11. Whnt bs nn nppropriate formulfthe energy etion for the simple casta exclhang

Question

11. Whnt bs nn nppropriate formulfthe energy etion for the simple casta exclhanger and the contlvone (dashed line) beot interl e le sthalpy) Control Volume (d) slcsalu+plSScs.atu+plp ds-Q-w 12. The stress tensor for aNewtonian fluid is a 2nd order tensor, and it accounts for... y forces and surface forces due to contributions from pressure and both normal and tangential viscous stresses (b) surface forces due to contributions from pressure and tangential viscous stresses (e) surface forces due to contributions from both normal and tangential viscous stresses. (d) surface forces due to contributions from pressure and both normal and tangential viscous stresses. (Note: the divergence of the stress tensor is a force per unit volume, c.f. Cauchy equation.) 13. In an inviscid, incompressible flow with no effects of elevation change, how does the stagnation pressure change through a gradual contraction? (a) The stagnation pressure does not change. (b) The stagnation pressure increases. (c) The stagnation pressure decreases. (d) The stagnation pressure first increases, then decreases. 14. Streamlines, defined by the equation i,x dE 0, can be described as: (a) For different times t, a streamline is the path described by a fluid particle. (b) At a given time t, streamlines are the paths described by fluid particles which passed through the same fixed point in space upstream. general flow direction. velocity field. (e) Streamlines are tracer lines in a fuid, which at some time t were perpendicular to the (d) At a given time t, streamlines are the curves which are tangent to the instantaneous

Explanation / Answer

11) assuming that no heat escaped,

so by energy conservation principle , heat lost by hot fluid = heat gained by col fluid

so (hA - hB )mhot = (hC - hD )mcol

so option c is correct

12) stress tensor of newtonian fluid contains pressure and only tangential viscous forces

so option b is correct

13) due to the contractions speed of flow increases. so due to the gradual contraction speed keep increasing , an the increase in this kinetic energy is achieved at expense of pressure energy so static pressure keep ereasing . But stagnation pressure is the pressure of the fluid at rest. so hen fluid stops again the hole kinetic energy converts into pressure energy , keeping stagnation pressure constant.

correct answer is option a) stagnation pressure does not change

14) streamline is the path of the fluid

so option a is correct

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