Greg Harrington
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 May 14 comment Internal pipe flow - Pressure Drop @Louis Thank you for the help anyway. I have not done any calculations with undeveloped flow either so this is my first time which is why its confusing. If it was fully developed then it would be very easy and I could in fact split the pipe into separate sections (for organization purposes) without having any difficulty May 14 comment Internal pipe flow - Pressure Drop @Louis So for undeveloped flow, I have an interpolation table that determines $f$ through Reynold's number and L/D. So I separated the pipe into like you said, a 3 ft straight, 2 ft bend, 3 ft straight and 2 ft bend. I then found the Reynold's number and L/D for each section to determine each section's $f$ and each section's Pressure drop. This did not end up being the same as taking the entire 10ft pipe and finding its L/D, f, and pressure drop. So separating the pipe gave me a different f at each section because each section had a different L/D than the entire pipe. Apr 13 comment Series of parallel thermal resistance connection for this enclosure? you are correct, I found my error in my derivation =D the resistances do turn out to be the same Mar 30 comment How does heat pass through glass? Let's say the glass is receiving heat from a heat source such as the sun. Won't a fraction of the radiation pass through the glass and act directly on the air to warm it up? Mar 24 comment What will happen to this fan in this situation? answering your one yes/no question does not provide one answer for my multiple questions. the answer to your question is Yes, but which question of mine does that answer? May 1 comment Is this how I find the rate of change of internal energy for filling a vessel? @KyleKanos how would I use the T-ds equation to find an expression for $\frac{ds}{dt}$? I wanted to use $T\frac{ds}{dt}=\frac{du}{dt}+P\frac{dv}{dt}$ but T in the tank is changing with time. And it doesn't look like i could apply the product rule to that since it's already in the differential form May 1 comment Is this how I find the rate of change of internal energy for filling a vessel? yes i have all the variables. I just wanted to know if that step was right. I was given the expression for the change in pressure, and i determined change in $v$ with the ideal gas law. and i found dhdt by the energy balance Apr 18 comment Thermal resistance of thermal interface materials? @ThePhoton It all makes sense now that I remember the coolant is being constantly replenished and I assume it's a constant temperature. Thanks guys Apr 18 comment Thermal resistance of thermal interface materials? Lets say the chip needs to operate at $T_H$ and it dissipates constant 2 W. If we have a low total resistance, then doesnt that make the coolant temperature very close to $T_H$? But you just said you want it as low as possible. This is why I am getting confused Apr 13 comment RMS Free Path vs Mean Free Path I have no idea what to even do with that honestly. I am not a molecular physics guy. I just need to find a formula for RMS free path and there is nothing on google. Apr 11 comment Molecular mean free path probability I'm not really sure what kind of variable the $\xi$ is. It is just the distance the molecule will travel without a collision. I'm guessing it's continuous since it can be 0.01 or 0.012 or 0.013. Are you essentially saying that I should take "at least" and "greater than" to be the same? Apr 4 comment Help with change in specific volume with time in piston cylinder? WOW. I cannot believe I overlooked that mistake the entire time. Thanks a lot for the help. I also did it the way you mentioned in the endnote and I found it much more convenient Apr 4 comment Help with change in specific volume with time in piston cylinder? I used the quotient rule and obtained $$\frac{d}{dm}(\frac{V(m)}{m})=\frac{m\frac{dV}{dm}-V(m)\frac{d}{dm}(\frac{1}{m}‌​)}{m^2}=\frac{m\frac{dV}{dm}+\frac{1}{m^2}V}{m^2}$$ The only way I could think of expanding $\frac{dV}{dm}$ is by making it $\frac{dV}{dt}\frac{dt}{dm}$ or $\frac{d}{dm}(mv)=v\frac{dm}{dm}+m\frac{dv}{dm}$ which just puts me back to where I began Apr 4 comment Help with change in specific volume with time in piston cylinder? when I used the quotient rule I reached $$\frac{dv}{dm}=\frac{d}{dm}(\frac{V(m)}{m})=\frac{1}{m}\frac{dV}{dm}+\frac{1}{m‌​^4}V(m)$$ and right away I realized I must have done something wrong because I have an $m^4$ when I should. Also, won't $\frac{dV}{dm}=\frac{d}{dm}(mv)$ just get me back to $\frac{dv}{dm}$ which was square one? Apr 4 comment Help with change in specific volume with time in piston cylinder? when I used the quotient rule I reached $$\frac{dv}{dm}=\frac{d}{dm}(\frac{V(m)}{m})=\frac{1}{m}\frac{dV}{dm}+\frac{1}{m‌​^4}V(m)$$ and right away I realized I must have done something wrong because I have an $m^4$ when I should. Also, won't $\frac{dV}{dm}=\frac{d}{dm}(mv)$ just get me back to $\frac{dv}{dm}$ which was square one? Mar 31 comment Which temperature to evaluate fluid properties in pipe? I figured I could use the inlet temperature to find the inlet density and viscosity which would allow me to find the mass flow rate which I know is constant. I would then use the average temperature between inlet and outlet to find the nusselt number. I could then account for property variation from temperature change using $$Nu = Nu_{m}(\frac{\mu_{m}}{\mu_{s}})^{n}$$ Does this sound like a reasonable approach? Or do you think I should evaluate the inlet density at the average of the inlet and the surface temp? Mar 11 comment Determine pipe outlet temperature without length? @gregsan Are you sure there is no other way to find heat flux? This problem was on my professor's past exam and I am using it for practice. He must have made an error Mar 3 comment Derivation of cylindrical line heat source problem? Unfortunately I do have to do it this way. I agree that SoV and Bessel functions would be much easier Feb 3 comment What does the absence of hydrodynamic entrance effects do to the momentum conservation Equation? Even though the flow is still developing? I know there is velocity in the radial direction while the flow is still developing so I figured there would also be velocity in the theta direction Feb 3 comment What does the absence of hydrodynamic entrance effects do to the momentum conservation Equation? this is awesome. Thank you. I have one more question. Assuming an axi-symmetric pipe, is there a fluid velocity in the theta direction when the flow is still developing? My professor said in an email that there is no fluid velocity in the theta direction when the flow is still developing but I don't see why this is. If there is no velocity in the theta direction when it is developing or when it is fully developed then is there ever a fluid velocity in the theta direction?