A wax motor is a
linear actuator
A linear actuator is an actuator that creates motion in a straight line, in contrast to the circular motion of a conventional electric motor. Linear actuators are used in machine tools and industrial machinery, in computer Peripheral, periphera ...
device that converts
thermal energy
The term "thermal energy" is used loosely in various contexts in physics and engineering. It can refer to several different well-defined physical concepts. These include the internal energy or enthalpy of a body of matter and radiation; heat, d ...
into
mechanical energy
In Outline of physical science, physical sciences, mechanical energy is the sum of potential energy and kinetic energy. The principle of conservation of mechanical energy states that if an isolated system is subject only to conservative forces, t ...
by exploiting the phase-change behaviour of
wax
Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to giv ...
es.
During melting, wax typically expands in volume by 5–20% .
A wide range of waxes can be used in wax motors, ranging from highly refined hydrocarbons to waxes extracted from vegetable matter. Specific examples include
paraffin wax
Paraffin wax (or petroleum wax) is a soft colorless solid derived from petroleum, coal, or oil shale that consists of a mixture of hydrocarbon molecules containing between 20 and 40 carbon atoms. It is solid at room temperature and begins to m ...
es in the straight-chain n-alkanes series. These melt and solidify over a well-defined and narrow temperature range.
Design
The principal components of a wax motor are:
*An enclosed volume of
wax
Waxes are a diverse class of organic compounds that are lipophilic, malleable solids near ambient temperatures. They include higher alkanes and lipids, typically with melting points above about 40 °C (104 °F), melting to giv ...
*A plunger or stroke-rod to convert the thermo-hydraulic force from the wax into a useful mechanical output
*A source of heat such as:
**Electric current; typically a
PTC thermistor
A thermistor is a type of resistor whose resistance is strongly dependent on temperature, more so than in standard resistors. The word thermistor is a portmanteau of ''thermal'' and ''resistor''.
Thermistors are divided based on their conduction ...
, that heats the wax
**Solar radiation; e.g. greenhouse vents
**Combustion heat; e.g. excess heat from internal combustion engines
**Ambient heat
*A
sink
A sink is a bowl-shaped plumbing fixture for washing hands, dishwashing, and other purposes. Sinks have a tap (faucet) that supply hot and cold water and may include a spray feature to be used for faster rinsing. They also include a drain t ...
to reject heat energy such as:
**Convection to cooler ambient air
**
Peltier effect
The thermoelectric effect is the direct conversion of temperature differences to electric voltage and vice versa via a thermocouple. A thermoelectric device creates a voltage when there is a different temperature on each side. Conversely, when ...
device arranged to transfer heat energy away
When the heat source is energized, the wax block is heated and it
expands, driving the plunger outwards by volume displacement. When the heat source is removed, the wax block contracts as it cools and the wax solidifies. For the plunger to withdraw, a biasing force is usually required to overcome the mechanical resistance of seals that contain the liquid wax. The biasing force is typically 20% to 30% of the operating force and often provided by a mechanical spring or gravity-fed dead weight applied externally into the wax motor .
Depending on the particular application, wax motors potentially have advantages over magnetic solenoids:
*They provide a large hydraulic force from the expansion of the wax in the order of 4000 N (corresponding to roughly 400 kg or 900 lb at standard gravity) .
*Both the application and the release of the wax motor is not instantaneous, but rather, smooth and gentle.
*Because the wax motor is a
resistive
The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels ...
load rather than an
inductive load, wax motors controlled by
TRIAC
A TRIAC (triode for alternating current; also bidirectional triode thyristor or bilateral triode thyristor) is a three terminal electronic component that conducts current in either direction when triggered. The term TRIAC is a genericised tradem ...
s do not require
snubber
A snubber is a device used to suppress ("snub") a phenomenon such as voltage transients in electrical systems, pressure transients in fluid systems (caused by for example water hammer) or excess force or rapid movement in mechanical systems.
Ele ...
circuits.
*Wax motors can be operated entirely passively by exploiting ambient sources of energy. Given that a variety of melting-points are possible for the wax used inside the motor, one can be selected to match the range of ambient operating temperatures in a given application. In this way the wax can be melted and solidified within this range by the transfer of thermal energy. When co-located with the heat source, wax motors can be operated without the need for an additional external power source.
Applications
Aerospace Controls
Wax motors are used heavily in the aerospace industry where they are utilized to control fuel, hydraulic, and other oils critical to safe flight today in modern airplanes.
Mixing Valves - HVAC
Wax motors are contained inside "self actuating"
thermostatic mixing valve
A thermostatic mixing valve (TMV) is a valve that blends hot water with cold water to ensure constant, safe shower and bath outlet temperatures, preventing scalding.
The storage of water at high temperature removes one possible breeding ground ...
s, where the wax motor senses thermal change and responds accordingly to yield a desired mixed fluid temperature.
Laundry washing machines
Some front load
washing machine
A washing machine (laundry machine, clothes washer, washer, or simply wash) is a home appliance used to wash laundry. The term is mostly applied to machines that use water as opposed to dry cleaning (which uses alternative cleaning fluids and ...
s use wax motors to engage the door lock assembly. When a cycle is started, a wax motor is actuated pushing a pin outward and locking the door. This design has cost, reliability and safety advantages. In moist conditions a wax motor costs less for equivalent reliability than an electromagnetic solenoid or motor latch. It has a predictable passive release delay. If power is lost the door remains briefly locked, designed to be longer than the high speed spin cycle coast-down time, then reliably unlocks as the wax cools.
Water heating systems
Wax motors are also commonly used to drive
zone valve
Zone or The Zone may refer to:
Places Climate and altitude zones
* Death zone (originally the lethal zone), altitudes above a certain point where the amount of oxygen is insufficient to sustain human life for an extended time span
* Frigid zone, ...
s in
hydronic
Hydronics () is the use of liquid water or gaseous water (steam) or a water solution (usually glycol with water) as Heat transfer, heat-transfer medium in heating system, heating and cooling systems. The name differentiates such systems from Oil ...
(hot water) heating systems.
Dishwashers
They are used in many
dishwasher
A dishwasher is a machine that is used to clean dishware, cookware, and cutlery automatically. Unlike manual dishwashing, which relies heavily on physical scrubbing to remove soiling, the mechanical dishwasher cleans by spraying hot water, ...
s to release the detergent dispenser door latch. The wax motor acts like a
solenoid
upright=1.20, An illustration of a solenoid
upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines
A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
when activated by the dishwasher's timer or control, and the piston operates the mechanism which then releases the catch for the dispenser door. They are also used to control the exhaust vent for the drying cycle.
Greenhouse vents
Wax motors are widely used to operate the temperature regulating vents of greenhouses.
In this application, as the ambient temperature within the greenhouse increases, the wax melts, activating the plunger and opening the vents. When the greenhouse temperature has cooled sufficiently, the wax cools and solidifies, allowing the vents to close again.
Paraffin microactuator
A paraffin microactuator is a type of wax motor, often fabricated by
microelectromechanical systems
Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...
(MEMS) technology or sometimes
precision mechanics
Precision mechanics (also "fine mechanics") is an engineering discipline that deals with the design and construction of smaller precision machines, often including measuring and control mechanisms of different kinds.
The study may be further defi ...
.
See also
*
Wax thermostatic element
The wax thermostatic element was invented in 1934 by Sergius Vernet (1899–1968). Its principal application is in automotive thermostats used in the engine cooling system. The first applications in the plumbing and HVAC, heating industries were i ...
References
*
*
*{{cite web , url=https://ntrs.nasa.gov/search.jsp?R=19880012086 , last=Tibbitts, first=Scott , year=1988 , title=High output paraffin actuators: Utilization in aerospace mechanism , location=Hanover, MD , publisher=NASA Center for AeroSpace Information (CASI) , website=NASA Technical Reports Server , access-date=May 31, 2019
External links
Wax Motor Manufacturer - Rostra VernathermGeneral Thermal Actuator - Wax Motor InformationWax Motor and Thermoactuator Manufacturer , iSwell img title="ISwell Thermoactuator"; style="text-decoration: none; height:150px;float: left; padding: 0px 3px 0px 0px;"src="https://upload.wikimedia.org/wikipedia/commons/4/4e/ISwell_Thermoactuator.jpg" >
Actuators