Estimation of heat transfer coefficients in oscillating flows: The thermoacoustic case

Thermal performance of finned-tube thermoacoustic heat exchangers in oscillatory flow conditions

“…It was shown that, when (ξ a − g)/L increases, the total heat flux, hence the heat transfer coefficient, increases before it reaches a maximum value and decreases. A local reverse heat flux could be observed at the edge of the plates, which was also observed by Piccolo and Pistone [8]. The result shows that there is an optimal heat exchanger length to keep the reverse heat flux minimum and to maximize the total heat flux for a given gas displacement amplitude.…”

“…It is considered to be partly caused by the variation of the effective heat exchange length. It is known that a net heat transfer between the oscillatory flow and its adjacent plate-form stacks or fin type heat exchangers takes place only at the plate edge [4,5,8,15]. It is within this heat exchange length that there is a non-zero time averaged heat flux from/to the plates.…”

“…It is within this heat exchange length that there is a non-zero time averaged heat flux from/to the plates. Piccolo and Pistone [8] reported that for a given oscillation amplitude of the flow, the heat exchange length rapidly increases with D/δ κ when D/δ κ < 2.0. The heat exchange length continues to increase till D/δ κ is around 5.0, after which there is little change in the heat exchange length.…”

“…These parameters in non-dimensional form include the heat exchanger length, the fin spacing and the gap between heat exchangers and plate stacks. In their numerical study of similar heat exchangers made of plate fins, Piccolo and his co-worker [6,7,8] introduced a model to predict the nondimensional heat transfer coefficients, i.e. the Nusselt number and the Colburn-j factor.…”

A Comprehensive Empirical Correlation for Finned Heat Exchangers with Parallel Plates Working in Oscillating Flow

“…However, the impact of relative fluid displacement amplitude is actually a result of comprehensive effects; an aspect which has been neglected in the previous study. Piccolo [22] numerically studied the relationship between the mean convective heat transfer coefficient h, and the relative displacement amplitude A r , under the same pressure ratio based on energy conservation. Results showed that remarkably, h increased with increasing A r when A r > 1, while h remained constant when A r ≤ 1, which does not reflect the results concluded in this paper.…”