http://orcid.org/0000-0002-3854-034X
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ABSTRACT
This paper presents an experimental and theoretical analysis of a 6-row horizontal microfin Heat Pipe Finned Heat Exchanger (HPFHE) used for energy recovery purposes inside an air conditioning unit. The experimental campaign investigated both the summer and the winter conditions for European countries by varying the operating conditions at the inlet of the HPFHE. New experimental tests are presented for the identification of low – global warming potential refrigerants, environmental friendly substitutes of the more traditional HFC134a. The results showed the interesting heat transfer capabilities of HFC152a as an alternative HPFHE working fluid. A simulation model previously developed by present authors was validated against the new experimental data collected and then used to simulate the thermal performance of the HPFHE under different operating test conditions, in order to assess the potentiality of seasonal energy savings with HFC152a.
Acknowledgments
This research project was partially funded by: CariVerona Foundation, Verona, Italy, Ricerca Scientifica e Tecnologica 2016-2019: “Sostenibilità e autenticazione nutrizionale di filiere lattiero-casearie a tutela del consumatore”.
Nomenclature
| A | = | - heat transfer area, [m2] |
| c | = | coefficient, [-] |
| cp | = | - specific heat capacity, [J kg−1K−1] |
| C | = | - heat capacity rate, [W K−1] |
| d | = | - diameter [mm] |
| e | = | - sensible thermal effectiveness, [-] |
| g | = | - gravitational acceleration, [m s−2] |
| GWP | = | - Global Warming Potential |
| h | = | - heat transfer coefficient, [W m−2 K−1] |
| HPFHE | = | - Heat Pipe Finned Heat Exchanger |
| HPHE | = | - Heat Pipe Heat Exchanger |
| HVAC | = | - Heating Ventilation and Air Conditioning |
| L | = | - length [m] |
| ln | = | - natural logarithm |
| m | = | - mass flow rate, [kg s−1] |
| M | = | - figure of merit, [N m−2] |
| MAX | = | - Maximum |
| MIN | = | - Minimum |
| NTU | = | - Number of transfer units, [-] |
| p | = | - pressure, [Pa] |
| pr | = | - row pitch [mm] |
| pt | = | - tube pitch [mm] |
| r | = | - capacity rate ratio ( = Cmin/Cmax), [-] |
| R | = | - thermal resistance, [K W−1] |
| RH | = | - Relative Humidity |
| q | = | - heat flux [W m−2] |
| Q | = | - heat flow rate, [W] |
| T | = | - temperature, [°C] |
| U | = | - overall heat transfer coefficient, [Wm−2K−1] |
Greek symbols
| βg | = | - helix angle, [°] |
| Δ | = | - difference |
| ΔhLG | = | - heat of vaporization, [J kg−1] |
| Δh’LG | = | - parameter defined by eq. (Equation13 |
| ΔTln | = | - logarithmic mean temperature difference, [K] |
| λ | = | - thermal conductivity, [W m−1 K−1] |
| μ | = | - viscosity, [kg m−1s−1] |
| ρ | = | - density, [kg m−3] |
| σ | = | - surface tension, [N m−1] |
| Ω | = | - finned surface efficiency, [-] |
Subscripts
| air | = | - air side |
| atm | = | - atmosopheric |
| c | = | - condensation |
| e | = | - evaporation |
| exh | = | - exhaust air |
| G | = | - gas |
| in | = | - inlet of the regenerative heat pipe heat exchanger |
| L | = | - liquid |
| ln | = | - logarithmic |
| max | = | - maximum |
| min | = | - minimum |
| out | = | - outlet of the regenerative heat pipe heat exchanger, outer |
| ref | = | - refrigerant side |
| sat | = | - saturation |
| supply | = | - supply air |
| tot | = | - total |
| w | = | - water |
Additional information
Notes on contributors
Giulia Righetti
Giulia Righetti received her Masters and PhD degrees at the University of Padova, Italy. She is a post-doctoral research fellow at the Department of Management and Engineering. Her research activity is mainly focused on new low-GWP refrigerants two-phase heat transfer in enhanced surfaces for air conditioning and refrigeration.
Claudio Zilio
Claudio Zilio is a Mechanical Engineer. He is a Full Professor at the University of Padova, Italy. He is the Secretary of commission B2 (Refrigerating equipment) of the International Institute of Refrigeration. He has been involved with several European research projects, primarily concerning refrigeration technology and heat transfer and he is the author or co-author of more than 160 papers dealing with topics such as thermodynamics of inverse cycles, heat transfer, both theoretical and technological aspects, energy applications related to refrigeration for foodstuff preservation, and refrigerating equipment. He is a member of the editorial board of ASHRAE Science and Technology for the Built Environment journal.
Simone Mancin
Simone Mancin is an Associate Professor at the Department of Management and Engineering of the University of Padova., Italy. He is member of Commission B1 - Thermodynamics & Transfer Processes of the International Institute of Refrigeration. His research is mainly focused on single- and two- phase heat transfer in enhanced surfaces and micro-geometries for electronic thermal management and air conditioning and refrigeration. He is author or co-author of about 70 papers, most published in the international scientific press.
Giovanni A. Longo
Giovanni A. Longo is a Full Professor of Technical Physics at the University of Padova, Italy. He is the head of the Department of Management and Engineering. He is vice-President of the Commission E1 – Air Conditioning of the International Institute of Refrigeration. His research activity deals with refrigerant two-phase heat transfer, absorption systems, and nano-fluids heat transfer. He is author or co-author of about 200 scientific papers published in referenced national and international journals or presented at national and international congresses and conferences.