• NaHCO3 Raw Readings

    Ahmed Hefnawi (Volta)04/18/2015 at 20:04 0 comments

    I added some NaHCO3 with water (exothermic reaction) into the sample vial and the reference vial contained sand at that time.

    The following is a plot of the raw calorimeter readings in micro-Volts versus the time in seconds, the plot was created in Python using matplotlib.

    I thought I should add the thermal power after conversion as well in milli-Watts,

  • Calibration Results + Heat Equations

    Ahmed Hefnawi (Volta)04/18/2015 at 02:41 0 comments

    Calibration Coefficient as well as baseline was calculated using the calibration procedure explained in the previous log.

    \color{White} \large \color{White} \large \varepsilon = 21.707,  U_{bl} = 62.50 \mu V

    Next, I'll start calculating the heat of hydration for a cement sample with the help of a PhD student at my University.

    \color{White} \large U(t\big) =  U(t\big) - U_{bl}

    \color{White} \large P \big(t\big) =  \varepsilon . U(t\big) \color{White} \large Q=  \int_{t=t_{i}}^{t_{f}} P . dt \color{White} \large Q \big(t_{f}\big) =  \frac{Q}{m_{c}}Where,

    U: Calorimeter Output in Volts (V)

    P: Thermal Power in Watts (W)

    Q: Heat Produced in Joules (J) or J/g

    mc: Cement Weight in grams (g)

    The duration of the experiment will be 3 days.

    Also the calorimeter readings are logged every 5 seconds onto the microSD card.

  • Calibrating the Calorimeter

    Ahmed Hefnawi (Volta)04/08/2015 at 16:07 0 comments

    Resistor in Sample Vial

    It's time for calibrating the calorimeter! There are two parameters I'm interested in for the cement hydration process, which are:

    • Calibration Coefficient
    • Baseline

    Read more »

  • Battery Power + PCB for Teensy 2.0

    Ahmed Hefnawi (Volta)04/01/2015 at 22:02 1 comment

    I'm busy at college so didn't have the chance to update the log much further.

    I created a PCB to plug-in the Teensy 2.0 board and handle external power using a single cell 3.7V LiPo 4000mAh, running the Teensy at 3V instead of 5V will consume less power and give the battery roughly 6-8 days of continuous data logging to the SD card. During the experiment we experienced periodic loss of power so that's why we are adding external power source.

    Also, I believe the battery powered device will reduce lots of the noise from the AC adapters.

    I'll be adding more photos after I finish etching the board and soldering the components.

  • Initial Prototype

    Ahmed Hefnawi (Volta)03/17/2015 at 10:25 0 comments

    The prototype is complete now, I calibrated my sensors with water in the reference vial so this calibration coefficient will work with solution but I will have to re-calibrate it for cement.

    The calibration for cement will require filling the reference (inert) vial with Sand or NaCl. Because the specific heat capacity for water is 4182 J/kg while Concrete is 880 J/kg which matches that of Salt and NaCl of 880 J/kg. Sand will be accessible in our Lab, and its specific heat capacity is 830 J/kg.

    A PhD student at my faculty is using the device now to perform the heat of hydration of cement experiment over an interval of 7 days. The data is being logged to a micro SD card into a CSV file every 5 seconds (which can be opened via libreOffice Calc or any spreadsheet program).

    I'll be adding more specific details about the build and the calibration process.

    The cement sample vial being lowered into the vial holder inside the calorimeter.