EXPERIMENTAL STUDIES ON NUCLEATE POOL BOILING HEAT TRANSFER TO ETHANOL/MEG/DEG TERNARY MIXTURE AS A NEW COOLANT

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1 Available on line at Association of the Chemical Engineers of Serbia AChE Chemical Industry & Chemical Engineering Quarterly 8 (4) (202) CI&CEQ M.M. SARAFRAZ S.M. PEYGHAMBARZADEH S.A. ALAVI FAZEL Department of Chemical Engineering, Mahshahr branch, Islamic Azad University, Mahshahr, Iran SCIENTIFIC PAPER UDC :66.8:66.04 DOI /CICEQ6033S EXPERIMENTAL STUDIES ON NUCLEATE POOL BOILING HEAT TRANSFER TO ETHANOL/MEG/DEG TERNARY MIXTURE AS A NEW COOLANT In this paper, nucleate pool boiling heat transfer coefficient of ternary mixtures of ethanol, monoethylene glycol (MEG) and diethylene glycol (DEG) as a new coolant with higher heat transfer coefficient has been investigated. Therefore, at varied concentrations of MEG and DEG and also at different heat fluxes, pool boiling heat transfer coefficients, α, have been experimentally measured. The results demonstrated higher heat transfer coefficient in comparison with water/meg/deg ternary mixture. In particular, at high heat fluxes, for ethanol/meg/deg mixture, higher boiling heat transfer coefficient is reported. Additionally, experimental data were compared to well-known existing correlations. Results of this comparison showed that the most accurate correlation for predicting the heat transfer coefficient of ethanol/meg/deg is the modified Stephan-Preußer correlation, which has been obtained in our earlier work. Keywords: nucleate pool boiling; heat transfer; ethanol; monoethylene glycol; diethylene glycol; ternary mixture. After the publication of our earlier work [], we were determined to test a new ternary mixture as a coolant with higher pool boiling heat transfer coefficient. The existing research studies indicate that understanding the mechanisms of boiling of mixtures and the prediction of their boiling heat transfer coefficient must be studied in depth. Research studies can influence the economic design of heating tools, particularly, estimating heat transfer coefficient at any power cycles or phase changing processes. Also, supplementary studies related to boiling and condensation operations can be considered as key parameters on optimizing and design calculations of heat transfer industries. Nuclear reactors, power plants and electronics packaging are the instances of boiling application in industries [2-4]. The main reason for this fact can be interpreted such that nucleate boiling is capable of transferring large amounts of energy per unit of heat transfer area in comparison to those transferred in forced convection or conduction. This Correspondening author: M.M. Sarafraz, Department of Chemical Engineering, Mahshahr branch, Islamic Azad University, Mahshahr, Iran. mohamadmohsensarafraz@gmail.com Paper received: 6 November, 20 Paper revised: 23 February, 202 Paper accepted: 7 April, 202 undoubtedly is the result of vapor bubbles formation on the heated surface. Experimental investigations on pool boiling of mixtures have shown that the physical processes associated with multi-components boiling are significantly different from those for pure liquids. The basic component of the ternary mixture described in the previous work was water, which was replaced with ethanol in this study. In fact, the main reason of this replacement refers to the lower saturation temperature and mass vaporization of ethanol. In brief, presence of ethanol instead of water, reduce the saturation bulk temperature of mixture and nucleate boiling will occur in lower temperature (around 83 C instead of 00.3 C). Likewise, it is noticeable that MEG and DEG with variety of their concentrations are widely used in anti-freeze and anti-boil water based fluids. Table gives a summary of well-known correlations related to estimating the pool boiling heat transfer coefficient of various hydrocarbon and none-hydrocarbon ternary mixtures []. The correlations have not been experimentally obtained for ternary mixtures, including the MEG/DEG and third part compound, but truly demonstrate treasonable values for pool boiling heat transfer coefficient of other ternary mixtures and can be kept as a reference for comparisons to experimental data. 577

2 Table. Some well-known existing correlations for predicting pool boiling the heat transfer coefficient of binary and ternary mixtures Author Presented correlation Application Ref Palen α [ 0.027( Tbo Tbi )] = e αid kl qd b Pd b ρl ρv cplμl αid = ( )( ) ( ) ( ) ( ) d δμ σ ρ k b L v L N = = α α α Stephan and Preußer d b 2 2 kl q ρv kl μl cpl αstephan 0. = ( ) ( Hfg db / kl ) 0.35 d b k L ρ ( δ d b ) k L T Calus-Rice Schlünder Unal Bajorek et al. Thome id i = α = αid ˆ α y x ( ) DAB α h = + αid Fujita α α = id + K ΔTe / ΔTid Inoue Vinayak-Balakrishnan id n 0 ( T )( ) ( exp ) i sn Tsi yi x = i h ρlδβll B 0 =, β 2 4 / LL = E m s i 0.7 α α = [ ( b b )( b )][ b ] id x.0 y x y.5 b 2 = ( x)ln + x ln + y x B q x for x y 0 y = = =, 0.00 b = 0, b = 52 Pr, b = 0.92 y x Pr ( ψ 2) exp( ψ 2) α h exp id dt = + ( y ) 2 x φ + φ α 2 2 id q dx ξ ξ ξ ξ y 2 x 2 y 2 x 2 φ = D 22 D 2 ξ 2, φ2 = D 22 D 2 ξ y x y x kq ξ kq ξ2 ψ =, ψ 2 = ρλ det[ D] hid le ρλ det[ D] hid le α = αid ΔT bp bq 0 + exp Tid βρ H Δ f g 5, K = 0.75exp( q) q ρ v K = 0.75exp ρvh fg σg ( ρl ρv ) α α = 5, K = 0.75 exp( q) ΔT id e + K Δ T id α D AB = y x α id ˆ α 0.62 Binary [26] Ternary and multi components [3] Binary [24] Ternary and multi components [8] Binary [9] ternary [27] Binary [] Binary, similar to Inoue [4] Binary [20] Binary [5] Similarly to this work, many researchers have studied the pool boiling heat transfer coefficient of ternary mixtures. Several authors proposed that the heat transfer coefficient in the nucleate boiling of ternary mixtures depends strongly on the difference in concentration of the more volatile component between the vapor and the liquid phases [2-5]. Other authors have investigated the influence of the liquid composition and the concentration difference between constituents of a solution on the bubble growth ratio and 578

3 heat transfer mechanism [6-8]. Alavi Fazel et al. [8] demonstrated that pool boiling heat transfer of pure liquids is strongly considered as a function of varied thermophysical properties. They found a new empirical correlation using dimensional analysis method including thermo physical properties such as mass heat of vaporization, surface tension and densities of liquid and vapor phase for determining the pool boiling heat transfer coefficient of pure liquids. Peyghambarzadeh et al. [7,9] experimentally studied the nucleate boiling of binary and ternary mixtures on horizontal cylinder and showed that the Schlunder correlation is the most accurate correlation for estimating the pool boiling heat transfer coefficient of water/mea/dea. They also discussed the impacts of important existing parameters on these correlations like ideal heat transfer coefficient on predicting of heat transfer coefficient. Sarafraz [] investigated the pool boiling heat transfer coefficient of citric acid around the smooth horizontal cylinder and proposed a new modified correlation for estimating the heat transfer coefficient using the thermo physical properties. In this paper, a new ternary compound of ethanol/meg/deg is compared to water/meg/deg (traditional anti-freeze) and for new mixture, a comparison between pool boiling heat transfer coefficients with well-known correlations is carried out. Additionally, the correlation obtained in previous work is examined for the new mixture. Further, the best composition with higher pool boiling heat transfer coefficient is determined based on the thermal toleration of main heater. In simple words, the results of this research demonstrate the enhancement of pool boiling heat transfer coefficient of anti-freezes and anti-boils in pool boiling circumstance via the new coolant mixture (ethanol based) in comparison with traditional (water based) mixtures. EXPERIMENTAL SETUP AND PROCEDURE The complete pool boiling apparatus is shown in Figure. The apparatus consists of a thick-walled cylindrical stainless steel tank containing 38 liters of test liquid and a vertical condenser to condense and recycle the evaporated liquid. The test section is mounted horizontally within the tank and can be observed and photographed through observation glasses at both sides of the tank. The tank and condenser are heavily insulated to reduce heat losses to the ambient air. The temperature in the tank is regulated by an electronic temperature controller and a variable transformer in conjunction with a band heater covering the complete cylindrical outside surface. The pressure in the apparatus is monitored continuously and a pressure relief valve is installed for safety reasons. Boiling occurs at the outside of a cylindrical stainless steel test heater with a diameter of 2 mm, and a heated length of 05 mm. The test heater consists of an internally heated stainless steel sheathed rod and four stainless steel sheathed thermocouples with an Figure. A scheme of experimental apparatus. 579

4 outside diameter of 2 mm are embedded along the circumference of the heater close to the heating surface. Regarding to the type of the heater used in this experiment (rod heater is a cylinder-type heater with super homogenized surface and all the generated heat are radially conducted) and accordingly all the places on the heating surface receives the same heat and therefore any places of heating section has a similar temperature. Moreover, thermocouples as seen in Figure 2 are installed at a depth of 50 mm of cylinder and it shows that heat transfer along the length of the heating section is uniform and furthermore temperature will be constant during the experiment runs. Details of the test heater are given in Figure 2. One thermocouple within the heated section was used as a safety trip to cut off the power if the thermocouple temperature exceeded 70 C. A PCbased data acquisition system was used to measure temperatures, pressure, and heat flux. The power supplied to the test heater could be calculated from the measured current and voltage drop. The average of five readings was used to determine the difference between wall and bulk temperature for each thermocouple. The temperature drop between the location of the wall thermocouples and the heat transfer surface was deducted from the measured temperature difference according to: T T = ( T T ) ( s / k)( q / A) () s b th b In this equation, s is the distance between the thermocouple locations and the heat transfer surface and k is the thermal conductivity of the heater material. The value of s/k was determined for each thermocouple by calibration of the test heater using pure water. The average temperature difference was the arithmetic average of the six thermocouple locations. The heat transfer coefficient h is calculated from: α = q A ( Ts Tb) ave Experimental procedure Initially, the test section and tank were cleaned and the system connected to a vacuum pump. Once the pressure of the system reached approximately 0 kpa, the test solution was introduced. Following this, the tank heater was switched on and the temperature of the system allowed rising. Once the system was de-aerated, it was left at the desired pressure and the corresponding saturation temperature for about five hours to obtain a homogenous condition throughout. Then, the power was supplied to the test heater and kept at a predetermined value. All experiment runs were carried out with decreasing heat flux. Some runs were repeated later to check the reproducibility of the experiments. Uncertainty To measure the uncertainty of experiment, mathematical least square method has been employed. According to heat flux estimating correlation: (2) VL W q " = 2πRL = 2πRL (3) o o Experimental uncertainty is obtained by the following equation: q " q " q " Δ q " = Δ w + Δ r + ΔL w r L (4) Values for Δw, Δr and ΔL are 0, 0.03 and 0.2, respectively. Accordingly, the pool boiling heat transfer coefficient uncertainty, according to the Δq values, is obtained by Eq. (4) as follows: Figure 2. Details and geometry dimensions of heating section. 580

5 2 2 α α Δ α = Δ q " + ΔT q " T (5) In this research, ΔT equals to ±0.2 K according to accuracy of each of thermocouple and Δq equals to.25% according to Eq. (4) and subsequently, uncertainty of estimating of heat transfer coefficient equals to ±2.35%. Physical properties To estimate the thermophysical properties of tested mixtures, some well-known correlations from chemical engineering handbooks have been employed based on their uncertainties. In fact, minimum uncertainties of correlations have been considered. Accordingly, the critical constants have been calculated using the Joback method [2]. The expected uncertainty is reported equal to 7 K ( %) for Tc; 2 bar ( 5%). Liquid density for mixtures has been calculated by Spencer et al. [3] method with the maximum expected uncertainty of 7%. Liquid thermal conductivities for liquids had been predicted by methods summarized by Bruce et al. [4]. The expected uncertainties are reported less than 0% for pure liquids and up to 8% for liquid mixtures. Heat capacities for liquids have been calculated using the Ruziicka and Domalski [5] method, with the expected uncertainty less than 4%. The heat capacities of liquid mixtures are estimated by mole fraction averages of the pure component values. For other key parameters, such as viscosity and surface tension, experimental apparatus were employed. For viscosity, a digital viscometer manufactured by Brookfield and for surface tension, a tension-meter (EW-59780) manufactured by Cole-Parmer were used. The minimum measurement errors of each apparatus were ± and ±2.5% reading, respectively. RESULTS AND DISCUSSIONS The experimental data indicated interesting results for nucleate pool boiling heat transfer coefficient of ethanol/meg/deg mixtures. In fact, a comparison between the water based mixture (water/meg/deg) and ethanol based mixture shows that at the same concentrations of MEG and DEG, higher heat transfer coefficients are reported for ethanol based mixture. Especially, deeply looking at higher heat fluxes indicates that heat transfer coefficient for boiling of ethanol ternary mixture is about 30% higher than water based mixture. In industries, particularly in nuclear reactors and power cycles needing coolants, it is important to transfer huge amounts of heat at high heat fluxes at minimum surface area. Furthermore, a coolant with high and superior heat transfer coefficient is required. As seen, pool boiling heat transfer coefficients for ethanol ternary mixture at higher heat fluxes (even in low and moderate heat fluxes) are dramatically higher. Figures 3 and 4 depict the experimental heat transfer coefficient for different volumetric concentrations of MEG and DEG in ethanol and water, respectively. Figure 3. Experimental pool boiling heat transfer coefficient for ethanol/meg/deg ternary mixture. 58

6 Figure 4. Experimental pool boiling heat transfer coefficient for water/meg/deg ternary (previous work). As clearly seen in Figure 3, regarding the mixture effect, the pool boiling heat transfer coefficient of mixture decreases with increasing MEG and DEG concentrations. In brief, due to the difference in vapor pressures of mixture substances particularly in the vapor /liquid interface, heavier components remain in the interface zone and lighter components due to the higher vapor pressure leave the interface, thus creating a mass transfer between the interface (rich with heavier components) and vapor phase (the least heavier component phase). Therefore, mass transfer acts as a resistance against the heat transfer. However, this phenomenon is not observed in pool boiling of pure substance, because in pure pool boiling the interface is composed of one component, as well as the vapor phase [7-23,25]. On the other hand, regarding the higher heat transfer coefficient of DEG relative to MEG, with increasing DEG concentration, the heat transfer coefficient of mixture significantly increases so that in comparison with similar condition for water/meg/deg, increase of heat transfer coefficient is observed. The best possible values of pool boiling heat transfer coefficient have been recorded at 25% volumetric concentration of MEG and DEG. Noticeably, the main heater does not have enough power to boil the mixture with higher concentration of 25% MEG and 25% DEG, because the boiling points of the tested mixtures are proportional to concentrations of MEG and DEG. Therefore, 25% of MEG and 25% of DEG are kept as bounds of concentration. On the other hand, owing to the higher prices of MEG and DEG in comparison with water and ethanol, it is more economical to use 25% of MEG and DEG. Figure 5 shows the comparison between water based and ethanol based mixtures and their pool boiling heat transfer coefficients simultaneously. A rough comparison between pool boiling heat transfer coefficient of pure water and pure ethanol helps understanding the positive influence of ethanol in enhancing the heat transfer coefficient. This comparison demonstrates that mostly, at any low, moderate and high heat fluxes, pure ethanol has a lower pool boiling heat transfer coefficient compared to pure water. However, in terms of thermophysical properties of ethanol, particularly due to lower and vapor pressure and mass heat of vaporization of ethanol relative to water (853.9 vs kj kg -, respectively) [40], in ethanol/meg/deg mixtures ethanol vaporizes faster (compared to pure water in water/meg/deg). Therefore, the more significant mass transfer mechanism appears inside the liquid mixture phase between vapor in bubbles and liquid phase, and also at the interface of liquid/vapor phase. Subsequently, the boiling phenomenon will be controlled with heat and more mass transfer mechanism compared to boiling of water/meg/deg mixture. Figure 6 shows the comparison of pure water and ethanol at similar conditions for low, moderate and high heat fluxes. To check the validity of experimentally measured data, some existing correlations have been compared to experimental data. In particular, the correlation results obtained in the previous work were 582

7 Figure 5. Comparison between ethanol-based and water-based heat transfer coefficient for MEG25%-DEG25% at the best composition condition. Figure 6. Comparison of pool boiling heat transfer for pure water and pure ethanol. examined. As expected, among the existing correlations, the Sarafraz et al. [] modified correlation was the most accurate correlation for glycol mixtures. The absolute average deviations of predicted values in comparison to experimental data for Palen [26], Stephan et al. [4] and Bajorek [27] are given in Table 2. For estimating the heat transfer coefficient at ideal conditions, the Stephan-Abdelsalam correlation [42] was employed. Figure 7 shows the results of comparing the experimental data with the predicted values of existing correlations. Table 2 represents the absolute average deviation for existing correlations. A.A.D% is obtained using Eq. (6): hexp h Calc AAD.. % = 00 (6) n h Exp 583

8 Table 2. Absolute average deviation of existing correlations in comparison to experimental data Correlation Palen Bajorek Stephan et al. Sarafraz et al. A.A.D% 38.4% 27.36% 4.54% 7.8% Figure 7. Comparisons between existing correlations and experimental data. CONCLUSION Experimental studies on nucleate pool boiling heat transfer of ethanol/meg/deg were performed at different concentrations of MEG and DEG and at various heat fluxes up to 4 kw m 2. In our previous work, ternary mixture of water/meg/deg was investigated however, in this work, comparison between pool boiling heat transfer coefficient of ethanol/deg/ /MEG and water/meg/deg was done. The comparison results indicated that, at the best condition of ethanol/meg/deg composition, in which volumetric concentrations of MEG and DEG are equal to 25%, the highest pool boiling heat transfer coefficients were recorded. It was shown that, at any flux, the ethanol based mixture has higher heat transfer coefficient compared to the water based mixture and the maximum enhancement is reported for 25% MEG-25% DEG which is about 30% relative to water based ternary mixture. Likewise, comparison with existing correlations demonstrated that the Sarafraz et al. modified correlation was the most accurate correlation among the other examined correlations with a deviation of 7.8%. Nomenclature A Area, m 2 B 0 Ratio of the interfacial area of heat transfer to the interfacial area of mass transfer b -b 5 See Unal equation C Heat capacity, J kg - K - D AB Diffusivity coefficient, m 2 s - d b Bubble departing diameter, m g Gravitational acceleration, m s -2 H fg Mass heat of vaporization, J kg - K Thermal conductivity, W m - K - N Number of components P Pressure, Pa q Heat, J (Watt) q Heat Flux, W m -2 R a Roughness, m o r Cylinder outer diameter, m s Distance, m T Temperature, K W Power, W x Liquid mass or mole fraction y Vapor mass or mole fraction. Subscripts b Bulk c Critical i Component id Ideal l Liquid o Reference 584

9 r s th v Reduced Saturated or surface Thermocouples Vapor. Greek symbols α Heat transfer coefficient, W m -2 K - ˆα Thermal diffusion, m 2 s - β Mass transfer coefficient, m s - Δ Difference ρ Density, kg m -3 σ Surface tension, Dy/cm or somewhere N m -. REFERENCES [] M.M. Sarafraz, S.A. Alavi Fazel, Y. Hasanzadeh, A. Arabi Shamsabadi, S. Bahram, 20, DOI: / /CICEQ062504S [2] E. Hahne, U. Grigull, Heat Transfer in Boiling, Hemisphere Publishing Corporation, 977 [3] Y. Fujita, Q. Bai, Int. J. Refrig. 20(8) (997) [4] K. Stephan, M. Körner, Chem. Ing. Technol. (969) [5] J.R. Thome, G. Davey, Int. J. Heat Mass Transfer 24 (98) [6] H.E. Alpay, F. Balkan, Int. J. Heat Mass Transfer 32 (989) [7] S.M. Peyghambarzadeh, M. Jamialahmadi, S.A. Alavi Fazel, S. Azizi, Braz. J. Chem. Eng. 26 (2009) [8] S.A Alavi Fazel, S. Roumana, Pool boiling heat transfer to pure liquids, WSEAS Conference, USA, 200 [9] S.M. Peyghambarzadeh, M.Jamialahmadi, S.A. Alavi Fazel, S. Azizi, Exp. Therm. Fluid. Sci. 33 (2009) [0] M.M. Sarafraz, Heat Mass Trans. 40 (20) -9 [] K.G. Joback, M.S. Thesis in Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MS, 984 [2] C.F. Spencer, R.P. Danner, J. Chem. Eng. Data 7 (972) [3] E. Bruce, J. Poling, J.M. Prausnitz, P. O Connell, The properties of gases and liquids, 5 th ed., The McGraw-Hill Companies, New York, 2004 [4] V. Ruzicka, E. S. Domalski, J. Phys. Chem. Ref. Data 22 (993) [5] W.R. McGillis, J.S. Fitch, W.R. Hamburgen, V.P. Carey, Boiling binary mixtures at subatmospheric pressures, Technical Note TN-23, Western Research Laboratory, Palo Alto, CA, USA, 992 [6] M. Jamialahmadi, A. Helalizadeh, H. Muller-Steinhagen, Int. J. Heat Mass Tran. 47 (2004) [7] E. Hahne, U. Grigull (eds.), Heat transfer in boiling, Hemisphere Publ. Corp., Washington, USA, 977 [8] Y. Fujita, Q. Bai, Int. J. Refrig. 20(8) (997) [9] K. Stephan, M. Korner, Chem. Ing. Technol. 4 (969) [20] J.R. Thome, G. Davey, Int. J. Heat Mass Tran 24 (98) [2] H.E. Alpay, F. Balkan, Int. J. Heat Mass Tran. 32 (989) [22] D. Jung, K. Song, K. Ahn, J. Kim, Int. J. Refrig. 26 (2003) [23] Y. Fujita, M. Tsutsui, Int. J. Heat Mass Tran 47 (2004) [24] G. Vinayak Rao, A.R. Balakrishnan, Exp. Therm. Fluid Sci. 29 (2004) [25] L.D. Boyko, G.N. Kruzhilin, Int. J. Heat Mass Tran 0 (967) [26] I.L. Mostinski, Teploenergetika 4 (963) 66-7 [27] E.U. Schlünder, Int. Chem. Eng. 23 (4) (983) [28] H. Jungnickel, P. Wassilew, W.E. Kraus, Int. J. Refrig. 3 (980) [29] T. Inoue, M. Monde, Y. Teruya, Int. J. Heat Mass Tran 45 (2002) [30] J.R. Thome, S. Shakir, AIChE Symp. Ser. 83 (987) 46-5 [3] Y. Fujita, M. Tsutsui, Int. J. Heat Mass Tran 37 (994) [32] B. Xiao, B. Yu, Int. J. Therm. Sci. 46 (2007) [33] W.F. Calus, P. Rice, Chem. Eng. Sci. 27 (972) [34] H.C. Unal, Int. J. Heat Mass Tran 29 (986) [35] J.W. Palen, W. Small, Hydrocarb. Process. 3 (964) [36] S.M. Bajorek, J.R. Lioyd, J.R. Thome, AIChE Symp Ser. 85 (989) [37] K.G. Joback, M.Sc. Thesis, Massachusetts Institute of Technology, Cambridge, MA,. 984 [38] C.F. Spencer, R.P. Danner, J. Chem. Eng. Data 7 (972) 236 [39] B.E. Poling, G.H. Thomson, D.G. Friend, R.L. Rowley, W.V. Wilding, Perry s chemical engineers handbook, 8 th ed., McGraw Hill, New York, 2008, p. 53 [40] K. Stephan, P. Preusser, Ger. Chem. Eng. 2 (979) 6 69 [4] K. Stephan, K. Abdelsalam, Int. J. Heat and Mass Trans. 23 (980),

10 M.M. SARAFRAZ S.M. PEYGHAMBARZADEH S.A. ALAVI FAZEL Department of Chemical Engineering, Mahshahr branch, Islamic Azad University, Mahshahr, Iran NAUČNI RAD EKSPERIMENTALNO ISPITIVANJE PRENOSA TOPLOTE PRI NUKLEATSKOM KLJUČANJU ZASIĆENE TERNERNE SMEŠE ETANOL/MEG/DEG KAO RASHLADNE TEČNOSTI U ovom radu ispitivan je koeficijent prenosa toplote pri nukleatskom ključanju ternernih smeša etanola, monoetilen-glikola (MEG) i dietilen-glikola (DEG) kao nove rashladne tečnosti. Pri različitim koncentracijama MEG I DEG, kao i različitim toplotnim fluksevima, koeficijent prenosa toplote je određivan eksperimentalno. Rezultati su pokazali veće vrednosti koeficijenta prenosa toplote u poređenju sa trokomponentnim smešama voda/meg/deg. Naročito pri velikim toplotnim fluksevima, određene su veće vrednosti koeficijenta prenosa toplote. Pored toga, eksperimentalni podaci su poređeni sa dobro poznatim korelacijama. Ovo poređenje je pokazalo da je modifikovana Stefan-Projserova korelacija, koja je dobijena ranijim istraživanjima, najpreciznija u predviđanju koeficijenta prenosa toplote za system etanol/meg/deg. Ključne reči: nukleatsko ključanje; prenos toplote; etanol; monoetilen-glikol; dietilen-glikol; trokomponentna smeša. 586