Refers to the quantitative analogy relationship among momentum transfer, heat transfer and mass transfer in the process of transfer.
These three transfer processes have the same transfer mechanism and the same mathematical expression. 1874 O. Reynolds first pointed out the similarity of heat and momentum transfer, and gave the quantitative relationship between friction coefficient and heat transfer coefficient. Subsequently, L. Planter improved the Reynolds analogy at 19 10, G. I. Taylor at 19 16 and T. Carmen at 1939. Some people put forward a new analogy relationship and extended it to the analogy of momentum transfer and mass transfer. On the basis of analogy, we can analogy the other two transmission laws according to a known transmission law.
There are four common analogies:
Reynolds assumes that a fluid micelle with a mass of m per unit time moves from a certain distance to the wall, and the velocity drops from u to zero. Based on the assumption that the whole flow field is turbulent, it is considered that the fluid micelle directly brings heat to the wall, ignoring the existence of the bottom of the near-wall surface flow.
Planter thinks that there is a laminar bottom near the wall, and after the fluid reaches the laminar bottom, it transfers heat not by convection but by heat conduction.
Carmen put forward a three-layer model on the basis of predecessors. He believes that there is a transition zone between the turbulent core and the laminar bottom.
A.P. Kirben applied the empirical formula Nu=0.023Re0.8Pr 1/3 for turbulent heat transfer in tubes and the empirical formula f=0.046Re for Fanning friction coefficient. When the other three analogies are applied to mass transfer, there are also corresponding relationships. In the range of HR = 0.5 ~ 50, J factor is often used to correlate the experimental data of heat and mass transfer. When boundary layer separation occurs, there is pressure resistance (flow resistance) in addition to friction resistance. At this time, analogy is no longer applicable, but jd and jh are still equal.