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ABSTRACT
Experiments are conducted on a laboratory-scale fixed bed combustor. This article discusses some of the data analysis methodologies that define the onset of steady state conditions, which are widely reported in the literature but poorly defined. The effects of using different methods to determine the onset of the steady state performance, and to correct thermocouple data so as to account for radiative effects, are also presented. Results show that using a combination of CO and NO emissions with free-board temperatures (at multiple axial positions) is more effective than other emissions, using temperatures (only) or the fuel burning rate (kg m–2 s–1). An important indicator is to analyze the percentile deviation of temperatures and emissions, compared to only using the time evolution of these variables. To characterize the significance of correcting thermocouple data for radiative (wall) losses, two numerical models (aspirated and bare bead) were compared. Radiative effects on thermocouples were found to be most prominent nearer to the downstream secondary air inlet due to the cooler wall temperature. Due to the likely radiative effects from freeboard deflectors, the sensitivity of these outcomes to the presence of downstream deflectors is also presented.
Acknowledgment
The authors gratefully acknowledge Ms. Araceli Regueiro Pereira of the University de Vigo for assisting with the data acquisition.
Funding
The PhD research project of Babak Rashidian was made possible by an Edith Cowan University International Postgraduate Research Scholarship (ECU-IPRS).
Nomenclature
| Ab | = | surface area of thermocouple bead (m2) |
| Aso | = | surface area of outer shield for single sheathed aspirated thermocouple (m2) |
| Cpg | = | heat capacity (J kg–1 K–1) |
| dTC | = | thermocouple diameter (m) |
| hg | = | flue gas convective heat transfer coefficient (W m–2 K–1) |
| hgb | = | convective heat transfer coefficient between aspirating gas flow and thermocouple bead for single sheathed aspirated probes (W m–2 K–1) |
| kg | = | gas thermal conductivity (W m–1 K–1) |
| Mi | = | measurement variable |
| = | burning rate (kg m–2 s–1) | |
| Nu | = | Nusselt number |
| Pr | = | Prandtl number |
| r | = | radial distance (mm) |
| R | = | percentile mean deviation |
| Re | = | Reynolds number |
| Tb | = | thermocouple bead temperature (K) |
| TgTj | = | gas temperature (K) |
| Tos | = | outer shield temperature for sheathed aspirated probes (K) |
| Tw | = | wall temperature (K) |
| Qp | = | primary air (lit min–1) |
| Qs | = | secondary air (lit min–1) |
| x | = | axial distance (mm) |
Greeks letters
| εb | = | bead emissivity |
| εso | = | thermocouple sheath emissivity |
| μg | = | flue gas dynamic viscosity (kg m–1 s–1) |
| σ | = | Stefan–Boltzmann constant, 5.67 × 10–8 (W m–2 K–4) |
Notes
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