Dong-Wook Oh

Effect of Initial Temperature of a Cylindrical Steel Block on Heat Transfer Characteristics of Staggered Array Jets During Water Jet Quenching

The effects of initial temperature of a cylindrical stainless steel block on heat transfer characteristics are investigated for a staggered-array circular jet during water jet quenching. The initial temperature of a block is set to change from 500°C to 1,000°C by an induction heating method. Transient temperature measurements are made at discrete locations near the surface along radial direction. The surface temperature and heat flux distributions can be numerically estimated by solving a two-dimensional axisymmetric inverse heat conduction problem. The heat transfer characteristics of staggered-array jets in the impingement jet zone are compared with those in the wall jet flow zone. The effect of initial temperature of the test block in the nucleate boiling regime is also examined to solve the difficulties in most water jet quenching of hot steel. The area-averaged heat flux curves are used to evaluate representative cooling performance of staggered-array jets. The maximum area-averaged heat flux linearly increases as the initial temperature of the test block increases. Regardless of initial temperature of the test block, the nucleate boiling regimes are remarkably similar to each other. The area-averaged heat flux is also provided for fully developed nucleate boiling.

Numerical Analysis of Thermal Mixing in a Swirler-Embedded Line-Heater for Flow Assurance in Subsea Pipelines:

Flow assurance issue in subsea pipelines arises mainly due to hydrate plugs. We present a new line-heater for prevention of hydrate plug formation in subsea pipelines. The line heater has modular compact design where an electrical heater and a swirl generator are embedded inside the housing pipe so that the stream can be heated efficiently and homogeneously. In this paper, flow and heat transfer characteristics of the line heater are investigated numerically, with a particular emphasis on the mixing effect due to the swirl generator.

Comparison of Heat Transfer Characteristics of Water Impinging Flow With a Single Circular Nozzle and an Insert Type Swirling Nozzle

Conventional impinging jets enhance heat transfer but produce non-uniform radial distributions of the local and surface Nusselt numbers. In attempt to improve the radial uniformity of heat transfer, many researchers have introduced the concept of the swirling flow.The swirling flow can be generated by strips or swirling generators. The swirling generator is a circular rod with helical blades. The swirling generator is inserted inside a tube. This swirling generator with helical blades can generate swirling flow at the outlet of the nozzle. First of all, flow visualization of swirling jet as varying swirling angles, the length of the swirl generators, and distance between nozzle exit and a swirl generator is investigated. Based on the flow visualization, it is found that the distance between nozzle exit and a swirl generator affects the performance of swirling jet. For heat transfer analysis, an induction heating method is used to heat a steel plate up to a certain level which is almost the same as temperature of steel in iron- and steelmaking processes. For obtaining temperature distribution on impinging surface, several thermocouples are inserted below 1mm from the surface of the sample. Based on temperature distributions on the surface of a sample, 2-D temperature contours are obtained according to time. Based on the contours, effect of distance from nozzle exit to a swirling generator on uniform cooling is investigated.Copyright