Effect of some geometric parameters on performance of PF2 heat exchangers in periodic frosting
Abstract
The thermal performance under conditions of initial frost growth and subsequent refrosting after a defrost is experimentally studied for the parallel flow parallel fin (PF2) heat exchanger, a new style of heat exchanger that uses louvered bent fins on flat tubes to enhance water drainage when the flat tubes are horizontal (typically outdoor heat exchanger in heat pump operation). This paper focuses on quantification of the effects of geometry (i.e. fin pitch 12–22fpi and louver pitch 1.4–2.8mm) on defrost and refrost times. Eight heat exchangers differing in louver pitch and fin spacing are studied. A series of tests are conducted in search for the best geometry. The effects of geometry on heat transfer (thermal performance) and pressure drop for air face velocities of 0.9, 2, and 3m/s are determined and used for comparison. Characteristics of initial heat transfer coefficient and pressure drop during the first frosting cycle are reported in terms of Colburn j0 factor and Fanning friction f0 factor, as a function of ReLp and geometry. The newly developed air-side correlations for PF2 heat exchangers (Colburn j0 factor and Fanning friction f0 factor) predict the test data within rms error of ±10%, and with mean deviation of 2.95% and 4.98%, respectively. The correlations are base on a very low Reynolds numbers in the range of 100–620, and 8 PF2 heat exchangers using 48 experimental data.
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Zhang and Hrnjak [37] proposed a friction factor correlation for a parallel-flow, parallel-fin heat exchanger under frosting conditions.
“Zhang and Hrnjak [37] proposed a friction factor correlation for a parallel-flow, parallel-fin heat exchanger under frosting conditions.”
The MCHX had better thermal performance when the louver pitch was 2.1 mm.
“Results showed that the MCHX had better thermal performance when the louver pitch was 2.1 mm.”
The Zhang and Hrnjak correlation predicts experimental data within a root mean square error of ±10%, with a mean and mean deviation of 2.95% and 4.98%, respectively.
“The newly developed correlation predicts experimental data within a root mean square error of ± 10%, with a mean and mean deviation of 2.95% and 4.98%, respectively.”
Heat transfer coefficient and overall heat transfer coefficient are higher for fin pitches of 16 and 18 and a face velocity of 0.9 m/s.
“The heat transfer coefficient and overall heat transfer coefficient were higher for fin pitches of 16 and 18 and a face velocity of 0.9 m/s (Fig. 7c and d).”
Heat transfer coefficient decreases with frosting time.
“Fig. 8 shows that the heat transfer coefficient decreased with frosting time.”
Under periodic frosting conditions, overall heat transfer coefficient decreases for face velocities of 0.9 and 3 m/s.
“Fig. 7a and b shows that the overall heat transfer coefficient decreased for periodic frosting conditions for face velocities of 0.9 and 3 m/s.”
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- Authors
- Zhang, P., & Hrnjak, P. S.
- Affiliations
- University of Illinois Urbana-Champaign (US)
- Corresponding author
- Hrnjak, P.S.
- Venue
- International Journal of Refrigeration
- Publisher
- Elsevier BV
- Published
- 2010-03
- Volume
- 33
- Issue
- 2
- Pages
- 334-346
- ISSN
- 0140-7007 (ISSN-L)
- OpenAlex
- W2056410721
- Semantic Scholar
- 695646897d480fc057c37eda60358469b567c5cc
- Cited by
- 38
- References
- 16
- Citations by year
- 2026: 5 · 2025: 4 · 2024: 5 · 2023: 2 · 2022: 4 · 2021: 2 · 2020: 3 · 2019: 3 · 2018: 2 · 2017: 4 · 2016: 1 · 2015: 1 · 2014: 1 · 2012: 1
- FWCI
- 0.67
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- International Journal of Refrigeration (publishedVersion)
- Topics
- Physical Sciences › Engineering › Mechanical Engineering › Heat Transfer and Optimization
- Physical Sciences › Engineering › Mechanical Engineering › Refrigeration and Air Conditioning Technologies
- Physical Sciences › Engineering › Mechanical Engineering › Heat Transfer Mechanisms
- Keywords
- thawing, fin spacing, fin geometry, air-side heat transfer, pressure drop, Colburn j-factor, Fanning friction factor, outdoor heat exchanger
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