Alwan Hibatullah

i use the average heat flux value along the wall of the helical coil

then for the Nusselt value, as validation I use the Manlapaz and Churchill correlation equations for helical coils in laminar flow. for example, for Re 500 the Nusselt number should be around 12, and for simple models the Nusselt number should be correct with an error below 10%. but for the full model, the value of the Nusselt number that I get ranges from 2, so it has a high error.

for the record I did the analysis using excel, so when changing the model, I only changed the temperature values on the walls and outlets, so there shouldn't be any errors in the analysis calculations