The enhancement and optimization of heat transfer are essential for energy conservation and environment protection, because heat transfer is related to almost % of total energy consumption in industry. Convective heat transfer is one of the common transport processes in industry. It is highly important to develop a theory and corresponding technology for enhancing convective heat transfer. Through numerical simulation and experimental analysis, researchers have developed many technologies to enhance the heat transfer in tube flow. Correspondingly, certain heat-transfer-enhanced tubes are exploited, such as inner-finned tubes [], spiral corrugated tubes [], and micro-finned tubes []. Bejan et al. [] divided the tube flow into two parts: boundary flow and core flow. The flow near the wall of tube is defined as boundary flow and the remaining is core flow. In the aforementioned heat-transfer-enhanced tubes, the surfaces in the boundary, which dominate the convective heat transfer between fluid and tube wall, are designed or improved to enhance heat transfer. The mechanism for heat transfer enhancement includes []: disturbing the boundary layer, extending the heat transfer surface, and changing the physical properties of the heat transfer surface. Therefore, this kind of method can be designated as surface-based heat transfer enhancement (abbreviated as the surface-based method). This method effectively enhances the convective heat transfer coefficient, but the increase in flow resistance may become significant and the comprehensive performance can be weakened.

در صورتیکه که جایی برای طراحی و اجرای مسیرهای پیاده روی عمومی در نظر گرفته می شود و این مسیر پیاده روی عمومی بخشی از مسیر خیابان های عمومی نیست، توسعه صنعتی مجاور نباید به گونه‌ای باشد که زیبایی و ایمنی مسیرهای پیاده‌روی را کاهش دهد.

The equilibrium equation of available potential is obtained, in which the local exergy destruction rate is defined to express the irreversibility loss of the convective heat transfer process. Different from the surface-based heat transfer enhancement method, the fluid-based method is put forward by considering both thermal and flow resistances. The optimal mathematical model is constructed by the two-region method to reflect the principle of fluid-based heat transfer enhancement. By numerically solving the governing equation deduced through functional variation for Lagrange function, the optimal velocity field is obtained. The theoretical analysis is benefit to the high-efficiency and low-resistance heat transfer enhancement technologies. Specific conclusions are summarized as follows. () Available potential represents the energy grade of the fluid, and its equilibrium equation expresses the transport process of available energy. By reducing the exergy destruction of the fluid, the irreversibility of transport process can be decreased. () An optimization method of convective heat transfer is constructed by setting exergy destruction rate as optimization objective in the core flow and fluid power consumption as optimization objective in the boundary flow in a circular tube, which supports the principle of fluid-based heat transfer enhancement. () Numerical results by solving the governing equations show that the optimized flow field in a circular tube is in a structure of longitudinal swirling flows, which shows alternating large and small vortexes in the cross section of tube, and heat transfer can be greatly enhanced with a slight increase in flow resistance.

تولید باریکه های مرجع پرتوهای یونساز با انرژی و دز مشخص، در آزمایشگاههای دزیمتری است.اندارد از اهمیت کاربردی زیادی برخوردار است.. است.انداردهای معینی در زمینه معرفی و نحوه تولید این پرتوها، توسط سازمانهای بین المللی ذیربط، از جمله ISO و IAEA  تدوین و منتشر شده اند. در این مقاله چگونگی تولید و تعیین مشخصات بخشی از باریکه های پرتو ایکس مرجع در سطح پرتودرمانی و حفاظت در برابر پرتوها را با است.فاده از یک دستگاه مولد ایکس نوع Philips RT و براساس است.انداردهای بین المللی موجود شرح داده و سعی کرده ایم تا پرتوهای ایکس حاصل در حد امکان نزدیک به پرتوهای ایکس مرجع و است.اندارد باشند.

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