Correlations For Flow Boiling Heat Transfer Research Articles

Local flow boiling heat transfer characteristics in three-dimensional enhanced tubes

Experimental study on local flow boiling heat transfer characteristics in two three-dimensional dimple-grooved tubes (2EHT) and an equivalent smooth tube was performed. All the three test copper tubes have the same inner diameter of 11.07 mm and outer diameter of 12.7 mm. The working fluid was the near-azeotropic mixture, R410A. All test runs were conducted in a 2 m long horizontal tube-in-tube heat exchanger. Constant evaporation temperature was maintained at 10 °C when heat flux ranged from 32.6 kW/m2 to 37 kW/m2. Refrigerant quality varied from inlet 0.1 to outlet 0.9 and mass flux was controlled from 70 kg/(m2 s) to 150 kg/(m2 s). The enhanced surface areas of two 2EHT tubes are 1.02 and 1.03 times of the smooth tube, respectively. The local HTC results of saturate flow boiling were presented and compared with the existing correlations. Wall temperature was measured and critical heat flux effect on the tube-side evaporation was discussed. Local wall temperature results showed that the 2EHT tubes produce a better saturate evaporation at a relatively lower wall superheat. HTC increases with increasing heat flux when heat flux is smaller than CHF and decreases when heat flux is larger than CHF. Based on the local thermal properties, a new flow boiling heat transfer correlation for these 2EHT tubes is derived. The new correlation can predict all the experimental heat transfer coefficients within an error band of ±30% and 96.89% of test data within an error band of ±20%.

Saturated flow boiling heat transfer correlation for carbon dioxide for horizontal smooth tubes

Literature comprises fewer studies about flow boiling modelling of refrigerants for in tube flows. In addition, researches on two phase flow heat transfer are based on the mathematical models which were derived in a very limited operational condition and correlated for their own measurements. In this study, a new flow boiling model including the superposed effects of nucleate and convective boiling mechanisms is proposed through the minimization of the cumulative error between the proposed mathematical model and actual data by means of artificial cooperative search algorithm and applied to the database of R-744 (carbon dioxide), available from different studies in the literature. Predictions obtained from the proposed model have been compared with those of retained from the literature correlations developed for flow boiling in tubes. The comparison results indicate that the new model outperforms the literature correlations in terms of prediction accuracy. Results of the comparisons reveal that the proposed flow boiling mathematical model has a mean absolute relative error of 14.6% and predicts 76.7% of the experimental data within ±20.0%.

Saturated Flow Boiling Heat Transfer Correlation for Small Channels Based on R134a Experimental Data

In the literature, the modeling of saturated flow boiling heat transfer characteristics of R134a flowing through small channels is still questionable since it is based on very limited operational data. This study proposes a new evaporative heat transfer model based on R134a for micro- and macro-tubes. The proposed correlation is developed from 3594 data points, which are obtained from 19 different studies. Ranges of the database cover mass fluxes between 50.0 and 1500.0 kg/m2 s, heat fluxes between 3.0 and 150.0 kW/m2, hydraulic diameter between 0.5 and 13.84 mm, saturation temperatures between −8.8 and \({52.4 ^{\circ} {\rm C}}\), and vapor qualities up to 1.0. Findings of the proposed method are compared with those of the most quoted flow boiling heat transfer correlations developed for micro- and macro-tubes. Results of the comparison indicate that new method, which has a mean absolute deviation of 19.1 % and captures 66.7 and 83.2 % of the experimental data within ±20 and ±30 % error bands correspondingly, outperforms the available flow boiling correlations in the literature in terms of prediction accuracy.

Numerical model of a parallel flow minichannel evaporator with new flow boiling heat transfer correlation

In this paper, a distributed parameter (DP) numerical model with the new proposed flow boiling heat transfer correlation was established for parallel flow minichannel (PFMC) evaporator. DP model validation was made by comparing the measured values obtained on experimental studies, which were conducted under refrigerant mass flow rate range of 34.6–245.6 kg h−1 and evaporation pressure of 200–500 kPa. The effects of four different flow boiling heat transfer correlations on DP model performance were investigated. Results showed that the new correlation predicted 99% of experimental data in ± 30% error bands. Moreover, the DP model with the new correlation yielded the mean absolute error (MAE) of 1.5%, 9.1%, 18.8%, 14.2% and 19.8% in prediction of cooling capacity, outlet air temperature, refrigerant superheat, air side and refrigerant side pressure drop, respectively. The presented DP model can be implemented to evaluate the performance of PFMC evaporator, and therefore can save efforts on component and system design and optimization.

A note on the Chen correlation of saturated flow boiling heat transfer

The Chen (Ind. Eng. Chem. Process Des. Dev., 1966, 5(3): 322–329) correlation of saturated flow boiling heat transfer is one of the most influential flow boiling heat transfer correlations. It adopted the additive concept and incorporated the Reynolds number factor F and the suppression factor S. Chen presented F and S as the best-fit curves without any parametric equation. However, the parametric equations of F and S were widely used in citing the Chen work, among which some were not accurate, and some had typos in the original sources and then used by others. The objective of this paper is to point out the incorrect and inaccurate equations in the literature. For this purpose, the existing expressions of F and S in the available literature are presented and compared with the Chen best-fit curves. The work provides a reference for the correct use of the Chen correlation.

Correlations of Flow Boiling Heat Transfer of R-134a in Minichannels: Comparative Study

R-134a is one of the most widely used refrigerants, and minichannel refrigeration systems with R-134a have rapidly developed in many fields, such as home, automobile and aircraft air conditioning systems, for high efficiency operations to save energy and space. A number of correlations for flow boiling hear transfer have been proposed. There is some literature to evaluate existing correlations for R-134a flow boiling heat transfer in minichannels. However, they were only based on the authors own experimental data. Therefore, results are often not consistent, even controversial. Our efforts are devoted to develop a better flow boiling heat transfer correlation for R-134a in minichannels, and this paper presents the first part of our efforts: A comparative study of existing correlations for flow boiling hear transfer of R-134a in minichannels. From 9 published papers, 1158 data points of flow boiling heat transfer of R-134a in minichannels are collected. Eighteen flow boiling heat transfer correlations, including almost all well-known ones, are reviewed and compared with the data collected. It is found that no correlation has satisfactory accuracy. The best one has a mean absolute relative deviation above 36%. It is interesting to note that among the six best correlations, one was developed for pool boiling and two were developed for conventional channels, and most of correlations developed specially for minichannels do not work quite well. More efforts should be made to better understand the mechanism of flow boiling heat transfer in minichannels for developing better correlations. Key words: R-134a; Flow boiling; Heat transfer; Correlation; Minichannel

Measurement and Correlation of Flow-Boiling Heat Transfer of a R-410A/Oil Mixture Inside a 4.18 mm Straight Smooth Tube

Two-phase flow patterns and heat transfer characteristics of a R-410A/oil mixture flow boiling inside a horizontal straight smooth tube with the inside diameter of 4.18 mm were investigated experimentally. The flow pattern observations for a R-410A/oil mixture match well with the flow pattern map of Wojtan et al. (2005) by using the refrigerant-oil properties instead of pure-refrigerant properties. The test results show that the heat transfer coefficient of a R-410A/oil mixture increases with mass flux of a refrigerant-oil mixture; the presence of oil enhances the heat transfer by a maximum of 60% at the range of low and intermediate vapor qualities. There is a peak of local heat transfer coefficient at about 2%–5% nominal oil concentration at higher vapor qualities, and the peak shifts to lower nominal oil concentration with the increase of vapor qualities. Higher nominal oil concentration gives a more detrimental effect at high vapor qualities. A new correlation to predict the local heat transfer of a R-410A/oil mixture flow boiling inside the horizontal smooth tubes was developed based on flow patterns and local properties of a refrigerant-oil mixture. The new correlation agrees with 92% of the experimental data of R-410A/oil in a 4.18 mm horizontal smooth tube within a deviation of ±30%, and it agrees with 96% of the experimental data (Hu et al. 2008a) of a R-410A/oil mixture in a 6.34 mm horizontal smooth tube within a deviation of ±20%.

Effects of heat flux, mass flux, vapor quality, and saturation temperature on flow boiling heat transfer in microchannels

Flow boiling heat transfer with the refrigerants R-134a and R-245fa in copper microchannel cold plate evaporators is investigated. Arrays of microchannels of hydraulic diameter 1.09 and 0.54 mm are considered. The aspect ratio of the rectangular cross section of the channels in both test sections is 2.5. The heat transfer coefficient is measured as a function of local thermodynamic vapor quality in the range −0.2 to 0.9, at saturation temperatures ranging from 8 to 30 °C, mass flux from 20 to 350 kg m −2 s −1, and heat flux from 0 to 22 W cm −2. The heat transfer coefficient is found to vary significantly with heat flux and vapor quality, but only slightly with saturation pressure and mass flux for the range of values investigated. It was found that nucleate boiling dominates the heat transfer. In addition to discussing measurement results, several flow boiling heat transfer correlations are also assessed for applicability to the present experiments.

Subcooled flow boiling and microbubble emission boiling phenomena in a partially heated microchannel

A simultaneous visualization and measurement study has been carried out to investigate subcooled flow boiling and microbubble emission boiling (MEB) phenomena of deionized water in a partially heated Pyrex glass microchannel, having a hydraulic diameter of 155 μm, which was integrated with a Platinum microheater. Effects of mass flux, inlet water subcooling and surface condition of the microheater on subcooled flow boiling in microchannels are investigated. It is found that MEB occurred at high inlet subcoolings and at high heat fluxes, where vapor bubbles collapsed into microbubbles after contacting with the surrounding highly subcooled liquid. In the fully-developed MEB regime where the entire microheater was covered by MEB, the mass flux, the inlet water subcooling and the heater surface condition have only small effects on the boiling curves. The occurrence of MEB in microchannel can remove a large amount of heat flux, as high as 14.41 MW/m 2 at a mass flux of 883.8 kg/m 2 s, with only a moderate rise in wall temperature. Therefore, MEB is a very promising method for cooling of microelectronic chips. Heat transfer in the fully-developed MEB in the microchannel is presented, which is compared with existing subcooled flow boiling heat transfer correlations for macrochannels.

New prediction methods for CO 2 evaporation inside tubes: Part II—An updated general flow boiling heat transfer model based on flow patterns

Corresponding to the updated flow pattern map presented in Part I of this study, an updated general flow pattern based flow boiling heat transfer model was developed for CO 2 using the Cheng–Ribatski–Wojtan–Thome [L. Cheng, G. Ribatski, L. Wojtan, J.R. Thome, New flow boiling heat transfer model and flow pattern map for carbon dioxide evaporating inside horizontal tubes, Int. J. Heat Mass Transfer 49 (2006) 4082–4094; L. Cheng, G. Ribatski, L. Wojtan, J.R. Thome, Erratum to: “New flow boiling heat transfer model and flow pattern map for carbon dioxide evaporating inside tubes” [Heat Mass Transfer 49 (21–22) (2006) 4082–4094], Int. J. Heat Mass Transfer 50 (2007) 391] flow boiling heat transfer model as the starting basis. The flow boiling heat transfer correlation in the dryout region was updated. In addition, a new mist flow heat transfer correlation for CO 2 was developed based on the CO 2 data and a heat transfer method for bubbly flow was proposed for completeness sake. The updated general flow boiling heat transfer model for CO 2 covers all flow regimes and is applicable to a wider range of conditions for horizontal tubes: tube diameters from 0.6 to 10 mm, mass velocities from 50 to 1500 kg/m 2 s, heat fluxes from 1.8 to 46 kW/m 2 and saturation temperatures from −28 to 25 °C (reduced pressures from 0.21 to 0.87). The updated general flow boiling heat transfer model was compared to a new experimental database which contains 1124 data points (790 more than that in the previous model [Cheng et al., 2006, 2007]) in this study. Good agreement between the predicted and experimental data was found in general with 71.4% of the entire database and 83.2% of the database without the dryout and mist flow data predicted within ±30%. However, the predictions for the dryout and mist flow regions were less satisfactory due to the limited number of data points, the higher inaccuracy in such data, scatter in some data sets ranging up to 40%, significant discrepancies from one experimental study to another and the difficulties associated with predicting the inception and completion of dryout around the perimeter of the horizontal tubes.

Convective boiling heat transfer and two-phase flow characteristics inside a small horizontal helically coiled tubing once-through steam generator

The pressure drop and boiling heat transfer characteristics of steam-water two-phase flow were studied in a small horizontal helically coiled tubing once-through steam generator. The generator was constructed of a 9-mm ID 1Cr18Ni9Ti stainless steel tube with 292-mm coil diameter and 30-mm pitch. Experiments were performed in a range of steam qualities up to 0.95, system pressure 0.5–3.5 MPa, mass flux 236–943 kg/m 2s and heat flux 0–900 kW/m 2. A new two-phase frictional pressure drop correlation was obtained from the experimental data using Chisholm’s B-coefficient method. The boiling heat transfer was found to be dependent on both of mass flux and heat flux. This implies that both the nucleation mechanism and the convection mechanism have the same importance to forced convective boiling heat transfer in a small horizontal helically coiled tube over the full range of steam qualities (pre-critical heat flux qualities of 0.1–0.9), which is different from the situations in larger helically coiled tube where the convection mechanism dominates at qualities typically >0.1. Traditional single parameter Lockhart–Martinelli type correlations failed to satisfactorily correlate present experimental data, and in this paper a new flow boiling heat transfer correlation was proposed to better correlate the experimental data.

Comparison of Six Typical Correlations for Upward Flow Boiling Heat Transfer with Kerosene in a Vertical Smooth Tube

The present article is aimed at evaluating six typical flow boiling heat transfer correlations selected from the open literature with experimental results. The selected correlations are correlations of Chen, Shah, Gungor and Winterton, Liu and Winterton, Klimenko, and Kandlikar. Experiments of upward flow boiling heat transfer with kerosene in a vertical smooth tube were conducted. The test tube has a length of 2.5 m and its outer and inner diameters are 19 mm and 15 mm, respectively. The experiments were performed at an absolute atmospheric pressure of 3. The input heat flux ranged from 28.5 to 93.75 kW/m² and the mass fluxes were selected at 410, 610, and 810 kg/m² s, respectively. The experimental flow boiling heat transfer coefficients were compared with flow boiling heat transfer coefficients calculated with the six typical correlations. By comparison, the most suitable correlations are recommended for the calculation of flow boiling heat transfer coefficients with kerosene in a smooth tube.