CO2 and propane blends: Experiments and assessment of predictive methods for flow boiling in horizontal tubes (original) (raw)
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Flow boiling heat transfer of propane in 1.0 mm tube
Experimental Thermal and Fluid Science
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2012
Flow boiling heat transfer characteristics of CO 2 with and without oil were investigated experimentally in horizontal smooth and enhanced tubes with an inner diameter of 11.2 mm. The visualization of flow pattern was also performed to provide the detailed attributes of the nucleate and the convective boiling heat transfer. In order to investigate the effect of the miscible oil on the heat transfer of CO 2 , POE (polyolester) RENSIO C85E oil is added to give an oil circulation rate (OCR) between 0.5 % and 2 %. Results are compared with those of pure CO 2. The experimental conditions include evaporation temperatures of-15 °C, mass fluxes from 40 to 200 kg/m 2 s, heat fluxes from 0.5 to 10 kW/m 2 , and vapor qualities from 0.1 to 0.8. Oil generally deteriorates the heat transfer coefficient of pure CO 2. The reduction in heat transfer coefficient is most apparent at low vapor qualities, 0.1 to 0.4, and at low mass fluxes, 100 and 200 kg/m 2. It is caused by the suppression of nucleate boiling due to increased surface tension. At conditions where the convective boiling contribution is dominant, vapor qualities above 0.5, oil increases heat transfer coefficients. Through visualization, it is shown that the wetted area on the perimeter of inner tube is enhanced due to formation of foaming in the smooth tube. However, such enhancement of heat transfer due to forming is negligible in the enhanced tube, because the enhanced factor due to micro-finned structures is dominant.
Void Fraction of Flow Boiling with Propane in Circular Horizontal Tube
International Journal of Technology, 2016
An investigation into flow boiling void fraction was conducted to observe its characteristics and to develop a new correlation of void fraction based on the separated model. The study used a natural refrigerant of R-290, flowed in a horizontal tube of 7.6 mm inner diameter under experimental conditions of 3.7 to 9.6 o C saturation temperature, 10 to 25 kW/m 2 heat flux, and 185 to 445 kg/m 2 s mass flux. The void fraction, calculated by the present experimental data, was used for comparison with 31 existing correlations, including model types as follows: homogeneous, slip ratio, Kαh correlation, drift flux, and a model based on the Lockhart-Martinelli correlation (Xtt). A new void fraction correlation, as a function of liquid and vapor Reynolds numbers, was proposed, based on the data. The measured pressure drop was compared with some pressure drop correlations that use the newly developed void fraction combination. The best prediction was shown by the homogeneous model.
A Comparative Analysis of Two-Phase Flow Boiling Heat Transfer Coefficient and Correlations for Hydrocarbons and Ethanol, 2023
This study will present a comprehensive review of the two-phase flow boiling heat transfer coefficient of hydrocarbons such propane (R- 290), butane (R-600) and iso-butane (R-600a) and ethanol at various experimental conditions. Studying the multiphase flow heat transfer coefficient has a crucial importance for many heat transfer equipment to achieve higher efficiency for more compact design and cost reduction. One reason behind choosing hydrocarbons as refrigerants in this study is because hydrocarbons have zero ozone depletion potential (ODP=0) and insignificant direct global warming potential (GWP = 3). Moreover, thermodynamic and thermophysical characteristics of hydrocarbons qualify them to be a strong candidate for more heat transfer applications. Initially, by constructing a database for the working fluids from various experimental work available in the literature. The current data that this study has collected for the flow boiling of spans wide ranges of parameters, such as: mass flux, heat flux, operating pressure, and saturation temperature, etc. Furthermore, by comparing the experimental multiphase heat transfer coefficient database with the anticipated values of each correlation, the prediction performance of 26 correlations found in the literature was assessed. This study leads to the selection of the best prediction method based on the minimum deviation of predicted results from the experimental database provided by calculated mean absolute error (MAE) from the assessed correlations. The findings of this study can also be useful in the development of more accurate correlation methods for these fluids and improve the prediction of their flow boiling characteristics.
Proceedings of the 4th World Congress on Momentum, Heat and Mass Transfer, 2019
In order to design evaporators for the CO2 thermal systems effectively, it is essential to understand the fundamentals and mechanisms of flow boiling heat transfer, flow patterns and two-phase flow characteristics of CO2 inside horizontal tubes including both the macro-and micro-channels. The proper prediction models for CO2 flow boiling heat transfer should be relevant to the physical mechanisms and corresponding flow patterns. This paper presents a comprehensive review of flow boiling heat transfer and two-phase flow of CO2 characteristics and their prediction methods. First, the review addresses the extensive experimental studies on flow boiling heat transfer and two-phase flow in macro-channels and micro-channels. Then, The studies of CO2 two-phase flow patterns are summarized. Furthermore, the effects of oil on the flow boiling heat transfer and two-phase pressure drops are analyzed. The generalized mechanistic models for flow boiling heat transfer and two-phase pressure drops of CO2 and a new flow pattern map specially for CO2, which cover both macro-and micro-channels developed by Cheng et al. are presented and compared to the experimental data in the literature. It has been proved that the models and flow maps favorably agree with the experimental data. In the application aspect, comparison of simulation results and the experimental data in the real thermal systems are presented.
International Journal of Heat and Mass Transfer, 2011
The present paper is part of a research program on two-phase flows and heat transfer studies in tube bundles. An experimental study was carried out to analyse the void fraction for vertical two-phase flows. Boiling across a horizontal tube bundle for three hydrocarbons (n-pentane, propane and iso-butane) under saturated conditions is investigated. The experiments were performed on a tube bundle with 45 plain copper tubes of 19.05 mm outside diameter in a staggered configuration with a pitch to diameter ratio of 1.33. An optical probe has been developed to determine the local void fraction at the minimum cross section between the tubes. The void fraction for the three hydrocarbons was found to be significantly less than the homogeneous prediction, and correlated well with the Zuber and Findlay (1965) model. A statistical analysis using Probability Density Functions (PDF) was performed to characterise the flow regimes. Two different flow regimes have been identified in the bundle, namely a "bubbly" and an "annular-dispersed" flow. A transition zone was evidenced by analysing the bubble size distribution. A comparison with the only preexisting map, established for adiabatic air-water flow, shows that the transitions between the flow regimes do not correspond to our results in boiling case.
International Journal of Refrigeration, 2007
Flow boiling heat transfer coefficient, pressure drop, and flow pattern are investigated in the horizontal smooth tube of 6.1 mm inner diameter for CO 2 , R410A, and R22. Flow boiling heat transfer coefficients are measured at the constant wall temperature conditions, while pressure drop measurement and flow visualization are carried out at adiabatic conditions. This research is performed at evaporation temperatures of À15 and À30 C, mass flux from 100 to 400 kg m À2 s À1 , and heat flux from 5 to 15 kW m À2 for vapor qualities ranging from 0.1 to 0.8. The measured R410A heat transfer coefficients are compared to other published data. The comparison of heat transfer coefficients for CO 2 , R410A, and R22 is presented at various heat fluxes, mass fluxes, and evaporation temperatures. The difference of coefficients for each refrigerant is explained with the Gungor and Winterton [K.E. Gungor, R.H.S. Winterton, A general correlation for flow boiling in tubes and annuli, Int. J. Heat Mass Transfer 29 (1986) 351e358] correlation based on the thermophysical properties of refrigerants. The Wattelet et al. A general correlation for flow boiling in tubes and annuli, Int. J. Heat Mass Transfer 29 (1986) 351e358] correlations give the best agreement with the measured heat transfer coefficients for CO 2 and R410A. Pressure drop for CO 2 , R410A, and R22 at various mass fluxes, evaporation temperatures and qualities is presented in this paper. The Müller-Steinhagen and Heck [H. Müller-Steinhagen, K. Heck, A simple friction pressure drop correlation for two-phase flow in pipes, Chem. Eng. Process. 20 (1986) 297e308], and Friedel [L. Friedel, Improved friction pressure correlations for horizontal and vertical two-phase pipe flow, in: The European Two-Phase Flow Group Meeting, Ispra, Italy, 1979 (paper E2)] correlation can predict most of the measured pressure drop within the range of AE30%. The relation between pressure drop and properties for each refrigerant is described by applying the Müller-Steinhagen and Heck correlation. The observed two-phase flow patterns for CO 2 and R410A are presented and compared with flow pattern maps. Most of the flow patterns can be determined by the Weisman et al. [J. Weisman, D. Duncan, J. Gibson, T. Crawford, Effect of fluid properties and pipe diameter on two-phase flow patterns in horizontal lines, Int. J. Multiphase Flow 5 (1979) 437e462] flow pattern map.
Flow boiling heat transfer coefficient of R-134a/R-290/R-600a mixture in a smooth horizontal tube
Thermal Science, 2008
(91%/4.068%/4.932% by mass) re frig er ant mix ture has been car ried out in a var ied heat flux con di tion us ing a tube-in-tube coun ter-flow test sec tion. The boil ing heat trans fer co ef fi cients at tem per a tures be tween -5 and 5 °C for mass flow rates varying from 3 to 5 g/s were ex per i men tally ar rived. Ac e tone is used as hot fluid, which flows in the outer tube of di am e ter 28.57 mm, while the test fluid flows in the in ner tube of di am e ter 9.52 mm. By reg u lat ing the ac e tone flow rate and its en try tem pera ture, dif fer ent heat flux con di tions be tween 2 and 8 kW/m 2 were main tained. The pres sure of the re frig er ant was main tained at 3.5, 4, and 5 bar. Flow pat tern maps con structed for the con sid ered op er at ing con di tions in di cated that the flow was pre dom i nantly strat i fied and strat i fied wavy. The heat trans fer co ef fi cient was found to vary be tween 500 and 2200 W/m 2 K. The ef fect of nu cle ate boil ing pre vailing even at high va por qual ity in a low mass and heat flux ap pli ca tion is highlighted. The com par i son of ex per i men tal re sults with the fa mil iar cor re la tions showed that the cor re la tions over pre dict the heat trans fer co ef fi cients of this mixture.
ENHANCEMENT AND PREDICTION OF FLOW BOILING HEAT
This paper presents an experimental study on heat transfer augmentation during convective boiling of R134a inside a 15.9 mm ID horizontal tube containing twisted-tape inserts. The use of twisted-tape inserts is a heat transfer enhancement technique applied on heat exchangers over more than one century ago. However, the heat transfer augmentation comes together with pressure drop increment, impacting the pumping power and, consequently, the system efficiency. Moreover, until now it is not clear when the effects on the heat exchanger efficiency of the heat transfer enhancement overcomes pressure drop penalties. In the present study, pressure drop and heat transfer coefficient experiments were performed. Experimental results were obtained during flow boiling of R134a for twistedtape ratios of 3, 4, 9 and 14, mass velocities ranging from 75 to 200 kg / m2 s, heat flux of 10 kW / m2 and saturation temperatures of 5 and 15 °C. The results obtained lead to the conclusion that higher heat transfer rates can be achieved using twisted-tape inserts at the expense of a reasonable pressure drop. In addition, a new correlation to predict the heat transfer coefficients during two-phase flow inside tubes containing twisted-tape inserts is proposed. The performance of the correlation can be deemed adequate, considering that it compares well with experimental results of different authors.