Experimental evaluation of the critical local wall shear stress around cylindrical probes fouled by diesel exhaust gases

Abstract

The problem of fouling in the heat exchangers of exhaust systems has yet to be resolved. This results in enormous costs for engine manufacturers due to the required over-sizing during design and due to unscheduled maintenance needs.This article presents an experimental layout developed for measuring fouling in diesel engine exhaust gas systems. This facility was based on a circular cylindrical cross-flow device, with one straight and smooth stainless steel probe positioned transverse to the flow of exhaust gases. The probe can be cooled from the inside with water and fouled on the outside as a result of particle deposition from exhaust gases.The tests were conducted under constant engine operating conditions. Therefore, the asymptotic depth of the fouling layer could be measured at different angular positions at the end of each test.The critical wall shear stress rate is proposed as the controlling mechanism of the local removal process that leads to different fouling depths around each probe. This is in contrast to the critical velocity concept, which cannot be applied at a local scale due to its formulation. The experimental results, although subject to the usual uncertainties of fouling processes, seem to support this idea.

Experimental study of soot particle fouling on ribbed plates: Applicability of the critical local wall shear stress criterion

“…In this study, an experimental layout was designed to measure the thickness of the fouling layer on enhanced surfaces that is produced by exhaust gas systems under operating conditions. Previous data from the literature [14,15] and our own analysis [16] suggest that particle deposition is the primary mechanism controlling the fouling process. In fouling dominated by particles, several researchers, such as Messerer et al [17] and Grillot and Icart [14], demonstrated the asymptotic evolution of deposits.…”

“…These ranges were chosen to extend previously obtained results [16]. In addition, the new test equipment introduces several dynamical features of the flow, thereby creating an environment more similar to that found in real heat exchangers.…”

“…The new layout was integrated into the facility that was developed in the study discussing the fouling of cylindrical probes [16]. The exhaust gas lines and measurement section of this layout are shown in Fig.…”

“…All of the details regarding the control system, measurement devices, and working conditions can be found in the study by Paz et al [16]. The design of the experimental device was based on a one-pass rectangular channel with two ribbed plates placed in a symmetrically staggered arrangement through which the exhaust gases flow.…”

“…The critical wall shear stress was proposed as a more local removal control parameter than the critical velocity by Paz et al [16]. The critical wall shear stress was evaluated and compared with the fouling thickness observed on cylindrical probes.…”