Evaluation of Contact Resistance and Fin Effectiveness of Enhanced, Brazed "Dogbone" Fin and Serpentine Tube Heat Exchangers for Air Conditioning and Heat Pump Applications

Conference · Thu May 27 04:00:00 EDT 2021

OSTI ID:1784733

Bacellar, Daniel ^[1]; Li, Song ^[1]; Martin, Cara ^[1]; Shabtay, Yoram ^[2]; Black, John ^[2]

---

1. Optimized Thermal Systems, Inc.
2. Heat Transfer Technologies, LLC

The energy consumption due to air conditioning is projected to increase by 1.3 and 4.5 times by 2050 compared to 2010 for members and non-members of the Organization of Economic Coordination and Development (OECD), respectively. Greenhouse Gas (GHG) emissions must be carefully managed to minimize their hazardous contribution to climate change. Air conditioners (AC) and heat pumps (HP) contribute with direct GHG emissions through systemic refrigerant leakage, which consequently degrades the system’s performance and therefore increases its indirect GHG emissions as well. To address this issue, the goals of new systems include minimizing leakage risk, using low global warming potential (GWP) refrigerants such as natural refrigerants, and increasing system efficiency. This paper presents part of the efforts in the development of a brazed “dogbone” fin to continuous serpentine tube heat exchanger (HX) for AC/HP applications. The main advantages of such technology are: 1) The potential to reduce 90% or more of the tube return-bends brazed joints compared to conventional tube-fin heat exchangers, thus minimizing leakage vulnerability, enabling the use of natural refrigerants like Propane and Ammonia that carry other concerning risks of flammability and toxicity ; and 2) The brazed fin to the tube joints should yield very low contact resistance. In order to quantify and estimate the impacts of contact resistance and fin effectiveness, a numerical-experimental study is investigated. The novel enhanced brazed “dog-bone” fin is compared to an equivalent pressure expanded fin. The results showed that the expanded fin has consistently greater effective heat transfer but greater contact resistance as well. Furthermore, the brazed fins have up to 20% lower pressure drop. The trade-off comparison shows that the thermal-hydraulic ratio between the two fins is equivalent for air velocities below 2m/s; for greater velocities, however, the expanded fin is favored since it has less fin efficiency penalty. For HVAC&R applications, the air velocities are typically low which makes the proposed technology competitive and a viable option in the pursuit of refrigerant leakage reduction.

• Research Organization: Optimized Thermal Systems, Inc.
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Building Technologies Office
• DOE Contract Number: EE0007680
• OSTI ID: 1784733
• Report Number(s): 2188
• Country of Publication: United States
• Language: English

Related Subjects

30 DIRECT ENERGY CONVERSION
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
42 ENGINEERING
tube-fin coil
thermal resistance
experimental
CFD
heat pump