Tham khảo tài liệu 'convection and conduction heat transfer part 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 260 Convection and Conduction Heat Transfer where 8ij is the kronecker delta function and k is the tissue thermal conductivity. Clearly this equation represents one of the most significant contributions to the bio-heat transfer formulation. But in practical situations this equation needs detailed knowledge of the sizes orientations and blood flow velocities in the countercurrent vessels to solve it and that presents a formidable task. Furthermore there are several issues related to the WJ model. First thoroughly comparison for both predicted temperatures and macroscopic experiments are required. Secondly the formulation was developed for superficial normal tissues in which the counter-current heat transfer occurs. In tumors the vascular anatomy is different from the superficial normal tissues and therefore a new model should be derived for tumors. Some Wissler 1987 has questioned the two basic assumptions of WJ model first that the arithmetic mean of the arteriole and venule blood temperature can be approximated by the mean tissue temperature and second that there is negligible heat transfer between the thermally significant arteriole-venule pairs and surrounding tissue. Thermally significant blood vessel model As CH and WJ models presented many investigators Baish et al 1986 Charny and Levin 1990 during late 1980 questioned mostly on blood perfusion term or how to estimate blood temperature and local tissue temperatures where blood vessels counter-current vessels are involved. As arterial and veinous capillary vessels are small their thermal contributions to local tissue temperatures are insignificant. However some larger vessel sizes than the capillaries do have thermally significant impacts on tissue temperatures in either cooling or heating processes. Several investigators Chato 1980 Lagendijk 1982 Huang et al 1994 examined the effect of large blood vessels on temperature distribution using theoretical studies. Huang et al Huang et al 1996 in 1996 presented
