- Research Article
- Open Access
Development of a gas/liquid phase change actuator for high temperatures
© Matsuoka et al. 2016
Received: 19 May 2015
Accepted: 7 January 2016
Published: 16 January 2016
Gas/liquid phase changes produce large volume changes in working fluids. These volume changes are used as the driving power sources in actuators such as micro-pumps and valves. Most of these actuators are utilized in ordinary temperature environments. However, the temperature range in which the phase change actuator can operate depends on the characteristics of the working fluid. We hypothesized that proper selection of the working fluid and the structure of the actuator can enable such actuators to be applied not only in ordinary environments but also in high temperature environments. Consequently, in this paper, we discuss the design and fabrication of a new gas/liquid phase change actuator for use in high temperature environments. Our proposed actuator consists of a bellow body, spring, heater, and working fluid. We used the Inconel super alloy, which is highly heat and corrosion resistant, for the bellow and moving parts of the actuator. For the working fluid, we prepared triethylene glycol, which has a boiling point of 287.3 °C and very low vapor pressure at ordinary temperature. As a result, our proposed actuator can be utilized in high temperature environments up to 300.0 °C. The results of several experiments conducted confirm that our proposed actuator generates 1.67 mm maximum displacement in a 300.0 °C atmospheric environment. In addition, we confirmed that the operation of the actuator is stable in that environment. Our results confirm that a gas/liquid phase change actuator can be used in high temperature environments.
Phase changes in materials, resulting from temperature changes, produce huge volume changes, especially in liquid/gas phase changes. This attribute is utilized to provide a power source for micro-pumps and valves in combination with MEMS (micro-electromechanical system) heaters, micro-channels, diaphragms, and membranes [1–10]. Kato et al. used this phenomenon to provide a power source for actuators and robots. They made a metal bellow actuator to control cutting equipment and a pipe inspection robot [11, 12]. Phase change is used not only in actuators but also in some kinds of pressure sources. For example, Kitagawa et al. used the triple point of carbon dioxide as a mobile pressure source , and Shibuya et al. developed a buoyancy control device for underwater robots using paraffin oil .
The actuators described above were developed for use in ordinary environments. In contrast, our aim is to utilize these phase change actuators in special environments. In particular, driving actuators in high temperature environments is a typical example of the special environments being considered. For example, in the hydrothermal synthesis method, which is one of the methods used to fabricate piezoelectric devices, the water solution inside the high temperature chamber needs to be agitated . In one instance where this process was used, the water solution was agitated using an autoclave—an end-over-end shaker with heat. Fabrication of the (Pb, La)(Zr, Ti)O3 (PLZT) film took 24 h. Not only the rotation condition but also the attitude of the sample will affect the quality of the fabrication. The actuators, which produce the inclination of the shaker, are predictably effective devices. Another example is the fabrication process for the ferric oxide crystal via the floating-zone melting method . In this process, the partially melted sample is turned and pulled inside the chamber for growth. Both the processes require 8–24 h and a single directional drive in order to fabricate the tiny sample. We believe that an actuator that can realize linear motion in high temperature environments can rectify these quality problems.
In previous work, we targeted these environments for utilization of actuators and proposed gas/liquid phase change actuators. We subsequently fabricated an actuator driven by the gas/liquid phase change of water. This actuator consisted of a cylinder as a vessel and actuation device, an external heater to excite the phase change, and a spring that controlled the speed of motion. Our proposed actuator was driven in a 180 °C environment. Thus, we realized directional motion with gas/liquid phase changes in a high temperature environment using that actuator [17, 18].
In this paper, we discuss the development of another actuator for utilization in high temperature environments. Our proposed actuator is composed of an Inconel alloy bellow (which is highly heat and corrosion resistant), a spring, a heater with built-in temperature sensor, and working fluid. The bellow produces direct motion without friction when it is moving. This friction is significant in cylinder type actuators; it can cause leaking of the working fluid and disturb the motion of the actuator. Although it has the same bellow shape, our proposed actuator can be sealed very easily and has a more simplified structure.
Springs change the speed of an actuator; when a hard spring is attached, the actuator is driven at a slow speed. Conversely, a soft spring produces a high speed for the actuator. These characteristics were confirmed in our previous study.
In this paper, we explain how we chose the new working fluid to facilitate operation of the actuator in high temperature environments. The triethylene glycol (TEG) working fluid has a liquid phase and a boiling point of 287.3 °C under ordinary atmospheric pressure conditions . These characteristics enable our proposed actuator to operate in a 300.0 °C environment.
In experiments conducted, in which the actuator was driven in a 300.0 °C atmospheric temperature environment by a heater assembled in the actuator, a maximum displacement of 1.67 mm with 2700 J of input power was produced. The results confirmed that our new gas/liquid phase change actuator can be driven in 300.0 °C high temperature environments with TEG working fluid.
Basic principle underlying the gas/liquid phase change actuator
Our proposed actuator is driven by the gas/liquid phase change of its working fluid. When the working fluid is heated, its vapor pressure increases and pushes out the chamber.
A bellow is a variable volume vessel. In previous work, we used a cylinder, but this structure has a sliding member in its body. As a result, there was much friction when it was being driven and the working fluid also leaked. Considering the application of our actuator to high temperature environments, we surmised that these issues would be a bottleneck. Consequently, we designed the bellow to be driven without friction because the expansion and contraction characteristics of a bellow are produced by its distinctive structure. In addition, the chamber also includes the spring properties itself.
The characteristics of the actuator also depend on the properties of the working fluid. The inherent vapor pressure curve of the working fluid determines the driving temperature range of the actuator. Thus, by selecting an appropriate working fluid, we can set the operating temperature range of the actuator.
Various kinds of modes of heating exist; for example, fire, electrical heating, chemical reaction, induction heating, Peltier heating, and IR light.
In our previous work, we confirmed the adequacy of these fundamental characteristics of gas/liquid phase change actuators and designed an actuator that could be driven by the phase change of water in a 180.0 °C environment.
Design of the actuator
The bellow, the most important part of the actuator, was fabricated using Inconel 600 super alloy—an austenite Nickel–Chromium based alloy. The target temperature, 300.0 °C, is the temperature used for low temperature annealing of stainless steel. This heat treatment process causes stainless steel to lose its corrosion resistance and its mechanical properties to change. By contrast, Inconel alloy has better corrosion and heat resistance than stainless steel as a result of its stable passivating oxide layer. Hence, we chose Inconel super alloy for the actuator. This bellow had outer diameter 22.0 mm, inner diameter 15.2 mm, and length 65.0 mm—with a welded 40 mm diameter flange and a tiny cap, 0.12 mm double layer thickness wall, 19 replications, and a 13.5 N/mm spring constant. The working fluid was poured into this chamber.
The compression coil spring was set on the top of the bellow. This spring was made from oil tempered SiCr-alloyed valve spring wire (SWOSC-V). When the actuator is driven, the bellow extends, and the spring is compressed. Consequently, the spring constant of the actuator is calculated by summing those of the bellow and the spring.
Basic characteristics of TEG
−14.3 °C/287.3 °C
Coefficient of expansion
Experiments and properties of the actuator
Static properties of the actuator
In this experiment, 15.9 g of degassed TEG was poured into the bellow and the actuator sealed while ensuring that no air was included. TEG has a thermal expansion ratio of 7.2 × 10−4/°C at 55.0 °C . Thus, an increase in temperature from room temperature to 300.0 °C results in a 22 % increase in the volume of TEG.
The SWOSC-V spring, with a spring constant of 13.9 N/mm, was inserted into the chassis. As discussed previously, the spring constant of an actuator has a small temperature dependence. In this case, a temperature increase from 25.0 to 300.0 °C resulted in a decrease in the spring constant from 27.4 to 26.1 N/mm.
Dynamic properties of the actuator
We proposed a new actuator that is driven by the gas/liquid phase of a working fluid for high temperature environments. Phase change actuators are driven by the heating of working fluids; thus, their characteristics depend on the characteristics of the working fluid and the springs that produce the reactive force against the vapor pressure.
We designed and fabricated an actuator that can be utilized in a 300.0 °C high temperature environment. The actuator consists of a bellow body, spring, heater with a built-in temperature sensor, and TEG working fluid. The bellow was fabricated from Inconel super alloy, which is highly heat and corrosion resistant, and can generate displacements without friction. The TEG working fluid has a very low vapor pressure at ordinary temperature and a boiling point of 287.3 °C. Consequently, the proposed actuator is controllable in 300.0 °C temperature environments.
The results of static evaluation of the characteristics confirmed that the theoretical properties are consistent with the experimental results. The actuator is heated by atmospheric temperature and produces a displacement using both vapor pressure and thermal expansion of the working fluid.
We operated this actuator using a heater assembled in the actuator in several temperature environments. The results showed that the actuator can be driven in all the environments tested. In the 300.0 °C environment, the actuator generated 1.67 mm maximum displacement using 2700 J of input power. In addition, we operated the actuator fitfully five times in a 300.0 °C environment in exactly the same condition. The results of this examination confirmed that the actuator is stably driven.
Thus, our proposed gas/liquid phase change actuator is suitable for operation in 300.0 °C environments. In order to put this actuator to practical use, the operating time needs to be reduced and a controlling system added. We believe that this actuator can be driven in even higher temperature environments in the future.
HM carried out design, experiment, evaluating of the actuator and drafted the manuscript. KS and TK conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.
HM was born in July 3, 1986. He received his B. Eng. and M. Eng. from Okayama University, Japan in 2010 and 2012, respectively. He has been a doctoral student at the graduate school of Okayama University since 2012. His current research interest is in the area of actuators for special environments.
KS was born in 1959. He received a Doctor’s Degree from Yokohama National University in 1990. He worked for the Toshiba R&D Center from 1984 to 2001 and for the Micromachine Center, Tokyo, from 1999 to 2001. He was a professor at Okayama University, Japan since 2001–2014. He has been a professor at Tokyo Institute of Technology, Japan since 2014. He is a member of the Japan Society of Mechanical Engineers, the Robotics Society of Japan, IEEE and the Institute of Electrical Engineers of Japan.
TK was born in Fukuoka, Japan, on June 18, 1972. He received his B. Eng., M. Eng., and Dr. Eng. in precision machinery engineering from the University of Tokyo, Japan in 1997, 1999, and 2002, respectively. From 2002 to 2007, he was a research associate and lecturer at Okayama University, Japan. Since 2007, he has been an associate professor at Okayama University. His research interests are micro sensors, micro actuators, micro systems, and piezoelectric film. He is a member of the Japan Society for Precision Engineering, the Institute of Electrical Engineers of Japan, IEEE, the Japan Society of Mechanical Engineers, and the Robotics Society of Japan.
We sincerely appreciate the help received from Dr. Y. Sakata and Mr. Y. Yamada through valuable discussions held. This study was partly supported by the Fluid Power Technology Promotion Foundation.
The authors declare that they have no competing interests.
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