Eun-Pil Kim

An experimental study of heat transfer characteristics of a pair of longitudinal vortices using color capturing technique

Abstract The flow and heat transfer characteristics of a pair of embedded counter-rotating vortices are studied experimentally. In order to control the strength of longitudinal vortices, angle of attack of the vortex generators is varied from ±20° to ±45°, and the spacing between the vortex generators is 4 cm apart. The heat transfer measurements using thermo-chromatic liquid crystal are made to provide the local surface distributions of heat transfer coefficients. The following conclusions are obtained from the present experiment. For the common-flow-down cases, two maximum values in the local heat transfer distributions exist for the three angles of attack. With the common-flow-up cases, only one maximum value exists. The common-flow-down cases show better heat transfer characteristics than the common-flow-up cases.

Heat transfer enhancement with a surfactant on horizontal bundle tubes of an absorber

Abstract This paper is concerned with the enhancement of heat transfer by surfactants added to aqueous lithium bromide (LiBr) solutions. Three different kinds of tubes in horizontally stagged arrangement are tested with and without an additive of normal octyl alcohol. The test tubes are a bare tube, a floral tube and a hydrophilic tube. The additive mass concentration is about 0.05–5.5 wt%. The heat transfer coefficient is measured as a function of the solution flow rate in the range 0.01–0.034 kg m −1 s −1 . The experimental results are compared with/without surfactants. Among three kinds of tubes, the hydrophilic tube shows the highest permeability. It has 4–73% higher wetted area than that of the bare tube, and 10–22% higher than that of the floral tube. Without surfactants, the hydrophilic tube is in the range 10–35% higher heat transfer coefficient than that of the bare tube, and 5–25% higher than that of the floral tube. With surfactants, the increase of the heat transfer coefficient is about 35–90% for the bare tube, 40–70% for the floral tube, and 30–50% for the hydrophilic tube.

Experimental study on freezing of water with supercooled region in a horizontal cylinder

The freezing phenomenon of saturated water with the supercooled region in a horizontal circular cylinder has been studied experimentally by using the holographic real time interferometry technique. From the experiments, it was found that there were three types of freezing patterns. The first is the annular ice layer growing from the cylinder surface at a high cooling rate, the next is the asymmetric ice layer at an intermediate cooling rate, and the last is the instantaneous ice layer growing over the whole region at a low cooling rate. As the water was cooled from room temperature to the subfreezing point passing through the density inversion point, the freezing pattern was largely affected by the inversion phenomenon, which had significantly affected the free convection and was susceptible to influences from the cooling rate. When the cooling rate is high, supercooling energy is released before water is sufficiently mixed by free convection. On the other hand, when the cooling rate is low, there is a lot of time for the water to be mixed by free convection. This seems to be the reason why different ice layer growths occur.

Experimental characteristics of a storage tank on a harvest-type ice storage system

This paper is concerned with the development of a new method for making and separating ice and saving floated ice by installing an evaporation plate at underwater within a storage tank. In a conventional harvest-type ice storage system, a tank saves ice by separating a formed ice from an installed evaporation plate, which is located above an ice storage tank as an ice storage system. A new harvest-type method shows better heat transfer efficiency than a convectional method. It is because the evaporation panel is directly contacted with water in a storage tank. Also, at a conventional system a circulating pump, a circulating water distributor and a piping are installed, but these components are not necessary in a new method. In this study two kinds of ice storage systems are experimentally investigated to study the thermal characteristics of ice storage tanks. The results show the applicable possibility and performance enhancement of a new type.