Theoretical and experimental heat transfer studies of the rat tail with application to the human digi

In this dissertation an experimental study is conducted to investigate the thermoregulatory function of the rat tail blood flow and the tail heat transfer. A non-uniform three-dimensional perfusion model of the tail heat transfer is presented to predict the heat transfer and temperature profile of the tail. The tail is the primary heat transfer organ in the rat and under conditions of heat stress can account for up to 40% of the rat's total energy exchange. The rat tail is believed to be a good model for heat exchange in the human fingers.;A brief introduction to the thermoregulatory and heat transfer mechanisms in the human limb, digit and rat tail is given in chapter 1. In chapter 2 a new approximate analytic solution technique is developed for treating the heat exchange between two or more axially interacting vessels which are arbitrarily positioned in the cross-section of a tissue cylinder. The cylinder exchanges heat by convection with the environment and has a non-uniform surface temperature due to the vessel eccentricity. The solution to this fundamental configuration can be used as a building block for modeling heat transfer in the rat tail, human digit and limb.;In chapter 3 the tail vascular anatomy is first examined experimentally and the crucial vascular elements in the tail blood flow regulation and heat transfer are identified. This anatomical study is then used to construct a simplified model of the rat tail heat transfer. The rat tail blood flow regulation and heat transfer in response to variant local and central temperatures are then investigated experimentally. The blood flow at the tail base and middle are measured by strain gauge plethysmography. The blood flow at the tail tip is measured by a new computerized balance technique. The tail surface temperature profile and the rat rectal temperature are measured by infra-red thermography and calibrated thermocouples. Experimental results show that the tail volumetric blood perfusion is highly non-uniform along its length. The primary mechanism for rat thermoregulation is the change in tail blood flow. The blood flow increases in an on-off manner in the tail middle and tip regions, and in a proportional manner with the rat core temperature in the base region for rats under body heating.;Based on the experimental studies in chapter 3, a new three-dimensional model is developed in chapter 4 to determine the heat transfer function of the rat tail at different local and central temperatures. This model takes into account the axial variation in tail anatomy and our experimental measurements of the axial blood flow distribution. Good agreement between the model predictions and the experimental measurements is obtained for the axial surface temperature distribution in the tail.