Effect of magnetic nanofluid on cooling of hot obstacles in a minichannel: Optimization of obstacle size and spacing

This study conducts a numerical simulation of laminar flow of water/alumina nanofluids (NFs) in a channel with 5 hot obstacles. Obstacles and the wall beneath them have a high temperature, and the top wall is insulated. Also, the beginning and end parts of the bottom wall are insulated. The low-temperature homogenous NFs flow increases in temperature after hitting the obstacles and leaves the channel of length 20. Under the obstacles and the hot wall, a downward magnetic field of constant strength is applied. By altering the height of obstacles (HOB) between 0.1 and 0.7, the width between 0.1 and 1, and spacing between 0.1 and 1, the streamlines, temperature, local Nu, and average Nusselt number (Nu) are examined in the channel. In addition, the response surface methodology is used to conduct an optimization to obtain the maximum Nu and maximum outlet NFs temperature (T-NFs) in the channel by changing the mentioned parameters in associated ranges. The control volume method and Simple algorithm are used for simulations. Results of this study indicated that increasing the obstacle spacing and height causes the local Nu on the bottom wall to increase, the T-NFs in the middle of channel to increase, and the Nu in the channel to decrease. The maximum Nu occurs for the minimum obstacle size and smallest obstacle spacing; in this case, the Nu is higher by 611% than that of the case with maximum obstacle size and largest obstacle spacing.