Slit Fin Research Articles

3D numerical simulation on fluid flow and heat transfer characteristics in multistage heat exchanger with slit fins

In this paper, a numerical investigation is performed for three-stage heat exchangers with plain plate fins and slit fins respectively, with a three-dimensional laminar conjugated model. The tubes are arranged in a staggered way, and heat conduction in fins is considered. In order to save the computer resource and speed up the numerical simulation, the numerical modeling is carried out stage by stage. In order to avoid the large pressure drop penalty in enhancing heat transfer, a slit fin is presented with the strip arrangement of “front coarse and rear dense” along the flow direction. The numerical simulation shows that, compared to the plain plate fin heat exchanger, the increase in the heat transfer in the slit fin heat exchanger is higher than that of the pressure drop, which proves the excellent performance of this slit fin. The fluid flow and heat transfer performance along the stages is also provided.

Optimum Design of Two-Row Slotted Fin Surface with X-Shape Strip Arrangement Positioned by “Front Coarse and Rear Dense” Princple, Part I: Physical/Mathematical Models and Numerical Methods

In this article, a comprehensive numerical investigation of the air-side fluid flow and heat transfer characteristics in a two-row finned-tube heat exchanger is conducted with a three-dimensional laminar conjugate model. Three groups including 15 types of slotted fin surface are studied. In the first group the strips are arranged in X shape with the principle of “front coarse and rear dense,” and the number of strips varies from three to six. The first series of the second group is formed by changing the strip length of slit fin 3 in the first group, and the second series of this group is formed by changing the strip lengths of slit 1 and slit 2 in the first group. The third group is formed by splitting one strip of slit fin 2 into two. The three groups are designed in order to enhance the values of j/f at the same Reynolds number and enhance the heat transfer at identical pumping power. The physical model/mathematical formulation and numerical methods are described. The authors' numerical experiences show that for the convergence criteria, apart from the relative variation of the key parameters, their variation trends versus some independent variables should also be taken into account. Reliable numerical solutions for the problem studied should possess consistency and smoothness in their variation trends. In Part II of this article, the specific flow and heat transfer characteristics of the 15 slotted fin surfaces and comparisons with a plain plate surface will be presented in detail.

Numerical simulation and field synergy analysis of heat transfer performance of radial slit fin surface

The finite volume method is used to numerically simulate the laminar heat transfer performances of a plate fin-and-tube heat exchanger surface with radially positioned slots and a plain plate fin-and-tube surface. It is found that at the identical pumping power or identical pressure drop, the performance of the slotted fin surface is much better than that of the plain fin surface, while under the identical mass flow rate, the performance of the slotted fin is inferior to that of the plain one, and where there is an enhanced heat transfer, there is a better synergy between velocity and temperature gradient.

Parametric study of the air-side performance of slit fin-and-tube heat exchangers in wet conditions

The air-side performance of three new slit fin-and-tube heat exchangers under dehumidifying conditions is reported. The effects of the number of rows of tubes, the fin pitch and the inlet relative humidity on air-side performance are reported. It is found that for type I slits, which are characterized by a small louvre angle (convex-louvre configuration), the test results show that the sensible heat transfer performances are relatively independent of fin pitch. However, for type III slits, which feature the smallest distance between adjacent slits, a drop of heat transfer performance for N= 1 and Fp = 1.81 mm is observed. It is very likely that this phenomenon is related to the ‘non-recovery wake effect’ caused by the slit geometry. A correlation is proposed for the slit fin configuration; the mean deviations of the proposed heat transfer and friction correlation are 8.0 and 8.1 per cent respectively.

A comparative study of compact enhanced fin-and-tube heat exchangers

Experimental study on the airside performance of compact slit fin-and-tube heat exchangers was carried out. Test results indicated the airside performance for compact slit fin geometry is relatively independent of the number of tube row and fin pitch. The results are quite different from previous studies concerning the slit fin geometry. This may be attributable to a smaller slit breadth of this study. Test results of the present slit fin were compared with louver fin and plain fin using various comparison methods. In all cases, the relevant airside performance of the interrupted surfaces (including louver and slit) is superior to that of plain fin surface. However, it should be pointed out that the associated superiority may decrease with decreasing fin pitch and Reynolds number. An updated correlation of the airside performance for the slit fin geometry describing 56 test samples is proposed. The mean deviation of the proposed heat transfer correlation is 7.26% and is 7.18% for frictional correlation.

Influence of design parameters on the heat transfer and flow friction characteristics of the heat exchanger with slit fins

This study systematically analyzes the effect of various design parameters on the heat transfer and pressure drop characteristics of the heat exchanger with a slit fin. The Taguchi method, known to be a very reasonable tool in a parametric study, is employed in the present work. Only seven cases of experimental factors are considered because of the difficulty in producing samples and the manufacturing cost. Eighteen kinds of scaled-up models are made by compounding levels on each factor, and the heat transfer and flow characteristics of each model are analyzed. The results allow us to quantitatively estimate the various parameters affecting heat exchanger performance, and the main factors for optimum design of a heat exchanger are selected. The optimum design value of each parameter is presented and the reproducibility of the results is discussed.

An investigation of the airside performance of the slit fin-and-tube heat exchangers

The airside performance of fin-and-tube heat exchangers having slit geometry is experimentally investigated in this study. A total of 12 samples were tested and compared. Effects of fin pitch and the number of tube row were examined. The test results indicated that the heat transfer performance increase with decrease of fin pitch for N=1. However, for N⩾4, the effect of fin pitch on the heat transfer performance is reversed. In addition to the effect of fin pitch, the heat transfer performance decrease with increase of the number of tube row and the friction factors are relatively independent of the number of tube row. Based on the present test results and those from previous investigations, a general correlation is proposed to describe the airside performance of the slit fin configuration, the mean deviations of the proposed heat transfer and friction correlation are 5.5 and 3.8%, respectively.

99/03362 Optimal climate protection strategies for space heating. The case of Austria

A 3-D numerical simulation is performed on laminar heat transfer and flow characteristics of a slit fin-and-tube heat exchanger with longitudinal vortex generators. Heat transfer enhancement of the novel slit fin mechanism is investigated by examining the effect of the strips and the longitudinal vortices. The structure of the slit fin is optimized and analyzed with field synergy principle. The result coincides with the guideline ‘front coarse and rear dense’. The heat transfer and fluid flow characteristics of the slit fin-and-tube heat exchanger with longitudinal vortex generators are compared with that of the heat exchanger with X-shape arrangement slit fin and heat exchanger with rectangular winglet longitudinal vortex generators. It is found that the Colburn j-factor and friction factor f of the novel heat exchanger with the novel slit fin is in between them under the same Reynolds number, and the factor j/(f1/3) of the novel heat exchanger increased by 15.8% and 4.2%, respectively.