A Comparative Study Of Tensile And Microstructural Characteristics Of Friction Welded Joints And Conventionally Welded Joints Of Aluminium Alloy 6061

Welding of high strength and low weight materials like Aluminium Alloys without any defects by conventional welding techniques is a major challenge in industries. Hence research on solid state welding techniques like Friction stir welding and Friction welding techniques have got much importance in joining of Aluminium alloys. However most of the industries are not changing conventional techniques as skilled workers are available on that area. Most common conventional welding techniques used for joining of Aluminium alloys are Gas welding and Arc welding. Friction welding is a solid-state welding process that generates heat through mechanical friction between a moving and a stationary component with the addition of a lateral force called “upset” to plast ically displace and fuse the materials. In this work, experimental study on tensile and micro structural characteristics of welded joints formed from conventional welding techniques and Rotary friction welding(suitable for weld specimens with circular cross section) has been carried out and the same were compared. The process parameters for arc welding used was 50-70 Amp reverse polarity DC and electrodes of 2.3mm diameter. In Gas welding, the parameters were oxy acetylene neural flame at 3200°C and 3mm electrodes . In the case of friction welding an axial pressure loading of 3Mpa with 5 MPa as upsetting pressure and 500 rpm were used to obtain good welded joints. Tensile characteristic studies of Arc welded joints and Gas welded joints showed 48% and 60 % variations respectively from the maximum load bearing characteristics of parent metal. In the case of friction welded joint, the variation was found to 46%. Micro structural evaluation of conventionally welded joints exhibited clear distinct zones of various weld regions. In the case of friction welded joint micro structural photographs showed comparable features both in parent metal and welded region. Thus the tensile characteristic study and microstructure evaluations proved that friction welded joints are good in both aspects compared to conventionally welded joints.

A Study of Single Stage Semi‐Dry Anaerobic Digestion of Organic Fraction of Municipal Solid Waste

Solid waste generation is a natural consequence of human activity and is increasing along with population growth, urbanization and industrialization. Improper disposal of the huge amount of solid waste seriously affects the environment and contributes to climate change by the release of greenhouse gases. Practicing anaerobic digestion (AD) for the organic fraction of municipal solid waste (OFMSW) can reduce emissions to environment and thereby alleviate the environmental problems together with production of biogas, an energy source, and digestate, a soil amendment. The amenability of substrate for biogasification varies from substrate to substrate and different environmental and operating conditions such as pH, temperature, type and quality of substrate, mixing, retention time etc. Therefore, the purpose of this research work is to develop feasible semi-dry anaerobic digestion process for the treatment of OFMSW from Kerala, India for potential energy recovery and sustainable waste management. This study was carried out in three phases in order to reach the research purpose. In the first phase, batch study of anaerobic digestion of OFMSW was carried out for 100 days at 32°C (mesophilic digestion) for varying substrate concentrations. The aim of this study was to obtain the optimal conditions for biogas production using response surface methodology (RSM). The parameters studied were initial pH, substrate concentration and total organic carbon (TOC). The experimental results showed that the linear model terms of initial pH and substrate concentration and the quadratic model terms of the substrate concentration and TOC had significant individual effect (p < 0.05) on biogas yield. However, there was no interactive effect between these variables (p > 0.05). The optimum conditions for maximizing the biogas yield were a substrate concentration of 99 g/l, an initial pH of 6.5 and TOC of 20.32 g/l. AD of OFMSW with optimized substrate concentration of 99 g/l [Total Solid (TS)-10.5%] is a semi-dry digestion system .Under the optimized condition, the maximum biogas yield was 53.4 L/kg VS (volatile solid).. In the second phase, semi-dry anaerobic digestion of organic solid wastes was conducted for 45 days in a lab-scale batch experiment for substrate concentration of 100 g/l (TS-11.2%) for investigating the start-up performances under thermophilic condition (50°C). The performance of the reactor was evaluated by measuring the daily biogas production and calculating the degradation of total solids and the total volatile solids. The biogas yield at the end of the digestion was 52.9 L/kg VS for the substrate concentration of 100 g/l. About 66.7% of volatile solid degradation was obtained during the digestion. A first order model based on the availability of substrate as the limiting factor was used to perform the kinetic studies of batch anaerobic digestion system. The value of reaction rate constant, k, obtained was 0.0249 day-1. A laboratory bench scale reactor with a capacity of 36.8 litres was designed and fabricated to carry out the continuous anaerobic digestion of OFMSW in the third phase. The purpose of this study was to evaluate the performance of the digester at total solid concentration of 12% (semi-dry) under mesophlic condition (32°C). The digester was operated with different organic loading rates (OLRs) and constant retention time. The performance of the reactor was evaluated using parameters such as pH, volatile fatty acid (VFA), alkalinity, chemical oxygen demand (COD), TOC and ammonia-N as well as biogas yield. During the reactor’s start-up period, the process is stable and there is no inhibition occurred and the average biogas production was 14.7 L/day. The reactor was fed in continuous mode with different OLRs (3.1,4.2 and 5.65 kg VS/m3/d) at constant retention time of 30 days. The highest volatile solid degradation of 65.9%, with specific biogas production of 368 L/kg VS fed was achieved with OLR of 3.1 kg VS/m3/d. Modelling and simulation of anaerobic digestion of OFMSW in continuous operation is done using adapted Anaerobic Digestion Model No 1 (ADM1).The proposed model, which has 34 dynamic state variables, considers both biochemical and physicochemical processes and contains several inhibition factors including three gas components. The number of processes considered is 28. The model is implemented in Matlab® version 7.11.0.584(R2010b). The model based on adapted ADM1 was tested to simulate the behaviour of a bioreactor for the mesophilic anaerobic digestion of OFMSW at OLR of 3.1 kg VS/m3/d. ADM1 showed acceptable simulating results.