Technical note: Techniques to obtain improved predictions of global radiation from sunshine duration

Data for 42 stations in different parts of the world in the northern hemisphere have been employed to partition monthly averaged daily global radiation and sunshine duration in a bid to obtain improved fits to Angstroms correlation. It has been found that regression fits to the correlation using data for biannual groups of months from March–August (months 3–8) and September–February (months 9–2), or March–September (months 3–9) and October–February (months 10–2), give an improvement in the rms error over the year, which is 25% or higher than the errors for annual fits for half of the cases. In no case is there an increase in rms error from the partitioning.It is found that biannual regression parameters for a pyranometer station may be used to predict with good accuracy global radiation for locations hundreds of kilometers away from the station if the climate, altitude and latitude are similar.A use of the seasonal partitioning of data leads to the following relations with station independent coefficients for     

MHD Mixed Convection with Joule Heating Effect in a Lid-Driven Cavity with a Heated Semi-Circular Source Using the Finite Element Technique

A computational fluid dynamics simulation of heat transfer characteristics on the conjugate effect of Joule heating and magnetic field acting normal to the lid-driven cavity with a heated semi-circular source on one wall under constant temperature is investigated. The left wall of the cavity moves in an upward (case I) or downward (case II) direction, and buoyancy forces are also effective. Horizontal walls are adiabatic. The governing mass, momentum, and energy equations along with boundary conditions are expressed in a normalized primitive variables formulation. The finite element method is used in the solution of the normalized governing equations. The study is performed for pertinent parameters such as the Rayleigh number, Hartmann number, and Joule heating parameter. It is found that the average Nusselt number can be decreased with the increasing of the Rayleigh number in the presence of Joule effect. The magnetic field can be a good control parameter for heat transfer and fluid flow.     

Modeling of Unsteady Natural Convection for Double-Pipe in a Partially Cooled Enclosure

In this article, a model is developed for unsteady natural convection heat transfer and fluid flow in a partially cooled enclosure with a hollow cylinder through it. The right vertical wall of the enclosure is cooled partially. The location of the partial cooling is set up in three different configurations; namely, bottom (P ₁), middle (P ₂), and top (P ₃). A hollow cylinder is located at the middle of the enclosure to simulate a double-pipe heat exchanger. Three values of Grashof number are applied in this work, i.e., 10⁴, 10⁵ and 10⁶, and three lengths of the cooler, i.e., 0.2, 0.4 and 0.6. Finite element method was utilized to solve the unsteady dimensionless conservation equations of mass, momentum and energy. It is found that the length and location of cooler does not have a significant effect on the natural convection for the case of the low Grashof number. The maximum heat transfer rate is reached when the cooler is located at the middle of the vertical wall.     

Unsteady analysis of natural convection in a carbon nanotube-water filled cavity with an inclined heater

ABSTRACT

A finite element solution has been performed in this work to solve unsteady governing equations of natural convection in a carbon nanotube–water-filled cavity with inclined heater. The temperature of ceiling and left vertical walls is lower than that of the heater while the other walls are adiabatic. The main governing parameters are nanofluid volume fraction and Rayleigh number (Ra). It is found that the heat transfer rate shows different trends based on Rayleigh number and it increases with increase in nanoparticle volume fraction. It has been estimated that average Nusselt number (Nu) is dependent onRa through power regression models with strong positive linear correlation between ln (Nu) and ln (Ra). In particular, for the maximum time, when the solid volume fraction is varied from 0 to 0.1 the dependence between average Nu and linear Ra, on a logarithmic scale, is very high.     

Optimization of Process Parameters for the Preparation of CaO/CaSO4/Coal Fly Ash Sorbent for Sulfur Dioxide (SO2) Removal: Part II

A two-step optimization strategy was employed to optimize the surface area of sorbent prepared from coal fly ash, calcium oxide (CaO) and calcium sulfate (CaSO₄) for flue gas desulfurization. In the first step, a 3 level full factorial design of experiment was used to develop a regression model equation to correlate the significant experimental sorbent preparation variables to the surface area of the resulting sorbent. The three experimental sorbent preparation variables studied are hydration period (x ₁), ratio of CaO to fly ash (x ₂) and amount of CaSO₄ (x ₃). In the subsequent step, response surface methodology was used to identify the experimental sorbent preparation variables that maximize the surface area of the sorbent. Through this two-step optimization strategy, it was found that at a hydration period of 10 hrs and drying temperature of 100°C, optimum surface area of 67.0 m²/g could be attained by using 5 grams of CaO, 13.7 grams of fly ash, and 7.4 grams of CaSO₄ in the preparation mixture. The prediction was verified with experimental runs.     

Optimization of the enzyme-catalyzed synthesis of amino acid-based surfactants from palm oil fractions

The feasibility of using palm oil fractions as cheap and abundant sources of raw material for the synthesis of amino acid surfactants was investigated. Of a number of enzymes screened, the best results were obtained with the immobilized enzyme, Lipozyme. The effects of temperature, solvent, incubation period, fatty substrate/amino acid molar ratio, enzyme amount, and water removal on the reactions were analyzed and compared to those on reactions with free fatty acids and pure triglycerides as fatty substrates. All reactions were most efficient when carried out at high temperatures (70-80 degrees C) in hexane as a solvent. However, while reactions with free fatty acids proceeded better when a slight excess of the free fatty acids over the amino acids was used, reactions with triglycerides and palm oil fractions were best performed at equimolar ratios. Also, the addition of molecular sieves slightly enhanced reactions with free fatty acids but adversely affected reactions with triglycerides and palm oil fractions. Although reactions with palm oil fractions took longer (6 d) to reach equilibrium compared to reactions with free fatty acids (4 d) and pure triglycerides (4 d), better yields were obtained. Such lipase-catalyzed transacylation of palm oil fractions with amino acids is potentially useful in the production of mixed medium- to long-chain surfactants for specific applications.     

Arsenic contamination of Bangladesh paddy field soils: implications for rice contribution to arsenic consumption

Arsenic contaminated groundwater is used extensively in Bangladesh to irrigate the staple food of the region, paddy rice (Oryza sativa L.). To determine if this irrigation has led to a buildup of arsenic levels in paddy fields, and the consequences for arsenic exposure through rice ingestion, a survey of arsenic levels in paddy soils and rice grain was undertaken. Survey of paddy soils throughout Bangladesh showed that arsenic levels were elevated in zones where arsenic in groundwater used for irrigation was high, and where these tube-wells have been in operation for the longest period of time. Regression of soil arsenic levels with tube-well age was significant. Arsenic levels reached 46 microg g(-1) dry weight in the most affected zone, compared to levels below l0 microg g(-1) in areas with low levels of arsenic in the groundwater. Arsenic levels in rice grain from an area of Bangladesh with low levels of arsenic in groundwaters and in paddy soils showed that levels were typical of other regions of the world. Modeling determined, even these typical grain arsenic levels contributed considerably to arsenic ingestion when drinking water contained the elevated quantity of 0.1 mg L(-1). Arsenic levels in rice can be further elevated in rice growing on arsenic contaminated soils, potentially greatly increasing arsenic exposure of the Bangladesh population. Rice grain grown in the regions where arsenic is building up in the soil had high arsenic concentrations, with three rice grain samples having levels above 1.7 microg g(-1).     

Heat transfer in rectangular microchannels during volumetric heating of the substrate

Convective heat transfer in microchannels with rectangular and square cross sections are analyzed for volumetric heat generation in the substrate due to an imposed magnetic field. Gadolinium was used as the substrate material and water as the working fluid. Gadolinium is a magnetic material that exhibits high temperature rise during adiabatic magnetization around its transition temperature of 295 K. A thorough investigation for velocity and temperature distributions was performed by varying channel aspect ratio, Reynolds number, and heat generation rate in the substrate. With the increase in Reynolds number, the outlet temperature decreased and the average Nusselt number increased.     

Spectrum Correlated Criteria and Their Impacts on High Altitude Platform Station (HAPS) and Fixed Satellite Service (FSS) Coexistence in Frequency Range 5,850–7,075 MHz

High altitude platform station (HAPS) is an innovative technology which delivers some unique features, contrary to conventional communications networks, such as fixed satellite service (FSS). The absence of confirmed spectrum emission mask (SEM) of HAPS and its diversity to work within FSS networks are significant issues in evaluating the coexistence of HAPS and FSS. At this juncture, a practical SEM for HAPS gateway links is proposed which will endeavor to assess its functionality and its ability to coexist with FSS. HAPS SEM’s impact on coexistence issues are exposed upon consideration of criteria such as MD, NFD and ACIR. These facets are well-described and their measured amounts for specific applicable SEMs are proposed. Therefore, reckoning process regarding these factors is ascertained. It must be said that the remarked criteria and their amounts for HAPS gateway links are unprecedented. The simulation parameters are well organized based upon International Telecommunication Union and World Radiocommunications Conferences periodicals. The aim of this article is to shed more light on the associated facets of the HAPS network spectrum and their impressions on HAPS and FSS networks coexistence. The assessments have been performed for HAPS gateway links in the 5,850–7,075 MHz frequency band where FSS uplink frequency band in C-band (5,925–6,725 MHz) partially intrude with HAPS gateway links. Therefore, HAPS gateway links channelization regarding FSS uplink channel is appraised and light is shed on the impact of HAPS and FSS coexisting in the same frequency band.