UNIT IIIPART A

1. What is dimensional analysis?

Dimensional analysis is the analysis of the relationships between different physical quantities by identifying their fundamental dimensions (such as length, mass, time, and electric charge) and units of measure (such as miles vs. kilometers, or pounds vs. kilograms vs. grams) and tracking these dimensions as calculations or comparisons are performed2. State Buckingham (- theorem

Buckingham theorem states that an equation involving n number of physical variables which are expressible in terms of k independent fundamental physical quantities can be expressed in terms of p = n - k dimensionless parameters.3. What are all the advantages and limitations of dimensional analysis?

Dimensional analysis has no information on dimensionless constants.

If a quantity is dependent on trigonometric or exponential functions, this method cannot be used.

In some cases, it is difficult to guess the factors while deriving the relation connecting two or more physical quantities.

This method cannot be used in an equation containing two or more variables with same dimensions.

It cannot be used if the physical quantity is dependent on more than three unknown variables.

This method cannot be used if the physical quantity contains more than one term, say sum or difference of two terms.4. What do you mean by Reynolds number (Re)? what are the significance of Reynolds number?

The Reynolds number is defined as the ratio of inertial forces to viscous forces

It is very useful in determining whether the flow is laminar or turbulent.5. State Prandtl Number.It is defined as the ratio of momentum diffusivity (kinematic viscosity) to thermal diffusivity. That is, the Prandtl number is given as:

6. State Nusselt number.Nusselt number (Nu) is the ratio of convective to conductive heat transfer across (normal to) the boundary.

7. What is Grashoff number ?

The Grashof number (Gr) is a dimensionless number in fluid dynamics and heat transfer which approximates the ratio of the buoyancy to viscous force acting on a fluid. It frequently arises in the study of situations involving natural convection. It is named after the German engineer Franz Grashof.

8. State Stanton number.

The Stanton number, St, is a dimensionless number that measures the ratio of heat transferred into a fluid to the thermal capacity of fluid

9. What is meant by Newtonion and non-newtonion fluids?

Newtonian fluid is a fluid in which the viscous stresses arising from its flow, at every point, are linearly proportional to the local strain ratethe rate of change of its deformation over time

Non-Newtonian fluid is a fluid whose flow properties differ in any way from those of Newtonian fluids. Most commonly, the viscosity (the measure of a fluid's ability to resist gradual deformation by shear or tensile stresses) of non-Newtonian fluids is dependent on shear rate or shear rate history.10. What is hydrodynamic boundary layer?

A thin immobile layer of fluid that always exists at a solid/moving-fluid interface. Whether the movement of the fluid is due to ""forced"" or ""natural"" convection, a thin layer of fluid will always remain completely immobile at the surface of the solid due to the solid-liquid interactive forces.

11. What is thermal boundary layer?

the layer of a liquid or gaseous heat-transfer agent between the free stream and a heat-exchange surface. In this layer the temperature of the heat-transfer agent changes from that of the wall to that of the free stream12. What is convection?

Convection is the concerted, collective movement of groups or aggregates of molecules within fluids (e.g., liquids, gases) and rheids, either through advection or through diffusion or as a combination of both of them13. State Newtons law of convection

Convection-cooling is sometimes called "Newton's law of cooling"[4] in cases where the heat transfer coefficient is independent or relatively independent of the temperature difference between object and environment.

14. What is meant by free or natural convection?

Natural convection is a mechanism, or type of heat transport, in which the fluid motion is not generated by any external source (like a pump, fan, suction device, etc.) but only by density differences in the fluid occurring due to temperature gradients.

15. What is meant by laminar flow and turbulent flow?

Laminar flow (or streamline flow) occurs when a fluid flows in parallel layers, with no disruption between the layers

Turbulent flow, type of fluid (gas or liquid) flow in which the fluid undergoes irregular fluctuations, or mixing

16. What is forced convection?

Forced convection is a mechanism, or type of transport in which fluid motion is generated by an external source (like a pump, fan, suction device, etc.).17. Enumerate the applications of boiling heat transfer?

Steam production Heat absorption

Distillation and refining of liquids

Concentration, dehydration and drying of foods and materials

18. Differentiate between pool boiling and forced convection. Boiling is called pool boiling in the absence of bulk fluid flow and flow boiling (or forced convection boiling) in the presence of it.

19. Give the applications of boiling and condensation Cooling of nuclear reactors and rocket motor.

Steam power plants

Refrigeration and air conditioning systems

Melting of metal in furnaces

Refineries and sugar mills

20. What are the modes of condensation?(i) Film Condensation

(ii) Dropwise Condensation