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Proceedings of the 22nd National and 11th International ISHMT-ASME Heat and Mass Transfer Conference December 28-31, 2013, IIT Kharagpur, India HMTC1300232 EXPERIMENTAL STUDY OF EFFECT OF ADDITIVES IN POOL BOILING HEAT TRANSFER Sameer S. Gajghate Dr. Daulatrao Aher College of Engineering Karad, Maharashtra, 415124 India [email protected] Anil R. Acharya Government College of Engineering Karad, Maharashtra, 415124 India [email protected] ABSTRACT The addition of additives to the water is known to enhance boiling heat transfer. In the present investigation, boiling heat transfer coefficients are measured for Nichrome wire, immersed in saturated water with & without additive. An additive used is ethyl alcohol with varying concentrations in the range of 0-700 ppm. Extensive experimentation of pool boiling is carried out above the critical heat flux. Boiling behavior i.e. bubble dynamics are observed at higher heat flux for nucleate boiling of water over wide ranges of concentration of additive in water. Results are encouraging and show that a small amount of surface active additive makes the nucleate boiling heat transfer coefficient considerably higher, and that there is an optimum additive concentration for higher heat fluxes. An optimum level of enhancement is observed up to a certain amount of additive 400 ppm in the tested range. Thereafter significant enhancement is not observed. This enhancement may be due to change in thermophysical properties i.e. mainly due to a reduction in surface tension of water in the presence of additive. The pool boiling phenomenon is recorded with camera to study behavior bubble as well as bubble size and its velocity. Here it is found that as Ethyl alcohol concentration increases in water, CHF (critical heat flux) is shifting towards the left in the pool boiling curve. Its maximum shifted at 400 ppm which means that as the concentration increases up to 0 -700 ppm in distilled water with additives Ethyl alcohol enhancement of heat transfer takes place at a low excess temperature. Additive promotes activation of nucleation sites; the bubbles appeared in a cluster mode; the lifetime of each bubble in the cluster is shorter than that of a single water bubble. The diameter of water bubble increases with increasing heat flux, whereas analysis of bubble growth in water with additive reveals the opposite effect: the detachment diameter of the bubble decreases with increasing heat flux. The kinetics of boiling was investigated by high-speed video recording. Boiling curves bubble behavior and the heat transfer mechanism for the surfactant solution are quite different from those of water with & without additive. Keywords- Surfactant, Pool boiling, additive, Surface Tension, Bubble behavior. NOMENCLATURE A ∆T σ q h hfg α Ra ρWire TWire Ashok T. Pise Government College of Engineering Karad, Maharashtra, 415124 India [email protected] Cross Sectional area of wire, m2 Excess Temperature, K Surface tension, N/m Heat flux, kW/m2 Boiling heat transfer coefficient, kW/ m2 K Latent heat, J/g Void Fraction Surface roughness, µ Resistivity, ohm-cm Wire Temperate, K INTRODUCTION There is a general need to increase the heat transfer rate in pool boiling applications for saving the energy required to phase change. Energy crises and global warming are forcing to exert more to save the energy from different applications. Hence the main motive here is to reduce the energy i.e. increases the heat transfer rate in pool boiling. Researchers are trying to find enhancement techniques in heat transfer for the boiling. The addition of surfactant or additive in the solution can be the cost effective technique and simple to handle. Some of the researchers had conducted the experiments on pool boiling enhancement-using additives. Author measured the surface tension of ethanol/water mixtures over the whole fractional range with and without the surface active agent. The boiling heat transfer coefficient, the onset of boiling and the critical heat flux were measured for water and ethanol/water mixtures, with and without the surface active agent, over a horizontal fine heated wire which is kept at a pressure of 0.1 MPa1. The experimentation was carried out in the whole range of the ethanol fraction and in a surfactant concentration varying from 0-5000 ppm for investigation the Bubble growth rate and boiling heat transfer is carried for different of concentration of ethyl alcohol–water mixture2. An experiment carried was carried out on nucleate boiling of aqueous solutions of Ethyl alcohol- water over relatively wide ranges of concentration and heat flux in pool boiling apparatus. The experimental results show that a small amount of surface active additive makes the nucleate boiling heat transfer coefficient h considerably higher, and that there is an optimum additive concentration for higher heat fluxes. Beyond the optimum point, further increase in additive concentration makes h lower3. The kinetics of boiling was investigated by high-speed video recording. Boiling curves for various concentrations were obtained and compared. The results show that the bubble behavior and the heat transfer mechanism for the surfactant solution are quite different from those of pure water. Specific features of boiling of non-ionic surfactant solutions were revealed4. Development of experimental technique for precise & systematic measurement of boiling curves under steady-state and transient conditions. Pool boiling experiments for good wetting fluids and fluids with a larger contact angle (FC-72, iso-propanol, water) yield single and reproducible boiling curves if the system is clean5. In saturated nucleate pool boiling of water, with constant wall heat flux q = 10 and 50 kW/m2, the captured images showed that the bubble shape is close to axially symmetric and vertically non-symmetric6. In nucleate pool boiling of dilute aqueous polymer solutions and compared with results for pure water. Solutes where Hydroxyethyl cellulose (HEC) of three molecular weights, poly acrylamide (PA) of two molecular weights, and acrylamide; solute concentrations ranged from 62- 500 ppm. Liquids were boiled at atmospheric pressure on horizontal nichrome plate. Results showed distinct differences in bubble size and dynamics, between polymeric and nonpolymeric liquids. The results produced by variations of concentrations and molecular weight appeared to be correlatable with the solution viscosity. The HEC is a surfactant but PA is not, so surface tension is believed to be only a minor variable7. The characteristics of deterioration in the heat transfer of mixtures have recently been clarified, but there are few reports on the heat transfer enhancement of binary mixtures. Here, the effects of surface-active agents in the boiling heat transfer were reported as a means of the heat transfer enhancement. This is the reason that surface tension is one of the important factors governing the boiling heat transfer. In this study, the effect of the surfactant concentration on surface tension was clarified in water and ethyl alcohol with a cationic surfactant as the fundamental study on boiling heat transfer enhancement in water. We clarified experimentally the effect of the surfactant on surface tension, the heat transfer coefficient, bubble velocity, bubble diameter, Leidenfrost point and the CHF. Here, the present surfactant was employed, because its surface tension is very small and its adsorption to a metal surface is excellent. EXPERIMENTAL METHOD Experimental Set Up The apparatus for experimental studies on pool boiling is shown in Fig. 1. It consists of cylindrical glass container housing (250mm X 110mm), the test heater and the heating coil for the initial heating of the water. The heater coil is directly connected to the mains (Auxiliary Heater R1, 1Kw) and the test heater (Nichrome wire, 0.3mm diameter & 10cm long) is connected to the mains via a dimmerstat (10 A, 230 V). An ammeter (range 0-10A) is connected in series while the voltmeter across it to read the current and voltage. The voltage selector switch is used to select the voltage range 100/200V. These controls are placed inside the control panel. K-type thermocouple is used to measure the temperature of nichrome wire (0-900ºC) which connected to Digital temperature indicator of 0-9999 ºC. To study the kinetics of vapor bubbles in pool boiling phenomena for water with and without surfactant a camera is fixed near to apparatus in such a way that boiling phenomenon can be recorded by camera to make observations in terms of bubble nucleation, growth and its departure. Electronic balance was used for the measurement of the mass of surfactants has least count of 1mg. Figure 1. EXPERIMENTAL SET UP 1. Glass Container 2. Wooden Platform 3. Auxiliary Heater (R1) 4. Test Heater (R2) 5. Thermometer 6. Thermocouple 7. Clay Lid 8. Nichrome Wire 9. Heater Connecting Cable 10. Digital Temperature Indicator 11.Control Panel 12.Ammeter 13.Voltage Range Selector Switch 14.Voltmeter 15.Dimmerstat 16.Electric Power Switch Test Procedure Various researchers have investigated a number of surfaceactive agents for the mass and heat transfer enhancement. The additive used here is Ethyl Alcohol. Ethyl Alcohol is an inorganic compound with the formula C2H6O. Ethyl Alcohol is a volatile, colorless liquid that has a slight odor. It burns with a smokeless blue flame that is not always visible in normal light. A water based solution for different ppm (parts per million) is prepared with Ethyl Alcohol viz 50, 100, 200, 300, 400, 500, 600 & 700 ppm. As the boiling heat transfer rate is very sensitive to the state of the heating surface, boiling of pure water was carried out until the reproducibility of the boiling curve became very good before beginning of each sets experiments with the addition of various amounts of additive. In the beginning, the glass container is cleaned with distilled water and then filled 2.5 litre distilled water in the container. One end of thermocouple is connected to test heater nichrome wire and is insulated properly and the other end is connected to the digital temperature indicator. Heater coil and test heater wire are connected across the studs and necessary electrical connections are made. It is confirmed that both the heaters are completely submerged in water. The water is heated by bulk heat to its Saturation temperature. Then the supply to nichrome wire heating is started and heat flux is adjusted by dimmerstat. Every moment is recorded by advanced Canon Camera with frame rate about 120fps. The rise in wire temperature, current and voltage at each position are measured carefully. The electric power is supplied gradually up to the point where nichrome wires break. As heating element is thin and long axial heat transfer due to conduction can be neglected. The heat flux released from the heating element to the liquid is controlled by adjusting the current supplied. A supplementary heater is installed for the purpose of bringing up the temperature of the liquid at the beginning of the experiment and maintains it at the boiling point of the test fluid during the period of operation. The procedure from the beginning is repeated by emptying the pool of distilled water and filling with aqueous surfactant of different concentrations. Every time nichrome wire is changed and thermocouple is attached. The pool temperature is measured by a calibrated thermometer. Boiling on the surface of the heating element can be illuminated, observed and photographed at the pool is of high class standard Borocil glass. 3.10 278.81 1 Ω. ∆Texcess is the difference between en the wire temperature and the bulk fluid temperature. The error on the boiling curve results from imprecision in the ammeter and voltmeter, it is too small to be seen the graph. It shows that the there is a sudden decrease in the current during the work; it means that at certain point heat flux decrease at a particular volt which can compare with the Nukiyama curve to study the boiling regimes8. A similar graph can be prepared for the different solution of water with & without surfactants. Figure 2. RAW EXPERIMENTAL DATA Comparative studies of results of surfactant were broadly discussed into two categories as boiling behavior and boiling curves. The boiling phenomenon mainly depends on physical properties of fluid that are density, surface tension and kinematic viscosity. The addition of a small amount of surfactant does not affect the density of the solution but it slightly increases the viscosity if surfactant factant is polymeric. Researchers esearchers measured the surface tension data with and a without surfactants in water, [See fig. 3.] This shows with an increase in surfactant concentration surface tension decreases. The enhancement of heat transfer is might be due to the depression of surface tension. The data collected during experimentation are tabulated in the form of graphs. The graphs are plotted for the heat transfer coefficient for water with and without varying concentration of surfactant and compare the results. The results are described as follows. Effects of Surfactants on Surface Tension The surface tension data with and without surfactant in the water is taken from the literature. The effect of surface tension of the water σ against temperature T is shown in the literature. The trend shows an increase in temperature surface tension decreases. The measurements of surface tension are carried out for different concentrations of Ethyl alcohol as a surfactant in pure water over a range of temperature 00–1200C. They found that the surface tension is decreased as the temperature increases with varying concentration10; it is found that at 400700 ppm concentration surface tension values fall nearer to zero, N/m which is shown in Fig. 3. 0.025 Surface tension (σ), N/m EXPERIMENTAL RESULTS As the work is in pool boiling it should be a comparative study of Nukiyama curve8, because it gives the extensive knowledge regarding the bubble regimes with varying heat flux & excess temperature. The extensive experimentation of pool boiling was carried for pure water with and without surfactant of varying concentrations of Ethyl Alcohol. From the obtained experimental data, results are plotted in terms of boiling curve as a heat flux vs. heater excess temperature. The raw data obtained from experiments is plotted in Fig. 2, the voltage drop across the nichrome wire was measured with a voltmeter, and the current was obtained from an ammeter (for deoinized water) were recorded after the circuit reached equilibrium. equilibrium The resistance across the nichrome rome wire was found using Ohm’s Law, and then the wire geometry was divided out to determine the resistivity of the wire in Ω-cm9. The nichrome n resistivity is linearly related to wire temperature erature by Eqn. E (1). 50ppm 200ppm 400ppm 600ppm 0.02 100ppm 300ppm 500ppm 700ppm 0.015 0.01 0.005 0 0 20 40 60 80 Temperature, °C 100 120 140 Figure 3. EFFECT OF TEMPERATURE AND CONCENTRATION OF ETHYL ALCOHOL ON SURFACE TENSION ON IN WATER10 Boiling Behavior Studies of the evolution of vapor bubbles in the pool boiling phenomena of water with and without surfactants were observed.. The growth of bubbles is one of the parameters determining the intensity of the heat transfer from a heated surface. The growth of the bubble in the liquid containing surfactants is affected by a number of specific factors. The pool boiling experiments are carried out under atmospheric pressure. In the present study, the height of the liquid phase over tthe heater is not less than 35 mm throughout all experiments. The bubble behavior is recorded at 120fps by the video camera. The typical stages of bubble growth analyzed for this study are shown in Fig. 4(a-k) & 5. Fig. 4(a-k) k) show typical pictures of pure water boiling on the Nichrome rome wire at heat fluxes 0.0186- 1.66 MW/m2 respectively. A population of bubbles was observed in the vicinity of the heated wire. The bubble dynamics for water are seen to depend on heat flux, similar to well well-known boiling visualization data. a) 0.0186 e) 0.255 b) 0.0186 c) 0.0651 d) 0.145 f) 0.392 g) 0.548 h) 0.743 i) 0.907 j) 1.280 k) 1.662 Figure 4. (a- k) PHOTO IMAGES OF BUBBLE OF PURE 2 WATER FOR DIFFERENT HEAT FLUXES (MW/m ) After the onset of nucleate boiling, the regime of single bubbles occurs close to the heated wall (Fig. 4.a). As the heat flux increases, bubble coalescence take place (Fig. 4.d). This phenomenon is more pronounced at a heat flux 0.392 MW/m2 (Fig. 4.f). For pure water, the average bubble size was observed to slightly increase with increasing heat flux. The bubbles have an irregular shape at all values of heat flux.The result obtained can be explained: for very low wall superheat the bubble departure is solely a function of the buoyancy and of the surface tension. For 50 ppm a) 6.34 For 200 ppm a) 6.37 For 300 ppm b) 38.1 b) 74.3 c) 74.0 c) 64.4 d) 93.4 d) 134.1 Velocity, m/s a) 1.74 For 100 ppm between detaching bubbles from wire and reaching the bubble up to free surface is measured in Windows movie maker and the distance between wire and free surface is measured in Adobe software. In Fig. 6 it is found that at various concentration with different heat flux the velocity decreases and after 400 ppm concentration velocity is slightly becomes constant, their no effect seems beyond 400 ppm. The diameter of bubble measured with the help of adobe photoshop (Fig. 7). The same procedure is repeated in three times for every concentration and average velocity & diameter is calculated. b) 93.4 c) 80.9 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 0.05 0 d) 134.4 Ethyl alcohol 0 100 200 300 400 500 600 700 Concentration, ppm Figure 6. EFFECT OF CONCENTRATION OF SURFACTANTS ON VELOCITY OF BUBBLES b) 95.9 c) 81.5 2.5 d) 11.8 Diameter, mm a) 6.68 For 400 ppm 2 Ethyl Alcohol 1.5 1 0.5 a) 6.79 For 500 ppm b) 75.8 c) 65.0 d) 134.8 0 0 100 200 300 400 Concentration, ppm 500 600 700 Figure 7. EFFECT OF CONCENTRATION OF SURFACTANTS ON BUBBLES DIAMETER b) 89.1 a) 6.37 For 700 ppm b) 74.3 c) 77.2 c) 94.2 d) 134.9 d) 79.8 a) 5.92 b) 89.8 c) 81.7 d) 100.3 Figure 5. PHOTO IMAGES OF BUBBLE DYNAMICS AT DIFFERENT HEAT FLUXES (kW/m2) Fig. 5. Shows the photographs of boiling of 50–700 ppm Ethyl Alcohol in pure water. As the surface temperature increases, the surface tension decreases (for most fluids), which should result in the decrease of the departure diameter. However, as the superheat increases, dynamic forces (i.e. Inertial forces) start dominating the bubble growth process and hence the bubble diameter increases with the surface temperature. A different trend is however observed in Ethyl alcohol which presents a sharp increase of the bubble departure diameter at low heat fluxes, but starts to decrease at higher heat fluxes.As compared to pure water boiling behaviour are different for aqueous ethyl alcohol for low heat flux. The approximate bubble velocity is measured using the software Windows movie maker and Adobe Photoshop 7.0 (Fig. 6). The time Fig. 7 show as the bubble diameter decreases with increasing concentration for higher heat flux, similarly its velocity also decreases it is due effect of surface tension of additive concentration in base fluid. Results show the difference of bubble diameter & velocity for the different additives in base fluid for higher heat flux. Boiling Curves Presence of Ethyl alcohol in the water, boiling phenomena shows violent incipient with larger and less distributed bubbles. Furthermore, the ethyl alcohol requires a higher superheat to reach the incipient boiling region, as depicted in Fig. 8. q, MW/m^2 a) 6.32 For 600 ppm 1.65 1.5 1.35 1.2 1.05 0.9 0.75 0.6 0.45 0.3 0.15 0 50ppm 100ppm 200ppm 300ppm 400ppm 500ppm 600ppm 700ppm water 0 25 50 75 100 125 150 175 200 225 250 275 300 325 ∆Texcess, ºC Figure 8. BOILING CURVES FOR VARYING CONENTRATION OF ETHYL ALCOHOL IN PURE WATER Conc. ppm 700 600 500 400 300 200 100 0 CHF Leidenfrost point 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 q, MW/m^2 Figure 9. EFFECT OF DIFFERENT CONCENTRATION ON CHF & LEIDENFROST POINT IN WATER WITH ETHYL ALCOHOL 110 100 ∆Texcess,°k 90 80 70 Ethyl Alcohol 60 50 0 100 200 300 400 500 600 700 Conc., ppm Figure 10. EFFECT OF CHF FOR DIFFERENT CONCENTRATION ON ∆TEXCESS IN WATER WITH ETHYL ALCOHOL However, once hfg is overcome, an “explosive boiling” occurs. This non-uniform boiling behavior seems to deteriorate the efficiency of the pool boiling heat transfer for Ethyl alcohol. The power required to reach the critical heat flux is low as compared to other surfactant solutions means heat required to reach the maximum heat flux is low at 400 ppm beyond this concentration heat flux increases with increasing excess temperature. This might be due to the solubility limit of surfactant in the solution is reached i.e. 400ppm. Fig. 11(a,b) shows the heat transfer co-efficient increases with increase of heat flux at low excess temperature for varying concentration of ethyl alcohol mixed with the water. 0.0035 0.003 h, MW/m^2.K 0.0025 0.002 50ppm 200ppm 400ppm 0.0015 0.001 0.0005 100ppm 300ppm 0 0 0.25 0.5 0.75 1 q, MW/m^2 a) 1.25 1.5 0.0035 0.003 h, MW/m^2K It is observed in figure that upto the solubility limit of concentration i.e. 400 ppm an increased in heat flux found lower excess temperature; beyond this concentration excess temperature goes on increasing. The Figures 9-10, are described in details of the concentration effect on CHF & Leidenfrost point with changing ∆Texcess, for ethyl alcohol. The figure shown optimum quantity of Ethyl alcohol can be selected for the boiling process in base fluid. At 400ppm the result was better for boiling process at low excess temperature with comparative water. Lower ∆Texcess was found at 400 ppm in fig. 10 which shows clearly heat transfer enhancement takes place in mixture of water with ethyl alcohol. 0.0025 0.002 500ppm 600ppm 700ppm water 0.0015 0.001 0.0005 0 0 0.25 0.5 0.75 1 1.25 1.5 1.75 q, MW/m^2 b) Figure 11. (a-b) HEAT TRANSFER COEFFICIENT VS. HEAT FLUX FOR VARIOUS CONCENTRATION OF ETHYL ALCOHOL IN WATER The pool boiling modes observed during the experimentation with and without surfactant are natural, nucleate, transition and film boiling is discussed. Boiling Curves, Natural Convection Boiling: In Natural convection there is insufficient vapor in contact with liquid phase to cause boiling at the saturation temperature; this condition is observed in Ethyl alcohol. As the excess temperature increases, bubble inceptions occur Ethyl alcohol which is due to free convection effects on fluid motion. As the water with different surfactants whose boiling point is different the heat flux varies as ∆Texcess to the 5/4 or 4/3 power fig. 11(a-b). At low temperature and with an increase in concentration at a varying flux range diameter of bubble decreases, also heat transfer co-efficient increases with increasing heat flux with a minimum temperature difference. Boiling Curves, Nucleate Boiling: In this regime, isolated bubbles are formed on nichrome wire with different sizes as the surface tension varies with different surfactants in the boiling with water; isolated bubbles separate from the surface with different bubble velocity. But these bubbles are dissipated in the liquid shortly after they separate from the surface. It happens due to increase in ∆Texcess of ethyl alcohol with different concentration in water. Bubble form in clusters on heater surface and the different CHF occur for different water with surfactants, the heat flux varies from 0.381- 1.28 MW/m2. With increasing heat flux Bubble velocity decreases and bubble diameter decreases with increasing concentration of different additives. Boiling Curves, Transition Boiling: In the transition boiling a continuous layer of vapor cover the heating surface and keeps the liquid from contacting the surface. The insulating effect of the vapor reduces the rate of heat transfer and the coefficient. As the temperature difference increases, the vapor film becomes thicker and eventually reaches a maximum thickness somewhere near Leidenfrost point and also the heat transfer coefficient slowly decreases. The transition from nucleate to film boiling involves a zone where the rapid vapor evolution blankets occur on the heated surface. At this stage of boiling, heat flux decreases due increased resistivity9 and hence low thermal conductivity (vapor act as insulation); therefore it observed that the heat flux value is low as compare to nucleate boiling stage i.e. 0.542– 0.908 MW/m2. The bubble velocity decreases as the bubble diameter increases and for a while heat transfer coefficient decreases with decreasing heat flux due low thermal conductivity with an increasing temperature difference. 1.75 Boiling Curves, Film Boiling: In this region the heater surface is completely covered by a continuous stable vapor film beginning from a Leidenfrost point till the end. The heat transfer rate increases with increasing excess temperature as a result of heat transfer from the heated surface to the liquid through the vapor film by radiation, which becomes significant at high temperatures. Due to high heat flux the bubble diameter is larger compared to other boiling phenomenon, also the velocity decreases for all different concentration of additives in the water. CONCLUSIONS The detailed studies of bubble dynamics in presence of surfactant in the water the following conclusions can be drawn. i) Bubble action is seen to be extremely chaotic, with extensive coalescence in the beginning for pure water. ii) Presence of the surfactant in the water quite different the boiling behavior. iii) The bubbles appeared in clusters form and its life-time is shorter than that of a single water bubble. They covered the surface of wire faster. iv) The detachment diameter of water bubbles increase with increasing heat flux, while the presence of surfactant the opposite effect was observed. v) At CHF point the boiling excess temperature ∆T becomes smaller upto surfactant concentration 400 ppm & the vapor bubbles are formed more easily. Also it promotes activation of nucleation sites in a clustered mode. vi) Presence of surfactant showed the enhancement in heat transfer coefficient increased up to the solubility limit. The addition of the surfactant beyond the solubility limit is not encouraging and on the other hand slightly decreases the heat transfer coefficient. vii) As additives in liquid evaporate on the heating surface, the vapor contains more amounts of the light component. This results in mass diffusion of the light component from the bulk. viii) The boiling curve shifted to the left side as the surfactant concentration increased. ix) It is observed beyond CHF the nichrome wire works even for radiation heat transfer; CHF and Leidenfrost point are at different heat flux for that of Platinum wire. Also the efforts are needed to find the boiling behavior in presence of surfactant in the different surface textures. UNCERTAINTY ANALYSIS Experimental measurements always involve uncertainties and error analysis is useful in assessing the scatter in data and identifying the source of any abnormal error. Here maximum uncertainties for 95% confidence level for heat flux at 100 ppm, 400 ppm and 600 ppm concentration of Ethyl alcohol in aqueous solution are obtained within limits. The voltmeter and ammeter used for experimentation are within ±1% accuracy and for area of wire uncertainty found within 0.11%. Method used here to evaluate uncertainty is proposed by J. P. Holman11. Error contributed due to Ethyl alcohol concentration is small and mentioned in the Table 1. TABLE . 1. ERROR ANALYSIS FOR HEAT FLUX AT VARIOUS CONCENTRATIONS OF AQUEOUS ETHYL ALCOHOL Ethyl Alcohol + water Heat Flux MW/m2 (max. error) Uncertainty 100 ppm 400 ppm 600 ppm 0.925 1.53 0.934 ±1.95% ±1.95% ±1.95% REFERENCES [1] Inoue, T., Teruya, Y., and Monde, M. 2004. “Enhancement of Pool Boiling Heat Transfer in Water & Ethanol/Water Mixtures With Surface Active Agent”. International Journal of Heat and Mass Transfer, Vol. 4, pp. 5555-5563. [2] Valent, V., and Afgan, N. H., 1973. “Bubble Growth Rate & Boiling Heat Transfer in Pool Boiling Of Ethyl Alcohol–Water Mixture”. Warme Stoffubertrag, Vol. 6, pp. 235–240. [3] Tzan, Y. L., and Yang, Y. M., 1990. “Experimental Study of Surfactant Effects on Pool Boiling Heat Transfer”. Journal of Heat Transfer, Vol. 112, pp. 207–212. [4] Hetsroni, G., Gurevich, M., Mosyak, A., Rozenblit, R., and Segal, Z. 2004. “Boiling Enhancement with Environmentally Acceptable Surfactants”. International Journal of Heat and Fluid Flow, Vol. 25, pp. 841-848. [5] Auracher, H., and Buchholz, M. 2005. “Experiments on the Fundamental Mechanisms of Boiling Heat Transfer”. ABCM Journal of the Brazilian Society of Mechanical Science & Engineering, Vol. XXVII, No. 1, January-March. [6] Hetsroni, G., Pogrebnyak, E., Sher, I., Mosyak, A. and Segal, Z. 2005. “Bubble Growth in Saturated Pool Boiling in Water & Surfactant Solution”. International Journal of Multiphase Flow, Vol. 32, October, pp. 159–182. [7] Kotchaphakdee, P. and Williams, Michael C. 1970. “Enhancement of Nucleate Pool Boiling with Polymeric Additives”. International Journal of Heat and Mass Transfer, Vol. 13, pp. 835-848. [8] Nukiyama, s. 1934. “The Maximum & Minimum Values of Heat Transmitted From Metal to Boiling Water Under Atmospheric Pressure”. Journal of Japan Society of mechanical Engineering, Vol. 37, pp. 367. (Translation: 1966, International Journal of Heat & mass transfer, Vol. 9, pp. 1419). [9] Barbuto, E., Gesecki, C., Lubers, A., Ryan, M., Shaughnessy, T., and Yaniglos, T. 2007. “The Dielectric Slide: the Group Nine Power Hour”. 06363 Transport Processes Laboratory, Carnegie Mellon University, 16th May. [10] Kaye & Laby, 1995. “Tables of Physical & Chemical Constants”, National physical Laboratory,16th Ed. http://www.kayelaby.npl.co.uk/gener al_physics/2_2/2_2_5.html [11] J. P. Holman, 1994.” Experimental Methods For Engineers”, McGraw- Hill, 8th Ed., p. no. 49- 57.