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As far as I catch the question (without going digged in math), pressure doesn't go instantly from a point to a point, but has certain speed, that is sound speed. No matter if your system is opened or closed, the air is the same. If you compress air in cylinder slowly, then the air well compressible, but if you try to move the piston quickly, let's say with ...

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The term "compressible flow" is rather misleading, but unfortunately, it is what the fluid-dynamics folks have chosen to use. "Compressible flow" refers to gas flow where the temperature of the gas is significantly affected by the conversion of pressure differences to kinetic energy. Bernoulli's principle states that the work done by a pressure difference is ...

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Poiseuille's law will tell you that a pipe of 0.1 m diameter will achieve a flow velocity of around $v=0.1\mathrm{~m/s}$, which is actually more than I expected. For pipes a bit wider than this, the flow will be turbulent (Re>2200), for which you can't apply Poiseuille. For turbulent flow, you can look into the Darcy-Weisbach equation. The interesting part ...

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The situation where the equation holds is when the fluid is imcompressible. In your example where you have a fluid flowing in a tube under gravity, you can imagine two situations. One is where there is no dissipative interaction between the fluid and the tube, and one where there is. In the situation with no dissipation, then the fluid should accelerate ...

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if the negative pressure is due to high velocity, there is possibility of cavitation to occur but if the negative pressure is due to height, it will just try to suck water, may be form other side or from the same side.

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The energy conservation equation can be written as below. I guess Cengel was making comments on each items. $$\delta U = Q -W + m_1(h_1+\frac 12 v_1^2 + gz_1)-m_2(h_2+\frac 12 v_2^2 + gz_2)$$ For steady state, we know $\delta U =0$, $m_1=m_2$ So reading the book, we can translate that to, q=0: $Q=0$ w=0: $W=0$ pe=0: $m_1gz_1 \approx m_2gz_2$ ke=0: ...

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If you have studied the open system version of the first law, you are aware that, for this mathematical representation of the energy balance, work is divided into two parts: shaft work and work to push fluid into and out of the control volume. The work to push material into and out of the control volume is combined mathematically into the energy of the ...

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The role of viscous forces with respect to turbulence is analogue to the one of diffusion for mixtures: it sets a scale below which it smoothes out gradients. So there are no vortices smaller than this. When this scale is much smaller than the scale of the experiment, tubulence can happen. Turbulence is not linked with a peculiarity of the molecules. It can ...

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You are missing that $$h=k\frac{Nu}{L}$$where L is the characteristic length. So, for a given value of the Nusselt number, increasing the thermal conductivity corresponds to an increase in the heat transfer coefficient. In any of the correlations that are out there, if you express Nu as a function of the Reynolds number and Prantdl number, and then solve ...

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