Numerical and experimental study of acoustically enhanced heat transfer from a single particle in flue gas

ABSTRACT

To investigate the heat transfer of pulverized coal particles under the effect of an acoustic field (without a superposed steady component), we derived and solved the two-dimensional, unsteady, laminar conservation equations for mass, momentum, and energy transport in the flue gas phase of a power plant boiler. The local, space-averaged, and space- and time-averaged Nusselt (Nu) numbers for the coal particles are discussed for the full audible frequency range. Experiments were also conducted to study the heat transfer, in particular the heat exchange at the surface, considering the effect of the acoustic wave around a stationary copper sphere. The sphere was exposed to different sound pressure levels of acoustic waves in air, and the temperature of the sphere was recorded. The range of the studied sound frequencies is between 500 Hz and 3 kHz. Both, numerical and experimental investigations indicate that the acoustic field can increase the heat transfer significantly. Higher sound pressure levels cause higher heat-transfer rate. However, there is a special frequency, at which Nu reaches a maximum, due to the flow separation caused by flow acceleration. This special frequency increases with increasing sound pressure level.

KEY WORDS:

• Acoustically enhanced heat transfer
• Nusselt number
• Phase lag
• Acoustic streaming
• Sound pressure level

Additional information

Funding

Support is acknowledged from the National Natural Science Foundation of China (11474091 and 11674093) and the Fundamental Research Funds for the Central Universities (2015XS105)