Surface modifications for phase change cooling applications via crenarchaeon Sulfolobus solfataricus P2 bio-coatings

Due to its high heat removal capability and exploitation of latent heat, boiling is considered to be one of the most effective cooling methods in industry. Surface structure and wettability are two factors imposing boiling phenomena. Here, we propose an effective and facile method for surface enhancement via crenarchaeon Sulfolobus Solfataricus P2 bio-coatings. The positive effects of such surfaces of bio-coatings were assessed, and enhancements in heat transfer and cooling were obtained. Visualization was also performed, and bubble dynamics of generated bubbles and vapor columns from the tested surfaces with bio-coatings are here presented. Superior performance in terms of boiling heat transfer and cooling was reached with the use of crenarchaeon Sulfolobus Solfataricus P2 coated surfaces. Thus, this study clearly demonstrates the potential of futuristic surfaces with bio-coatings to achieve substantial energy saving and efficiency.


Supplementary Figure 1
Schematic representation of the sample preparation Sulfolobus solfataricus P2, was grown at 80°C, pH of 3 in a batch culture under mild agitation. Cultures were started from −80 °C stock; cells were inoculated into 50 mL fresh culture medium. After 24 h of propagation, the cell culture was transferred to 500 mL of the pre-heated new medium. Cell growth was then monitored with UV Spectrophotometer at 600 nm following each 24 h till 96 h.
Archaeon culture (OD 600=1, after almost 72 h later) was cooled down on ice, then centrifuged for 15 min at 4000 g and washed twice with ice cold phosphate buffer. Pellet was then resuspended in 5 ml PBS (0.1 g/ml), and 2.5 ml of this solution was mixed with 1 ml Poly-L-lysine (0,01 % (w/v) in H20) to cover 500µ thickness silicon wafer substrate with heat cure method. For this purpose, we used 60 °C incubator and we administrated the mixture on the silicon wafer substrate then waited until all liquid evaporate (after almost 30 min).

Supplementary Figure 2
Scanning electron microscopy images: Archaeon colonies with different thicknesses and shapes are shown in figure   2. A scanning electron microscope (FEG-SEM Leo Supra 35, Oberkochen, Germany) was used to obtain the microstructural images of the specimen surfaces before and after the treatment. SEM scans an electron beam on the surface of a specimen and measures a number of signals resulting from the interaction between the beam and specimen.
One particularly useful imaging method is collecting low energy secondary electrons (SE) signals which originate within a few nanometers from the specimen surface. Due to this process, SE method allows imaging of the surface with a high spatial resolution 1 . The micrographs were collected using SE mode in low voltage (2 KV) within different tilts to allow a full imaging of the surface area and the cross sectional area.

Supplementary Figure 3
Locations of the temperature measurements There are five holes for thermocouples to read temperatures. The vertical temperature readings were used to obtain the vertical temperature gradient, while the horizontal temperature readings (located 1 mm beneath the sample) were used for wall temperature measurements. The surface temperature was calculated with the help of vertical measurements of T5, T4 and average temperature of the experimental setup right beneath the test section, Tave = (T1+T2+T3)/3. The surface temperatures are obtained by using the thermal contact resistance from the Tave to the silicon surface with the average of the thermocouple measurements. Five T-type thermocouples were used to record the temperatures.

Note 1. Data reduction
The net heat flux is calculated as follows: Here, V is the applied voltage, I is the current, loss Q is the heat loss and A is the heated surface area. Heat loss is the difference between input power and the amount of cooling energy in single-phase flow regime in boiling experiments. For minimizing the amount of heat loss, the aluminium heating part is surrounded by a Teflon block which is a prevalent as of insulator. To calculate the amount of heat loss for each test, a natural convection analysis was performed. The heat loss is expressed as: Accordingly, the heat losses are less than 5%. The boiling heat transfer coefficient, h, is calculated as: where Ts is the surface temperature, and f T is fluid bulk temperature. Tf is measured using a thermocouple, while for saturated boiling the saturation temperature is considered as the saturated temperature at the local liquid pressure. The surface temperatures are obtained by using the thermal contact resistance from the Tave to the silicon surface with the average of the thermocouple measurements, as:

Note 2. Uncertainty analysis
An uncertainty analysis is used for measuring instruments and experimental data based on the error propagation methodology proposed by Coleman and Steele 2 . The general formulation is expressed as:  Hz, respectively. The bubble departure diameters on biocoated surfaces were obtained within the range of 1-3.5 mm size, while the uncoated surface has the departure diameter within the range of 1-2 mm. One of the main reasons for the difference in bubble departure frequency and departure diameter between biocoated and uncoated surfaces is the presence of porous layer and the bubble departure mechanism prior to the departure process 8 .

Supplementary Figure 4.
Determination of bubble departure frequency and diameter