Effect of graphene oxide coating on bubble dynamics and nucleate pool boiling heat transfer

Materials coating has been proved to be an effective mean to increase the number of active nucleating sites, and therefore generate more vapor bubbles and lead to better pool boiling heat transfer performance. In this work, graphene oxide (GO) is coated on a boiling surface by self-assembly method, to enhance critical heat flux (CHF). The pool boiling is carried out on a smooth copper surface to study the effect of GO coating using distilled water as the working fluid along with bubble dynamic visualization. GO coating facilitates bubble nucleation by providing numerous microscale cavities. The visualization investigation of bubble dynamic behavior shows that the CO-coated surface exhibits a higher bubble departure frequency, a smaller bubble departure diameter and smaller bubble diameters in the pool, indicating greatly enhanced heat transfer effects. Meanwhile, the GO-coated surface exhibited a smaller contact angle than the copper surface, revealing that surface becomes more hydrophilic after GO coating. Consequently, GO-coated surface with a coating time of 4 h provides a CHF of 224.3 W/cm² and a heat transfer coefficient (HTC) of 8.79 W/(cm²·K), representing an improvement of 94.0% in CHF and 83.5% in HTC compared to smooth copper surface.     

Influence of heat flux and pressure on heat transfer associated with fully developed nucleate pool boiling

Heat transfer in the pool boiling of helium is investigated experimentally. The dependence of the heat-transfer coefficient on the heat flux and pressure is determined for the fully developed nucleate boiling regime.Notation q heat flux, W/m² - T temperature differential, °K - heat-transfer coefficient, W/m²·°K - P pressure, N/m² - P_cr critical pressure, N/m² - P_* reference pressure, N/m² - n a power exponent - C a proportionality factor - , F₁ special functions Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 5, pp. 828–831, November, 1977.     

Heat transfer intensity at forced flow boiling of cryogenic liquids in tubes

A generalized correlation for heat transfer with forced flow boiling of cryogenic liquids (nitrogen, hydrogen and neon) in tubes is presented. The correlation describes, with a ± 35% accuracy, all known experimental data for vertical and horizontal channels (without stratified regimes) in the pressure range 0.9 – 22 bar, mass flow rates from 20 to 2200 kg m^?2 S^?1, and heat fluxes from 400 to 210 000 W m^?2. The boundary line between channels of a large and a small diameter has been established; a simple method of taking into account the higher heat transfer intensity in capillaries has been suggested.     

Influence of oil on nucleate pool boiling heat transfer of refrigerant on metal foam covers

Nucleate pool boiling heat transfer characteristics of refrigerant/oil mixture on metal foam covers were experimentally investigated. The refrigerant is R113, and the oil is VG68. The copper foams, having ppi (pores per inch) of 10 and 20, porosity from 90% to 98%, and thickness of 5 mm, are selected in this study. Experimental conditions include a saturation pressure of 101 kPa, oil concentrations from 0 to 5%, and heat fluxes from 0 to 80 kW m⁻². The experimental results indicate that the nucleate pool boiling heat transfer coefficient on copper foam covers is larger than that on flat heated surface by a maximum of 160% under the present experimental conditions; the presence of oil deteriorates the nucleate pool boiling heat transfer on copper foam covers by a maximum of 15% under the present experimental conditions, and the deterioration of oil on nucleate pool boiling heat transfer on copper foam covers is lower than that on a flat heated surface. A correlation for predicting the nucleate pool boiling heat transfer coefficient of refrigerant/oil mixture on copper foam cover is developed, and it agrees with 95% of the experimental data within a deviation of ±20%.     

Effect of gravity on pool boiling heat transfer on thermal spray coating

This study deals with heat transfer enhancement surface manufactured by thermal spraying. Two thermal spraying methods using copper as a coating material, wire flame spraying (WFS) and vacuum plasma spraying (VPS), were applied to the outside of copper cylinder with 20 mm OD. The surface structure by WFS was denser than that by VPS. The effect of gravity on boiling heat transfer coeffcient and wall superheat at the onset of boiling were experimentally evaluated under micro- and hyper-gravity condition during a parabolic trajectory flight of an airplane. Pool boiling experiments in saturated liquid of HCFC123 were carried out for heat fluxes between 1.0 and 160 kW/m² and saturated temperature of 30 °C. As a result, the surface by VPS produced higher heat transfer coefficient and lower superheat at the onset of boiling under microgravity. For the smooth surface, the effect of gravity on boiling heat transfer coefficient was a little. For the coating, a large difference in heat transfer coefficient to gravity was observed in the moderate heat flux range. The heat transfer coefficinet decreased as gravity changed from the normal to hypergravity, and was improved as gravity changed from the hyperto microgravity. The difference in heat transfer coefficient between the normal and microgravity was a little. Heat transfer enhancement factor was kept over the experimental range of heat flux. It can be said that boiling behavior on thermal spray coating might be influenced by flow convection velocity.     

Influence of thermophysical properties on pool boiling heat transfer of refrigerants

The correct prediction of the heat transfer performance of the boiling liquid within the evaporator of a refrigeration unit is one of the essential features for the successful operation of the whole unit. A theoretically consistent calculation method for the heat transfer coefficient α in nucleate boiling, which should be based on the physical phenomena connected with vapour bubbles growing, departing and sliding on the wall and with the interactions of bubbles and of neighbouring nucleation sites within the microstructure of the heating surface, does not yet exist, despite the increasing number of papers on the subject in the recent past. Instead, the predictive methods for α available at present are empirical or semiempirical, especially for heat transfer conditions relevant in practice. Many of these correlations have been established in the form of power laws in which the relative influences of the main groups of variables on α are treated by separate factors. One of these may stand for the influence of the thermophysical properties of the boiling liquid or these properties will be included in several of the factors.New experimental results are presented for pool boiling heat transfer from a single horizontal copper tube (8 mm OD) to HFC-refrigerants (R32, 125, 134a, 143a, 152a, 227ea) and hydrocarbons (propane, i-butane). The results are compared to experimental data from the literature, and methods are discussed, how to incorporate the data in semiempirical correlations to describe the influence of the thermophysical properties of the fluids on the heat transfer performance.     

The influence of electric field on heat transfer in a boiling cryogenic liquid

An experimental technique to investigate how an electric field affects heat transfer in boiling nitrogen is described. Experiments were performed in natural convection and nucleate boiling zones using cylindrical surfaces to simulate wires conducting a current.     

沸腾表面对液氮临界热流密度的影响实验

采用液氮作为沸腾工质,通过可视化液氮沸腾实验台,对不同材料和直径的沸腾表面在液氮中进行相关稳态沸腾实验研究,总结分析沸腾表面材料、表面直径对临界热流密度及其对应过热度的影响规律.     

Review on pool boiling heat transfer of carbon dioxide

Although application of carbon dioxide as working fluid in many fields of refrigeration technology has been recommended very often in the recent past, the data on nucleate boiling heat transfer of carbon dioxide in free convection are very scarce in the open literature and new investigations are almost entirely focussed on forced convective flow boiling. In the interpretation of the respective results, heat transfer to carbon dioxide is often characterized as being superior to other refrigerants due to the outstandingly favourable thermophysical properties of carbon dioxide for boiling heat transfer. Different from this view, the discussion of recent results on pool boiling heat transfer of carbon dioxide in this review demonstrates that the high heat transfer coefficients measured for carbon dioxide in comparison to hydrocarbon or halocarbon refrigerants are mainly due to the fact that application of carbon dioxide is mostly envisaged for conditions where reduced saturation pressure p*=p_s/p_c (p_c, critical pressure) is higher than for common refrigerants.

In the first part of the review, the three main influences—by heat flux, saturation pressure and fluid properties—on pool boiling of carbon dioxide are discussed using recent measurements for CO₂ by Kotthoff et al. [S. Kotthoff, U. Chandra, D. Gorenflo, A. Luke, New measurements of pool boiling heat transfer for carbon dioxide in a wide temperature range, Proceedings of the Sixth IIR-Gustav Lorentzen Conference, Glasgow, 2004 [paper 2/A/3.30]; see also S. Kotthoff, U. Chandra, D. Gorenflo, Neue Messungen zum Behältersieden von Kohlendioxid in einem grösseren Temperaturbereich, DKV-Tagungsbericht 22 (2004) [Bd.II. 1] 233–256 and other organic substances (Gorenflo et al.) [D. Gorenflo, S. Kotthoff, U. Chandra, New measurements of pool boiling heat transfer with hydrocarbons and other organics for update of VDI—Heat Atlas calculation method, Proceedings of the Sixth IIR-Gustav Lorentzen Conference, Glasgow, 2004 [paper 1/C/1.00]; Kotthoff and Gorenflo, [S. Kotthoff, D. Gorenflo, Influence of the fluid on pool boiling heat transfer of refrigerants and other organic substances, Proceedings of the IIR-Commission B1 Conference, Vicenza, 2005 [paper #TP-98]. In the second part, a comparison is given with the few former data available and with new results of Loebl and Kraus [S. Loebl, W.E. Kraus, Pool boiling heat transfer of carbon dioxide on a horizontal tube, Proceedings of the Sixth IIR-Gustav Lorentzen Conference, Glasgow, 2004 [paper 1/A/1.20]; S. Loebl, W.E. Kraus, Zum Wärmeübergang bei der Verdampfung von Kohlendioxid am horizontalen Rohr, DKV-Tagungsbericht 22 (2004) [Bd.II.1] 219–232 on the influence of the heating wall (material and surface roughness). Finally, analogies between nucleate pool boiling and new flow boiling data are shown for those domains of flow boiling in which nucleation provides the dominant contribution to heat transfer and convective effects are of secondary importance.     

Experimental investigation of heat transfer in boiling of some cryogenic liquids and condensation of their vapors

The results of an experimental investigation of heat transfer in the boiling and condensation of nitric oxide, carbon monoxide, and boron trifluoride are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 3, pp. 486–490, September, 1977.     

Critical heat fluxes in the pool boiling of liquids at reduced pressure

The authors report the results of a study of the critical heat fluxes and boiling mechanism of certain liquids at reduced pressures.     

Effect of cylindrical heater dimensions on critical heat fluxes during boiling of cryogenic liquids

Experimental data on critical heat fluxes during cryogenic liquid boiling (helium and nitrogen) on cylindrical heaters are presented for a wide pressure range (45–760 mm Hg). The effect of heater dimensions (diameter, length and wall thickness) on critical heat fluxes is studied. The data on the relation between this effect and heater material and orientation are obtained.     

Effect of CuO nanolubricant on R134a pool boiling heat transfer

This paper quantifies the influence of CuO nanoparticles on the boiling performance of R134a/polyolester mixtures on a roughened, horizontal, flat surface. A lubricant based nanofluid (nanolubricant) was made with a synthetic ester and CuO particles. For the 0.5% nanolubricant mass fraction, the nanoparticles caused a heat transfer enhancement relative to the heat transfer of pure R134a/polyolester (99.5/0.5) of between 50% and 275%. A smaller enhancement was observed for the R134a/nanolubricant (99/1) mixture, which had a heat flux that was on average 19% larger than that of the R134a/polyolester (99/1) mixture. Further increase in the nanolubricant mass fraction to 2% resulted in a still smaller boiling heat transfer improvement of approximately 12% on average. Thermal conductivity measurements and a refrigerant/lubricant mixture pool-boiling model were used to suggest that increased thermal conductivity is responsible for only a small portion of the heat transfer enhancement due to nanoparticles.     

Effect of brief thermal pulses on intensity of heat liberation in helium boiling

Results are offered from a study of heat liberation in boiling of liquid helium upon a heated wall under impulsive thermal action conditions.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 3, pp. 373–376, September, 1987.     

Pool boiling heat transfer at finned tubes: influence of surface roughness and shape of the fins

Pool boiling heat transfer from finned tubes with different shapes of fins (trapezoid-shaped, T-shaped, or Y-shaped) to various hydrocarbons and partly fluorinated hydrocarbons has been investigated at the Laboratorium für Wärme- und Kältetechnik, Universität-GH Paderborn during the recent past. Compared to corresponding measurements on plain tubes, heat transfer on traditionally finned tubes with trapezoid-shaped fins is considerably improved, and even better results are achieved with T-shaped or Y-shaped fins. The influences of the macrostructure (i.e. fin geometry) or microstructure (i.e. surface roughness) on the heat transfer coefficient have been studied separately, in order to evaluate the improvement of heat transfer by either influence.     

The influence of three-dimensional capillary-porous coatings on heat transfer at liquid boiling

The process of heat transfer at pool boiling of liquid (Freon R21) on tubes with three-dimensional plasma-deposited capillary-porous coatings of various thicknesses has been experimentally studied. Comparative analysis of experimental data showed that the heat transfer coefficient for a heater tube with a 500-μm-thick porous coating is more than twice as large as that in liquid boiling on an otherwise similar uncoated tube. At the same time, no intensification of heat exchange in the regime of bubble boiling is observed on a tube with a 100-μm-thick porous coating.     

Rheological and thermal properties of the surface layer of liquids

A grid model of the surface liquid layer at the boundary with the gas and its rheological and thermophysical properties (temperature dependence of the surface tension and surface heat capacity) have been described. It has been obtained that the mole heat capacity of the surface layer is nearly the same (5.6 J/(mole·K)) for many liquid metals. It has been shown that for calculation of the rheological properties it is expedient to use the Kelvin model. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 5, pp. 160–163, September–October, 2005.     

Experimental correlation of pool boiling heat transfer for HFC134a on enhanced tubes: Turbo-E

The objectives of this paper are to study the heat transfer characteristics for enhanced surface tubes in the pool boiling and to provide a guideline for the design conditions for the evaporator using HFC134a. The shape of tube surfaces, the wall superheat, and the saturation temperature are considered as the key parameters. Copper tubes (d_o = 19.05 mm) are treated with different helix angles and the saturation temperatures are controlled from 3 to 16 °C. It is found that the pool boiling heat transfer coefficient decreases with increasing the wall superheat. It is also found that boiling heat transfer coefficients for Turbo-II and Turbo-III are 1.5–3.0 times and 1.2–2.0 times higher than that for Turbo-I without the helix angle, respectively. The higher heat transfer performance from Turbo-II and Turbo-III can be explained by the “bubble detention” phenomenon on the surface without the helix angle for the Turbo-I. The experimental correlations for the pool boiling heat transfer on the present enhanced tubes without (Type I) and with the helix angle (Type II and Type III) are developed with the error bands of ±30%, respectively.