Heat transfer to blood vessels

Area of Science:

• Biomedical Engineering
• Thermodynamics
• Physiology

Background:

• Understanding heat transfer in blood vessels is crucial for thermoregulation and medical applications.
• Previous models often simplified the complex thermal interactions between blood and surrounding tissues.

Purpose of the Study:

• To investigate heat transfer dynamics in individual blood vessels under various configurations.
• To determine the influence of vessel size, arrangement, and proximity to the skin surface on thermal exchange.

Main Methods:

• Analysis of heat transfer in three configurations: single vessel, counterflow vessels, and superficial vessels.
• Utilized the Graetz number (Gz) as a key parameter to characterize heat exchange efficiency.
• Examined the impact of vessel separation, counterflow mass transfer, and film coefficients on heat transfer.

Main Results:

• Small vessels (arterioles, capillaries, venules) with low Gz (< 0.4) function as efficient heat exchangers, equilibrating blood and tissue temperatures.
• Large vessels (arteries, veins) with high Gz (> 10^3) exhibit negligible heat exchange.
• Counterflow heat transfer is primarily governed by vessel separation and mass transfer, with flow film coefficients playing a secondary role.
• Superficial vessel effects on skin temperature and environmental heat transfer depend on depth-to-radius ratio and Biot number.

Conclusions:

• Blood vessel size significantly dictates its role in local heat transfer, ranging from perfect exchangers to near-adiabatic conduits.
• Vessel proximity and arrangement, particularly in counterflow, are critical factors influencing thermal interactions.
• The thermal impact of superficial vessels on the skin is predictable based on geometric and convective parameters.