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Abstract
Ammonia (NH3 or R717) is an important refrigerant whose flow boiling heat transfer needs to be determined in many engineering applications. There have been some studies evaluating the correlations of flow boiling heat transfer coefficients for NH3. However, the number of the correlations evaluated or the number of data points used was limited, which resulted in inconsistent results. This work presents a comprehensive study of the applicability of existing correlations of flow boiling heat transfer coefficients to NH3. From seven independent laboratories, a database consisting of 1157 experimental data points of NH3 flow boiling heat transfer is compiled. The experimental parameter ranges cover mass flux from 10 to 600 kg/m2s, heat flux from 2.0 to 240 kW/m2, vapor quality from 0.002 to 0.997, saturation pressure from 0.19 to 1.6 MPa, and channel inner diameter from 1.224 to 32 mm. Based on the NH3 database, 37 correlations are evaluated and analyzed. The results show that the best correlation has a mean absolute deviation of 40.9%, indicating the need for developing a more accurate correlation for NH3 flow boiling heat transfer. Several topics worthy of further studies are identified.
NOMENCLATURE
| Bd | = | Bond number, |
| Bo | = | Boiling number, q/(hlgG) |
| C | = | constant |
| Co | = | confinement number, |
| cp | = | specific heat at constant pressure |
| Cv | = | convection number, |
| D | = | inner diameter (m) |
| DA | = | the departure diameter of bubble (m) |
| Dh | = | hydraulic diameter (m) |
| Eo | = | Eötvös number, |
| Fr | = | Froude number, |
| G | = | mass flux (kg/m2-s) |
| g | = | acceleration due to gravity (m/s2) |
| h | = | heat transfer coefficient (W/m2-K) |
| hlg | = | latent heat of vaporization (J/kg) |
| L | = | heated length of experimental tube (m) |
| M | = | molecular mass (kg/kmol) |
| MAD | = | mean absolute deviation |
| MRD | = | mean relative deviation |
| N | = | parameter defined in Shah [Citation3] correlation |
| Nu | = | Nusselt number |
| p | = | pressure (Pa) |
| PR | = | reduced pressure, p/pcrit |
| Pr | = | Prandtl number |
| q | = | heat flux (W/m2) |
| Re | = | Reynolds number |
| t | = | temperature (°C) |
| X | = | Martinelli parameter |
| x | = | vapor quality |
Greek Symbols
| α | = | thermal diffusivity (m2 s−1) |
| λ | = | thermal conductivity (W/m-K) |
| μ | = | dynamic viscosity (Pa-s) |
| ρ | = | density (kg/m3) |
| σ | = | surface tension (N/m) |
| φ2l | = | two-phase friction multiplier, |
| Ψ | = | parameter defined in Shah [Citation3] correlation |
Subscripts
| bs | = | bubble suppression region |
| cb | = | convective boiling |
| exp | = | experimental |
| g | = | gas, saturated vapor |
| l | = | saturated liquid |
| lo | = | liquid only, all flow taken as liquid |
| nb | = | nucleate boiling |
| pred | = | predicted |
| sat | = | saturated |
| sp | = | single-phase |
| t | = | turbulent |
| tp | = | two-phase |
| tt | = | turbulent liquid/turbulent vapor |
| v | = | viscous |
Additional information
Notes on contributors
Hao Wang
Hao Wang is a graduate student in the School of Aerospace Engineering at Nanjing University of Aeronautics and Astronautics, Nanjing, China. He received his B.S. degree in heating, ventilation, and air conditioning (HVAC) from Nanjing University of Aeronautics and Astronautics. His area of specialty is in-tube two-phase flow heat transfer.
Xiande Fang
Xiande Fang is a professor at the Institute of Air Conditioning and Refrigeration, Nanjing University of Aeronautics and Astronautics (NUAA), China, the editor-in-chief of American Journal of Heat and Mass Transfer, and P.Eng. with Professional Engineers Ontario, Canada. He received his Ph.D. in engineering thermophysics from University of Science and Technology of China in 1990, M.Sci. in thermal engineering from Tsinghua University, China in 1984, and B.Eng. in environmental control engineering from NUAA in 1982. His research areas are air conditioning and refrigeration, solar thermal energy, aircraft environmental control, two-phase flow and heat transfer in various gravities, supercritical flow and heat transfer, and thermal-fluid applications in thermal-fluid equipment and systems.