Thermal Analysis

KarthikRajan · 2015-10-19T17:42:01+00:00

Hi Dudes, I'm currently working on a project where i'm using Ni-chrome wire as a heating element. I stuck in a place where I cannot exactly find the increase in temperature of the Ni-chrome wire theoretically at various time period that could match the experimental value. so, someone please help me out. Here is the situation, I'm using a Ni-chrome wire of 1 m length, diameter of 0.37 mm, current and voltage to be 1.5 A and 18.4 V respectively. The resistivity value of the wire is found to be 1.3x10^-6 ohm m which lies in the resistivity range of the Ni-chrome wire. By joules law of heating I can be able to find the heat dissipated by the wire, As the voltage and the temperature are maintained constant. (H=I^2*R*t) so i find the heat dissipated by the wire in joules. In order to find the increase in temperature of the wire I'm using Enthalpy relation H=m*cp*dt as the internal energy changes because of the heat generation/dissipation of the wire due to the supplied voltage. I know the mass of the wire and the specific heat capacity of the wire by this I should be able to find the change in temperature. But the fact I cannot able to find the change in temperature as experimented. Here are my experimental values . The mass of the wire is 4grams and the specific heat capacity value is 450J/kg K. Time (sec) Temperature (degree Celsius) 10 27.4 20 28.8 30 29.9 40 31.0 50 31.8 60 32.5 Some one help me out. Thanks in advance

Thermal Analysis

KarthikRajan

Member

Updated: Oct 26, 2024

Views: 1.7K

Hi Dudes, I'm currently working on a project where i'm using Ni-chrome wire as a heating element. I stuck in a place where I cannot exactly find the increase in temperature of the Ni-chrome wire theoretically at various time period that could match the experimental value. so, someone please help me out.
Here is the situation, I'm using a Ni-chrome wire of 1 m length, diameter of 0.37 mm, current and voltage to be 1.5 A and 18.4 V respectively. The resistivity value of the wire is found to be 1.3x10^-6 ohm m which lies in the resistivity range of the Ni-chrome wire. By joules law of heating I can be able to find the heat dissipated by the wire, As the voltage and the temperature are maintained constant. (H=I^2*R*t) so i find the heat dissipated by the wire in joules. In order to find the increase in temperature of the wire I'm using Enthalpy relation H=m*cp*dt as the internal energy changes because of the heat generation/dissipation of the wire due to the supplied voltage. I know the mass of the wire and the specific heat capacity of the wire by this I should be able to find the change in temperature. But the fact I cannot able to find the change in temperature as experimented. Here are my experimental values . The mass of the wire is 4grams and the specific heat capacity value is 450J/kg K.

Time (sec) Temperature (degree Celsius)
10 27.4
20 28.8
30 29.9
40 31.0
50 31.8
60 32.5
Some one help me out. Thanks in advance

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Shashank Moghe

Member • Oct 23, 2015

In the experimental data, the wire must be surrounded by air, which has its own specific heat. It absorbs some of the heat released due to Joule Heating. Do an energy balance H = m_wire*Cp_wire*deltaT_wire + m_air*CP_air*deltaT_air.

The challenge for you is to find out:
1) Can Joule Heating value be considered to be available for the air on its complete volume?

2) Do you want to make it more realistic and consider heat transfer to the air only at the interface of wire-air? In which case it comes to a natural convection boundary condition. Eventually the natural current will even out the temperature gradient anyway, but if you want intermediate time solutions, well, that is a possibility as well.

3) If the air is neglected (assuming a vacuum enclosure consisting only the wire), do you want to consider heat loss by radiation?

Enjoy.

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KarthikRajan

Member • Oct 28, 2015

😀
Shashank Moghe
In the experimental data, the wire must be surrounded by air, which has its own specific heat. It absorbs some of the heat released due to Joule Heating. Do an energy balance H = m_wire*Cp_wire*deltaT_wire + m_air*CP_air*deltaT_air.

The challenge for you is to find out:
1) Can Joule Heating value be considered to be available for the air on its complete volume?

2) Do you want to make it more realistic and consider heat transfer to the air only at the interface of wire-air? In which case it comes to a natural convection boundary condition. Eventually the natural current will even out the temperature gradient anyway, but if you want intermediate time solutions, well, that is a possibility as well.

3) If the air is neglected (assuming a vacuum enclosure consisting only the wire), do you want to consider heat loss by radiation?

Enjoy.
Thanks Shashank Moghe😀😉 ,
Sorry for the inconvenience from my side I failed to add a data in my description. I'm using the wire in a closed enclosure where i'm using electrical insulating sheets to avoid short circuit and also for a better uniform thermal conduction 😀 but still I face the same problem in solving the problem😔

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