• Title, Summary, Keyword: Heat/mass transfer

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A study on the Analogy between Heat Transfer and Mass Transfer (열전달과 물질전달의 유사성에 관한 연구)

  • 유성연;노종광;정문기
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.10
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    • pp.2624-2633
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    • 1993
  • Mass transfer experiment by naphthalene sublimation method has great advantages in measurement of local transfer coefficients in the region of a three dimensional flow or for a model of complex geometry, which is considered to be very difficult with conventional heat transfer measurements. Mass transfer data obtained by naphthalene sublimation technique are converted to the heat transfer data through heat/mass transfer analogy. This analogy is valid for a simple or laminar flow, but new insight is needed when applying to a turbulent flow or complex flow such as separation, reattachment and recirculation, The purpose of this research is to investigate how geometries and flow conditions incorporate heat/mass transfer analogy. Mass transfer experiments are performed using naphthalene sublimation technique for a flat plate, a circular cylinder, and rectangular cylinders. And mass transfer data are compared with earlier heat transfer measurements for the same geometries. Usefulness of analogy relation between heat and mass transfer is examined with these results.

A Naphthalene Sublimation Study on Heat/Mass Transfer for Flow over a Flat Plate

  • Park, Jong-Hark;Yoo, Seong-Yeon
    • Journal of Mechanical Science and Technology
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    • v.18 no.7
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    • pp.1258-1266
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    • 2004
  • It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer. In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to dimensionless parameters such as Sherwood number, Stanton number and Colburn j-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more suitable for turbulent boundary layer. But average Sherwood number and average Colburn j-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar boundary layer as well as turbulent boundary layer.

Experimental Study on Heat and Mass Transfer Characteristics in bundles of horizontal absorption tubes (수평관군 흡수기의 열 및 물질 전달특성에 관한 실험적 연구)

  • 설원실;정용욱;문춘근;윤정인
    • Journal of the Korean Society of Marine Engineering
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    • v.24 no.3
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    • pp.113-120
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    • 2000
  • On the absorber of absorption chiller/heater, LiBr solution at high concentration is sprinkled on a bundle of horizontal tube cooled by cooling water. In this case, the conditions of LiBr solution and cooling water have an influence on heat/mass transfer coefficient in this system. Therefor it is important to find optimal operation conditions of absorption chiller/heater to save energy. Heat and mass transfer coefficient increased with the increase of solution flow rate, and also heat and mass transfer rate increased but overall heat and mass transfer coefficient decreased by increasing the solution concentration within the experimental range. The superheating of the solution resulted in superior heat transfer character to a state of equilibrium from the point of heat flux and overall heat transfer coefficient.

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Heat/Mass Transfer and Pressure Drop of Square Duct with V-shape Ribs (쐐기형 요철이 설치된 사각덕트에서의 열전달 및 압력강하 특성)

  • Choi, Chung;Rhee, Dong-Ho;Cho, Hyung-Hee
    • Proceedings of the KSME Conference
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    • pp.280-287
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    • 2001
  • The present study investigates convective heat/mass transfer and flow characteristics inside the rib-roughened cooling passage of the gas turbine blades. A square duct with rectangular ribs is used and $\wedge-$ and V-shape ribs with $60^{\circ}$ attack angle are installed on the test plate surfaces. Naphthalene sublimation technique is employed to determine the detailed local heat transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wall and the vortices near the side-wall. The local heat transfer and the secondary flow in the duct are changed largely according to the rib orientation. A square duct with $\wedge$ and V-shape ribs has two pairs of secondary flow because of the rib arrangement. So, the duct has complex heat/mass transfer distribution. The average heat/mass transfer coefficient and pressure drop of $\wedge-$ and V-shape ribs are higher than those with $90^{\circ}$ and $60^{\circ}$ attack angles. The average heat/mass transfer coefficient on the $\wedge-shape$ ribs is higher than that on the V-shape ribs. Also, the uniformity of heat/mass transfer coefficient on discrete ribs is higher than that on continuous rib.

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Heat/Mass Transfer for Impingement/Effusion Cooling System with Circular Guide (원형가이드 설치에 따른 충돌제트/유출냉각에서 열/물질전달 특성)

  • Hong, Sung-Kook;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.30 no.12
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    • pp.1147-1154
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    • 2006
  • An experimental investigation was conducted to enhance the heat/mass transfer for impingement/effusion cooling system when the initial crossflow was formed. For the improvement of heat transfer, the circular guide is installed on the injection hole. At the fixed jet Reynolds number of 10,000, the measurements were carried out for blowing ratios ranging from 0.5 to 1.5. The local heat/mass transfer coefficients on the effusion plate are measured using a naphthalene sublimation method. The result presents that the circular guide protects the injected jet from the initial crossflow, increasing the heat/mass transfer. The heat transfer of stagnation region is hardly changed regardless of the blowing ratio. The secondary peak is obviously formed by flow transition to turbulent flow. At high blowing ratio of 1.5, the circular guide produces $26{\sim}30%$ augmentation on the averaged heat/mass transfer while the case without circular guide leads to the low and non-uniform heat/mass transfer. With the increased heat/mass transfer, the installation of circular guide is accompanied by the increase of pressure loss in the channel. However, the pressure drop caused by the circular guide is lower than that for other cooling technique with the circular pin fin.

Heat/Mass Transfer Characteristics for Variation of Injection Hole in Rotating Impingement/Effusion Cooling System (회전하는 충돌제트/유출냉각기법에서 분사홀 변화에 따른 열/물질전달 특성)

  • Hong, Sung-Kook;Cho, Hyung-Hee
    • The KSFM Journal of Fluid Machinery
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    • v.10 no.3
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    • pp.25-32
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    • 2007
  • The present paper deals with the heat/mass transfer characteristics for the rotating impingement/effusion cooling system. By changing the size and number of injection hole, its effects on heat/mass transfer are investigated and three different injection hole cases are considered such as LH, DH and SH, respectively. Reynolds number based on the effusion hole diameter is fixed to 3,330 and two jet orientations are considered. A naphthalene sublimation method is used to obtain the heat/mass transfer coefficients on the effusion plate. The LH case shows that the local heat/mass transfer is significantly varied by the rotation. Moreover, the low and non-uniform Sh distributions occur because the impinging jet is deflected by Coriolis force. Meanwhile, for DH and SH cases, the local heat/mass transfer coefficients are enhanced significantly compared to LH case and the rotation effect decreases with increasing the jet velocity. The averaged Sh value of DH and SH case rises up to 45%, 85% than that of LH case. However, the uniformity of heat/mass transfer deteriorates due to the steep variation of heat/mass transfer.

Heat/Mass Transfer Characteristics on Shroud with Turbine Blade Tip Clearances (터빈 블레이드 말단과 슈라우드 사이의 간극변화에 따른 슈라우드에서의 열/물질전달 특성)

  • Lee, Dong-Ho;Choe, Jong-Hyeon;Jo, Hyeong-Hui
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.25 no.3
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    • pp.414-421
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    • 2001
  • The present study is conducted to investigate the local heat/mass transfer characteristics on the shroud with blade tip clearances. The relative motion between blade and shroud has little influence on the overall heat transfer characteristics, except some local effects. Therefore, the relative motion between the blade and shroud is neglected in this study. A naphthalene sublimation method is employed to determine the detailed local heat/mass transfer coefficients on the surface of the shroud. The tip clearance is changed from 0.66% to 2.85% of the blade chord length. The flow enters the gap between the blade tip and shroud at the pressure side due to the pressure difference. Therefore, the heat/mass transfer characteristics on the shroud are changed significantly from those with endwall. At first, high heat/mass transfer occurs along the profile of blade at the pressure side due to the entrance effect and acceleration of the gap flow. Then, the heat/mass transfer coefficients on the shroud increase along the suction side of the blade because tip leakage vortices are generated and interact with the main flow. The results show that the heat/mass transfer characteristics are changed largely with the gap distance between the tip of turbine blade and the shroud.

Heat/Mass Transfer and Pressure Drop in A Square Duct with V-Shaped Ribs (쐐기형 요철이 설치된 사각덕트에서의 열/물질전달 및 압력강하 특성)

  • Choi, Chung;Rhee, Dong-Ho;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.26 no.11
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    • pp.1542-1551
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    • 2002
  • The present study investigates the convective heat/mass transfer characteristics and pressure drop inside the rib-roughened cooling passage of gas turbine blades. The internal cooling passage is simulated using a square duct with h- and V-shaped rectangular ribs which have a 60。attack angle. A naphthalene sublimation technique is employed to determine the detailed local heat/mass transfer coefficients using the heat and mass transfer analogy. The ribs disturb the main flow resulting in the recirculation and secondary flows near the ribbed wail. The secondary flow patterns and the local heat transfer in the duct are changed significantly according to the rib orientation. A square duct with ∧ - and V-shaped ribs have two pairs of secondary flow due to the rib arrangement. Therefore, the average heat/mass transfer coefficients and pressure drop of ∧ - and V-shaped ribs are higher than those of the continuous ribs with 90$^{\circ}$ and 60$^{\circ}$attack angles. The ∧-shaped ribs have higher heat/mass transfer coefficients than the V-shaped ribs, and the uniformity of heat/mass transfer coefficient are increased with the discrete ribs due to the flow leakage and acceleration near the surface.

Flow and Heat Transfer Within a Rectangular Film Cooling Hole of Normal Injection Angle (수직분사각도를 갖는 직사각 막냉각홀 내부에서의 유동 및 열/물질전달 특성)

  • Hong, Sung-Kook;Lee, Dong-Ho;Kang, Seung-Goo;Cho, Hyung-Hee
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.28 no.4
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    • pp.456-466
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    • 2004
  • An experimental study has been conducted to investigate the flow and heat/mass transfer characteristics within a rectangular film cooling hole of normal injection angle for various blowing ratios and Reynolds numbers. The results are compared with those for the square hole. The experiments have been performed using a naphthalene sublimation method and the flow field has been analyzed by numerical calculation using a commercial code (FLUENT). The heat/mass transfer around the hole entrance region is enhanced considerably due to the reattachment of separated flow and the vortices generated within the hole. At the hole exit region, the heat/mass transfer increases because the main flow induces a secondary vortex. It is observed that the overall heat/mass transfer characteristics are similar to those for the square hole. However, the different heat/mass transfer patterns come out due to increased aspect ratio. Unlike the square hole, the heat/mass transfer on the trailing edge side of hole entrance region has two peak regions due to split flow reattachment, and heat/mass transfer on the hole exit region is less sensitive to the blowing ratios than the square hole.

Enhancement of Heat and Mass Transfer for a Vertical Type Absorber (수직흡수기의 열 및 물질전달 촉진)

  • 권오경
    • Journal of the Korean Society of Marine Engineering
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    • v.22 no.3
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    • pp.362-370
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    • 1998
  • Absorption systems require a heat source for working but they have a great merit in that relatively low-temperature and low-quality types of thermal energy such as solar heat and exhaust heat can be effectively utilized as heat source. However details research related to absorbers which have a great effect on performances has been rarely done and thus there has been a strong hope for positive developments to improve their efficiencies. This paper describes absorption experiments made with different inside tube diameters and shapes. The purpose of this study is to acquire basic knowledge about heat and mass transfer in a falling film type absorber with vertical inner tubes. Heat and mass transfer were measured for water vapor absorption into a water/LiBr solution flowing down an absorber of vertical inner tubes. As a result absorption acceleration tube compares bare tube and heat transfer improved by order of insert spring tube corrugated tube grooved tube. And the acceleration that is good provided in inserting spring tube for both sides of heat and mass transfer.

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