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heating coil advice(resistance wire) Answered

hi, my name is david. im working on a project, for a device that is roughly .25-.5 inches long. im trying to find the right material resistance wire for the application. the components are submerged in coolant to maintain a low temperature. i wish to have a resistance wire of some kind wrapped around the components to heat them to about 90 degrees as quickly as a possibly can, for only a brief time(fractions of a second) i am using a variable power supply to determine my power needs. im hoping to be able to send a quick "signal" through the resistance wire, and use heat as a sort of input/output system. the internal components will melt at temperatures above 100 degrees.  so regulating the temperatures is key. 

now obviously since they will be submerged in coolant, the resistance wire will need to heat to higher temperatures in order to heat the other components. ive been doing some research on nichrome and kanthal wire. but from what ive seen so far, it almost heats up to quickly, to higher temperatures than i require. it is hard for me to do the calculations, since i dont know how many watts/amps etc i will be using. 

so to recap:
temperature required about 90 degrees. (as quickly as possible, "flash heating" to 90degrees would be great)
length is .25-.5 inch (the size will actualy be determined by the resistance wire i would prefer it to be as small as possible but i could make the module larger if i have to)
variable power supply to determine my power needs(preferably the lowest possible power usage to conserve battery power)

any suggestions on an appropriate material would be appreciated. i dont mind testing out different materials. i just dont want to spend thousands of dollars buying a little bit of everything and testing each one out one at a time. ><

some experiments have suggesting silver coated nylon, but requires 20watts and a pretty sizable heating time. the heating coil will most likely have direct contact with the components, unless it is required to provide space between the coil and the components to heat it appropriately. i would prefer direct contact though to make the modules as compact as possible. currently the coolant is being pumped continuously through the whole system, but ive been working on plans for a valve to interupt the flow of the coolant during cycles where the coil is activated, if the need arises to keep the coolant from preventing the resistance wire from heating up appropriately. 

Discussions

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Downunder35m

3 years ago

Your biggest hurdle is the heating time, no matter what you use to heat.

Only chance I can see is by using PID control for a PWM heating system.
You also need a temp sensor, thermistor or thermocouple.
Of course you can also try to create the heating element to be on the danger side of burning up to decrease the heat up time and then just use a short impulse to heat - which requires a decent timer and testing.

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DavidW433Downunder35m

Reply 3 years ago

I'm hoping to avoid having to use any kind of thermostat or controlling mechanism. I'm hoping to let the coolant maintain a low temperature, and then send a very short ,small signal theough the resistant wire, to heat it for only as long as it takes the signal to travel through it, then the coolant cool the components and the resistance wire. I'm not wanting a prolonged flow of electricity through the resistance wire. I do plan on using a temp sensor though just for testing perpouses, but I expect once the testing phase is over, as long as there isn't a malfunction on the board. It should be safe. The modules will be designed to be quickly, cheaply and easily replaced. When worn our or damaged.

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gmoon

3 years ago

There are multiple ways to do this, but the basic physics is the same -- the amount of energy required to raise the temp will be very predictable. The heating element isn't really important. What's the byproduct of inefficiency? Heat.

Which is what you want.

So it's more of a design question. Mechanical design, so it's compact and the heat goes where you want it, and electrical design, so that little current is wasted elsewhere.

But your requirements are complex: the fluid is constantly moving, you seem to have limited power reserves. Unless the environmental temp is constant, you'll also need some kind of temp monitor / thermostat.

A long winded way of saying -- no way of knowing without actually building and testing it...

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DavidW433gmoon

Reply 3 years ago

yeah, exactly, which is the phase I'm currently in. I've constructed the initial module for testing. I just have to find the heating element to make it function efficiently. I just don't want to spend a fortune on 40 different materials. If I can narrow it down to as few as possible. And then begin testing which is the most efficient. Currently the module is roughly 1.5 inches long and .5 inches wide, with its most narrow point at .25 inches wide (the tubing the coolant and components are encased in)

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gmoonDavidW433

Reply 3 years ago

I know nichrome is a standard, and should do what you want.

If it's heating too fast, you may need to change the length or gauge of the element, or the voltage. Or use some sort of a pulse controller.

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Toga_Dan

3 years ago

carbon ribbon is used in jackets, gloves and such.