• 대한기계학회논문집B
• /
• 제34권3호
• /
• pp.291-299
• /
• 2010

본 연구에서는 열의 수가 세 개인 원형관 및 종횡비가 고려된 납작관-평판휜 형상의 밀집형 열교환기 내 공기의 유동 및 열전달 특성을 RNG $k-{\varepsilon}$ 난류모델을 적용하여 수치적으로 해석하였다. 수치조건의 범위는 원형관인 경우 1,000<$Re_D_h$<10,000이며, 납작관인 경우 1,000<$Re_{D_h}$<10,000 및 3.06$f\;=\;CRe^m_{D_h}$의 형태로, Colburn j 계수는 $j\;=\;CRe^m_{D_h}$ 형태로 상관관계식을 제시하였다. 이러한 상관관계식은 향후 원형관 및 납작관-평판휜 형상의 열교환기 설계시에 기본적인 자료로 충분히 활용될 수 있을 것으로 판단된다.

• 대한기계학회논문집B
• /
• 제34권12호
• /
• pp.1111-1119
• /
• 2010

본 연구에서는 내경 5.0mm 원관을 납작하게 한 납작관에 대하여 R-410A 를 사용하여 응축열전달 실험을 수행하였다. 실험은 포화온도와 열유속을 각각 $45^{\circ}C$ 와 10kW/$m^2$으로 고정한 상태에서 질량유속과 건도를 변화시키며 수행되었다. 실험결과 납작관의 종횡비가 열전달계수에 미치는 영향은 유동양식에 따라 달리 나타났다. 환상류에서는 종횡비가 증가할수록 증가하고 성층류에서는 종횡비가 증가할수록 감소하였다. 한편 납작관의 마찰손실은 종횡비가 증가할수록 증가하였다. 기존 상관식들은 납작관의 열전달계수와 마찰계수를 적절히 예측하였다.

• 대한기계학회논문집B
• /
• 제37권4호
• /
• pp.395-404
• /
• 2013

본 연구에서는 내경 5.0mm 원관을 납작하게 한 납작관에 대하여 R-410A를 사용하여 증발열전달 실험을 수행하였다. 실험은 포화온도를 $15^{\circ}C$로 고정한 상태에서 열유속을 $5{\sim}15kW/m^2$, 질량유속을 $200{\sim}400kg/m^2s$로 변화시키며 수행되었다. 실험결과 납작관의 종횡비가 증가할수록 열전달계수와 압력손실 모두 증가하였는데 특히 종횡비 4 인 경우 증가폭이 현저하였다. 납작관의 실험결과를 기존 상관식들과 비교한 결과 열전달계수는 Shah 상관식, 마찰계수는 Jung and Radermacher 상관식이 적절히 예측하였다.

• 한국산학기술학회논문지
• /
• 제16권5호
• /
• pp.3006-3013
• /
• 2015

원관 열교환기보다 납작관 열교환기를 사용하면 전열성능을 한층 향상시킬 수 있다. 납작관 열교환기를 적절히 설계하기 위해서는 관 내측 열전달계수를 알아야 한다. 본 실험에서는 수력직경 1.41mm인 알루미늄 납작관 내 R-410A 대류 비등 열전달계수를 구하였다. 실험범위는 질량유속 $200{\sim}600kg/m^2s$, 열유속 $5{\sim}15kg/m^2$, 포화온도 $5{\sim}15^{\circ}C$이다. 실험 결과 열전달계수는 임계 건도를 기점으로 감소함을 보였다. 임계 건도는 열유속이 증가할수록 감소하고, 질량유속이 감소할수록 감소하였다. 이는 높은 열유속 또는 낮은 질량유속에서 대류의 영향이 작게 되고 따라서 조기에 dryout이 발생되기 때문에 나타나는 현상으로 판단된다. 열전달계수는 질량유속이 증가할수록 증가하였다. 그러나 낮은 건도에서는 질량유속의 영향은 미미하였다. 열전달계수는 포화온도가 증가할수록 증가하였다. 하지만 이런 경향은 열유속이 작아지면 감소하였다. Shah와 Kaew-On et al. 상관식은 본 실험자료를 적절히 예측하였다.

• 설비공학논문집
• /
• 제13권5호
• /
• 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.

• 대한기계학회논문집B
• /
• 제24권8호
• /
• 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.

• 대한기계학회논문집B
• /
• 제33권5호
• /
• 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.

• 대한기계학회논문집B
• /
• 제32권9호
• /
• 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.

• 설비공학논문집
• /
• 제14권11호
• /
• 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.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2009년도 하계학술발표대회 논문집
• /
• 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.