A mathematical model is presented and validated for predicting the temperature of thin polymeric films bonded to substrate materials. The National Institute of Standards and Technology provided specimen temperature and simultaneous weather data for tests during 2006 2008. Recognizing that some of the material property data are handbook values and the variety of specimen configurations are limited; initial comparisons of calculated and measured temperatures are favorable. The investigation indicates that the proposed mathematical model is satisfactory for supporting the thermal aspects of service life research on organic coatings. An aggregated-capacity temperature model is justified and used for temperature simulations. The temperature model is applicable to coatings on metallic or other substrate materials when the ratio of the thermal resistance across the substrate to the resistance across the coating to ambient is less than approximately 0.1. The solution is by an analytical rather than a numerical method to circumvent formulation difficulties and calculation constraints associated with the latter approach for extremely thin coatings. Periodic measurements of ambient dry-bulb and dew-point temperature, wind speed (to estimate convection coefficients), sky temperature, precipitation, and solar irradiation are inputs for determining heat exchange at coating surfaces. In addition to convection and solar irradiation, the model accounts for the effects of infrared exchange with the surrounding sky, dew formation on coating surfaces, and precipitation along with insulation and ambient convection at the back surface of the substrate. Based on comparisons with data recorded during typical climatic conditions, the analytical model correlated measured temperatures well. It provides a tractable, computationally efficient, and validated solution for predicting long-term transient temperatures in thin-coated specimens.
Citation: Polymer Degradation and Stability
Pub Type: Journals
Organic coatings, temperature prediction, outdoor exposure