| Self-heating in dairy powders is a cause of fires and explosions in processing equipment and storage facilities in the dairy industry. Prevention offers the best method of limiting the occurrence. Thus, prediction of the conditions which are conducive to the commencement and propagation of heating in milk powders is essential.;A finite element model was developed to simulate self-heating of a sphere of powder for variable environmental and product conditions including finite surface and internal resistance to heat transfer. The solution is accurate and stable over the range of parameters and properties likely to be encountered commercially.;The Differential Scanning Calorimeter (DSC) provided kinetic data for the model which was subsequently validated by predicting the Minimum Ignition Temperature (MIT) of the milk powder under the test conditions. In the experiments commercial powders were subjected to a high-temperature environment in a standard oven and MIT values determined. Experimental inaccuracies in the DSC resulted in simulated MIT values averaging 13% above the experimental results.;The model was further employed to estimate the MIT values using the oven-derived kinetic data. Thus, for a 2$sp{primeprime}$ sphere of skim-milk powder, the oven predicts an MIT of 161$spcirc$C, compared to a predicted MODEL/OVEN value of 159$spcirc$C, and a MODEL/DSC value of 179$spcirc$C. The model specifically identifies the lowest ambient temperature at which ignition occurs, giving a better combustion indicator than the traditional 'MIT'.;Experimental and simulation results show that the TtI (Time to Ignition) increases as the sphere radius increases. The TtI decreases exponentially when the ambient temperature increases linearly. The model predicts an exponential decrease in the TtI for a linear decrease in the Activation Energy.;As a result of the findings, a number of specific practical recommendations are made regarding the prevention of self-heating/self-ignition in dairy powders. |
