1 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Tube diameter influence on heat exchanger performance and design. Single phase flow

2 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Influence of diameter laminar case: Exchange a heat exchanger for another one with different diameter. Assume: –Same pressure drop,  p –Same temperature difference,  t –Same capacity, Q –Same mass flow, m Allow shorter tubes and more parallel tubes

3 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration I.e. ”black box” with given performance: –Same  p –Same  t –Same Q –Same m

4 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Possible options: –Same  p –Same  t –Same Q –Same m or

5 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Heat transfer : In laminar flow (fully developed): Heat transfer: To keep Q and  t constant: Total Area

6 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Pressure drop: Pressure drop (laminar flow, circular tube): To keep pressure drop and volume flow constant:

7 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Laminar flow: To keep Q and  t constant: To keep pressure drop constant:

8 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Conclusions, laminar case Half diameter gives: –Half necessary area –Double heat transfer coefficient –Quadruple no of channels –Channel length 1/4

9 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Similar analysis for the turbulent case gives: Conclusions, turbulent case

10 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Half diameter gives: –Area reduced by  12% –Heat transfer coeff increased by  13% –Four times as many tubes –Tube length reduced by 57% Conclusions, turbulent case

11 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Turbulent and laminar : Assume reference case: Fluid: Water Diameter: 16 mm Length: 10 m No of tubes:1

12 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Turbulent and laminar :

13 Dept. of Energy Technology, Div. of Applied Thermodynamics and Refrigeration Turbulent and laminar : Original hx: Diameter: 16 mm Length: 10 m No of tubes:1 New hx: Diameter: 0.4 mm Length: 67 mm No of tubes:2700