Sunao Kawai

Heat transfer and pressure drop characteristics of enhanced titanium tubes

The present study investigated the characteristics of heat transfer and pressure drop for various types of enhanced titanium tubes. The heat transfer experiments were conducted using a steam-condensing flow facility at a constant inlet temperature of cooling water, and the Reynolds number range varied from 15,000 to 65,000. The heat transfer coefficients were determined using a modified version of the Wilson plot technique and the friction factors were calculated from pressure drop measurements. The experimental results reported enable practical design to be achieved for the heat exchanger using enhanced titanium tubes and optimization of tube geometry for specific conditions.

Study on the start-up characteristics of double-effect absorption refrigerator driven by waste steam

Absorption refrigerators can be driven by waste heat. In particular, the double-effect type of absorption refrigerator, which is highly efficient, is drawing a great deal of attention as a waste heat recovery system. This research examines the double-effect absorption refrigerator driven by steam, assuming waste heat from the fuel cells is applied. In the start-up of the double-effect absorption refrigerator, the solution temperature is almost equal to the temperature of the air. Due to the large temperature difference between the solution and the heat sources, the solution is overheated. In the worst case, it will be crystallized. Additionally, some solution is circulated due to the existence of a pressure difference between the heat exchangers. If the solution pump is started before an adequate pressure difference is obtained, the absorption refrigerator cannot be started normally. To investigate these problems, a simulation model is constructed. An experiment is conducted to investigate the performance of this model. As a result, the validity of this model is confirmed and the detailed start-up characteristics are clarified.

りん酸形燃料電池冷却系の排熱回収に関する検討 : 第1報, セル冷却系における水蒸気熱回収方式の簡易動特性モデルの提案

Waste heat recovery of the fuel cell stack cooling system is very important from the viewpoint of effective use of energy. Simultaneously, temperature control of the fuel cell stack is necessary to maintain high electrical efficiency and to prevent the cell stack from oxidation. In phosphoric acid fuel cell system, coolant temperature is controlled to keep constant the temperature of cell stack. The purpose of this paper is to propose the simple dynamic model for designing the temperature control system and heat recovery system of fuel cell stack cooling system. In addtion to this, experimental research and simulation analysis reveal the dynamic characteristics of fuel cell stack cooling system with control equipments. Throughout the researches, concentrated parameter dynamic model is proposed and the validity of the model is confirmed by experimental results. When the transient response to disturbances such as make-up water pump start up is calculated, it is clarified that the coolant temperature of fuel cell stack can be controlled.