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Effect of inclination on thermal performance of a louver-finned aluminum heat exchanger having a drainage channel

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Abstract

Heat exchangers are frequently installed at an inclined angle to reduce the height of the air-conditioning unit. The inclination may deteriorate the thermal performance of the heat exchanger, and the effect will be more severe for an aluminum heat exchanger compared with a conventional fin-and-tube heat exchanger. However, the literature shows very limited investigations on this subject. In this study, a series of tests were conducted for a newly-developed aluminum heat exchanger, which has an additional drainage channel at downstream of the fin. Results showed that the pressure drop increased as inclination angle increased. However, the heat transfer coefficient showed a minimum behavior at approximately 45° inclination angle. This was true both for dry and wet conditions. The effect of inclination angle on the ratio between wet and dry j and f factor was not significant, which suggested that the inclination did not alter the condensate pattern on the louver fin (louver-bridging, fin-bridging, etc.) significantly. Comparison of the thermal efficiency indices (j/f1/3) of the present sample with those of the conventional sample (having no drainage channel) showed that the thermal performance improvement is significant under wet condition, which confirms the excellent condensate drainage of the present sample.

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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/kg · K

b p :

Slope of the air saturation curve between the outside and inside tube wall temperature, J/kg · K

b r :

Slope of the air saturation curve between the mean tube and water temperature, J/kg · K

b wm :

Slope of the air saturation curve at the mean water film temperature of the airside surface, J/kg · K

C p :

Specific heat, J/kg · K

C r :

Heat capacity ratio (dimensionless)

D h :

Hydraulic diameter, m

F D :

Depth of fin array in flow direction, m

F p :

Fin pitch, m

f :

Airside friction factor (dimensionless)

f i :

Tube-side friction factor (dimensionless)

H :

Fin height, m

h :

Heat transfer coefficient, W/m2· K

i :

Enthalpy, J/kg

j :

Colburn j factor (dimensionless)

k :

Thermal conductivity W/m · K

K c :

Contraction coefficient (dimensionless)

K e :

Expansion coefficient (dimensionless)

l :

Fin length, m

L p :

Louver pitch, m

ṁ :

Mass flow rate, kg/s

NTU :

Number of transfer units (dimensionless)

Pr:

Prandtl number (dimensionless)

Q :

Heat transfer rate, W

ReLp :

Reynolds number based on Lp (dimensionless)

ReDh :

Tube-side Reynolds number based on Dh (dimensionless)

t :

Tube wall thickness, film thickness, m

T :

Temperature, K

t f :

Fin 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

W :

Absolute humidity

α :

Louver angle, deg

β :

Inclination angle, deg

ε :

Thermal effectiveness (dimensionless)

ΔP :

Pressure loss, Pa

η :

Fin efficiency (dimensionless)

η ∘ :

Surface efficiency (dimensionless)

ρ :

Density, kg/m3

μ :

Dynamic viscosity, kg/m · s

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

f:

Fin

m:

Mean

max:

Maximum

min:

Minimum

o:

Outside

out:

Outlet

t:

Tube

w:

Water, wet surface

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Author information

Authors and Affiliations

  1. Department of Mechanical Engineering, Incheon National University, Incheon, Korea

    Nae-Hyun Kim

Authors
  1. Nae-Hyun Kim
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Correspondence to Nae-Hyun Kim.

Additional information

Nae-Hyun Kim is a Professor in School of Mechanical Engineering, Incheon National University. He received Ph.D. from Penn State University in 1989. His interest includes heat transfer enhancement, heat and mass transfer modeling of an enthalpy exchanger, boiling and condensation in mini-channels, flow distribution in parallel flow heat exchangers, etc.

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Kim, NH. Effect of inclination on thermal performance of a louver-finned aluminum heat exchanger having a drainage channel. J Mech Sci Technol 35, 381–389 (2021). https://doi.org/10.1007/s12206-020-1238-5

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  • DOI: https://doi.org/10.1007/s12206-020-1238-5

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