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In this study, the variations of spray characteristics are tested with air-assisted siphon type different size liquid atomizers. The spray characteristics are analyzed considering three atomizers having the same inlet diameter, with different constricted areas and exit diameters for the flow rates of 42, 57, and 71l pm. Three different mixtures of Oleic Acid with Ethanol, and three different mixtures of Di-Octyl Phthalate (DOP) with Ethanol are employed as working fluids along with the six different suction heights. Experimental outcomes show that, for the same flow rates, solution, and suction height, the droplet size changes by varying the diameter of the constricted area and exit area. The change of any area in atomizer changes the level of turbulence in flow that results in the variation of droplet size and its distribution. The increasing flow rate also assists in increasing the droplet size. Since the droplet size distribution decreases with the increasing viscosity, the use of DOP and Ethanol mixture increases the droplet size as it is more viscous than the Oleic Acid and Ethanol mixture. It is also noticed that at a constant airflow rate, Number Median Aerodynamic Diameter (NMAD), and liquid consumption rate are inversely proportional, whereas the Geometrical Standard Deviation (GSD) and Mass Median Aerodynamic Diameter (MMAD) is directly proportional to the suction height.

This paper presents a numerical study of a well-established vortex flow receiver and a proposed recirculating flow Solid particle solar receiver (SPSR) capable of achieving high air temperature which is perfectly suitable for the hybrid solar thermal power plant. Solar particle receivers are modeled using discrete particle model (DPM), RNG k- e flow model and discrete ordinate (DO) radiation model. Numerical analysis is done by considering two cases (i) Recirculating flow solar receiver with non-reacting particle and without non-reacting particle as a medium of transferring heat (ii) Vortex flow solar receiver with non-reacting particle and without non-reacting particle as a medium of transferring heat. The examination is carried out to compare the parametric sensitivity of both solar particle receivers with particle and air and without particle as a medium of transferring heat by considering the solar flux that incident on the aperture of the receiver and varying the air flow rate and particle concentration, recirculation rate. The results depict that use of particle enhance the heat transfer for both cases. It is concluded from the thermal behavior of recirculating flow SPSR that about 30% higher cavity thermal efficiency and exhibit higher and uniform heat transfer than a vortex flow SPSR.

Solar distillation is the lowest energy consuming desalination process as it only uses heat from solar radiation. In this study, a solar still is developed to utilize maximum solar irradiation to evaporate water andincrease the rate of condensation by an external condenser. The system is improved by modifying absorber plate with rectangular and triangular channels. This increases surface area of the absorber plate for increasing heat transfer between basin and basin water as well as surface to volume ratio of basin water. To increase condensation of vapor, the effect of an external condenser cooled by feed water is also tested. Feed water flows through the copper tubes of the condenser, cools it and maintains its temperature always below dew point. The condenser also provides extended surface area for condensation when glass surface condensation rate decreases due to excessive film condensation. The water inside tubes of the condenser pick up latent heat of condensation from the vapor condensed on its surface and preheat water. The water is further preheated by solar collector before entering the still. The experiments have been conducted to test the effect of the condenser on overall distillate output against primary glass surface condenseroutput during various temperatures of the glass surface. Different designs of absorber plate are testedfor their effects on rate of evaporation under various hours and weather conditions of several days at Rajshahi, Bangladesh. The maximum average yield obtained is 3.15 L/m2 with triangular channeled absorber plate. The effect of using the external condenser also increased the productivity by 24-30%.

Solar distillation is one of the significant methods of getting fresh water from brackish and sea water by using free energy source from the sun. This is considered as the best solution for water production in remote, barren to semi- barren, small communities where fresh water is inaccessible. An experimental investigation is performed on a single slope solar still in the weather of Rajshahi, Bangladesh. The main purpose of this study is to evaluate the effect of phase change material (PCM) in a solar still and thus enhance its productivity. A single slope solar still with a basin area of 0.44105m2 is designed and constructed for this investigation. In this study,Bitumen has been used as phase change material to store thermal energy in the form of latent heat which offersgreat storage capacity per unit volume and per unit mass and provides heat during sunshine-off period. Results show that the efficiency of current solar still with PCM is comparatively higher than that of the still without PCM.

This study focuses on the enhancement of potable water productivity of an active double slope modified solar still (SS) considering the combined effect of solid rectangular fin, paraffin wax as a thermal energy storage medium, black cotton cloth as wick material, and an external condenser. The performance of three double slope SSs (modified, finned, and traditional) is evaluated considering five different cases. A comparative assessment of the performances of three double slope SSs is performed and it is perceived that the supreme productivities are 3.07, 2.70, and 2.46 L/m2 for modified, finned, and traditional SSs, respectively. The maximum efficiency of the modified SS with and without external condenser are found as 39.74% and 30%, respectively. An external condenser insertion in the modified SS boosts the productivity by approximately 10%. The average daily efficiency of the modified SS is 14.23% and 22.33% higher than the finned and traditional SS, respectively. The economic analysis is also conducted, and the cost per liter (CPL) values for traditional SS, the finned one, and the modified one are found as 0.0135, 0.0133, and 0.0117 $/L/m2, respectively. The novel modification of SS could be a propitious alternative to meet up the potable water demand in remote regions with low cost.

The use of Concentrated Solar Power technology for energy generation relies on the heating of fluids to high temperatures. One of the limitations of this technology is the low working efficiency of current solar receivers which hinders its application and utilization as a renewable clean energy source. This paper presents a novel concept to improve concentrated solar receiver efficiency through the recirculation of solid particles laden flow within the receiver. The recirculating characteristic of the fluid and solid particle mixture is expected to generate higher output fluid temperature than conventional solar receivers. This is expected to lead to significant improvements in the working performance of the concentrated solar receiver. The numerical study investigates this concept, using a commercial CFD package, employing the discrete particle model (DPM), a RNG k- e flow model and a discrete ordinate (DO) radiation model. It is found that the use of recirculating solid particles improves the energy absorption within the receiver and with it the thermal efficiency of the proposed solar receiver reaches to around 70%. Moreover, comparing this with a conventional solar receiver, this new concept exhibits a more uniform temperature distribution inside the cavity, which is mainly due to the recirculating flow characteristic and the well-controlled mixing of air and particles. The advantages of this novel concept of the solar receiver present its potential benefits in further applications in the process of energy conversion providing on enhanced heat transfer medium.

Biodiesel has been identified as an alternative and promising fuel source to reduce the dependency on conventional fossil fuel in particular diesel. In this work, waste cooking oil (WCO) of restaurants is considered to produce biodiesel. A well-established transesterification reaction by sodium hydroxide (NaOH) catalytic and supercritical methanol (CH3OH) methods are applied to obtain biodiesel. In the catalytic transesterification process, biodiesel and glycerine are simultaneously produced. The impact of temperature, methanol/WCO molar ratio and sodium hydroxide concentration on the biodiesel formation were analysed and presented. It was found that the optimum 95% of biodiesel was obtained when methanol/WCO molar ratio was 1:6 under 873 K temperature with the presence of 0.2% NaOH as a catalyst. The waste cooking oil blend proportions were 10%, 15%, 20% and 25% and named as bio-diesel blends B-10, B-15, B-20, and B-25, respectively. Quality of biodiesel was examined according to ASTM 6751: biodiesel standards and testing methods. Important fuel properties of biodiesel, such as heating value, cetane index, viscosity, and others were also investigated. A four-stroke single cylinder naturally aspirated DI diesel engine was operated using in both pure form and as a diesel blend to evaluate the combustion and emission characteristics of biodiesel. Engine performance is examined by measuring brake specific fuel consumption and fuel conversion efficiency. The emission of carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), and others were measured. It was measured that the amount of CO2 increases and CO decreases both for pure diesel and biodiesel blends with increasing engine load. However, for same load, a higher emission of CO2 from biodiesel blends was recorded than pure diesel.

This study presents a numerical modeling of a downdraft gasifier. Wood (biomass) was considered as a feedstock for gasification as it is a cheap biomass and locally available. The numerical study was carried out to predict the flow behavior, the performance of the downdraft gasifier and the syngas composition precisely. The current downdraft gasifier was modeled using standard k–e turbulence model, DPM for discrete phase, nonpremixed combustion model for combustion and DO radiation model for radiation modeling. The flow behavior and the temperature distribution of the downdraft wood gasifier were addressed which helped to understand the internal combustion phenomenon. Results also showed that the predicted syngas compositions were as follows: Nitrogen-54.12%, Hydrogen-8.10%, Carbon Monoxide-16.04%, Carbon Dioxide-13.01%, Methane-2.35%, Water vapor-05.10% by volume. In addition gasifier, thermal efficiency was found about 72%. This gasification process produces syngas which is directly usable as an alterna...

The study presents an analysis and suggests about how renewable sources of energy can be an alternative option to produce electricity in an off-grid area. A case study is done by surveying 235 households in an off-grid area. Techno-economic analysis of the hybrid energy system is employed by using Hybrid Optimization of Multiple Energy Resources (HOMER) software. Four solar-PV modules (each of 1kW), two biogas generators (each of 3kW), three diesel generators (each of 5kW), five batteries (each of 160 Ah) and 5kW converter is found to be the best configuration in terms of Cost of Energy (COE), environmental conditions and Renewable Fraction (RF). The Cost of Energy (COE), Net Present Cost (NPC), capital cost of this configuration is found BDT15.382, BDT10007224, and BDT2582433 respectively. The renewable fraction of this system is found 75% which indicates a lower emission compared with thegrid based system and stand-alone diesel system. Although the COE is higher than grid electricity, this system offers a cheaper option than using kerosene oil and solar home systems (SHSs).

A recirculating flow solar particle cavity absorber (receiver) is modeled to investigate the flow behavior and heat transfer characteristics of a novel developing concept. It features a continuous recirculating flow of non-reacting metallic particles (black silicon carbide) with air which are used as a thermal enhancement medium. The aim of the present study is to numerically investigate the thermal behavior and flow characteristics of the proposed concept. The proposed solar particle receiver is modeled using two phase discrete particle model (DPM), RNG k-flow model and discrete ordinate (DO) radiation model. Numerical analysis is carried out considering a solar receiver with only air and the mixture of non-reacting particles and air as a heat transfer as well as heat carrying medium. The parametric investigation is conducted considering the incident solar flux on the receiver aperture and changing air flow rate and recirculation rate inside the receiver. A stand-alone feature of the recirculating flow s...

article i nfo In the present study, the heat transfer performance and friction factor characteristics in a circular tube fitted with twisted wire brush inserts were investigated experimentally. The twisted wire brush inserts were fab- ricated with four different twisted wire densities of 100, 150, 200, and 250 wires per centimeter by winding a 1 mm diameter of the copper wire over a 5 mm diameter of two twisted iron core-rods. Heat transfer and friction factor data in tubes were examined for Reynolds number ranging from 7,200 to 50,200. The results indicated that the presence of twisted wire brush inserts led to a large effect on the enhancement of heat transfer with corresponding increase in friction factor over the plain tube. The Nusselt number and friction factor of using the twisted wire brush inserts were found to be increased up to 2.15 and 2.0 times, respective- ly, than those over the plain tube values. Furthermore, the heat transfer performance was evaluated to assess the real benefits of using those type of inserts and the performance was achieved 1.85 times higher compared to the plain tube based on the constant blower power. Finally, correlations were developed based on the data generated from this work to predict the heat transfer, friction factor, and thermal performance factor for tur- bulent flow through a circular tube fitted with the twisted wire brush inserts in terms of wire density (y), Reynolds number (Re), and Prandtl number (Pr).