Energy efficiency of a quartz tungsten halogen lamp: Experimental and numerical approach

Despite quartz tungsten halogen (QTH) lamps being employed in research and industrial applications for many decades, the thermal performance of these infrared (IR) sources has yet to be comprehensively studied. Consequently, neither the radiative efficiency of these lamps nor the effect of operating conditions on the radiative efficiency are well understood. This poses a significant challenge when modelling or designing QTH based heating systems. This research, therefore, presents the results of an investigation into the radiative efficiency of a QTH lamp over a range of operating temperatures using a Schmidt-Boelter heat flux sensor. A procedure to comprehensively characterise the performance of the QTH source is outlined and a new equation is derived to estimate the diameter and surface area of the filament. The results indicate that the efficiency of the lamp is highly dependent on the filament temperature with a minimum radiative efficiency of 91% and a maximum of 95% measured at approximately 2500 K and 3000 K, respectively. The radiative efficiency was also predicted to be as low as 54% at a filament temperature of ~1000 K using a numerical model of the lamp. The change in thermal efficiency with the temperature of the source was found to be driven by the non-linear dependence of the convective and radiative heat transfer coefficient on the source-ambient temperature difference. Finally, a new efficiency curve for the QTH lamp over a wide range of filament temperatures is provided, which can be used to estimate the efficiency of similar QTH sources.