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I am try to size a plate heat exchanger for a Batch heater. The problem is that I stack to find the final temperatures.
Note: I found a software that calculated the temperature but I don’t understand how.
Heating Medium DATA:
Hot Water @ T1 = 97 DegC
Specific Heat Of Hot Water Cp = 4,220 J/KgK @ 97 DegC
Density of Hot Water ρ = 960 Kg/m3 @ 97 DegC
Hot Water flow rate mh = 4 kg/s (BATCH HEATER)
BATCH DATA:
Batch Content = 1,000 Kg
Heating Milk From tinitial = 4 DegC àt final = 94 DegC In 30 min
Specific Heat Of Milk Cpc = 3,950 J/KgK @ 49 DegC
Density of Milk ρ = 1,013 Kg/m3 @ 49 DegC
Milk Circulated via a pump through the PHEX and back to the tank with a flow rate mc = 2.78 kg/s
Solution:
Heat Duty Qduty = MC*ΔT/ Heating time
Qduty = (1,000*3,950*(94 - 4)/(30*60))/1,000 = 197.5 Kw
Qduty = mh*Cph*(T1-T2) = >T2 = T1- Q/mh*Cph
T2 = 97- ((197.5*1,000)/(4*4,220)) = 85.29 DegC
T2 = 85.29 DegC
Qduty = m *Cpc*(t2 - t1)
(t2 - t1) = Q/m*Cpc = (197.5*1000)/(2.78*3950)
(t2 - t1) = ΔT = 17.98DegC
I try many solutions but I stack again and again and as i realized (I’AM NOT SURE) that the program include efficiency and from the Equation n = Qduty/Qmax calculated the Qmax.
Known The Qmax and from the usual equation calculated t1 = T1-(Qmax/mc*Cpc) = 70.79 DegC and with combination of ΔT = 17.98 DegC = t2 - t1 found the t2 = 17.98 DegC + 70.79 = 88.77 DegC but again I don’t understand how calculated the efficiency in order to found the Qmax. Or how to find the Qmax to find the efficiency.
I try to calculated the Qmax with Qmax = mc*Cpc*(T1 - t1) but is too high.
Software Results:
n, efficiency = 68%
Product inlet Temp = 70.79 DegC
Product Outlet Temp = 88.77 DegC
Please Advice how can I calculated the final temperatures .
Note: Area And Overall Heat Transfer Of PHEX are Unknown.
Edited by Art Montemayor, 16 September 2012 - 10:51 AM.
Fonts too small; unreadable. No spaces between numbers & units, sentences, words, etc.
