Heat Transfer Of Binary Mixtures Research Articles

Mixing and heat transfer of binary mixtures of monodispersed spherical particles with different densities and thermal diffusivities

Mixing and heat transfer among particles in rotating drums are widely applied in numerous industrial processes. Generally, mixing and heat transfer occur simultaneously. Consequently, the interrelationship between mixing and heat transfer must be investigated for industrial applications. In this study, the radial mixing and heat transfer of spherical granular materials (3mm) with various properties in batch rotating drums are investigated numerically using the discrete element method. The evolution of mixing and heat transfer characteristics with rotation speed is analyzed from the perspective of time and number of revolutions, respectively. The results indicate that, depending on the physical parameters and thermal properties of particles, the mixing quality does not always accurately reflect the heat transfer effect. In binary granular beds of monodispersed spherical particles with different densities and thermal diffusivities, the main heat transfer mechanism is related to the ratio of the thermal conductivity of the particles to that of the fluid.

A Review on Nucleate Pool Boiling Heat Transfer of Binary Mixtures

A Review on Nucleate Pool Boiling Heat Transfer of Binary Mixtures

Semi-empirical modeling of pool boiling heat transfer in binary mixtures

Pool boiling heat transfer has been investigated for various binary mixtures, including acetone/isopropanol, water/acetone, water/methanol, water/ethanol, water/isopropanol, water/monoethanolamine, water/diethanolamine and water/triethyleneglycol as test solutions. Many correlations have been developed to predict the pool boiling heat transfer coefficient in mixtures in the past few decades, however the predicted values are not confirming. In addition, the application of many existing correlations requires some individual adjusting parameters that may be not available for every system. In this investigation, a new set of experimental data are presented. These data have been compared to major existing correlations. It is observed that the pool boiling heat transfer coefficients in mixtures are less than the ideal boiling heat transfer coefficient. A new semi-empirical model has been proposed based on the mass transfer resistance to predict the boiling heat transfer coefficient with satisfactory accuracy. The new model does not include any tuning parameter and is applicable to any given binary system. The performance of the proposed model is superior to most existing correlations.

Experimental investigation of pool boiling heat transfer enhancement of alumina–water–ethylene glycol nanofluids

One of the most recent techniques for improvement of boiling processes is using nanofluids. As a simple explanation, adding nanoparticles to regular fluids makes nanofluids. Present article investigates nucleate boiling heat transfer of alumina–water–ethylene glycol nanofluids under atmospheric pressure, experimentally. The experimental setup accuracy has been evaluated for deionized water and mixture of water and ethylene glycol, which shows very good agreement with available correlations in the open literature. Six different volume concentrations of the nanofluids have been used to evaluate the impact of nonoparticles on nucleate boiling heat transfer of binary mixture of water and ethylene glycol with a same volume concentration. The results show the high effectiveness of the nanoparticles on heat transfer coefficient. In addition, the experimental results indicate that there is an optimum volume concentration of nanoparticles, in which the heat transfer coefficient has its maximum value. Furthermore, the optimum volume concentration of nanoparticle and the maximum increment of boiling heat transfer coefficient in the present study are 0.75% and 64%, respectively.

Critical heat flux on flow boiling of methanol–water mixtures in a diverging microchannel with artificial cavities

This study constitutes an experimental investigation into the convective boiling heat transfer and critical heat flux (CHF) of methanol–water mixtures in a diverging microchannel with artificial cavities. Flow visualization shows that bubbles are generally nucleated at both the artificial cavities and side walls of the channel. This confirms the proper functioning of such artificial cavities. Consequently, the wall superheat of the onset nucleate boiling is significantly reduced. Experimental results show that the boiling heat transfer and CHF are significantly influenced by the molar fraction ( x m ) as well as the mass flux. The CHF increases with an increase in mass flux at the same molar fraction. On the other hand, the CHF increases slightly from x m = 0 to 0.3, and then decreases rapidly from x m = 0.3 to 1 at the same mass flux. The maximum CHF is reached at x m = 0.3, particularly for a mass flux of 175 kg/m 2 s, due to the Marangoni effect. Flow visualization confirms that the Marangoni effect helps a region with a liquid film breakup persist to a higher heat flux, and therefore a higher CHF. Moreover, a new empirical correlation involving the Marangoni effect for the CHF on the flow boiling of methanol–water mixtures is developed. The present correlation prediction shows excellent agreement with the experimental data, and further confirms that the present correlation may predict the Marangoni effect on the CHF for the convective boiling heat transfer of binary mixtures.

NUCLEATE POOL BOILING HEAT TRANSFER OF BINARY MIXTURES WITH DIFFERENT BOILING RANGES

The nucleate pool boiling heat transfer data on a smooth flat surface were measured for three binary mixtures of HC600a/HFC134a, HC600a/HC290, and HC600a/HFC23. Much effort was made to investigate the influence of the boiling range on the pool-boiling heat transfer performance. From the experimental results, the HC600a/HFC23 mixture with a wide boiling range showed lower heat transfer coefficients (HTCs) than the mixture with a narrow boiling range such as HC600a/HFC134a and HC600a/HC290 systems. The measured data were also compared with the results predicted by five well-known correlations. It can be found that the average deviation is less than 25% for mixtures with narrow boiling ranges, but a larger deviation for mixtures with wide boiling ranges.

Identification of Physical Phenomena Governing Nucleate Boiling Heat Transfer of Binary Mixtures

AbstractA model based on first principles is presented to compute nucleate boiling heat transfer coefficients. It includes microscale heat and mass transfer phenomena in the so‐called micro region, i.e., the thin film area where the liquid vapor phase interface approaches the wall. The model is verified by comparing calculated to measured heat transfer coefficients. Parameter studies allowed to identify physical phenomena governing the typical reduction of binary mixture heat transfer coefficients compared to the ideal heat transfer coefficient, i.e., the molar average of the heat transfer coefficients of the two pure components of the mixture. These are bubble site density and departure diameter that deviate from the corresponding values of the two pure components. Furthermore, overall heat transfer is decreased by strong concentration gradients in the micro region.

Pool boiling heat transfer in binary mixtures of ammonia/water

Nucleate boiling heat transfer coefficients were measured during pool boiling of the mixtures of ammonia/water on a horizontal heated wire. The experiment was carried out at pressures of 0.4 and 0.7 MPa, at heat fluxes below 2000 kW/m 2 and over all ranges of fraction. The heat transfer coefficients in the mixtures are markedly less than those in single component substances and, in particular, are dramatically deteriorated in the vicinity of both single component substances. An applicability of existing correlations to the present experimental data is discussed. As a result, it is difficult for any existing correlation to predict the coefficients over all ranges of fraction. In the mixtures of ammonia/water, heat of dilution and of dissolution are generated near a vapor–liquid interface, while vapor with a richer concentration of ammonia is condensed and then diffused into a bulk liquid; while in most other mixtures, little heat is generated during any dilution and dissolution. The effect of the heat of dilution and of dissolution on pressure and temperature in a system (pressure vessel) is shown.

Pool boiling heat transfer in binary mixtures of ammonia/water: Effect of heat of dilution and dissolution on heat transfer coefficient

AbstractNucleate boiling heat transfer coefficients were measured on a horizontal heated wire during the pool boiling of non‐azeotropic mixtures of ammonia/water. The experiment was carried out at pressures of 0.4 and 0.7 MPa, at heat fluxes below 2.0 × 106 W/m2, and over a range of mass fraction. The heat transfer coefficients in the mixtures were smaller than those in single‐component substances. No existing correlation is found to predict boiling heat transfer coefficients over the range of mass fraction of interest. In the mixtures of the ammonia/water, the heats of dilution and dissolution were generated near a liquid surface while vapor with a rich concentration of ammonia was condensed and then was diffused into the bulk liquid; while in most other mixtures, little heat was generated during any dilution and dissolution. In relation to the heat generated, the effect of the heats of dilution and dissolution on pressure and temperature in a system (pressure vessel) is shown herein. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(4): 272–283, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.10034

Interfacial effects on nucleate boiling heat transfer of binary mixtures

Experimental and theoretical analyses were conducted to investigate the effects of interfacial behavior on the nucleate boiling heat transfer of ethanol–water, methanol–water, methanol–n-pentane, ethanol–n-pentane and methanol–ethanol binary mixtures. It is demonstrated that binary mixture vapor–liquid interfacial behavior greatly influences boiling dynamics, such as bubble detachment, flow or heat transfer in microlayer, and stability of microlayer. The associated nucleate boiling heat transfer of binary mixtures will, thus, be significantly altered by Marangoni effect caused by surface tension gradient. The experimental results would not correlate with theoretical results if the Marangoni effects at interface had not been considered.

Nucleate Boiling Heat Transfer of Binary Mixtures at Low to Moderate Heat Fluxes

A model for nucleate pool boiling heat transfer of binary mixtures has been proposed based on an additive mechanism. The contributing modes of heat transfer are (i) the heat transferred by microlayer evaporation, (ii) the heat transferred by transient conduction during the reformation of the thermal boundary layer, and (iii) the heat transferred by turbulent natural convection. The model takes into account the microroughness of the heating surface which has been defined quantitatively. The model compares satisfactorily with data obtained in the present study and in the literature. These data were obtained on a variety of heating surfaces such as a vertical platinum wire, a horizontal stainless steel tube and flat horizontal aluminium, and stainless steel surfaces (with various surface finishes) thereby demonstrating the validity of the model.

Effects of Surface Orientation on the Pool Boiling Heat Transfer in Water/2-Propanol Mixtures

To explore the role of Marangoni effects in the pool boiling heat transfer of binary mixtures, experiments have been conducted with water/2-propanol mixtures at three different concentrations under normal gravity with different orientations of the heater surface. The system pressure was subatmospheric (∼5.5 kPa) and the bulk liquid temperature was near the saturation temperature of the fluids tested. The molar concentrations of2-propanol tested were 0.015, 0.025, and 0.1. These concentrations of 2-propanol are selected because their strong variation of surface tension with concentration gives rise to high surface tension gradients near the heater surface during nucleate boiling. Boiling curves were obtained both for an upward-facing and a downward-facing heater surface. For each concentration of 2-propanol, the critical heat flux has been reached in both orientations of the heater surface. Models of pool boiling heat transfer and the critical heat flux condition for binary mixtures are tested to correlate the data. Comparison of boiling curves and CHF obtained at different orientations of the heater surface indicates that there is strong gravity independent mechanism of boiling heat transfer in these mixtures.

A general correlation for pool film boiling heat transfer from a horizontal cylinder to saturated binary liquid mixtures

An approximate analytical solution of theoretical pool film boiling model of binary mixtures without radiation effect is derived by using an integral method. By including radiative contribution through a radiation parameter, a general correlation for predicting pool film boiling heat transfer coefficient of binary mixtures over horizontal cylinder is then proposed. As examined by five nonazeotropic and azeotropic binary systems, the predictions by this general correlation are shown to agree well with the rigorous numerical results. Furthermore, the proposed correlation is given an advantage over previous correlations in that it predicts also the extent of the mass diffusion effect on pool film boiling heat transfer of binary mixtures.

Two phase flow heat transfer of binary mixtures inside enhanced surface tubing

The primary heat transfer parameters such as coefficient of heat transfer and pressure drop observed during condensation of binary azeotropic refrigerant mixtures R-410a (R125/R32: 50/50), and R-507 (R125/R143a: 50/50) are presented in this paper. Experiments showed that for Reynolds numbers higher than 4.2 E06, R-410a appears to have greater heat transfer rates more than the other blends under investigation. Furthermore, it is quite evident from this data that R-507 has the highest pressure drop among the refrigerants under investigation.

Prediction of film boiling heat transfer coefficients for binary mixtures

Film boiling of binary liquid mixtures may be significantly different from that of single-component liquids due to the mass diffusion effect. A theoretical analysis is performed to outline the effects of mass diffusion phenomena on film boiling heat transfer process from a horizontal cylinder heating surface to the binary liquid mixtures of ethylene oxide/water and ethanol/benzene over whole range of compositions. These two binary systems are chosen for illustrating the strong and weak mass diffusion effects, respectively, on film boiling. Furthermore, a simple correlation for predicting heat transfer coefficient is proposed to demonstrate the idea that the dimensionless F factor can satisfactorily account for the mass diffusion effect on film boiling heat transfer of binary mixtures.

Nucleate pool boiling of pure liquids and binary mixtures: Part II — Analytical model for boiling heat transfer of binary mixtures on smooth tubes and comparison of analytical models for both pure liquids and binary mixtures with experimental data

A combined physical model of bubble growth is proposed along with a corresponding bubble growth model for binary mixtures on smooth tubes. Using the general model of Wang et al.[1] and the bubble growth model for binary mixtures, an analytical model for nucleate pool boiling heat transfer of binary mixtures on smooth tubes is developed.

Investigation of boiling heat transfer of binary mixture from vertical tube embedded in porous media

Ethanol-water binary mixtures with 7 different mole fractions of ethanol ranging from 0 to 1 were adopted as testing liquids in the experiment. The vertical heating tube was inserted in porous matrix composed of five well sorted glass beads whose diameters range from 0.5 to 4.3 mm. Due to the effect of composition, the trend of combination of vapor bubbles was reduced, resulting in the increase of peak heat flux of binary mixture. With the increase of ethanol mole fraction, 0.5 mm diameter bead had lower value of peak heat flux, while for pure liquid the critical state is difficult to appear. With given diameter of glass bead, there existed an optimum value of mole fraction of ethanol, which was decreased with the increase of bead diameter. A dimensionless heat transfer coefficient was predicted through the introduction of a dimensionless parameter of porous matrix, which agreed with the experimental results satisfactorily.

Heat Transfer in Nucleate Boiling of Binary Mixtures. Heat Transfer Measurement and Assessment of Available Correlations.

Heat transfer coefficients in nucleate pool boiling of binary mixtures were measured on a circular copper plate, 40 mm in diameter, for a wide range of heat fluxes and concentrations. Measurements were done for five mixtures of methanol/water, ethanol/water, methanol/ethanol, ethanol/n-butanol, and methanol/benzene, each in the saturated boiling under atmospheric pressure. Measured data were expressed in the form α=Cqn for each concentration including pure components, where α is the heat transfer coefficient, q is the heat flux, and C and n are constants. The validity of available correlations for the boiling heat transfer of binary mixtures was assessed based on the measured data. Of the five correlations compared, the Stephan and Korner correlation is found the most appropriate although it needs an empirical constant that varies according to the mixture.

Nucleate pool boiling heat transfer in binary mixtures

Experimental studies have been made for heat transfer during nucleate pool boiling on a horizontal platinum wire in nonazeotropic binary mixtures of R12+R113, R134a+R113, R22+R113 and R22+R11 at a pressure from 2 to 8 bar and at a heat flux up to 1.0 × 105 W/m2. The substances employed were chosen such that the components of a given mixture have a large difference in saturation temperatures. A correlation was derived by improving Thome's correlation, predicting the heat transfer coefficients for the mixtures within an accuracy of ±25 percent. It is also shown that the correlation can be applicable for mixtures with a small difference in saturation temperatures within an accuracy of ±20 percent. The heat transfer coefficients for the mixtures are smaller than that for the single components over the entire concentration range. The heat transfer coefficients for the mixtures depend on the system pressures and heat fluxes at a lesser extent than that for the single components.

Pool Boiling Heat Transfer in Binary Mixtures.

Experimental studies have been made for heat transfer during nucleate pool boiling on a horizontal platinum wire in nonazeotropic binary mixtures of R12+R113 and R134a+R113 at pressures from 2 to 8 bar and at heat fluxes below 1.0×105W/m2. The substances employed were chosen such that the pure substances have a large difference in saturation temperatures. A correlation was derived by improving J. R. Thome's correlation, predicting the heat transfer coefficients for mixtures with a large difference in saturation temperatures within an accuracy of ±20%. It is also shown that the correlation is applicable for mixtures with small differences in saturation temperatures within the same accuracy. The heat transfer coefficients using the mixtures are smaller than those using the pure substances over the entire concentration range. The heat transfer coefficients for the mixtures depend on the pressures of the system and the heat fluxes at a lesser extent than for the pure substances