Small-sized heater is usually used to make the hot water in resting place, factory, household affairs and so on. One of methods to obtain hot water in short time is known as using instantaneous electric water heater. In this study, numerical analysis for small-sized hot water heater with straight double tube-type was tried to achieve the basic design data. This study aims to investigate the characteristics of thermal flow, for instance, such as pressure difference, outlet mean temperature and velocity, due to clearance. As the clearance is decreased, outlet mean temperature and pressure difference(Pmax.-Pmin.) are increased. Therefore appropriate relations between area of heat source and pressure difference should be set up. Further small-sized hot water heater in this study must be equipped with electric device capable of heating over 90℃.

In this paper, we developed the hydraulic leveling jack(HLJ) with double-tube type structure which could be applicable to excessive lateral load area. In order to develop HLJ, the design requirements, such as the vertical and lateral loads where applied to hydraulic jack, were selected. To verify the structural stability of the HLJ, the structure analysis was performed. In order to verify the operational performance and structural stability of the developed HLJ, test bench was designed. The performance of HLJ was verified via various test using test bench.