Flat surfaces with different patterns of hydrophobic spots were employed for experimental investigation of boiling heat transfer. In one case, hydrophobic spots were created on a smooth copper surface and on a surface coated with arrays of micrococoons from silicon oxide nanowires by vapor deposition of a fluoropolymer. In the second case, a hydrophobic coating was deposited on heater surfaces with cavity microstructures formed by laser ablation and chemisorption of fluorinated methoxysilane. Water under saturation conditions at atmospheric pressure was used as the working liquid. The temperature of the heating surface was varied from 100 to 125 °C, and the maximum value of the heat flux was 160 W/cm². Boiling heat transfer on the test biphilic surfaces was significantly (up to 600%) higher than on non-biphilic surfaces. Surface texture, the shape of hydrophobic regions, and the method of their creation tested in this study did not show a significant effect on heat transfer. The boiling heat transfer rate was found to depend on the size of hydrophobic spots, the distance between them, and hence the number of spots. The highest heat transfer efficiency was detected for the surface with the largest number of hydrophobic spots. After long-term experiments (up to 3 years), the heat transfer coefficient on the obtained surfaces remained higher than on the smooth copper surface. Biphilic surfaces with arrays of cavities formed by laser ablation turned out to be the most stable during prolonged contact with boiling water.

A study was carried out on the process of boiling water in a large volume of liquid at atmospheric pressure on surfaces with cavities obtained by laser ablation and hydrophobized by chemisorption of fluorinated methoxysilane from vapors at a temperature of 105°C. The results of the experiment are analyzed and compared with previously obtained and literary data. The influence of the size, shape, and location of hydrophobic cavities is studied on the intensity of heat transfer during boiling. It is shown that the main parameter determining the intensity of heat transfer is the specific density of hydrophobized cavities on the heating surface, or the step between them. The shape and size of the cavities do not have a significant effect on heat transfer. Removal of the water repellent from the cavities leads to a significant reduction in the intensity of heat transfer.

In this work, we studied the effect of radial surface finning and hydrophobic fluoropolymer coating of finned surfaces on the intensity of heat transfer at boiling. Two samples were used: 16 fins and 32 fins. At first, experiments were carried out without a hydrophobic coating. After that, the samples were covered with a layer of fluoropolymer and a series of experiments were carried out. During these experiments, the state of the fluoropolymer coating was analyzed. Experiments on a sample with 16 fins showed that deposition of fluoropolymer leads to significant intensification of heat transfer. For the sample with 32 fins, the opposite effect was observed: hydrophobization negatively affected the efficiency of heat transfer. Maximal enhancement of heat transfer, in comparison with finely finned and smooth surfaces, was achieved on a surface with large fins coated with fluoropolymer.

In this work, the influence of high-frequency pulsations of the liquid flow rate on the heat and mass transfer enhancement during flow boiling in a rectangular minichannel is investigated experimentally. The authors obtained a flow regime with controlled high-frequency pulsations of the liquid flow rate in which high values of the critical heat flux can be achieved due to a short-term increase in the liquid flow rate. This makes it possible to “wash off” large dry spots, prevent occurrence of flow and drying zones, and inhibit vapor film formation, which would reduce the heat transfer in the system. A flow regime with high-frequency pulsations will enable thermal stabilization of element surfaces exposed to unstable thermal loads. Visualization with an IR camera showed that a temporary increase in the liquid superficial velocity “washes off” dry spots, delaying the onset of heat transfer crisis in the system. High-frequency pulsations (0.1–1 Hz) enable increase in the critical heat flux in the system by 25% at the same average liquid flow rates.

Experiments were carried out on biphilic surfaces made using technology consisted in the deposition (105℃) of fluorinated methoxysilane on a copper surface with arrays of grooves preliminarily created by laser ablation, as a result of which deposition the grooves became superhydrophobic. Grooves were two types: parallel grooves and groove lattice. Size of grooves was 30-43 um, pitch for parallel grooves was 1-1,5 mm and for grove lattice – 1 mm. The experiments were carried out on distilled water at atmospheric pressure. For all surfaces, a significant intensification of heat transfer has been achieved, compared with a smooth copper surface. It was shown, that boiling heat transfer depend only from pitch between grooves for both types of grooves. Dependence of heat transfer coefficient from size of grooves was not observed. Most efficient type of surfaces was groove lattice with smallest pitch.

Experiments were performed to study water pool boiling at atmospheric pressure on biphilic surfaces with grooves (open microchannels) produced by laser ablation and hydrophobized owing to chemisorption of fluorinated methoxysilane from vapor at a temperature of 100–110 ◦C. Surfaces with arrays of parallel grooves, as well as with arrays of grooves intersecting at right angles (groove grids with square cells), were used. The experimental data were analyzed and compared with literature and previous data. The influence of the size and location of hydrophobic regions on boiling heat transfer enhancement was studied. It has been shown that the main parameter determining the heat transfer enhancement for a surface with an array of parallel grooves is the pitch between them. For groove grids, this is also true, but only for large heat fluxes. Removal of the hydrophobizer from the grooves leads to a significant decrease in heat transfer. A comparison of the results of this study with previous data for arrays of hydrophobic cavities and arrays of hydrophobic round spots on a flat surface shows enhanced heat transfer on biphilic surfaces compared to a flat smooth surface. These surfaces are characterized by a strong dependence of heat transfer on the pitch between the hydrophobic regions. The maximum effect on heat transfer was observed on surfaces with a 3D biphilic pattern, namely on arrays of microcavities and arrays of intersecting grooves (groove grids with square cells).