Freezing point measurement test of antifreeze
Freezing point measurement test of antifreeze
The freezing point of antifreeze refers to the first temperature at which solid particles begin to form within the antifreeze solution. At this temperature, the antifreeze is still in liquid form, but the presence of solid particles indicates that the freezing process has begun.
In some cases, the pour point (which is used for petroleum products) is confused with the freezing point. It should be noted that the pour point, scientifically speaking, is the lowest temperature at which a liquid loses its ability to flow, making it fundamentally different from the freezing point.
The antifreeze freezing point test apparatus, in compliance with National Standard 1448, is shown in the figure below.
Antifreeze Freezing Point Test Method
To measure the freezing point, first, a 50% concentrated antifreeze solution with distilled water must be prepared, and the system should be cooled inside the device at a specified cooling rate. In this test, a temperature vs. cooling time curve is plotted, and the flat or horizontal part of the curve is used to determine the freezing point.
After transferring the solution into the freezing tube of the device, it is turned on, and the stirrer speed is set to 60–80 rpm. As the process begins, the temperature of the solution is recorded at regular intervals. As we approach the freezing point, the intervals for data recording and the cooling rate in the system decrease.
Upon the formation of the first crystal, the apparent freezing point is reached. Then, the freezing point is recorded at 10–15 second intervals for 5 minutes. Experience has shown that two phenomena occur in the solution at this point:
First case: After the formation of the first crystal, the temperature rises toward higher values and then decreases (with a gentle slope).
**Second case:** After the formation of the first crystal in the solution, the temperature remains constant for a period and then decreases with a very slight slope. This temperature is reported as the freezing point.
