수직 상향기류 및 하향기류에 의한 평형 액막류의 열전달에 관한 실험적 연구

Abstract

Saturated steam, in general, for the industrial heat exchangers, homes, and local heating systems has a superior heat transfer feature that leads to latent heat characters without any temperature change when it is compared to superheated steam. The areas currently demanding for the saturated steam and the superheated steam are LNG carrier propulsion system, power station and oil refinery plant. On the processing procedure to convert superheated steam to saturated steam is called the de-superheating

and the device for the de-superheating is the de-superheater.

The de-superheater is normally classified with two types. One is the outer-fitted type that shouldn't be directly allowed to contact two fluids such as water and superheated steam, and the other is the inter-fitted type which makes the two components directly contact each other. Among the inter-fitted types named the venturi type, the spray type and the steam atomizing type are now in use of practical service. On the other hand, there are two kinds for the outer-fitted type, which are shell & tube type and trombone type. These are hardly used for the land, but some are used for the marine section with the restricted purposes.

The de-superheating system has an industrial demands largely and it is good for lifting the energy efficiency that governments try to get currently. In order to research the performance of the de-superheater, it is necessary to figure out the fluid characteristics and heat transfer mechanism between refrigerant and superheated steam. However, achievements for this research aren't enough to meet the questions. Thus, prior to this research, an experimental study on fluids characteristics of atomized droplets in pipes was carried out and it found out fluid mechanism of de-superheater.

According to the results of study, liquid film flow generated from atomized droplets when it has collided with surface of pipe disturbs the heat transfer because of the reduction of heat transfer area. However, the liquid film naturally has been taken place on account of the de-superheater's fluids characters.

In this reason, the research on heat transfer of droplets is necessary to design the de-superheater and produce it. So experimental study with parameters such as air temperature, air velocity, liquid film flux was carried out in order to get a fundamental data regarding the heat transfer characteristics for design and production of de-superheater. Then, the liquid film flow based on the experimental conditions was heated by vertical upward steam and vertical downward steam. The heat transfer coefficient of fluids has increased when air velocity is elevated and liquid film flow is raised, but it has reduced when air temperature goes up slightly. Especially the effect of wind velocity is tremendous. The heat transfer coefficient of counter film flow has indicated a significant value when it is compared to value of parallel film flow. This comes from the difference of relative velocity more than other causes between counter film flow and parallel film flow.