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Abstract
Sprays used for enhanced heat transfer are reviewed, starting from the spray characteristics, measurement methods, and spray dynamics, to spray heat transfer. Some results for spray heat transfer at large Reynolds numbers and surface boiling are also presented, including some recent results summarizing the effects of various injection parameters. It is recommended that basic principles of heat transfer be used to integrate various effects, such as coolant and surface temperatures, water and air flow rates, and injection conditions, into a concise form so that the results can be generalized and be applied to a large range of conditions.
NOMENCLATURE
| Ac | = | cross-sectional area of the droplet |
| Ad | = | surface area of the droplet |
| C | = | a constant in EquationEq. (26) |
| CD | = | discharge coefficient |
| Cd | = | drag coefficient of the droplet |
| D | = | arithmetic mean of the diameter |
| Dm | = | number median diameter |
| Dv | = | median volume diameter |
| D1 | = | a correlation constant in EquationEq. (24) |
| D2 | = | a correlation constant in EquationEq. (25) |
| D32 | = | Sauter mean diameter |
| d | = | droplet diameter |
| dd | = | diameter of smooth spherical droplet |
| dinj | = | diameter of the orifice |
| do | = | injector diameter |
| dv | = | volume diameter (6Vold/π)1/3 |
| ds | = | surface diameter (Ad/π)1/2 |
| d32 | = | Sauter diameter |
| F | = | forces on the droplet |
| FWHM | = | full width at half maximum |
| Fb | = | buoyancy force |
| Fd | = | drag force |
| Fg | = | gravitational force |
| Fl(d) | = | log-normal drop size cumulative function |
| Fr(d) | = | Rosin–Rammler drop size cumulative function |
| Fv | = | flow rate |
| fg(d) | = | Gaussian drop size distribution function |
| fl(d) | = | log-normal drop size distribution function |
| g | = | gravitational acceleration |
| H | = | vertical distance from the injector to the surface to be cooled |
| HTC | = | heat transfer coefficient |
| h | = | heat transfer coefficient (this notation is used for the generic heat transfer coefficient) |
| hs | = | heat transfer coefficient at the surface |
| hs,max | = | maximum heat transfer coefficient |
| = | average heat transfer coefficient | |
| k | = | thermal conductivity |
| keff | = | effective thermal conductivity of the thermal boundary layer |
| L | = | length scale |
| linj | = | length of the orifice |
| MVD | = | median volume diameter |
| m a | = | constant in EquationEq. (26) |
| Nt | = | total number of droplets |
| Nu | = | Nusselt number hL/k |
| n | = | exponent in the Rosin–Rammler drop size distribution function |
| n1, n2, n3 | = | correlation constants in EquationEq. (25) |
| Oh | = | Ohnesorge number |
| PDA | = | phase Doppler anemometer |
| p | = | gage pressure |
| pa | = | air pressure |
| pw | = | water pressure |
| Qa | = | airflow rate |
| Qw | = | water flow rate |
| qh | = | heat flux |
| qh,max | = | maximum or critical heat flux |
| R | = | correlation coefficient |
| Re | = | Reynolds number, = ρUL/μ |
| RSF | = | relative span factor |
| SMD | = | Sauter mean diameter |
| TLei | = | Leidenfrost temperature |
| Ts | = | surface temperature |
| U | = | mean velocity |
| V | = | droplet velocity |
| Vold | = | volume of the droplet |
| Vi | = | average impingement speed |
| Vo | = | initial velocity |
| Vt | = | terminal velocity |
| We | = | Weber number |
| wf | = | full width at half maximum (FWHM) |
| X | = | (air core area)/(discharge orifice area) |
| x | = | quality |
Greek Symbols
| Δp | = | nozzle exit pressure difference |
| δd | = | standard deviation in the drop diameter |
| δl | = | logarithm of the standard deviation in the drop diameter |
| μ | = | viscosity |
| θ | = | spray cone angle |
| θi | = | impingement angle |
| θs | = | spray angle in degree |
| ρ | = | density |
| σf | = | surface tension of the fluid |
Subscripts
| a | = | air |
| do | = | injector diameter |
| f | = | liquid |
| g | = | gas or vapor |
| o | = | injector exit |
| x x | = | direction, for F and V |
| y y | = | direction |
| w | = | water |
Additional information
Notes on contributors
Ampere A. Tseng
Ampere A. Tseng, now retired, has been a professor at Arizona State University and also an invited chair professor in the Mechanical Engineering Department of Brno University of Technology, Czech Republic. Before joining Arizona State University in 1996, he had been a professor of mechanical engineering at Drexel University for more than 10 years. He received his Ph.D. in mechanical engineering from Georgia Institute of Technology. Currently he is interested in doing research in fabrication and prototyping of micro-/nanoscale structures and devices. He has published more than 200 technical papers, and nine U.S. patents in the past 5 years. He is heavily involved in professional society activities and has been a member of the editorial boards of several professional journals.
Miroslav Raudensky
Miroslav Raudensky is the director of the Laboratory of Heat Transfer and Fluid Flow, Mechanical Engineering at Brno University of Technology, Czech Republic. He has B.S., M.S, and Ph.D. degrees, all from the Brno University of Technology, where he has been a faculty member since 1995. He has more than 200 journal and conference publications in various areas of heat transfer, including spray cooling, material processing, and novel heat exchangers. Some of this work has resulted in 12 domestic (Czech Republic) and international patents. Aside from spray heat transfer and fluid research, he flies a small aircraft to exotic locations around the world.
Tae-Woo Lee
Tae-Woo Lee is an associate professor of mechanical and aerospace engineering at Arizona State University, Tempe, AZ. His degrees are in aeronautical and astronautical engineering (B.S.A.E.E.) from the Ohio State University, and an M.S.E. and Ph.D. in aerospace engineering from the University of Michigan. His range of interest varies from combustion, to spray atomization, urban heat islands, and applied thermal fluids processes such as spray cooling. He has approximately 100 technical papers in journals and conference proceedings. His current interests are on energy methods to analyze complex problems, and nonlinear inverse methods for modeling of difficult problems in chemical kinetics, atmospheric systems, and economics.