Numerical Investigations on the Effects of Transient Heat Input and Loading Conditions on the Performance of a Single-phase Closed-loop Thermo-syphon

One of the most important sources of renewable energy is solar energy, which is readily available throughout the world. There is a requirement to make the solar energy affordable for everyday use in order to minimise the present reliance on fossil fuels. This would also assist in meeting the requirements of limiting greenhouse-gas effects, and hence conserve the environment from pollution, global warming, ozone layer depletion, etc. Thermo-syphons are systems that capture solar energy using a working fluid. In the present study, Computational Fluid Dynamics based solver has been employed to carry out an extensive investigation on the performance analysis of a thermo-syphon operating under transient conditions. There has been limited research conducted on the transient performance of thermo-syphons. This study focuses on the effects of various heat flux inputs and thermal loading conditions on the performance of a closed-loop solar hot water thermo-syphon system. The study reveals that the effect of heat flux input on heat transfer coefficient is dominant as compared to thermal loading. The results provided here can be used to optimally design thermo-syphon systems. Furthermore, it has been demonstrated that Computational Fluid Dynamics can be used as an effective tool to analyse the performance of a thermo-syphon with reasonable accuracy

Numerical studies of the velocity distribution within the volute of a centrifugal pump

Centrifugal pumps play an essential role in engineering systems since they are widely used in the process and power industries. The performance of a centrifugal pump needs to be maximised due to its importance and this depends on the flow structure within the pump. The flow structure within a pump is very complex due to the presence of a rotating impeller and its interaction with the volute casing. In this paper, a numerical investigation using CFD analysis has been carried out to determine the effect of volute geometry on the flow field within a centrifugal pump. The results obtained from the numerical investigation have been validated with the experimental data. Further analyses have been carried out to investigate the effect of volute cross-sectional area on the velocity distribution. The overall results indicate that the head increases as the volute cross-sectional area increases

Effects of Sand Particle Size on the Performance Characteristics of a Vertical Axis Wind Turbine

Vertical Axis Wind Turbines (VAWTs) are used to harness wind energy to meet renewable energy targets. Operations in dusty environments, such as in deserts, could adversely impact on its performance output. In order to analyse this, both clean and dusty environments have been numerically simulated using Computational Fluid Dynamics (CFD) based techniques, where the dusty environments constitute of various sand particle sizes. Comparative studies between clean and dusty environments have been presented. Critical analysis of the erosion rate on a rotor blade of the VAWT has also been carried out. It has been shown that sand particles decrease the torque output of the VAWT. It has also been shown that increase in sand particle size decreases the performance of the VAWT. The results obtained have been used to develop a novel semi-empirical prediction model for the torque output of the VAWT as a function of sand particles’ size

Numerical studies of the velocity distribution within the volute of a centrifugal pump.

Centrifugal pumps play an essential role in engineering systems since they are widely used in the process and power industries. The performance of a centrifugal pump needs to be maximised due to its importance and this depends on the flow structure within the pump. The flow structure within a pump is very complex due to the presence of a rotating impeller and its interaction with the volute casing. In this paper, a numerical investigation using CFD analysis has been carried out to determine the effect of volute geometry on the flow field within a centrifugal pump. The results obtained from the numerical investigation have been validated with the experimental data. Further analyses have been carried out to investigate the effect of volute cross-sectional area on the velocity distribution. The overall results indicate that the head increases as the volute cross-sectional area increases

Comparison of operational effectiveness of a turbocharger volute.

Centrifugal compressors are commonly used across a wide range of applications such as in the automotive industry for engine turbocharging. A turbocharger has four main components i.e. inducer, impeller, diffuser and volute. Turbocharger volutes are commonly designed by neglecting the effects of friction, however, in the real-world, frictional effects have a significant influence on the performance and efficiency of the volute and the turbocharger. This study focuses on the operational effectiveness of the turbocharger volute, making use of two asymmetric type volute models that have been designed for high-pressure centrifugal compressors. For this purpose, advanced Computational Fluid Dynamics (CFD) based techniques have been employed. Three dimensional models of the turbocharger compressor stage have been developed and analysed by monitoring the pressure fluctuations through the volutes. Incorporating frictional effects has been noticed to have prominent influence downstream of the tongue, in the tail of the turbocharger compressor volute. This study shows that designing the turbocharger volute, by overlooking the frictional effects, results in an overestimation of the pressure fluctuations observed within the volute. Therefore, from an operations perspective, it is beneficial to design the volute incorporating frictional effects for high-pressure centrifugal compressor applications

Thermal characterization of commercial electric radiators.

Electric radiators with a storage element are commonly used to provide heating in cold weather. The thermal performance of an electric radiator is dependent on a number of key design features such as the core material, shape of radiator’s outer surfaces, gap between the core and the outer surfaces. The effectiveness of an electric radiator can be improved by optimally designing these key features. Researchers around the world have been working to achieve this using a range of different methodologies. In the present study, two commercial electric radiator models have been considered for their thermal characterisation during their individual heating and cooling cycles. This has been carried out in order to evaluate the thermal behaviour of the two models. To achieve this aim, a purpose built test rig has been developed and the thermal testing has been carried out in a controlled environment. A thermal camera has been used to take thermal images of the front surfaces of the two models at every 5 minutes’ interval enabling quantification of temperature field. It has been observed that the two electric radiator models considered depict different thermal characteristics. The heat dissipation characteristics of both the models have also been noticed to be different to each other

Computational Fluid Dynamics Based Optimal Design of Vertical Axis Marine Current Turbines

Marine turbines are being increasingly used to harness kinetic energy of water and convert it into other useful forms of energy. Widespread commercial acceptability of these machines depends upon their efficiency. This largely depends upon the geometric features of the marine turbines such as number of blades, shape of blades etc. Researchers have been using experimental facilities to optimise these machines for maximum power generation. With the advent of advanced computational techniques, it has now become possible to numerically simulate the flow of water in the vicinity of marine turbines and monitor their performance output. In this work Computational Fluid Dynamics (CFD) based techniques have been used to analyse the effects of number of blades within the stator and rotor, of an in-house built Vertical Axis Marine Current Turbine (VAMCT), on the performance output of the turbine. Furthermore, an effort has been put forward towards better understanding of the flow structure in the vicinity of the blades during transient interaction between rotor and stator blades. This study provides vital information with regards to the flow sensors’ requirements and placements in order to monitor various blade configurations of a VAMCT in real world. The results of this study show that the torque output from a VAMCT is a strong function of blade configurations and there is a significant degradation in the performance output of marine turbines as the inequality between the number of rotor and stator blades increases. Hence, CFD has the potential to optimise the design of marine turbines and can be used as a potential modelling tool in the near future for on-line health monitoring of such systems

FLOW CHARACTERISTICS AND DESIGN METHODOLOGY FOR A CENTRIFUGAL COMPRESSOR VOLUTE

Throughout the years, many studies have been carried out on engines with every effort to save fuel, reduce emissions and produce more power. Turbochargers have been developed and installed in the exhaust system of an engine to use exhaust emissions for boosting power within an internal combustion engine, which would otherwise be wasted. The turbocharger characteristics are essential to determine its performance. There are three stages in a turbocharger, namely being, the turbine stage where energy is extracted from the exhaust gases; bearing housing where energy is being transferred to the compressor stage; and the compressor stage where ambient air is drawn in and compressed to increase the fluids density and pressure prior to being delivered into the intake system. The compressor stage consists of four main components, namely being, the inducer, impeller, diffuser and volute. The volute of a turbocharger compressor is the third most important component within the compressor stage and has therefore, not received the attention that is needed. However, manufacturers are continuously seeking to obtain a realistic design methodology where variables exposed in real conditions, such as frictional effects are accounted for to minimise losses during performance. For this reason, it is essential to develop a thorough understanding of the flow phenomena the turbocharger compressor stage experiences under steady and transient conditions from a macroscopic level to a microscopic level. This creates a solid foundation for conducting the presented research. In this study, a realistic design methodology for a turbocharger compressor volute has been presented. Detailed qualitative and quantitative flow field analyses of the turbocharger compressor stage have been numerically carried out under steady and transient flow conditions using Computational Fluid Dynamics (CFD) based techniques. The numerical investigations carried out in this study allow a clear visualisation of the flow structure within the turbocharger compressor stage volute, which makes it a cost effective method to undertake this research study. Approximations have been presented to design the symmetric and asymmetric type volutes, which have been applied into practice and analysed under steady and transient conditions to validate the presented compressor volute design methodology for turbocharging applications