Experimental study on frost growth patterns and surface wettability effects of precooler module

•Two different frost growth patterns in precooler is discovered, revealing the structural risk firstly.•The ultra-low temperature surface wettability reduces the pressure loss and enhances heat transfer in engineering.•Frost collapse on surface of precooler micro-tube buddle is a new phenomenon, closely related to the structure of frost layer.•The tendency of normal distribution of surface temperature cooling rates is discovered during the frost process. A thorough understanding of frosting and frost layer growth mechanisms inside the precooler of a hypersonic precooled engine is of crucial importance for controlling the deterioration of heat transfer and pressure loss caused by frosting, and ensuring the normal operation of the engine. In this study, ultra-fine thermocouples were used to measure temperature variations longitudinally during the frosting process of the precooler module. Combined with optical images, an investigation was conducted into the frost layer growth patterns of precooler heat exchange modules and the influence of surface wettability. The research results indicate that there are two different frosting patterns in the precooler: under low Reynolds numbers (≤1500), the pattern is CRT, while under high Reynolds numbers (≥2000), the pattern is ALT. Frosting at Re ≤1500 may cause serious deformation of the precooler tubes. The collapse phenomenon caused by the instability of the frost layer structure reduces the pressure loss coefficient relative to the local maximum by 4 % to 7 %. The higher the incoming Reynolds number, the later the collapse occurs. When Re is too low, collapse will not occur. The surface wetting characteristics reduce the pressure loss coefficient by 13.3 % to 24.2 % in the local range of Reynolds numbers from 1500 to 2800, and cause the pressure loss coefficient curve to rotate clockwise as a whole, enhancing heat transfer to some extent. Last but not least, the normal distribution of surface temperature cooling rates and the functionalization of axial temperature gradients of the tube indicate the possibility of a rapid prediction method for three-dimensional frosting under complex engineering conditions in precooler.