Microscale-modulated porous coatings: fabrication and pool-boiling heat transfer performance

The manufacture of microscale-modulated coatings (periodic, porous stacks with a thin base layer) under mass-production conditions was investigated experimentally to establish robust process parameters. Copper powders (average diameter of 100 mu m) were compacted on a copper substrate under controlled pressure, temperature, surface geometry and processing sequences (e.g., sintering before and after compaction). Porosity, stack height, pitch and base thickness of coatings were measured. Results show that a minimum temperature of 350 degrees C and pressure of 25 MPa are required for permeable coatings, when sintering is carried out after compaction. When 'sintering before compaction' is followed, pressure values in excess of 100 MPa are needed and surfaces from this approach block the pores and diminish permeability. Pool boiling heat transfer experiments were conducted on selected coatings, showing that the best enhancement is by low-pressure compation coatings.