RylEnfield
Mechanical
- May 9, 2003
- 11
Hello all
Sorry about this always seem to be asking , a bit one sided on my part .I have trawled through the achives , but no help hence the post
I have to agree with one post, for a re invented wheel . there is precious little info out there ! anyway
I need to size a small cross flow heat exchanger ( a small oil cooler on a bike) , Now the smaller the better ! But I am not confident of my proceedure
How I am attacking this problem is by
1 The overall heat transfered from the oil to the air Q= mcp( Tin- Tout) I get 4 watts /sec
2 Estimate the area for each part of the heat path , convection, conduction, convection
As in 1/h1*A1= 1/UT where h is the heat co efficient
3 Work out the total resistance path
Rt =1/h1a1 + ln(r2/r1)/2*pi*L *K +1/h2A2= 1/UA ) where K is the marerial conductivity 384 W/mk
4 Finally Qf?@= UAF(LMTD) and if this Qf is within 10 % of the Overall Q in part 1 I ll be happy
LMTD is log mean temp difference
My uncertainties are, that I have little experience with these numbers , so when I tried to estimate a figure for say h1 I am not sure if this is meaningfull, I mean what is a useful figure for U ) after trawling the internet I found a figure of 500 for a similar application , but is this reasonable ??
I then found a passage which recommended for forced convection ( I assume that what I have ) a Nusselt number of 3.65 and a formula for H of h = k / d where K = fluid conductivity ( oil 0.15) and d in my case is 4mm this gave a h of 50
Reasonable to assume??
The variable data I have is oil used 20/50 at 100 deg c , with a flow rate of 0.077 gallons per min at a velocity of 1.1 ft /sec ( 0.350 m/s) to be cooled to 68 is deg c with an air flow of 11m/sec to 22m/sec at ambient temp
If Someone could set my mind at ease that I am heading in the right direction I would be most pleased especially with the look of some of those numbers, what sort of order of magnitude should I be looking at
Kind Regards
and wishing everyone a safe and happy Xmas
Stephen
Sorry about this always seem to be asking , a bit one sided on my part .I have trawled through the achives , but no help hence the post
I have to agree with one post, for a re invented wheel . there is precious little info out there ! anyway
I need to size a small cross flow heat exchanger ( a small oil cooler on a bike) , Now the smaller the better ! But I am not confident of my proceedure
How I am attacking this problem is by
1 The overall heat transfered from the oil to the air Q= mcp( Tin- Tout) I get 4 watts /sec
2 Estimate the area for each part of the heat path , convection, conduction, convection
As in 1/h1*A1= 1/UT where h is the heat co efficient
3 Work out the total resistance path
Rt =1/h1a1 + ln(r2/r1)/2*pi*L *K +1/h2A2= 1/UA ) where K is the marerial conductivity 384 W/mk
4 Finally Qf?@= UAF(LMTD) and if this Qf is within 10 % of the Overall Q in part 1 I ll be happy
LMTD is log mean temp difference
My uncertainties are, that I have little experience with these numbers , so when I tried to estimate a figure for say h1 I am not sure if this is meaningfull, I mean what is a useful figure for U ) after trawling the internet I found a figure of 500 for a similar application , but is this reasonable ??
I then found a passage which recommended for forced convection ( I assume that what I have ) a Nusselt number of 3.65 and a formula for H of h = k / d where K = fluid conductivity ( oil 0.15) and d in my case is 4mm this gave a h of 50
Reasonable to assume??
The variable data I have is oil used 20/50 at 100 deg c , with a flow rate of 0.077 gallons per min at a velocity of 1.1 ft /sec ( 0.350 m/s) to be cooled to 68 is deg c with an air flow of 11m/sec to 22m/sec at ambient temp
If Someone could set my mind at ease that I am heading in the right direction I would be most pleased especially with the look of some of those numbers, what sort of order of magnitude should I be looking at
Kind Regards
and wishing everyone a safe and happy Xmas
Stephen
