Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

First Advisor's Name

Cheng-Xian Lin

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Yiding Cao

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

George Dulikravich

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Shekhar Bhansali

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

Chad Bowers

Fifth Advisor's Committee Title

Committee Member

Keywords

Low Reynolds Number Flow, Microchannel Heat Exchangers, Compact Heat Exchangers, Thermal Hydraulic Performance of Heat Exchangers

Date of Defense

11-10-2016

Abstract

This study focuses on the investigation of flow behavior at low Reynolds numbers by the experimental and numerical performance testing of micro-channel heat exchangers. An experimental study of the heat transfers and pressure drop of compact heat exchangers with louvered fins and flat tubes was conducted within a low air-side Reynolds number range of 20 < ReLp < 225. Using an existing low-speed wind tunnel, 26 sample heat exchangers of corrugated louver fin type, were tested. New correlations for Colburn j and Fanning friction f factor have been developed in terms of non-dimensional parameters. Within the investigated parameter ranges, it seems that both the j and f factors are better represented by two correlations in two flow regimes (one for ReLp = 20 – 80 and one for ReLp = 80 – 200) than a single regime correlation in the power-law format. The results support the conclusion that airflow and heat transfer at very low Reynolds numbers behaves differently from that at higher Reynolds numbers. The effect of the geometrical parameters on the heat exchanger performance was investigated.

The numerical investigation was conducted for further understanding of the flow behavior at the range of experimentally tested Reynolds number. Ten different heat exchanger geometries with varied geometrical parameters obtained for the experimental studies were considered for the numerical investigation. The variations in the louver angle were the basis of the selection. The heat transfer and pressure drop performance was numerically investigated and the effect of the geometrical parameters was evaluated. Numerical results were compared against the experimental results. From the comparison, it is found that the current numerical viscous laminar models do not reflect experimentally observed transitional two regime flow behavior from fin directed to the louver directed at very low Reynolds number ranging from 20 to 200.

The flow distribution through the fin and the louver region was quantified in terms of flow efficiency. The flow regime change was observed at very low Reynolds number similar to the experimental observations. However, the effect of two regime flow change does not reflect on the thermal hydraulic performance of numerical models. New correlations for the flow efficiency � have developed in terms of non-dimensional parameters.

Identifier

FIDC001195

 

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