Predicting the Air-Side Thermal -Hydraulic Performance Characteristics of Flat-Tube Louver-Fin Heat Exchangers Under Dry and Wet Conditions

A simple area-partitioning method for analyzing the wind-tunnel data is developed for flat-tube heat exchangers under partially wet conditions, and new air-side performance correlations are presented for both dry- and wet-surface conditions. Correlations between the Colbum j or f factors and the Reynolds numbers are developed in the conventional way and compared to multivariate non-parametric regressions. The conventional correlations significantly extend prior work by expanding the parameter space and establishing a physical basis for the form of the fits. However, it is found that multivariate non-parametric regressions can dramatically reduce the RMS errors if a large, well-structured dataset is used. Furthermore, this method provides statistical indicators that can be used to prevent over-fitting when the dataset is limited. Important condensate retention and drainage mechanisms are identified and modeled using analytical and numerical methods. When condensate obstructs the louver gap, boundary layer re-starting does not occur, and the most important heat transfer enhancement mechanism in these flows lost. It is shown that surface tension can maintain inter-louver condensate bridges against gravity and flow-generated shear and pressure forces, even at air-side Reynolds numbers much higher than are typical to the applications of interest. Thus, maintaining wet-surface heat transfer performance depends on avoiding the initial formation of inter-louver bridges.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Mechanical Engineering

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Park, Young-Gil

Contributors dc:contributor

• Jacobi, Anthony M.

• Engineering, Mechanical

Language dc:language

eng

Identifier

(MiAaPQ)AAI3270001

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/83874