Comparison of the heat transfer per

Comparison of the heat transfer performance over the whole heat exchanger is presented in Fig. 10 along with experimental results,UC exp, and numerical results, UC corr , which were calculated using Eqs. (19) and (29).
The deviation of the comparison is approximately 5.0%. From that result, the following relation of UC corr to
UC exp was obtained.UCcorr ¼ 1=1:050 UCexp ð32Þ
Numerical results of heat transfer performance were about 5%smaller than the experimental result for the overall heat transfer coefficient. Therefore, the new Nusselt number correlations are useful to evaluate the experimental performance of the heat exchanger.The reasons for underestimation by the correlations are presumed as follows. The actual MCHE has some roundness in its flow channel because of the chemical etching process (see Fig. 11). The roundness changes the flow profile and might cause a difference of the overall heat transfer coefficient. The simulation calculation was
examined for the geometry presented in Fig. 12, in which the radius of roundness is 0.2 mm. The overall heat transfer coefficient of the rounded model is about 0.5% smaller than that of non rounded model when the heat transfer area of the rounded geometry is presumed to be equal to that of the non-rounded one. The effect of roundness on heat transfer performance is small. Consequently,no clear reason for the underestimation was found. However,underestimation of the total heat transfer performance is