal field is located in a depression close to the coast line. The system is characterized by very high reservoir temperature (>350°C), and a high salinity production fluid. Geological analysis shows that the main reservoir in this field occurs in a fractured zone developed around a dacite intrusion located in the center of the field. High permeability zones recognized by drilling data are found to be associated with fault zones. One of these zones is clearly associated with a NW–SE trending andesite dike swarm which was encountered in some wells.Alteration in the system can be divided into four zones, in order of increasing temperature, based on calcium–magnesium aluminosilicate mineral assemblages: i.e., the smectite, transition, chlorite and epidote zones. The feed zone is located in the chlorite and epidote zones, which can be further divided into three sub-zones according to their potassium or sodium aluminosilicate mineralogy, from the center of the discharge zone: K-feldspar–quartz, sericite–quartz, and albite–chlorite zones.Chloride concentration of the sea-water is 19,800 mg/l, and Br/Cl mole ratio is 1.55. Based on geochemical information, the reservoir chloride concentration of this field ranges from 11,600 to 22,000 mg/kg. The Clres (Cl in reservoir), Br/Cl ratios and stable isotope data indicate that the Fushime geothermal fluid originated from sea-water and is diluted by ground water during its ascent. Some fluids produced from geothermal wells show low pH (about 4). It is thought that sulfide mineral (PbS, ZnS) precipitation during production produces this acidic fluid.     

应用激光多普勒测速仪研究湍流有旋自由射流

用激光多普勒测速仪对旋流器产生的强湍流有自由射流的速度场和湍流场进行了实验研究。实验结果表明,这种旋流器十分有利于中心回流区的形成,射流的平均速度分布沿轴向快速地衰减,有旋自由射流呈现湍流各向异性,特别是在回流区域中,本文对流场中湍流动量传递的方向进行了讨论。     

Effect of different substrate concentrations and salinity on hydrogen production from mariculture organic waste (MOW)

In this paper, the influence of substrate concentrations and salinity on hydrogen production from mariculture organic waste (MOW) at mesophilic condition in batch reactors was determined. It was found that the hydrogen yield and hydrogen content were influenced by the initial substrate concentrations and salinity. The optimum concentration for hydrogen production was 20 g/L. The salinity could produce inhibit effect for hydrogen production. The low hydrogen content was detected at high salinity condition. The nutrients changing and metabolites composition could also be significantly influenced by the salinity. The releasing of carbohydrate from MOW could be easily used for hydrogen production, and protein could be accumulated and assimilated during the hydrogen fermentation. The enhancing of salinity was disadvantage for total metabolites accumulation.     

具有不停车换工况功能的液力传动装置

该液力传动箱加装有同步控制装置,在机车运行过程中,通过对传动箱输出轴上的离合器主、从动部分的同步控制,实现调车和小运转工况的动态转换,扩大了液力传动机车的高效区范围,提高了机车在整个运行过程中的牵引能力。