• The Journal of the Acoustical Society of Korea
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• v.14 no.1
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• pp.108-114
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• 1995

Cylindrical chamber mufflers with an extended inlet or outlet are extensively used in many application fields to reduce the propagated noise in ducts. The basic attenuation effectivencess in the low frequency region can be explained by the reactive wave action inside the expansion chamber associated with the geometric configurations of the inlet and outlet locations, and the area expansion of the jacket. In this study, an acoustic analysis is carried out for a concentric extended pipe inserted into a simple expansion chamber. An algebraic equation is derived by using the eigenfuction expansion and orthogonality principle in which the acoustic pressures and particle velocities defined on each subdivided surface are expressed by the separable coordinates. By using the proposed analytical method, transmission losses are predicted for several configurations of the concentric extended systems and they agree very well with experimental results.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.827-830
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• 2002

A direct numerical simulation is performed for turbulent heat transfer in a concentric annulus at $Re_{Dh}=8900\;and\;Pr=0.71$ for two radius ratios ($R_{1}/R_{2}=0.1\;and\;0.5$) and $q^{\ast}=1.0$. Main emphasis is placed on the transverse curvature effect on near-wall turbulent thermal structures. Near-wall turbulent structures close to the inner and outer walls are scrutinized by computing the lower-order statistics. The fluctuating temperature variance and turbulent heat flux budgets are illustrated to confirm the results of the lower-order statistics. The present numerical results show that the turbulent structures near the outer wall are more activated than those near the inner wall, which may be attributed to the different vortex regeneration processes between the inner and outer walls.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.5
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• pp.670-679
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• 1986

본 논문은 내관 외벽에 나선형 인공조도가 있는 동심 이중관 사이의 유동특성 을 관찰하기 위해 일정 나선각에 대하여 피치비를 변화시키면서 선회속도, 축방향속도 압력을 측정하였으며, Han등의 연구에서 발표된 조도함수를 도입하여 유한차분법으로 수치계산을 수행하였다.

• Journal of the Korean Magnetics Society
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• v.23 no.2
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• pp.77-81
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• 2013

The objective of this study is experimentally to investigate natural convective heat transfer characteristics of the ferrofluid for a concentric annuli under rotating magnetic field with variations of the revolution and the magnetic field strength. The rotating magnetic field was provided by induction motor with 6 poles and 3 phases and the revolution and the magnetic field strength were controlled by an inverter driver and a voltage meter, respectively. Temperatures of the inner pipe and the outer pipe in the tested concentric annuli were maintained at $30^{\circ}C$ and $25^{\circ}C$, respectively, during the test and the direction of the rotating magnetic field was a counterclockwise. As a result, the natural convective heat transfer characteristics of the ferrofluid for a concentric annuli were increased with the rise of the revolution and magnetic field strength due to the increased heat dissipation between hot side and cold side of the concentric annuli.

• Journal of the Korean Society for Heat Treatment
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• v.22 no.3
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• pp.162-168
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• 2009

A horizontal tube furnace with a wide uniform-temperature zone was developed using isothermal characteristics of a heat pipe. The heat pipe heating system consists of a concentric annular shaped stainless-steel container, sodium as a working fluid and a screen mesh wick structure. The performance test of the heat pipe revealed that temperature changes along seven consecutive positions of the heat pipe outer wall were less than${\pm}0.1^{\circ}C$, thereby ensuring the high isothermal property. The isothermal property of the heat pipe-adapted tube fumace was investigated and compared to a conventional non-heat pipe type tube furnace. The temperature distribution measurement showed that the uniform temperature zone, in which temperature change is less than${\pm}$1$^{\circ}$C, of the heat pipe employed tube furnace system was about three times longer compared to the conventional tube furnace system.

• Journal of Convergence for Information Technology
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• v.9 no.12
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• pp.147-156
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• 2019

Numerical study was performed to investigate the convective heat transfer of Al₂O₃/water nanofluid flowing through the concentric double pipe counterflow heat exchangers. Hot fluid flowing through the inner pipe transfers its heat to cooling fluid flowing in the outer pipe. Effects of important parameters such as hot and cold volume flow rates, fluid type in the outer and inner pipes, and nanoparticles concentration on the heat transfer and flow characteristics are investigated. The results indicated that the heat transfer performance increases with increasing the hot and cold volume flow rates, as well as the particle concentrations. When both outer and inner pipes are nanofluids with 8% nanoparticle volume concentration, nanofluids showed up to 17% better heat transfer rate than basic fluids. Also, the average heat transfer coefficient of the base fluid for annulus-side improved by 31%. Approximately 20% enhancement in the heat exchanger effectiveness can be achieved with the addition of 8% alumina particles in base fluid. But, addition of nanoparticles to the base fluid enhanced friction factor by about 196%.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.22 no.4
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• pp.90-97
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• 1986

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.965-969
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• 2006

This study investigated heat transfer characteristics between absorber and heat pipe used to extract heat from concentric evacuated tubular collectors. In order to experiment, T-type thermocouples are attached to a evaporator of heat pipe and absorber of inner tube. A wall temperature distribution of absorber and heat pipe were carried out by experimental method under actual various ir-radiance and outdoor conditions. As a result, As to increase an irradiance, a wall temperature of absorber and heat pipe is gradually increased. The heat pipe was required about 20min to obtain steady state operation after start up and operates stable during various irradiance conditions. And the collector efficiency was about $50{\sim}70%$ when a mass flow rate is about $1.3{\ell}/min$.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.16 no.1
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• pp.65-84
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• 2012

We present an application of the variational multiscale methodology to the computation of concentric annular pipe flow. Isogeometric analysis is utilized for higher order approximation of the solution using Non-Uniform Rational B-Splines (NURBS) functions. The ability of NURBS to exactly represent curved geometries makes NURBS-based isogeometric analysis attractive for the application to the flow through the curved channel.

• Proceedings of the SAREK Conference
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• 2005.06a
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• pp.129-129
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• 2005