2. Materials and Methods
2.1. Experimental Setup
2.2. Experiment Procedure
- Fill the groove with DI water.
- Turn on the Peltier element to start the cooling of the plate.
- Remove the chamber and wipe the surface from all natural frost that has been formed from the moisture content of the air.
- Fill the pipette with the mix of DI water and particles and lower it into the chamber.
- Turn on the laser and start filming.
- Wait until the plate is at −8 °C.
- Release the droplet.
- When the singular tip can be observed and it is completely frozen, stop filming, turn off the laser and turn off the cooling of the plate.
- Wait until the droplets have melted and wipe all water off the plate and repeat.
2.3. Data and Uncertainty Analysis
3. Results and Discussion
3.1. Droplet Radius and Contact Angle
3.2. Freezing Time
3.3. Velocity Profile
- From the experiments it can be concluded that the contact radius and angle of a droplets impact on a substrate can be controlled to a higher degree when using a groove filled with ice rather than impinging on a flat surface covered with a layer of natural frost. The repeatability study of 81 experiments showed to a rather high degree that, when introducing a groove in the plate, the contact radius could be predetermined with a standard deviation of 0.85%.
- The experimental results show that the freezing time is dependent on the contact angle and hence also the height of the droplet. A higher contact angle will increase the time of freezing. Dependence on contact radius is not as visible in this work since the contact radius between metal and droplet is rather constant due to the groove.
- The velocity profile was determined inside the droplet before and after the direction change for the three substrate materials. At the point where the velocity was highest (75% between the top and freezing front), copper had the highest velocity, followed by aluminium and then steel. The internal velocities thus follows the thermal conductivites with copper having the highest thermal conductivity and steel the lowest. This order only applies for the fastest point; both at the top and at a height of 50%, steel had a higher velocity than aluminium. The overall velocity difference between aluminium and steel is, however, rather small. Copper is 16.39% faster than aluminium, and aluminium is 5.78% faster than steel at the highest velocity. There is thus a difference in internal flow between the substrates, but the difference between aluminium and steel is not as distinct as for copper.
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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|Material||Thermal Conductivity [W m K ]|
|Pre Turn||Copper [%]||Aluminium [%]||Steel [%]||After Turn||Copper [%]||Aluminium [%]||Steel [%]|
|Ice front||0.2478||0.3743||0.3556||Ice front||0.1785||0.2288||0.2339|
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