- Test the instantaneous defrosting performance by Joule heating at the frost-surface interface
- Record the defrosting process from side view using DSLR cameras
- Identify the optimal energy pulse that requires minimum time and energy to clean the surface during defrosting
Mechanical: Liquid Nitrogen (LN2) is used as the cooling fluid. A solid L-shaped copper block is submerged into an LN2 bath. A glass substrate (Sigma Aldrich, 25 mm × 25 mm × 1.1 mm, 7.5 Ω electrical resistance) coated with thin layer (≈550 nm) of Indium Tin Oxide (ITO) is used as the test substrate. In order to establish a firm electrical contact, two bus bars are attached to the substrate using a silver epoxy resin (Epo-Tek H20E) as shown on the right and left hand sides of the inset image of Fig. 3(e). The substrate is attached to the copper block using a thin layer (≈50 µm) of thermal paste (Apiezon N Grease). At steady state, the temperature of the substrate is measured using a thermocouple (Omega, K type, 0.5 accuracy) to be equal to = -85.2 3.1.
Electrical: The ITO sample is connected in series with a transistor as shown. Pulses of varying lengths are supplied to the transistor gate driver with a waveform generator (Agilent 33522A) in order to control the amount of time that current would conduct through the ITO sample. The amplitude of the current pulse is controlled by setting the current limit of the dc power supply (Kenwood PD56-10D). Since the circuit has inductance from the long connection cables, the pulse waveform contains ringing and is non-ideal as shown. A gate resistance of 20 mΩ is employed so that the ringing would be minimized and the energy from the pulse could be estimated using the ideal waveform approximation.