Laminar flow is one of the two fundamental types of fluid motion and contrasts with turbulent flow. This type of flow is of great importance in engineering, physics, and even biology due to the order and calm observed in fluid motion. In stratified flow, the fluid moves in parallel and regular layers with very little mixing between the layers. This article covers the basic concepts, properties, governing equations, and applications of stratified flow.
1. Basic concepts of shift flow
Stratified flow is a slow and smooth fluid motion in which layers of fluid move parallel and without significant mixing. This type of flow is typically observed at low velocities and in highly viscous fluids. The Reynolds number is used to distinguish stratified flow from turbulent flow. The Reynolds number is a dimensionless parameter that indicates the ratio of inertial forces to viscous forces. This is visible. In stratified flow, the Reynolds number is typically below 2000.
2. Layered flow properties
Stratified flow has unique characteristics that distinguish it from turbulent flow. These characteristics include:
A) Regular and parallel movement of the layers
In stratified flow, fluid layers move parallel without mixing. This makes the flow highly predictable and controllable.
b) Constant speed per shift
In stratified flow, the fluid velocity is constant in each layer and changes slowly and linearly. This differs from turbulent flow, where the velocity changes irregularly.
c) Low pressure drop
Due to the smooth and uniform movement of the fluid, the pressure drop in stratified flow is lower than in turbulent flow. This property is very important in the design of fluid pumping systems.
d) Lower heat transfer and weight
In a stratified flow, heat and mass transfer occurs primarily through thermal conductivity and diffusion. For this reason, the heat and mass transfer rate in a stratified flow is lower than in turbulent flow.
3. Equations for controlling stratified flow
Sheet flows are described by partial differential equations that govern fluid dynamics. These include the continuity equation, the Navier-Stokes equations, and the energy equation. In sheet flows, these equations are usually solvable analytically or numerically due to the simplicity of the fluid motion.
A) Continuity equation
The continuity equation states that mass is conserved in a closed system. For an incompressible flow, the equation is:
∇⋅v=0
Where v is the velocity vector of the fluid.
b) Navir-Stokes equation
The Navier-Stokes equation describes the motion of a fluid. For an incompressible sheet flow, the equation is:
ρ(∂v∂t+v⋅∇v)=−∇p+μ∇2v+f
Where is the density of the liquid , p , μ is the dynamic viscosity and f is the external force.
B) Energy equation
The equation describes the heat transfer energy in a fluid. For a stratified flow, the equation is:
ρcp(∂T∂t+v⋅∇T)=k∇2T+Φ
Where is the temperature, cp heat capacity, k is the thermal induction coefficient and
4. Application of layer flow
Due to its unique properties, stratified flow has a wide range of applications in industry and science. These include:
a) Liquid and gas transport systems
In fluid transport lines and channels, stratified flow is preferred due to its low pressure drop and smooth motion. This is important for the design of irrigation systems, oil and gas pipelines, and cooling systems.
b) Microfluids
Microfluidic devices are used to transport tiny amounts of fluid and are characterized by layered flow. They are used in medicine, biotechnology, and analytical chemistry.
c) Coating and painting
In coating and painting processes, the lamella flow produces uniform, high-quality layers through slow and controlled movement.
D) Food and pharmaceutical industries
In the food and pharmaceutical industries, lamella flow is used to transport shear-sensitive materials. This is important, for example, in the production of milk, juice, and liquid medications.
d) Biomedical engineering
In medical devices such as dialysis and blood transfusion systems, layer flow is preferred due to its slow movement and lack of fluid turbulence.
5. Advantages and disadvantages of stratified flow
Layer flow has advantages and disadvantages that should be considered when designing different systems.
Advantages:
- Orderly and predictable movement
- Low pressure drop
- Reduction of shear stresses
- Improved control of heat and mass transfer
Defects:
- Lower heat and mass transfer rate compared to turbulent flow
- Flow rate restrictions
- To avoid turbulence in the flow, careful design is required.
6. Conclusion
Sheet flows play an important role in industry and science as one of the fundamental fluid motion modes. Due to its orderly and slow fluid motion, this flow mode is widely used in fluid handling systems, microfluidics, coatings, and food processing. However, limitations such as low heat transfer and mass velocity must be considered during system design. With technological advances, simulations and rigorous testing have enabled the analysis and optimization of sheet flows in various applications, leading to improved efficiency and reduced costs.