Experimental investigation into different selectively coated receivers and silver-coated selective surface compound parabolic reflector using regression modelling for industrial heating

The paper explores the experimental results of the prototype compound parabolic trough made of mild steel and silver-coated selective surface. This prototype has been tested with top cover. The performance of the collector has been evaluated with two kinds of receivers coated with three types of black coatings. First receiver is of copper coated with black copper, second receiver is of mild steel coated with black copper and third receiver is of copper coated with black zinc. From actual field experiments, it has been observed that the efficiency of the system achieved with copper receiver coated with black copper is comparatively higher than the other two types of receivers. A simple regression analysis is used to correlate the thermal performance parameters of the system.     

Performance analysis of solar water heating system in Centre for DNA Fingerprinting and Diagnostics (CDFD), Southern region of India

In the present study, a natural circulation thermosyphon flat plate solar water heater has been tested at the CDFD, Hyderabad (17.37°N, 78.43°E) Andhra Pradesh, India. Experimental data were noted on a sunny day. Dynamic response of the system to variations in solar insulation was studied and analyzed. T _inlet °C and T _outlet °C temperatures were recorded. The performance of the system can be improved by using aluminum tape inserts into the collector fins. The objective of the present study is to evaluate the performance of flat plate collector with and without inserts (aluminum strip of 1 mm thick, 3 mm width and 203 mm length). It is expected that with the same collector with the same flow rate, higher efficiency can be obtained by inserting the tapes inside the collector copper fins (9 mm). Thus, the cost of the system can be further bringing down by enhancing the collector efficiency.     

Experimental analysis of thermal performance of evacuated tube and flat-plate solar air collectors at different air flow rates

The thermal performances of an evacuated tube collector (ETC) and flat-plate solar air collector (FPC) are experimentally investigated at different air flow rates. To investigate the performance of the ETC and FPC, experimental set-ups were fabricated. Air was used as a working fluid and tested at the same climatic conditions. The ETC had 15 evacuated tubes with a surface area of 1.66 m². The experimental set-up consisted of a header with a hollow pipe (square pipe) in the centre through which the air flowed. The flat-plate collector had a surface area of 1.35 m². The FPC had a black painted absorber sheet which divides the collector into two sections. The air flowed through the upper and the lower sections parallel to the collector to minimize the overall heat loss. The temperature of the outlet air depends on several factors along with the airflow rate and the intensity of the solar radiation. It was found that during the day at high flow rates, the efficiency of the ETC varies from 0.12 to 0.5, and for the flat plate it was from 0.29 to 0.68. The maximum temperature of the air was 56.7°C for the ETC and 25.7°C for the FPC.     

Energy and exergy analysis of solar hybrid adsorption refrigeration system

In this paper, performance of a solar hybrid adsorption refrigeration (AR) system is investigated experimentally. Such a system was built and tested under the conditions at National Institute of Technology Calicut, Kerala, India. The hybrid system has been designed for heating 50 l of water from 25 to 90°C as well as cooling 10 l of water from 25 to 10°C. The experimental results demonstrate that the refrigerator has a cooling capacity of 47–78 W with a cycle coefficient of performance (COP) of 0.19 and maximum possible COP of 0.45. In exergy analysis of the system, the irreversibility and exergetic efficiency of each component of the system have been calculated. The exergy analysis reveals that the main source of irreversibility is the adsorbent bed of the AR system, emphasising that the input heat energy is not utilised efficiently due to material constraints. The exergetic efficiencies of condenser, expansion device, evaporator and adsorbent bed are found as 42.3%, 79.8%, 54.7% and 11%, respectively.     

The performance of solar powered desiccant dehumidifier in India: an experimental investigation

The regeneration and adsorption of desiccant wheel for producing the dry air was experimentally investigated. The air needed for regeneration was heated in an evacuated tube solar collector with surface area 4.44 m². The desiccant wheel is regenerated at the temperature in the range of 43.9–72.6°C. The regeneration and adsorption performances are affected by the regeneration temperature, wheel rotation, air flow rate (process and regeneration) and ambient conditions. By comparing the adsorption and regeneration performance at different air flow rate and constant rph, it was found that maximum adsorption and regeneration rates are obtained at air flow rate of 210.789 kg/h. Regeneration temperature directly affects the effectiveness of the desiccant wheel. Maximum desiccant wheel effectiveness of regeneration sector and adsorption sector is obtained at air flow rate of 105.394 kg/h. The regeneration performance of desiccant wheel with evacuated tube solar air collector is suitable for the Indian climate.     

Performance of a hybrid solar collector system in days with stable and less stable radiative regime

The aim of this work is to analyse the performance of a solar energy collector system for water and air heating in real working conditions. Two coupled mathematical models have been developed. One of them describes the thermal behaviour of the Hybrid Solar Collector (HSC) and the second one describes the simultaneous operation of the HSC and of a fully mixed water storage tank. The dependence of the performance of the HSC system on the following three parameters has been studied: (1) water and air mass flow rate; (2) water pipe diameter and air channel height; (3) water storage tank volume. The mathematical models were used to evaluate the HSC system performance during 29 different days, covering all four seasons. A higher water flow rate generally enhances the thermal efficiency of the HSC system, but the enhancement became significantly smaller at higher air flow rates. Positive but small values are recommended for the difference between the fluid temperature at solar collectors exit and the water temperature in the tank. The thermal efficiency of the HSC system is higher on nearly clear sky and decreases in case the amount of clouds on the sky increases.     

Fuel efficiency enhancement of modified diesel engine operated in dual fuel mode using renewable and sustainable fuels

ABSTRACT

Renewable and sustainable fuels for diesel engine applications provide energy protection, overseas exchange saving and address atmospheric and socio-economic concerns. This study presents the investigational work carried out on a single cylinder, four-stroke, direct injection diesel engine operated in dual fuel (DF) mode using renewable and sustainable fuels. In the first phase, a Y-shaped mixing chamber or venture was developed with varied angle facility for gas entry at 30°, 45° and 60°, respectively, to enable homogeneous air and gas mixing. Further effect of different gas and air mixture entry on the DF engine performance was studied. In the next phase of the work, hydrogen flow rate influence on the combustion and emission characteristics of a compression ignition (CI) engine operated in DF mode using diesel, neem oil methyl ester (NeOME) and producer gas has been investigated. During experimentation, hydrogen was mixed in different proportions varied from 3 to 12 l/min (lpm) in step of 3 lpm along with air-producer gas and the mixtures were directly inducted into engine cylinder during suction stroke. Experimental investigation showed that 45° Y-shaped mixing chamber resulted in improved performance with acceptable emission levels. Further, it is observed that investigation showed that at maximum operating conditions and hydrogen flow rate of 9 lpm, Diesel–producer gas and NeOME–producer gas combination showed increased thermal efficiency by 13.2% and 3.8%, respectively, compared to the DF operation without hydrogen addition. Further, it is noticed that hydrogen-enriched producer gas lowers the power derating by 5–10% and increases nitric oxide (NO_x) emissions. However, increased hydrogen addition beyond the 12 lpm leads to sever knocking.

Abbreviations: NeOME: Neem oil methyl ester; BTE: brake thermal efficiency; CI: compression ignition; ITE: indicated thermal efficiency; PG: producer gas; CA: crank angle; K: Kelvin; BP: brake power; IP: indicated power; H₂: hydrogen; HC: unburnt hydrocarbon; CO: carbon dioxide; CO₂: carbon dioxide; NO_x: nitric oxide; HRR: heat release rate; %: percentage; PPM: parts per million; CMFIS: conventional mechanical fuel injection system.     

Comparison of the energetic performance of a binary cycle and a flash evaporation binary cycle,using low-enthalpy geothermal energy

In this article, the comparison of the energetic performance of a binary cycle and a modified binary cycle with flash evaporation is presented, both using a low-enthalpy geothermal resource. The comparative analysis is based on two main discourses: the first one evaluates a conventional binary cycle (CBC) with isopentane as working fluid in order to validate and compare the generated data with those reported in similar studies; the second one uses the same input parameters for both cycles, obtaining the cases in which the modified binary cycle is the most viable choice to use. In addition to the above, several aspects are considered when selecting the most suitable working fluid, and the use of water as working fluid is introduced. When the temperature of the geothermal resource is below 140 °C, and the ambient temperature is 25 °C, the flash evaporation binary cycle, using water as working fluid, shows an improved performance compared to a CBC, with a theoretical output over 1000 kWe. This may encourage new areas of opportunity for power generation, not only with low- and medium-enthalpy geothermal energy, but also with other renewable energy sources such as solar.     

Mechanical performance and capillary water absorption of sewage sludge ash concrete (SSAC)

Disposal of sewage sludge from waste water treatment plants is a serious environmental problem of increasing magnitude. Waste water treatment generates as much as 70 g of dry solids per capita per day. Although one of the disposal solutions for this waste is through incineration, still almost 30% of sludge solids remain as ash. This paper presents results related to reuse of sewage sludge ash in concrete. The sludge was characterised for chemical composition (X-ray flourescence analysis), crystalline phases (X-ray diffraction analysis) and pozzolanic activity. The effects of incineration on crystal phases of the dry sludge were investigated. Two water/cement (W/C) ratios (0.55 and 0.45) and three sludge ash percentages (5%, 10% and 20%) per cement mass were used as filler. The mechanical performance of sewage sludge ash concrete (SSAC) at different curing ages (3, 7, 28 and 90 days) was assessed by means of mechanical tests and capillary water absorption. Results show that sewage sludge ash leads to a reduction in density and mechanical strength and to an increase in capillary water absorption. Results also show that SSAC with 20% of sewage sludge ash and W/C = 0.45 has a 28 day compressive strength of almost 30 MPa. SSAC with a sludge ash contents of 5% and 10% has the same capillary water absorption coefficient as the control concrete; as for the concrete mixtures with 20% sludge ash content, the capillary water absorption is higher but in line with C20/25 strength class concretes performance.     

Performance studies of a low heat rejection engine operated on non-volatile vegetable oils with exhaust gas recirculation

During recent decades, considerable effort has been expended world-wide to reduce dependency on petroleum fuels for power generation and transportation through the search for suitable alternative fuels that are environmentally friendly. In this respect, vegetable oils are a promising alternative to diesel fuel. However, the high viscosity, poor volatility and cold flow characteristics of vegetable oils can cause some problems such as injector coking, severe engine deposits, filter gumming and piston ring sticking and thickening of lubrication from long-term use in diesel engines. These problems can be eliminated or minimised by transesterification of the vegetable oils to form monoesters. Although transesterification improves the fuel properties of vegetable oil, the viscosity and volatility of biodiesel are still worse than those of petroleum diesel fuel. The performance of a diesel engine with such biodiesel operation can be improved further with the concept of the low heat rejection (LHR) engine. In the LHR engine, combustion surfaces on the pistons, cylinder walls and valves can be coated with ceramic materials. The objective of this study was to apply the LHR engine concept for improving engine performance when either honge biodiesel, known as honge oil methyl ester (HOME), or neem biodiesel, known as neem oil methyl ester (NOME) oils was used as an alternative fuel. For this purpose, experiments were conducted on a single cylinder, four-stroke, direct injection, water-cooled compression ignition engine using diesel, HOME and NOME oils at different injection timings of 19, 23 and 27° before top dead centre (BTDC) with and without the induction of exhaust gas recirculation (EGR). The percentage of EGR was varied from 5 to 20% in steps of 5%. The results showed that specific fuel consumption and brake thermal efficiency were improved for both of the biodiesel fuels in the LHR engine. An EGR of 10% resulted in better performance with trade-off between oxides of nitrogen and hydrocarbons/carbon monoxide emissions and hence 10% EGR is taken as the best of the range from 5 to 20%. However, readings with other EGR ratios are not reported.     

Comparing and evaluating the nationally determined contributions of the top six emitters under the Paris Agreement goals

ABSTRACT

Comparing and evaluating the Nationally Determined Contribution (NDC) is an important element in global stocktake in the post-Paris climate negotiations, aimed at closing the emissions gap with the Paris Agreement goals. To date, however, there has still been no explicit guideline or method. By applying emissions allowance allocated by 16 schemes as benchmarks, this paper tries to compare and evaluate the NDCs of the top six emitters, which jointly account for about 70% of the world’s CO₂ emissions. Results show that the four developed countries’ NDCs lack ambition with respect to most allocations under 2°C and all under 1.5°C, indicating they need to substantially ratchet up their NDCs and lead elevating mitigation. Evaluating cumulative emissions is more likely to clarify the ambition and fairness of China’s NDC. If considering cumulative emissions, China’s NDC is aligned with the median of cumulative allowances under 2°C and within the 1.5°C range. The Paris Agreement invited the Parties to communicate the mid-century low emissions strategies. This paper also tries to explore the mid-century mitigation in the perspective of allocations, which might provide decision-makers with some useful information when envisaging the post-NDC mitigation.     

Contrasting impacts of climate change across seasons: effects on flatfish cohorts

The Senegal sole, Solea senegalensis, is a species of flatfish that has several distinct cohorts of 0-group juveniles which use estuarine nurseries in summer and winter. The early cohort is more abundant and grows faster than the late cohort that stays in the nurseries during winter; however, climate warming may have an impact on the dynamics of this species’ juveniles. This study aimed to compare mortality, metabolic response and growth of S. senegalensis juveniles at different temperatures, reflecting present-day temperature (winter—12 °C; summer—24 °C) and future temperature (plus 3 °C) conditions, in estuarine nurseries in the southern European population. Mortality was low at 12 °C, being only 10 %, increasing to 30 % at 15 °C, 40 % at 24 °C and at 27 °C it hit 70 %. Metabolic rate increased steadily with increasing temperatures, yet it increased steeply from 24 to 27 °C. Thermal sensitivity was high for the temperature interval between 24 and 27 °C. Growth was very slow at 12 °C, at a rate of 0.03 mm day^?1, increasing to 0.22 mm day^?1 at 15 °C, and to 0.60 mm day^?1, at 24 °C. However, at 27 °C growth rapidly declined to 0.12 mm day^?1. Warming will be beneficial for the late cohort, resulting in a major increase in growth. However, the early cohort will not benefit from warming, due to high mortality and arrested growth, which clearly indicates that this species is under severe thermal stress at 27 °C. Thus, here we show, for the first time, that climate change may induce contrasting seasonal impacts on fish bio-ecology and physiology, namely in species with several cohorts over the course of the year. Phenotypic and/or genotypic plasticity may limit the impacts of climate change.     

Solar-driven technology for freshwater production from atmospheric air by using the composite desiccant material “CaCl<Subscript>2</Subscript>/floral foam”

In this communication, experiments have been performed to check the capability of the newly formed composite desiccant material (CaCl₂/floral) for the extraction of freshwater from atmospheric air. Three numbers of solar glass desiccant box type system (SGDBS) with a captured area of 0.36 m² each, have been used. The design parameters for the water production are height of glass from desiccant bed at 0.22 m, inclination in angle as 30°, the effective thickness of glass as 3 mm and number of glazing as single. The maximum yield by the new composite desiccant material is 0.35 ml/cm³/day. The efficiency of the system SGDBS with 37 % concentration of CaCl₂ is 76.44 %.     

Changing patterns of the temperature–mortality association by time and location in the US,and implications for climate change

The shape of the non-linear relationship between temperature and mortality varies among cities with different climatic conditions. There has been little examination of how these curves change over space and time. We evaluated the short-term effects of hot and cold temperatures on daily mortality over six 7-year periods in 211 US cities, comprising over 42 million deaths. Cluster analysis was used to group the cities according to similar temperatures and relative humidity. Temperature–mortality functions were calculated using B-splines to model the heat effect (lag 0) and the cold effect on mortality (moving average lags 1–5). The functions were then combined through meta-smoothing and subsequently analyzed by meta-regression. We identified eight clusters. At lag 0, Cluster 5 (West Coast) had a RR of 1.14 (95% CI: 1.11,1.17) for temperatures of 27 °C vs 15.6 °C, and Cluster 6 (Gulf Coast) has a RR of 1.04 (95% CI: 1.03,1.05), suggesting that people are acclimated to their respective climates. Controlling for cluster effect in the multivariate-meta regression we found that across the US, the excess mortality from a 24-h temperature of 27 °C decreased over time from 10.6% to 0.9%. We found that the overall risk due to the heat effect is significantly affected by summer temperature mean and air condition usage, which could be a potential predictor in building climate-change scenarios.     

嘉陵江流域坡耕地“生态农业旅游”垂直景观模式

从治理水土流失角度出发，提出了坡耕地“生态农业旅游”技术与示范。其垂直生态景观模式按坡度和等高线布置：在坡度大于25°的山坡顶形成水保林木区，坡上15°～25°的陡坡种植桃树，坡中5°～15°的斜坡种植枇杷，坡下小于5°的缓坡地带种植特种水果、瓜类及蔬菜，坡底形成“稻—鱼”和“藕—鱼”特色水域区。道路系统设计为环山而下的水泥主路、观景石板干路、埂边地界小路三级，道路两侧实施还林还草。“农家乐”型旅游接待自然分布在试验区内，同时在坡上建立旅游“一条街”、坡底试验旅游产业化经营。果园内实施多熟作物覆盖、间种套种。垂直生态景观产生了独特而丰富的景观效果，并具有较好的生态功能、经济功能和社会功能。     

Dependence of demographic parameters and results of competition on temperature in cladocerans

Laboratory experiments and computer simulations have been performed to study the influence of increased temperatures on the structure of cladoceran communities. Analysis of changes in the rate of population growth and demographic parameters has shown that smaller cladoceran species are less sensitive to decreased concentrations of food at any of the test temperatures (18, 21, and 27°C). An increase in temperature from 18°C to 27°C has been shown to facilitate the establishment of acute competition conditions. At 18°C, periods of food deficiency are shorter, and competition is therefore less manifested than at 27°C. According to the results of computer simulations, alleviation of competition in waters with “low” temperatures results from reduction of the periods of food deficiency because of prolonged juvenile development.     

Integrated hydrologic–economic decision support system for groundwater use confronting climate change uncertainties in the Tunuyán River basin,Argentina

This study presents an integrated hydrologic–economic model as decision support system for groundwater use and incorporates uncertainties of climate change. The model was developed with the Vensim software (Ventana Systems) for system dynamic simulations. The software permitted the integration of economic variables along with hydrologic variables, in a unified format with the aim of evaluating the economic impacts of climate change on arid environments. To test the model, we applied it in one of the upper Tunuyán River sub-basin, located in the Mendoza Province (Argentina), where irrigation comes from groundwater. The model defines the best mix of crops and the total land use required to maximize the total river sub-basin monetary income, considering as a limit the amount of water that does not exceed the natural annual aquifer recharge. To estimate the impacts of climatic changes, four scenarios were compared: the business as usual (with the number of existing wells) in a dry year with a temperature increase of 4 °C; the business as usual in a wet year with an increase in temperature of 1.1 °C; an efficient use of wells in a dry year and a temperature increase of 4 °C and an efficient use of wells in a wet year with a temperature increase of 1.1 °C. Outputs calculated by the model were: land use per crop, total sub-basin net benefit, total sub-basin water extraction, water extraction limit depending on river discharge and total number of wells required to irrigate the entire area. Preliminary results showed that the number of existing wells exceeded the optimized number of wells required to sustainably irrigate the entire river sub-basin. Results indicated that in an average river discharge year, if wells were efficiently used, further rural development would be possible, until the limit of 350 million m³ of water extraction per year was reached (650 million m³ for a wet year and 180 million m³ for a dry year). The unified format and the low cost of the software license make the model a useful tool for Water Resources Management Institutions, particularly in developing countries.     

Comparative study of solar-powered water production from atmospheric air using different desiccant materials

In this paper, experiments have been performed in order to determine the quantity of water produced from the atmospheric air using different desiccant materials named Silica gel, Activated alumina and Molecular sieve 13 X. On the bases of experimental results, a correlation is derived among the different temperatures and water production using Central Composite Design (CCD) of Response Surface Methodology. A newly designed solar glass desiccant box type system (SGDBS), three in number, has been used. Design parameters for the production of water has been taken as depth of material from the glass is 0.22 m, inclination in angle as 30°, effective thickness of glass as 3 mm and number of glazing as single. It has been found experimentally that the maximum quantity of water produced by Silica gel, Activated alumina and Molecular sieve 13 X is 160, 20 and 35 ml/kg/day, respectively. Whereas theoretically, value of water produced by the Silica gel, Activated alumina and Molecular sieve 13 X is 600, 28 and 60 ml/kg/day, respectively.     

Effects of collector types in sampling of atmospheric depositional fluxes

The bulk gross alpha, gross beta and ⁷Be depositional fluxes were measured in Málaga (36.7°N, 4.5°W), a coastal Mediterranean station in the south of Spain for one whole year. In order to quantify the local variation of deposition rates, we have analysed the monthly results from two deposition collectors: a “pot “collector with a continuous water-covered surface and a “funnel” collector. In general, the alpha and beta depositional fluxes from the funnel collector were approximately two times lower than the pot collector. Whereas for the cosmogenic ⁷Be, the depositional flux of ⁷Be from funnel collector was also approximately two times lower than the pot collector. A good correlation of the depositional flux of ⁷Be has been obtained from both collectors.     

Spatio-temporal analysis of climatic variables in the western part of Bangladesh

Monitoring and detecting trends of climatic variables like rainfall and temperature are essential for agricultural developments in the context of climate change. The present study has detected trends in annual and cropping seasonal rainfall and temperature data for the period of 1961–2011 using Mann–Kendall (MK) test, Spearman’s rho (SR) test and modified Mann–Kendall test that has been applied to the significant lag-1 serial correlated time series data, and slope has been estimated using Sen’s Slope estimator for twelve meteorological stations located in the western part of Bangladesh covering about 41 % of the country. Almost 71 % trends explored by MK test in annual rainfall are statistically insignificant, and SR test also complies it. The spatial distribution of rainfall trend shows insignificant positive trends in major part of the area. Significant positive trends both by MK test and by SR test at 95 % confidence levels are observed at rates of 8.56, 11.15 and 13.66 mm/year at Dinajpur, Rangpur and Khepupara stations, respectively, and the Kharif season rainfall of these stations also shows significant increasing trends except Dinajpur. On the other hand, significant decreasing trends in annual rainfall are found at Bhola (?11.67 mm/year) and Rajshahi (?5.951 mm/year) stations and decreasing trends in rainfall dominated the Pre-Kharif season over the area. But, 83.33 % of the stations show rising trends in annual mean temperature with significant positive trends (as observed by both MK test and SR test) at Rangpur, Bogra, Faridpur, Jessore and Bhola stations where the rate of changes vary from 0.013 °C/year at Faridpur to 0.08 °C/year at Bhola. Most of the trends in Rabi and Pre-Kharif seasons of mean temperatures are not statistically significant. However, all stations except Barisal show significant rising trends in temperature in Kharif season. To cope with this changing pattern of rainfall and temperature, effective adaptation strategies should be taken to keep up the agricultural production that is related to livelihood of the most people and to ensure the country’s food security.