• 한국지열·수열에너지학회논문집
• /
• 제14권4호
• /
• pp.20-26
• /
• 2018

In this study, the performance characteristics of a welded plate heat exchanger was investigated experimentally. Performance tests were carried out according to the flow rate and inlet temperature of working fluid. As a result, the heat transfer capacity increased by 335.5 kW with an increasing the flow rate and temperature difference between hot and cold side. However, the overall heat transfer coefficient was increased with the increase of flow rate, and it was not effected significantly from inlet temperature difference between hot and cold working fluid. The pressure drop was increased by 55.78 kPa with an increasing the frow rate when the flow rate ratio between hot and cold side 1:1. However, the tendency of pressure drop was difference when flow rate ratio wasn't 1:1. In case that the flow rate ratio between hot and cold side was not 1:1, the pressure drop at the low flow rate side was higher than that when the flow rate ratio was 1:1, while pressure drop of the other side was decreased compared to that when the flow rate ratio was 1:1.

• Journal of Mechanical Science and Technology
• /
• 제16권3호
• /
• pp.344-353
• /
• 2002

A reliable computational heat transfer model has been investigated to define the heat transfer characteristics of a spray column direct contact heat exchanger, which is often utilized in the process involving counterflows for heat and mass transfer operations. Most of the previous studies investigated are one-dimensional unsteady solutions based on rather fragmentary experimental data. Development of a multidimensional numerical model and a computational algorithm are essential to analyze the inherent multidimensional characteristics of a direct contact heat exchanger. The present study has been carried out numerically and establishes a solid simulation algorithm for the operation of a direct contact heat exchanger. Operational and system parameters such as the speed and direction of working fluid droplets at the injection point, and the effects of aspect ratio and void fraction of continuous fluid are examined thoroughly as well to assess their influence on the performance of a spray column.

• 드라이브 ㆍ 컨트롤
• /
• 제13권1호
• /
• pp.27-33
• /
• 2016

In hydraulic machinery, the hydraulic fluid acts primarily as working fluid and secondarily as a lubricant. Hence, the viscous friction force acting on the sliding components should be reduced to improve the mechanical efficiency. It is now well known that the surface texturing is a useful method for friction reduction. In this study, using a commercial computational fluid dynamics (CFD) code, FLUENT, the lubrication characteristics of a surface textured slider bearing under high boundary pressure difference is studied. The streamlines, velocity profiles, pressure distributions, load capacity, friction force and leakage flowrate are highly affected by the film thickness ratio and the textured region. Partial texturing at the inlet region of the inclined slider bearing can reduce both friction force and leakage flowrate than in the untextured case. The present results can be used to improve the lubrication characteristics of hydraulic machinery.

• Journal of Advanced Marine Engineering and Technology
• /
• 제38권1호
• /
• pp.8-14
• /
• 2014

본 연구에서는 R-245fa를 작동유체로 하는 250kW급의 선박폐열회수 발전 시스템을 설계하고 과열기의 구성에 따른 사이클 특성을 연구 하였다. 과열기와 증발기의 직렬연결과 병렬연결의 2가지 조건을 시뮬레이션 하였다. 과열기와 증발기의 직렬연결 시뮬레이션에서는 작동유체 과열에 따른 엔탈피 증가로 4.7%의 출력상승을 얻을 수 있었고, 목표출력을 250kW로 정하였을 경우에는 사이클유량을 4.1% 감소시킬 수 있었다. 과열기와 증발기의 병렬연결 시뮬레이션에서는 사이클의 목표출력을 250kW로 정하였을 경우에 과열기로 가는 열원유체의 유량이 증가함에 따라 사이클 유량이 감소하여 작동유체펌프의 소요동력이 최대 7.9% 감소 하였으며, 유량비율에 따른 사이클효율과 정미효율은 큰 변화가 없었다.

• 한국정밀공학회지
• /
• 제18권2호
• /
• pp.161-170
• /
• 2001

Synthetic water-based metal-cutting fluids are increasingly popular in the metal-working industry because of its environmental friendliness. The propose of this study is to investigate the synergistic effect of combining polyethylene glycol and common fatty acid in formulating a metal-cutting fluid. The tested metals were aluminum, copper and steel, and the test was performed with a modified drilling machine. From the study, it was found that there existed some synergistic effects on the drilling efficiency of the metals to decrease of cutting time, cutting energy, torque as well as the smoothness of surface depended on the formulation ratio of the two fluids.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집B
• /
• pp.741-745
• /
• 2001

The necessity of a Z-shape heat pipe may occur in a special application such as a cooling module for an electronic equipment having a limited accessible space. Either of the two end part works as evaporator or condenser and the length of the middle part is 200mm. The heat pipe was made of 3/8 inch copper tube having 60 spiral groove with screw angle of 10 degrees. Water and acetone were used as working fluids. The fill charge ratio of the working fluid was varied for different values of thermal loads. The thermal resistance was calculated based on the temperature measurements along the heat pipe axis. The maximum thermal loads were 80W for water and 100W for acetone heat pipe. The optimum fill charge ratio was identified through a series of experiments.

• 설비공학논문집
• /
• 제3권2호
• /
• pp.87-96
• /
• 1991

A two-phase closed thermosyphon is applied to an ice storage system. The thermosyphon is used to freeze the water in a storage tank. The experiment has been performed to investigate the effects of the important parameters such as the quantity of the fluid filled with, the ratio of the length of the evaporator to the condenser, and the temperature and the mass flow rate of the brine. It is found that the higher thermal performance of the thermosyphon is obtained as the ratio of the length of the evaporator section to that of the condenser section is decreased and the temperature of the brine is lowered. The increase of the quantity of the working fluid also favors the performance of the system. The experimental data can be utilized for the basic design of ice storage systems with thermosyphons.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2003년도 유체기계 연구개발 발표회 논문집
• /
• pp.391-396
• /
• 2003

A cross-flow fan relatively produces higher dynamic pressure at low speed because a working fluid passes through an impeller blade twice and blades have a forward curved shape. The performance of a cross-flow fan is influenced 25% by the impeller, 60% by the rearguider and the stabilizer, and 15% by the heat exchanger. At the low flow rate, there exist a rapid pressure head reduction, a noise increase and an unsteady flow against a stabilizer and a rearguider. The purpose of this study is to investigate the reciprocal relation among each parameter Experiments are conducted to study the effects of a rearguider and a diameter ratio of impeller on the performance analysis of a cross-flow fan. Comparing with the rearguider of radial type, the Archimedes type shows excellent results for various diameter ratios.

• 설비공학논문집
• /
• 제18권4호
• /
• pp.370-376
• /
• 2006

The paper concerns an experimental study of fully developed laminar flow of a Newtonian and non-Newtonian liquid in concentric annuli with combined bulk axial flow and inner cylinder rotation. Pressure losses and skin friction coefficients have been measured for Newtonian fluid, water and non-Newtonian fluids, 0.2% aqueous of sodium carboxymethyl cellulose (CMC) and 5% bentonite solutions, when the inner cylinder rotates at the speed of $0{\sim}500$ rpm. The influences of rotation, radius ratio and working fluid on the annular flow field are investigated. And the new correlations among the skin friction coefficient, the Reynolds number and the Rossby number are presented with reasonable limits of accuracy in laminar flow regime.

• 한국분무공학회지
• /
• 제1권1호
• /
• pp.63-75
• /
• 1996

The purpose of this study is to investigate the break-up characteristics by taking advantage of a two-phase coaxial nozzle. Air and water are utilized as working fluids and the mass ratio air/water has been controlled to characterize the atomization, diffusion and development of mixing process. By way of a photographic technique, conventional developing structures and diffusion angles have been analyzed systematically with variations of mass ratios. The turbulent flow components of the atomized particles were measured by a two channel LDV system and the data were treated by an on-lined measurement equipment. According to the photographic results the spreading angles decreased because the axial inertia moment was relatively higher than the lateral one with respect to the increase of mass ratio. It is found the jet flow diffuses linearly in a certain limit region while the atomizing characteristics, in terms of the distributions of particle diameters did not show particular differences. It may be expected that these fundamental results can be used as reference data in studying the atomization, breakup and diffusions.