Tuesday, 22 December 2009 09:39
Thermal Testing Methodology/Specification
I continue to follow the standard methodology and procedures that Martin used time and time again in his tests, his methods are the most logical and scientific out there. The methods and specs we use are the most accurate and thorough of any radiator reviews you will read For radiator testing, the best way to conduct the tests is to apply a heat load, just like your CPU, GPU(s) and other components you can put a block on and add to your loop. In order to supply the heat load for testing, I use modified aquarium heaters. Aquarium heaters are available in a variety of different wattages, lucky for us wattage is exactly what we are looking for in heat dissipation results. However, the tricky part with aquarium heaters is circumventing the safety mechanism that shuts off the heater when the set temperature is reached. Modifying the aquarium heater allows for a constant heat load to be applied to the loop rather than heating the water to a given temperature and shutting off. Measurements and calculations, what exactly are we going for here? One of the best means to determine the capabilities of a radiator is C/W, Martin turned me on to this in one of his early tests. Ultimately, C/W is a calculation of Water Out temperature minus the Air Temperature being pulled or pushed through the radiator divided by the heat load (wattage). This calculation gives you the delta in degrees of the radiator leaving water for each watt of heat applied to the radiator. Confused yet? An easier way to think of C/W is the temperature of the water over ambient temperature for each watt of heat in your loop. Now that we have this equation and results we can specify a set delta and figure out what heat load the radiator can dissipate at that specified delta. In short, this helps answer the question, can this radiator handle a CPU and GPU and get me decent temps. A bit more on C/W, this time in relation to Fan RPM. On several charts later in the test report you will see Fan RPM charted with C/W. This is to show the effect on radiator performance in using different speed fans, some radiators perform very well using low speed/cfm fans and get better the more cfm you push/pull through the radiator. Where some radiators perform sub-par with low speed/cfm fans and require high speed/cfm fans to effectively dissipate heat from your loop. Yes this has a lot to do with how the radiator was design, but I feel it is an important piece of data to show as a misconception I had early on in the start of my liquid cooling addiction was low speed/cfm fans could not be used on radiators optimized for high speed/cfm fans. I was quickly shown how wrong my thinking was. Besides the typical Fan RPM, air temps and water temp measurements you will see Air Capacity Used listed in the data table.
Test Note: Maintaining a constant wattage for each test is nearly impossible even with a AC Transformer (Variac). You will see slight wattage variations amongst the test results.
A total of 3 tests per round were completed with a total of 2 rounds (1 set wattage per round), each one of the tests used a different Fan RPM to represent different fan scenarios. This gives a best coverage of uses of the radiator out in the wild, not everyone will want to use the same fans or run their fans at a specific RPM, so I tried to cover 6 different RPM settings. Each test consisted of a 30 minute warm-up period with the heat load applied to the loop and a 60 minute logged test run. The heat load was applied by adding the modified aquarium heater in a custom built half-gallon reservoir. Below is list of all of the tools
- Temperature Monitoring and Logging: CrystalFontz CFA-635 with SCAB attachment – Used to log 12 temperatures (9 air, 3 water) and three Fan RPM sensor at 10 second intervals.
- Thermal Sensors: Dallas DS18B20 Digital one-wire sensors – .5C absolute accuracy overall with a .2C mean error between 20-30C.
- Test Bench Sensors Deployed:
- 1 air in sensor per fan (total of 3)
- 2 air out sensors per fan (total of 6)
- 2 water out sensors
- 1 water in sensor
- Flow Rate: King Instruments 7520 0-5GPM, 10″ Scale – Accuracy 2% of scale. Flow Rate controlled by a brass gate valve with 1/2″ NPT 5/8″ Barbs
- Water: Local Grocery store steam distilled water
- Yate Loon D14SM-12 140mm x 25mm – 62CFM/1400RPM/29dB
- Silent Speed Fans – Undervolted to 650 RPM
- Slow Speed Fans – Undervolted to 1000 RPM
- Slow-Med Speed Fans – Volt adjusted to 1350 RPM
- Data Logging: Each temperature sensor and fan RPM channel is logged for 60 minutes after the 30 minute warm-up period. Having two sensors in one location (ie: water out) allows me to average the sensors together to rule out fluctuations. This also helps to ensure the system has stabilized and remained constant during the test.
- Air Inlet Temperature Data: Each test uses one air inlet sensors per fan logged every 1 second for the duration of the test. The air inlet data is averaged using 10800 data points per test.
- Water Temperature Data: Each test uses two water outlet and 1 water inlet sensors logged every 1 second for the duration of the test. The water data is averaged using 10800 data points per test.
- Fan RPM: Fan RPM is monitored via the Crystal Fontz CFA-635 and logged at the same interval as all temperature sensors. The Power is adjusted via the CrystalFontz to an RPM setting and logged very 1 second during the test period.
- Heat Load: Wattage for the aquarium heaters are measured via a KILL-A-WATT every 10 minutes during the test, I’m quite lucky to have stable power as this does not seem to fluctuate much at all during the test. The aquarium heater wattage is added to the pump wattage (volts x amps) measured by a Fluke 23 Series II Digital Multimeter with power and additional monitoring from a Mastech HY3005D Variable DC Power Supply. These two inputs give us the total heat load applied, then averaged for the test duration.
- Test Lab Environment: Unfortunately, I do not have an environment test chamber. All tests are performed in 10×13 room in my basement which is temperature controlled via a wall thermostat and on a separate zone from the rest of the house. I am able to maintain a consistent room temperature this way. For the test fixture, I am using about 4′ of 1/2″ ID 3/4″ OD Masterkleer tubing (un insulated). The loop consists of a custom 1/2 gallon reservoir, Swiftech MCP655 (EK D5 X-Top Rev.2 top), King Instruments flow meter (5/8″ fittings) and a 3/4″ brass gate valve (5/8″ fittings).
One major change from the initial Radiator tests to now is the move from Water Out only for calculating Delta and C/W. We used to just use water outlet averaged temperature in the calculation, but now we are using the loop water average in the calculation. This change was brought on by a brave fact finding mission by Martinm210. I have mixed feelings about the use of loop average versus water out, but this method does result in more accurate C/W. All radiator tests have been updated to use the water average calculations. Without further delay, on to the thermals…