Studying - cost of a heat exchanger?
Studying - cost of a heat exchanger?
(OP)
Hi all
I'm new so I hope you'll be able to help out and don't find this question beneath contempt!
I'm a chemist retraining in chemical process engineering and I'm faced with a very abstract maths problem. Here goes:
"The cost of a heat exchanger is estimated to be $10,000. Estimate the cost of a heat exchanger that is twice the size"
I don't know what is meant by size - area, duty, geometry? I think this is the point, the exercise is about using rules of thumb and empirical models to get start-point estimates to complex problems instead of working through a lengthy modelling exercise.
Being a chemist I suspect I'm missing something obvious here so.... Where do I start?!
I hope someone out there can shed some light!
Thanks
I'm new so I hope you'll be able to help out and don't find this question beneath contempt!
I'm a chemist retraining in chemical process engineering and I'm faced with a very abstract maths problem. Here goes:
"The cost of a heat exchanger is estimated to be $10,000. Estimate the cost of a heat exchanger that is twice the size"
I don't know what is meant by size - area, duty, geometry? I think this is the point, the exercise is about using rules of thumb and empirical models to get start-point estimates to complex problems instead of working through a lengthy modelling exercise.
Being a chemist I suspect I'm missing something obvious here so.... Where do I start?!
I hope someone out there can shed some light!
Thanks





RE: Studying - cost of a heat exchanger?
To ratio up or down costs, the general formula as presented in my books at school and others says this:
Cost of scale = cost of base * (size scale/size of base) ^.8 or 1.74 times as much for the unit twice as large.
RE: Studying - cost of a heat exchanger?
When I used to trend costs for equipment back in the mid-nineties, in the case of S&T heat exchangers, a good "estimate" for cost was $25.00 CDN per square foot of bare tube surface area. For aerial coolers it was closer to $40.00-$45.00 CDN per square foot of bare tube surface area.
Regards,
SNORGY.
RE: Studying - cost of a heat exchanger?
rmw
RE: Studying - cost of a heat exchanger?
If the duty doubles, the area doubles (?)
If the length of a shell/tube exchanger doubles, the area doubles
So assuming cost/area is a sensible way to estimate, the cost will just be x2 i.e. $20k
Right?!
RE: Studying - cost of a heat exchanger?
One would almost think that, but in my opinion, it wouldn't quite work that way. Consider, for example, a 24" diameter NEN S&T exchanger doubling in length (and hence area) from 15 feet to 30 feet between tubesheets. Much of the materials and fabrication costs would go into the tubesheet rolling and the tubesheets themselves, and these costs are higher than a few extra baffles and longer tubes. So, you would lose the economies of scale in the smaller unit; conversely, you would gain some economies of scale in the larger unit. However, it wouldn't be 1:1.
Regards,
SNORGY.
RE: Studying - cost of a heat exchanger?
As an ancient mechanical engineer that has wandered into process equipment design, you should know that I am getting out....too many slick salesmen, MBAs and BS artists selling services and hiring temporary staffs.
Your question sound too much like a homework problem.....
"Twice the size" means twice the surface.....to me.
Suggest that you consult the text "Plant Design and Economics for Chemical Engineers" -- Peters & Timmerhaus Chapter 14
-MJC
RE: Studying - cost of a heat exchanger?
Regards,
SNORGY.
RE: Studying - cost of a heat exchanger?
@MJC - it is a homework problem!
RE: Studying - cost of a heat exchanger?
it's the same as dcasto's expression
The way this should be solved is:
if you are looking to find the cost for heat exchanger B while you already have the cost of heat exchanger A = $ 10 000:
cost h.e. B = cost h.e. A (size of B / size of A)^exponent
the exponent as a rule of thumb is either 0.6 or 0.7 as suggested above by SNORGY
particularly for heat exchanger from Peters / Timmerhaus:
heat exchanger, shell-and-tube, floating head, c.s 10-40 m2 (100-400 ft2) =0.6
heat exchanger, shell-and-tube, fixed sheet, cs 10-40 m2 (100-400 ft2) =0.44
so in your case:
cost = 10 000 (2)^0.6
cost = 15 157
this is an example of the economy of scale