Theoretical prediction of temperature difference between prefrontal cortex and forehead skin for fever screening

Abstract

To improve reliability of fever screening, many studies have been conducted on the relationship between forehead skin and core temperatures. However, all studies thus far were based on only statistical analyses of temperature data, and it remains unsolved how forehead skin temperature is determined and controlled by environmental temperature as well as face details of individual. This study examined heat transfer in a free convection thermal boundary layer on the human forehead theoretically and experimentally to propose a theoretical model describing the relationship between prefrontal cortex (PFC) and forehead skin temperatures. Temperature distributions across the forehead boundary layer measured using a resistance thermometer probe showed that the convective heat flux on the forehead, including the case of wearing face mask, could be estimated similarly to that in a laminar free convection boundary layer on a heated vertical plate. It was also shown that the difference between PFC and forehead skin temperatures measured using a zero-heat-flux core-temperature monitoring probe and a thermocouple attached to the forehead was well represented by a simple formula derived from analyses of radiative and convective heat fluxes over a normal range of environmental temperature. Wearing a face mask little affected the temperature difference between PFC and forehead skin. These results provide a scientific basis for fever screening from thermo- and fluid-dynamics viewpoints.