The effect of heater orientation on the critical heat flux in a saturated pool boiling with honeycomb porous plate on nanoparticle deposited surface

One of the main concerns in In-Vessel Retention (IVR) for a severe accident is to guarantee the sufficient cooling performance in order to avoid melt-through of pressure vessel. Under a severe accident condition, the vessel is submerged in water, and then boiling is occurred. The heat removal is limited by critical heat flux (CHF) at the outer surface of the reactor vessel. Therefore, in order to enhance the capability of the IVR in the severe accident of the light-water reactors, methods to increase the CHF should be considered. Various surface modifications of the boiling surface, e.g., integrated surface structures, such as channels and micro-pin fins, and the coating of a micro-porous layer using sintered metal powders and nanoparticle deposition onto the heat transfer surface, have been proven to effectively enhance the CHF in saturated pool boiling. In particular, the critical heat flux by the attachment of a honeycomb-structured porous plate on a flat heated surface facing upward increases more than approximately twice compared to that of a plain surface under saturated pool boiling condition (Mori and Okuyama (2009)). This is attributed to the honeycomb porous plate which provides automatic liquid supply due to capillary action and the reduction of the vapor escape flow resistance due to the separation of the liquid and vapor flow paths. Moreover, it is well-known that the CHF with nanoparticle deposited heated surface is greatly enhanced. However, the effect of the heated surface orientation on the CHF with honeycomb porous plate on nanoparticle deposited surface is not clarified yet. Therefore, we focus on the use of honeycomb porous plate and nanoparticle coated surface to improve the IVR capability in the severe management strategy implemented by light-water reactors. (author)