An Experimental Study of Bubble Rise Characteristics in non – Newtonian (Power-Law) Fluids

Air bubbles are used in chemical, biochemical, environmental, food process such as sugar industries for improving the heat and mass transfer. In particular, the bubble rise characteristics in massecuite - a fluid made from sugar crystals and sugar syrup have a great influence on vacuum pan operation which is an important process for the production of raw sugar in sugar industries. An experimental study of the bubble rise characteristics in xanthan gum solutions, a non-Newtonian (Power-Law) massecuite equivalent fluid are presented in this paper. The main characteristics, i.e. the bubble velocity, the bubble trajectory, and the drag relationship were investigated as a function of volume of air bubbles. The bubble rise velocity and trajectory were measured using a combination of non-intrusive (high speed photographic) method and digital image processing. The parameters that significantly affect the rise of air bubble are identified. The effect of different bubble volumes and liquid heights on the bubble rise velocity and bubble trajectory are analysed and discussed. A relationship between the Reynolds number and the drag coefficient is presented and discussed

A comparative study of bubble rise phenomena in water and low concentration polymer solutions

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.Bubbles are used in polymer, metallurgy, biotechnology and especially in process industries for improving the heat and mass transfer from a dispersed gaseous phase to viscous liquid phase. A comparative study of the bubble rise characteristics in water and a few selected low concentration polymer solutions is presented in this paper. The characteristics, namely, the bubble velocity, the bubble trajectory, the bubble volume and the drag relationship are investigated. The experiments were conducted in 125 mm cylindrical column at liquid heights of 1 m, 1.2 m, 1.4 m and 1.6 m by introducing different bubble volumes (from 0.1 mL to 5.0 mL ) corresponding to each height. The bubble rise velocity and trajectory were measured using a combination of non-intrusive (high speed photographic) method and digital image processing. The parameters that significantly affect the rise of air bubble are identified. The effect of different bubble volumes and liquid heights on the bubble rise velocity and bubble trajectory are analysed and discussed. The correlation between the Reynolds number and the drag coefficient is developed and presented. The results of this study are compared with the results of other analytical and experimental studies available in the literature.cs201

Thermal performance modelling of data centre– a case study

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.This paper presents a computational study of thermal modelling of the data centre located at CQUniversity, Rockhampton Campus, Australia. The data centre was modeled and analyzed using computational fluid dynamics (CFD) model to study the effectiveness of cooling within the racks and aisles of the centre. CoolSim- software was used for designing a graphical user interface (GUI) that allows data centre components to be positioned, sized and characterized in a plan view. Modelling of airflow and temperature distribution in the data centre was performed using the CFD code Fluent. The CFD model based on thermal mass and energy balance principles was calibrated with the actual measurements of energy consumption, pressure and temperature from a standard rack filled with a set of rack mounted processor and storage units. The simulation results identified the potential high temperature zone within the computer rack in the data centre, and provide a detailed 3D analysis of how cold air is moving through the data centre. The results also provide the performance analysis of computer room air conditionings (CRACs), detailed rack-by-rack inlet and exit temperatures and 3D thermal mapping of the data centre and racks highlighting trouble areas. The model developed was capable of evaluating the airflow rates and thermal loads for optimizing and designing a new or existing data centre.dc201

Analysis and comparison of engine performance and exhaust emissions of internal combustion engine for three different fuel efficiency devices

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.The engine performance and exhaust emissions characteristics of an internal combustion engine using three different fuel efficiency devices, namely Hiclone, Supermax and FFC are analyzed compared and discussed in this paper in order to identify the best fuel efficiency device among three. The testing was done in a 2.4L 4-cylinder Toyota Camry 2AZ- FE engine. The procedure recommended by Environmental Protection Agency (EPA) Aftermarket Retrofit Device Evaluation Program was used for engine testing. All the results obtained were when the devices were fitted and compared with results when no device was fitted with the engine. This study found that there is no significant increase/decrease of brake power, brake torque, fuel consumption and exhaust emissions for these fuel efficiency devices. Further study is recommended in order to come to an acceptable conclusion.dc201

Modelling of baffles in electostatic precipitator (ESP0 to achieve optimum flow distribution

Papers presented to the 11th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 20-23 July 2015.Electrostatic Precipitators (ESP) are the most reliable emission control devices that are used in coal fired power plants to capture fine particles for reducing exhaust emission. Its efficiency is more than 99% or more. However, capturing submicron particles are still a problem due to complex flow distributions and design limitations of ESP. In this study, two different shapes of baffles inside the ESP have been considered to assess their influence on the flow pattern using computational fluid dynamics (CFD) code ‘ANSYS FLUENT’.. Due to different shapes, the flow distribution will be changed inside the ESP which is expected to affect and increase the residence time of flue gas. The results of this paper indicate that the proposed shapes can influence in collecting more fine particles.am201

Numerical modeling of vertical earth pipe cooling system for hot and humid subtropical climate

Energy crisis is one of the major problems facing the progress of human society. There are several energy-efficient technologies that can be applied to save energy and make a sustainable environment. Passive air cooling of earth pipe cooling technology is one of them to reduce the energy consumption for hot and humid subtropical climates. The technology works with a long buried pipe with one end for intake air and the other end for providing air cooled by soil to the desired space such as residential, agricultural, or industrial buildings. It can be an attractive economical alternative to conventional cooling since there are no compressors or any customary mechanical unit. This chapter reports the performance of a vertical earth pipe cooling system for a hot and humid subtropical climatic zone in Queensland, Australia. A series of buried pipes were installed in vertical arrangement in order to increase earth pipe cooling performance. To measure the performance of the system, a numerical model was developed and simulated using the CFD software Fluent in ANSYS 15.0. Data were collected from two modeled rooms built from two shipping containers and installed at the Sustainable Precinct at Central Queensland University, Rockhampton, Australia. The impact of air temperature and velocity on room cooling performance has also been assessed. A temperature reduction of 1.82 °C was observed in the room connected to the vertical earth pipe cooling system, which will save the energy cost for thermal cooling in buildings

A landscape review on biodiesel combustion strategies to reduce emission

The study presents state-of-the-art literature on biodiesel combustion strategies for improving engine performance and reducing emissions. The application of those strategies in compression ignition engines is a prominent approach to reducing harmful emissions. The literature reveals that biodiesel can significantly reduce CO, HC, and PM emissions. However, the higher NOxemission characteristics of biodiesel compared to fossil fuel is a concerning factor for its application. In addition, its physicochemical properties have also shown some complications during the combustion process. This article covers fundamental aspects, challenges, prospects, and the pros and cons of advanced biodiesel combustion strategies such as low-temperature combustion (LTC), chamber modifications, and injection modifications that directly influence combustion rate and emission formation. In addition, the exhaust gas after-treatment systems and the effect of operating parameters are briefly discussed and presented in this article. The study found that LTC strategies and retarded injection timing showed significant reductions in NOxemission in the leaner mixtures but with poor combustion control. Besides, chamber modifications and higher injection pressure showed better combustion through high turbulence and swirl rates, but leading to more NOxemission. The review critically analyzed those strategies and concluded that incorporating leaner mixture combustion with chamber modifications will form better combustion under low in-cylinder temperature conditions, favoring reducing the NOxemission. Finally, the study recommends that more studies are needed to obtain a low in-cylinder temperature atmosphere by altering the equivalence ratio and optimizing the chamber (geometry and nozzle) modifications and varying injection parameters with biodiesel to reduce emissions

A hydrogen supply-chain model powering Australian isolated communities

This article proposes a supply chain-based green hydrogen microgrid modelling for a number of remote Australian communities. Green hydrogen can be used as an emissions-free fuel source for electricity generation in places where large-scale renewable energy production is impossible due to land availability, population, or government regulations. This research focuses on the Torres Strait Island communities in northern Australia, where the transition from diesel to renewable electricity generation is difficult due to very limited land availability on most islands. Due to geographical constraints, low population and smaller electrical load, the green hydrogen needs to be sourced from somewhere else. This research presents a green hydrogen supply chain model that leverages the land availability of one island to produce hydrogen to supply other island communities. In addition, this research presents a model of producing and transporting green hydrogen while supplying cheaper electricity to the communities at focus. The study has used a transitional scenario planning approach and the HOMER simulation platform to find the least-cost solution. Based on the results, a levelised cost of energy range of AU$0.42 and AU$0.44 was found. With the help of a green hydrogen supply chain, CO2 emissions at the selected sites could be cut by 90 %. This study can be used as a guide for small clustered communities that could not support or justify large-scale renewable generation facilities but need more opportunities to install renewable generation