Interview Questions.

Question 1. Is The Derivation For Composite Axis Symmetric Bar Subjected To Torsion Similar To The Composite Beam Derivation?

Answer :

Yes. Since plane sections stay aircraft assumption holds correct for composite bar subjected to torsion, similar principle as derivation for composite beam may be used to remedy for stresses in a composite bar subjected to torsion.

Question 2. Why Do They Have A Tapering Change In C.S. For Stepped Shafts?

Answer :

For stepped shafts, faraway from the abrupt trade within the cross-section, the stresses may be computed the use of the same formulae derived taking appropriate diameter of the shaft component in to consideration. At the place of exchange in geometry, stress concentrations can arise because of abrupt trade radius.

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Question 3. Why Is The Variation Of Shear Strain With Radius Linear?

Answer :

For non-linear elastic materials again, the elastic module are one of a kind and are functions of the strains. Therefore, at the same time as solving for stresses, suitable constitutive law must be used earlier than applying the equilibrium situations.

Question four. Why Do We Have To Make The Assumption That Plane Sections Plane?

Answer :

In order to make calculation of stresses due to torsion smooth, we need to make sure simplifying assumptions at the deformation pattern which is sensible. It is has been located from the rigorous answer manner (elasticity solution) and from the experiments that the circular cross segment contributors subjected to pure torsion inside the elastic variety fulfill very carefully this condition of aircraft sections stay aircraft and rigid. 

By making this assumption, the solution process will become easy as proven in the simple ideas segment within the derivation for tensional stresses.

Question five. What If Material Is Non-isotropic?

Answer :

If the fabric is non-isotropic (i.E. Anisotropic), then the elastic module will range and accordingly the hassle could be completely unique with extra stresses appearing considering there may be a coupling between shear stresses and ordinary stresses for an anisotropic cloth.

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Question 6. How About Bars With Non-axis Symmetric Cross Section?

Answer :

For bars with non-ax symmetric cross section, the assumption of aircraft section remain plane isn't happy. Regions of the go-phase undergo deformations within the axial path main to warping of the section. There are once more positive simplifying assumptions that are rest of the ax symmetric bar assumption that may be used to find stresses in a non-ax symmetric bar.

Question 7. What If Material Goes To Plastic Range?

Answer :

Even, if the material goes to plastic variety, plane sections stay aircraft assumption is thought to hold. Therefore, the lines can be located out from which distribution of stresses can be derived from equilibrium principles.

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Question 8. The Formula Derived Look Very Similar To Beam And Axial Deformation Formula?

Answer :

Yes, that is authentic. In all of the 3 derivations concerning axial, beam and torsional deformations, the idea of plane section stays plane is used and it leads to very comparable formulae for these three kinds of structural participants.

Question nine. If A Surface Emits 2 hundred W At A Temperature Of T, How Much Energy Will It Emit At A Temperature Of 2t?

Answer :

Since E u T4, a 2-fold increase of temperature brings a (24) = 16-fold boom in electricity. Thus the surface will emit (16)(2 hundred) = 3200 W.

Question 10. Explain Why The Temperature Boundary Layer Grows Much More Rapidly Than The Velocity Boundary Layer In Liquid Metals?

Answer :

Liquid metals are characterised through very low Prandtl numbers considering their thermal conductivity is high, hence the warmth diffusion is lots quicker than momentum diffusion.

Question eleven. What Is The Fourier Number?

Answer :

The Fourier wide variety is described as: FO = at/L2 wherein a = thermal diffusivity, t = time L = feature duration

The Fourier range is a dimensionless measure of time used in temporary conduction issues.

Question 12. Define A Black Surface?

Answer :

A black surface is described through 3 criteria: it absorbs all radiation that is incident on it emits the most electricity possible for a given temperature and wavelength of radiation (consistent with Planck’s regulation) the radiation emitted via a blackbody isn't always directional (it's far a diffuse emitter)

A black floor is an appropriate emitter and absorber of radiation. It is an idealized concept (no surface is exactly a black floor), and the traits of actual surfaces are in comparison to that of a super black surface.

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Question thirteen. Your Friend Asserts That, In A Heat Exchanger, It Is Impossible For The Exit Temperature Of The Cold Fluid To Be Greater Than The Exit Temperature Of The Hot Fluid When Both Fluids Are Single Phase Fluids. What Is Your Response?

Answer :

The announcement is genuine for a parallel waft warmth exchanger. However, in a counter flow heat exchanger the hole temperature of the cold fluid can in reality exceed the opening temperature of the new fluid.

Question 14. What Is A Diffuse Surface?

Answer :

A diffuse surface is described as one for which the emissivity (e) and the absorptive (a) are unbiased of direction (q).

Question 15. What Is The Difference Between Diffusion And Radiation Heat Transfer?

Answer :

Diffusion warmth switch is because of random molecular movement. Neighboring molecules pass randomly and switch energy between each other - but there may be no bulk motion. Radiation heat transfer, however, is the delivery of heat power via electromagnetic waves. All bodies emit thermal radiation.

In unique, note that not like diffusion, radiation heat transfer does not require a medium and is for this reason the handiest mode of heat transfer in space. The time scale for radioactive heat switch is a good deal smaller than diffusive warmth switch.

Question 16. What Are The Conditions To Be Satisfied For The Application Of A Thermal Circuit?

Answer :

The problem must be a regular country, one-dimensional warmness switch trouble.

Question 17. Define And State The Physical Interpretation Of The Biot Number?

Answer :

The Biot quantity is given by using:

Bi = hL/okay

Where

h = convective warmness transfer coefficient,

k = thermal conductivity

L = function duration.

It is a ratio of the temperature drop in the stable material and the temperature drop the stable and the fluid. So whilst the Bi <<1 , most of the temperature drop is inside the fluid and the stable can be considered isothermal.

Question 18. Define Overall Heat Transfer Coefficient?

Answer :

The general warmness switch coefficient is defined in terms of the overall thermal resistance among  fluids. If there are some of thermal resistances among the two fluids,

the general warmth transfer coefficient is given with the aid of:

U = 1/SR

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Question 19. You Might Have Observed Early Morning Frost On A Clear Day Even When The Minimum Air Temperature During The Night Was Above 0 Degree C. On A Clear Day, The Effective Sky Temperature Can Be As Low As -45 Degree C. Explain How Such Frost Formulation Takes Place?

Answer :

The frost is created due to radioactive losses to the sky.

Question 20. How Is Natural Convection Different From Forced Convection?

Answer :

In herbal convection, the motion of the fluid is due totally to density gradients inside the fluid (e.G. Warm air rises over bloodless air). There is no outside tool or phenomenon which causes fluid motion. In forced convection, the fluid is pressured to glide by means of an external thing - e.G. Wind inside the environment, a fan blowing air, water being pumped via a pipe. 

Typically warmth transfer below pressured convection situations is better than herbal convection for the identical fluid.

Question 21. What Is The Range Of Values For The Emissivity Of A Surface?

Answer :

The emissivity e stages among zero and 1.

Question 22. State The Condition Which Must Be Satisfied To Treat The Temperature Distribution In A Fin As One-dimensional?

Answer :

When ht/ok <<1 where h is the convective warmness switch coefficient, t is the thickness of the fin and ok is the thermal conductivity of the fin, you can still don't forget that the temperature gradient in the thickness route could be very small and the analysis may be taken into consideration as one-dimensional.

Question 23. What Is A Lumped System?

Answer :

A lumped machine is one wherein the dependence of temperature on function (spatial dependence) is left out. That is, temperature is modeled as a feature of time handiest.

Question 24. A Greenhouse Has An Enclosure That Has A High Transmissivity At Short Wavelengths And A Very Low Transmissivity (nearly Opaque) For High Wavelengths. Why Does A Greenhouse Get Warmer Than The Surrounding Air During Clear Days? Will It Have A Similar Effect During Clear Nights?

Answer :

Solar radiation is skewed in the direction of shorter wavelengths. On a clean day the glass of the greenhouse admits a huge percentage of the incident radiation. Inside the greenhouse, the various surfaces (flora and many others.) mirror the radiation; but the meditated radiation is spectrally different, having greater of a excessive wavelength contribution. 

Thus the contemplated radiation isn't transmitted nicely with the aid of the glass, and is reflected again into the greenhouse. The indoors heats up due to this trapped radiation. The same impact will no longer be visible on a clean night time, due to the fact that there may be no solar radiation.

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Question 25. Define A View Factor?

Answer :

A view thing is described inside the context of two surfaces A and B. It is defined as the fraction of radiation leaving A that's incident without delay on surface B. A view element need to be defined in phrases of floor A to floor B (FAB).

Question 26. What Is The Effect Of The Prandtl Number Of A Fluid On The Relative Thicknesses Of Velocity And Temperature Boundary Layers When The Fluid Flow Is Parallel To A Flat Plate?

Answer :

For laminar float, the ratio of the boundary layer thickness d to that of the thermal boundary layer, dt, is given through:

d/dt u Prn.

The better the Prandtl range, the bigger is the ratio.

Question 27. What Is Internal Energy Generation? Give Examples Where Internal Energy Generation Occurs?

Answer :

Internal electricity technology is the era of heat within a body by using a chemical, electrical or nuclear process. Examples are the heating of a nuclear gas rod (due to fission in the rod), the heating of electrical wires (due to the conversion of electrical to warmth energy), microwave heating and the era of warmth inside the Earth. The heat generated in every case is being transformed from a few other form of strength.

Question 28. What Do You Understand By The Terms Fully Developed Velocity And Temperature Profile Regions In Internal Flow?

Answer :

In the fully advanced place, the go-sectional velocity/temperature profile is of a regular shape at any axial place. Thus the profile has ceased to alternate. Also there may be no radial element of speed i.E. Every particle of fluid is flowing only inside the axial course.

Question 29. What Is A Gray Surface?

Answer :

A grey floor is defined as one for which the emissivity (e) and the absorptive (a) are impartial of wavelength (l).

Question 30. Both The Nusselt Number And The Biot Number Have The Same Form. What Are The Differences Between Them In Terms Of The Variables Employed And Their Physical Significance?

Answer :

Both the Biot quantity and the Nusselt variety are of the form (hL/k). However, for the Biot range, the thermal conductivity okay used is that for the stable; for calculating Nusselt range the okay price as that of the fluid. The Biot range is a measure of the ratio of the temperature drop within the stable cloth and the temperature drop among the solid and the fluid. The Nusselt number is a dimensionless version of the temperature gradient at the floor between the fluid and the strong, and it as a consequence gives a measure of the convection happening from the surface.

Question 31. What Do You Understand By Stability Criterion For The Solution Of Transient Problems?

Answer :

When solving brief troubles using finite-distinction techniques, it's far feasible that the solution undergoes numerically induced oscillations and becomes risky i.E. The temperature values diverge. The stability criterion is a limit on the values of Dt and Dx which guarantees that the answer remains strong and converges. The criterion is usually expressed as a function of Fourier’s wide variety.

Question 32. Will The Thermal Resistance Of A Rectangular Slab Be Increased Or Decreased If The Thermal Conductivity Is Increased?

Answer :

Thermal resistance will decrease.

Question 33. In A Particular Case Of Fluid Flow Over A Flat Plate The Temperature Boundary Layer Thickness Is Much Smaller Than The Velocity Boundary Layer Thickness. What Can You Conclude About The Nature Of The Fluid?

Answer :

The fluid is a high Prandtl range fluid. E.G. Oil.