Calculation of Convective and Radiative Heat Transfer Coefficient Using Thermography During a Physical Exercise

A detailed model of human thermoregulation and a numerical algorithm to predict thermal comfort is a novel field of research and has wide applications in the auto/transportation industry and in the heating, ventilating, and air-conditioning (HVAC) industry. Anatomically specific convective and radiative heat transfer coefficients for the human body will be required to understand the human thermal physiological and comfort models.

Thermally uncomfortable indoor climates cause not only the usability of the space but also minimizes the performance of occupants which might end up with a loss of productivity in a workplace and sometimes it might induce sickness in the occupants. It necessitates creating hygienic and thermally comfortable spaces for the users. The physiological nature of thermal comfort during a transient condition such as a physical exercise or travel in an automobile is not yet well understood.

In this paper, three different recovery processes were considered after the running of a human model on a treadmill with a range of speeds starting from 2 miles/hour to 10 miles/hour for a stretch of twenty minutes. The recovery process included, (a) fan-assisted cooling with an air velocity of 2.5 m/s for 30 minutes, (b) fan-assisted cooling with an air velocity of 5 m/s for 30 minutes, and (c) natural cooling with no assistance of fan for 30 minutes. Thermal images were taken for forehead, trunk, arms, hands, legs of the models and the convective heat transfer coefficient and the radiative heat transfer coefficient were calculated. The human models included both male and female and belonged to three different age groups of less than 15, between 15 to 30, and above 40 with a total of 24 participants. The results show that though the temperatures, measured using thermography, for various parts of the human body changed locally, the overall calculated radiative heat transfer coefficients matched with the ASHRAE handbook values, and the calculated convective heat transfer coefficient increased with the increase of air velocity, while the models cooled down after the workout. Interestingly, the skin temperature decreased, initially, as the exercise progressed. After the completion of the exercise, the skin temperature exhibited a quick rise during the recovery period with a subsequent decrease in the temperature, later. This trend was the same with all different age groups and sex of the models. The results also confirm that thermal images can be relied on for calculating the convective and radiative heat transfer coefficients of the human body to determine the heat transfer rate.