Hanim Salleh

The transient response for different types of erodable surface thermocouples using finite element analysis

The transient response of erodable surface thermocouples has been numerically assessed by using a two dimensional finite element analysis. Four types of base metal erodable surface thermocouples have been examined in this study, included type-K (alumel-chromel), type-E (chromel-constantan), type-T (copper-constantan), and type-J (iron-constantan) with 50 mm thick- ness for each. The practical importance of these types of thermocouples is to be used in internal combustion engine studies and aerodynamics experiments. The step heat flux was applied at the surface of the thermocouple model. The heat flux from the measurements of the surface temperature can be commonly identified by assuming that the heat transfer within these devices is one-dimensional. The surface temperature histories at different positions along the thermocouple are presented. The normalized surface temperature histories at the center of the thermocouple for different types at different response time are also depicted. The thermocouple response to different heat flux variations were considered by using a square heat flux with 2 ms width, a sinusoidal surface heat flux variation width 10 ms period and repeated heat flux variation with 2 ms width. The present results demonstrate that the two dimensional transient heat conduction effects have a significant influence on the surface temperature history measurements made with these devices. It was observed that the surface temperature history and the transient response for thermocouple type-E are higher than that for other types due to the thermal properties of this thermocouple. It was concluded that the thermal properties of the surrounding material do have an impact, but the properties of the thermocouple and the insulation materials also make an important contribution to the net response.

The effect of scratch technique on the thermal-product value of temperature sensors

The effect of different scratch techniques, mainly abrasive papers and scalpel blades used to form the junctions of temperature sensors, on the thermal-product value of these sensors, was examined. A dynamic calibration procedure of scratched sensors in a shock tube facility which allows easy evaluation of their thermal-product value is outlined. The thermal product of a particular sensor was found to be dependent on the flow Mach number, junction scratch technique, junction location, and also on the enthalpy conditions. It was shown that using different scratch techniques normally results in different thermal-product values of sensors. The experimental procedure used in the present study has yielded practical data on characteristics of scratched temperature sensors; these data can be used in accurate measurement of transient heat transfer under hypersonic flow conditions.

Fast response surface temperature sensor for hypersonic vehicles1

This paper describes the design, fabrication, and evaluation technique of fast response Surface Temperature Sensor (STS). This STS was made of chromel-constantan elements with 2.2 and 0.8 mm in diameter. The calibration technique using shock tube facility for measuring the transient surface temperature and heat transfer rate is also presented. It has been proved that the STS response time is very short (less than 50 µs), and a rise time in studies of a transient surface temperature is less than 0.5 µs.

Effect of cantilever shape on the power output of a piezoelectric bimorph generator

This paper discusses the effect of the cantilever shape of piezoelectric bimorph bender on the power output. ANSYS® program was used to study the distribution of stress strain in each model design and MATLAB® program was used to simulate the effect of each variable on the output power. Triangular, rectangular and trapezoidal cantilevers were chosen with wide range of frequencies between (50Hz – 150 Hz) with the same input excitation conditions and same volumetric size, to analyze the effect of each design in the power. The result shows that maximum stress-strain value can be produced in the triangular shape with equal distribution on all the surface area. The analytical simulation showed that the maximum value of power of 5 mW at 85 Hz was produced by the triangular cantilever beam. Thus, triangular shape can produce maximum power comparing with the others.

Dynamic calibration and performance of reliable and fast-response coaxial temperature probes in a shock tube facility

An experimental dynamic calibration technique of reliable, rugged, low-cost, and fast-response coaxial temperature probes is presented. These probes were successfully designed and fabricated in-house, in conjunction with its signal processing circuit, which can be used for transient heat transfer measurements in a hypersonic testing facility. These probes have a response time less than 50 μs with a rise time less than 0.3 μs. Two types of scratches were used, mainly abrasive papers with different grit sizes and scalpel blades with different thicknesses to form the probe junction. The effect of the scratch technique on the probes thermal product is investigated. The probes were tested and calibrated in the test section and end wall of the UNITEN shock tube facility at different axial and radial locations. The effects of placing the coaxial temperature probe at different axial and radial distances, different working fluids, and different Mach numbers on the transient surface temperature rise were examined. It was observed from the dynamic calibration results that the thermal product of a particular coaxial temperature probe depends on Mach number, junction scratch technique, and junction location, as well as on the enthalpy conditions. It was also noticed that the calibrated coaxial temperature probe using the scalpel blade technique with a particular blade size gives consistent thermal product values. Thus, it does not require an individual calibration. However, for a coaxial temperature probe whose junction was created using the abrasive paper technique with different grit sizes, a calibration for each coaxial temperature probe is likely to be needed.

Approaches and developments in MEMS power harvesting generators

This paper presents designs and optimizations for two types of micro electromechanical generators system, first one is the narrow band generators which have a particular resonant frequency the second one is wide band generators (tunable generators) where the resonant frequency can be controlled by adjusting the cantilever length, changing the distance between magnets, and etc. The work and developments done by researchers are presented and for comparison, their results are listed below: The Laser-micro generator was fabricated with a total volume of 1cm3, output power of ∼830µW, frequencies (60 – 110) Hz. The output power of the (body-worn) generator was 2–25 µW, volume of 0.25 cm3. The vibration-powered generator for intelligent sensor systems has an overall volume of 0.84 cm3 with an average power of 157 µW when tested on a car engine. One type of Paddle generator produced an output power of 2 mW at a frequency of 9.81 kHz. In the frequency sweeper generator, the device generates 0.4 µW with frequency range of 4.2–5 kHz. For Tunable energy harvesting piezoelectric cantilever generator, a natural frequency was successfully tuned over a frequency range of 22–32 Hz to produce power output of 240–280 µW. The resonant frequency of the vibration-based electromagnetic micro-generator was tuned from 67.6 to 98 Hz to produce a power of 61.6–156.6 µW. The tuning of the wide band generators seemed to be effective.

Theoretical modeling and simulation of MEMS piezoelectric energy harvester

Energy harvesting devices, capable of converting wasted ambient energy to electrical power are rapidly gaining popularity as a source of green and renewable energy. This work presents the design and simulation of MEMS based piezoelectric cantilever beam which can both harvest energy as well as monitor critical vibration frequencies in power plant gas turbines. The design of the energy harvesters consists of a cantilever beam structure with the interdigitated electrodes on the zinc oxide piezoelectric layer with nickel proof mass at the end of the beam. A mechanical finite element simulation was conducted using CoventorWare¯. This paper illustrates the proposed theoretical modeling and simulation of piezoelectric energy harvesters.

Comparison of energy harvesting power management techniques and application

There has been a significant increase in the research on energy harvesting device for low power applications in recreant years. This is due to smaller electronics power applications such as wireless and mobile electronics and the demand for better lifespan of batteries. One of the challenges of the harvesting energy from ambient is to convert, transfer and store the usable power effectively. In this context, there is a need to understand and design and efficient energy harvesting power management circuitry. In view of the issues, this paper compares several energy harvesting power management techniques and applications. Based on the comparison, suggestion on the design improvement are also included. This paper proposed improvement on the adaptive circuit as to get better efficiency. This paper will propose by using full bridge AC-DC rectifier to convert AC input voltage to usable DC voltage. In order to reduce power consumption of the circuit and power losses, comparator circuit is implementing as an adaptive approach to the DC-DC step-down converter. Simulation results are presented that output voltage from power management energy harvesting circuit is 3.0V with output power is 30mW. The efficiency reported as 80%. The total power losses are 7.5mW. Lastly this design presents a stand-alone system, single supply voltage and compatibility for micro-scale circuit integration.

Structural Modification Strategies to Improve Piezoelectric Energy Harvester Performance

Harvesting energy from vibrations has received massive attention due to it being a renewable energy source that has a wide range of applications. Over the years of development, there is always research to further improve and optimise piezoelectric energy harvesters. This paper presents work on improving piezoelectric energy harvesters based on the structural modifications. Four different strategies of structural modification are employed for optimization by using additional beam structure as well as incorporation of rubber layer. This work summarized the optimum performance of the strategies at a resonance frequency of 60 + 2 Hz at 0.25g. The parameters compared among the strategies are voltage, power, PZT power density, spatial power density and specific power density. The results are also compared with other similar work. In general, structure with an addition of silicon rubber beam was found to give the best power density output and produce 253% increase of power ouput as compared to basic PZT energy harvester.

Enhancement of piezoelectric energy harvester power density using natural rubber

Development of an energy harvesting system has become crucial due to the advancement of electronic devices. Vibration based Energy Harvesting has received growing attention over the last decade. Lead Zirconate Titanate (PZT) sheet used as the active material of the energy harvester. However it has limited power density and it is rather brittle. Thus, the purpose of this work is to enhance the PZT energy harvester power density using natural rubber. The natural rubber addition is in the foam of specific latex as Medium Rubber Latex. The PZT was dipped in the latex to form 1 to 4 layers and shaked at acceleration of 0.25g and 1g. It was found that the percent voltage increase was in between 1.4% to 18% at natural frequency of 55 to 60Hz. Also, the power density was increased in between 10.7% to 38%.