Yur-Tsai Lin

Sensible heat and friction characteristics of plate fin-and-tube heat exchangers having plane fins

Abstract In the present study, 15 samples of plate fin heat exchangers with different geometrical parameters, including the number of tube rows, fin spacing and fin thickness are tested and compared in an induced flow open wind tunnel. Results are presented in the form of friction factor and Colburn j -factor against Reynolds number based on the tube collar diameter in the range of 300 to 7500. Comparisons with the existing plate fin correlation are also reported. It is found that the fin spacing does not affect the heat-transfer coefficient. The number of tube rows has negligible effect on the friction factor, and the fin thickness does not affect the heat-transfer or friction characteristics.

Performance of Plate Finned Tube Heat Exchangers Under Dehumidifying Conditions

Systematic studies of continuous fin-and-tube tube heat exchangers under dehumidifying conditions are reported in the present study. The heat exchangers consist of nine fin-and-tube heat exchangers having plane fins. The effects of fin spacing, the number of tube row, and inlet conditions are investigated. Data are presented in terms of j factors and friction factors f . It is found that the inconsistencies in the open literature may be associated with the wet fin efficiency. A correlation is proposed for the present plate fin configuration; this correlation can describe 92 percent of j , and 91 percent of the f data within ±10 percent.

Empirical correlations for heat transfer and flow friction characteristics of herringbone wavy fin-and-tube heat exchangers

This study presents an empirical correlation describing the airside performance of herringbone wavy fin pattern. A total of 61 samples containing approximately 570 data points are used in the regression analysis. The proposed heat transfer correlation can describe 91% of the test data within ±15% with a mean deviation of 6.98% while the proposed friction correlation can describe 85% of the database within ±15% with a mean deviation of 8.82%.

Flow visualization of annular and delta winlet vortex generators in fin-and-tube heat exchanger application

Abstract This study presents flow visualization and frictional results of enlarged fin-and-tube heat exchangers with and without the presence of vortex generators. Two types of vortex generators and a plain fin geometry were examined in this study. For plain fin geometry at Re=500, the horseshoe vortex generated by the tube row is not so pronounced, and the horseshoe vortex separates into two streams as it flows across the second row and consequently loses its vortical strength. This phenomenon may supports the “maximum phenomenon” in low Reynolds number region reported by previous studies. With the presence of annular vortex generator, the presence of a pair of longitudinal vortices formed behind the tube is seen. The strength of the counter-rotating vortices increases with the annular height and the strength of the longitudinal vortices is so strong that may swirl with the horseshoe vortices and other flow stream. For the same winlet height, the delta winlet shows more intensely vortical motion and flow unsteadiness than those of annular winlet. This eventually leads to a better mixing phenomenon. However, it is interesting to know that the corresponding pressure drops of the delta winlet are lower than those of annular winlet. Compared to the plain fin geometry, the penalty of additional pressure drops of the proposed vortex generators is relatively insensitive to change of Reynolds number.

Heat and momentum transfer for compact louvered fin-and-tube heat exchangers in wet conditions

Abstract The air side performances of two louvered fin surfaces under dehumidifying conditions were examined in this study. The test results indicated that the effect of fin pitch on the heat transfer performance is comparatively small, and the friction factors increase significantly with fin pitch for fully wet conditions. The effect of inlet relative humidity on the sensible heat transfer performance is negligible. However, there is a detectable effect of inlet condition on the friction factors for type (I) louver due to condensate retention. A correlation of heat, momentum, and mass transfer was proposed to correlate the present database with a mean deviation of 5.94%, 6.1%, and 7.89%, respectively.

Performance of Rectangular Fin in Wet Conditions: Visualization and Wet Fin Efficiency

An experimental study concerning the performance of a rectangular fin in both dry and wet condition was carried out. The visual observation of the dehumidifying phenomenon identified four regions, including the fully dry, very fine droplet, larger droplet, and film-like region, Experimental results showed that the effect of dry bulb temperature on the wet fin efficiency is very small. The dry fin efficiency is about 15-25 percent higher than that of the corresponding wet fin efficiency. For fully wet condition, the effect of relative humidity on the fully wet fin efficiency is also small. For partially wet surface, a considerable influence of the relative humidity on the fin efficiency is encountered. Test results for the fully wet fin efficiency agree well with some of the previous studies but disagree with some of the previous investigations. The main cause to this controversy may be attributed to the formulation of the relation between the humidity ratio and the fin temperature. The fully wet fin efficiency decrease slightly with increase of fin base temperature, However, the effect of fin base temperature on the dry fin efficiency is relatively small.

Flow visualization of wave-type vortex generators having inline fin-tube arrangement

Abstract This study presents visual observation of enlarged fin-and-tube heat exchangers with and without the presence of vortex generators. Three samples of fin-and-tube heat exchanger having inline arrangements are examined, including one plain fin and two wave-type vortex generators. For plain fin geometry at Re=500, the horseshoe vortex generated by the tube row is not so pronounced, and a very large secondary flow circulation is seen between the first and second row. This flow re-circulation phenomenon is almost disappeared with the presence of proposed vortex generators. The presence of vortex generators significantly increase the vortrical motions of the horseshoe vortices hitting on the tubes. A much better mixing characteristics is seen by introducing the vortex generators. The frictional penalty of the proposed vortex generators are about 25–55% higher than that of the plain fin geometry. The penalty of pressure drops of the proposed vortex generators relative to plain fin geometry is relatively insensitive to change of Reynolds number.

Performance of the herringbone wavy fin under dehumidifying conditions

Abstract An experimental study reporting the airside performance of the herringbone wavy fin geometry in wet conditions is conducted. In the visualization of the condensate flow pattern, a very special “locally dry” spot of the corrugation wavy channel having a corrugation angle of 15° and a fin spacing of 8.4 mm is seen. This phenomenon is related to the recirculation of the airflow across the apex. Conversely, this phenomenon is not so clearly seen either for a fin pitch of 2.6 mm with a corrugation angle of 15° or a corrugation angle of 25°. Flow visualization of the non-uniform distribution of the condensation in the facets results in a dependence between axial length and friction factor. Based on the present test results, airside performance in terms of Nusselt number and Fanning friction factor for the present herringbone wavy fin geometry in wet conditions are developed. The mean deviations of the proposed correlations are 2.52% and 4.81%, respectively.

A performance comparison between coiled and straight capillary tubes

The present study examines the performance difference between straight and coiled capillary tubes. The test results indicate that the helical effect increased with decrease of the diameter of coiling, and the effect of inlet conditions is relatively small. Based on the present test results, a simple relation is proposed which can quantitatively describe the difference between coiled and straight capillary tubes.The present study examines the performance difference between straight and coiled capillary tubes. The test results indicate that the helical effect increased with decrease of the diameter of coiling, and the effect of inlet conditions is relatively small. Based on the present test results, a simple relation is proposed which can quantitatively describe the difference between coiled and straight capillary tubes.