Applied Mechanics and Materials Vol. 787

Abstract: Industrial or Trade effluent defines, in legal term, any liquid, gaseous or solid substance discharged from industry premises. The discharge of untreated effluents is injurious to public health besides to the life and health of animals or plants or of aquatic organisms. Effluent treatment involves mechanical, physical, chemical and biological processes; in majority of non-natural processes, mechanical equipment is used to breakdown the wastes into environmentally stable components, and their suitability depends on the type of the generated waste, process, efficiency of equipment used, etc. A few of these include – diffusers, fixed and floating aerators for injecting compressed air, Bio-discs which rotate on shafts for biological treatment, incinerators for burning solid wastes, cyclones and wet/dry Scrubbers for air treatment, Filter press, Centrifuge to remove water/moisture. Petrochemical product manufacturing activity is a highly polluting industry. The effect of mechanical equipments in such a petrochemical unit, manufacturing Phthalic Anhydride, Maleic Anhydride, Fumaric Acid and Maleic Acid, at Tamil Nadu has been studied and the performance of the equipment in the aeration components of the ETP system evaluated; the study concludes with suggestions for supplementary improvement.

Abstract: In order to cope with ever increasing demands from the electronic, automotive and aerospace industries, cooling devices have to be small in size, light-weight and of high performance.The search for a more efficient cooling technology becomes one of the bottle neck problems of the further development of the electronic and automotive industry. Microchannel liquid cooling is one of the candidates for this purpose. The most important parameter in the microchannel is the distribution of the coolant inside the channel. A uniform flow in the microchannel leads to uniform heat transfer.A numerical simulation is carried out to minimize the flow maldistribution inside the microchannel. The microchannel was made as wavy shaped channel. There are six channels with hydraulic diameter of 1mm each. Header is the major part in the microchannel which supplies fluid into different channels. In this work, five different shapes of the header were considered namely circular, frustum conical, rectangular, triangular and trapezoidal. From the simulation results it was found that the mal-distribution is significantly affected by flow rate and shape of the header.

Abstract: The photovoltaic system converts electrical energy from solar radiation energy. It is preferable because it has no moving parts and low pollution to the environment. The performance of photovoltaic system has been decided with environmental aspects apart from the photovoltaic system specifications and incident solar radiation. In this research, the influence of relative humidity on photovoltaic system is considered for evaluating the performance and to draw the characteristic curves during winter (December and January) period. The photovoltaic system which installed at Chennai city, India, is exposed to high relative humidity even during winter season. The 3kW photovoltaic system behaviour is considered and measures the photovoltaic output voltage and output current with the effect of relative humidity. The performance curves shows that high relative humidity reduces the output voltage and current from photovoltaic system. It is same as the influence of other adverse environmental factors to degrade the operation and life span of photovoltaic system.

Abstract: HHeat exchangers have been used since the start of industrialisation, and since then have been modified in a plethora of complex and intricate ways to suit the needs of the corresponding application, but in this paper a simple modification on the existing design has been investigated numerically, which has proven to be effective. A standard tube-in-tube heat exchanger has been modified such that the external tube tapers (converges) to a smaller diameter. The inner tube carries the cold working fluid which absorbs the heat energy carried by the fluid in the outer tube. A numerical simulation has been carried out, taking into account the mass flow rate, fluid temperatures, heat transfer etc., which are governed by fundamental heat transfer equations. The results of the simulation are used to analyse the effect of this modification (convergent tube) on the efficiency of the heat exchanger, which has been found to increase significantly along with the rate of heat transfer.

Abstract: Pyrolysis process in a fixed bed reactor was performed to derive pyrolytic oil from groundnut shell. Experiments were conducted with different operating parameters to establish optimum conditions with respect to maximum pyrolytic oil yield. Pyrolysis process was carried out without catalyst (thermal pyrolysis) and with catalyst (catalytic pyrolysis). The Kaolin is used as a catalyst for this study. The maximum pyrolytic oil yield (39%wt) was obtained at 450°C temperature for 1.18- 2.36 mm of particle size and heating rate of 60^°C/min. The properties of pyrolytic oil obtained by thermal and catalytic pyrolysis were characterized through Fourier Transform Infrared Spectroscopy (FT-IR) and Gas Chromatography-Mass Spectrometry (GC-MS) techniques to identify the functional groups and chemical components present in the pyrolytic oil. The study found that catalytic pyrolysis produce more pyrolytic oil yield and improve the pH value, viscosity and calorific value of the pyrolytic oil as compared to thermal pyrolysis.

Abstract: Nanofluids are fluids containing nanometer-sized particles of metals, oxides, carbides, nitrides, or nanotubes. They exhibit enhanced thermal performance when used in a heat exchanger as heat transfer fluids. Alumina (Al₂O₃) is the most commonly used nanoparticle due to its enhanced thermal conductivity. The work presented here, deals with numerical simulations performed in a tube-in-tube heat exchanger to study and compare flow characteristics and thermal performance of a tube-in-tube heat exchanger using water and Al₂O₃/water nanofluid. A local element-by-element analysis utilizing e-NTU method is employed for simulating the heat exchanger. Profiles of hot and cooling fluid temperatures, pressure drop, heat transfer rate along the length of the heat exchanger are studied. Results show that heat exchanger with nanofluid gives improved heat transfer rate when compared with water. However, the pressure drop is more, which puts a limit on the operating conditions.

Abstract: Thermal Energy Storage using phase change materials (PCM) has become an interesting area of energy research because of its high energy storage density, isothermal nature of storage process and small volume changes. In the present work paraffin wax (PW) and Palmitic acids(PA) are chosen as phase change materials and mixed in different proportions(40-60% PW-PA, 50-50% PW-PA and 60-40% PW-PA) to prepare eutectic PCMs. And also paraffin is combined with Copper oxide nano powder to prepare composite PCM. Differential Scanning Calorimetric (DSC) Tests have been conducted to find the latent heat capacity of the above combination of PCMs. The results showed that 40-60%PW-PA eutectic mixture is effective in increasing the latent heat of fusion compared to the other combinations.

Abstract: The objective of present study is to conduct exergy analysis on flat plate solar photovoltaic thermal (PV/T) hybrid system. The solar insolation, current, voltage, inlet and outlet air temperature of the cooling duct, ambient air temperature, and solar panel surface temperature are the major parameters used to calculate the energy and exergy efficiency. An amended electrical efficiency is used to estimate the electrical output and performance of PV/T hybrid system. Further, an enriched equation for the exergy efficiency of a PV/T hybrid system has been used for exergy analysis. Finally, parametric studies have been carried out. An extensive energy and exergy analysis is carried out to calculate the electrical and thermal parameters. The experimental results are in good agreement with the earlier studies. In addition to that, the electrical efficiency, thermal efficiency, electrical thermal efficiency, overall energy efficiency and exergy efficiency of PV/T hybrid system is found to be about 9.78%, 24.22%, 27.17%, 44.84% and 11.23% respectively.

Abstract: The purpose of thermal energy storage systems (TES) is to store the heat energy supplied to it for a considerable time period and give the energy back when ever need arise. On many of occasions, part of the heat energy of various systems is unutilized. If this excess heat energy be stored in such systems as TESS, utilization of energy improves. If the use of such systems is widespread, fuel is conserved and national economy is saved.Different materials can be used in TESS to store heat energy and in the present work two such materials, which are popular phase change materials (PCM) namely (a) Paraffin (b) Stearic acid are used and subsequently the performance of the TESS is studied. The PCMs are used in the form of spherical capsules made up of high density poly ethylene (HDPE) of diameter 58 mm. Charging time and amount of heat energy recovered are studied for the two PCMs mentioned above and compared. Though paraffin as PCM gives little better heat energy recovery, performance of both the materials are almost the same. Hence as the cost of stearic acid is less when compared to paraffin on economical grounds and on ease of availability basis stearic acid has advantages over paraffin.

Abstract: The very low efficiency of solar cells can be attributed to a plethora of reasons. The most important reason being, reflection of sunlight from the solar cell surface. Most of the sunlight incident on the solar cells gets reflected back due to the smooth surface of the silicon wafers. This paper presents a novel method to avoid this by using black silicon solar cells. Black silicon tends to make use of the concept of black body radiation to absorb all the rays incident on it and thereby reducing the reflectivity of the solar cell. The nano-fabrication technique involves usage of special wet-etch techniques to achieve nano-sized pores on the surface of silicon. In case of normal solar cells, usually layers of a suitable anti-reflective coating are given which tend to minimize the amount of reflection. This unfortunately increases the manufacturing cost. The unfavourable conditions of heat and dirt further tend to soil the layer of anti-reflective coating, reducing the gains of anti-reflective coating. Thus, black silicon solar cells provide better efficiency while simultaneously reducing the fabrication cost.