Optimizing the Benefits of Pulse Combustion Impingement for Paper Drying

Abstract

Numerical simulation results, quantifying the effects of impingement zone geometry on pulse-combustion-driven and steady-impingement heat transfer, are used to investigate the design tradeoffs between heat transfer rate (i.e., drying rate), heat transfer (jet thermal energy) effectiveness, and heat transfer enhancement due to the pulsating jet. At equal area-average heat flux, it was found that nozzle spacing and, thus, jet thermal energy effectiveness may be as much as three times greater for pulsating impingement jets as for steady-flow jets having the same temperature and mean velocity. Alternatively, at equal jet thermal energy effectiveness, the average heat flux (drying rate) with pulsating impingement may be around 2.4 times greater than with steady impingement.

Pulse Combustion Drying

“…On the basis of numerical results, a small-sized pulse combustor was designed and tested that provided a good agreement with experimental observations. By using a CFD model, Ahrens et al (2011) determined the nozzle spacing in the impingement zone during pulse combustion and the steady impingement drying of tissue ("Yankee dryers"). These authors also proved that the jet thermal energy effectiveness may be threefold higher for pulsating impingement jets than for steady-flow jets at the same temperature and mean velocity.…”

“…However, oscillations in the large recirculation zone between the dryer axis and the wall are observed during each cycle of combustor operation. As the experimental analysis of the PCD process is known to be difficult, hostile, and expensive, CFD models have become increasingly valuable tools not only for delivering information on the mechanism of PCD but also assisting in the design of pulse combustion systems, including the shape of the drying chamber (e.g., Wu, 2007), the increased efficiency of a drying process (e.g., Ahrens et al, 2011;Widiyastuti et al, 2007), and reductions in noise emissions (e.g., Zbicinski et al, 1999). However, a confident and effective scale-up presupposes the development and use of validated CFD models of PCD processes (Wu and Mujumdar, 2006b;Kudra, 2008).…”

Drying of paper: A review 2000–2018

“…Two of the main conclusions were that efficient drying extended up to three diameters of the tail pipe and that near the stagnation point heat transfer is governed by the impingement jet flow while outside this region the impingement vortex is of major importance. Patterson and Ahrens [43] and Ahrens et al [44] studied the process both experimentally and by performing CFD calculations. The experiments were performed with three different prototype combustors; aerodynamic valve, pressurized combustion chamber and a multifunctional system.…”