Proceedings of the rd 33 National Heat Transfer Conference August 15-17, 1999. Albuquerque, New Mexico
NHTC99-78
AN EXPERIMENTAL INVESTIGATION ETHYLENE-GLYCOL/WATER
ON FLOW BOILING MIXTURE
OF
Satish G. Kandlikar and Murat Bulut Mechanical Engineering Department Rochester Institute of Technology Rochester, NY 14623, USA Phone: 716-475-6728 Fax: 716-475-7710
[email protected] V - flow velocity, m/s Vt - Volatility parameter, defined by Kandlikar (1998c), eq. (3) xt - liquid mass fraction of ethylene glycol in aqueous solution yt - vapor mass fraction of ethylene glycol in aqueous solution
ABSTRACT Mixtures of ethylene glycol and water are used in cooling the engines in automotive applications. To avoid the two-phase flow in the engine, the mixture is subcooled in the radiator before entering the engine block. Heat transfer is therefore essentially under subcooled flow boiling conditions. Very little information is available in the literature on the subcooled flow boiling characteristics of this mixture, and there is no predictive method established in this region. The present work focuses on obtaining experimental heat transfer data for mixtures of ethylene-glycol (0 to 40 percent mass fraction, limited by the maximum allowable temperature in the present setup) and water in subcooled flow boiling region. The experimental setup is designed to obtain local heat transfer coefficient values over a small circular aluminum heater surface, 9.5-mm in diameter, placed at the bottom wall of a rectangular channel 3mm x 40-mm in cross-section. The applicability of the available model for subcooled flow boiling of pure liquids to the mixtures is examined.
Greek Letters (r - heat transfer coefficient, W/m2K a* - a based on (T,-T,,,), eq. (1) K - thermal diffusivity, =W(pc,r), m2/s h - thermal conductivity, W/mK p - viscosity, N-s/m2 p - density, kg/m3 Subscripts conv = convective component 6 bulk fluid lo = liquid only nb = nucleate boiling component snf = saturation value tp = two phase w = wall
NOMENCLATURE
” Bo - Boiling number = q I G i,fg
INTRODUCTION A major application of flow boiling of ethylene-glycol Although this mixtures is in automotive engine cooling. mixture has been used for over several decades, there is very little information available in the open literature on its heat The transfer characteristics under flow boiling conditions. present work is aimed toward obtaining experimental data and characterizing the mixture effects on the heat transfer performance. Subcooled flow boiling of binary mixtures involves the combination of two phenomena that are quite extensively
cP,r- specific heat of liquid, J/kgK D12- diffusion coefficient of 1 (ethylene glycol) in 2 (water) Dh - hydraulic diameter of the flow channel, m Fn - Mass diffusion induced suppression factor, eq. (4) Fo - fluid surface parameter in Kandlikar (1990) correlation G - mass flux, kg/m’s i, - latent heat of vaporization, J/kg 4” - heat flux, W/m2 Re - Reynolds number, pVD&t T - temperature, K
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studied: subcooledflow boiling of pure components,and flow boiling of binary mixtures. A brief overview of these topics is presentedhere. I
SubcooledFlow Boiling of Pure Components Figure 1 shows Ute lteat transfer cltamcteristics during subcooledflow boiling of a pure liquid. Heat flux is plotted as a function of local wall temperature in this plot. The plot represents conditions existing at a certain location in a uniformly heated tube with constO.2. Figure 12 shows the variation of volatility parameter with Applying the concentration for ethylene glycol mixtures. criteria described above, the mixture can be treated as a pure component below a concentration of 0.15, and eq. (1) applies in the fully developed boiling region. For concentrations between 0.15 and 0.4, the mixture falls under moderate suppression region, and eq. (2) applies. The experimental data obtained in this investigation does not cover the severe suppression region. In a separate study, McAssey and Kandlikar (1999) compared their ethylene glycol/water mixture data obtained from automotive engine cooling application with eq. (2) and found good agreement to within +30 percent. They also indicated that the prediction accuracy would improve with the incorporation of accurate Fn for ethylene glycol, inclusion of he factor Fu, and the extension of the Kandlikar’s (1998a) lartial boiling methodology to mixtures. It should be noted that there is some uncertainty involved in he present comparison due to the non-availability of the fluidlependent factor for ethylene glycol. Experimental data for lure ethylene glycol could not be obtained (to evaluate Ffl) in ie present work due to its high boiling point.
Data,
Re=Z296
X
Data,
Re=6687
350 y!
$5 300 'w x" 250 s 200 Ii Q) 150 z al 100 0
't
n
50
czo400 L N0
*,i xm/
. _ - - - .FDB
:
correlaticmwith constantdX7.2, Re=6887
n :’ ::
x
,'
#'
**
-FDB -I
5 10 15 20 25
Wall superheat,
correlation,with constant=1058.
Re=6887
AT (K)
Fig. 14 Comparison of the present data with the FDB correlation (asymptote to data at high superheats), eqs. (1) and (2), 5% solution of ethylene glycol in water at atmospheric pressure Figures 13-17 compare the present data with the fully developed boiling correlation given by eqs. (1) and (2). Note that the FDB region exists at higher wall superheat values. In the lower range of wall superheat, the data points fall under single-phase and partial boiling regions, and the correlation is not applicable. The data points therefore should merge into the FDB correlation as wall superheat is increased. Figure 13 shows the comparison of data for pure water at Re=7339 with Kandlikar’s (1998a) FDB correlation given by
11 wt. % ethylene
glycollwater
400, $
n
Data, Re=2090
X
Data, Re=6271
5K
350 -
5 300 =cr . 250 =4 200 g
40 wt. % ethylene glycoliwater subcooling
9 K subcooling
- - - - - .FDB correlation, with constant=667.2, Re=6271 -FDB correlation constant=1056, F&=6271
150-
0 loo-
0
5
Data, Re=1276
Data, Ae=3633
with -FDB
0
10 15 20 25
Wall superheat,
0
5
The data in Fig. 13 for Re=2446 lies in the laminarkransition region, and eq. (1) is not applicable. However, since the velocity has very little effect in the fully developed boiling region, the two data sets merge into the same In the following discussion, data for both FDB curve. Reynolds number ranges are shown, but the correlation is plotted for the higher Reynolds number cases only. Figure 14 shows the experimental data for 5% ethylene glycol solution at two flow rates. Also shown in the figure are the predictions from eqs. (1) and (2). At this concentration, the value of V1 from Fig. 12 is seen to be close to zero, and the diffusion effects are expected to be small. The data reflects this expected behavior, as it lies between the two prediction curves. As the concentration increases to 1I%, the results shown in Fig. 15 indicate a better agreement between the data in the FDB region at high wall superheats and the predictions from eq. (2). Figures 16 shows the results for 30% concentration. Here the diffusion effects are expected to be somewhat higher, and eq. (2) should be applicable. Further effects of mass diffusion are seen in Fig. 17 for 40% solution, and eq. (3) needs to be considered at higher concentrations. Final conclusions must wait until Fn for ethylene glycol is determined first from experiments. The present setup is not designed to handle the resulting higher saturation temperatures with pure ethylene glycol or mixtures with higher ethylene glycol concentration (>40%).
5 K
n
Data, I%=1577
X
Data, Re=4730
me--e
FDB correlatm,wth conslant=667.2. F&=4730
-FDB
correlation constant=1058, Ix!=4730
wth
10 15 20 25
Wall superheat,
AT (K)
Fig. 17 Comparison of the present data with the FDB correlation (asymptote to data at high superheats), eqs. (1) and (2), 40% solution of ethylene glycol in water at atmospheric pressure
of the present data with the FDB Fig. 15 Comparison correlation (asymptote to data at high superheats), eqs. (1) and (2), 11% solution of ethylene glycol in water at atmospheric pressure 30 wt. % ethylene glycol/water subcooling
with
5 10 15 20 25
Wall superheat,
AT (K)
correlation constant=l056, Re3633
AT(K)
Fig. 16 Comparison of the present data with the FDB correlation (asymptote to data at high superheats), eqs. (1) and (2), 30% solution of ethylene glycol in water at atmospheric pressure eq. (1). As the wall superheat increases, the data approaches the fully developed boiling region for which eq. (1) is applicable. It is seen that the data merges into the FDB correlation at high wall superheats. At lower wall superheats, the data lies in the partial boiling region, and the FDB correlation is not applicable here. It is seen that the results obtained in the present investigation using a rectangular flow -hannel and a circular spot heater are correlated well with the :orrelation derived for flow boiling in circular tubes.
CONCLUSIONS
AND FUTURE WORK
The following conclusions are drawn on the basis of the present study.
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Kandlikar, S. G., 1998a, “Heat Transfer and Flow Characteristics in Partial Boiling, Fully Developed Boiling, and Significant Void Flow Regions of Subcooled Flow Boiling,” ASME Journal of Heat Transfer, Vol. 120, pp. 395401. Kandlikar, S. G., 1998b, “Boiling Heat Transfer in Binary Systems: Part I - Pool Boiling,” ASME Journal of Heat Transfer, pp. 380-387. Kandlikar, S. G., 1998c, “Boiling Heat Transfer in Binary Systems: Part II - Flow Boiling,” ASME Journal of Heat Transfer, pp. 388-394. McAdams, W. H., Minden, C. S., Carl, R., Picornell, D. M., Dew, J. E., 1949, “Heat Transfer at High Rates to Water with Surface Boiling,” Ind. Eng. Chern., Vol. 4 1, No. 9, pp. 1945-63. McAssey, E.V., and Kandlikar, S.G., 1999, ‘Convective Heat Transfer of Binary Mixtures under Flow Boiling Conditions,” Paper to be presented at the International Conference on Two-Phase Flow Modeling and Experimentation, Pisa, Italy. McAssey, E. V., Stinson, C., and Gollin, M., 1995, “Evaluation of Engine Coolants Under Flow Boiling Conditions,” Proceedings of the ASME Heat Transfer Division, HTD-Vol. 3 17-1, pp. 193-200. Mikic, B. B., and Rohsenow, W. M., 1969, “New Correlation of Pool Boiling Data Including the Effect of Heating Surface Characteristics,” Journal of Heat Transfer, Vol. 91, pp. 24 l-250. Shah, M. M., 1977, “A General Correlation for Heat Transfer During Subcooled Boiling in Pipes and Annuli,” ASHRAE Trans., Vol. 83, Part 1, pp. 205-215. Thorn, J. R. S., Walker, W. M., Fallon, T. A., and Reising, G. F. S., 1965, “Boiling in Subcooled Water during Flow up Heated Tubes or Annuli,” Paper presented at the Symposium on Boiling Heat Transfer in Steam Generating Units and Heat Exchangers, Manchester, Sept. 15-16, Institute of Mech. Eng., London.
1. An experimental study is conducted to study the subcooled flow boiling heat transfer of aqueous ethylene glycol solutions. Experimental results are obtained for surface heat flux as a function of wall superheat by systematically varying the mass concentration of ethylene glycol in the range of 0 to 40%. The flow configuration is a rectangular flow channel 3-mm x 40-mm c/s with a circular heater 9.5-mm diameter. 2. The results for flow boiling of pure water in the fully developed boiling region (at higher wall superheats) are in excellent agreement (Fig. 13) with the Kandlikar (1998a) model. The data approaches the fully developed curve asymptotically as the wall superheat increases. This indicates that the flow boiling model for circular tubes is applicable to the present rectangular channel geometry as well. 3. As the concentration of ethylene glycol increases, the heat transfer performance deteriorates, and becomes dominated by convective effects. 4. The experimental data is in good agreement with the predictions from the fully developed boiling correlations, eqs. (1) and (2) for binary mixtures. 5. Further work is warranted to determine accurate values of the fluid-dependent parameter Fn for ethylene glycol. 6. Further refinement is warranted in the correlation in the transition zones from near-azeotropic region to moderate suppression region, and from moderate suppression region to severe suppression region. 7. Future experiments should focus on higher wall superheats and higher concentrations of ethylene glycol to quantify the diffusion effects in the entire range of concentrations. REFERENCES Ambrogi, G, McAssey, E. V., Cozzone, G., Hoover, C., 1997,“The Effect of Off-Design Operation on the Thermal Performance of Propylene-glycol and Ethylene-glycol Engine Coolants,” SAE Paper No. 971827, Vehicle Thermal Management Conference, Indianapolis, IN. Bhowmick, S., Branchi, C., McAssey, E. V., and Gollin, M., 1996, “Heat Transfer Performance of Engine Coolants Under Subcooled Boiling Conditions,” ASME ICE-Vol. 26-2, 1996 Spring Technical Conference. Bhowmick, S., Branchi, C. McAssey, E. V., Gollin, M. and Cozzone, G., 1997, “Prediction of Heat Transfer in Engine Cooling Systems,” Proceedings of the 4th World Conference on Experimental Heat Transfer, Fluid Mechanics, and Thermodynamics, Brussels, Belgium. Chen, J. C., 1966, “A Correlation for Boiling Heat Transfer to Saturated Fluids in Convective Flow,” Industrial and Engineering Chemistry, Process Design and Development, Vol. 5, No. 3, pp.322-329. Finlay, I. C., Boyle, R. J. , Pirault, J. P., and Biddulph, T., 1987, ‘Nucleate and film Boiling of Engine Coolants Flowing in a Uniformly Heated Duct of Small Cross Section,” SAE I‘echnical Paper Series 870032.
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