I want to determine the specific heat capacity of my composite samples(CF/PEEK), however I get different Cp if I use the heat flow data on heating or cooling. I thought the Cp should be the same when heating up or cooling down the material. I checked the baseline corrected heat flow data of the samples on heating and cooling and they differ the same way as their resultant Cps. Has anyone also come across this problem or knows what could cause it?
Hello Márton Farkas ,
Can you describe exactly how you are making the Cp measurements? Is it a steady-state, or a transient method?
Regards,
Thomas Cuff
Hello Márton Farkas ,
I apologize, after rereading your question, I finally realized that you are using a transient method of measuring Cp. The answer to your question is that your sample is undergoing a phase transition (semi-crystalline to glass) when your are heating and cooling it. Check the material's {PolyEtherEtherKetone (PEEK), reinforced with Carbon-Fiber} data sheet for any documented phase transitions. For example, PEEK has a semi-crystalline to glass phase transition at 145°C.
Regards,
Thomas Cuff
The heat transfer coefficient at a wall varies with the ratio of wall viscosity to bulk viscosity to the power 0.14, (This is called the Seider-Tate correction, which was developed to allow for wall effects). Viscosity is strongly dependent upon temperature which is why heating and cooling have different heat transfer coefficients.
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