Department of Mechanical Engineering

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This paper deals with the study of a submerged jet for the suction of unwanted fluid. This submerged jet is caused by the fluid coming out from a source. The presence of a sink in front of this source facilitates the suction of the fluid depending upon the source and sink flow rates, the axial and lateral separations of the source and sink, and the angle between the axes of the source and sink. The main purpose is the determination of the sink flow rate for 100 % removal of the source fluid as a function of these parameters. The experiments have been carried using a source nozzle 6 mm in diameter and two sizes for the sink pipe diameter: 10 mm and 20 mm. The main diagnostics used are flow visualization using dye and particle image velocimetry (PIV). The dependence of the required suction flow rate to obtain 100 % effectiveness on the suction tube diameter and angle is relatively weak compared to the lateral separation. © 2012 American Society of Mechanical Engineers.

World University root node

Journal of Fluids Engineering, Transactions of the ASME

Study of submerged jet for suction of fluid

Safe operation of nuclear power plants is one of the major concerns and relies primarily on the integrity of the reactor pressure vessel. Neutron exposure induces temperature dependent embrittlement and can lead to loss of fracture toughness of reactor pressure vessel steel. Conventional fracture mechanics suffers from a serious limitation of non-transferability of fracture data from specimen level to component level as fracture resistance data obtained is largely geometry dependant. This difficulty is largely overcome by Gurson-Tvegaard-Needleman (GTN) model which models the drop in load carrying capacity of a material with the increase in plastic strain, considering nucleation, growth and coalescence of micro-voids in the material. However, determination of the model-parameters with experiments is extremely difficult and doubtful. Hence, a parametric study was undertaken to find out the effects of different parameters on material behaviour of reactor pressure vessel steel and to asses the parameter for best practical result with least metallographic study using a hybrid approach. The model parameters were finally verified by predicting ductile fracture in compact tension and three point bend specimen made from reactor pressure vessel steel. © 2011 Elsevier Ltd.

Materials and Design

Micromechanical modelling of reactor pressure vessel steel

Bimetallic welds made between ferritic steels and austenitic stainless steels are conventionally fabricated using arc welding procedures such as Tungsten Inert Gas, Metal Inert Gas, Shielded Metal Arc Welding and Submerged Arc Welding. However friction welding provides a new and unique solid state approach for joining many similar and dissimilar materials, which may not be possible to join by other welding techniques available without adding any external filler metal. This approach is mostly used in joining of dissimilar materials. The reason for increased utility being the absence of any external filler material which may otherwise add to the heterogeneity of the weld structure. In this paper, the fabrication and effect of friction welding parameters on mechanical-micro structural changes of bimetallic weld joints has been discussed. An attempt has also been made to relate the effect of friction welding parameters on the peak temperature values taken near faying surface and micro hardness changes measured in various zones of weld. © (2012) Trans Tech Publications, Switzerland.

Advanced Materials Research

Optimization of process parameters for friction welding of bimetallic welds

Bimetallic welds (BMWs) have been a necessity within the steam generators of nuclear power plants, where the heavy section low alloy steel components are usually connected to stainless steel primary piping systems. These welds represent zones with metallurgical discontinuities, which tend to localize the strains and cause failures. The other critical issues which must be taken care of while welding of bimetallic joints include solidification cracking, thermal fatigue and residual stresses in welds. The occurrence and severity of all these problems associated with bimetallic welds depend upon the type of welding process used along with the other variables like welding consumables, heat input etc. In shielded metal arc welding (SMAW), welding electrode consumables/coatings play an important role in deciding the weld metal quality. The development of welding electrode coatings is quite difficult due to very rapid complex reactions taking place during welding and the involvement of many controlled process variables. The present paper is an effort to highlight the general issues and challenges for the systematic and scientific development of welding electrode coatings for bimetallic welds. The experimental procedure contains three sets of coated electrodes having varying ferro-alloys, silica and carbon content. In the first set of electrodes, non-ferrous elements are also introduced into the weld metal through flux addition. Further, the welded joints are subjected to various tests and then evaluated to ascertain their mechanical as well as metallurgical behaviour.

Effect of electrode coatings on diffusible hydrogen content, hardness and microstructures of the ferritic heat affected zones in bimetallic welds

Journal of Sound and Vibration

Reply to the "comments on parametric instability of a cantilever beam with magnetic field and periodic axial load"

The knowledge of convective heat transfer coefficient hcpf (absorber plate to flowing air) is necessary to predict or evaluate thermal performance of any solar dryer. In order to determine hcpf, laboratory models of direct (cabinet), indirect and mixed mode solar dryer are designed and constructed to perform no-load steady state experiments for natural and forced air circulation. The dryers are operated under indoor simulation conditions for absorbed thermal energy and air flow rate for the range of 300-800 W/m2 and 1-3 m/s, respectively. Separate methods depending on mode of heat utilisation are proposed for determination of hcpf for different dryers. Correlations of hcpf in terms of dimensionless numbers are developed for each dryer operating under natural and forced convection. Levenberg-Marquardt algorithm is used to develop temperature dependent correlations. A close agreement between experimental and predicted hcpf values obtained from proposed correlations for natural convection dryers demonstrates their reliability. However, for forced convection dryers, there is a need to use temperature dependent Nu-Re correlation for more accurate results. The low uncertainty ranging from 0.3% to 0.8% in the determination of hcpf confirms the accuracy of experimental data obtained for various dryer designs operated under different conditions. © 2012 Elsevier Ltd. All rights reserved.

Energy Conversion and Management

Development of convective heat transfer correlations for common designs of solar dryer

It is necessary to develop thermal test procedure that can assist performance comparison between various solar dryer designs on common basis. In order to achieve this objective, the laboratory model of mixed-mode solar dryer is specially designed to perform indoor drying experiments with cylindrical potato samples. Sixteen drying kinetic curves are obtained over a wide range of various drying process variables. The variables investigated are absorbed thermal energy, air mass flow rate, food sample thickness and loading density. Based on experimental data of moisture content ratio-drying time, new concept to develop standard test method for performance evaluation of a given dryer is proposed. The proposed methodology facilitates to generate single generalized characteristic curve representing 16 drying kinetics and dimensionless parameter called dryer performance index (DPI) characterising the effectiveness of dryer system is identified. Different solar dryers with potato, banana and wheat are also tested in real climatic conditions to validate the proposed methodology. DPI with consistent values for all test conditions, indicating high degree of independence of operating conditions and food product characteristics, can therefore be used as a test parameter for performance comparison between different dryer designs on equitable basis. © 2012 Elsevier Ltd.

Solar Energy

New approach for thermal testing of solar dryer: Development of generalized drying characteristic curve

The present paper discusses the flow visualization for turbulent free convection in a tank of water with the bottom surface being a smooth or a grooved surface and the top of the water surface exposed to ambient. The grooved surface is of parallel 90° V-grooves with groove height of 10mm and groove width of 20mm. The experiment is carried out with aspect ratio (AR) of 2.9 and Rayleigh number (Ra) in the range, 1.3×10 7-4×10 7. Here AR is the aspect ratio (= width of fluid layer/height of fluid layer). Heat flux at the bottom surface is from electrical heating. From the pH-dye visualization, interesting flow structures are observed and these structures are analyzed with the help of plumes dynamics and temperature variations with time. © 2011 Elsevier Ltd.

International Communications in Heat and Mass Transfer

Flow visualization in turbulent free convection over horizontal smooth and grooved surfaces

Natural ventilation of a model room with water as the fluid medium is studied. It is insulated by air gaps on the four sides and at the top. A constant heat flux has been maintained on the bottom surface of the room. This room is surrounded by a large exterior tank containing water. There are three openings each on two opposing sides of the model room. For any experiment, only one opening on each side is kept open. Fluid enters or leaves these openings and the flow is driven entirely by buoyancy forces. Shadowgraph technique is used for visualization. The buoyancy causes flow to enter through the bottom opening and leaves through the top opening. At the openings, buoyant jets are observed and which have higher or lower relative density compared with that of its environment. The buoyant jet at the inlet interacts with the plumes on the heated bottom plate. From these visualizations, it appears that free convection at bottom plate will be affected by the buoyant jets at the openings and the degree to which it is affected depends on the position and size of openings and distance between inlet and outlet. The flow rate due to the natural ventilation depends on the bottom surface heat flux and the height difference between the openings. The temperatures of the floor, the interior and the exterior are calculated using a simple mathematical model. The values of temperatures obtained in the experiments are reasonably well predicted by the mathematical model. © 2012 American Society of Mechanical Engineers.

Journal of Thermal Science and Engineering Applications

Natural Ventilation in a Model Room

This study investigates the free convection and plumes dynamics over horizontal surfaces with parallel V-grooves. The convection is studied in a tank of water with the bottom surface being a smooth or grooved surface and the top of the water surface exposed to ambient. Two groove heights were used - 10 mm and 3 mm - and the experiment was done with two values of aspect ratio - 2.9 and 1.8 (aspect ratio is the width of the fluid layer/height of fluid layer). Heat flux at the bottom surface was from electrical heating. Beyond a certain critical temperature difference, enhanced heat transfer is obtained on the grooved surface compared to a smooth surface. Nusselt numbers are evaluated for both smooth and grooved surfaces and correlated using modified Rayleigh numbers. Visualization shows that the enhanced heat transport in the rough cavities cannot be ascribed to the increase in the contact area; rather, it must be the local dynamics of the thermal boundary layer. © 2012 Copyright Taylor and Francis Group, LLC.