A thermokinetic model for dropwise condensation on a planar substrate with conical pores

Within the framework of the classical theory of heterogeneous condensation, a thermokinetic model has been developed for dropwise condensation on a planar substrate with conical pits. The development or the dissolution of the nucleated droplet is accounted due to both interfacial and peripheral mass transfer and by considering various geometric configurations, i.e. formed droplet within the conical pore, at the pore edge, and outside the pore respectively. Along with the principle of exergy maximization, detailed-balance-based kinetic approach has been employed to investigate the influence of the pore size and the substrate wettability on the thermokinetics of droplet nucleation of water vapor. The available energy for droplet formation and the time rate of nucleation are obtained. The twice-nucleation phenomenon is supposed to take place for some particular pore sizes and its thermokinetic trait is different from that obtained from the classical condensation theory. For a given conicity, there is an appreciable amount of reduction in the free energy barrier with increase in the contact angle. The slant height of the conical pit is found to have a great influence in the condensation enhancement or suppression. The barrier reduces considerably when the slant height reduces. These outcomes indicate a physical insight into the context of surface engineering for the promotion or the hindrance of dropwise condensation on real or engineered surfaces.Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .International centre for heat and mass transfer.American society of thermal and fluids engineers

Modelling Process Robustness: A Case Study of Centrifugal Casting

A robust process minimises the effect of the noise factors on the performance of a product or process. The variation of the performance of a robust process can be measured through modelling and analysis of process robustness. In this paper, a comprehensive methodology for modelling and analysis of process robustness is developed considering a number of relevant tools and techniques such as multivariate regression, control charting and simulation within the broad framework of Taguchi method. The methodology as developed considers, in specific terms, process modelling using historical data pertaining to responses, inputs variables and parameters as well as simulated noise variables data, identification of the model responses at each experimental setting of the controllable variables, estimation of multivariate process capability indices and control of their variability using control charting for determining optimal settings of the process variables using design of experiment-based Taguchi Method. The methodology is applied to a centrifugal casting process that produces worm-wheels for steam power plants in view of its critical importance of maintaining consistent performance in various under controllable situations (input conditions). The results show that the process settings as determined ensure minimum in-control variability with maximum performance of the centrifugal casting process, indicating improved level of robustness