Unit conversion:lbm/lbf*h to (N/s)/N

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  • #26
yecko
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As a guy who has been working with these unit all my life, I can tell you that 1 lbm/hr is the same as 0.4536 kg/hr. The weight of this is (0.4546)(9.8)=4.448 N/hr. And we know that 1 lbf=4.448 N. So, to convert from imperial to metric in this case, all you need to do is divide by 3600.
cT=0.5279lblbf⋅h=(0.5279lblbf⋅h)⋅(4.448Nlbf)⋅(0.4536kglbm)−1⋅(3600sh)−1 cT=0.5279lblbf⋅h=(0.5279lblbf⋅h)⋅(4.448Nlbf)⋅(0.4536kglbm)−1⋅(3600sh)−1​
\ cT=\frac{0.5279lb}{lbf\cdot h}=\frac{(0.5279lb}{lbf\cdot h})\cdot(\frac{4.448N}{lbf})\cdot(\frac{0.4536kg}{lbm})^{-1}\cdot\left(\frac{3600s}{h}\right)^{-1}
=1.49e−5 kgN−1s−1 ⋅9.81ms2=1.46e−4 NNs​
Thanks... I finally found that the two ways finally give the same answer!
 
  • #27
jbriggs444
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$$\ cT=\frac{0.5279lb}{lbf\cdot h}=\frac{(0.5279lb}{lbf\cdot h})\cdot\left(\frac{3600s}{h}\right)^{-1}=1.46e−4 N/Ns $$​
You are equating ##\frac {\text{lb}_{\text{force}}} {\text{lb}_{\text{mass}}}## with ##\frac {\text{N}_{\text{mass}}} {\text{N}_{\text{force}}}##.

That appears to be OK, since the intended output units do appear to be implicitly using Newton-mass. [Ordinarily, I'd run screaming if someone tried to use the Newton as a unit of mass instead of the kilogram.
 
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  • #28
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You are equating ##\frac {\text{lb}_{\text{force}}} {\text{lb}_{\text{mass}}}## with ##\frac {\text{N}_{\text{mass}}} {\text{N}_{\text{force}}}##.

That appears to be OK, since the intended output units do appear to be implicitly using Newton-mass. [Ordinarily, I'd run screaming if someone tried to use the Newton as a unit of mass instead of the kilogram.
Actually, the weight of 1 lbm is 1 lbf. So the original units were really ##\frac{lb_f}{lb_f-h}=1/h##
 
  • #29
yecko
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the weight of 1 lbm is 1 lbf
oh i see... i thought 1lbf is only equal to 1 slug and equal to 1 lgm times g (gravity)...
sorry for my confusion about imperial units...
 
  • #30
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That’s one of the problems of imperial units, they often lead to confusion.
 

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