What are the advantages of baffle rod heat exchangers?

The characteristic of the tube bundle support structure in a baffle rod heat exchanger is that each heat exchange tube is fixed by baffle rods in all four directions. The baffle rod is welded to the baffle rings; four baffle rings form a set, which clamp the heat exchange tube from four directions. The tube bundle support structure made of baffle rings functions like a large cage, offering excellent shock absorption properties. A baffle rod heat exchanger gets its name from the fact that the support for the tube bundle is replaced from arc-shaped plates with rod-based support; moreover, the flow pattern of the fluid in the shell side changes from cross-flow to co-current flow, which results in a significant reduction in the flow resistance of the fluid in the shell side – generally it is 1/7 to 1/10 of the resistance associated with arc-shaped plate tube bundles. In the shell side of a single-arch plate heat exchanger, the resistance is primarily incurred in the tube bundle; therefore, enhancing heat transfer by increasing the flow rate is limited by pressure drops. The introduction of baffle support members solves this problem. In a baffle rod heat exchanger, the fluid in the shell side flows axially through parallel tube bundles. When the fluid distribution at the inlet is optimal, it enables uniform flow of the fluid across the entire cross-section of the tube bundle, thus allowing full utilization of the heat transfer area. The heat transfer coefficient is generally low in parallel flow, but the addition of baffles causes the fluid to separate as it passes through these baffles, resulting in vortex wake flows behind them (also known as vortex streets). After the intensity of the vortex ahead weakens, the baffle rods behind generate new vortex wake flows. Therefore, uniform vortices are generated throughout the entire pipe length and on the heat transfer surface. These vortices are beneficial for improving heat transfer in parallel flow; the greater the flow velocity, the more intense the turbulence. Due to the extremely low fluid resistance in the shell side of the baffle rod heat exchanger, the flow velocity can generally be increased to 2-3 times that of an arch plate heat exchanger. Therefore, at the same pressure drop, the heat transfer coefficient of the baffle rod heat exchanger is more than 1.5 times higher than that of the single arch plate heat transfer tube.

Why are baffled rod heat exchangers rarely encountered?