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

Morphological and Morphometrical Description of Trichostrongylus Species Isolated from Domestic Ruminants in Khuzestan Province, Southwest Iran

Backgrounds: Genus Trichostrongylus (Nematoda: Trichostrongylidae) is one of the most impor­tant zoonotic nematodes with wide geographic distribution in the world. The purpose of the present study was to describe morphological and morphometrical characteristics of male Trichostrongylus species, currently prevalent in domestic ruminants of Khuzestan Province, south­west Iran.Methods: Gastro-intestinal organs of 1600 sheep, goats, cattle, and buffalos, slaughtered in Khuzestan Province, southwest Iran, were examined for infectivity with Trichostrongylus spe­cies. For examination and measurements of helminthes, Azo-carmine staining was per­formed, followed by camera lucida drawings of morphological characters and measurements of morphometrical criteria with a calibrated microscope. Using valid nematodes systematic keys, almost all the parasites were identified at the level of species.Results: Overall, 114 animals were found infected with at least one species of Trichostrongy­lus. Considering morphological characteristics of male Trichostrongylus, six species were identi­fied including T. colubriformis, T. vitrinus, T. probolorus, T. capricola, T. longispicu­laris and Trichostrongylus sp. Conclusion: Although, compared to the previous decades, currently Trichostrongylus is much less prevalent in the domestic ruminants of the study area, but still different species occur in these animals

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

SOIL SPECTRAL PROPERTIES OF ARID REGION, KASHAN AREA, IRAN

This study determined some spectral characteristics and relationship between Landsat spectral reflectance and soil surface color in the arid region of Iran (Kashan). The study carried out in the kashan area that covers 90000 ha. Consisting of mountain, hills and flood plain. Enhanced Thematic Mapper (ETM+) data collected on July 2002 were used for this research. The color composite images produced from ETM+7, ETM+4 and ETM+2 as red, green and blue respectively used in order to choose sample sites. The twelve sample sites were chosen based on resampled 3*3 pixels (90*90 m). In each site, the soil surface conditions and the munsell color of the soil surface were investigated in the field. Some physico-chemical properties of soil samples were also determined in the laboratory. Soil surface particle sizes were categorized into three classes: bare soil 2mm in diameter and vegetated soil. The results of this study indicates that munsell notation of hue, value and chroma are significantly correlated to the visible bands of Landsat (ETM+) data. From this study it may be concluded that visible reflectance of Landsat can be used to estimate soil color, if very precise result is not expected .More investigation are necessary in order to improve the obtained results

Prevalence of isolated hepatitis B core antibody among injection drug users in Central Province of Iran

Numeración errónea en el original

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

Evaluation of Toxoplasma gondii infection in western Iran: Seroepidemiology and risk factors analysis

Background: Toxoplasmosis is a parasitic infectious disease, and Toxoplasma gondii is the causative factor of this intracellular protozoan disease. Due to the lack of information about the rate of T. gondii in general papulation of Markazi Province in Iran, the current study was conducted to determine the prevalence of toxoplasmosis and the related risk factor analysis in the general population of Markazi Province. Methods: This cross-sectional study was performed within 6 months on individuals who were referred to diagnostic laboratories in Markazi Province. The demographic and background information of the subjects were collected using a questionnaire. Three milliliters of blood samples was collected from the participants under sterile conditions. The sera were separated and evaluated for levels of anti-Toxoplasma IgG antibody using a commercial enzyme-linked immunosorbent assay (ELISA) method. The collected data were analyzed by the SPSS software using descriptive statistics and chi-square test. Results: Out of 824 people from the general population of Markazi Province who were investigated in this study, 276 (33.5) had anti-Toxoplasma antibodies in their blood. According to the logistic regression model, gender variables, location, marital status, and having a cat at home do not affect the chances of contracting the parasite. Furthermore, the chance of contracting the parasite in 41- to 50-year-olds is 0.85 times the one in the 20- to 30-year-olds. The prevalence of toxoplasmosis in men and women in Markazi Province was 33 and 34.5, respectively. Conclusion: The mean prevalence of T. gondii infection in the age groups of 20-40, and � 40 years was estimated to be 24.7, and 40.8, respectively. These rates were significantly lower than the national results (44, and 55, respectively). Therefore, regarding to the health authorities, it is necessary to raise the level of awareness of people of the region, especially at-risk groups about the transmittance and prevention methods, and infection risk factors in order to prevent the occurrence of T. gondii infection and reduce the prevalence and incidence of the disease. © 2020 The Author(s)