Abstract
A novel heating efficiency analysis of the microwave heated stop-flow (i.e. stagnant
liquid) and continuous-flow reactors has been presented. The thermal losses to the surrounding
air by natural convection have been taken into account for heating efficiency calculation of
the microwave heating process. The effect of the load diameter in the range of 4–29 mm on
the heating efficiency of ethylene glycol was studied in a single mode microwave cavity under
continuous flow and stop-flow conditions. The variation of the microwave absorbing properties
of the load with temperature was estimated. Under stop-flow conditions, the heating efficiency
depends on the load diameter. The highest heating efficiency has been observed at the load
diameter close to the half wavelength of the electromagnetic field in the corresponding
medium. Under continuous-flow conditions, the heating efficiency increased linearly. However,
microwave leakage above the propagation diameter restricted further experimentation at
higher load diameters. Contrary to the stop-flow conditions, the load temperature did not
raise monotonously from the inlet to outlet under continuous-flow conditions. This was due to
the combined effect of lagging convective heat fluxes in comparison to volumetric heating.
This severely disturbs the uniformity of the electromagnetic field in the axial direction and
creates areas of high and low field intensity along the load length decreasing the heating
efficiency as compared to stop-flow conditions.
liquid) and continuous-flow reactors has been presented. The thermal losses to the surrounding
air by natural convection have been taken into account for heating efficiency calculation of
the microwave heating process. The effect of the load diameter in the range of 4–29 mm on
the heating efficiency of ethylene glycol was studied in a single mode microwave cavity under
continuous flow and stop-flow conditions. The variation of the microwave absorbing properties
of the load with temperature was estimated. Under stop-flow conditions, the heating efficiency
depends on the load diameter. The highest heating efficiency has been observed at the load
diameter close to the half wavelength of the electromagnetic field in the corresponding
medium. Under continuous-flow conditions, the heating efficiency increased linearly. However,
microwave leakage above the propagation diameter restricted further experimentation at
higher load diameters. Contrary to the stop-flow conditions, the load temperature did not
raise monotonously from the inlet to outlet under continuous-flow conditions. This was due to
the combined effect of lagging convective heat fluxes in comparison to volumetric heating.
This severely disturbs the uniformity of the electromagnetic field in the axial direction and
creates areas of high and low field intensity along the load length decreasing the heating
efficiency as compared to stop-flow conditions.
| Original language | English |
|---|---|
| Pages (from-to) | 83-92 |
| Journal | The Journal of microwave power and electromagnetic energy |
| Volume | 46 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 2012 |
Keywords
- Continuous flow
- Heating efficiency
- Microwave
- Single mode cavity
- Stop flow