Hydraulic and Thermal Effects of Coke Deposition during Pyrolysis of Hydrocarbon Fuel in a Mini-Channel

Coke deposition in a mini-channel reduced the effective diameter greatly during pyrolysis of hydrocarbon fuel. In the paper, the hydraulic resistance method (HRM) was introduced to quantitatively evaluate the coke deposition. Pyrolysis of hydrocarbon fuel was carried out at fuel temperature up to 725 degrees C at supercritical pressure of 4 MPa in an electrically heated mini-channel (heated length, 508.0 mm; inner diameter, 2.0 mm; wall thickness, 0.5 mm). The test run was maintained at steady state for 30 min. The post-test coke evaluation by HRM is nondestructive and onboard performed at normal temperature and pressure. Compared with the optical microscope visualization, the HRM was validated to be feasible and effective. Experimental results show that the thickness of coke deposit along the channel, varying from several to about 130 mu m, is a function of film temperature (average of the wall and bulk fuel temperature). Contributing to the coke deposition during fuel pyrolysis, the hydraulic resistance continuously increased. However, depending on the deposit thickness, the thermal effects can be contrary. The gully coke nature at high Re turbulent flow and the large deposit thickness as a thermal resistance can dominate to enhance and reduce the heat transfer, respectively.