- #1
timmayy
- 7
- 0
Hi, I've recently been given a series of questions on heat transfer to do and have done most of them with general ease, but this one question I've been stuck on for ages and i can't seem to figure out:
"A double pipe heat exchanger is made up from a length of 25mm i.d. steel pipe of 2.5mm thickness, and a length of 75mm i.d. pipe. The fluid in both pipes is water. Estimate the heat transfer coefficients at the outside and inside of the inner pipe for the following conditions.
Outer pipe flow-rate 5kg/s @ 23˚ C
Inner pipe flow-rate 0.5kg/s @ 51˚C
Use the correlation for turbulent flow:
Nu = 0.023 Re0.8 Pr0.33 (μ/μw)0.14
The physical properties of water are:
Cp of water @ 23˚C = 4.187kJ/kgK
Cp of water @ 51˚C = 4.184kJ/kgK
k of water @ 23˚C = 0.670W/mK
k of water @ 51˚C = 0.635W/mK"
Included in the question is also a density and viscosity to relevant temperatures table
Ive been working through it and have calculated all cross sectional areas, but then i can't seem to put it into any equations (nusselts etc), as i am unable to find the in temperature (and so relevant density/viscosity) - i tried finding log means of the temperatures, densities and viscosities but nothing seems to work...
any help would be great thanks :)
Tm
"A double pipe heat exchanger is made up from a length of 25mm i.d. steel pipe of 2.5mm thickness, and a length of 75mm i.d. pipe. The fluid in both pipes is water. Estimate the heat transfer coefficients at the outside and inside of the inner pipe for the following conditions.
Outer pipe flow-rate 5kg/s @ 23˚ C
Inner pipe flow-rate 0.5kg/s @ 51˚C
Use the correlation for turbulent flow:
Nu = 0.023 Re0.8 Pr0.33 (μ/μw)0.14
The physical properties of water are:
Cp of water @ 23˚C = 4.187kJ/kgK
Cp of water @ 51˚C = 4.184kJ/kgK
k of water @ 23˚C = 0.670W/mK
k of water @ 51˚C = 0.635W/mK"
Included in the question is also a density and viscosity to relevant temperatures table
Ive been working through it and have calculated all cross sectional areas, but then i can't seem to put it into any equations (nusselts etc), as i am unable to find the in temperature (and so relevant density/viscosity) - i tried finding log means of the temperatures, densities and viscosities but nothing seems to work...
any help would be great thanks :)
Tm