Client
Hythane
Project Objectives
- Determine the technical viability of an acoustic based gaseous hydrogen sensor
- Design a prototype hydrogen sensor
- Determine the following for the sensor
- Size or spatial resolution of the sensor
- Hydrogen concentration resolution
- Hydrogen concentration range
- Temporal resolution
- Estimates of durability and range of operating environmental conditions
- Initial cost estimates for prototypes and volume production
Summary of Project and Results (Non-Confidential)
- Constructed a hydrogen sensor consisting of two piezoelectric transducers separated by a plastic tube
- A binary mixture of hydrogen and nitrogen was introduced into the plastic tube
- A voltage impulse was delivered to one transducer and then the voltage response of the second transducer was recorded
- The physics of the hydrogen sensor are as follows:
- The speed of sound in a gas is a function of the square root of the average molecular weight of the gas
- Hydrogen has a relatively small molecular weight of 2 compared to the molecular weight of other large common gases
- As the hydrogen concentration in a binary mixture changes, the speed of sound of the mixture will change
- Therefore the time of flight of an acoustic wave between two transducers can be used to determine the hydrogen concentration in a binary mixture
- The relatively large molecular weight difference between hydrogen and other common gases can provide adequate sensitivity in most cases for an accurate hydrogen sensor
- The voltage impulse delivered to the first transducer excited the transducer and the connecting plastic tube. A train of acoustic waves propagated through the binary mixture of gases to the second transducer. The acoustic waves then excited the second transducer.
- The response of the second transducer was recorded by an analog to digital acquisition system. The resolution of the A/D system was 1 nanosecond.
- The time of flight as defined by the difference in time between the initial voltage impulse to the first transducer and the first rising wave of the second transducer was recorded
- The hydrogen concentration of the binary mixture was systematically varied and the time of flight of the sensor was measured
- A length of the sensor or distance between the transducers was chosen to match a size criteria for the sensor
- A hydrogen concentration resolution of the sensor was determined and this corresponded to the temporal resolution of the A/D acquisition system
- The hydrogen concentration measurement range of the sensor was also determined. At very high concentrations of hydrogen it was found that the sensor was not very sensitive. It was determined that the response of the piezoelectric transducers was very low at high concentrations of hydrogen. The transducers had been designed to have a large resonant response in air. The high speed of sound of pure hydrogen moved the transducer response out of the resonant range. Piezoelectric transducers specifically designed for high hydrogen concentrations can be used to provide a hydrogen sensor for the corresponding hydrogen levels.
- The temporal response of the sensor was also measured. The temporal response was determined by the rate dissipation of the acoustic waves. After the waves had dampened, another trigger impulse was sent the first transducer and the response of the second transducer was measured. This process was continually repeated and provided a very fast sensor.
- An estimate of the cost to build a series of prototypes of the sensor was made. In addition, the cost to obtain UL and CE compliance was determined.
- The range of operating environmental conditions for the sensor was estimated
- The results of the project were as follows:
- Initial design of the hydrogen sensor
- Estimates of durability and range of operating environmental conditions
- Size or spatial resolution of the sensor
- Hydrogen concentration resolution
- Hydrogen concentration range
- Temporal resolution
- Initial cost estimates for prototypes and volume production
- The end result of this project was that an acoustic based hydrogen sensor may provide a marketable product and economic opportunity. The sensor is inexpensive with high hydrogen concentration resolution, range, and fast response.
