On the measurement of the mean radiant temperature by means of globes: An experimental investigation under black enclosure conditions

Mean radiant temperature is one of the four physical quantities required for the objective assessment of thermal environments. Due to its simplicity and relatively good accuracy, the most common measurement method is the black globe thermometer. Most studies have investigated the effects of diameter on the response time, of globe materials on its accuracy and the heat transfer modelling. Unfortunately, results seem to be inconsistent due to the difficulty of calibrating and metrologically characterizing globe thermometers under uniform black enclosure conditions. Besides, few studies have been focused on the accuracy of small globes that could result in a wrong assessment of the thermal environment. To answer to these open issues, this study will be focused on a metrological analysis of a wide sample of globes (metallic-made and plastic-made with different diameters) carried out in a testing apparatus specifically designed to reproduce a black uniform enclosure whose temperature can be strictly controlled. Obtained results revealed high errors of the mean radiant temperature measurement by tennis-table globes (up to 6 degrees C) which require a specific reformulation of convective heat transfer modelling, and lower response time (3-4 min) of table-tennis globes if compared with large ones (6-9 min).