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## Main Question or Discussion Point

Hello all, I am trying to heat a wire (nitinol, shape memory alloy, or nickel titanium).

Well my problem here is that i need to heat the wire with a DC current from the wall outlet, usually generate 110 volts but using a AC to DC converter to generate approximently 20 volts, and need a certain capacitor to store the electric charge that upon release will instantaneously heat that wire to approx. 90 degress celcius.

Givens:

wire diameter is .085 inches or .00212 meter

wire length is 7 inches or .1778 meter

measured with multimeter resistance of wire is .5 ohms

calculated the current to be 30 amps

calculated the voltage with ohms law to be 15 volts, but due to losses of heat add an additional 5 volts(approx. 1/3 of the total volts)

now i used the Heat Transfer thermal equilibrium equation: to calculate current

density(roe) * specific heat(Cp) * volume(V) * change in tem.(dT)/change in time(dt) =

resistance(R) * current^2(i^2) - convection ht. transfer coeff. (k)* area (A)(Tem max - Tem room).

used Ohms law : to find voltage

V = IR

I'm looking at Q = C * V which is the charge = capacitance * voltages

and i know that Power = IV and I = change in Q/t and Power = Work / time

Using those equation i need a 2 farad capacitor to actuate the wire within 1 sec and at a temperature of 90 degrees Celcius.

Using the same equation and inputting it for 5 sec yields a larger capacitor, which doens't make since.

Can someone please help me with this problem

here is some properties of nitinol

http://www.tiniaerospace.com/sma.html [Broken]

Well my problem here is that i need to heat the wire with a DC current from the wall outlet, usually generate 110 volts but using a AC to DC converter to generate approximently 20 volts, and need a certain capacitor to store the electric charge that upon release will instantaneously heat that wire to approx. 90 degress celcius.

Givens:

wire diameter is .085 inches or .00212 meter

wire length is 7 inches or .1778 meter

measured with multimeter resistance of wire is .5 ohms

calculated the current to be 30 amps

calculated the voltage with ohms law to be 15 volts, but due to losses of heat add an additional 5 volts(approx. 1/3 of the total volts)

now i used the Heat Transfer thermal equilibrium equation: to calculate current

density(roe) * specific heat(Cp) * volume(V) * change in tem.(dT)/change in time(dt) =

resistance(R) * current^2(i^2) - convection ht. transfer coeff. (k)* area (A)(Tem max - Tem room).

used Ohms law : to find voltage

V = IR

I'm looking at Q = C * V which is the charge = capacitance * voltages

and i know that Power = IV and I = change in Q/t and Power = Work / time

Using those equation i need a 2 farad capacitor to actuate the wire within 1 sec and at a temperature of 90 degrees Celcius.

Using the same equation and inputting it for 5 sec yields a larger capacitor, which doens't make since.

Can someone please help me with this problem

here is some properties of nitinol

http://www.tiniaerospace.com/sma.html [Broken]

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