Research Papers: Heat Exchangers

Multiscale Computational Fluid Dynamics Methodology for Predicting Thermal Performance of Compact Heat Exchangers

[+] Author and Article Information
A. Ciuffini

Department of Mechanical and
Aerospace Engineering,
Politecnico di Torino,
Turin 10129, Italy

A. Scattina

Department of Mechanical and
Aerospace Engineering,
Politecnico di Torino,
Turin 10129, Italy
e-mail: alessandro.scattina@polito.it

F. Carena, M. Roberti, G. Toscano Rivalta

DENSO Thermal Systems/
Technical European Centre,
Poirino 10046, Italy

E. Chiavazzo, M. Fasano, P. Asinari

Department of Energy,
Politecnico di Torino,
Turin 10129, Italy

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received December 20, 2014; final manuscript received January 28, 2016; published online April 5, 2016. Assoc. Editor: Gongnan Xie.

J. Heat Transfer 138(7), 071801 (Apr 05, 2016) (11 pages) Paper No: HT-14-1824; doi: 10.1115/1.4032980 History: Received December 20, 2014; Revised January 28, 2016

Computational fluid dynamics (CFD) is a powerful tool for analyzing the performance of heat exchangers. However, such an approach may be often limited by unaffordable computational time. In this paper, a multiscale CFD capable of accurately and efficiently prediction of the heat transfer of compact heat exchangers is presented. This methodology is based on a small-scale CFD analysis of a single tube and a small element of the compact heat exchanger, and it is able to predict the thermal performance of an entire heat exchanger in a wide range of inlet conditions, with a reduced computational time. The proposed up-scaling procedure makes use of specific approximations and correlations derived from the CFD model and literature, in order to consider the typical phenomena occurring in compact heat exchangers under laminar flow conditions. Results demonstrate an excellent accuracy when compared to experimental data (discrepancies <4.3%). This novel up-scaling method may have a strong impact on modeling and design strategy of compact heat exchangers in the industrial field.

Copyright © 2016 by ASME
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Fig. 1

Small portion (12.8 mm × 2.5 mm) of the heat exchanger considered as building block in the CFD simulations

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Fig. 2

Left-hand side: domain subdivision. Right-hand side: periodic boundary conditions.

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Fig. 3

Flow chart of the main steps to introduce a variable heat transfer coefficient

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Fig. 4

Flow chart of the methodology for the water–glycol side

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Fig. 5

Flow chart of the methodology for the water–glycol and air sides. The procedure is the same represented in Fig. 4, but the upscaling procedure is refined by means of a corrected correlation for the air side. The user can also decide the inlet characteristics of air.

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Fig. 6

Configuration of the single tube simulation, with the mesh details in a section of the considered tube geometries

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Fig. 7

Detail of the mesh used for simulating the building block of the Welded tubes heat exchanger

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Fig. 8

Two-dimensional temperature profiles in y-z plane for the considered building blocks of heat exchangers with different types of tube

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Fig. 9

Temperature profile and air streamlines on the x-y plane, at z = 4 mm: (a) welded, (b) 7 port, and (c) 11 port

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Fig. 10

Three-dimensional temperature profiles for the considered types of tube

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Fig. 11

Nu–Gr curve for the tube with welded profile

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Fig. 12

U and UA trends function of the distance x from the inlet section for the considered types of tube

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Fig. 13

Local heat transfer Q˙ function of the distance x from the inlet section for the considered types of tube

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Fig. 14

Heat transfer for variable water–glycol volume flow rates. The air velocity is constant and equal to 3 m/s.

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Fig. 15

Heat transfer at different air velocities for a water–glycol flow rate equal to 1000 l/h

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Fig. 16

Thermal performances for a welded heat exchanger with a combined variation of the flow rates at both sides

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Fig. 17

Fluid dynamics test bench system, where the light brown air tunnel guarantees the perpendicularity of the flow

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Fig. 18

Comparison between the ε-NTU curves derived by Eq.(18) and the K&L curves (Eq. (9)) for the heat exchanger with welded tubes




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