Research Status Update

The four paraffins to be used in initial testing have arrived, meaning that the initial experimentation phases can begin. General melting points are known, however, the research requires more exact values for a numerical comparison of regression rate data. I have begun collecting melting point data on the paraffins by two distinct methods.

The first is a direct method of slow heating in a MEL-TEMP apparatus. Here, a small sample of paraffin is carefully forced to the bottom of a capillary tube and placed into a slot in a voltage-controlled heating block. A thermometer is used to monitor the internal block temperature, which is assumed equal to the instantaneous temperature of the paraffin sample given sufficiently slow heating allowing for diffusion and reduced thermal gradients. A viewing lens is used to monitor the phase of the sample. The temperature at which the sample begins to melt and is fully melted are recorded as a range on the order of single degrees. The actual melting point lies on this range, making the average a good estimator.

The second method is the determination of melting point based on a heating curve. A thermal probe is used to plot the temperature of a sample of liquid paraffin as it cools. Provided the assumption of high rates of heat transfer between solid and liquid phases leading to low thermal gradients within the sample, temperature will remain constant during the phases change process. It is critical that the solid phase undergo minimal cooling in the presence of the liquid which heats the solid. The interval is found in which the graph of temperature is most level, indicating the change and the temperature at which it occurs. Based on a preliminary trial, shown bellow, the assumptions needed for accurate measurement may not be met due to the low conductivity of the paraffin. The rounding at the bounds of level intervals is evidence of thermal gradients present within the sample, meaning that the propagation of the solid phase was uneven within the sample. This phenomenon was observed during the trial. The downward slopes of intervals considered "level" indicates that heat was lost from the solid at a greater rate than the liquid could supply it, also indicating higher thermal gradients.

Cooling Curve for n-Paraffins A and B

Cooling Curve for n-Paraffins C and D

Note: The two "level" portions of the red temperature plot for n-paraffin "D" may indicate a bimodal distribution of carbon chain lengths in the sample. All other curves appear to be well behaved. Rounding at the boundaries of "level" intervals may also be the result of a distribution of carbon chain lengths about a mean.

I will be posting all data collected to date. I am presently designing the primary testing apparatus including the hybrid rocket motor device, nitrous oxide feed system, and test stand. The injector will be ordered first along with a male coupler for the nitrous tubing and the aluminum blank for the forward closure. Based on the dimensions and threading of the injector and coupler, the injector face and forward closure will be machined. Also, I will be purchasing and calibrating the two pressure transducers to be used in the experiment. This will require its own apparatus consisting of a variable pressure vessel in which the pressure data is known and compared to voltages across the transducers.