Is turbulence beneficial for heat exchange in plate exchangers?
Thread Content
Recently, I came across a presentation on plate heat exchangers, which stated that in order for heat exchange to occur effectively, the water flow must be made to experience intense turbulence at low speeds, in order to enhance heat transfer. So the question arises: ① Can strong turbulence form at low levels? According to available information, turbulence occurs only at high speeds; then why can vulgarity generate intense turbulence? ②Turbulence is an irregular fluid behavior that is uncontrollable. So how can we determine that turbulence enhances heat transfer? If strong turbulence does occur, could it cause damage to the plates? I would appreciate some guidance from the experts
If only the Reynolds number is considered, low flow velocities prevent turbulence from occurring; however, changing the design of the heat exchanger can alter the flow pattern of the fluid
The fluid inside the shell-and-tube heat exchange tubes must be in a turbulent state; if turbulence does not occur, heat transfer is uneven in the laminar state, resulting in very poor performance
For example, oblique corrugated plates can induce turbulence in fluids at very low Reynolds numbers
Turbulence is definitely beneficial for heat transfer, as is plate heat exchangers. The presence of corrugations on the plate exchanger is intended to generate turbulence at low flow rates.
Turbulence can also occur at low speeds, and this is because there are many contacts between the two plates; these contacts perturb the fluid flowing through them. Additionally, the shape of the plates is not flat – the most common shape is herringbone, meaning that the path of the fluid within the channel is not straight. The winding paths and the effect of these contacts cause the fluid to flow in an irregular manner, which results in turbulence. If the plates were flat with no contacts, turbulence would not be possible, but obviously they are not flat. Even in a zigzag pattern, turbulence will not occur if the flow velocity is too low; generally, the flow velocity between the plates needs to be at least 0.2 to induce turbulence. This is just my personal opinion for reference only.
The herringbone corrugated plates in a plate heat exchanger are installed in an inverted position with respect to one another, creating complex flow channels that enable the fluid to flow in a three-dimensional swirl pattern within the channels between the plates. As a result, turbulence can be generated at lower Reynolds numbers (23–400), and this turbulence enhances the heat transfer efficiency of the plate heat exchanger.