Department of Mechanical Engineering

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IIT Jodhpur

The objective of the present work is to study the influence of curvature on local boiling heat transfer coefficient and two-phase pressure drop in helically coiled tubes with water as the working medium. In helically coiled tubes, the geometric parameters like pipe diameter and coil diameter vary the curvature and hence secondary flow which affects the heat transfer distribution and pressure drop. The present work investigates the characteristics of flow boiling in helically coiled tubes. Very less information is available on the influence of curvature on flow boiling system. The local wall temperature is measured not only in the axial direction (along the length of coil) but also in the circumferential direction using thermal imaging technique. Experiments are performed with six helically coiled test sections made of SS 304 tubes having inner diameters varying from 6 to 10 mm. The coil diameter to the tube diameter ratio ranges from 14 to 58 and coil pitch is 50 mm. The effect of geometric and operating parameters like tube diameter, coil diameter, heat flux and mass flux on local boiling heat transfer coefficient and two-phase pressure drop is analysed. In the subcooled region and in a low quality region, boiling heat transfer coefficient in helical coils is much higher (12%–100%) than in straight tubes. However, in a high quality region, the boiling heat transfer coefficient in helical coils is same as in straight tubes. A correlation is suggested for two-phase pressure drop in helical coils. © 2016 Elsevier Masson SAS

World University root node

International Journal of Thermal Sciences

Boiling pressure drop and local heat transfer distribution of helical coils with water at low pressure

Wave energy converter (WEC) devices harness the renewable ocean wave energy and convert it into useful forms of energy, e.g. mechanical or electrical. This paper presents an advanced 3D computational framework to study the interaction between water waves and WEC devices. The computational tool solves the full Navier–Stokes equations and considers all important effects impacting the device performance. To enable large-scale simulations in fast turnaround times, the computational solver was developed in an MPI parallel framework. A fast multigrid preconditioned solver is introduced to solve the computationally expensive pressure Poisson equation. The computational solver was applied to two surface-piercing WEC geometries: bottom-hinged cylinder and flap. Their numerically simulated response was validated against experimental data. Additional simulations were conducted to investigate the applicability of Froude scaling in predicting full-scale WEC response from the model experiments. © 2017 Informa UK Limited, trading as Taylor & Francis Group.

European Journal of Computational Mechanics

Advanced computational simulations of water waves interacting with wave energy converters

In the present experimental study, we investigate thrust production from a pitching flexible foil in a uniform flow. The flexible foils studied comprise a rigid foil in the front (chord length cR) that is pitched sinusoidally at a frequency f , with a flexible flap of length cF and flexural rigidity EI attached to its trailing edge. We investigate thrust generation for a range of flexural rigidities (EI) and flap length to total chord ratio (cr), with the mean thrust (CT ) and the efficiency of thrust generation being directly measured in each case. The thrust in the rigid foil cases, as expected, is found to be primarily due to the normal force on the rigid foil (CTN) with the chordwise or axial thrust contribution (CTA) being small and negative. In contrast, in the flexible foil cases, the axial contribution to thrust becomes important. We find that using a nondimensional flexural rigidity parameter (R∗) defined as R∗=EI.0:5pU2c3F/appears to combine the independent effects of variations in EI and cF=c at a given value of the reduced frequency (k=φfc=U) for the range of cF=c values studied here (U is free-stream velocity; p is fluid density). At k∼6, the peak mean thrust coefficient is found to be about 100% higher than the rigid foil thrust, and occurs at R value of approximately 8, while the peak efficiency is found to be approximately 300% higher than the rigid foil efficiency and occurs at a distinctly different R value of close to 0.01. Corresponding to these two optimal flexural rigidity parameter values, we find two distinct flap deflection shapes; the peak thrust corresponding to a mode 1 type simple bending of the flap with no inflection points, while the peak efficiency corresponds to a distinctly different deflection profile having an inflection point along the flap. The peak thrust condition is found to be close to the 'resonance' condition for the first mode natural frequency of the flexible flap in still water. In both these optimal cases, we find that it is the axial contribution to thrust that dominates (CTACTN), in contrast to the rigid foil case. Particle image velocimetry (PIV) measurements for the flexible cases show significant differences in the strength and arrangement of the wake vortices in these two cases. © 2017 Cambridge University Press.

Journal of Fluid Mechanics

Thrust generation from pitching foils with flexible trailing edge flaps

Volumetric expansion and shrinkage due to different densities of solid and liquid phases are common phenomena during solidification process. Simple analytical models addressing effect of volumetric expansion/shrinkage during solidification are rarely found. The few existing 1-D solidification models are valid only for semi-infinite domain with limitations of their application for finite domain size. The focus of the present work is to develop a 1-D semi-analytical solidification model addressing effects of volumetric expansion/shrinkage in a finite domain. The proposed semi-analytical scheme involves finding simultaneous solution of transient 1-D heat diffusion equations at solid and liquid domain coupled at the interface by Stefan condition. The change of the total domain length during solidification due to volumetric expansion/shrinkage is addressed by using mass conservation. For validation of the proposed model, solidification of water in a finite domain is studied without considering volumetric expansion/shrinkage effect and results are compared with those obtained from existing enthalpy updating based numerical model. After validation, case studies pertaining to volumetric expansion and shrinkage are performed considering solidification of water and paraffin respectively and physically consistent results are obtained. The study is relevant for understanding unidirectional crystal growth under the effect of controlled boundary condition. © 2017 Elsevier B.V.

Physics Letters, Section A: General, Atomic and Solid State Physics

1-D diffusion based solidification model with volumetric expansion and shrinkage effect: A semi-analytical approach

This paper presents a novel and generic reactionless visual servo controller for a satellite-based multi-arm space robot. The controller is designed to complete the task of visually servoing the robot's end-effectors to a desired pose, while maintaining minimum attitude disturbance on the base-satellite. Task function approach is utilized to coordinate the servoing process and attitude of the base satellite. A redundancy formulation is used to define the tasks. The visual serving task is defined as a primary task, while regulating attitude of the base satellite to zero is defined as a secondary task. The secondary task is defined through a quadratic optimization problem, in such a way that it does not affect the primary task, and simultaneously minimizes its cost function. Stability analysis of the proposed control methodology is also discussed. A set of numerical experiments are carried out on different multi-arm space robotic systems. These systems are a planar dual-arm robot, a spatial dual-arm robot, and a three-arm planar robot. The results of the simulation experiments show efficacy, generality and applicability of the proposed control methodology. © 2016 Elsevier B.V.

Robotics and Autonomous Systems

Reactionless visual servoing of a multi-arm space robot combined with other manipulation tasks

With increase in prices of food grains and non-renewable fuel, the scientific community has turned to nature for answers. Biomass and bio-fuel production system must be optimized to enhance bio-fuel production. This can be done with a bio-energy crop production system concentrating on farm profitability and resource energy management. The system defined here stands on climatic and geo-spatial characteristics of potential energy crops, production and availability of infrastructure, socioeconomic parameters, public (subsidies) as well as private fuel consumption, qualitative and quantitative analysis of bio-fuel crops, cultural guards and intrusions. This article presents a linear programming model considering the above parameters as inputs. The model seeks to accurately determine the profitability of each bio-fuel crop pair which can be rotated in a specific geography. Simulations to relate mean distance to bio-refinery and net biomass crop profit are performed for four region specific bio-fuel crop pairs in the United States. The model helps in understanding the connections that agricultural management is having with various parameters connected with production starting from cost of seeds to value of the final biomass in hand. This helps in the derivation of a stochastic model providing an insight on statistical impacts of multiple parameters on improving the feasibility of the proposed bio-fuel production system. This analysis implies closer bio-refinery spacing than current grain elevator spacing under most anticipated circumstances signifying that transportation infrastructure plays a significant, perhaps dominant, role in creating successful regional biofuel production programs and policies.

Optimizing Bio-energy Crop Farm Profitability with Spatial Distribution of Bio-fuel Refinery Sites

Off-white water pots have had sustained traditional acceptance for a long period of time in Jodhpur compared to red colored water pots imported from the neighboring Gujarat state. Both types of pots hold 20 liters of potable water. The fluorescence spectroscopy reveals dominance of silica, alumina and iron oxide in red pots from Gujarat whereas off-white pots from Rajasthan also have a slight excess of CaO and MgO. Fourier transform infrared spectroscopy reveals a firing temperature of 800 °C for off-white pots, which is comparatively less than that for red pots. A lower amount of Fe2O3 and higher MgO in off-white compared to red water pots is responsible for the color differentiation. Off-white pots show a better degree of cooling compared to red pots. Better resistance to load was observed in off-white pots compared to red pots. This study may imply influence of hidden techno-functional aspects towards sustainability of off-white pots in Jodhpur, Rajasthan. © 2017 Materials Research Society.

MRS Advances

Functional Demarcation of Traditional Off-White Colored Water Pots Manufactured from Rajasthan Clayey Soils and Red Colored Water Pots from Gujarat Clayey Soils Using Spectrographic, Cooling and Strength Studies - A Case Study from Jodhpur, Rajasthan, India

The paper discusses the potential ingress and combined effect of moisture and temperature on pre-fatigued glass fibre-reinforced polymers standard test specimens. An experimental investigation was conducted to analyse the behaviour of glass fibre-reinforced polymers' in environmental conditions similar to that of tropical environments. The standard pre-fatigued glass fibre-reinforced polymers specimens were subjected to varying hygrothermal conditions: three different temperatures, i.e. natural bath, 45 °C and 55 °C to study the degradation in strength and related properties. Several macro-structural and micro-structural tests were conducted to determine the damage. The effect of these conditions on characteristics such as diffusivity, weight gain, resin volume fraction, conductivity and deterioration of ultimate tensile strength was determined. The maximum reduction in strength is found to be approximately 39% for the specimen exposed to 55 °C water bath for 60 days. This study shall be helpful in estimating the characteristics of glass fibre-reinforced polymers composites subjected to cyclic fatigue loads in the tropical conditions. © IMechE 2016.

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

Effect of combined fatigue and hygrothermal loading on structural properties of E-glass/polymers

Thermal emittance is an important parameter for the solar thermal collectors as thermal radiative losses from the solar thermal collector increase to the fourth power of temperature. This should be minimized using infrared reflectors in designing spectrally selective absorber coatings for solar thermal applications. The thermal emittance of zirconium (Zr) film as an infrared reflector has been investigated for the use in the spectrally selective absorber. The Zr metallic films are deposited using DC magnetron sputtering process on stainless steel and glass substrates and the deposition process has been optimized to achieve the minimum thermal emittance. The effect of structural, microstructural and surface morphological properties of Zr films is investigated on the emittance of fabricated structures. The X-ray diffraction analysis revealed that the Zr film coatings consist of both cubic and hexagonal Zr crystallographic phase. The optimized deposition time and temperature showed 0.12 and 0.14 emittance values for Zr film coatings on stainless steel and glass substrates respectively. © 2017 Elsevier B.V.

Department of Mathematics

Department of Physics

Thin Solid Films

Optimization of sputtered zirconium thin films as an infrared reflector for use in spectrally-selective solar absorbers

In surface modification applications, cermets such as Cr3C2–NiCr are used to enhance the wear resistance of the substrate. Friction surfaced cladding is a recently developed solid-state surface modification process in which the deposition of the clad layer is accomplished below it’s melting temperature, so that degradation of the substrate is minimized. The present investigation discusses the friction surfaced cladding of Cr3C2–NiCr using consumable die steel rod. It was observed from the micrographs, that with the suitable combination of tool plunging rate (plunging speed), tool rotational speed and traverse rate, successful cladding of Cr3C2–NiCr was achieved. A plan of full factorial experiment was followed for determining the process variables for the successful deposition of Cr3C2–NiCr clad layer with the substrate. A mathematical model was developed to predict the composite clad dimensions and microhardness with respect to the process variables. Depending upon the process parameter, it was observed that the hardness of the clad and clad geometrical feature varied. The microstructural analysis exhibited sound and uniform bonding of clad layer to the substrate and near uniform distribution of Cr3C2–NiCr. Desirability based multi-response optimization procedure was followed to arrive at optimized Cr3C2–NiCr clad. © 2016, The Indian Institute of Metals - IIM.