Circular Tube Heat Exchanger Research Articles

5:1의 형상비를 갖는 사각덕트에서 직조 스크린 리입(rib)이 열전달과 마찰계수에 미치는 영향

직조 금속 스크린 리브(rib) 이 바닥에 설치된 사각 덕트에서 열전달과 유체유동의 압력강하를 측정하기 위해 실험적 연구를 수행하였다. 시험부의 치수는 200 mm(W) <TEX>${\times}$</TEX> 40 mm(H) <TEX>${\times}$</TEX> 712 mm(L)이고 수력직경은 66.6 mm이다. 입구영역에는 1.72m 길이의 가열되지 않은 동일한 치수의 채널을 설치하였다. 메쉬가 다른 4가지의 직조금속 스크린 리브에 대해 측정하였다. 그리고 비교를 위해 일체형 리브에 대해서도 측정하였다. 국부 열전달 계수의 측정에는 스테인레스 강제 포일(foil) 히터와 T형 열전대률 이용하였다. 레이놀즈 수는 23,000에서 58,000의 범위이다. 덕트의 수력직경(<TEX>$D_h$</TEX>)에 대한 직조 금속 리브의 높이(e)의 비(<TEX>$e/D_h$</TEX>)는 0.075 이고 리브 간격(p)과 높이의 비(p/e)는 10이다. 실험 결과 메쉬가 없는 일체형 리입에서 가장 누셀트 수와 마찰계수가 컷다.

Numerical simulation on flow and heat transfer at shell-side of flat-tube heat exchangers

The fluid flow and heat transfer of the shell-side in one type of flat-tube heat exchangers (FHE) were studied through numerical simulation and experimental methods. In the numerical simulation, hot/cold air was set as working fluid, and the standard k-ɛ turbulence model supplemented by boundary conditions was used, and also the control volume method was used to the discrete control equations. Compared with the same type of circular-tube heat exchangers (CHE), the numerical simulation results show that the pressure drop at the shell-side of FHE decreases by 12%–20%, and heat transfer coefficient increases by about 24%. The coefficient of integral performance Nu/ζ 0.29 has an increment of 22%–34%. Under the same conditions, the experimental results of temperature and the overall pressure drop show that the deviation percentage with those of numerical simulation are less than 8% and 25%, respectively. Both results verify that the heat transfer efficiency and flow resistance characteristics of FHEs are superior to that of CHEs.

원형휜-원형관 열교환기에 대한 자연대류 열전달상관식

An experimental study has been conducted on the natural convection heat transfer for the 7 kinds of circular finned tube heat exchangers. Empirical correlation was suggested at the range of 3,500＜Ra＜800,000, 1.6＜Do/Di＜3.0, 0.19＜Pf/Di＜0.34. The 92% of experimental data agreed with the correlation within 10%.

A numerical study of flow and temperature fields in circular tube heat exchanger with elliptic vortex generators

The two-dimensional fluid flow and heat transfer in a circular tube heat exchanger with two elliptic obstacles at the back is studied numerically. The computational domain consists of a circular tube and two elliptic obstacles that are situated after the tube, such that the angle between their centerlines and the direction of free coming flow is 45 degrees. The numerical solution is achieved by numerical integration of full Navier-Stokes and energy equations over the computational domain, using finite volume method. The fluid flow is assumed to be laminar, incompressible and steady-state with constant thermo-physical characteristics. In this study major thermo-fluid parameters such as temperature, pressure and velocity fields as well as Nusselt number and friction factor variations are computed and some results are presented in the graphs. It is shown that using of elliptic obstacles leads to an increase in the average Nusselt number and also pressure. .

Numerical solution of staggered circular tubes in two-dimensional laminar forced convection

This paper aims to demonstrate the importance of adequately estimating the discretization error intrinsic in the result of any numerical simulation. The problem under consideration is forced convection in a staggered circular tube heat exchanger. The problem is solved to analyze the effect of the distance between the tubes, aiming to optimize the heat exchanger’s geometrical configuration by two Reynolds numbers (50 and 100). The present work did not confirm the existence of an optimal geometrical point for the operation of staggered circular tube heat exchangers, as claimed in a numerical study published in the literature.

Optimization study and heat transfer comparison of staggered circular and elliptic tubes in forced convection

In this study, a two-dimensional (2-D) heat transfer analysis was performed in circular and elliptic tube heat exchangers. The finite element method was used to discretize the fluid flow and heat transfer governing equations and a 2-D isoparametric, four-noded, linear element was implemented for the finite element analysis program, FEAP (O.C. Zienkiewicz, R.L. Taylor, The Finite Element Method, vol. 1, McGraw-Hill, London, 1989, Chapter 15). The numerical results for the equilateral triangle staggering configuration, obtained with the new element were then validated qualitatively by means of direct comparison to previously published experimental results for circular tubes heat exchangers (G. Stanescu, A.J. Fowler, A. Bejan, Int. J. Heat Mass Transfer 39 (2) (1996) 311–317). Next, a numerical geometric optimization was conducted to maximize the total heat transfer rate between the given volume and the given external flow both for circular and elliptic arrangements, for general staggering configurations. The results are reported for air in the range 300⩽ Re L⩽800, where L is the swept length of the fixed volume. Circular and elliptical arrangements with the same flow obstruction cross-sectional area were compared on the basis of maximum total heat transfer. The effect of ellipses eccentricity was also investigated. A relative heat transfer gain of up to 13% is observed in the optimal elliptical arrangement, as compared to the optimal circular one. The heat transfer gain, combined with the relative pressure drop reduction of up to 25% observed in previous studies (H. Brauer, Chem. Process Eng., August (1964) 451–460; S.N. Bordalo, F.E.M. Saboya, Determinação experimental dos coeficientes de perda de carga em trocadores de calor de tubos circulares e elípticos aletados, in: Proceedings of the 13th COBEM, Congresso Brasileiro de Engenharia Mec a ̂ nica (in Portuguese), Belo Horizonte, Brasil, 1995) show that the elliptical arrangement has the potential for a considerably better overall performance than the traditional circular one.