RD training - heat pipe I - v01.ppt

* * * 1 Heat Transfer RD @ 中山 Presented by: Rickey Chen May 5, 2006 Principles of Heat Pipe 热管原理 Part I agenda presentation Heat pipe and T-S diagram Heat pipe operational limitations A variety of heat pipes Heat pipe and T-S diagram Review of Entropy and a Rankine Cycle boiler turbine condenser pump Qh Qc Wout WS 1 2 3 4 Tin Tout 1 2 3 4 T S 将?Q视为一load，则dS为在某一温度下所能负载的热量，其类似一温度负载的观念。当系统有mass flow的情形下，entropy也会因mass的改变而有所改变。 Qin Qin 1 1 2 3 4 T S 4 3 Qout / fin Qout / fin heat flux vapor stream 2 Liquid flow Evaporator 1 2 Vapor flow 3 Condenser 4 Qwall Evaporate Isothermal Condense Function block T-S diagram An Introduction to Heat Pipe Wick or Capillary Structure 热管由三个主要的构件所组成：封闭容器、毛细结构以及工作液体。这三种构件具有相等的重要性。而热管可分成三个部份： 蒸发段( Evaporator Section)、绝热段(Adiabatic/isothermal Section)以及凝结段(Condenser Section)。 当热管运作时，蒸发段的工作流体经管壁吸热而汽化，此时生成高压的蒸汽，高的蒸汽压会驱动生成之蒸汽，经由绝热段冲向凝结段因冷凝而释放潜热并凝结饱和液体。从T-S图上可看到相对蒸发段的低压，此高低压差就是蒸汽的驱动力。冷凝生成之工作液体，会藉由毛细结构与表面张力所产生之毛细压力而回流至蒸发段。当毛细压力足够时，可将工作液体持续不断的送回至蒸发段。这样就能使蒸发 - 凝结的过程重复而成为ㄧ循环。 通常在管内灌入液体后，会进行抽真空的程序，此主要目的在降低管内的饱和蒸汽压，使得工作流体在比较低温的情形下就可以蒸发，带动热力循环。 热管原理简介 Heat pipe could be operated as Rankine cycle. 1 2 3 4 T S Is it correct ? Question ! No! It is not a really case. 1 T S 3 saturated vapor / lower pressure 4 saturated vapor / high pressure 2 saturated liquid compressed liquid In this cycle, a small degree of subcooling is evident in the condenser as shown by the small dip down to point 1. Small amount of subcooling will increase the heat flux rate since additional heat has been removed from the cycle to the cooling water as heat rejected. This is a T-s diagram of a heat pipe thermal cycle which more closely approximates actual processes. The pump (capillary structure) and turbine (vapor stream) in this cycle more closely approximate real ones and thus exhibit an entropy increase (2?3 and 4?1) across them. More Actual Processes of Heat Pipe Thermal Cycle 2? superheated vapor Do you understand what is the RD key points? Are there capillary force, rem