Jai P. Gupta

Bio: Jai P. Gupta is an academic researcher from Shiv Nadar University. The author has contributed to research in topics: Poison control & Boiling. The author has an hindex of 22, co-authored 57 publications receiving 1355 citations. Previous affiliations of Jai P. Gupta include Texas A&M University System & Texas A&M University.

A model for transitional breakage probability of droplets in agitated lean liquid-liquid dispersions

Abstract: A model for transitional breakage probability of droplets in agitated lean fiquid-liquid dispersions is proposed based on the mechanism of breakage of droplets due to their oscillations resulting from relative velocity fluctuations. A universal transitional breakage probability in terms of non-dimensionalized drop diameter is derived for all dispersed phases whose density and viscosity are almost the same as that of continuous phase. The maximum stable drop diameter ds derived from the model, shows a dependence of NWe−0.6. It is shown that a “power law” approximation Kvn is valid for transitional breakage probability for d/ds up to 2. The exponent 2.67, predicted by this model corresponds rather well with an estimate of 2, obtained from experimental observations. A functional relation for the rate constant K in terms of the parameters and physical properties of the system is derived. A universal non-dimensionalized equilibrium drop-size distribution for agitated lean liquid-liquid dispersions is derived by analytical solution of a population balance equation simplified by order of magnitude estimates. Interestingly enough, this analytical solution is the same as the Gaussian distribution suggested empirically by Chen and Middleman.

A simple graphical method for measuring inherent safety

Abstract: Inherently safer design (ISD) concepts have been with us for over two decades since their elaboration by Kletz [Chem. Ind. 9 (1978) 124]. Interest has really taken off globally since the early nineties after several major mishaps occurred during the eighties (Bhopal, Mexico city, Piper-alfa, Philips Petroleum, to name a few). Academic and industrial research personnel have been actively involved into devising inherently safer ways of production. The regulatory bodies have also shown deep interest since ISD makes the production safer and hence their tasks easier. Research funding has also been forthcoming for new developments as well as for demonstration projects.A natural question that arises is as to how to measure ISD characteristics of a process? Several researchers have worked on this [Trans. IChemE, Process Safety Environ. Protect. B 71 (4) (1993) 252; Inherent safety in process plant design, Ph.D. Thesis, VTT Publication Number 384, Helsinki University of Technology, Espoo, Finland, 1999; Proceedings of the Mary Kay O'Connor Process Safety Center Symposium, 2001, p. 509]. Many of the proposed methods are very elegant, yet too involved for easy adoption by the industry which is scared of yet another safety analysis regime. In a recent survey [Trans. IChemE, Process Safety Environ. Prog. B 80 (2002) 115], companies desired a rather simple method to measure ISD. Simplification is also an important characteristic of ISD. It is therefore desirable to have a simple ISD measurement procedure. The ISD measurement procedure proposed in this paper can be used to differentiate between two or more processes for the same end product. The salient steps are: Consider each of the important parameters affecting the safety (e.g., temperature, pressure, toxicity, flammability, etc.) and the range of possible values these parameters can have for all the process routes under consideration for an end product. Plot these values for each step in each process route and compare. No addition of values for disparate hazards (temperature, pressure, inventory, toxicity, flammability, etc.) is being suggested to derive an overall ISD index value since that conceals the effects of different parameters. Further, addition of numbers with different units ( degrees C for temperature, atm/bar for pressure, t for inventory, etc.) is inappropriate in scientific sense. The proposed approach has a major advantage of expanding consideration in future to incorporate economic, regulatory, pollution control and worker health aspects, as well as factors such as the experience one has or 'the comfort level' one feels with each of the processes under consideration. Additionally, it would also guide the designers and decision makers into affecting specific changes in the processes to reduce the unsafe features. We demonstrate our simple approach by using the example of six routes to make methyl methacrylate as documented by Edwards and Lawrence [Trans. IChemE, Process Safety Environ. Protect. B 71 (4) (1993) 252; Quantifying inherent safety of chemical process routes, Ph.D. Thesis, Loughborough University, Loughborough, UK, 1996] and show that the decision could well have been different if addition of disparate hazards had not been done.

Analysis of drop size distributions in lean liquid‐liquid dispersions

Abstract: Experimental measurements of transient drop size distributions in a stirred liquid-liquid dispersion (with low dispersed phase fraction) have been used concomitantly with population balance theory to recover the transition probability of droplet breakage, based on a similarity concept. The data remarkably uphold the proposed similarity hypothesis, and the estimated probability function displays the same qualitative trend as the model due to Narsimhan et al. (1979).

Site Security: for Chemical Process Industries

Abstract: Chemical process industries such as oil refineries, fertiliser plants, petrochemical plants, etc., which handle hazardous chemicals, are potential targets for deliberate actions by terrorists, criminals and disgruntled employees. Security risks arising out of these threats are real and must be assessed to determine whether the security measures employed within the facility are adequate or need enhancement. The essential steps involved are threat analysis, vulnerability analysis, security countermeasures, and emergency response. Threat analysis involves the study of identifying sources, types of threats, and their likelihood. Vulnerability analysis identifies the weaknesses in a system that adversaries can exploit. Depending on the threat likelihood and vulnerabilities, various security countermeasures are suggested to improve the plant security. Appropriate emergency response measures that could mitigate the consequences of a successful attack and concepts of inherently safer processes in the light of process security are also discussed in the paper. It is recognised that serious terrorist threats exist to the transport system of hazardous chemicals (by road, rail cars, ships, pipelines, etc.). However, that is not a part of this study, which concentrates on process plants and hazardous materials within immovable boundaries. A case study of a fertiliser plant is used to show the application of ideas presented.

Inherently Safer Design—Present and Future

Abstract: Inherently Safer Design (ISD) has evoked deep interest in the process industries since the 1990s. Two books and many articles have been written about it and a few specific conferences have been held on the topic. However, its adoption by industry appears to be less than expected. In order to increase its adoption by industry and to make ISD more user friendly, the UK Engineering and Physical Sciences Research Council (EPSRC) has funded a project at Loughborough University. As a first step, we desired to know the status of use of ISD in industry, its teaching and research in academies, and the role of the regulators in its adoption. We also wished to discover the reasons for slow adoption, obtain views on how to increase it and find out about successful applications. To do this, we carried out a survey amongst industrialists, academics and regulators. We enlisted the help of numerous research and trade journals, professional conferences and web sites. 63 completed responses were received from 11 countries representing a whole spectrum, from those who have only recently heard of ISD to those who have practised it successfully for over two decades. Several responders said that they will henceforth start to use ISD. Most were either not familiar with the indices developed for ISD or thought them too complicated. Amongst the reasons cited for limited adoption were: lack of case studies dealing with economic benefits; lack of a tried and tested yet simple methodology of application; lack of desire to change; lack of knowledge about ISD amongst research chemists, engineers, managers and regulators; no enforcing regulation; lack of specific research funds for academics in this area, etc. Tackling these will result in the spread of ISD. Suggestions are made towards achieving this end.

A fixed grid numerical modelling methodology for convection-diffusion mushy region phase-change problems

Abstract: An enthalpy formulation based fixed grid methodology is developed for the numerical solution of convection-diffusion controlled mushy region phase-change problems. The basic feature of the proposed method lies in the representation of the latent heat of evolution, and of the flow in the solid-liquid mushy zone, by suitably chosen sources. There is complete freedom within the methodology for the definition of such sources so that a variety of phase-change situations can be modelled. A test problem of freezing in a thermal cavity under natural convection is used to demonstrate an application of the method.

Enthalpy-porosity technique for modeling convection-diffusion phase change: application to the melting of a pure metal

Abstract: The melting of pure gallium in a rectangular cavity has been numerically investigated using the enthalpy-porosity approach for modeling combined convection-diffusion phase change. The major advantage of this technique is that it allows a fixed-grid solution of the coupled momentum and energy equations to be undertaken without resorting to variable transformations. In this work, a two-dimensional dynamic model is used and the influence of laminar natural-convection flow on the melting process is considered. Excellent agreement exists between the numerical predictions and experimental results available in the literature. The enthalpy-porosity approach has been found to converge rapidly, and is capable of producing accurate results for both the position and morphology of the melt front at different times with relatively modest computational requirements. These results may be taken to be a sound validation of this technique for modeling isothermal phase changes in metallurgical systems.

On the solution of population balance equations by discretization—II. A moving pivot technique

Abstract: A new framework for the discretization of continuous population balance equations (PBEs) is presented in this work. It proposes that the discrete equations for aggregation or breakage processes be internally consistent with regard to the desired moments of the distribution. Based on this framework, a numerical technique has been developed. It considers particle populations in discrete and contiguous size ranges to be concentrated at representative volumes. Particulate events leading to the formation of particle sizes other than the representative sizes are incorporated in the set of discrete equations such that properties corresponding to two moments of interest are exactly preserved. The technique presented here is applicable to binary or multiple breakage, aggregation, simultaneous breakage and aggregation, and can be adapted to predict the desired properties of an evolving size distribution more precisely. Existing approaches employ successively fine grids to improve the accuracy of the numerical results. However, a simple analysis of the aggregation process shows that significant errors are introduced due to steeply varying number densities across a size range. Therefore, a new strategy involving selective refinement of a relatively coarse grid while keeping the number of sections to a minimum, is demonstrated for one particular case. Furthermore, it has been found that the technique is quite general and yields excellent predictions in all cases. This technique is particularly useful for solving a large class of problems involving discrete-continuous PBEs such as polymerization-depolymerization, aerosol dynamics, etc.

A novel concept for convective heat transfer enhancement

Abstract: An analog between convection and conduction with heat sources is made to have a further understanding of the mechanism of convective heat transfer. There are three ways to raise the strength of heat sources/convection terms, and consequently to enhance the heat transfer: (a) increasing Reynolds and/or Prandtl number, (b) increasing the fullness of dimensionless velocity and/or temperature profiles, (c) increasing the included angle between the dimensionless velocity and temperature gradient vectors. Some approaches of heat transfer enhancement are suggested based on such a novel concept of heat transfer enhancement.

A literature review of theoretical models for drop and bubble breakup in turbulent dispersions

Abstract: This paper presents a literature review on mechanisms and models for the breakage of bubbles and drops (fluid particles) in turbulent dispersions. For the mechanisms, four categories are summarized, namely, turbulence fluctuation, viscous shear stress, shearing-off process and interfacial instability. The models for breakup frequency and daughter size distribution available in literature are reviewed thoroughly. The development and limitation of the existing models are studied and possible improvements are proposed.