• Title/Summary/Keyword: 납작관

Search Result 15, Processing Time 0.025 seconds

Convective Heat Transfer Correlations for the Compact Heat Exchanger with Circular Tubes and Flat Tubes-Plate Fins (원형관 및 납작관-평판휜 형상의 밀집형 열교환기에 대한 대류열전달 상관관계식)

  • Moh, Jeong-Hah
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.34 no.3
    • /
    • pp.291-299
    • /
    • 2010
  • Aspect-ratio-based numerical analysis is carried out to investigate the air-side convective heat transfer characteristics in compact heat exchangers with circular tubes and flat tubes-plate fins. The RNG $k-{\varepsilon}$ model is adopted for turbulence analysis. The numerical analysis is carried out for aspect ratios ranging from 3.06 to 5.44 and for Reynolds numbers ranging from 1,000 to 10,000. The calculated results indicate a correlation between the friction factor and Colburn j factor in the compact heat exchanger system for the range of aspect ratios under consideration. The results obtained for circular tubes and flat tubes-plate fins in this study can be utilized to realize the optimal design of an air conditioning system.

Condensation Heat Transfer and Pressure Drop in Flat Tubes with Different Aspect Ratios (종횡비가 다른 납작관 내 응축열전달 및 압력손실)

  • Kim, Nae-Hyun;Park, Ji-Hoon;Cha, Sang-Jin
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.34 no.12
    • /
    • pp.1111-1119
    • /
    • 2010
  • In this study, condensation heat transfer coefficients of R-410A were obtained in flattened tubes made from round tubes with an inner diameter of 5.0 mm. The saturation temperature was $45^{\circ}C$; the heat flux, 10 kW/$m^2K$; the mass flux, 100-400 kg/$m^2s$; and the quality, 0.2-0.8. The results showed that the effect of the aspect ratio on the condensation heat transfer coefficient depended on the flow pattern. For annular flow, the heat transfer coefficient increased as the aspect ratio increased. For stratified flow, however, the reverse was true: the pressure drop increased as the aspect ratio increased. Existing correlations adequately predicted the heat transfer coefficients and pressure drops of the flattened tubes.

Effect of Aspect Ratio of Flat Tube on R410A Evaporation Heat Transfer and Pressure Drop (납작관의 종횡비가 R-410A 증발열전달 및 압력손실에 미치는 영향)

  • Kim, Nae Hyun;Lee, Eul Jong;Byun, Ho Won
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.37 no.4
    • /
    • pp.395-404
    • /
    • 2013
  • In this study, R-410A evaporation heat transfer tests were conducted in flattened tubes made from 5-mm round tubes. The test range covered a saturation temperature of $15^{\circ}C$, heat flux of $5{\sim}15kW/m^2K$, and mass flux of $200-400kg/m^2s$. The results showed that both the condensation heat transfer coefficient and the pressure drop increased as the aspect ratio increased, with a pronounced increase for an aspect ratio of 4. A comparison of the flattened tube data with existing correlations revealed that the heat transfer coefficients were reasonably predicted by the Shah correlation, and the pressure drops were reasonably predicted by the Jung and Radermacher correlation.

Convective Boiling of R-410A in an Aluminum Flat Tube for Air-Conditioning Application (공조용 알루미늄 납작관 내의 R-410A 대류 비등)

  • Kim, Nae-Hyun
    • Journal of the Korea Academia-Industrial cooperation Society
    • /
    • v.16 no.5
    • /
    • pp.3006-3013
    • /
    • 2015
  • Flat tube heat exchangers can improve the thermal performance significantly compared with round tube heat exchangers. For proper design of flat tube heat exchangers, one should know the tubeside heat transfer coefficients. In this study, convective boiling heat transfer coefficients of R-410A were obtained in a flat extruded aluminum tube with $D_h=1.41mm$. The test range covered mass flux from 200 to $600kg/m^2s$, heat flux from 5 to $15kW/m^2$ and saturation temperature from $5^{\circ}C$ to $15^{\circ}C$. The heat transfer coefficient curve shows a decreasing trend after a certain quality(critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kaew-On et al. correlations reasonably predicted the present data.

Analysis of Mixed Convection Heat Transfer in Arbitrarily Shaped Flat Tubes (임의형상을 갖는 납작관에서의 혼합대류 열전달 해석)

  • 박희용;박경우;이상철
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.13 no.5
    • /
    • pp.398-410
    • /
    • 2001
  • The flow and heat transfer characteristics for three-dimensional mixed convection flows in a radiator flat tube with U--shaped grooves are analyzed numerically. The flow and temperature fields are calculated by using the modified SIMPLE algorithm for irregular geometry. One tube specification among the various flat tube exchangers is recommended by considering the heat transfer and pressure drop. The effects of variation of coolant flow conditions and external air conditions on the flow and the thermal characteristics for the selected tube are investigated. the results show that inlet velocity of coolant flow is the very important factor in heat transfer and pressure drop, and top side is better position than the others as fin cleave to tube.

  • PDF

Flow and Thermal Analyses for the Optimal Specification of Flat Tube at Radiator (라디에이터용 납작관의 최적형상 도출을 위한 열.유동해석)

  • Park, Kyoung-Woo;Pak, Hi-Yong
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.24 no.8
    • /
    • pp.1046-1055
    • /
    • 2000
  • The flow and thermal phenomena in flat tubes of radiator are analyzed numerically. To predict the characteristics of heat transfer and pressure drop, the flow analysis program for three-dimensional complex geometry is developed, which adopted an non-staggered grid system and Cartesian velocities as dependent variables of the momentum equations. Using the developed program, the effect of tube specifications on the heat transfer characteristics is investigated for various flat tubes. From this study, the following results are obtained; (1) For the same hydraulic diameter($D_h{\doteq}5.2$mm), the Nusselt numbers of three basic modeis(D, J, and H-model) are 8.71, 8.92, and 10.58, respectively, and the pressure drops of D-, J-, and H-model are predicted as $-3.08{\times}10^{-2}\;Pa,\;-3.12{\times}10^{-2}\;Pa,\;and\; -3.98{\times}10^{-2}$ Pa, (2) In case of the same flat tube specification, the fins must be brazed at upper tube surface because the heat is more vividly transferred. Therefore, it is found that the H- model is the most effective tube as a heat exchanger and these results are used as a fundamental data for the design of tube.

Analysis of Convective Heat Transfer Characteristics for the Compact Heat Exchanger with Flat Tubes and Plate Fins Having a Non-symmetric Staggered Arrangements (비대칭 엇갈림 배열로 구성된 납작관-평판휜 형상의 밀집형 열교환기에 대한 대류열전달 특성 해석)

  • Moh, Jeong-Hah;Lee, Sang-Ho
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.33 no.5
    • /
    • pp.318-325
    • /
    • 2009
  • Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in compact heat exchanger with flat tubes and continuous plate fins having a symmetric and non-symm etric staggered arrangements. Simulation results such as air velocity and temperature distributions are presented, and heat transfer coefficients are compared with previous experimental results. In order to investigate the flow and heat transfer features by periodic boundary conditions, the three blocks were used. Predicted heat transfer coefficients between the three blocks are similar while there are relatively differences, compared with the experimental data. From the calculated results a correlation for Colburn j factor in the compact heat exchanger system is suggested. The predicted results in this study can be applied to the optimal design of air conditioning system.

Numerical Analysis for the Air-Side Convective Heat Transfer Characteristics in a Compact Heat Exchanger with Flat Tubes and Plate Fins According to the Aspect Ratio (종횡비에 따른 납작관-평판휜 형상의 밀집형 열교환기 내공기 측 대류열전달특성에 대한 수치해석)

  • Moh, Jeong-Hah
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.32 no.9
    • /
    • pp.695-703
    • /
    • 2008
  • Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in a compact heat exchanger with flat tubes and continuous plate fins according to the aspect ratio. RNG k-$\varepsilon$ model is applied for turbulence analysis. Simulation results such as air velocity and temperature distributions are presented, and heat transfer coefficients are compared with previous correlations for circular tubes. The numerical conditions are considered for the aspect ratios ranging from 3.06 to 5.44 and Reynolds number ranging from 1000 to 10,000. The results showed that heat transfer coefficients decreased with the increase of aspect ratio. From the calculated results a correlation of Colburn j factor for the considered aspect ratio in the compact heat exchanger system is suggested. The predicted results in this study can be applied to the optimal design of air conditioning system.

An Experimental Study on the Local and Overall Heat Transfer Characteristics of a Fin-Flat Tube Heat Exchanger (납작관형 핀-관 열교환기의 국소 및 총합 열전달 특성에 관한 실험적 연구)

  • 유성연;정민호;박동성;이상섭
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.14 no.11
    • /
    • pp.939-947
    • /
    • 2002
  • Local and overall heat transfer characteristics of fin-flat tube heat exchangers with and without vortex generators are investigated. Local heat transfer coefficients are measured with the heat exchanger model using naphthalene sublimation technique. In case of a fin-flat tube heat exchanger without vortex generators, only the horseshoe vortices formed around tubes augment the heat transfer. On the other hand, longitudinal vortices created artificially by vortex generators enhance heat transfer dramatically in case of a fin-flat tube heat exchanger with vortex generators. Overall heat transfer coefficients are measured with the prototype of the fin-flat tube heat exchanger with and without vortex generators in a wind tunnel and results are compared with those of a fin-circular tube heat exchanger with wavy fin. Friction losses for heat exchangers are also measured and compared. The fin-flat tube heat exchanger with vortex generators is found to be more effective than the fin-circular tube heat exchanger with wavy fin.

Analysis for Air-Side Convective Heat Transfer Characteristics in Compact Heat Exchangers (밀집형 열교환기 내 공기 측 대류열전달특성)

  • Moh, Jeong-Hah;Lee, Sang-Ho
    • Proceedings of the SAREK Conference
    • /
    • 2009.06a
    • /
    • pp.1443-1448
    • /
    • 2009
  • Numerical analysis has been carried out to investigate air-side convective heat transfer characteristics in compact heat exchangers with continuous plate fins. Simulation results such as air flow and temperature distributions are presented, and heat transfer characteristics are compared for various inlet conditions. Results from various turbulence models are also compared for applicability. There is large difference between the local heat transfer coefficient distributions along the cylinder wall for circular tubes. Colburn j factors from the calculated results of circular and flat tubes in the heat exchangers are compared for various Reynolds number. The predicted results in this study can be applied to the optimal design of air conditioning system. with compact heat exchanger.

  • PDF