Home Thermodynamic properties of the bubble growth process in a pool boiling of water-ethanol mixture two-component system
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Thermodynamic properties of the bubble growth process in a pool boiling of water-ethanol mixture two-component system

  • Mohammad Sattari and Leila Mahdavian EMAIL logo
Published/Copyright: February 22, 2019

Abstract

Saturated pool boiling in a two-component water-ethanol solution was studied at a pressure of one atmosphere in a horizontal stainless steel cylinder. Solutions with volumes of 3%, 7%, and 12% of water-ethanol solution were examined at a heat flux of 1.8 to 60 kW/m2. Videos and photos were analyzed and changes in bubble diameter, growth, and departure parameters were recorded. The results showed that the bubble departure diameters increased with increasing heat flux, but diameters decrease with increasing ethanol mass fraction. The experimental data are evaluated with two models of Alavi Fazel and Hamzehkhani’s model, have better fitting with Hamzehkhani’s model.

Graphical Abstract

1 Introduction

Nuclear boiling is an application of heat transfer that, as the subject of many studies, has led to many empirical results. Nowadays, many researchers in various fields, including petroleum, petrochemical, nuclear power, and so on, have focused on the boiling phenomenon due to a significant increase in the heat transfer coefficient [1]. Most energy conversion systems and heat exchangers use boiling heat transfer to maximize efficiency. Boiling is a common issue in complex engineering problems, especially when in situations involving the transfer of heavy heat loads. A key problem in boiling is bubble dynamics, including bubble departure diameters, density of sources of bubble production per unit area, and bubble generation frequency [2]. More accurate understanding and modeling of the boiling process requires modeling of the sub-processes [3].

The process of bubble formation, growth, and movement in the boiling process significantly increases the boiling heat transfer coefficient compared to the convection mechanism without a phase change [4]. Studies of bubble dynamics during nuclear pool boiling reduce the computational cost. Bubble dynamics in pool boiling was extensively studied by Lord Rayleigh as he considered the sound created in the kettle of boiling water [5]. Bubble formation occurs when the surface temperature (Tw) is higher than the temperature of liquid at a pressure of saturation (Tsat) and heat is thereby transferred from the solid to liquid. The resulting heat flux depends on the temperature difference between the surface and the saturated liquid. The liquid is stagnant (the flow of liquid is zero) at pool boiling and movement adjacent to the solid surface is caused by the free convection in the growth of the bubble. Increasing heat flux activates more nucleation sites resulting in elevated bubble movement and the emergence of individual bubbles [6, 7]. With a further increase in the heat flux, the bubbles appear as continuous flows or bubble columns. Further increases in the heat flux prevent the liquid from being heated because the heating surface becomes completely covered with steam. The increased surface temperature disperses the applied heat flux and the vapor layers act as a resistance [8]. The departure point of nuclear boiling is attained by increasing the flux to a point referred to as the critical heat flux.

The saturated pool boiling in a two-component water-ethanol solution was studied in a stainless steel horizontal cylinder at a pressure of one atmosphere. Bubble growth was predicted after examining the impacts of concentration, volume, heat flux, and a comparison between experimental results and theoretical models.

2 Experimental methods

All chemicals used in this study are from Merck Co., Germany.

2.1 Device preparation

The pool boiling heat transfer device, known as the Goren flow measuring device, is one of the most common and the most suitable devices for measuring the boiling heat transfer coefficient. The device has a central rod heater section consisting of a cylinder of stainless steel 316 , which has an electrical conductivity of 0.75 m W-1mm-2, low thermal conductivity (15 W·m−1·K−1), and significant corrosion resistance. The rod heater length and diameter were 250 and 25 mm, respectively, with four holes (50 mm in depth) in its cross-section for the placement of thermocouple sensors using silicon paste. An auto-transformer (power source with an electrical potential between zero and 300 volts) applied a heat flux in the range of 30 to 240V. The boiling vessel is made of tempered glass to allow boiling observation and recording. The glass is resistant to high temperatures up to approximately 550°C has dimensions of 151×244×230 mm. The tests were performed in distilled water at a heat flux of 1800 to 60000 W/m2. During pool boiling, films and photos were taken by a video camera (Imaging System) at 1200 frames for each heat flux.

The instrumentation consists of a thermocouple (K-type in the range of 0 to 700°C), a temperature display, and an ammeter (Multimeter, 0.1A precision). After each test, the data were recorded and processed. Figure 1 shows the arrangement of the equipment.

Figure 1 Overview of the pool boiling heat transfer device.
Figure 1

Overview of the pool boiling heat transfer device.

In this experiment, the test container was filled to a certain volume (7×10-3 m3) of solution with the intended ethanol:water ratio, and four thermocouple sensors were installed on the cylinder body. The pre-heating heater was turned on until the solution reached the saturation temperature. The solution was kept at the saturation temperature until all air bubbles were removed from the liquid phase. After the system reached steady state, the voltage was changed systematically, and resulting data were recorded.

Physical properties of the solution used, including vapor and liquid phase densities, surface tension, viscosity, specific heat capacity, enthalpy of vaporization, and thermal conductivity, were determined before measuring and analyzing the diameters of bubbles. The salts used in this study were sodium chloride and sodium sulfate because these salts result in relatively small de-sedimentation as the electrolyte on the surface of the heater [9].

In models and in previous studies, surface tension was found to be a very important factor in the boiling process. The images of bubble growth in pure water in the presence of sodium sulfate and sodium chloride at a heat flux of 17.356 kW.m-2 were examined to investigate the impact of surface tension. The addition of impurities to the water correlates with a decrease in bubble diameter and an increase in cohesion. According to the physical properties of solutions as described in the literature, the surface tension of a water-ethanol solution is lower than that of pure water [10]. Figure 2 provides the images of bubbles with different diameters created in pure water and in solutions containing the salts sodium sulfate and sodium chloride.

Figure 2 Boiling in a) pure water, b) in the presence of sodium sulfate, and c) in the presence of sodium chloride at a heat flux of 17.356 kW.m-2.
Figure 2

Boiling in a) pure water, b) in the presence of sodium sulfate, and c) in the presence of sodium chloride at a heat flux of 17.356 kW.m-2.

Ethical approval: The conducted research is not related to either human or animal use.

3 Results and discussion

During thermal movement accompanying natural convection, the wall temperature rises due to increasing heat flux. The first bubbles (nuclei) are formed in the small holes on the rod heater surface in the temperature range of 5 to 30°C. The bubble departure process begins at 87°C and the boiling process begins around the central heater at 100°C. The system is maintained until it reaches stability within 10 min, after which the central heater is inserted.

In this study, the bubble formation steps were conducted first for pure water, then water-ethanol solutions were prepared at concentrations of 3%, 7%, and 12% by volume, and the test was repeated as for pure water. The control of saturation temperature and concentration are more important to the analysis of water-ethanol solutions than of pure water. After completion of all the tests, images of 20 bubbles in each heat flux were selected, and the bubble diameters were measured individually with EDIUS software. Afterwards, the average bubble diameter in each heat flux was determined.

For most pure liquids, at least one saturated liquid phase density is experimentally available. The saturation density can be calculated using a modification of Rocket’s equation (Equation (1)) [11].

(1)ρl=PcRTcZRA[1+[1Tr]27]

where Pc is the critical pressure, R is the general constant for gases, Tc is the critical temperature, ZRA is the constant defined by experimental data [11], and Tr is the reduced temperature. The liquid phase density in relation to temperature was obtained given the experimental data of part of (a) in Figure 3. All tests were conducted at atmospheric pressure. At this pressure, the vapor can be assumed to be completely in the gas phase; therefore, the density of pure components were calculated with equation (2) [11].

Figure 3 The amounts of a) liquid density, b) vapor density, c) surface tension, and d) vaporization enthalpy of water-ethanol solution (3% by volume) at different temperatures.
Figure 3

The amounts of a) liquid density, b) vapor density, c) surface tension, and d) vaporization enthalpy of water-ethanol solution (3% by volume) at different temperatures.

(2)ρv=PMWRT

Since most of the resultant vapor originates from the boiling water, the vapor density can be approximated to that of water vapor ( ρv= 598.05 kg/m3). Figure 3b displays the experimentally determined vapor densities. One important factor in bubble dynamics is the liquid surface tension. This parameter is present in almost all predictive equations of the bubble departure and diameter. The equation for surface tension versus temperature is presented as equation (3):

(3)σ=a-bθ

Where θ is temperature (°C) and σ is surface tension (N/m), the a and b constants are different for various materials and have been determined for a variety of pure liquids. It is necessary to use equations in order to measure this parameter for water-ethanol solutions to calculate the surface tension in the experiments carried out. The surface tension of such solutions is not a simple function of the solution components, because the solution composition is different at the air interface as compared to the composition within the bulk liquid. Prediction of the surface tension of aqueous solutions is far more difficult than non-aqueous solutions due to the nonlinear dependence on the molar components. Very low concentrations of organic matter can significantly affect the surface tension values of aqueous solutions. The following equation is used for aqueous-organic solutions:

(4)σmix1/4=ψwσw1/4+ψ0σ01/4

where σmix is the surface tension of an aqueous solution, σw is the surface tension of pure water, σ0 is the surface tension of a pure organic composition. The factor ψw is defined by equation (5):

(5)Log(ψw)q(1ψw)=Log[(xwvw)qx0v0(xw+x0)1q]+0.441qT[σ0v0239σwvw23]

where xw is the molar mass of a liquid in the solution, x0 is the molar component of pure organic composition in the solution, and V0 is the molar volume of the salt. Changes in the surface tension of the water-ethanol mixture are shown in Figure 3c The specific heat capacity is directly correlated with the enthalpy of formation, which can be obtained for the reduced temperature in the range of 0.6 to 7 using Equation (6) as follows:

(6)HfgRTc=7.08(1Tr)0.345+10.95(1Tr)0.456

The vaporization enthalpy can be calculated for pure liquids (water vapor enthalpy: 2257 kJkg)as shown for two-component water-ethanol solution in Figure 3d

In addition to the above parameters, the viscosity of liquids in aqueous solutions with one or more polar component, including organic systems, is obtained as follows:

(7)LnμL,mix=X1Lnμ11+X2Lnμ12+2X1X2G12

In equation (7), G12 represents the regulated parameter, which is measured using experimental data from a variety of systems [12], and X is the liquid molar fraction with an error of about 15%. Figure (3) displays the experimental data on the viscosities of the liquid and vapor tested.

The thermal conductivity of most organic liquids is the range of 0.25- 0.4 (wmk)at a temperature below the boiling temperature. Highly polar liquids such as water have thermal conductivities two or three times the above amounts. The temperature dependence of the thermal conductivity in weak electrolytes has the reverse ratio. The equation is summarized for two-component systems as follows:

(8)Kl,mix=ϕ12kl1+2ϕ1ϕ2+ϕ22

as:

(9)ϕi=xivixkvk

In the above equations, xi is the molar fraction of component i, and Vi is the molar volume of pure component i. The accuracy and computational error of the above equation is not more than 4%.

Figure 4 depicts the thermal conductivity of a two-component water-ethanol solution at various temperatures. Figure 4 indicates that an increase in temperature reduces the viscosity of a liquid and in return increases vapor viscosity. The thermal conductivity of a mixture decreases with increasing temperature.

Figure 4 Changes in liquid and vapor viscosities, and thermal conductivity of two-component water-ethanol solution (3% by volume) at different temperatures.
Figure 4

Changes in liquid and vapor viscosities, and thermal conductivity of two-component water-ethanol solution (3% by volume) at different temperatures.

In the evaluation of the boiling process, the growing bubble diameter was examined for the two-component water-ethanol solution at concentrations of 3, 7, and 12% by volume at an experimental heat flux of 1.8 to 60 kW/m2. Different heat fluxes were tested in the water-ethanol system followed by the determination of the surface

and internal tank temperatures. After reviewing and analyzing the images taken during bubble growth (Fig. 5), bubble diameter was measured in each heat flux and density condition. Figure 5 indicates that bubble diameter increased with rising heat flux, suggesting high bubble cohesion at a high heat flux.

Figure 5 A view of bubble growth in two-component water-ethanol solution at a) low and b) high heat fluxes.
Figure 5

A view of bubble growth in two-component water-ethanol solution at a) low and b) high heat fluxes.

Evaluation of the impact of heat flux was repeated for all three concentrations (3, 7, and 12% by volume) of water-ethanol solution, and their changes are shown in Figure 6. The bubble diameter increased with increasing heat flux. This correlation is likely due to the increased liquid mixing with rising heat flux.

Figure 6 Bubble diameter measured for water-ethanol solution in different heat fluxes.
Figure 6

Bubble diameter measured for water-ethanol solution in different heat fluxes.

Experiments dealing with the boiling process of water-ethanol solutions were also carried out at different concentrations to determine the effect of concentration alongside heat flux on the bubble diameter with further precision. It is known that the higher the percentage of impurities in a solution, the higher the heat required to reach the boiling point. As shown in Figure 7, increasing ethanol concentration correlates with reduced bubble diameter in the solution with heat flux of 56715.18 W.m-2.

Figure 7 Changes in the bubble diameter by mixing different volumes of water-ethanol solution.
Figure 7

Changes in the bubble diameter by mixing different volumes of water-ethanol solution.

A model proposed by Alavi Fazel [11,12] was used to evaluate the diameter of the bubbles as follows:

(10)Db=MNCan(σg(ρlρv))0.5
Table 1

The absolute average error (A.A.E) evaluation by the theoretical models for different volumetric percentage of water-ethanol solution at various heat fluxes.

A.A.E%Heat flux
12%.V7%.V3%.V(W.m-2)
HamzehkhaniAlavi FazelHamzehkhaniAlavi FazelHamzehkhaniAlavi Fazel
modelmodelmodelmodelmodelmodel
24.2048.0224.8046.8020.7065.072352.95
19.7042.3019:0544.4014.9056.505928.20
17.1038.1015.9042.7014:5051.6511184.14
15.5035.0614:0241.5014.9049.9017356.80
14.3032.4012.6040.5014.6046.4024751.78
13.4030.1011.6039.6013:3045.3033369.06
12.6027.9010.7038.8013:0742.4044278.18
11.9025.9010.3035.9014.9041.4056715.18

where Db is bubble diameter (m), M is molecular weight (g mol-1), Nca is the dimensionless capillary number, g is gravity (m s-2), n is total mass flux, and σ is surface tension (N.m-1). In addition, bubble diameter was calculated using a model proposed by Hamzeh Khani [2] as follows:

(11)Bo=CaaArbJac

where Bo is the dimensionless bond number, Ca is capillary number, Ja the dimensionless Jacob number, and Ar is Archimedes number. After adjusting the data, the values obtained were: a = 0.18089, b = 0.02052, and c=0.55811. The results of comparing the two theoretical models for different volume composition of the water-ethanol solution against heat flux are shown in Table 2. The absolute average error (A.A.E) and experimental diameter (Dexp) with its computed diameter (Dcal) are calculated by Eq. (11) to evaluate the model used:

(12)A.A.E%=|DcalDexpDexp|×100

Table 1 shows, with increasing heat flux, the absolute average error decreases. The comparison of the two theoretical models used reveals that the A.A.E% is lower in Hamzehkhani’s model indicating that the two-component water-ethanol solution follows this dynamic model, its lowest error (A.A.E%=10.30) is in composition of 7% and for Alavi Fazel model is in 12%.V (A.A.E%=25.90).

4 Conclusion

This study investigated bubble diameter at heat fluxes ranging from 1.8 to 60 kW.m-2. The results show that bubble diameter is increased with rising heat flux due to mixing and homogenization of the solution. Increasing the temperature decreases the concentration and density of the liquid phase resulting in elevated heat flux, more heat transfer to the liquid in contact with the metal cylinder, and, ultimately, increased bubble diameter and reduced liquid phase viscosity. The surface tension changed with increasing of solute concentration, and data of the presented theoretical models at composition of 7% have fitting with the experimental results. Furthermore, most dynamic models for bubble growth become divergent with rising concentration.


Mahdavian_leila@yahoo.com

Acknowledgment

I would like to thank Islamic Azad University Doroud branch, for providing me with all the necessary facilities for this research.

  1. Conflict of interest: Authors declare no conflict of interest.

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Received: 2017-06-21
Accepted: 2018-09-07
Published Online: 2019-02-22

© 2019 Mohammad Sattari, Leila Mahdavian, published by De Gruyter

This work is licensed under the Creative Commons Attribution 4.0 Public License.

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  106. The effect of selected substances on the stability of standard solutions in voltammetric analysis of ascorbic acid in fruit juices
  107. Determination of the content of Pb, Cd, Cu, Zn in dairy products from various regions of Poland
  108. Special Issue on IC3PE 2018 Conference
  109. The Photocatalytic Activity of Zns-TiO2 on a Carbon Fiber Prepared by Chemical Bath Deposition
  110. N-octyl chitosan derivatives as amphiphilic carrier agents for herbicide formulations
  111. Kinetics and Mechanistic Study of Hydrolysis of Adenosine Monophosphate Disodium Salt (AMPNa2) in Acidic and Alkaline Media
  112. Antimalarial Activity of Andrographis Paniculata Ness‘s N-hexane Extract and Its Major Compounds
  113. Special Issue on ABB2018 Conference
  114. Special Issue on ICCESEN 2017
  115. Theoretical Diagnostics of Second and Third-order Hyperpolarizabilities of Several Acid Derivatives
  116. Determination of Gamma Rays Efficiency Against Rhizoctonia solani in Potatoes
  117. Studies On Compatibilization Of Recycled Polyethylene/Thermoplastic Starch Blends By Using Different Compatibilizer
  118. Liquid−Liquid Extraction of Linalool from Methyl Eugenol with 1-Ethyl-3-methylimidazolium Hydrogen Sulfate [EMIM][HSO4] Ionic Liquid
  119. Synthesis of Graphene Oxide Through Ultrasonic Assisted Electrochemical Exfoliation
  120. Special Issue on ISCMP 2018
  121. Synthesis and antiproliferative evaluation of some 1,4-naphthoquinone derivatives against human cervical cancer cells
  122. The influence of the grafted aryl groups on the solvation properties of the graphyne and graphdiyne - a MD study
  123. Electrochemical modification of platinum and glassy carbon surfaces with pyridine layers and their use as complexing agents for copper (II) ions
  124. Effect of Electrospinning Process on Total Antioxidant Activity of Electrospun Nanofibers Containing Grape Seed Extract
  125. Effect Of Thermal Treatment Of Trepel At Temperature Range 800-1200˚C
  126. Topical Issue on Agriculture
  127. The effect of Cladophora glomerata exudates on the amino acid composition of Cladophora fracta and Rhizoclonium sp.
  128. Influence of the Static Magnetic Field and Algal Extract on the Germination of Soybean Seeds
  129. The use of UV-induced fluorescence for the assessment of homogeneity of granular mixtures
  130. The use of microorganisms as bio-fertilizers in the cultivation of white lupine
  131. Lyophilized apples on flax oil and ethyl esters of flax oil - stability and antioxidant evaluation
  132. Production of phosphorus biofertilizer based on the renewable materials in large laboratory scale
  133. Human health risk assessment of potential toxic elements in paddy soil and rice (Oryza sativa) from Ugbawka fields, Enugu, Nigeria
  134. Recovery of phosphates(V) from wastewaters of different chemical composition
  135. Special Issue on the 4th Green Chemistry 2018
  136. Dead zone for hydrogenation of propylene reaction carried out on commercial catalyst pellets
  137. Improved thermally stable oligoetherols from 6-aminouracil, ethylene carbonate and boric acid
  138. The role of a chemical loop in removal of hazardous contaminants from coke oven wastewater during its treatment
  139. Combating paraben pollution in surface waters with a variety of photocatalyzed systems: Looking for the most efficient technology
  140. Special Issue on Chemistry Today for Tomorrow 2019
  141. Applying Discriminant and Cluster Analyses to Separate Allergenic from Non-allergenic Proteins
  142. Chemometric Expertise Of Clinical Monitoring Data Of Prolactinoma Patients
  143. Chemomertic Risk Assessment of Soil Pollution
  144. New composite sorbent for speciation analysis of soluble chromium in textiles
  145. Photocatalytic activity of NiFe2O4 and Zn0.5Ni0.5Fe2O4 modified by Eu(III) and Tb(III) for decomposition of Malachite Green
  146. Photophysical and antibacterial activity of light-activated quaternary eosin Y
  147. Spectral properties and biological activity of La(III) and Nd(III) Monensinates
  148. Special Issue on Monitoring, Risk Assessment and Sustainable Management for the Exposure to Environmental Toxins
  149. Soil organic carbon mineralization in relation to microbial dynamics in subtropical red soils dominated by differently sized aggregates
  150. A potential reusable fluorescent aptasensor based on magnetic nanoparticles for ochratoxin A analysis
  151. Special Issue on 13th JCC 2018
  152. Fluorescence study of 5-nitroisatin Schiff base immobilized on SBA-15 for sensing Fe3+
  153. Thermal and Morphology Properties of Cellulose Nanofiber from TEMPO-oxidized Lower part of Empty Fruit Bunches (LEFB)
  154. Encapsulation of Vitamin C in Sesame Liposomes: Computational and Experimental Studies
  155. A comparative study of the utilization of synthetic foaming agent and aluminum powder as pore-forming agents in lightweight geopolymer synthesis
  156. Synthesis of high surface area mesoporous silica SBA-15 by adjusting hydrothermal treatment time and the amount of polyvinyl alcohol
  157. Review of large-pore mesostructured cellular foam (MCF) silica and its applications
  158. Ion Exchange of Benzoate in Ni-Al-Benzoate Layered Double Hydroxide by Amoxicillin
  159. Synthesis And Characterization Of CoMo/Mordenite Catalyst For Hydrotreatment Of Lignin Compound Models
  160. Production of Biodiesel from Nyamplung (Calophyllum inophyllum L.) using Microwave with CaO Catalyst from Eggshell Waste: Optimization of Transesterification Process Parameters
  161. The Study of the Optical Properties of C60 Fullerene in Different Organic Solvents
  162. Composite Material Consisting of HKUST-1 and Indonesian Activated Natural Zeolite and its Application in CO2 Capture
  163. Topical Issue on Environmental Chemistry
  164. Ionic liquids modified cobalt/ZSM-5 as a highly efficient catalyst for enhancing the selectivity towards KA oil in the aerobic oxidation of cyclohexane
  165. Application of Thermal Resistant Gemini Surfactants in Highly Thixotropic Water-in-oil Drilling Fluid System
  166. Screening Study on Rheological Behavior and Phase Transition Point of Polymer-containing Fluids produced under the Oil Freezing Point Temperature
  167. The Chemical Softening Effect and Mechanism of Low Rank Coal Soaked in Alkaline Solution
  168. The Influence Of NO/O2 On The NOx Storage Properties Over A Pt-Ba-Ce/γ-Al2O3 Catalyst
  169. Special Issue on the International conference CosCI 2018
  170. Design of SiO2/TiO2 that Synergistically Increases The Hydrophobicity of Methyltrimethoxysilane Coated Glass
  171. Antidiabetes and Antioxidant agents from Clausena excavata root as medicinal plant of Myanmar
  172. Development of a Gold Immunochromatographic Assay Method Using Candida Biofilm Antigen as a Bioreceptor for Candidiasis in Rats
  173. Special Issue on Applied Biochemistry and Biotechnology 2019
  174. Adsorption of copper ions on Magnolia officinalis residues after solid-phase fermentation with Phanerochaete chrysosporium
  175. Erratum
  176. Erratum to: Sand Dune Characterization For Preparing Metallurgical Grade Silicon
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