4 research outputs found
Method for Determining Air Side Convective Heat Transfer Coefficient Using Infrared Thermography
Air side convective heat transfer coefficients are among the most important parameters to know when modeling thermal systems due to their dominant impact on the overall heat transfer coefficient. Local air side convective heat transfer coefficients can often prove challenging to measure experimentally due to limitations with sensor accuracy, complexity of surface geometries, and changes to the heat transfer due to the sensor itself. Infrared thermography allows local heat transfer coefficients to be accurately determined for many different surface geometries in a manner which does not impact the results. Moreover, when determining convective heat transfer coefficients for a large number of samples, it is less costly in terms of both time and materials than other experimental methods. The method determines the heat transfer coefficient for an arbitrary region by determining the rate at which the surface temperature changes due to a step change in air temperature. To utilize the method a simple calibration is first done to determine the local thermal time constant under natural convection. Alternatively, if the thermal properties of the object are well known, a model may be used. In subsequent tests, the ratio of thermal time constant to that from the calibration test can be determined. As the material properties of the solid object are unchanged, the convective heat transfer coefficient scales inversely with the thermal time constant. A computer script has been created which automates the entire analysis process with the exception of determining the region of interest. The experimental method has been validated by comparison to other experimental methods, values from literature, and numerical simulations
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High Efficiency R-744 Commercial Heat Pump Water Heaters
The project investigated the development and improvement process of a R744 (CO2) commercial heat pump water heater (HPWH) package of approximately 35 kW. The improvement process covered all main components of the system. More specific the heat exchangers (Internal heat exchanger, Evaporator, Gas cooler) as well as the expansion device and the compressor were investigated. In addition, a comparison to a commercially available baseline R134a unit of the same capacity and footprint was made in order to compare performance as well as package size reduction potential