• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.13 no.2
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• pp.1-9
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• 1984

This paper presents design conditions due to the NTU of counter and cross flow type cooling tower. In the calculation of optimum design conditions for above two types which are widely used in our country, standard water-air ratio, ambient wet bulb temperature and bulk water temperature were adopted by domestic wheather conditions. The important result of this study is obtained as follows : Under the constant value of Ka and L, the number of transfer unit of cross flow type cooling tower Is about 1.1 times as large as that of counter, so the volume of cross flow type is about $10\%$ greater than that of counter.

• Journal of Korea Water Resources Association
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• v.37 no.7
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• pp.527-540
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• 2004

In order to investigate characteristics of the primary flow and the secondary currents in the meandering channel, laboratory experiments were conducted in the meandering channel made up of alterative bends haying 120。 arc angle. Experiments were performed in two types of cross-sections, a rectangular cross-section and a curved cross-section which was made to adopt a beta probability function. Three-dimensional velocity fields were measured using a micro-ADV. As the result of experiments, in case of the rectangular cross-section, the primary flow occurred taking the shortest course, which is similar to the result of previous researches. In case of the curved cross-section, the primary flow was expected to occur along the thalweg. but it occurred almost along the shortest way. This is considered due to effects of bottom roughness and sinuosity Not only a main cell but also a secondary cell of secondary currents were clearly shown by mean of the stream function. The secondary current intensity has the maximum value near the apex of the second bend for cases of both rectangular and curved cross-sections. However, the value of the secondary current intensity for the curved section is slightly larger than that for the rectangular cross-section. Also, in case of the rectangular cross-section, the higher the ratio of width to depth is, the larger the secondary current intensity is.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.2
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• pp.181-188
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• 2004

The frequency characteristics in an axial flow fan operating at a design and three off-design operating conditions have been investigated by measuring the velocity fluctuation of a tip leakage vortex and a wake flow. Two hot-wire probe sensors rotating with the fan rotor. a fixed and a moving ones, were introduced to obtain a cross-correlation coefficient between two sensors as well as the fluctuating velocity. The results show that the spectral peaks due to the fluctuating velocity near the rotor tip are mainly observed in the reverse flow region of higher flow rates than those in the peak pressure operating condition. However, no peak frequency presents near the rotor tip for near stall condition. Detailed wake flow just downstream of the rotor blade was also measured by the rotating hot-wire sensor. The peak frequency of a high velocity fluctuation due to Karman vortex shedding in the wake region is mainly observed at the higher flow rate condition than that in the design point.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.411-416
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• 1999

The measurement of unsteady flow rate is of vital importance to clarify and improve the dynamic characteristics in pipeline, hydraulic components and system. There is also demand for a real time flow sensor of ability to measure unsteady flow rate with high accuracy and fast response to realize feedback control of flow rate in fluid power systems. In this paper, we propose an approach for estimating unsteady flow rate through a pipeline and components under high pressure condition. In the method, unsteady flow rate is estimated by using hydraulic pipeline dynamics and the measured pressure values at two distant points along the pipeline. The distributed parameter model of hydraulic pipeline is applied with consideration of frequency dependent viscosity friction and unsteady velocity distribution at a cross section of a pipeline. By using the self-checking functions of the method, the validity is investigated by comparison with the measured and estimated pressure waveforms at the halfway section on the pipeline. The results show good agreement between the estimated flow rate waveforms and theroetical those under unsteady laminar flow conditions. the method proposed here is useful in estimating unsteady flow rate through an arbitray cross section in hydraulic pipeline and components without installing an instantaneous flowmeter.

• Particle and aerosol research
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• v.12 no.1
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• pp.21-26
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• 2016

In order to realize In-line and convenient measurement for solid-gas two phase flows, Light Transmission Fluctuation (LTF) based on the random variation of transmitted light intensity, light scattering theory and cross-correlation method was presented for online measurement of particle size, concentration and velocity. The statistical relationship among transmitted light intensity, particle size and particle number in measurement zone was described by Beer-Lambert Law. Accordingly, the particle size and concentration were determined from the fluctuation signal of transmitted light intensity. Simultaneously, the particle velocity was calculated by cross-correlation analysis of two neighboring light beams. By considering the influence of concentration variation in industrial applications, the improved algorithm based on spectral analysis of transmitted light intensity was proposed to improve measurement accuracy and stability. Therefore, the online measurement system based on LTF was developed and applied to measure pulverized coal in power station and raw material in cement plant. The particle size, concentration and velocity of powder were monitored in real-time. It can provide important references for optimal control, energy saving and emission reduction of energy-intensive industries.

• Membrane and Water Treatment
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• v.3 no.3
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• pp.151-168
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• 2012

Gas sparging is one of the techniques used to control the concentration polarization during ultrafiltration. In this work, the effects of gas sparging in stratified flow regime were investigated during gel layer controlling cross flow ultrafiltration in a rectangular channel. Synthetic solution of pectin was used as the gel forming solute. The liquid and gas flow rates were selected such that a stratified flow regime was prevalent in the channel. A mass transfer model was developed for this system to quantify the effects of gas flow rates on mass transfer coefficient (Sherwood number). The results were compared with the case of no gas sparging. Gas sparging led to an increase of mass transfer coefficient by about 23% in this case. The limitation of the developed model was also evaluated and it was observed that beyond a gas flow rate of 20 l/h, the model was unable to explain the experimental observation, i.e., the decrease in permeate flux with flow rate.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.14-21
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• 2001

An experimental study has been conducted to investigate the heat/mass transfer characteristics within a square film cooling hole with asymmetric inlet flow conditions. The asymmetric inlet flow condition is achieved by making distances between side walls of secondary flow duct and film cooling hole different; one side wall is $2D_h$ apart from the center of film cooling hole, while the other side wall is $1.5D_h$ apart from the center of film cooling hole. The heat/mass transfer experiments for this study have been performed using a naphthalene sublimation method and the flow field has been analyzed by numerical calculation using a commercial code. Swirl flow is generated at the inlet region and the heat/mass transfer pattern with the asymmetric inlet flow condition is changed significantly from that with the symmetric condition. At the exit region, the effect of mainstream on the inside hole flow is reduced with asymmetric condition. The average heat/mass transfer coefficient is higher than that with the symmetric condition due to the swirl flow generated by the asymmetric inlet condition.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.11a
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• pp.403-408
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• 1996

The subchannel analysis was performed to verify the behavior of hot channel characteristics and obtain the information to support the core thermal-hydraulic behavior at post-trip steam line break with low flow condition. During this postulated accident, buoyancy-induced cross flow occurs, and the coupled nuclear and thermal-hydraulic interactions become important. The code predictions with TORC are in good agreement with the test data. Under such conditions, the mass flow increase in the hot channel by buoyancy-induced cross flow depends on the parameter $GR^{*}\;/\;Re^2$, and buoyancy effect becomes more noticeable as $GR^{*}\;/\;Re^2$ increases.

• Nuclear Engineering and Technology
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• v.38 no.1
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• pp.69-80
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• 2006

Fluid-elastic instability in an air-water two-phase cross-flow has been experimentally investigated using two different arrays of straight tube bundles: normal square (NS) array and rotated square (RS) array tube bundles with the same pitch-to-diameter ratio of 1.633. Experiments have been performed over wide ranges of mass flux and void fraction. The quantitative tube vibration displacement was measured using a pair of strain gages and the detailed orbit of the tube motion was analyzed from high-speed video recordings. The present study provides the flow pattern, detailed tube vibration response, damping ratio, hydrodynamic mass, and the fluid-elastic instability for each tube bundle. Tube vibration characteristics of the RS array tube bundle in the two-phase flow condition were quite different from those of the NS array tube bundle with respect to the vortex shedding induced vibration and the shape of the oval orbit of the tube motion at the fluid-elastic instability as well as the fluid-elastic instability constant.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.1
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• pp.138-149
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• 1986

A numerical method is developed for the solution of fully developed turbulent recirculating flow whose cross-sectional area varies periodically. This enalbes the flow field analysis to be confined to a single isolated module, without involvement with the entrance region problem. This method are applied to the analysis of the turbulent flow field and heat transfer in artificially roughened annulus with repeated square rib.