Mechanical Behavior of Mushy Zone in DC casting using a Viscoplastic Material Model

Direct Chill (DC) casting is a semi-continuous metal manufacturing process for producing non-ferrous alloys such as aluminum and magnesium. During the solidification of the alloy, there exists a semi-solid state of material known as mushy zone which is more prone to hot tearing. Precise modeling of hot tearing is the most challenging task due to the interaction of many physical fields. The deformation of the partially coherent solid strongly influences the hot cracking. This work focuses on the material behavior of the mushy zone which is the prerequisite for the development of hot tearing criteria. The rate-dependent nature plays a crucial role at higher temperatures. Therefore, the viscoplastic material models with temperature-dependent coefficients are implemented for the characterization of the mushy zone. The numerical integration of the constitute equations are explained in detail. The liquid flow is neglected, and the momentum and energy equations are solved for the mushy and solid phases. With the help of a viscoplastic material models, the stress and strain evolution in the mushy zone is captured. It is found that the state of stress in mushy region is tensile in nature which is a favorable situation for the hot cracks. The influence of the casting speed and secondary cooling on the mushy stress state are analyzed in detail

Anaerobic digestion of screenings for biogas recovery

Screenings comprise untreatable solid materials that have found their way into the sewer. They are removed during preliminary treatment at the inlet work of any wastewater treatment process using a unit operation termed as a screen and at present are disposed of to landfill. These materials, if not removed, will damage mechanical equipment due to its heterogeneity and reduce overall treatment process, reliability and effectiveness. That is why this material is retained and prevented from entering the treatment system before finally being disposed of. The amount of biodegradable organic matter in screenings often exceeds the upper limit and emits a significant amount of greenhouse gases during biodegradation on landfill. Nutrient release can cause a serious problem of eutrophication phenomena in receiving waters and a deterioration of water quality. Disposal of screenings on landfill also can cause odour problem due to putrescible nature of some of the solid material. In view of the high organic content of screenings, anaerobic digestion method may not only offer the potential for energy recovery but also nutrient. In this study, the anaerobic digestion was performed for 30,days, at controlled pH and temperature, using different dry solids concentrations of screenings to study the potential of biogas recovery in the form of methane. It was found screenings have physical characteristics of 30% total solids and 93% volatile solids, suggesting screenings are a type of waste with high dry solids and organic contents. Consistent pH around pH 6.22 indicates anaerobic digestion of screenings needs minimum pH correction. The biomethane potential tests demonstrated screenings were amenable to anaerobic digestion with methane yield of 355,m3/kg VS, which is comparable to the previous results. This study shows that anaerobic digestion is not only beneficial for waste treatment but also to turn waste into useful resources

Design of Diaphragm Based MEMS Pressure Sensor with Sensitivity Analysis for Environmental Applications

In this paper Micro-electromechanical System (MEMS) diaphragm based pressure sensor for environmental applications is discussed. The main focus of this paper is to design, simulate and analyze the sensitivity of MEMS based diaphragm using different structures to measure the low and high pressure values. The simulation is done through the finite element tool and specifications related the maximum convinced stress; deflection and sensitivity of the diaphragms have been analyzed using the software INTELLISUITE 8.7v. The change in pressure is to bending of the diaphragm that modifies the measured displacement between the substrate and the diaphragm. This change in displacement gives the measure of the pressure in that environment. The design of these studies can be used to improve the sensitivity of these devices. Here the diaphragm based pressure sensor produced better displacement, sensitivity and stress output responses are obtained from the square diaphragm. The pressure range from 0.6 MPa to 25 MPa and its maximum displacement is accordingly 59 mm over a pressure range of 0 to 2 MPa. Its sensitivity is therefore 2.35 [10E-12/Pa]