To reduce the invasiveness of cryosurgery, a miniaturized cryoprobe is necessary. The authors have developed an ultrafine cryoprobe for realizing low-invasive cryosurgery by local freezing. The objectives of this stud...To reduce the invasiveness of cryosurgery, a miniaturized cryoprobe is necessary. The authors have developed an ultrafine cryoprobe for realizing low-invasive cryosurgery by local freezing. The objectives of this study are to estimate the heat transfer coefficient and investigate the characteristics of the phase change heat transfer in the ultrafine cryoprobe. This cryoprobe has a double-tube structure consisting of two stainless steel microtubes. The outer diameter of the cryoprobe was 550 μm. The alternative Freon HFC-23, which has a boiling point of ?82?C at 0.1 MPa, was used as a refrigerant. To evaluate the characteristics of boiling flow in the cryoprobe, the heat transfer coefficient was estimated. The derived heat transfer coefficient was higher than that obtained from the conventional correlation. Additionally, a bubble expansion model was introduced to evaluate the heat transfer mode of the phase change flow in the ultrafine cryoprobe. This model can estimate the liquid film thickness during the expansion of a single bubble in a microchannel. The experimentally measured wall superheat was much lower than that obtained from the model. Therefore, this result also implied that the heat transfer mode in the ultrafine cryoprobe should be nucleate boiling.展开更多
Accurate prediction of thermal radiation by applying rigorous model for the radiative heat transfer combined with the conduction and the convection has been performed for a single and double window glazing subjected t...Accurate prediction of thermal radiation by applying rigorous model for the radiative heat transfer combined with the conduction and the convection has been performed for a single and double window glazing subjected to solar and thermal irradiation. The glass window is analysed as a non-gray plane-parallel medium disctritized to thin layer as-suming the glass material as participating media in one-dimensional case, using the Radiation Element Method by Ray Emission Model (REM2). The model allows the calculation of the steady-state heat flux and the temperature distribution within the glass cover. The spectral dependence of the relevant radiation properties of glass (i.e. specular reflectivity, refraction angle and absorption coefficient) is taken into account. Both solar and thermal incident irradiations are applied at the boundary surfaces using the spectral solar model proposed by Bird and Riordan. The optical constant of a commercial clear glass material have been used. The calculation has been performed during winter period and the effect of the thickness of the glass for a single glazing and of the air layer between the two panels for double glazing has been studied. The result shows that increasing the air layer, the steady heat flux decreases and the temperature distribution within the glass changes.展开更多
文摘To reduce the invasiveness of cryosurgery, a miniaturized cryoprobe is necessary. The authors have developed an ultrafine cryoprobe for realizing low-invasive cryosurgery by local freezing. The objectives of this study are to estimate the heat transfer coefficient and investigate the characteristics of the phase change heat transfer in the ultrafine cryoprobe. This cryoprobe has a double-tube structure consisting of two stainless steel microtubes. The outer diameter of the cryoprobe was 550 μm. The alternative Freon HFC-23, which has a boiling point of ?82?C at 0.1 MPa, was used as a refrigerant. To evaluate the characteristics of boiling flow in the cryoprobe, the heat transfer coefficient was estimated. The derived heat transfer coefficient was higher than that obtained from the conventional correlation. Additionally, a bubble expansion model was introduced to evaluate the heat transfer mode of the phase change flow in the ultrafine cryoprobe. This model can estimate the liquid film thickness during the expansion of a single bubble in a microchannel. The experimentally measured wall superheat was much lower than that obtained from the model. Therefore, this result also implied that the heat transfer mode in the ultrafine cryoprobe should be nucleate boiling.
文摘Accurate prediction of thermal radiation by applying rigorous model for the radiative heat transfer combined with the conduction and the convection has been performed for a single and double window glazing subjected to solar and thermal irradiation. The glass window is analysed as a non-gray plane-parallel medium disctritized to thin layer as-suming the glass material as participating media in one-dimensional case, using the Radiation Element Method by Ray Emission Model (REM2). The model allows the calculation of the steady-state heat flux and the temperature distribution within the glass cover. The spectral dependence of the relevant radiation properties of glass (i.e. specular reflectivity, refraction angle and absorption coefficient) is taken into account. Both solar and thermal incident irradiations are applied at the boundary surfaces using the spectral solar model proposed by Bird and Riordan. The optical constant of a commercial clear glass material have been used. The calculation has been performed during winter period and the effect of the thickness of the glass for a single glazing and of the air layer between the two panels for double glazing has been studied. The result shows that increasing the air layer, the steady heat flux decreases and the temperature distribution within the glass changes.