Small Grants for Exploratory Research: Rapid Heat Transfer Coefficient Measurement in a Computer Integrated Manufacturing Environment

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Determination of heat transfer coefficients for manufactured objects subjected to a flow field is an important engineering consideration for stress analysis and useful life prediction. A new measurement technique to obtain pointwise heat transfer coefficients over complex geometric objects is proposed. The method represents an alternative procedure to the traditional and time-consuming experimental technique which uses distributed heaters and temperature transducers implanted in a design prototype of a manufactured object to set and measure the thermal field at the surface of the object. The new method has the potential to provide rapid determination of the heat transfer to, and temperature distribution on engineering devices, subjected to various flow regimes without the need for expensive and time-consuming instrumentation of the devices. It is proposed as an integral step in a Computer Integrated Manufacturing scheme based on Computer-Aided-Design (CAD) of prototype engineering stems. The new method involves existing measurement tools and/or technology (CAD, multiple-event liquid crystals, a robotically controlled hot-air jet for the application of surface temperatures, and numerical thermal regime modeling), and these tools are applied iteratively to obtain the heat transfer coefficients. In sequence: 1) a prototype engineering object is designed and manufactured via CAD; 2) the object is coated with liquid crystals so that optical measurements of surface temperature may be obtained; 3) the object is "painted" with a prescribed temperature distribution using the robotically-controlled hot jet; 4) the object is subjected to a flow field; 5) the new surface temperature distribution is determined optically; 6) a numerical model is used to calculate the surface temperatures using an estimated (best guess) distribution for the surface heat transfer coefficients; 7) if the numerical model predicts the same temperature distribution as that measured, then the estimated heat transfer distribution is correct. If not, the sequence returns to step 3, and finally, after several iterations, the correct distribution of heat transfer coefficients over the object is obtained.