# Mission Possible/Thermal Devices

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## Heating devices

### Nichrome wire

 Heated Nichrome wire Nichrome is metal that is usually formed into either wire or a thin strip. It is a resistive heater, meaning that when power is passed through it, the wire heats up. By hooking a circuit with nichrome wire up to a battery, heat can be quickly generated to affect bimetallic strips, melt fishing line, burn string, light candles/matches, and other possible applications.

### Peltier device

 Generic peltier module A Peltier device is an electrically operated device where, if a voltage is applied, one side of the device gets hot and the other side gets cold. As it is a type of thermocouple, it may or may not be allowed, depending on the year's rules.

#### Acquisition

Small electric cooling pads (talking about active cooling here, not just fans) may be using a Peltier device. Beverage heaters/warmers usually use resistive heaters, so those won't help you.

As of this writing, these surplus retailers offered Peltier devices. Just search for "peltier" or "thermoelectric".

Most other surplus electronics retailers probably carry them too. Expect to pay $10 to$15 dollars for a small one.

### Matches

 Man's best friend May or may not be allowed, depending on the year. Can be ignited with candles or nichrome wire.

### Candles

 Standard candle May or may not be allowed, depending on the year. Can be lit with matches or nichrome. Nichrome can be wrapped around the wick for dependable ignition. Tea light candles can be bought cheap in bulk so that you don't have to worry about the candle being at different heights, depending on how often it has been used.

### Rocket Ignitor

 These are used in model rockets to ignire the engine Also called Glow Plugs, these contain a tiny nichrome element that heats up. More expensive than buying a toaster from Good Will, but more easily mounted.

### Oxidizing Iron

 Winter glove warming packets These one-use packets oxidize iron filings to produce heat.

## Cooling devices

### Peltier device

See above section.

### Fans

 A DC hair dryer fan Fans can be used to mechanically blow objects or to heat/cool objects using the supplied air. There are a wide variety of fans that can be used for different events, such as MagLev, but some fans are not legal, depending on the allowed electronics.

### Ice

 Ice cubes! Low tech, but always an option. Bring a cooler!

### Ammonium Chloride and Water

 Supermarket coldpack This reaction produces a rapid decrease in temperature. The easiest way to get the chemicals is from the instant cold packs (not the kind you stick in the freezer, the one time use ones). The package will contain a larger number of ammonium chloride pellets and a water bladder. Rather than use all the pellets at once, they can be stored and used in whatever quantity is needed for the transfer. Tap water works fine.

## Sensing devices

### Bimetallic strip

See Bimetallic strip for more information.

 A coil of bimetallic strip A bimetallic strip is composed of two different kinds of metals that have been bonded to each other in a strip. Since the metals react to changes in temperature differently, the strip will curl in one direction or the other (or curl and uncurl, if it is formed into a coil). This can be used to make a transfer that reliably reacts to changes in temperature.

### Thermistor

Thermistors are resistors whose resistance is closely tied to the ambient temperature. All resistors respond to temperature changes, but thermistors are designed specifically to respond to temperature changes. Thermistors are extremely inexpensive ways to detect changes in temperature. If the current rules allow digital electronics, thermistors are very versitile and can be put in circuits capable of reacting to small changes in temperature. In years without digital electronics, thermistors are less ideal, but still an option; large changes in temperature will have to be used to affect a large enough change in resistance to be useful.

Generic thermistor. Appearance and coloration vary widely

#### Acquisition

All surplus electronics retailers should carry thermistors. Expect to pay \$1 for a package of one or more. Look for the cool and hot resistances to determine whether they would be useful in your application.

### Thermal switch

 Resettable Thermal Switch Thermal switches are broadly classified into resettable devices (trigger and then, after they have returned to the normal temperature, reset) and one-shot devices (act as fuses: they work once and cannot be reset). You can probably buy a bag of thermal fuses for the cost of a single resettable thermal switch, but the ressetable switch requires no maintenance or replacement. Like other switches, thermal switches can be found in Normally Open and Normally Closed configurations. They also respond to different temperature ranges, so picking one appropriate for what you can do in your machine is important.