Prediction of air-side particulate fouling of HVAC&R heat exchangers

Abstract

Air-to-refrigerant heat exchangers used in heating, ventilation, air-conditioning, and refrigeration systems routinely experience air-side fouling due to the presence of particulates in outdoor and indoor environments. The influence on the performance of the heat exchanger, in terms of heat transfer efficiency and pressure drop imposed, depends on the extent of air-side fouling. Fouling of a heat exchanger is determined by a variety of parameters such as the dimensions of the heat exchanger, physical properties of the airborne particulates, and airflow conditions over the heat exchange surfaces. A comprehensive model is developed to deterministically calculate the extent of fouling of a heat exchanger as a function of these parameters by accounting for each of the possible deposition mechanisms. The study enhances modeling approaches previously employed in the literature by accounting for time-dependent accumulation of particles as well as the effects of the streamwise distribution of accumulated dust on subsequent fouling; the calculations for the deposition due to several of the mechanisms are also refined to improve prediction accuracy. Particulate matter deposits already present on the surface are found to accelerate the process of fouling by decreasing available area for airflow; an existing deposit layer effectively decreases the distance that a particle must travel to collide with a surface and increases the surface area available for deposition. The modified model predictions are compared against extant experimental deposition fraction data; an improved agreement is observed compared to previous models in the literature.

Two- and four-way coupling of cohesive poly-disperse particulate foulants on a metal foam fibre immersed in quiescent fluid

“…The restitution coefficient for particle-particle is 0.50. This assumption based on 100 % sticking probability for various heat transfer equipment, such as HVAC&R, is used by various authors (Inamdar et al, 2016;Muyshondt et al, 1998, Siegel 2002, Siegel & Nazaroff, 2003Yang et al, 2012). The cohesion energy density and adhesion energy density between the particle-particle and particle-wall contacts is, respectively, 50000 J/m 3 (Qian et al, 2013).…”

“…The poly-disperse solid foulants are injected at the inlet plane based on a normal Gaussian size distribution with a minimum particle diameter of 5 μm, maximum diameter of 20 μm, mean diameter of 10 μm, and variance of 25. The dust diameter and densities are based on the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) standard test dust (Inamdar et al, 2016). Furthermore, the particulate fouling patterns is investigated based on various particle injection rates, which is based on the total number of particles injected per second (pps) at the inlet plate.…”

“…In particular, the U.S. Department of Energy (2006) enunciated the potentially high fuel savings could be achieved by improving existing operating practices and capital equipment in refineries. Particulate fouling in indoor and outdoor environments are responsible for degrading the performance of heat exchangers in heating, ventilation, air-conditioning, and refrigeration systems (HVAC&R) (Inamdar et al, 2016). Recent technological advancements in electronics cooling have seen an increase in the compactness of heat sink fins (Moore D.A., 2009); however, it is worth mentioning that the dust particles have a detrimental effect on these very small and dense heat sinks.…”

Representing Small Commercial Building Faults in EnergyPlus, Part II: Model Validation

“…Several previous studies focused on capturing the impact of a fault in the building component with experimental measurements. These are either full experimental studies to measure the performance degradation caused by the fault [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] or studies focusing on developing fault models or FDD algorithms that use experimental measurements as a basis for development and validation [29][30][31][32][33][34][35][36][37][38][39][40]. These studies cover various faults that occur in buildings at the component level:…”

“…Envelope material [17,24,25,28] -Air ducts [10] -Heat exchangers [11,19,23,36] Or in system-level equipment:…”