Heat and Mass Transfer Enhancement in Rotating Disk Systems

Abstract

The design of an efficient cooling system comprising of a rotating disk arrangement is essential owing to the ever-growing demand in the power output and thermal efficiency of turbomachinery systems, gas turbine, transport engineering, chemical engineering, aircraft engineering, rotating disk contractors, and many other rotating heat exchanging devices. The engineering sophistication and economic incentives of industries do also require to improve the performance of heat exchangers in order to obtain the optimum use of energy, and materials, to achieve further thermal control, and to meet the compactness requirements. Ranging from the simple turbomachinery to the state - of - the - art aerospace vehicles most of the practical rotating systems have strong connections with the rotating disk configuration, either rotating freely or in a housing. This signifies the importance of the geometrical configuration of rotating disk system as it relates to a large number of practical applications, namely, spin coating, rotational air-cleaners, disk drivers, atomizers, jet cooling, food processing, rotating machinery, medical equipment and many more. Further understanding of the convective transport mechanism due to a rotating disk, whose surface is flat and also not essentially flat, is an important area of research. Explanation to the non-trivial augmentation in heat transfer and the identification of the agents contributing there are the fundamental reasons behind this study. Therefore, the present monograph focuses on the prediction of the enhanced heat transfer rate in some complex flows arising in the rotating disk system as it directly links to the cooling performance of such systems. On the other hand the consequential mitigation of environmental degradation has provoked many techniques of heat transfer augmentation. In this context, different approaches, such as active, passive and combined (i.e. both active and passive), techniques are employed to achieve the heat transfer augmentation. The primary objective of this work is to investigate the impact of non-homogenous distribution of nanoparticles, non-uniform disk temperature distribution, disk transpiration, waviness of the disk and the external forced flow to the rotating disk geometries. The detailed discussion of obtaining the heat transfer enhancement via Nanofluid is given in Chapter 2 where the weak prediction of homogeneous models (as compared to non-homogeneous model) on heat transfer enhancements is identified. Almost 67% enhancement in heat transfer rate is noted for the non-uniform nanoparticle distribution (non-homogeneous modeling) for some fixed values of the involved parameters whereas the uniform distribution (homogeneous model) yields only 22% which signifies the role of nanoparticle distribution in heat transfer augmentation. The research work presented in Chapter 2 are published in Thermal Science: Year 2018, Vol. 22, No. 6A, pp. 1-16. Some new classes of rotating disk temperatures have been considered in Chapter 3 due to which increased heat transfer rates were noticed. For instance, exponentially increasing disk temperature of a free rotating disk in the quiescent air yields 27% augmentation in heat transfer rate while a radially increasing non-linear disk temperature corresponds to 15% intensification in heat transfer rate as compared to isothermal disk. The heat transfer augmentation has also been acquired by the mass addition/removal to flow inside the gap between a cone and a disk. Chapter 4 highlights this analysis in detail. A serious lack of work is felt in the study of surface roughness effects on rotating disk boundarylayer and this is focused in Chapters 5 and 6. The sinusoidal-shaped (wavy) disk has been opted as it can be dealt quite easily with the mathematical modeling. A comprehensive discussion has been made in the aforementioned Chapters highlighting the role of surface texture in different flow regimes like non-isothermal distribution of disk temperature and under uniform forced flow. The findings of Chapter 5 are published in International Journal of Heat and Mass Transfer: Year 2019, Vol. 129, pp. 96-102. Finally, inferences are drawn in the Conclusions section which are very helpful in order to understand the heat transfer enhancement mechanisms in rotating disk systems. It is important to mention here that the existence of the analogy between convective heat and mass transfer phenomena leads this study to cover the topic of mass transfer in a rotating disk systems as well.