Improving the Cleaning of Heat Exchangers

We study displacement flows in strongly eccentric annuli, where the in situ fluid is viscoplastic and the displacing fluid is Newtonian. This mimics the situation found in the cementing of horizontal oil and gas wells. In this configuration, it is common that the yield stress of the displaced fluid prevents displacement from the narrow side of the annulus, where it remains static. We address the question of whether a turbulent flow of the displacing fluid will be effective in removing the static narrow side channel and by what means. The flows proceed with rapid displacement along the wide side of the annulus, leaving behind a gelled channel of fluid on the narrow side. The narrow side is displaced either slowly or not at all. This depends on both the yield stress of the displaced fluid and the turbulence characteristics of the displacing fluid. We influence the latter through the use of drag-reducing polymers. We show that secondary flows in the turbulent displacing fluid are essential to the displacement and also the increased pressure drops in the turbulent flow. We hypothesize that the displacement is enhanced by the transmission of normal stresses into the gelled layer.

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A diffusion‐driven model for deposit removal during water rinse

Fan,

Kim,

Heldman

2024

Int J of Food Sci Tech

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SummaryThe objective of this study is to develop a model that is based on water diffusion for predicting the cleaning procedure during water rinse of Clean‐in‐Place operation. The kinetics of dairy foulant generated by using dairy product was analysed. The foulants removal with three different moisture contents (6.7%, 13.4%, and 39.3%) and four different wall shear stresses (WSS, 0.013, 0.39, 0.84, and 2.42 Pa) were evaluated. It was found that the lag time decreased with increase of WSS. In addition, the maximal removal and cleaning rate was found to increase along with the elevation of the wall shear stress. Moisture contents of the deposit determines the minimum magnitude of the wall shear stress to initiate the removal process. By combining the water diffusion and removal kinetics obtained from the experiment, a model to describe the removal of the deposits has been developed. Diffusion assuming 1‐D infinite plate was used to simulate the change in moisture content. The model confirms that the foulants with a higher initial moisture content is more rapidly removed. Furthermore, the foulant removal is affected by the permeation of water into foulants as well as the wall shear stress.

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Improving the Cleaning of Heat Exchangers

Cited by 4 publications

References 127 publications

Fouling in Dairy Processes

Fouling in Dairy Processes

Turbulent displacement flow of viscoplastic fluids in eccentric annulus: Experiments

A diffusion‐driven model for deposit removal during water rinse

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