Heat transfer and hydraulic performance models for a family of aluminum plate heat exchanger with transversal offset strip fins

ABSTRACT

This paper presents the experimental analysis of aluminum BPHX, with dimensions of 215 × 80 × 61 mm, having transversal offset strip fins with two pitches of 5 and 6.8 mm using liquid to liquid to measure the heat transfer and pressure drop performance in the Reynolds range of transitional to turbulent regime [10³, 10⁴]. Firstly, the heat exchangers were tested using water on both sides. A heat transfer and friction coefficients empirical correlations were determined, and the resulted functions were compared with two other models presented in the literature. Secondly, the heat exchangers were measured using water and engine oil as hot fluid.

KEYWORDS:

• heat exchangers
• offset strip fins
• convection coefficient
• friction coefficient

Acknowledgments

This study was carried out with the help of Romanian Company of RAAL which supplied the BPHEs and testing facilities for this study. We also want to thank the University Politehnica of Timișoara for its documentation and know how support received.

Nomenclature

A – heat exchange surface (m²)

B – friction criterial equation coefficient

C – Nusselt criterial equation coefficient

Cmin, Cmax – heat capacity flow = ṁ cp (W/K)

cp – heat capacity of the stream (J/kgK)

Dh – hydraulic diameter (mm)

f – friction coefficient (Fanning)

Fp – pitch ratio

g – strip fin thickness (mm)

h – strip fin height (mm)

j – Colburn number

k – global heat transfer coefficient (W/m²K)

L – strip fin width (mm)

ṁ – mass flow (kg/s)

Nu – Nusselt number

NTU – number of thermal units

p – strip fin pitch (mm)

Pr – Prandtl number

Q̇ – heat transferred (W)

Q̇̅ – mean value

Re – Reynolds number

s – offset of the next strip (mm)

x – general variable in measurements

x̅ – mean value

α – convection coefficient (W/m²K)

ϵ – heat exchanger efficiency

λ – aluminum conductivity (W/mK)

μ – heat capacity flow ratio

σ – standard deviation of the population sample

σ’ – uncertainties in the measurement defined

Subscripts

c – cold stream

h – hot stream

i – index

min – minimum between two or more values

max – maximum between two or more values