Heat Exchanger Thermal Calculation

This is a heat-exchanger thermal rating calculator. i.e. it will enable you to predict heat transfer coefficient or U of a heat exchanger based on actual heat exchanger geometry consequently sizing it.

Use illustration.
Design a shell and tube heat exchanger for following use.

1. Shell side 5000 kg/hr n-Hexane to be cooled from 80 C to 50 C with water at tube side. CW supply 28 C and return at 32 C.

Procedure

1. Input shell mass flowarte as 5000kg/hr , Cp of 2.45 kJ/kg.K, inlet temp 80 C and outlet temp of 50 C. In tube side, input Cp of 4.186, inlet temp of 28 C and outlet temp of 32 C.
   
   
2. Click on shell details and enter density of 650 kg/m3,Viscosity 0.21 cp,Wall viscosity 0.21 cp, k 0.1 w/mK,Shell ID 500 mm (estimated) ,Baffle spacing 100 mm and fouling factor of 0.0002 m2K/W. Click Done. 
   
   
3. Click on tube details and enter ID 8 mm, OD 12 mm, L 3000 mm, Passes 1, pitch of 6 mm, density of 1000 kg/m3 , viscosity of 0.9 cp, wall viscosity of 0.9 cp, k of 0.179 W/mK, n of 0.4, fouling factor of 0.0002 m2K/W.
   
   
4. Enter Estimated U of 400 W/m2K . Click on calculate.
   
   
5. Evaluate the calculated figures. First being shell dia as you estimated the dia in your inputs. Min shell dia recommended in 144 mm while we selected 500 mm. Change the shell dia to 150mm and calculate again.
   
   
6. Evaluate calculated figures. Tube side pressure drop is 27 Pa. Typical allowable pressure drops are 15 Pa. To get lower pressure drops number of tubes need to be increased. Increase the tube number in tube side inputs to 100 and calculate again. Min. shell dia recommended increases to 177. Input shell dia 200 and calculate again.
   
   
7. Calculated U is 491 with 44% excess area. We could have reduced excess area but that would increase the pressure drop tube side. Thus this is the final design. We need excess area to have reasonable pressure drop and velocity.
   
   The final design is.
   
   A 11.31 m2 heat exchanger is required with 100 tubes of 8mm ID,12 mm OD tubes of 3m length with 1 pass arrangement. This fits into a 200 mm shell.with 40% cut baffles at 100 mm baffle spacing. This would have a overall heat transfer coefficient of 491 W/m2K. (Please note there could be many other alternate designs.