Abstract-Body sensor networks are increasingly popular in healthcare, sports, military and security. However, the power supply from conventional batteries is a key bottleneck for the development of body condition monitoring. Energy harvesting from human motion to power wearable or implanted devices is a promising alternative. This paper presents an airflow energy harvester to harness human motion energy from footstep. An air bladder-turbine energy harvester is designed to convert the footstep motion into electrical energy. The bladders are embedded in shoes to induce airflow from foot-strike. A ducted radial-flow turbine is employed to generate electrical energy from airflow. The design parameters of the turbine rotor, including blade number, the inner diameter of the blades, were optimized using computational fluid dynamics (CFD). A prototype was developed and tested with footsteps from a 65 Kg person. The peak output power of the harvester was first measured with different resistors. The value was 90.6 mW with a 30.4 Ω load. The harvested energy was then regulated and stored in a power management circuit. 14.8 mJ energy was stored in the circuit from 165 footsteps, which means 89.7 µJ was obtained per footstep. The regulated energy was finally used to fully power a fitness tracker which consists of a pedometer and a Bluetooth module. 7.38 mJ was consumed by the tracker per Bluetooth configuration and data transmission. The tracker operated normally with the harvester working continuously.
A turbocharger turbine in an internal combustion engine is fed with continuously pulsating flow due to nature of the exhaust flow of a reciprocating engine. It is generally acknowledged that the performance of the turbine deteriorates due to this pulsation. In order to address the problem, a novel pulse-optimized flow control method is introduced in this paper, which involves a specially-designed nozzle ring upstream of the radial or mixed flow turbine. Unlike a traditional turbocharger, in which the nozzle ring is stationary, the nozzle ring is rotating. The inception of this new flow control method is based on the fact that the variable magnitude of the unsteady exhaust flow can be converted into the variation of the flow angle by means of the rotating nozzle ring. The new method is then validated by a steady-state, single passage numerical model. Calculations with different nozzle rotating speeds under both high and low mass flow rate conditions were executed and the results demonstrated significant improvements in both stage efficiency and power output. The results predicted that the new pulse-optimized flow control method was able to enhance the turbocharger performance to a great extent by means of addressing the potential energy within the highly dynamic exhaust flows.
The turbocharger is continuously fed with highly unsteady exhaust flow from a reciprocating engine. Despite that, the pulsating exhaust flow can provide more kinetic energy to the turbine compared with the moderated flow in a constant pressure turbocharging, it still significantly deteriorates the efficiency of the turbocharger, as the turbocharger turbine works at off-design point at most instances in an exhaust cycle. In order to address the issue, a novel mechanism named ‘rotating nozzle ring’ has been developed. It was shown that by rotating a nozzle ring around the turbine, the deviation of the flow angle from the design point can be reduced and, therefore, the performance of the turbocharger can be improved. This novel idea is further presented in this paper, by introducing a passive control method to control the speed of the rotating nozzle ring. It will be demonstrated that the rotating nozzle ring can be controlled by the exhaust flow by means of pre-setting a particular nozzle angle, and the rotation will stabilise at an approximately constant speed. An optimised nozzle profile will also be presented, with the intention to reduce the incidence loss on the rotating nozzle ring. A detailed full-stage computational fluid dynamics model will be built to investigate this passive control method. Results of both quasi-steady and transient calculation will demonstrate that, the passively controlled rotating nozzle ring can effectively suppress the unsteadiness level of turbine’s unsteady operation. As a result, the performance of the turbocharger turbine is improved, with the variation of the velocity ratio through a pulse cycle reduced by 8.5% and the isentropic energy weighted cycle averaged efficiency increased by 4.7%, compared to a traditional stationary nozzle ring.
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