only 5.0%. The correlations were verified as having sufficient accuracy
to predict the heat transfer performance.
6. Conclusions
Nusselt number calculations for the hot water supplier of microchannel heat exchanger with S-shaped fin configuration were obtained. The Nusselt number correlations were obtained numerically for each cold/hot side using the small temperature difference between the fluid inlet and the wall.
The deviations of the correlations were r = 1.47% for the water side and r = 0.90% for the CO2 side. The deviations were small; a very small difference was found between correlations obtained using logarithmic mean temperature difference and those obtained using generalized mean temperature difference. Therefore, the simulation calculations with a small temperature difference yielded the more accurate prediction, although the fluid properties
varied rapidly around the pseudo-critical point.A method was proposed to assemble these correlations to evaluate
the heat transfer performance of the whole heat exchanger.The method was validated by comparing the overall heat transfer coefficient with those obtained by another method using largescale calculations and experimental results. The deviations of comparisons were, respectively, about 2.3% with another numerical result and about 5.0% with experimental results. Therefore, correlations for a single side obtained using small computational
resources can provide an accurate evaluation of the whole heat exchanger performance.
Flow characteristics in the S-shaped fin configuration were also examined. Water flow in the configuration showed rather more turbulent behavior than in the laminar one, although the Reynolds number of the water flow is less than 1500. A smaller exponent of the Reynolds number in the correlations for S-shaped fin configuration
suggests that turbulence is promoted by that configuration.Appendix A. Accuracy of the experiments
The measurement accuracies of each sensor are presented in Table
5. Considering that the transferred heat was calculated onlyfrom cold (water) side temperature and flow rate, the total uncertainty of the experiment is calculated as 2.12%.
only 5.0%. The correlations were verified as having sufficient accuracy
to predict the heat transfer performance.
6. Conclusions
Nusselt number calculations for the hot water supplier of microchannel heat exchanger with S-shaped fin configuration were obtained. The Nusselt number correlations were obtained numerically for each cold/hot side using the small temperature difference between the fluid inlet and the wall.
The deviations of the correlations were r = 1.47% for the water side and r = 0.90% for the CO2 side. The deviations were small; a very small difference was found between correlations obtained using logarithmic mean temperature difference and those obtained using generalized mean temperature difference. Therefore, the simulation calculations with a small temperature difference yielded the more accurate prediction, although the fluid properties
varied rapidly around the pseudo-critical point.A method was proposed to assemble these correlations to evaluate
the heat transfer performance of the whole heat exchanger.The method was validated by comparing the overall heat transfer coefficient with those obtained by another method using largescale calculations and experimental results. The deviations of comparisons were, respectively, about 2.3% with another numerical result and about 5.0% with experimental results. Therefore, correlations for a single side obtained using small computational
resources can provide an accurate evaluation of the whole heat exchanger performance.
Flow characteristics in the S-shaped fin configuration were also examined. Water flow in the configuration showed rather more turbulent behavior than in the laminar one, although the Reynolds number of the water flow is less than 1500. A smaller exponent of the Reynolds number in the correlations for S-shaped fin configuration
suggests that turbulence is promoted by that configuration.Appendix A. Accuracy of the experiments
The measurement accuracies of each sensor are presented in Table
5. Considering that the transferred heat was calculated onlyfrom cold (water) side temperature and flow rate, the total uncertainty of the experiment is calculated as 2.12%.
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