1. 4/12/2011Controller Cooling Test1 Array Controller Cooling Test Bill Hoffmann April 12, 2011 This is a report on a test of the chilled water-to-air heat exchanger designed for cooling the electronic controllers for the LMIRCAM, NOMIC, and MIRAC IR cameras. Requirements: 50 Watt heat load Cooling water at LBT at dome ambient temperature (-20 to +15 C) Cooled air temperature to be between 10 and 25 C Continuous air flow through electronics to avoid hot spots. No water inside electronics enclosure Operate safely with LBTI cooling water pressure of 70-80 psi Design The design provides for an external duct and fan to provide a continuous air flow and a compact heat exchanger to provide the cooling. The heat exchanger consists of a copper coil soldered to one side of a copper plate, swaged-pin assemblies soldered to the other side, and an attached fan. The amount of cooling by the heat exchanger can be reduced for low water temperature by reducing the speed of the heat exchanger fan. The test setup consists of an insulated chamber divided into two parts. The lower part representing the electronics enclosure contains a 50 Watt heater. The upper part representing the duct contains the heat exchanger and circulating fan. A number of thermocouples were installed to monitor the temperature. The cooling water was provided by a Betta-Tech Controls CU400 Heater-Chiller. Results The designed unit satisfies all the requirements with the following extremes Cooling water Air temperature 15 C 22 C -10 C 2 C with heat exchanger fan fully on -10 C 10 C with heat exchanger fan turned off -20 C cooling water would have to be throttled Details The test setup is shown in Figure 1. The heat exchanger is shown in Figures 2-4 and the heat source in Figure 5. Figure 6 shows the measured water and air temperatures. Figure 7 gives the measured and extrapolated air versus water temperature.

2. 4/12/2011Controller Cooling Test2 Figure 1. Cooling test chamber. The lower part represents the electronics enclosure. It contains a 50 Watt heater and a temperature sensor in the warm air flow returning to the heat exchanger. The upper part represents the duct. It contains the heat exchanger, circulating fan, and additional temperature sensors. Heat exchangerCooling water linesCirculating fan 50 Watt heater

3. 4/12/2011Controller Cooling Test3 Copper coil Swaged-pin assembly Heat exchanger fan Figures 2 and 3. Heat exchanger showing ¼ inch copper tubing coil, 1/8 inch copper plate, swaged-pin assembly, and 120 mm heat exchanger fan The fan is a 12V 0.5A DC brushless ran. Copper plate

4. 4/12/2011Controller Cooling Test4 Figure 4. Heat exchanger showing four 2x2 inch swaged-pin assemblies Figure 5. 50 Watt heater with two 25 ohm resistors in parallel and an aluminum swaged-pin assembly

5. 4/12/2011Controller Cooling Test5 Figure 6. Plot of measured water and air temperatures versus the cooling water temperature Figure 7. Plot of measured and extrapolated air versus water temperature. The red line gives the air temperature with the heat exchanger fan fully on. The blue line gives the temperature with the fan off.