Performance of Finned Heat Exchangers after Air-side Foulingand Cleaning
Air-side fouling of enhanced surface heat exchangers by particulate matter may significantly reduce their performance. Hence, the effect of particulate fouling and subsequent cleaning on the performance of finned heat exchangers is investigated. It is anticipated that heat exchanger geometry and operating conditions such as air velocity, air humidity, and concentration of dust in air will impact the process of fouling and subsequent performance degradation of heat exchangers. In the experimental phase of research, heat exchangers being tested are installed in a wind tunnel where all air-side parameters can be controlled. ASHRAE standard test dust is injected into the air stream in a controlled manner leading to fouling of the heat exchanger. The mass of dust deposition on the heat exchanger is indirectly measured to quantify the extent of fouling of the heat exchanger. In addition, the pressure drop across and heat transfer through the heat exchanger are also measured to quantitatively evaluate degradation in performance due to fouling. A small set of in-situ cleaning strategies are attempted coupled with a standard detergent-based cleaning procedure to evaluate their efficacy. In the modelling phase of research, a mathematical model is developed to predict the deposition rate and distribution of dust as a function of time using heat exchanger geometry and operating conditions as inputs. Published and measured experimental data are compared against model predictions. To improve prediction accuracy and fidelity of the model with experiments, fundamental measurements are necessary to acquire knowledge of the interaction parameters between the heat exchanger surface and the fouling agent. When this information is lacking, the use of estimated values or tuning factors becomes necessary. It is proposed to extend the developed fouling model to predict the performance of fouled heat exchangers. The predicted fouled heat exchanger performance will then be used to estimate degradation in system performance due to fouling. With this project, it is envisioned to predict the extent of fouling of fielded heat exchangers, and set target cleaning schedules based on the maximum degradation in performance of the heat exchanger that can be tolerated by the system in which the heat exchanger is installed. A comparison of prior-fouling and post-cleaning performances will enable an understanding of the efficacy of cleaning procedures. The experimental procedure developed as part of this research is proposed as a robust and repeatable test protocol for simulating heat exchanger fouling in laboratory conditions.
Garimella, Purdue University.
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