Studies of Inertial Deposition of Particles onto Heat Exchanger Elements

• Main Author: Fuhs, Susan Elizabeth
• Format: Others
• Language: en
• Published: 1988
• Online Access: https://thesis.library.caltech.edu/4365/3/Fuhs_se_1988.pdf; Fuhs, Susan Elizabeth (1988) Studies of Inertial Deposition of Particles onto Heat Exchanger Elements. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/jh2a-bh94. https://resolver.caltech.edu/CaltechETD:etd-11012007-135053 <https://resolver.caltech.edu/CaltechETD:etd-11012007-135053>

<p>Although the magnitude of the fouling problem in heat transfer equipment is well recognized, few investigations have been conducted into the mechanisms that lead to such fouling. The work reported in this thesis has been designed to examine gas-side fouling mechanisms that involve the inertial impaction of small particles onto tubular heat exchanger surfaces.</p> <p>An aerosol processes wind tunnel has been constructed which facilitates quantitative studies of particle interactions with heat exchanger surfaces. Three sets of experiments were performed. First, single heat exchanger tubes were exposed to a cross-flow of particle laden air. Stainless steel tubes coated with a thin layer of grease to ensure that particle collisions resulted in capture were used to verify a numerical model for the inertial transport of ammonium fluorescein particles to the tube surface. Particle bounce has been quantified for the case of clean tubes and solid particles. Experimental results compared favorably with the results of a numerical simulation based on the concept of a critical incident particle velocity normal to the surface needed to induce the particle to bounce with enough energy to escape collection by the tube.</p> <p>Second, the transient deposition of particles onto single heat exchanger tubes in cross-flow was studied. It was found that a steady-state condition could be reached for cases in which particle bounce occurred. Finally, the deposition patterns for the aerosol particles as they passed through a tube bank were studied. The quantities of aerosol deposited on various tubes depended on tube surface condition, tube position within the tube bank, and the overall geometry of the bank.</p> <p>Conditions have been identified in which the aerosol deposits that lead to gas-side heat exchanger fouling can be kept to very low levels by deliberately selecting high fluid velocities that induce solid particles to bounce upon impact with the heat exchanger surfaces. Transient fouling experiments have identified conditions under which high fluid velocities can be used to achieve very low, steady-state particle accumulations on tubes in a cross-flow of solid particles. Using these findings, heat exchangers can be designed that will resist gas-side fouling.</p>