Mechanism of Asphalt Heating with Thermal Oil Based on Biomass Boilers

Abstract

Biomass-fired thermal oil heaters are green and efficient heating devices that use heated thermal oil as the heat transfer medium. This study investigated how thermal oil thermophysical properties and heating temperature affect asphalt heating. A physical model incorporating thermal convection and conduction was established, computational fluid dynamics (CFD) simulations using hypothetical single-factor property combinations were conducted to analyze the effects of thermal oil density, specific heat capacity, and thermal conductivity. An independent experimental platform using a biomass thermal oil boiler and real thermal oils was constructed to examine the simulated property effects. Results show that the specific heat capacity and density of thermal oil dominate heat transfer during the early heating stage by altering the internal energy carried by the fluid. In contrast, the extremely low thermal conductivity of asphalt constitutes the primary bottleneck for system heat transfer, limiting the influence of thermal oil thermal conductivity on overall heating performance. Experimental trends support the simulated property effects. Within the tested property ranges, the influence ranking based on experimental temperature differences is: specific heat capacity > density > thermal conductivity. At 1000 s, the corresponding absolute temperature differences between the high- and low-parameter cases are 1.97, 0.91, and 0.2 °C. These findings provided theoretical support and design guidance for the matching of operating conditions and thermal oil selection in biomass-powered indirect heating systems.