Numerical analysis of the melting characteristics of a frozen urea-water solution by heat spreaders with a positive temperature coefficient heater

The objective of the numerical analysis in this study involved the design optimization of a heat spreader with a positive temperature coefficient (PTC) heater to obtain a liquid urea-water solution of 340 mL from a frozen urea-aqueous solution within 1200 s. Commercial software STAR-CCM+(9.06) was used to analyze the performances of various heat spreader designs according to liquid fraction, temperature distribution, and phase-interface velocity under the same input current condition. With respect to the validation of the numerical results, those were in good agreement with the values of the urea thawing experiments. The wide lateral surface area of the heat spreader represented that the area adversely influenced the amount of molten urea-water solution within the specified time period. The heat spreader model of four hooks like turbine blades corresponded to the optimal shape necessary to prepare a sufficient amount of the molten urea-water solution for the normal de-NOx performance of a urea-SCR system within the shortest time of a cold start. In addition, it was reasonable to set the thickness of the high-density polyethylene (HDPE) coating in the range of 1-2 mm to obtain a large amount of molten urea-water solution without inhibiting the heat transfer.