The pressure at the two circular outlets have a pressure of 1 atm or 101.325 Pa.Īnother boundary condition that I used was that the entire domain of the probe was initially at room temperature, 298 K. The flow rate into the entrance of the probe is defined as 3.33E-6 m 3/s. Therefore I chose one for my model that provided an inlet flow rate and an outlet pressure. So this value would be used as a temperature boundary condition at the entrance of the cryoprobe.ĭifferent cryoprobe designs use different boundary conditions, parameters, etc.
Liquid nitrogen exists inside of the gas cylinder that stores it at 77 K. Some decisions that I had to make during pre-processing included what to use for boundary and initial conditions. This temperature value will be used as an idealized case and Shannon's compressed gas model will be compared to it.ĭesign used to make assumptions for my model This model will be ran for 3 seconds and the value at the tip of the probe will be recorded. The main goal of this model was to get the amount of time that it takes for liquid nitrogen to travel down the entire probe and cool the tip of the probe.Īfter a time value was achieved using liquid nitrogen, I created a new model which had the same geometry as the previous one, but entered all of the values for carbon dioxide instead of liquid nitrogen. After all values were entered I solved the model to obtain velocity and temperature profiles for the flow of liquid nitrogen. I would then need to enter values for initial and boundary conditions, which will be discussed more in depth below. I then used the material browser to enter Nitrogen as the material for my model. I will use a time-dependent study so that I can show the amount of time that it takes to cool the shaft. The chamber contains two circular outlets for the nitrogen gas to escape through.
I then created the probe geometry, which consists of a long cylindrical tube connected to a slightly larger chamber. I began this model by choosing a 3-D space dimension with non-isothermal fluid flow as the physics.