Relative importance of conductive resistance in liquid-cooled heat sinks for electronics

Five hybrid water blocks used for CPU cooling were experimentally studied and a relationship between thermal resistance and flow rate was developed. Each of the water block designs studied in this research combine impinging jet designs with a micro-channel or micro-pin-fin base plate for efficient heat removal. Each water block was installed on a test computer that was tasked to a consistent 100% load. While the computer was loaded, the flow rate through each water block was varied between 0.8 and 7.6 lpm in increments of 0.04 lpm. Temperatures at the inlet and outlet as well as pressure drop measurements were made for 10 minutes at each flow rate. The standard deviation of experimental values was calculated to be 0.04°C and less than 10 kPa with an average variance of 0.001 and 5*10-7 for temperature and pressure measurements respectfully. This data was then used to calculate the heat removed from the system and overall thermal resistance. The average heat removed by each of the water blocks varied between 37 and 62 W with uncertainty of between ±7 and ±29 W. A correlation relating flow rate to conductive and convective thermal resistance was developed. Despite problems with model fit indications were found that convective resistance scales as the flow rate to 0.5. It was concluded that WB D was the most efficient design for heat removal based on heat removed per energy input.