A Novel Technique to Reduce Measurement Errors due to Flow–Sensor Interactions in Multi-‎Sensor Conductivity Probes

Multi-sensor conductivity probes rely on multiple sensors intruding into the flow field for the measurement of conductivity variations. This may cause sensors to deflect due to flow-sensor and flow-body interactions. Since this deflection relocates the sensor tips causing inaccuracy in the flow property measurements, many techniques have been used to overcome this issue [1-6]; such as increasing the sensors diameter and reducing the sensors length. However, most of these methods increase the bubble-sensor interactions. In the present work, a novel technique has been developed with the aid of Computational Fluid Dynamics (CFD) and Finite Element Analysis (FEA) based solvers to reduce the errors that may arise because of the sensor’s and probes body’s deflections. The developed technique compensates for the errors within the signal processing stage. The CFD model has been validated against experimental data obtained from the literature. Different variables have been investigated to quantify the sensor tip relocation process as a function of pipe diameter, flow velocity and radial probe locations. The results have been presented in the form of mathematical equations using multiple variable regression analyses, and thereafter embedded into the signal processing code

Design, Development and Application of a Novel Seven-Sensor Probe System for the Measurement of Dispersed Phase Flow Properties in Multiphase Flows

Local measurements of the dispersed phase properties in air-water bubbly flows are of primary importance to understand the hydrodynamic characteristics of multiphase flows. One of the essential requirements in designing multiphase flow systems is to determine its flow regime since many constitutive models are flow regime dependent. In bubbly multiphase flow, the bubble diameter plays a vital role in hydrodynamics of flow. In this study, a novel invasive measuring instrumentation system has been designed and developed to determine the bubble size and shape accurately by minimising the effects of the bubble-sensor interactions. This instrumentation system has been used to determine the effects of the bubble size on the volume fraction distribution and the hydrodynamic behaviour of air-water two-phase flow. The novelty of this probe arises from the fact that the data is collected from the first bubble-sensor contact, unlike the previous methods in which the data has been collected from two points namely, first when the sensors’ tips immersed a bubble and second when the sensors’ tips left the bubble. The seven-sensor conductivity probe subsequently has been used to determine the dispersed phase local parameters. These parameters include bubble velocity, time-averaged local void fraction and bubble shape and size. The data from this probe has been acquired using National Instruments Data Acquisition (DAQ) and LabVIEW software. The experiments have comprised of two methods, namely bubble column and flow loop. For the bubble column experiments, a new image processing code has been developed for capturing the dispersed phase properties, including the void fraction from the images that have been captured by the high-speed cameras. From the comparison between both methods, the seven-sensor probe and the high-speed camera measurements, good agreement has been achieved. In the flow loop experiments, the novel seven-sensor probe system has been used for measuring the dispersed phase properties from the first bubble sensor contact; moreover, the effect of variation of gas superficial velocity, with the values of 0.05, 0.07 and 0.1 m/s, on the dispersed phase properties have been also investigated

Effect of the shape of connecting pipes on the performance output of a closed-loop hot water solar Thermo-syphon

In order to conserve the environment from pollution, which is caused by the use of the fossil fuels, numerous research works have been carried out in renewable energy area to minimize the dependency on the fossil fuels. There are several energy sources naturally available, and solar energy is considered to be the best amongst them. Therefore it became a motivating area for the researchers in recent years. Thermo-syphon is one of many devices that use solar energy for power generation. Thermo-syphon converts solar energy into internal energy of the working fluid; mainly water. In this work, a computational fluid dynamics (CFD) code has been used to analyse the natural convection phenomenon in a thermo-syphon. The thermo-syphon model consist of steel pipes with an internal diameter of 25mm, along with a condenser having diameter equal to five times the pipe’s diameter, has been considered. The study has been carried out under no-loading conditions, for two thermo-syphon models comprising of straight and helical shaped pipes of 10, 20 and 30. A practical solar heat flux of 500W/m2 has been applied on the pipes. The numerical results depict that the working fluid within the condenser, in case of helical pipes, gains higher temperature as compared to the straight pipes. Furthermore, increase in the number of helical pipes has negligibly small effect on the temperature of the fluid within the condenser, and hence on the performance output of the thermo-syphon

Flow diagnostics

The measurement of flow properties within fluid handling systems is of utmost importance for efficient operation and control of such systems. For single phase flow systems, extensive research has been carried out world over to diagnose the flow properties both globally and locally. Considerable advancements are being made to perfect these technologies. For multiphase flows there is still a lot of scope for technological development that needs to take place to diagnose the flow conditions accurately efficiently and effectively. In this present paper two methods are described that can be used effectively for measurement of flow properties in solid-liquid flows and gas-liquid flows. One of the methods relies on isokinetic sampling used in conjunction with impact probe for the determination of solid distribution and solid velocity in solid-liquid flows through a pipeline. The other method relies on electrical resistance method to calculate local flow velocity corresponding to the dispersed phase as well as volume fraction and interfacial area concentration

Effect of a swirl on void fraction profiles in multiphase flows

In this paper, experimental and numerical analyses of bubbly air-water flow in a vertical pipe at low volumetric flow rates has been carried out to quantify the effect of swirl on void fraction profiles. These investigations have been carried out at a dispersed phase volume fraction of 0.051% and at superficial flow velocities of 0.041 m/s for air and 0.76 m/s for water. The investigations revealed that the presence of swirl alters the volume fraction profiles considerably