Boiling Heat Transfer Coefficient Correlation Research Articles

Phenomenological correlations for two phase heat transfer and pressure drop performance of electrohydrodynamic horizontal convective boiling of dielectric fluids

EHD is an active heat transfer enhancement technique for convective boiling or condensing dielectric fluids whose performance varies widely in the literature for even the same geometry and fluids. As such, the performance of EHD convective boiling devices remains largely unpredictable. Two empirical EHD convective boiling heat transfer coefficient correlations exist in the literature with good performance when compared to their exact test dataset and geometry, however they have been shown to have poor correlations in predicting the performance for external test datasets. In this paper, a phenomenological approach is taken in the development of a new EHD convective boiling heat transfer coefficient correlation and a novel EHD convective boiling pressure drop correlation. The performance correlations are based on widely-used free-field convective boiling correlations for heat transfer coefficient and pressure drop with phenomenological enhancement factors based on the two phase flow pattern as predicted using the EHD two phase flow pattern map which accounts for the effect of electric field strength on flow pattern redistribution, as described in a previously published paper (Nangle-Smith and Cotton, 2018). A review of the EHD convective boiling experimental literature was conducted to determine confounding factors that can impact the large variance in the reported performance. Flow pattern and applied heat flux were identified as common parameters not maintained constant in the experimental data. Two datasets, including data from the present study, in which flow pattern and applied heat flux are maintained constant were used in the development of the performance correlations. Considerable improvement over previous EHD convective boiling performance correlations was found both in error and the physical significance of coefficients. The correlations were developed for thermodynamic qualities in the range of 20–60% below the onset of dryout or mist flow patterns and for applied heat fluxes < 30 kW/m2. Furthermore, test conditions in this study were chosen to focus on the dielectrophoretic effect and therefore studies with significant electrophoresis were not included. Thus, the correlation is limited to positive applied voltages, saturated flow boiling conditions, and field strengths below the onset of charge injection. The authors recommend this approach for EHD two phase performance correlation development as it is more mechanistic, is analogous to the state-of-the-art approaches for free-field two phase performance, and is likely to yield more accurate models as more experimental data becomes available.

Flow Boiling Heat Transfer of R134a in a Vertical Helically Coiled Tube

ABSTRACTThe boiling heat transfer characteristics of R134a in a helically coiled tube under high heat flux condition were investigated experimentally in present paper. The inner diameter and the coil diameter of the coil were 8 mm and 205 mm, respectively. Experiments were carried out with the heat flux in the range of 10–60 kW/m2, pressure 0.8–1.1 MPa, mass flux 195–400 kg/(m2 s) and vapor qualities 0.1–0.9. The results show that nucleate boiling plays a significant role even at high vapor quality. Inversely, the convective boiling was weakened in the high quality region under high heat flux conditions. The available boiling heat transfer coefficient correlations were compared with present experimental results. A new boiling heat transfer coefficient correlation for R134a in helically coiled tube was proposed based on the boiling mechanisms analysis. The new correlation was also proved to be applicable for high mass flux and low heat flux conditions.

Thermal performance of an internally finned two phase closed thermosyphon with refrigerant R134a: A combined experimental and numerical study

In this work, the heat transfer performance of a two phase closed internally finned thermosyphon has been studied by both experimental and numerical investigations. The working fluid considered for the experiments is R134a, which is compatible with copper material and is environment friendly. The thermosyphon comprises an evaporator of length 200 mm, adiabatic length 100 mm and a condenser section 200 mm long. Rectangular cross section fins are placed internally along the length of the condenser. These are of constant area and are 5 mm wide and 1 mm thick. The fill ratios considered in this study are 20, 35, 50, 65 and 80%. Experiments are carried out for different cooling water mass flow rates of 10, 30, and 40 LPH. A lumped parameter model is developed to validate the experimental results, wherein the heat transfer equations are coupled with the mass transfer equations and the resulting equations are discretized explicitly. A boiling heat transfer coefficient correlation is developed with the experimental data to calculate the thermal resistance at the evaporator wall. The thermosyphon is tested between power levels of 25 and 150 W. The heat transfer performance of the R134a charged internally finned thermosyphon is found to be superior to that of a water charged thermosyphon.

Saturated flow boiling heat transfer investigation for nanofluid in minichannel

In the present paper, a theoretical saturated flow boiling heat transfer coefficient correlation for nanofluid in minichannel has been proposed based on the contributions of convective boiling and nucleate boiling. For convective heat transfer, the absorbed heat amount of nanoparticles from fluid has been deduced by the fractal distribution theory. For nucleate boiling, the probability density equation of bubbles random growth is obtained on the basis of a Markov process. As a result, the nucleate flow boiling heat transfer coefficient formula is derived. In addition, three mass fractions for 0.2%, 0.5% and 1.0% Al2O3/H2O nanofluid are prepared by ultrasonic vibration and saturated flow boiling heat transfer coefficients in different rectangular minichannels with cross section 0.3×2mm, 0.6×2mm, 2×2mm are experimentally investigated. The results show that the heat transfer performance is enhanced after adding nanoparticles in base fluid and the average saturated flow boiling heat transfer coefficients of 0.2wt.%, 0.5wt.% and 1.0wt.% Al2O3/H2O nanofluid respectively increase by 11.2%, 15.4% and 18.7% compared with that of deionized water. Meanwhile, the average saturated flow boiling heat transfer coefficients for 1.0wt.% Al3O2/H2O nanofluid are increased by 21.1%, 26.2% in channels with cross section 0.3mm×2mm, 0.6mm×2mm compared with the average heat transfer coefficients in channels with cross section 2mm×2mm, which illustrates that the capillary effects are strengthened with the hydraulic diameter decreasing. Furthermore, a comparison is made between the experimental and theoretical data. The results show that the theoretical heat transfer model has a good universal prediction for nanofluid saturated flow boiling heat transfer in minichannel.

Assessment of subcooled boiling wall boundary correlations for two-fluid model CFD

Abstract An assessment of the heat and mass transfer wall boundary conditions used for subcooled boiling simulations with a CFD two-fluid model has been performed. This assessment was focused on the wall heat flux partitioning model using the state-of-the-art multidimensional Freon experimental data available in the literature. Various constitutive relations used to close the vapor generation rate at the heated wall were studied in order to obtain the best suited combination(s). The current study was restricted to vertical flows through pipe and annulus geometries. Two Freon data sets from the literature were considered: the first with R12 at about 2.6 MPa pressure and the second with R113 at 269 kPa pressure. In these data sets, the bubble diameter distribution measurements across the ducts were available. Bubble diameter estimation is the largest uncertainty in the boiling two-fluid model predictions and hence using the data with known bubble sizes allowed to focus on the assessment of other parameters to model vapor generation rate at the wall, in particular bubble nucleation site density and bubble departure frequency. From the parametric simulations with different combinations of the nucleation site density and frequency models, the discrepancy in obtaining a consistent frequency model for Freon became evident. The state-of-the-art frequency model under consideration is a function of the wall temperature which is estimated using a well-known empirical nucleate boiling heat transfer coefficient correlation. The frequency model provided inaccurate predictions in cases where the nucleate boiling heat transfer coefficient was inadequate to predict the wall superheat. The frequency model is now improved by using a more recent nucleate boiling heat transfer coefficient correlation with wider applicability, i.e., Freon. The simulations were carried out using the CFD code CFX (version 12). The Freon data used here corresponds to fluid-vapor density ratios ranging from 6 to 76. This assessment validated a consistent site density-departure frequency correlation combination for subcooled boiling simulations which has not been used so far for CFD simulations and an extension of the applicability of the correlation combination to high pressure steam–water conditions due to the favorable scaling of Freon physical properties.

수평미세관내 NH3비등열전달 특성

ABSTRACT:This paper is presented an experimental study of flow boiling heat transfer charac-teristics of ammonia, and is focused on pressure gradient and heat transfer coefficient of the refri-gerant flow inside horizontal small tube with inner diameter of 3.0mm and length of 2000mm. The direct heating method is applied for supplying heat to the refrigerant, where the test tube is uni-formly heated by electric current. The local heat transfer coefficients were obtained over a heat flux range of 20 to 80 kW/㎡, a mass flux range of 50 to 500 kg/㎡s, a saturation temperature range of 0 to 10°C, and quality up to 1.0. The pressure drops increase with increasing mass flux and heat flux, and with decreasing saturation temperature. The heat transfer coefficients increase with increasing mass flux and saturation temperature in middle and high quality region. And the local heat transfer coefficient increase with increasing heat flux in low quality region. The heat transfer coefficient of the experimental result was compared with six existing heat transfer coeffi-cient correlation. A new boiling heat transfer coefficient correlation based on the superposition model for ammonia in small tubes is developed average deviation of -0.17% and mean deviation of 10.85%.Keywords:Horizontal small tube(수평미세관), Ammonia(암모니아), Flow boiling(흐름비등), Heat transfer coefficient(열전달계수), Pressure drop(압력강하), Correlation(상관식)

Effect of nanoparticle size on nucleate pool boiling heat transfer of refrigerant/oil mixture with nanoparticles

Effect of nanoparticle size on nucleate pool boiling heat transfer of refrigerant/oil mixture with nanoparticles was investigated experimentally. For the preparation of the test fluid, refrigerant R113, ester oil VG68, and Cu nanoparticles with three different average diameters of 20, 50 and 80 nm were used. Experimental conditions include a saturation pressure of 101.3 kPa, heat fluxes from 10 to 80 kW m −2, nanoparticle concentrations in the nanoparticles/oil suspension from 0 to 30 wt%, and nanoparticles/oil suspension concentrations from 0 to 5 wt%. The experimental results indicate that the nucleate pool boiling heat transfer coefficient of R113/oil mixture with Cu nanoparticles is enhanced by a maximum of 23.8% with the decrease of nanoparticle size from 80 to 20 nm under the present experimental conditions, and the enhancement increases with the decrease of nanoparticles/oil suspension concentration or the increase of nanoparticles concentrations in the nanoparticles/oil suspension. A general nucleate pool boiling heat transfer coefficient correlation for refrigerant/oil mixture with nanoparticles is proposed, and it agrees with 93% of the existing experimental data of refrigerant/oil mixture with nanoparticles within a deviation of ±20%.

Experimental investigation on two-phase flow boiling heat transfer of five refrigerants in horizontal small tubes of 0.5, 1.5 and 3.0 mm inner diameters

An experimental investigation on two-phase flow boiling heat transfer with refrigerants of R-22, R-134a, R-410A, C 3H 8 and CO 2 in horizontal circular small tubes is presented. The experimental data were obtained over a heat flux range of 5–40 kW m −2, mass flux range of 50–600 kg m −2 s −1, saturation temperature range of 0–15 °C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 0.5, 1.5 and 3.0 mm, and lengths of 330, 1000, 1500, 2000 and 3000 mm. The experimental data were mapped on Wang et al. (1997) [5] and Wojtan et al. (2005) [6] flow pattern maps. The effects of mass flux, heat flux, saturation temperature and inner tube diameter on the heat transfer coefficient are reported. The experimental heat transfer coefficients were compared with some existing correlations. A new boiling heat transfer coefficient correlation that is based on a superposition model for refrigerants in small tubes is presented with 15.28% mean deviation and −0.48% average deviation.

Two-phase flow heat transfer of propane vaporization in horizontal minichannels

Experiments were performed on the convective boiling heat transfer in horizontal minichannels using propane. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm and lengths of 1000 mm and 2000 mm, respectively, and it was uniformly heated by applying an electric current directly to the tubes. Local heat transfer coefficients were obtained for a heat flux range of 5–20 kW m−2, a mass flux range of 50–400 kg m−2 s−1, saturation temperatures of 10, 5, and 0°C and quality ranges of up to 1.0. The nucleate boiling heat transfer contribution was predominant, particularly at the low quality region. Decreases in the heat transfer coefficient occurred at a lower vapor quality with a rise of heat flux and mass flux, and with a lower saturation temperature and inner tube diameter. Laminar flow appeared in the minichannel flows. A new boiling heat transfer coefficient correlation that is based on the superposition model for propane was developed with 8.27% mean deviation.

Heat transfer correlation for a refrigerant mixture in a vertical helical coil evaporator

The flow boiling heat transfer study of R-134a/R-290/R-600a refrigerant mixture is carried out in a vertical helical evaporator test section. The test section is immersed in an agitated ethylene glycol-water bath maintained at constant temperature. An aluminum test section with a height of 0.22 m, tube inside diameter of 6.35 mm, outside diameter of 8 mm and coil length of 8 m is used. The influences of various operating parameters such as evaporating temperature, bath temperature, and refrigerant composition on the heat transfer coefficient are investigated experimentally. Using the same experimental results the shell side flow boiling heat transfer coefficient correlation in helical evaporator is also evolved.

Single-phase and two-phase heat transfer characteristics of low temperature hybrid micro-channel/micro-jet impingement cooling module

This study examines the single-phase and two-phase cooling performance of a hybrid micro-channel/micro-jet impingement cooling scheme using HFE 7100 as working fluid. This scheme consists of supplying coolant from a series of jets that deposit liquid into the micro-channels. A single-phase numerical scheme that utilizes the k–ε turbulent model and a method for determining the extent of the laminarized wall layer shows very good predictions of measured wall temperatures. It is shown jet velocity has a profound influence on single-phase cooling performance. High jet velocities enable jet fluid to penetrate the axial micro-channel flow and produce a strong impingement effect at the wall. On the other hand, the influence of jets at low jet velocities is greatly compromised compared to the micro-channel flow. During nucleate boiling, vapor layer development along the micro-channel in the hybrid module is fundamentally different from that encountered in conventional micro-channels. Here, subcooled jet fluid produces repeated regions of bubble growth followed by bubble collapse, rather than the continuous growth common to conventional micro-channel flow. By reducing void fraction along the micro-channel, the hybrid scheme contributes greater wall temperature uniformity. Increasing subcooling and/or flow rate delay the onset of boiling to higher heat fluxes and higher wall temperatures, and also increase critical heat flux considerably. A nucleate boiling heat transfer coefficient correlation is developed that fits the present data with a mean absolute error of 6.10%.

Boiling heat transfer of R-22, R-134a, and CO 2 in horizontal smooth minichannels

This study examined convective boiling heat transfer in horizontal minichannels using R-22, R-134a, and CO 2. The local heat transfer coefficients were obtained for heat fluxes ranging from 10 to 40 kW m −2, mass fluxes ranging from 200 to 600 kg m −2 s −1, a saturation temperature of 10 °C, and quality up to 1.0. The test section was made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm, and a length of 2000 mm. The section was heated uniformly by applying an electric current to the tubes directly. Nucleate boiling heat transfer was the main contribution, particularly at the low quality region. An increasing and decreasing heat transfer coefficient occurred at the lower vapor quality with increasing heat flux and mass flux. The mean heat transfer coefficient ratio of R-22:R-134a:CO 2 was approximately 1.0:0.8:2.0. Laminar flow was observed in the minichannels. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants in minichannels was developed with a mean deviation of 11.21%.

Two-phase flow heat transfer of CO 2 vaporization in smooth horizontal minichannels

Experiments were performed on the convective boiling heat transfer in horizontal minichannels with CO 2. The test section is made of stainless steel tubes with inner diameters of 1.5 and 3.0 mm and with lengths of 2000 and 3000 mm, respectively, and it is uniformly heated by applying an electric current directly to the tubes. Local heat transfer coefficients were obtained for a heat flux range of 20–40 kW m −2, a mass flux range of 200–600 kg m −2 s −1, saturation temperatures of 10, 0, −5, and −10 °C and quality ranges of up to 1.0. Nucleate boiling heat transfer contribution was predominant, especially at low quality region. The reduction of heat transfer coefficient occurred at a lower vapor quality with a rise of heat flux, mass flux and saturation temperature, and with a smaller inner tube diameter. The experimental heat transfer coefficient of CO 2 is about three times higher than that of R-134a. Laminar flow appears in the minichannel flows. A new boiling heat transfer coefficient correlation that is based on the superposition model for CO 2 was developed with 8.41% mean deviation.

Forced convective boiling heat transfer of R-410A in horizontal minichannels

Convective boiling heat transfer experiments were performed in horizontal minichannels with binary mixture refrigerant, R-410A. The test section is made of stainless steel tubes with inner diameters of 1.5 mm and 3.0 mm and with lengths of 1500 mm and 3000 mm, respectively, and is uniformly heated by applying electric current directly to the tubes. Local heat transfer coefficients were obtained for a heat flux range of 10–30 kW m −2, a mass flux range of 300–600 kg m −2 s −1, and quality ranges of up to 1.0. The experimental results were mapped on Wang et al.'s (C.C. Wang, C.S. Chiang, D.C. Lu, Visual observation of two-phase flow pattern of R-22, R-134a, and R-407C in a 6.5-mm smooth tube, Experimental, Thermal and Fluid Science 15 (1997) 395–405) and Wojtan et al.'s (L. Wojtan, T. Ursenbacher, J.R. Thome, Investigation of flow boiling in horizontal tubes: part I – a new diabatic two-phase flow pattern map, International Journal of Heat and Mass Transfer 48 (2005) 2955–2969) flow pattern maps to observe the flow regimes. Laminar flow appears in flow with minichannels. A new boiling heat transfer coefficient correlation based on the superposition model for R-410A was developed with 11.20% mean deviation; it showed a good agreement between the measured data and the calculated heat transfer coefficients.