Abstract
ABSTRACT This research was conducted with the objective of evaluating the thermal inertia and hysteresis of the following materials in a wind tunnel: hollow copper sphere with 150.0 mm diameter used as standard in globe thermometers, hollow brass sphere with 75.0 mm diameter, and two hollow plastic spheres with 115.5 and 69.7 mm diameter. The results showed that the thermal inertia and hysteresis for the hollow copper sphere were approximately 24 and 28 min, respectively; these values were bigger than those obtained for the other spheres, implying faster responses of these. While there were no statistical differences in the measurements conducted by globe thermometers which are used to indicate the black globe temperature with the different types of spheres mentioned above under indoor environment conditions, i.e., with no wind and solar radiation, the wind causes faster cooling in smaller spheres under outdoor environment conditions, which may denote erroneous interpretations of the measurements at those instants. It was concluded that it is possible to replace the hollow copper sphere of diameter 150 mm by other types of spheres to measure the black globe temperature. However, this requires knowledge of the response times of the spheres as well as corrections to be made in the measurements with respect to the globe thermometer standard.
Highlights
IntroductionThe black globe thermometer is an environment energy receiver, widely used to assess the effects of radiant and convective heat transfer on humans and animals.Measurements conducted by the black globe thermometer combine the effects of radiant energy from the sun and neighboring surfaces, temperature and air velocity to assess the effective environmental temperature.This instrument has been used in studies on dairy, beef cattle, swine, equine and poultry (Rojas-Downing et al, 2017; Tavares et al, 2016; Carneiro et al, 2015; Pérez et al, 2015; Silva et al, 2015; Nascimento et al, 2014; Neto& Nääs, 2014; Rosselle et al, 2014; Purswell & Davis, 2008) as well as in studies on humans (Saliba & Lanza, 2016; Oliveira Júnior et al, 2015; NR-15 (MTE, 1978).The ISO standard 7726/1996 describes the use of the globe thermometer to determine the average radiant temperature, as its spherical shape presents an approximation of the shape of the human body in the case of a person sitting repose
The Vsphere/Asphere relation is valid because its largest value represents high thermal inertia and its lowest value represents faster heating at the beginning
The hysteresis using the copper sphere of 15 cm diameter as reference was evaluated as 28 min
Summary
The black globe thermometer is an environment energy receiver, widely used to assess the effects of radiant and convective heat transfer on humans and animals.Measurements conducted by the black globe thermometer combine the effects of radiant energy from the sun and neighboring surfaces, temperature and air velocity to assess the effective environmental temperature.This instrument has been used in studies on dairy, beef cattle, swine, equine and poultry (Rojas-Downing et al, 2017; Tavares et al, 2016; Carneiro et al, 2015; Pérez et al, 2015; Silva et al, 2015; Nascimento et al, 2014; Neto& Nääs, 2014; Rosselle et al, 2014; Purswell & Davis, 2008) as well as in studies on humans (Saliba & Lanza, 2016; Oliveira Júnior et al, 2015; NR-15 (MTE, 1978).The ISO standard 7726/1996 describes the use of the globe thermometer to determine the average radiant temperature, as its spherical shape presents an approximation of the shape of the human body in the case of a person sitting repose. The black globe thermometer is an environment energy receiver, widely used to assess the effects of radiant and convective heat transfer on humans and animals. Measurements conducted by the black globe thermometer combine the effects of radiant energy from the sun and neighboring surfaces, temperature and air velocity to assess the effective environmental temperature. This instrument has been used in studies on dairy, beef cattle, swine, equine and poultry The black globe temperature is obtained by a thermometer inserted into the globe up to the center of the sphere, which presents a manifestation of the thermal balance that occurs within the sphere between the heat gained (or lost) by radiation and the heat lost (or gained) by convection
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