I might be going crazy or searching at the wrong places. Is there an empirical formula for solving the hydrodynamic entry length of laminar flow through a circular annulus? Thanks!
The entry length for a circular tube is going to be longer than for an annulus if the Re is defined in terms of the outer diameter for both. So, to be conservative, why not just use the value K=20.Disquoveri said:Thanks for your help, Chet. (Also, thanks for answering my question on displacement, momentum, enthalpy, etc. thicknesses in circular pipes.)
The gap between the cylinders is not small compared to the inner cylinder though. I have the gap to be 0.015 m, the the inner cylinder radius is 0.012 m, but the outer cylinder radius is 0.027 m. Can I still use the estimate of entry length for flow between parallel plates? The estimation of entrance length is given as L_e = Re*D/K, where K = 20 for circular tube and K = 100 for parallel plates. From simulations done on COMSOL, I know that fully developed velocity profile is achieved within the tube length. The entry length for a circular tube overestimates the entry length/point of fully developed velocity profile.
The hydrodynamic entry length of flow through circular annulus refers to the distance that a fluid must travel before reaching fully developed flow in a circular annular channel. It is an important parameter in fluid mechanics that is used to determine the behavior of fluid flow in this type of channel.
The hydrodynamic entry length can be calculated using the equation L = 0.05ReD, where L is the entry length, Re is the Reynolds number, and D is the diameter of the inner cylinder in the annular channel. This equation is based on empirical data and is applicable for laminar and turbulent flow.
The hydrodynamic entry length is affected by several factors, including the geometry of the annular channel, the velocity of the fluid, and the properties of the fluid, such as viscosity and density. Additionally, the type of flow (laminar or turbulent) will also affect the entry length.
The hydrodynamic entry length is important because it affects the behavior of fluid flow in circular annulus channels. When the fluid is not fully developed, there may be variations in velocity and pressure along the channel, which can impact the accuracy of any calculations or experiments being performed using this type of channel.
The hydrodynamic entry length can be reduced by increasing the velocity of the fluid, decreasing the viscosity of the fluid, or changing the geometry of the annular channel. Additionally, using a smaller diameter for the inner cylinder can also help to reduce the entry length. However, it is important to note that the entry length cannot be completely eliminated, as there will always be a distance required for the fluid to reach fully developed flow.