ONKOCET Ltd. has exhibited the devices from its portfolio on the MEDTEC UK exhibition in Birmingham, April 2011 through our partner Medical & Partners.
Humans, and animals in general, are usually in a thermal steady state with respect to their surroundings. In particular, endotherms seek to control their body temperatures. Heat generated by metabolic processes is lost to the environment though several mechanisms: radiation, conduction, convection, and evaporation. Unless the organism has more heat than can be eliminated by radiation and convection, evaporation (through perspiration) is not required and conduction is negligible.
Convective thermal flux
The cooling of human body through convection mechanism we cam determine using thermal flux equation
where:
Q/A is the thermal flux (W/m2),
L is the characteristic length of the body,
k is the thermal conductivity of the fluid,
?T is the temperature difference between the body and the surrounding fluid
?T = Tskin – Tambient.
Nu is Nusselt number can be found by computing the Rayleigh number.
Ra ?Rayleigh number Ra = (?/??)g?TH3 Human body: Ra ~ 108
The relationship between Nu and Ra is empirical.
Human body radiation rate is determined by the Stefan-Boltzmann Law,
where:
T0 is the ambient absolute temperature,
? is the emissivity,
? is the Stefan-Boltzmann constant.
For skin or clothing, emissivity is near unity. This approximation is valid when ?T is small compared to the ambient temperature, T0.
The ratio of convective to radiative transfer is only weakly dependent on temperature difference:
Hence, the assumed value for ?T of 10°C is not critical to the comparison of the relative importance of convection and radiation. The convective heat loss rate is about half the radiative rate.
Convection is an important mechanism in cooling the human body. Under room conditions, convection accounts for about 1/3 the thermal loss of the human body in cool, radiation assumes a minor role in human thermal balance.
Heat balance (thermal equilibrium) is the balance between the rate of heat production and the rate of heat loss. The rate at which heat is produced depends primarily on our metabolic rate.