Purpose: This closed loop windtunnel setup is used to test the performance of heat exchangers during condensation and frosting. The ambient conditions inside the windtunnel are adjustable, including but not limited to the ones shown in Figure 1. An air cooling loop is used to cool and dehumidify the air, a PID controlled humidifier is used to generate steam that is used for humidification, an in-house chiller is used to supply cooling fluid at a high flow rate, and a hot water bath is used for hot water defrosting. We use multiple DSLR cameras to visualize the frost formation and condensate retention mechanisms on the fins of the heat exchanger. Heat exchangers can be suspended from a mass scale to measure the exact mass of frost that grows on the surface. The test section (Figure 2) is specially designed to be able to handle a variety of heat exchangers. We can measure the amount of water retained in the airflow using a desiccant pack or by the amount of water collected by the condensate collection pan at the bottom of the test section.
- Heat exchanger dimensions : 27 cm x 18 cm x variable depth (2 – 10 cm)
- Imaging: DSLR cameras (Pentax K-50), Infrared imaging camera (FLIR A655sc).
- Data Acquisition: National Instruments NI PXIe systems for measurement and some control applications.
- Temperature measurements:
- PT100 RTD for cooling fluid measurements at the inlets and outlets and outlets of both the air cooling and test heat exchangers.
- Two thermocouples grids (each containing 24 K-type thermocouples) to measure the inlet and outlet air temperature difference.
- Adhesive thermocouples to measure the surface temperatures
- Relative humidity: Two probe type Omega HX94a hygrometers are place at the inlet and outlet of the test section
- Flowmeter: Micromotion flowmeter to measure the flow rate of the cooling fluid. Alicat flowmeter to measure the flowrate of the hot water defrosting system.
- Air flowrate: Setra model 234 pressure transducer is used to measure the pressure drop across a air flow nozzle, air flow rate is calculated from the pressure drop.
- Pressure drop across the test sample is measure using a Setra model 234 pressure transducer.
- Mass scale: Ohaus explorer 10200 with data transfer capability to the computer.
- Heaters: PID controlled resistance heating.
- Custom built in-house chiller circulating 50% ethylene glycol mixture to the test section. This chiller has wide range of temperature and flowrate settings.
- Thermo Scientific Merlin M150 circulating 50% ethylene glycol mixture to the air cooling heat exxchanger. Temperature range (-20°C to 30°C).
- Polyscience AP07 hot water bath supplies hot ethylene glycol mixture for defrosting.
(-20° to 200°C)