• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.2 s.233
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• pp.197-204
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• 2005

The under-expanded jet discharged from a nozzle or an orifice has been extensively employed in industrial applications and aerospace technologies. A number of studies have been made to investigate the under-expanded jet structures such as Mach disk, barrel shock wave, jet boundary configuration, etc. In the current study, a computational work is performed to investigate the effect of non-equilibrium condensation of moist air on the under-expanded jet, which is discharged from a sonic nozzle. The results obtained are compared with an available experimental data. It is found that non-equilibrium condensation of moist air alleviates the oscillations of the under-expanded jet, and can increase Mach disk diameter, without changing the location.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.3
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• pp.13-19
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• 2000

In the present study, a program for predicting thermal performance of an air cooled condenser is illustrated. Heat transfer equations of single phase and two phase flow are formulated into the form that is convenient to incorporate the local analysis method. The resulting equations are solved by temperature and mass correction methods. Empirical equations for both side fluids are incorporated in the caculation procedures. In order to compare the calculation results, superheat temperature of steam are varied. The tube length of superheated zone, wall temperature, temperature profile along the tube and steam qualities are predicted.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.460-463
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• 2008

the present study, the addresses the hysteric phenomenon of under-expanded jets with a help of a computational fluid dynamics methods. The under-expanded jets of both dry and moist air have been employed to the transient processes for the pressure ratio. It is known that under-expanded air jet produced during the process of increase in pressure ratio behaves different from the reducing process, leading to a hysteric phenomenon of under-expanded jet. It is also known that moist air jet significantly reduces the hysteric phenomenon found in the dry air jet, and that non-equilibrium condensation which occurs in the under-expanded moist air jet is responsible for these findings.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.514-519
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• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.562-567
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• 2003

A computational study is performed to clarify the characteristics of supersonic moist air jet issuing from a simple sonic nozzle. The effects of the initial supersaturation on the Mach disk diameter and location, the barrel shock wave and jet boundary structures are investigated in details. The axisymmetric, compressible, Navier-Stokes equations, coupled with droplet growth equation, are solved using a third-order MUSCL type TVD finite-difference scheme. It is found that the Mach disk diameter increases with an increase in relative humidity of moist air. while its location is not significantly dependent on the relative humidity. As the relative humidity increases, the barrel shock wave and jet boundary are more expanded due to the local static pressure rise of nonequilibrium condensation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.543-544
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• 2006

3-methyl-2-cyclopentenone is a valuable reaction intermediate for various high value added products. 3-methyl-2-cyclopentenone is not only expensive but also difficult to produce. 3-methyl-2-cyclopentenone can be synthesized by base catalyzed intermolecular aldol condensation. In this work, we studied a simple and practical method for synthesizing 3-methyl-2-cyclopentenone. Experimental results showed the advantages of the continuous flow process using a microreactor with kenic mixers for the synthesis of 3-methyl-2-cyclopentenone.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.15 no.4
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• pp.356-361
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• 1986

An optimum design condition for a basic refrigeration cycle is defined as the condition which minimizes the total cost of heat exchanges (condenser and evaporator) and compressor for the refrigeration effect. Thermodynamic properties of ammonia (R717) are approximated by rational functions in order to obtain the optimum condition for a basic refrigeration cycle. Optimum condition depends on the heat capacity rates (mass flow rate times specific heat) of cooling water and brine used in condenser and evaporator. The difference between the cooling water temperature and condensation temperature at the optimum condition increases as the heat capacity rates and the coat of heat exchangers relative to the cost of compressor increase. Numerical examples of optimum conditions are obtained when the condensation temperature is $30^{\circ}C$ and the evaporator temperature is $-10^{\circ}C$.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.141-147
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• 2011

A two-phase numerical model for plate-fin heat exchangers with plain fins and wave fins is studied incorporating the thermodynamic properties and the characteristics of fluid flow. The numerical simulations for the two fins in cryogenic conditions are earned out by employing a homogenous two-phase flow model with the CFD code ANSYS CFX. The heat transfer coefficients and the friction factor for nitrogen saturated vapor condensation process inside two types of plate fin heat exchanger are evaluated including the effects of saturation temperature (pressure), mass flow rate and inlet vapor quantity. The convective heat transfer coefficients and friction factors will be used for design of plate-fin type heat exchangers operating under cryogenic conditions.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.95-98
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• 2007

A general purpose program NUFLEX has been extended for two-phase flows with topologically complex interface and cavitation flows with liquid-vapor phase change caused by large pressure drop. In analysis of two-phase flow, the phase interfaces are tracked by employing a LS(Level Set) method. Compared with the VOF(Volume-of-Fluid} method based on a non-smooth volume-fraction function, the LS method can calculate an interfacial curvature more accurately by using a smooth distance function. Also, it is quite straightforward to implement for 3-D irregular meshes compared with the VOF method requiring much more complicated geometric calculations. Also, the cavitation process is computed by including the effects of evaporation and condensation for bubble formation and collapse as well as turbulence in flows. The volume-faction and continuity equations are adapted for cavitation models with phase change. The LS and cavitation formulation are implemented into a general purpose program for 3-D flows and verified through several test problems.

• International Journal of Aeronautical and Space Sciences
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• v.9 no.2
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• pp.98-106
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• 2008

The motive gas of a supersonic ejector is supplied from different sources depending on the application. The performance of an ejector that is represented by the secondary flow pressure, starting and unstarting pressures heavily depends on the molecular properties of the motive gas. The effects of specific heat ratio of the motive gas were investigated experimentally for an axi-symmetric annular injection type supersonic ejector. Both the starting pressure and unstarting pressure, however, decreased with the increase of the specific heat ratio of the motive gas. It was discovered that the secondary flow pressure increased as the specific heat ratio of the motive gas decreased even if the stagnation pressure of the motive flow was invariant. However, when the motive gas flow nozzle area ratio is large enough for the motive gas to be condensed, different tendency was observed.