Yasuo Koizumi

Study on Drop Wise Condensation by Using Functionalized Heat Transfer Surface

Condensation heat transfer experiments were performed by using steam at 0.1 MPa The enhancement of drop wise condensation heat transfer by functionalizing a heat transfer surface was examined. A gold-plated surface was used to produce the drop wise condensation. Grooved heat transfer surfaces were adopted to functionalize the heat transfer surface. The shape and the size of the grooves were rectangular and 2 mm × 2 mm × 2 mm, 3 mm × 3 mm × 3 mm and 2 mm × 3 mm × 2 mm (groove depth × groove top part width × groove bottom width), respectively. The heat flux of the grooved surface was larger than that of the plain gold-plated surface. When the groove size was 2 mm × 2 mm × 2 mm and the top parts and the walls of grooves were plated with gold, the heat transfer rate augmentation was highest; the augmentation rate was 1.53. Since to increase the width of the top part of the grooves tends to bring the quality of the surface structure close to the plain surface, to increase the top width of the grooves is not right direction. It was also implied that to make summits and troughs on the surface tends to expose the summit part to steam more, which might result in the heat transfer augmentation.Copyright

CHF-Transition Boiling

This chapter deals with topics on critical heat flux (CHF) point and transition boiling in aspects of heat-transfer mechanisms based on both model simulations and measurements of each authors research in recent decades. n nFirst three sections report heat-transfer modeling on CHF based on measurements and visualization results; i.e., macrolayer dryout model (Section 3.1), microlayer evaporation model (Section 3.2), and contact-line-length density model (Section 3.3). Section 3.4 demonstrates unique surface structures for enhancement of CHF. n nThe following three sections cover other aspects of CHF and transition boiling mechanisms. Section 3.5 reports unified explanations for heater size dependence of CHF. Section 3.6 shows unique characteristics of transition boiling, i.e., negative differential resistance, and focuses on uniformity of surface temperature and heat flux during transition boiling. Section 3.7 discusses liquid–solid contact fraction in transition boiling region and derives correlation for transition boiling curve. n nThe last four sections deal with CHF in flow boiling conditions. Section 3.8 discusses CHF triggering mechanisms and prediction methods in subcooled flow boiling. Section 3.9 shows influence of flow oscillation on convective boiling phenomena. Section 3.10 reports relation between appearance of dry patches and CHF in forced flow boiling. The last section 3.11 focuses on boiling transition phenomena and CHF for boiling water reactor (BWR) fuel assembly.

Outline of Boiling Phenomena and Heat Transfer Characteristics

The objective of this book is to collect research works achieved during recent 20 years in the progress of boiling research in Japan. This book is edited for a person who has some experience or basic knowledge on boiling heat transfer. The fundamental outlines of pool nucleate boiling and flow boiling, and also new trend that boiling is considered to be a basic science that can be studied by numerical simulation or from the aspect of microscopic physics are briefly covered.