I'm currently working on a project of heat exchanger with helical baffles with both water entering in the tube and the annulus side. Dimensions of the geometry is used attached here. I am just confused because only a little temperature change for both tube and annulus side are present. Is it just because the dimensions are too small, or did i miss to consider some of the parameters? I

DPHE size:

Material: Stainless Steel

Inner Tube Internal Dia - 10 mm

Inner Tube Thickness    - 1 mm

Outer Tube External     - 16mm

Outer Tube Thickness    - 1mm

Annulus side baffles spacing - 100-25mm

Heat exchanger length         - 100mm

Pitch (40deg) - 10.908295205305