Nussuelt number in microchannel
 

Hi guys, I'm doin simulation on heat transfer in microchannel. My case is a 2D rectangular model with 500 micro-meter height and 4000 micro-meter length. The heater length is 750 micro-meter which placed on the top wall of the channel.

The fluids velocity is 0.5m/s from left to the right. I'm using transient k-w model to simulate, time-step is 0.0001s. I plotted the surface heat transfer coeff. at the heated wall and used it to calculate the Nusselt number based on heater length (Nu= h*L/k).

h=surface heat transfer coeff., L= heater length, k=thermal conductivity of air

Based on my calculation, I got a similar graph compared to the journal im referring. But, i do not know why my graph shown a max value on 2nd point and an increased Nusselt number on the end of the heater.

I hope some1 could help me out. I really appreciate your help. I attached JPEG file of my graph and journal.

Thank you,
chong