• Nuclear Engineering and Technology
• /
• 제37권5호
• /
• pp.479-490
• /
• 2005

The thermalhydraulic performance of a CANDU-6 reactor loaded with various CANFLEX fuel bundles is evaluated by the NUCIRC code, which is incorporated with recent models of pressure drop and critical heat flux (CHF) predictions based on high-pressure steam-water tests for the CANFLEX bundle as well as a 37-element bundle. The distributions of channel flow rate, channel exit quality, critical channel power (CCP), and critical power ratio (CPR) for the CANFLEX bundles (with natural or recycled uranium fuel) in the CANDU-6 reactor fuel channel are calculated by the code. The effects of axial and radial heat flux on CCP are evaluated by assuming that the recycled uranium fuel (CANFLEX-RU) has the same geometric data as the natural uranium fuel bundle (CANFLEX-NU), but a different power distribution due to different fuel composition and refueling scheme. In addition, the effects of pressure tube creep and bearing-pad height are examined by comparing various results of uncrept, and $3.3\%\;and\;5.1\%$ crept channels loaded with CANFLEX bundles with 1.4 mm or 1.7 mm high bearing-pads with those of the 37-element bundle. The distributions of the channel flow rate and CCP for the CANFLEX-NU or -RU bundle show a typical trend for a CANDU-6 reactor channel, and the CPRs are maintained above at least 1.444 (NU) or 1.455 (RU) in the uncrept channel. The enhanced CHF of the CANFLEX bundle (particularly with 1.7mm height bearing-pads) produces a higher thermal margin and considerably less sensitivity to CCP reduction due to the pressure tube creep than the 37-element bundle. The CCP enhancement due to the raised bearing-pads is estimated to be about $3\%\~5\%$ for the CANFLEX-NU and $2\%\~6\%$ for the CANFLEX-RU bundle, respectively.

• 설비공학논문집
• /
• 제27권4호
• /
• pp.195-200
• /
• 2015

The thermal performance in the channels with two-wall rectangular convergent/divergent cross-sectional areas along the axial distance was investigated experimentally. The ribbed rectangular convergent/divergent channels were manufactured with a fixed rib height (e) = 10 mm and the ratio of rib spacing (p) to height (e) = 10. Three different parallel angled ribs (a = $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$) were each placed on the channel's one sided wall only. The convergent channel of $D_{ho}/D_{hi}=0.67$ and the divergent channel of $D_{ho}/D_{hi}=1.49$ were considered. The ribbed divergent channel produced better thermal performance than the ribbed convergent channel in three different restrictions; identical flow rate, identical pumping power, and identical pressure loss.

• 대한기계학회논문집B
• /
• 제27권9호
• /
• pp.1351-1359
• /
• 2003

This study presents a numerical procedure to optimize shape of streamwise periodic ribs mounted on both of the principal walls to enhance turbulent heat transfer in a rectangular channel flow. The response surface method is used as an optimization technique. The optimization is based on Navier-Stokes analysis of flow and heat transfer with $k-{\varepsilon}$ turbulence model. The width-to-height ratio of a rib, rib height-to-channel height ratio and rib pitch to rib height ratio are chosen as design variables. The object function is defined as a function of heat transfer coefficient and friction drag coefficient with weighting factor. Optimum shapes of the rib have been obtained for the range of 0.02 to 0.1 of weighting factor.

• Journal of Electrical Engineering and information Science
• /
• 제2권3호
• /
• pp.99-104
• /
• 1997

A novel driving theory on the electrohydrodynamic (EHD) pump driven by traveling electric fields without the temperature gradient is proposed. The equations of the generating pressure and the flow rate are derived. The EHD micropump is fabricated by micromachining technology and tested. The channel heights are 50$\mu\textrm{m}$, 100$\mu\textrm{m}$ and 200$\mu\textrm{m}$ are respectively an the channel width is 3 mm. The spacing and width of the electrodes are both 40$\mu\textrm{m}$. The maximum pressure is 70.3 Pa, 35.4 Pa and 17.2 pa at he frequency of 0.2Hz for each channel height (50$\mu\textrm{m}$, 100$\mu\textrm{m}$ and 200$\mu\textrm{m}$) and the maximum flow rate is 0.90x10\ulcorner ${\mu}$$\ell$/min, 1.88x10\ulcorner ${\mu}$$\ell$/min and 4.85x10\ulcorner ${\mu}$$\ell$/min at the frequency of 0.4H for each channel height.

• 설비공학논문집
• /
• 제7권3호
• /
• pp.461-472
• /
• 1995

The interaction of laminar mixed convection and surface radiation in a two-dimensional channel with an array of rectangular blocks is analyzed numerically. Three blocks are maintained at high temperature and the other bottom and top horizontal walls are insulated. Discrete ordinate method(DOM) is introduced to analyze the radiative heat transfer. The effects of the variations of Reynolds number and channel specifications on the heat transfer characteristics are investigated. The average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number and dimensionless geometric parameters such as the block spacing, height and channel spacing. For the conditions considered in this study, average Nusselt numbers along the block surfaces are strongly influenced by the channel spacing and Reynolds number but weakly influenced by the block spacing and block height.

• Nuclear Engineering and Technology
• /
• 제37권6호
• /
• pp.565-574
• /
• 2005

The CANFLEX Mk-V bundle is designed to improve upon the critical heat flux (CHF) characteristics of the CANFLEX Mk-IV bundle. The main difference between these two bundles is an increase in bearing pad height of about 0.3 mm in the CANFLEX Mk-IV bundle. This change in bearing pad height leads to an increase in gap flow at the bottom of the bundle, primarily eliminating the localized narrow-gap effect that limits the CHF of the CANFLEX Mk-IV bundle. The objective of this paper is to examine the effects of bearing pad height and pressure tube creep on the sheath-temperature distribution, dryout power, and dryout location, as observed ken full-scale bundle tests, between CANFLEX Mk-IV and Mk-V bundles In uncrept and crept channels. A comparison of surface-temperature differences between the top and bottom elements of the bundles showed that increasing the bearing pad height has led to a more homogeneous enthalpy distribution in subchannels of the bundle. Initial dryout locations of the CANFLEX Mk-V bundle were mainly observed at the mid-spacer plane of either the $10^{th}$ (about $80\%$) or $11^{th}$ ($20\%$) bundle in the 12-bundle string, as compared to the mid-spacer and downstream-button planes for the CANFLEX Mk-IV bundle. Dryout power and boiling-length-average (BLA) CHF values exhibit consistent trends and little scatter with varying flow conditions for both types of CANFLEX bundles in uncrept and crept channels. An increase in pressure tube creep has led to a reduction in dryout power (about $20\%$ far the $3.3\%$ crept channel and $27\%$ for the $5.1\%$ crept channel as compared to dryout powers for the uncrept channel). Increasing the bearing pad height of the CANFLEX bundle has led to an increase in the dryout power. Overall, the dryout power of the CANFLEX Mk-V bundle is 7 to $10\%$ higher than that of the CANFLEX Mk-IV bundle at the inlet temperature range of interest (i.e., between 243 and $290^{\circ}C$).

• 한국통신학회논문지
• /
• 제38C권8호
• /
• pp.706-712
• /
• 2013

본 논문에서는 간접 조명 환경에서 가시광(VLC : Visible Light Communication) 통신을 위한 채널 특성을 모델링하였다. 간접 조명은 직사 조도가 없이 모든 광속이 천정 및 벽을 반사한 후에 실내 바닥 면에 고르게 도달하는 방식이며, 광원에서 출발한 광 입자(Photon)는 간접경로(NLOS : None Line of Sight)를 통하여 수신부(PD, Photodiode)에 도달한다. 실내 간접 조명 환경으로서 가로(6m), 세로(4m), 높이(2.2m) 크기의 방(room)을 가정하였으며, 4개의 LED(Light Emitting Diode) 간접 조명을 2m 높이에 위치하여 벽과 천정을 향하여 빛을 비추도록 하였다. 바닥으로부터 50cm 위에 위치한 PD에서 수신 전력의 크기와 지연 수신된 신호를 통하여 채널 특성을 추출하였다. 도출된 채널은 BPSK 기반 통신 시뮬레이션을 통해서 그 유효성을 입증하였다.

• Journal of Advanced Marine Engineering and Technology
• /
• 제30권2호
• /
• pp.275-283
• /
• 2006

Experiment and three dimensional numerical investigations of incompressible turbulent flow through square channels with one- and two-sided ribbed walls are performed to determine pressure drop and heat transfer. The CFX(version 5.7) software package is used for the computation. The ribbed walls have a $45^{\circ}$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The numerical results coincide with experimental data that obtained for $7,600{\le}Re{\le}24.900$, the pitch-to-rib height ratio (p/e) of 8.0. and the rib height-to-channel hydraulic diameter ratio ($e/D_h$) of 0.0667. The results show that values of local heat transfer coefficient and friction factor in the channel with two-sided ribbed wall are higher than those in the channel with one-sided ribbed walls.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2008년 영문 학술대회
• /
• pp.39-44
• /
• 2008

In this paper, heat transfer coefficients were measured in a channel with one side dimpled surface. The sphere type dimples were fabricated and the diameter and depth of dimple was 16mm and 4mm, respectively. Two channel heights of about 0.6 and 1.2 time of the dimple diameter, two dimple configuration were tested. The Reynolds numbers based on the channel hydraulic diameter was varied from 30000 to 50000. The improved hue detection based transient liquid crystal technique was used in the heat transfer measurement. Heat transfer measurement results showed that high heat transfer was induced downstream of dimples due to flow reattachment. Due to the flow recirculation on the upstream side in the dimple, the heat transfer coefficient was very low. As the Reynolds increased, the overall heat transfer coefficients also increased. With same dimple arrangement, the heat transfer coefficients and the thermal performance factor were higher for the lower channel height. As the distance between dimples became smaller, the overall heat transfer coefficient and the thermal performance factor were increased.

• 설비공학논문집
• /
• 제8권4호
• /
• pp.561-575
• /
• 1996

The interaction of turbulent mixed convection and surface radiation in a three-dimensional channel with the heated blocks is analyzed numerically. Two blocks are maintained at high temperature and the other bottom and horizontal walls are insulated. S-4 method is employed to calculate the effect of the radiative heat transfer. The low Reynolds number k-$\varepsilon$ model proposed by Launder and Sharma is used to estimate the turbulent influence on the heat transfer enhancement. From above modeling, the effects of various channel specifications on the flow and heat transfer characteristics are investigated. The variables used for the present study are Reynolds number, block spacing, the channel height spacing for block and the emissivity. Average Nusselt numbers along the block surfaces are correlated and presented in terms of Reynolds number, emissivity and dimensionless geometric parameters. For the range of conditions in this study, average Nusselt numbers along the block surfaces are strongly influenced by the Reynolds numbers and channel height spacing for block but weakly influenced by the block spacing and the emissivity of the adiabatic walls.