Deposition of dry particles on a fin-and-tube heat exchanger by a coupled soft-sphere DEM and CFD

Turo Välikangas,Jakob Hærvig,Heino Kuuluvainen,Miikka Dal Maso,Petteri Peltonen,Ville Vuorinen

doi:10.1016/j.ijheatmasstransfer.2019.119046

Turo Välikangas, Jakob Hærvig + Show 4 more

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https://doi.org/10.1016/j.ijheatmasstransfer.2019.119046

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Abstract

In this study, a novel computational model is utilized for investigating fouling of two commonly encountered heat exchanger fin shapes in an air-conditioning application. The computational method utilizes the discrete element method (DEM) coupled with a large-eddy simulation (LES) framework. The fin-and-tube heat exchangers (FTHE) are investigated for three different Reynolds numbers (ReDh=243, 528, 793), three different particle sizes (Dp= 5, 10, 20 µm) and two different adhesive particle types based on the experimental values in the literature. The code is first benchmarked from the CFD and DEM viewpoints. A comprehensive fouling study of the FTHE’s, consisting of altogether 36 simulations, is then carried out. The major numerical findings of the paper consist of the following four features. First, with low adhesive particles, the plain fin shape has a 3.45 higher volume fouling rate with ReDh=793 than at ReDh=264. With the herringbone fin shape, and the low adhesive particles, the volume fouling rate is 1.76 higher with ReDh=793 than at ReDh=264. Second, for the high adhesive particles, the plain fin has a 5.4 times higher volume fouling rate at ReDh=793 than for ReDh=264. The herringbone fin shape has a 3.92 times higher volume fouling rate with the highest Reynolds number of ReDh=793 compared to ReDh=264. Third, high adhesive particles have 3.0 times higher volume fouling rate than low adhesive particles for both fin shapes, all particle sizes and all Reynolds numbers combined. And finally, herringbone fins have 1.74 times higher volume fouling rate than plain fins for low adhesive particles. For high adhesive particles, herringbone has 1.8 times higher volume fouling rate and when both particle types are summed together, herringbone has a 1.78 times higher volume fouling rate than the plain fin shape. As a major finding of the study, the high adhesive particle collection efficiency increases monotonously with the Stokes and Reynolds numbers while low adhesive particle collection efficiency poses a non-monotonous trend.

Highlights

Around 10 − 20% of the energy consumption in developed countries is used by the Heating Ventilation and Air Conditioning (HVAC) systems of buildings [1]
The most traditional design of a Fin-and-Tube Heat Exchanger (FTHE) with plain fins [5, 6] can be made smaller by making the fin wavy [7, 8, 9]
The present results indicate the trade-off between FTHE Reynolds number and the fouling rate

Summary

Introduction

Around 10 − 20% of the energy consumption in developed countries is used by the Heating Ventilation and Air Conditioning (HVAC) systems of buildings [1]. Used type of a heat exchanger in the air conditioning unit is a Fin-and-Tube Heat Exchanger (FTHE). Inside the FTHE, heat is exchanged between the flowing air between the fins and the fluid flow in the tubes. The most traditional design of a FTHE with plain fins [5, 6] can be made smaller by making the fin wavy [7, 8, 9] In this way, smaller heat exchangers could be designed. As enabled by louvered [10] and slit [11] fins even more compact heat exchangers have been made for various different air conditioning applications. New designs obtained with CFD are only valid for a new heat exchanger for a short period of time

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