This paper presents the effect of number of tubes, unequal baffle spacing and tube diameter on heat transfer and pressure drop characteristics of a typical shell and tube type heat exchanger. Upon geometrical optimization, the second phase of this research work aims at studying the influence of Al2O3 nanofluid of 0.5%, 0.75%, 1%, 1.25% and 1.5% concentrations by admitting water along the tubes and Al2O3 nanofluid along the shell side. The shell and tube heat exchangers of various geometrical configurations are modeled using SOLIDWORKS 2015. The heat transfer and fluid flow characteristics through the heat exchanger are obtained by solving the governing equations namely continuity, momentum and energy equations using ANSYS CFX 15 CFD code. Temperature, pressure contours and velocity streamlines along the mid-plane of the shell and tube heat exchanger are obtained for various geometrical configurations and for different volume concentration of nanofluid. The heat transfer coefficient and the pressure drop for various volume fraction concentrations of the nanofluid are plotted. The use of nanofluid resulted in increase of both the pressure drop and heat transfer coefficient. The heat transfer coefficient at 1.25% volume concentration of nanofluid is found to be the optimum value.

The present work is concentrated to study the effect of varying inlet pressures on the dynamics of the suction valve obtained from a hermetic reciprocating compressor. The effect of valve functioning on the efficiency of a compressor is highly acceptable. Rather than the delivery valve, the suction valve has a significant impact on the compressor efficiency. The reed valve in a hermetic compressor is a cantilever type arrangement. The valve operates due to the pressure difference between the suction muffler and the cylinder. The numerical analysis which includes Fluid-structure interaction is used in the present study. The flow and structural domain employed in the present study are modelled with Solidworks 15.0. The fluid structure interaction analysis is a combination of ANSYS Fluent and ANSYS structural. These two are coupled with a system coupling in ANSYS Workbench 16.0. The numerical results obtained from the simulation are validated with the experimental data. The setup consists of a stainless steel reed valve taken from a Samsung model compressor which is attached to a fixed base. Air is taken as working medium and supplied to the valve for measuring the valve lift. The valve lift is measured with a strain gauge fitted on the valve near the fixed end. The results from both the experimental and numerical method are compared to 0.5 bar, and the results are in good agreement. Various parameters like valve deflection, stress on the valve, velocity vectors and pressure contours are plotted. Further, the analysis is carried out for varying pressure from 0.5 bar to 2 bar. Also, the material of the reed valve is changed to Sandvik Hiflex steel which is known for its high fatigue strength and the corresponding results are plotted.

Hermetic reciprocating compressors are widely used in domestic refrigeration systems, and their performance is strongly influenced by suction valve dynamics. Accurate prediction of valve lift, flutter behaviour and backflow losses remains challenging due to the complex fluid–structure interaction (FSI) between the working fluid and the flexible reed valve. Therefore, the present study aims to investigate the influence of compressor speed and valve material on suction valve dynamics using both experimental and numerical approaches. An experimental setup was developed to measure in-cylinder pressure and suction valve lift, while a three-dimensional two-way coupled FSI model was established and validated against experimental measurements. The validated model was subsequently used to investigate the effects of compressor rotational speed and valve material on valve behaviour. The numerical predictions showed good agreement with the experimental results, with deviations of 16.82% for cylinder pressure and 9.57% for valve lift. The results revealed that compressor speed significantly influences valve flutter characteristics, whereas the effect of valve material is comparatively small. Increasing compressor speed reduced valve flutter and improved valve dynamic stability, while the variation in valve lift between stainless steel and Sandvik Hiflex was limited.