Effects of pyrolysis on heat transfer enhancement for hydrocarbon fuel flow in unilateral heated channels with dimples

Abstract

• Pyrolysis aggravates the non-uniformity of secondary flow intensity by two times. • Pyrolysis causes nonlinear correspondence between heat flux and wall temperature. • Dimples weaken the stratification of secondary flow intensity for pyrolysis fuel. • Dimple cannot disturb aggravated non-uniformity of properties for pyrolysis fuel. • Dimple cannot effectively enhance heat transfer for cracking fuel at high heat flux. Heat transfer enhancement of hydrocarbon fuel is essential to improve the regenerative cooling performance for scramjet engines, especially under hypersonic flights ( Ma >6). Aiming to investigate the effects of fuel pyrolysis on heat transfer enhancement design in the channel, this study exploits the local secondary flow intensities for non-pyrolysis and pyrolysis fuel flow. Flow and heat transfer characteristics of pyrolysis n-Decane in smooth and dimpled channel are compared at 0∼4 MW/m 2 . Parametric analysis of dimple geometry is conducted. Among five dfferent dimensions dimples, h p =0.3 mm, d p =1.5 mm, p =3 mm obtains the best heat transfer performance but it still cannot effectively reduce wall temperature compared with smooth channel. Fuel pyrolysis intensively aggravates the non-uniformity of fluid properties and secondary flow intensities. Besides, the deep-degree pyrolysis in near wall region causes nonlinear correspondence between fluid temperature and heat flux. Above two factors brings enormous difficulties for heat transfer enhancement design in the cooling channel. Dimples weaken the secondary flow intensities stratification and significantly improve the adaptability for the heat transfer of pyrolysis fuel to the changing heat conditions. But dimples cannot sufficiently disturb the strengthened properties stratification induced by severe pyrolysis non-uniformity. Therefore, under high heat flux, dimples cannot perform good heat transfer enhancement for pyrolysis hydrocarbon fuel.