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The present investigation aims to reuse the heat rejected in the condenser unit of an NH3-based dairy plant to preheat the groundwater used for pasteurization of milk. A detailed thermodynamic analysis (both energetic and exergetic) of the refrigeration unit of an existing dairy plant and the boiler unit used for pasteurization is carried out in the current work. The chemical exergy of the air–water vapour mixture and the standard Indian coal is considered while analysing the evaporative condenser and the boiler unit. Cascading of the existing system with a transcritical vapour compression cycle is proposed to effectively use the heat rejected by the combined system to preheat the boiler feed water. A comparative study for different modifications, such as the inclusion of an expander and an ejector in place of the throttle valve in the top cycle of the proposed cascade system, is carried out. Additionally, the cascade systems are being analysed for two different refrigerants, i.e., CO2 and N2O. The study demonstrates that the cascade system with an expander employing N2O as the refrigerant gives the maximum benefit in terms of saving of $16.5 to $21.5 per day, 1.5 to 2% reduction in total CO2 emission, and a 2.5% reduction in total exergy destruction, as compared to the existing NH3 system. [ABSTRACT FROM AUTHOR]

Pressure-driven, shear-driven and combined pressure and shear driven flow of a non-Newtonian Sisko fluid through rectangular channels is investigated. Inclusion of the aspect ratio in the formulation yields a highly nonlinear partial differential equation, which is not reported in the existing literature. Thus, neither analytical nor numerical solution to this equation is available in the open literature. In the present study, the partial differential equation, describing the flow, is solved employing the finite difference method. Explicit method is adopted, and the solution for the non-dimensional velocity and wall shear stress is obtained. An exact solution for the flow of a Sisko fluid, for a special case (for non-Newtonian index 2), through large parallel plates (aspect ratio to be zero) is obtained. Expression for the friction factor, including the effect of the aspect ratio, is given. The effects of the aspect ratio, Sisko fluid parameter, non-Newtonian index on the non-dimensional velocity distribution and shear-stress distribution are analyzed both for shear-thinning and shear-thickening fluids. The results indicate that for pressure-driven flow, the effect of the aspect ratio on the velocity is negligible when it is less than 0.1. In case of shear-driven flow and combined pressure and shear driven flow also, the characteristics of flow through large parallel plates exist in nearly 50% of the channel for the aspect ratio of 0.1 or less, which means that for up to 50% of the channel, near the core, the parallel plates assumption will generate reasonably accurate results. [ABSTRACT FROM AUTHOR]