Discussion Forum

Posted: 1 decade ago 14.03.2013, 04:39 GMT-4

Hi but how is the temperature changing your capacitance ? Through mechanical thermal expansion of the "solid" and or of dielectric changes in your oil ? And what else ? Then use a oil with a dielectric constant depending explicitly on T (if you have this), and use "sold for the structure and change the temperature and reference temperature. now how is your temperature evolving ? ... Probably via conduction, perhaps also convection in the oil => need sole conjugated heat flow module to solve that, but perhaps also through electric conduction in the "sold => also joule heating Your model is becoming complex. My advise: start simple consider one at the time, then start to couple ;) -- Good luck Ivar

Posted: 1 decade ago 19.03.2013, 02:13 GMT-4

[QUOTE] Hi but how is the temperature changing your capacitance ? Through mechanical thermal expansion of the "solid" and or of dielectric changes in your oil ? And what else ? Then use a oil with a dielectric constant depending explicitly on T (if you have this), and use "sold for the structure and change the temperature and reference temperature. now how is your temperature evolving ? ... Probably via conduction, perhaps also convection in the oil => need sole conjugated heat flow module to solve that, but perhaps also through electric conduction in the "sold => also joule heating Your model is becoming complex. My advise: start simple consider one at the time, then start to couple ;) -- Good luck Ivar [/QUOTE] Hi Mr. Ivar, First of all thanks a lot for your meaningful reply. But actually I am designing an Electrical Capacitance Sensor for Electrical Capacitance Tomography (ECT) which has 12 electrodes mounted on its outer boundary of the pipe. Typically an ECT measurement protocol excites one electrode in a rotational manner. When one electrode is energized with an electric potential the other electrodes (called detecting electrodes) are kept at ground potential. For e.g. i have 12 electrode sensor, when electrode 1 is energized with a known potential U1, the electrodes 2 to 12 are kept at 0V. This will be part of known boundary conditions when solving the domain equation and finding the potential distribution/electric field. Using the post-processing capabilities in COMSOL and calculate the charge resting on the detecting electrodes (electrode 2 to 12, when electrode 1 is energized with the predefined potential U1), yielding Q2 to Q12. Based on this the capacitance can be calculated using C12 = Q2/U1, C13 = Q3/U1, ...., C1,12 = Q12/U1. But now I want to see if its possible to change the temperature in Electrostatic module as i am using the crude oil and want to see its behavior by simulation that how the value of capacitance be affected by change in temperature. My background is mainly from Electrical and Electronic so i am unable to understand your last reply. Sorry for that. Hope you understand my problem. Thanking for your consideration. Regards, Areeba

Posted: 1 decade ago 22.03.2013, 00:20 GMT-4

Can anyone else reply me for my query !!

Posted: 1 decade ago 22.03.2013, 02:42 GMT-4

Hi indeed it was not clear if your oil is "static" or had fluid motion, as now I understand it's a static fluid, isolating, hence no electric current flow, no Joule heating ,etc, indeed you do NOT need any conjugated heat flow model. But I'm astonished: why you haven't told us what is changing your capacitance: OK it's driven by the temperature of the oil, so for me that means the dielectric constant of the oil is changing with T. Well if that is what you are looking for, you need to get the epsilon_r values for the oil for different T set up in a material interpolation function (or analytical one if you know that), depending on a variable T, and you define the variable T as a Parameter, and do a parametric study based on varying T from a Tmin to a Tmax (here T isaa scalar or a predefined field T(x,y,z,t) or you get the value of the full field T (implicitly T(x,y,z,t)) defined by a HT in fluid via the solving of heat source, sink ... But heat flow through a fluid tends to induce buoyancy forces etc hence we are back to conjugated heat flow ;) -- Good luck Ivar

Posted: 1 decade ago 27.03.2013, 04:42 GMT-4

Hi, Yes i have a static fluid and want to see that on change in temperature does the values of epsilon or Capacitance will be affected. As i mentioned in last post that I need to measure an inter electrode capacitance. So how or from which command in Comsol ver 3.5 we can do this change in temperature ? how we define Temp as a scalar or predefined field ?

Posted: 1 decade ago 27.03.2013, 16:17 GMT-4

Hi You can define T as a scalar (parameter) or as a variable from an interpolation function, and there you can map to a filed of (x,y,z,t). But to see any changes, you need to male epsilon_r depend on T too -- Good luck Ivar