Question

a shell and tube heat exchanger is required to heat brine for a food processing plant. Hot waste water from another part of the plant is available at 90°C and a flow rate of 0.7kg/s to perform the heating duty. An existing heat exchanger is available that has twoshell passesand 4 tube passes. Each tube pass has a total length of 20m and the tubes are found to be thin walled copper with a nominal diameter of 25mm.

The brine will be delivered from cool storage to the exchanger tubes at a rate of 1.5 kg/s and a temperature of 5°C. It must be heated to at least 30°C in the heat exchanger.

The specific heat capacity of the brine is 4.45 kJ/kg°C and the specific heat capacity of the hot waste wateris4.1kJ/kg°C

you estimate the tube-side(brine)convection heat transfer coefficient to be 1500W/m2°C and the shell-side convection heattransfer coefficient to be 2500W/m2°C. You also estimate the inside and outside fouling factors to be 0.0004m2°C/W and 0.0002m2°C/W respectively.

Show that the existing heat exchanger is able to heat the brine to above30°C in the clean condition, but in the fouled condition the brineoutlet temperature is lessthan 30°C.Clearly state any charts you used in your answer.(25marks)

numerical answers:

Question 5: Clean: Uclean from chart (d) e 0.77, Q =187.84 kW so Thrinc, 937.5 W/m2°C, Cmin =2.87 kW/°C, Cmax 33.1°C (> 30°C). 6.675 kW/°C, NTU =2.05, out

Answer 1

Thi 9o KJ Tuo sheel p ass 4 1abe pass 20 L 20 m 02 mm Tu S СЬ Mр 2.87 Kuw .x4. C Cmc) man C Cnio Cman 2.87 SE9 -9 UA Cmin NTU - 937-5 'bs00 Yiseo Чк+ Yno clean 2 2-29 1-256 Az TdLe To4 Jerjts 937-5 x 256 S NTV 2.oS 2 87x1o3 woo1 Foun Tube ?ass witeziven C-Cmin Cme Fe om chant Vs E NTV erlectiveness E .\1 Qman

2-31X Cq0-5) Amanz Cmin ATmau baine 8.842 /Sx 4us Tco - 5) Tco 33- Cen ce ho hi [ς0 UA 600 Cmin ET.9h 009 2-8x1 NTVE3l Fnon cha 2-31 X 8S 165.89 K S XY4SyCTS Tco 29.85 (Hence prt