P. S. Ghoshdastidar

Computational investigation on bubble detachment from submerged orifice in quiescent liquid under normal and reduced gravity

In this work numerical simulations have been carried out to study the problem of dynamic air bubble formation from a submerged orifice in quiescent liquid, under constant inflow condition, at normal and reduced gravity levels. A coupled level-set and volume-of-fluid method is used to simulate the bubble formation, bubble detachment, and the bubble rise above the orifice. For the described study, the authors have mainly focused on low and medium air flow rate for simulation of bubble formation at the orifice. The employed gravity levels g/ge are in the range of 100, 10−1, and 10−2. The influence of buoyancy on the bubble shape has been studied. The study includes the bubble volume, formation frequency, pinch-off rate, detached bubble diameter, and the bubble growth history for different air flow rates. Even for the static contact angle θs=00, it is observed that at low gravity levels the bubble base spreads along the surface of the orifice plate away from the orifice rim during the expansion stage, and dur...

NANO-FINISHING OF STAINLESS-STEEL TUBES USING ROTATIONAL MAGNETORHEOLOGICAL ABRASIVE FLOW FINISHING PROCESS

A new polishing method called Rotational (R)-Magnetorheological Abrasive Flow Finishing (MRAFF) process has been proposed by rotating a magnetic field applied to the Magnetorheological polishing (MRP) medium in addition to the reciprocating motion provided by the hydraulic unit to finish internal surface of cylindrical stainless steel (non-magnetic) workpiece. By intelligently controlling these two motions uniform smooth mirror-like finished surface in the range of nm has been achieved. For parametric analysis of the process, the experiments have been planned using design of experiments technique and response surface regression analysis is performed to analyze the effects of process parameters on finishing performance. Analysis of Variance (ANOVA) is conducted and contribution of each model term affecting percent improvement in surface finish is calculated. The experimental results are discussed and optimum finishing conditions are identified from optimization study. The present study shows that rotational speed of the magnet has most significant effect on output response (percentage improvement in surface roughness, %ΔR a ). The best surface finish obtained on stainless steel workpiece with R-MRAFF process is 16 nm.

A study of heat transfer effectiveness of circular tubes with internal longitudinal fins having tapered lateral profiles

Abstract This paper presents a finite-difference based numerical simulation of steady, laminar heat transfer in circular tubes fitted with four identical longitudinal fins having tapered lateral profiles. The lateral view of the tip of each fin is a circular arc. The tube is exposed to constant heat flux. The temperature dependence of thermal conductivity and viscosity has been taken into account. The flow is assumed to be locally fully developed but thermally undeveloped. The momentum equation for the fluid and energy equations for the fluid and the tube wall with/without fins are solved iteratively and simultaneously. At each axial location, bulk velocity, bulk temperature of the fluid and Effectiveness which is an indicator of the enhancement of heat transfer due to addition of fins are calculated. A parametric study of effectiveness vs. axial distance for various combinations of fin materials and coolants reveals interesting results. The velocity profiles, friction factors and comparisons with respect to constant property solutions have also been discussed.

The Out-of-Roundness of the Internal Surfaces of Stainless Steel Tubes Finished by the Rotational–Magnetorheological Abrasive Flow Finishing Process

This article reports the experimental findings about the improvement in out-of-roundness (OOR) of stainless steel tubes finished by Rotational–Magnetorheological Abrasive Flow Finishing (R-MRAFF) process. In this process, a rotating motion is provided to the magnetorheological polishing (MRP) medium by means of a rotating magnetic field, and simultaneously, a reciprocating motion is provided to the polishing medium by a hydraulic unit. By controlling these two motions, nano level uniform smooth mirror like finished surface has been achieved and simultaneously OOR of internal surface of tube is reduced. Experiments are planned according to the central composite rotatable design of response surface methodology based on the selected range of process parameters obtained from the preliminary experiments. Analysis of Variance (ANOVA) is conducted and contribution of each model term affecting OOR improvement is calculated. It has been found that R-MRAFF process potentially reduces roundness error of axisymmetric parts (maximum improvement in OOR=2.04 µm) improving their reliability and wear resistance. The present study shows that, OOR improves with an increase in the rotational speed of the magnet up to an optimum value beyond which the improvement in OOR reduces. From the scanning electron micrographs and atomic force micrographs it has been found that the abrasive cutting marks in R-MRAFF process generate cross-hatch pattern which helps in oil retention in cylindrical workpieces to reduce friction.

Experimental validation of a quasi three-dimensional conjugate heat transfer model for the metering section of a single-screw plasticating extruder

Abstract This paper presents a quasi three-dimensional computer model and its validation with experimental results of the thermal transport processes in the metering section of a single-screw plasticating extruder. A finite volume based approach (SIMPLEC) has been used to obtain flow, thermal and pressure fields of a power-law fluid in the screw channel. The accuracy of the present model has been confirmed by the satisfactory tally of the numerical results with the experimental data for the extruder with fully open exit valve, and also by the excellent matching of the dimensionless exit pressure gradient with the experimental data.

Heat Transfer in the Non-reacting Zone of a Cement Rotary Kiln

This paper presents a steady-state heat transfer model for a rotary kiln used for drying and preheating of wet solids with application to the non-reacting zone of a cement rotary kiln. A detailed parametric study indicates that the influence of the controlling parameters such as percent water content (with respect to dry solids), solids flow rate, gas flow rate, kiln inclination angle and the rotational speed of the kiln on the axial solids and gas temperature profiles and the total predicted kiln length is appreciable.

COMPUTER SIMULATION OF HEAT TRANSFER DURING DRYING AND PREHEATING OF WET IRON ORE IN A ROTARY KILN

ABSTRACT In the present study, an improved numerical heat transfer model has been developed for a rotary kiln used for drying and preheating of wet iron ore. The present model includes radiation exchange among hot gas, refractory wall and the solid surface, transient conduction in the refractory wall, and mass and energy balances of the hot gas and the solids. The contribution of gas convection has also been taken into account in terms of a fraction of the radiative heat transfer to the inner refractory wall and the solid surface. The computer results show that the present model can predict the length of the kiln as well as axial solid and gas temperature distributions with reasonably good accuracy. A detailed parametric study reveals that a good design of a rotary kiln requires medium gas flow rate, small angle of inclination and low rotational speed of the kiln.

Parametric analysis of MR polishing fluid using statistical technique

Magnetorheological abrasive flow finishing (MRAFF) process has been developed for nanofinishing of parts especially for complicated geometry for a wide range of industrial applications. The finishing efficiency and finishing quality of MRAFF process relies mainly on the rheological properties (i.e., yield stress and viscosity) of magnetorheological polishing (MRP) fluid which must be characterised before it is used in any specific application. These properties are responsible for bonding strength of abrasive particles surrounding carbonyl iron particle (CIP) chains. Design of MRP fluid composition and volume ratio has an impact on rheological properties and stability directly. Response surface methodology (RSM) is applied to predict the effect of volume concentration of each component on yield stress and viscosity of MRP fluid.

Computational fluid dynamics simulation and experimental investigations into the magnetic-field-assisted nano-finishing process

This article deals with a new approach to understand the magnetic-field-assisted nano-finishing process in which computational fluid dynamics is used to simulate the forces. A finite element method is used to evaluate the magnetic field intensity, mathematical modelling is applied to model the nano-finishing operation, and the experiments are conducted to compare the experimental results with the simulated results. A flexible polishing tool comprising a magnetorheological polishing medium is used for this process. The relative motion between the polishing medium and the workpiece surface provides the required finishing action. In the present work, a two-dimensional computational fluid dynamics simulation of a magnetorheological polishing medium inside the workpiece fixture is performed to evaluate the axial and radial stresses developed owing to the flow of magnetically stiffened magnetorheological polishing medium. A finite element analysis is performed in order to find out the direction and the magnitude of the magnetic field. A microstructure of the mixture of magnetic and abrasive particles in the magnetorheological polishing medium is proposed in order to calculate forces acting on an active abrasive particle. Modelling of the surface finish is performed after analysing the surface roughness profile data. Further finishing experiments are conducted in order to compare the simulated surface roughness value with the experimental results and they are found to agree well.

Computer simulation of three-dimensional transport during moistened defatted soy flour processing in the metering section of a single-screw extruder

Abstract A quasi-three-dimensional steady state finite-volume-based computer model for a power-law fluid is used to describe the three-dimensional transport during the processing of defatted soy flour with 25, 28 and 33 per cent moisture contents by weight in the metering section of a single-screw extruder. The numerical results have been compared with the earlier experimental results of Fong. The results are found to be reliable only for the highest moisture content dough (33 per cent by weight). The conclusion is that the quasi-three-dimensional model showing a viscous drag flow mechanism using a power-law equation for viscosity may be effectively used for predicting the behaviour of moist doughs during the extrusion process while the same model may not be very reliable for drier doughs which show plug flow behaviour during processing.