Thermal Performance

Everything needed—monitor, peripherals, motherboard w/CPU and GPU, radiator, PSU, and so forth—is placed in a sealed, climate-controlled box at 25°C +/- 0.05 °C. Each radiator is connected by Koolance QD3 quick disconnects for easily changing the fans and radiator. The flow rate is held at 1 GPM constant flow rate. The CPU, an Intel Core i7-4770K at 4.6 GHz and 1.3 V, is held at a constant load using a custom Intel XTU profile, and the GPU, an EVGA GTX 780 Ti Classified under load from Unigine Heaven 4.0 at 1080p with extreme HD settings, is overclocked and overvolted in such a way that the total system power draw is 550 W as measured by an external power meter.

A near-constant heat load into the liquid loop by the addition of the CPU and GPU helps quickly achieve stable liquid-loop temperatures as measured by three separate in-line temperature sensors hooked up to an Aquacomputer Aquaero 6 XT. The tubing and fittings are insulated by a sleeve heater, but its heat function is not utilized. Every single measurement is done twice as a means of verification. Any possibility of running a fan outside of its static maximum RPM is minimized as much as possible by using a comprehensive series of separate fans (Noiseblocker eLoop, B12-1 through B12-4) to cover a broad RPM range while minimizing fan speed variance and, thus, airflow. The results below are the ∆T (coolant temperature - ambient temperature) in degrees Celsius.


I have recently gone ahead and removed the 2200 RPM results because the trend is clearly against much higher speed fans, especially as better performance/noise fans than the NB-eLoops are used here. As expected, this radiator is not really all that much better than brass alloy radiators. If anything, performance is held back more by the geometry of the core with average thermal dissipation early on getting progressively worse. Alphacool used the same fins as in its thicker radiators, so perhaps this is where using non-louvered fins might have helped the ST25 be a better low-airflow optimized radiator rather than this so-so performer throughout the tested fan-speed range.