• Energy Research

Abstract The effects of hydrogen enrichment in a naturally aspirated spark ignition engine fuelled with compressed natural gas were investigated. A mixer that can control the enrichment fraction and assure homogeneity of hydrogen in CNG was used in the experiments. Hydrogen enrichment mitigates some of the inherent problem with natural gas engine by improving combustion due to its higher heating value, wider flammability limits, lower ignition energy and faster flame speed. The work aimed at analyzing effect of hydrogen enrichment between 10% and 30% by volume the on performance and emission at full load conditions across various engine speeds. Results show that hydrogen enrichment leads to gain in volumetric efficiency resulting in more power. High enrichment fraction is more favorable at low speed with respect to output power, while exhaust emissions of CO, CO2 and unburned hydrocarbons decrease with increasing fraction. The optimal engine speed to benefit from this system is 3000 rpm which showed good balance between output power and emissions. The optimal enrichment fraction will depend largely on the engine speed, loads and the intended balance between power and emissions.

The importance of ventilation is highlighted through the recent COVID pandemic particularly in populated societies with crowded buildings. The application of single solar chimney ventilator with and without fin, at different tilt angles, is evaluated for Hong Kong climate using transient 3D validated numerical simulation in present research from energy and environmental viewpoints. The results show that the ventilation performance of the solar chimney ventilator is significantly enhanced by selecting an optimum value for the tilt angle of the chimney. Moreover, the maximum air mass flow rate increases from 0.06 to 0.14 kg/s by reducing the tilt angle from 80° to 20°. Energy saving performance of the solar chimney ventilator with tilt angle of 20° is around 144% higher than that of the solar chimney ventilator with the tilt angle of 80°. During the morning time (sunrise to noon), the highest performance is achieved under the tilt angle of 40°. From the environmental viewpoint, the solar chimney ventilator with the tilt angle of 20° and 40° can prevent 0.098 kg and 0.108 kg CO2 production through the morning. Prevention of the CO2 production through the afternoon is 0.209 kg and 0.151 kg for the mentioned tilt angles respectively.

AbstractWith recent surge in fossil fuel prices and demand for cleaner renewable energy sources, wind turbines have become an alternative technology for power generation. Greenhouse gases such as carbon dioxide (CO2) emitted into the atmosphere contribute to the global climate change. This paper investigates the design of a Savonius type vertical axis wind turbine and its potential to generate power. To enhance the performance of the turbine, a flow restricting cowl is incorporated into the turbine. The airflow behavior of the turbine was investigated both experimentally and computationally. Three different configurations were studied (open position, centred position and a closed position). It is found that a partially cowled turbine in a centred and closed position resulted in a better performance of the turbine than a fully cowled turbine with the same configuration.

Abstract Aero/hydrodynamics plays a vital role in speed sports (athletes, athletes’ outfits, sports balls, sports equipment, etc.). Sports balls (spherical - golf, cricket, tennis, soccer, baseball, softball, etc. and oval shape - rugby, American football, Australian football), sports garments (swimsuits, ski jumping & alpine skiing suits, cycling skin suits, skating suits) are affected by aerodynamic and hydrodynamic behavior of fluids (air and liquids). The aero/hydrodynamics dictates the curved flight path of a soccer, tennis, cricket, baseball or golf ball and the course of a surfboard and sailboat through water. It affects speed, motion (position and placement) and ultimately athlete’s performance. Ignoring the effect of aerodynamic and hydrodynamics, it is almost impossible to achieve the desired success in any competitive speed sports. Due to stiff competition, the outcome of most sports aero/hydrodynamics research work undertaken by commercial organizations as well as individual sports teams/organizations are kept in-house, and scant information is available in the public domain. The RMIT University’s Sports Aerodynamics Research Group has been active in aerodynamics and hydrodynamics research related to some popular speed sports. This paper highlights some research work on sports aerodynamics and hydrodynamics undertaken at RMIT University

Spring-wire has been recently suggested as a turbulator for curved based helical and spiral tubes because of its flexibility nature. Spring-wire can be fabricated by twisting a wire around a rod. However, common circular wire is the only one normally employed in the fabrication process of the spring-wire while the outcomes of this research show that the other wire cross-section shapes can provide much higher thermal performance and Nu number. Novel wire cross-sections for such as triangular, hexagonal, square, and rectangular are numerically simulated in this research (see graphical abstract). All recommended shapes are evaluated from frictional, exergetic and thermal viewpoints for a selected range of Dean number. Nu number of triangular cross section is almost double compared to the common circular cross section. Pressure drop also increases which can be considered as an important criterion depending on the application of the heat exchanger. Interesting thermal-fluid behavior are found through the spiral pipe under the mentioned spring-wire turbulator all of which are reported in this paper.

In this paper, the effect of combined usage of twisted tape turbulators and air injection on the heat transfer augmentation was probed. The tube was under heat flux, which was produced using heater wire. Three twisted tapes with three different pitches were used for conducting the experiments. In order to better understand the flow properties, the flow patterns were recorded utilizing a Canon SX540 camera. Flow patterns, pressure drop, heat transfer coefficient, and cost per benefit ratio factors were the parameters that were studied in this paper. Results showed that the patterns of two-phase flow in the presence of twisted tape turbulator are significantly different from those of smooth tubes. Besides, a significant increment in the heat transfer and pressure drop was observed. It was found that air injection could lead up to 30.3% and 62% increment in the heat transfer coefficient and pressure drop, respectively. The best values of the cost per benefit ratio (C.B.R) factor was about 0.93 and was occurred at the air and water flow rate of 1 and 5 lit/min. This value was reached at the twisted tape turbulator with the largest pitch.

Flow-induced vibrations of a flexible cantilever plate, placed in various positions behind two side-by-side cylinders, were computationally investigated to determine optimal location for wake-excited energy harvesters. In the present study, the cylinders of equal diameter D were fixed at center-to-center gap ratio of T / D = 1.7 and immersed in sub-critical flow of Reynold number R e D = 10 , 000 . A three-dimensional Navier–Stokes flow solver in an Arbitrary Lagrangian–Eulerian (ALE) description was closely coupled to a non-linear finite element structural solver that was used to model the dynamics of a composite piezoelectric plate. The cantilever plate was fixed at several positions between 0.5 < x / D < 1.5 and − 0.85 < y / D < 0.85 measured from the center gap between cylinders, and their flow-induced oscillations were compiled and analyzed. The results indicate that flexible plates located at the centerline between the cylinder pairs experience the lowest mean amplitude of oscillation. Maximum overall amplitude in oscillation is predicted when flexible plates are located in the intermediate off-center region downstream of both cylinders. Present findings indicate potential to further maximize wake-induced energy harvesting plates by exploiting their favorable positioning in the wake region behind two side-by-side cylinders.

Abstract Usual commercial thermoelectric modules are produced in the form of flat shapes. However, tube-bundle arrangement of tubular thermoelectric modules as an air cooler (proposed for the first time in this paper as shown in the graphical abstract) is very meaningful and straightforward compared to the coolers made by flat-shape thermoelectric modules. It is assumed that, the water fluid moves through the inside of the tube-bundle thermoelectric (to adjust the hot surface temperature of the thermoelectric) while the air fluid moves through the outer surface of the tubular thermoelectric (cold side) in cross-section direction. In order to clarify the applicability of the tubular thermoelectric for aforementioned aim, thermal behavior of the tubular thermoelectric legs (in terms of temperature distribution through the legs, heat transfer rate and COP of the cooling process) are comprehensively studied in this paper via a validated 3D numerical simulation by consideration of appropriate boundary conditions. Moreover, geometric characteristics of tubular thermoelectric as an air cooler are investigated and presented in this study which have not been reported before. The results showed that tubular thermoelectric can be appropriately employed for said aim if thermal and geometric parameters are selected in desired range.