Despite a century of progress in understanding steady-state condensation, less is known about transient condensation. However, several industrial systems and devices operate in transient mode, dissipating high heat load for very short time intervals, and dissipating much less heat for the rest of the time. Sett et al. study transient pulse condensation of ethanol vapor.
The researchers attained up to eight times higher condensation heat transfer during transient condensation of ethanol. Transient condensation would allow designers to create more compact condensers, which is particularly important for applications where mass and volume is important, such as air and naval platforms.
“What surprised us most was the magnitude of the heat transfer enhancement,” said author Nenad Miljkovic. The researchers also found that the condensation heat transfer enhancement can be realized on any surface and is independent of condensation mode. Furthermore, repeated cycles or pulses can lead to a moderate 30% higher time-averaged heat transfer performance when compared to steady state.
The researchers conducted pulse condensation, during which repeated cycles of a cold surface were exposed to vapor followed by vapor evacuation. The evacuation process cleans the existing condensed droplets on the cold surface, exposing a larger surface area to the incoming vapor of the next cycle and enhancing the condensation rate. The condensation rate is directly related to heat transfer and hence using this method, the researchers enhanced the transient heat transfer.
This mode of condensation could be utilized for any system operating in transient conditions that have fluctuating electrical or heat loads. Now scientists have a new mechanism to enhance condensation heat transfer other than changing the mode of condensation from filmwise to dropwise using surface chemistry or roughness.
Source: “Transient pulse condensation,” by Soumyadip Sett, Peter Sokalski, Manan Mehta, Kazi Fazle Rabbi, Alperen Gunay, and Nenad Miljkovic, Applied Physics Letters. The article can be accessed at https://doi.org/10.1063/5.0015311.