Abstract
This study extends the investigations of Kim [11] to a wet condition, who tested heat exchangers having fins of the smooth wave or herringbone wave geometry on 12.7 mm tubes under dry condition. Results showed that the j and f factors were independent of the fin pitch. Furthermore, the smooth wave fin geometry yielded 22 % to 28 % higher j factors, and 24 % to 28 % higher f factors compared with the herringbone wave geometry. The ratios of the j/f1/3 between the smooth wave and the herringbone wave configuration were 1.07, 1.14 and 1.19 for 1 row, 2 row and 4 row, respectively. These ratios were approximately the same as those obtained under dry condition [11]. Both for the smooth and the herringbone wave fin samples, the wet surface yielded higher j and f factors than the dry surface. For example, at a fin pitch of 3.0 mm of the smooth wave fin geometry, the j factors under wet condition were 2 % to 40 % higher than those under dry condition. Similarly, the f factors under wet condition were 56 % to 64 % higher than those under dry condition.
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Abbreviations
- A :
-
Heat transfer area, m2
- b r12 :
-
Slope of the air saturation curve between the inlet and exit air temperature, J/kgK
- b p :
-
Slope of the air saturation curve between the outside and inside tube wall temperature, J/kgK
- b r :
-
Slope of the air saturation curve between the mean tube and water temperature, J/kgK
- b wm :
-
Slope of the air saturation curve at the mean water film temperature of the airside surface, J/kgK
- C p :
-
Specific heat, J/kgK
- C r :
-
Heat capacity ratio (dimensionless)
- D o :
-
Tube outer diameter, m
- f :
-
Airside friction factor (dimensionless)
- h :
-
Heat transfer coefficient, W/m2K
- i :
-
Enthalpy, J/kg
- j :
-
Colburn j factor (dimensionless)
- k :
-
Thermal conductivity W/mK
- K c :
-
Contraction coefficient (dimensionless)
- K e :
-
Expansion coefficient (dimensionless)
- m :
-
Mass flow rate, kg/s
- N :
-
Number of tube row (dimensionless)
- NTU :
-
Number of transfer units (dimensionless)
- P d :
-
Waffle depth, m
- Pi :
-
Longitudinal tube pitch, m
- P t :
-
Transverse tube pitch, m
- Pr:
-
Prandtl number (dimensionless)
- Q :
-
Heat transfer rate, W
- Re Do :
-
Tube-side Reynolds number based on Do (dimensionless)
- t :
-
Tube wall thickness, film thickness, m
- U :
-
Overall heat transfer coefficient, W/m2·K
- V :
-
Velocity in the tube, m/s
- V max :
-
Velocity based on the minimum flow area of the frontal surface, m/s
- X f :
-
Half the waffle spacing, m
- ε :
-
Thermal effectiveness (dimensionless)
- ΔP :
-
Pressure loss, Pa
- η o :
-
Surface efficiency (dimensionless)
- ρ:
-
Density, kg/m3
- V :
-
Kinematic viscosity, m2/s
- σ :
-
Contraction ratio of the cross-sectional area (dimensionless)
- a :
-
Air
- c :
-
Heat exchanger core
- i :
-
Tube-side
- in :
-
Inlet
- m :
-
Mean
- max :
-
Maximum
- min :
-
Minimum
- o :
-
Outside
- out :
-
Outlet
- p :
-
Tube
- r :
-
Water
- w :
-
Water, wet surface
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Nae-Hyun Kim is a Professor in School of Mechanical System Engineering, University of Incheon. He received Ph.D. from Penn State University in 1989. His interest includes heat transfer enhancement, boiling and condensation in minichannels, flow distribution in flow heat exchangers, etc.
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Kim, NH. Thermo-hydraulic characteristics of heat exchangers having the smooth or the herringbone wave fins on 12.7 mm tubes under dehumidifying condition. J Mech Sci Technol 35, 5225–5232 (2021). https://doi.org/10.1007/s12206-021-1039-5
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DOI: https://doi.org/10.1007/s12206-021-1039-5