**2. Test facility – fin-and-tube heat exchanger with oval tubes**

Figure 1 presents the scheme of a car radiator, for which the heat transfer coefficients will be determined [19].

The heat exchanger is used for cooling the spark ignition engine with a cubic capacity equal to 1, 580 cm3 . Hot water, which flows inside the aluminum tubes of the heat exchanger, is cooled down by the air flowing across the intertubular space.

The two-pass /two-row fin and tube heat exchanger is considered. The following characteristics are given:


Computer-Aided Determination of the Air-Side Heat Transfer Coefficient and Thermal Contact Resistance for… http://dx.doi.org/10.5772/60647 261

the heat transfer formulas for the Nusselt number, determined with the CFD simulations, can be directly implemented in the thermal designing procedure of the cross-flow heat exchangers. The results of the numerical computations will be validated experimentally, using the

The numerical studies of the performance of plate fin-and-tube heat exchangers encounter difficulties in the proper prediction of the total gas side temperature difference. This problem occurs, because of the flow maldistribution of mediums flowing through the heat exchanger and thermal contact resistance between the fin and tube. The thermal contact resistance, which can significantly reduce the thermal performance of heat exchange apparatus, is difficult to determine [15, 19]. It is considerable when the oval tubes are inserted into the holes, which are stamped in metal strips. Then, the tubes are expanded to create the so-called interference fit. Since the gap exists between the fin and tube, the corrosion residuals can cumulate within the gap, leading to the decrease in heat transfer ability. It should be noted, that the direct investi‐ gation of thermal contact resistance is difficult to conduct. Therefore, the alternative methods are needed. This study discusses the alternative approach to determining the thermal contact resistance between fin and tube, based on the CFD simulation and experimental data. More‐ over, the methods for determining the heat transfer coefficient correlations for the air side are

**2. Test facility – fin-and-tube heat exchanger with oval tubes**

cooled down by the air flowing across the intertubular space.

= 0.52 m.

11.82 mm, respectively, with thickness of *δ<sup>t</sup>*

*p*1=18.5 mm *p*2=17 mm (Fig. 2, [19])

Figure 1 presents the scheme of a car radiator, for which the heat transfer coefficients will be

The heat exchanger is used for cooling the spark ignition engine with a cubic capacity equal

The two-pass /two-row fin and tube heat exchanger is considered. The following characteristics

**•** Total number of tubes: 38, including 20 tubes in the first pass and 18 tubes in the second

**•** The radiator width, height, and thickness is equal to 520 mm, 359 mm and 34 mm, respec‐

**•** The aluminum (*k* = 207 W/(m K)) oval tubes of outer diameters *dmin* = 6.35 mm and *dmax* =

**•** Total number of plate fins (359 mm height, 34 mm width and 0.08 mm thickness) along the

**•** The fin pitches in the perpendicular and longitudinal directions to the air flow are as follows:

= 0.4 mm are used

. Hot water, which flows inside the aluminum tubes of the heat exchanger, is

procedures described in [14, 17, 20].

260 Heat Transfer Studies and Applications

also presented.

determined [19].

to 1, 580 cm3

are given:

tively

**•** The tube length is *Lt*

tube length is 520

**Figure 1.** Flow scheme of two-row car radiator with two passes: 1 – inlet manifold, 2 – intermediate manifold, 3 – out‐ let manifold, 4 – second row of oval tubes, 5 – first row of oval tubes, 6 – plate fin.

**Figure 2.** Scheme of the narrow air flow passage across the car radiator.

The path of the water flow is U-shaped, this means that the water reverses in the intermediate manifold. In the first pass (upper), the hot water with temperature *T'w* flows from the inlet header (1) thround the two rows of the oval tubes, with the length *Lt* = 0.52 m. Then, in the intermediate header (2), the mixing of the water streams from the first (4) and second (5) row occurs. The intermediate temperature of the water is equal to *T"w*. Next, the water reverses and flows into the two rows of the tubes located in the second (lower) pass. Finally, the liquid, cooled down to temperature *T'''w* flows out of the heat exchanger through the outlet manifold (3). The air with inlet temperature *T'a* flows in the normal direction to the both rows of the finned tubes. After the first and second row, air temperature is *T"a* and *T'''a*, respectively (Fig. 1). The plate fins (6) are used to enhance the heat transfer from the air side.

For the CFD calculations presented in this paper (section 4), the flow in a narrow passage formed between two consecutive fins is considered.
