CO2 life cycle analysis and on-tube condensation heat transfer performance of low global warming pot
Abstract
The overall objective of this project is to select lower global warming potential (GWP), R134a alternative refrigerants that reduces, net CO2 emissions while meeting chiller and HVAC system performance requirements. The technical approach of the proposed project ha,s two tasks: Task 1 includes a CO2 life cycle analysis using the Total Equivalent Warming Impact (TEWI)/Life Cycle Climate Performan,ce (LCCP) frameworks. Task 2 investigates on-tube condensation of R134a alternatives on 12.7-mm and 15.875-mm-outer-diameter tubes,,commensurate with chiller geometries, and models tube bundle performance. Due to the need to mitigate risks to military personnel an,d equipment, and maintain performance with large system charges, this project focuses on ASHRAE A1 refrigerants (i.e., lower toxicit,y and non-flammable).The technical approach centers around Tasks 1 and 2. In Task 1, the research team (i.e., PI and students) will,conduct a life cycle analysis for total equivalent CO2 emissions for A1 candidates in water-cooled chillers using the TEWI/LCCP fram,eworks. Direct and indirect CO2 emissions from will be quantified. For refrigeration systems, the two largest drivers of emissions a,re generally 1) emissions produced from the energy source used to power the system and 2) leakage of refrigerant from the system; mo,deling will determine the Coefficient of Performance under a range of conditions and therefore calculate energy consumption of the s,ystem using R134a and A1 alternative refrigerants. TEWI/LCCP models will utilize a wide range of parameters (e.g., leak rates of 0.5,-30%, annual operating hours of 2190-8760, etc.) to thoroughly investigate potential emissions from new refrigerant candidates. Foll,owing the life cycle analysis, the team will select two A1 candidates while optimizing for GWP, low total CO2 emissions, and availab,ility.There are limited data regarding the performance of A1 alternatives for R134a during on-tube condensation. Task 2 includes mea,suring measure on-tube condensation heat transfer coefficients while simultaneously visualizing condensate film thickness. Heat flux,es are measured directly using a temperature gradient in the wall to avoid the large uncertainties associated with the Wilson plot m,ethod. The experimental apparatus will be validated using energy balances. Condensation heat transfer performance in tube bundles ca,n be impacted by the position of the tube in the bundle, the condensate drainage pattern, and vapor shear stresses. Inundation will,be studied in the experimental apparatus, and the impacts of vapor shear stresses on the condensate film will be simulated in ANSYS,FLUENT. The project will investigate the impacts of long-term storage of refrigerant blends on condensatio,lude TEWI/LCCP models tailored to chillers with a range of operating parameters, life cycle analyses to support the selection of an,alternative refrigerant to R134a which reduces net CO2 emissions, on-tube condensation heat transfer and flow visualization using A1, alternatives to R134a, modeling of condensation heat transfer in tube bundles, and quantification of the impacts of long-term stora,ge on condensation heat transfer.The project directly supports the Office of Naval Research s target of reducing 85% of HFC refriger,ants. Nontoxic, nonflammable A1 refrigerant alternatives will be selected for incorporation in chillers based on the Total Equivalen,t Warming Impact/Life Cycle Climate Performance (LCCP) frameworks. The on-tube condensation studies proposed directly support the ch,iller geometry.This Project Summary/Abstract is approved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Mar 05, 2022
- Source ID
- N000142212328
Entities
People
- Melanie Derby
Organizations
- Kansas State University
- Office of Naval Research
- United States Navy