I am new to using DSC and I am trying to use it to measure the heat capacity of nanofluid with the classical three steps procedures. And since there is no clear guidance regarding the ramp rate and isothermal holding time, I decided to test different programs to see if this will affect my results. The DSC curve for three tested programs came as shown in the attached image. As shown even the base curve and reference material (DI water) is inconsistent. And the Nanofluid NF curve is even worse, it even shows sometimes endothermic and exothermic curve. Which I don't understand, how the NF exhibits an exothermic behavior when I am measuring the heat capacity. I would be grateful if some can help me with this problem.
Note that the three runs where as follows:
Run 1
1) Hold for 1.0 min at 25.00°C
2) Heat from 25.00°C to 50.00°C at 10.00°C/min
3) Hold for 1.0 min at 50.00°C
Run 2
1) Hold for 0.5 min at 25.00°C
2) Heat from 25.00°C to 50.00°C at 20.00°C/min
3) Hold for 0.5 min at 50.00°C
Run 3
1) Hold for 2.0 min at 25.00°C
2) Heat from 25.00°C to 50.00°C at 5.00°C/min
3) Hold for 2.0 min at 50.00°C
Thanks
There are two measurements that you can take using DSC usually, the Latent Heat and the sensible heat. For the case of latent heat, an endothermic/exothermic peak will be present for phase change process. For the case of sensible heat, the specific heat capacity of the material is calculated. This is the energy that needs to supplied to raise the temperature by degree Celsius per kilogram.
In your case, the nanofluid is not undergoing any phase change process, therefore there is no endothermic/exothermic peak. I think, you need to check the configuration of your DSC instrument whether it is set for latent heat measurement or specific heat measurement.
I have attached a file showing how an endothermic peak will look like.
Ref: DOI: 10.1016/S0196-8904(03)00154-7
It seems you have a problem with the baseline of the instrument. First, each heating rate will have a a different baseline (most probably). Also, having the same thermal link between the crucible and the pan is important to get a good and reliable baseline subtraction. Maybe one option is to increasing the isotherm time at 25°C, it seems the instrument has different "catching up" times with the setpoint temperature, probably due to the different thermal masses or thermal links involved in the different sample runs (empty/DI/NF).
Hope it helps somehow...
The article given below may help you to calculate specific heat capacity using DSc
https://www.researchgate.net/publication/315713341_'Thermal_analysis_of_ABSPA6_polymer_blend_using_differential_scanning_calorimetry'
Hi Mohamed,
As Mathew said, your nanofluid is not undergoing any phase change, and you can not interpret data based on a phase change or a reaction.
For your case, it seems that the heating rate of 10 or 20 C/min is too much. think of 5 C/min or less. Moreover, the overshoot at the beginning of the experiment might be attributed to this high heating rates. I recommend you to first, calibrate the DSC by indium precisely (you probably have the standard at your lab), then use lower heating rates i.e, bellow 5 C/min, and keep the samples at 25 C for a few minutes before starting the test. Moreover, I believe you should use hermetic pans and dont forget to pierce it with a thin needle. combination of these things probably result in better results.
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