Fluid Mechanics and Heat Flow and its Properties

Fluid Dynamics Moody Diagram and Basic Fluid Properties

1. Fluid Flow and Heat Transfer: Fluid Properties 1

2. Fluid Properties Fluid and Non-Fluids: Fluid refer to Liquid, vapour and gas and Non-fluid refer to the solid state of matter only. It is the intermolecular force that may differentiate them. E.g., Liquid may acquire the shape of a container while vapor and gases may fill in a container while a solid wont 2 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

3. Fluid Properties Shear Force (Fluid): A fluid deforms continuously under the action of shear force. The tendency of continuous deformation of a substance is called “fluidity” and the act of continuous deformation is called “flow”. Shear Force (Solid): A solid has a tendency to resist deformation or it deforms within elastic limits under the action of shear force. 3 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

4. Fluid Properties Fluid Mechanics: The field of fluid mechanics deals with the study of the motion of fluid governed by the laws of conservatin of mass and laws of mechanics. The laws of mechanics referred to as newton’s laws of motion. 4 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

5. Fluid Properties Fluid Properties: Density or mass density: Mass of a substance per unit volume  = m/v (kg/m 3 ) The reciprocal of density is specific volume which is the volume per unit mass (m3/kg) 5 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

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7. Fluid Properties Where the constant of proportionality ( ) is called the co-efficient of viscosity or the dynamic or absolute viscosity (kg/ m.s or N.s/m 2 ) Kinematic Viscosity: The ratio of dynamic viscosity to density is called kinematic viscosity ( ). The unit of kinematic viscosity is m 2 /s or stoke (0.0001 m 2 /s) = /  7 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

8. Fluid Properties Internal versus External Flow: The flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe is external flow . The flow in the pipe is internal flow if the fluid is completely bounded by solid surfaces. 8 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

9. Fluid Properties Compressible and Incomressible Flow: A flow is incompressible if the density of the flow remains nearly constant while the flow with varying densities is referred to as compressible flow . 9 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

10. Fluid Properties Laminar and Turbulent Flow: An orderly fluid with smooth layers of fluid is called laminar while a highly disordered fluid motion that typically occurs at high velocities with fluctuations is called turbulent flow. 10 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

11. Fluid Properties Laminar and Turbulent Flow: An orderly fluid with smooth layers of fluid is called laminar while a highly disordered fluid motion that typically occurs at high velocities with fluctuations is called turbulent flow. Reynolds No. ro *ul/µ U=0.5* uo 11 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

12. v               Reynolds Numbrer and Boundary layer 12

13. No Slip Condition/ Boundary Layer When a fluid flows at high Reynolds's no. over a body , the viscous effects may be neglected every where except in a thin region in the vicinity of the wall. The region is termed as the boundary layer by Prandlt. The boundary layer is necessitated by the required no slip condition at wall. A condition that can not be satisfied without considering viscous effects. Consider a flat plate as shown in fig (1), the flow over this flat plate can be divided into two regions “outer flow region” or “ free stream flow region ” or “fully developed flow region” where the flow is considered as in-viscous, irrotational or potential. And inner flow region where the viscous effects can’t be neglected. The viscous flow region is a thin region of flow near solid wall and is termed as boundary layer . In order to solve the problem of flow, the outer flow region is solved first using Euler’s equation and the thin region is solved using boundary layer equations. It can be seen from figure that the boundary layer is growing on the flat plate in its downstream since, the boundary layer must diverges slightly upward in a down stream of flat plate in order to satisfy conversation of mass. 13

14. As we go down to the flat plate, with the larger values of x Reynolds’s number increases and at some point disturbances in the flow begins to grow and the boundary layer can’t remain laminar. For a smooth flat plate with uniform free stream the transition process begins when critical Reynolds's no. “Re” is approximately and continues until the boundary layer is fully turbulent and the Reynolds’s number reaches to . The factors such as roughness along the surface, free stream disturbances, vibrations and curvature of the wall contribute to an earlier transition location. This is why an engineering critical Reynolds’s no. i.e. Re= approximately is often used to determine whether the boundary layer is most likely laminar (Re < Re cr ) or most likely turbulent ( Re > ) . The Eddie's caused by the disturbances discussed before cause local mixing and create disturbances that very quickly convert to a turbulent boundary layer.     14

15. Fluid Properties Steady and unsteady Flow: A steady flow is the one that shows no change at a point with time. The opposite is un-steady when changes occur with time. It is also referred to as transient. 15 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

16. Fluid Statics, Kinematics and Dynamics: Fluid Statics This deals with the forces applied by fluids at rest. The fluid property responsible for those forces is pressure. Fluid Kinematics: Fluid kinematics deals with the motion of fluids without necessarily considering the forces and moments that cause motion. 16 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.

17. Fluid Statics, Kinematics and Dynamics: Fluid Dynamics This deals with the motion of the fluid and the forces that cause that motion. 17 Prof. Dr. Rizwan Ahmed Memon Department of Mechanical Engineering, Mehran University of Engineering & Technology, Jamshoro.