Enhanced flow boiling heat transfer from 3D printed substrates

• Main Author: Chua, Barnabas Wei Li
• Other Authors: Leong Kai Choong
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/67385
• Institution: Nanyang Technological University

Ever since Moore's law earned its place as an annual target for the semiconductor industry, it is evident that the exponential surge in circuit density is not exempted from huge increase in heat flux. Thus, the need to manage heat transfer is crucial as we expect heat dissipation to rise along with the increase in transistor count. This project seeks to study techniques and parameters which contribute to enhanced flow boiling heat transfer, in search for improved thermal management. In this project, experimental research was carried out to investigate the effects of coolant mass flux, structure modification, substrate pore size, graded pore size and copper substrate. Experiments were conducted on seven 3D printed substrates, which were inspired out of two main design structures, namely "Square" and "Sphere". During each experiment, using FC-72 as the liquid coolant, the substrate to be tested is attached to the base of evaporator channel at the testing section where heat is transferred by conduction from a heater below. Each substrate was tested at three mass fluxes of 6.5, 10.0 and 13.5 kg/m²·s, over a range of heat flux from 0 to 74.5 W/cm². For each experiment, the coolant volumetric flow rate, power reading, wall temperature of the substrate and coolant pressure reading were monitored and recorded periodically across the range of tested heat flux. From the experimental results, a higher coolant mass flux was found to realise enhancement in flow boiling heat transfer for all substrates tested which includes "Square 3.25" and "Sphere 2". An enhancement of 23.5% was obtained for "Sphere 2", when mass flux was increased on 6.5 to 13.5 kg/m²·s. All porous substrates tested for enhancement over an empty channel have found positive enhancement, with "Sphere 2" offering an enhancement of 87.7% for mass flux of 13.5 kg/m²·s. The substrates designed with larger pore, have also found enhancement of up to 14.8% for "Square 4" at mass flux of 6.5 kg/m²·s. While "Graded Sphere" was recorded to produce the highest average flow boiling heat transfer coefficient of 2.382 W/cm²·K, when conducted at mass flux of 13.5 kg/m²·s, "Copper Sphere 2", the counterpart of the aluminium alloy "Sphere 2" was found to offer a slight enhancement of up to 7.3% at mass flux of 6.5 kg/m²·s.