Evaporation heat transfer and pressure drop characteristics of R-600a in horizontal smooth and helically dimpled tubes

An experimental investigation was performed to evaluate the heat transfer and pressure drop characteristics of the hydrocarbon refrigerant R-600a during flow boiling inside a horizontal smooth tube with an inside diameter of 8.25 mm and a newly developed dimpled tube. The inner surface of the helically dimpled tube is enhanced by a newly modified pattern consists of both shallow and deep protrusions. The experimental tests were carried out varying: the refrigerant mass fluxes within the range of 155–470 kg/m2 s; the vapor qualities up to 0.8; the constant heat flux of 15.8 and saturation temperature of 56.5 °C. Observations clearly indicate that the heat transfer performance is improved as tube’s inner surface enhanced by this new pattern of protrusions. The experimental results show that the heat transfer coefficients of the dimpled tube are 1.29–2 times larger than a smooth tube with a pressure drop just ranging between 7% and 103% larger than the smooth tube. The highest enhancement in the heat transfer coefficient occurs at vapor quality of 0.2 and mass flow rate of 155 kg/m2 s. On the other hand, the maximum increase of pressure drop takes place at vapor quality of 0.8 and mass flow rate of 305 kg/m2 s

Condensation heat transfer and pressure drop characteristics of R-600a in horizontal smooth and helically dimpled tubes

In the present study, condensation heat transfer and frictional pressure drops of refrigerant R-600a (iso-butane) inside a helically dimpled tube and a plain tube of internal diameter 8.3 mm were measured and analyzed. All tests were performed at different vapor qualities up to 0.82 and average saturation temperatures ranging between 38 and 42 °C. Refrigerant mass fluxes varied in the range of 114–368 kg/m2 s. The inner surface of the helically dimpled tube has been designed and reshaped through three-dimensional material surface modifications consists of both shallow and deep protrusions which are placed evenly in helical directions on the tube wall. The experimental results show that the heat transfer coefficients of the dimpled tube are 1.2–2 times of those in smooth tube with a pressure drop penalty just ranging between 58% and 195. The highest heat transfer coefficient is occurred at vapor quality of 0.53 and mass flow rate of 368 kg/m2 s. On the other hand, the maximum increase of pressure drop takes place at vapor quality of 0.55 and mass flow rate of 368 kg/m2 s

Visual study of flow patterns during evaporation and condensation of R-600a inside horizontal smooth and helically dimpled tubes

In this paper, flow patterns and their transitions for the refrigerant R-600a during flow boiling and condensation inside a helically dimpled tube and a smooth tube were observed and analysed. The inner surface of the helically dimpled tube was enhanced by a modified pattern consisting of both shallow and deep protrusions. For evaporation, the experiments were performed for refrigerant mass velocities in a range of 155 kg/m2 s to 467 kg/m2 s, all at an average saturation temperature of 56.5 °C with the vapour qualities up to 0.8. Stratified-wavy, intermittent, and annular flows were observed for the smooth tube; for the dimpled tube, the stratified-wavy flow was not seen. For condensation, all tests were conducted at vapour qualities up to 0.8, and average saturation temperatures ranging between 38 °C and 42 °C. The refrigerant mass fluxes varied in the range of 114–368 kg/m2 s. Annular, intermittent, and stratified-wavy flows were recognized for the plain tube, but there was no stratified-wavy flow in the flow pattern visualization of the dimpled tube. The investigation clearly shows that the dimples in both evaporation and condensation have a significant impact on the two-phase flow pattern. Inside the helically dimpled tube, the transition from intermittent to annular (or vice versa) occurred at a lower vapour quality value than for the smooth tube

First-principles study of the optoelectronic properties and photovoltaic absorber layer efficiency of Cu-based chalcogenides

Cu-based chalcogenides are promising materials for thin-film solar cells with more than 20% measured cell efficiency. Using first-principles calculations based on density functional theory, the optoelectronic properties of a group of Cu-based chalcogenides Cu$_2$-II-IV-VI$_4$ is studied. They are then screened with the aim of identifying potential absorber materials for photovoltaic applications. The spectroscopic limited maximum efficiency (SLME) introduced by Yu and Zunger is used as a metric for the screening. After constructing the current-voltage curve, the maximum spectroscopy dependent power conversion efficiency is calculated from the maximum power output. The role of the nature of the band gap, direct or indirect, and also of the absorptivity of the studied materials on the maximum theoretical power conversion efficiency is studied. Our results show that Cu$_2$-II-GeSe$_4$ with II=Cd and Hg, and Cu$_2$-II-SnS$_4$ with II=Cd and Zn have a higher theoretical efficiency compared to the materials currently used as absorber layer

Climate change impact on bioclimatic deficiency, using microLEIS DSS in Ahar soils, Iran

Regional impact studies of the future climate change effects are necessary because projected changes in meteorological variables differ from one region to another, and different climate systems can react in varied ways to the same changes. In this study, the effects of climate change on bioclimatic deficiency were compared in two cultivation methods (irrigated and rainfed) in a semi-arid region, Ahar (East Azarbaijan, IRAN). The agricultural land uses selected for evaluation were wheat (Triticum aestivum), alfalfa (Medicago sativa), sugar beet (Beta vulgaris), potato (Solanum tuberosum), and maize (Zea mays). In this way, Terraza model included in the land evaluation decision support system, called MicroLEIS DSS, was used. Terraza gives a quantitative prediction of a site bioclimatic deficiency. Soil morphological and analytical data were obtained from 44 sampling points based on a grid survey. Agro-climatic data, referred to temperature and precipitation, were collected from weather stations located in Ahar region, which benefits from more than 20 consecutive years of weather data. A future scenario of climate change was calculated according to the Intergovernmental Panel on Climate Change (IPCC) on regions of Asia under scenario A1FI (highest future emission) for 2080s. Although, increasing of precipitation being available by climate change in the future scenario, humidity index will be reduced because of high temperature. The results showed that climate change is likely to cause severe water stress in irrigated cultivation of alfalfa, sugar beet, potato, and maize, the use of irrigation methods being essential to maintain agricultural productivity. Although irrigation is indicated as very important in this regime of semi-arid agriculture, cultivation of rainfed wheat can be possible instead of the irrigated one. Also, it is revealed that climate perturbation effects on rainfed conditions are more serious than those on the irrigated conditions in the area.The authors wish to thank Tabriz University for funding this research work, a dissertation of Ph. D. program undertaken by Farzin Shahbazi. They also thank Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), Sevilla, Spain for their sincere cooperation during the candidate’ s sabbatical studies.Peer Reviewe

Detection of cadmium acute toxicity in oyster, Crassostrea sp.

Heavy metals in high concentrations in the environment, is caused serious damage in metabolic, physiologic and structural organisms. Cadmium as the second most toxic metal in marine environments is considered. Bivalvia especially oysters are Suitable bioindicators due to its high filtration rates, immobility and lack of regulatory systems for removing of heavy metals. Crassostrea sp. is new species has wide distribution in Bandar Emam Khomeini. This species is the best for using toxicity testing to determine the effects of heavy metal pollutants in the environment. The aim this study is determination of Medium Lethal Concentration (LC5096h), Maximum Allowable Toxicant Concentration (MATC) and Lowest Observed Effect Concentration (LOEC) of Cadmium in Crassostrea sp. oyster. Fifty oysters (5.3±0.76 gr) were collected from Bandar Emam Khomaini and transported to laboratory. After Acclimatization (for 7 days), the 96-h LC_50 tests were conducted (static Method) according to standard instruction O.E.C.D. The 96 h LC_50, NOEC and LOEC were 15.8, 1.58 and 2.9 mg/l respectively. The LC_50 correlation whit in 24 h and 96 h were showed Linear equation y=-0.4225x+54.35

GIS-Based Land Capability and Suitability Evaluation for Irrigated Agriculture (Case Study: Karaj-Qazvin)

Introduction Farmers and agricultural products face many risks, including adverse weather conditions, pests, diseases, and changes in product prices, laws, and regulations. The first step in managing and minimizing many of these risks is often choosing the right crops for the area under cultivation; Therefore, knowing whether these lands are suitable for a particular crop can determine the success or failure of agricultural strategies. Because farmers are exposed to climate change and the economy, where agricultural frameworks are changing at an unprecedented rate, it is vital for them to be able to adapt to new trends. Increasing the availability of land suitability information for agricultural products will be a valuable aid for farmers and managers in this field to develop new agricultural strategies. At the same time, the growth of computational capabilities and increased access to geographic data has made land suitability assessment faster and easier.Materials and Methods The study area is located in Abik city, a city located in Qazvin province of Iran, between 50 degrees and 40 minutes to 50 degrees and 41 minutes east longitude and 35 degrees and 52 minutes to 36 degrees and 21 minutes north latitude. The average annual soil temperature at depth of less than 50 cm is 15.8 °C and has thermal heating regime. Furthermore, according to the average rainfall of the region, 222.7 mm, the humidity regime of the region is of Eridic type. Moisture and heat regimes were obtained by Newhall software. According to regional conditions and the size of the area, 60 profiles were drilled for network description and sampling. Field studies including determination, drilling, description of profiles, slope percentage, etc. were determined at the site. Information on soil physical and chemical properties were tested. Parametric, American (USDA) and LSP methods were used to evaluate the land. Necessary climatic characteristics for annual plants include the climatic variables that are necessary to determine the growing season, planting date and type of cultivar. The information of Buin Zahra synoptic station has been used. In this study, CROPWAT software was used to calculate the potential evapotranspiration. Land information such as slope, drainage Condition and flood absorption, as mentioned in the profile description card, was used to assess land suitability. Growth period was also obtained for the region using the area agronomical calendar. To calculate potential of production, the model AEZ which is provided by FAO, is used in this research.Results and Discussion The decrease in the suitability of the studied lands for the wheat crop is due to the salinity and sodium content of the lands and the presence of surface gravel and shallow soil depth. According to the provided tables and maps, 18% of the study area is unacceptable, 12.5% is average, 12.5% is good, 25% is very good, or very good and 31.25% of the total study area are in the excellent fitness class. The above values have been obtained by considering the rangeland and saline sections as well as the type of product in preparing the fit map. The accuracy of the preferred rational scoring method in land suitability is higher than the parametric method because in this method the land suitability maps of the area are obtained by logical collectors and the output map is the result of all parameters and constraints that the area may have. To have the desired. In the parametric method, this problem is summarized in soil properties and climatic conditions. Due to the lack of direct measurement of product performance, more accurate comparisons were not possible.Conclusion Most of the restrictions were in shallow hilly areas with shallow soils and pebbles, and salinity, alkalinity and gypsum did not impose any restrictions in these areas. Traffic in these areas was difficult and they were mostly in the S3 class by the parametric method and the poor and unacceptable class in the LSP. In land evaluation using LSP method, understanding the relationships of criteria with each other and the amount of impact that each has on the potential of land for different uses is essential. The LSP method is sensitive yet flexible, and may not work well if the data accuracy and number of parameters are low. The application of GIS-based LSP method showed a suitable tool to create accurate, flexible and rationally justifiable criteria in assessing the capability and suitability of land in agriculture. In such studies, by using the Bayer LSP method, prerequisites such as precisely defining the goals of users, managers and agricultural expertise should be considered. This method is a multi-criteria evaluation method that has been improved for measurement among decision makers, land management and other specialties

Alcor and Aljarafe models application for exploring the agro-ecological limits of sustainability in Ahar area (Iran)

Comunicación oral y póster presentados en la citada conferencia, sesión 3, celebrada del 21-24, septiembre, 2009, en Bratislava, Slovakia.Peer reviewe

Suitability of wheat, maize, sugar beet and potato using MicroLEIS DSS software in Ahar area, north-west of Iran

8 pages, 4 figures, 3 tables, 17 references.Sustainable agriculture is the main goal of land evaluation. The current study deals with land suitability evaluation of Ahar soils, 9000 ha approximately, located in East Azarbaijan. The decision support system, MicroLEIS DSS (Microcomputer land evaluation Information system) was used to evaluate the suitability for wheat (Triticum aestivum), maize (Zea maize), sugar beet (Beta vulgaris) and potato (Solanum tubersum). To date, a computerized program has never been used before to evaluate an area in Islamic Republic of Iran. Therefore, Almagra model constituent of this DSS software was selected in order to make strategies related to land suitability evaluation at a regional level. Soil morphological and analytical data were carried out for 44 sampling points based on grid survey and stored in SDBm plus database. The control section data between 0 and 50 cm appropriate to annual crops were calculated by “soil layer generator” to apply and run the Almagra model. Flunentic Haploxerepts and Vitrandic Calcixerepts in total of the 1050 ha were identified as marginal and/or not arable lands while the rest of soil subgroups can be considered as the best agricultural land. Typic Xerorthents under cultivation of all crops were classified as moderate suitable soil (S3). Vertic Haploxerepts has high suitability for all of the selected crops except potato. In this research, the main recognized soil limitation factor was texture in the total of 1670 ha of lands for potato cultivation and 274 ha for the rest of crops (S3t). Calcium carbonate was the secondary limitation factor where the soils of the study area were classified as highly suitable (S2c) soil mainly for maize and potato. The obtained results reveal that the evaluated crops could be arranged according to their soil suitability classes as follows: wheat < maize < sugar beet < potato. This arrangement reflects the priority for agricultural utilization.The authors wish to thank Tabriz University for its support during the course of PhD thesis work of Farzin Shahbazi. We also thank the Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), Sevilla, Spain.Peer reviewe