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Hiroshi Honda - One of the best experts on this subject based on the ideXlab platform.
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prediction of evaporation heat transfer coefficient based on gas liquid two phase Annular Flow Regime in horizontal microfin tubes
Applied Thermal Engineering, 2009Co-Authors: Yueshe Wang, Yanling Wang, Guoxiang Wang, Hiroshi HondaAbstract:Abstract A physical model of gas–liquid two-phase Annular Flow Regime is presented for predicting the enhanced evaporation heat transfer characteristics in horizontal microfin tubes. The model is based on the equivalence of a periodical distortion of the disturbance wave in the substrate layer. Corresponding to the stratified Flow model proposed previously by authors, the dimensionless quantity Fr0 = G/[gdeρv(ρl − ρv)]0.5 may be used as a measure for determining the applicability of the present theoretical model, which was used to restrict the transition boundary between the stratified-wavy Flow and the Annular/intermittent Flows. Comparison of the prediction of the circumferential average heat transfer coefficient with available experimental data for four tubes and three refrigerants reveals that a good agreement is obtained or the trend is better than that of the previously developed stratified Flow model for Fr0 > 4.0 as long as the partial dry out of tube does not occur. Obviously, the developed Annular model is applicable and reliable for evaporation in horizontal microfin tubes under the case of high heat flux and high mass flux.
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modified theoretical models of film condensation in horizontal microfin tubes
International Journal of Heat and Mass Transfer, 2002Co-Authors: Hua Sheng Wang, Hiroshi Honda, Shigeru NozuAbstract:The previously proposed theoretical models of film condensation in horizontal microfin tubes have been modified to describe the characteristics of condensing two-phase Flow more accurately. The stratified Flow Regime and the Annular Flow Regime were considered. For the stratified Flow Regime, the previously proposed theoretical model was modified to take account of the curvature of stratified condensate due to the surface tension force. For the Annular Flow Regime, a more accurate expression for the interfacial shear stress was incorporated. Generally, the modified theoretical models predicted a lower circumferential average heat transfer coefficient than the previously proposed ones. Comparison of the theoretical predictions with available experimental data for six tubes and five refrigerants revealed that a good agreement (r.m.s error of less than 21.1%) was obtained for all cases when the higher of the two theoretical predictions were adopted as the calculated value.
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condensation of refrigerants in horizontal spirally grooved microfin tubes numerical analysis of heat transfer in the Annular Flow Regime
Journal of Heat Transfer-transactions of The Asme, 2000Co-Authors: Shigeru Nozu, Hiroshi HondaAbstract:A method is presented for estimating the condensation heat transfer coefficient in a horizontal, spirally grooved microfin tube. Based on the Flow observation study performed by the authors, a laminar film condensation model in the Annular Flow Regime is proposed. The model assumes that all the condensate Flow occurs through the grooves. The condensate film is segmented into thin and thick film regions. In the thin film region formed on the fin surface, the condensate is assumed to be drained by the combined surface tension and vapor shear forces. In the thick film region formed in the groove, on the other hand, the condensate is assumed to be driven by the vapor shear force. The present and previous local heat transfer data including four fluids (CFC11, HCFC22, HCFC123, and HFCl34a) and three microfin tubes are found to agree with the present predictions to a mean absolute deviation of 15.1%.
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condensation of refrigerants in horizontal microfin tubes numerical analysis of heat transfer for Annular Flow Regime
Transactions of the Japan Society of Mechanical Engineers. B, 1998Co-Authors: Shigeru Nozu, Hiroshi HondaAbstract:A method for predicting the local heat transfer coefficient is presented for film condensation of vapor in a spirally grooved horizontal microfin-tube. Based on the Flow observation study performed by the present authors, film Flow model between fins in the Annular Flow Regime is proposed. For the fin surface, laminar condensate film controlled by the combined effects of vapor shear and surface tension forces is analyzed. While, in the groove, thick condensate film driven by the vapor shear force is taken into consideration. A parameter which accounts for the transition from Annular-to stratified Flow Regimes is also derived. The present and previous local heat transfer data for fluorocarbon refrigerants in the Annular Flow Regime are found by the present numerical analysis to have a mean absolute deviation of 15.1 percent.
John R Thome - One of the best experts on this subject based on the ideXlab platform.
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fine resolution two phase Flow heat transfer coefficient measurements of refrigerants in multi microchannel evaporators
International Journal of Heat and Mass Transfer, 2013Co-Authors: Sylwia Szczukiewicz, Navid Borhani, John R ThomeAbstract:The time-averaged two-phase Flow heat transfer coefficients were determined with a very fine resolution based on infra-red (IR) temperature measurements conducted over a 1 cm(2) heated area of a multi-micro-, channel evaporator. This experimental investigation included two low-pressure refrigerants, R245fa and R236fa, as well as one medium-pressure new refrigerant R1234ze(E) Flowing in four different test sections. The number of microchannels and their cross-sectional areas were the same for all the tested micro-evaporators, respectively, 67 and 100 x 100 mu m(2). Channel entrances with and without inlet micro-orifices were tested for establishing stable Flow. Using 90 x 90 pixel grid (and then averaged width-wise), 90 local heat transfer coefficients were measured from inlet to outlet, yielding a U-shape of the heat transfer coefficient trend, where the descending branch of the curve corresponds to the coalescing elongated bubble Flow Regime (CB), while ascending one represents the increasing heat transfer coefficient in the Annular Flow Regime (AF). The effects of channel mass flux, wall heat flux, orifice expansion ratio, and fluid properties on the wall heat transfer coefficient were identified for a selected number of data sets. In terms of predicted heat transfer coefficient values, in both the CB and AF Flow Regimes, the experimental results were found to be in a good agreement with respective existing Flow pattern-based heat transfer prediction methods. Whereas, in order to better reflect the obtained experimental U-shaped trend of the heat transfer coefficient close to the CB-AF Flow transition (which is a churn Flow), the joined model of these two was modified by proposing a new vapor quality buffer for the width of the transition. (C) 2013 Elsevier Ltd. All rights reserved.
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Flow pattern maps for convective boiling of co2 and r410a in a horizontal smooth tube experiments and new correlations analyzing the effect of the reduced pressure
International Journal of Heat and Mass Transfer, 2012Co-Authors: R Mastrullo, A W Mauro, John R Thome, D Toto, Giuseppe Peter VanoliAbstract:In this work Flow visualizations and measurements are made and analyzed to identify Flow Regime transitions, slug-to-intermittent, intermittent-to-Annular and the dry-out inception, during the Flow boiling of CO2 in a horizontal smooth tube of 6.00 mm of internal diameter, varying the reduced pressure between 0.57 and 0.64, the mass velocity between 150 and 500 kg/m(2) s and the heat flux between 5 and 20 kW/m(2). Additional experiments for R410A show the effect of the reduced pressure over a wider range, from 0.19 to 0.52, varying the other operating parameters in the same ranges. All together, the new experimental dataset of 1420 observations and heat transfer measurements were utilized to determine the location of the Flow pattern transitions, which showed a strong dependency of the vapor quality on the mass velocity for each transition line, for fixed reduced pressure. The dry-out inception line was influenced by the heat flux, as expected. The influence of the reduced pressure was also identified as an important parameter with a remarkable impact. This Flow pattern database was then statistically compared with well established methods (Wojtan et al. (2005) [1] for R410A, Cheng et al. (2008) [2] for CO2) and recent methods [3,4], showing poor agreement in the determination of the intermittent-to-Annular Flow Regime transition for all the methods and in the prediction of the dry-out inception for all the methods, except for Wojtan et al. (2005) [1]. Finally, new easy-to-use correlations are proposed to provide better agreement with the experimental dataset and to explicitly illustrate the effect of the reduced pressure in an effort to generalize this diabatic Flow pattern map for broader application. (C) 2011 Elsevier Ltd. All rights reserved.
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prediction of two phase pressure gradients of refrigerants in horizontal tubes
International Journal of Refrigeration-revue Internationale Du Froid, 2002Co-Authors: M Ould B Didi, Nakhle Kattan, John R ThomeAbstract:Abstract Two-phase pressure drop data were obtained for evaporation in two horizontal test sections of 10.92 and 12.00 mm diameter for five refrigerants (R-134a, R-123, R-402A, R-404A and R-502) over mass velocities from 100 to 500 kg/m2 s and vapor qualities from 0.04 to 1.0. These data have then been compared against seven two-phase frictional pressure drop prediction methods. Overall, the method by Muller-Steinhagen and Heck (Muller-Steinhagen H, Heck K. A simple friction pressure drop correlation for two-phase Flow in pipes. Chem. Eng. Process 1986;20:297–308) and that by Gronnerud (Gronnerud R. Investigation of liquid hold-up, Flow-resistance and heat transfer in circulation type evaporators, part IV: two-phase Flow resistance in boiling refrigerants. Annexe 1972-1, Bull. de l'Inst. du Froid, 1979) were found to provide the most accurate predictions while the widely quoted method of Friedel (Friedel L. Improved friction drop correlations for horizontal and vertical two-phase pipe Flow. European Two-phase Flow Group Meeting, paper E2; June 1979; Ispra, Italy) gave the third best results. The data were also classified by two-phase Flow pattern using the Kattan-Thome-Favrat (Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 1: development of a diabatic two-phase Flow pattern map. J. Heat Transfer 1998;120:140–7; Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 2; new heat transfer data for five refrigerants. J Heat Transfer 1998;120:148–55; Kattan N, Thome JR, Favrat D. Flow boiling in horizontal tubes. Part 3: development of a new heat transfer model based on Flow patterns. J. Heat Transfer 1998;120:156–65) Flow pattern map. The best available method for Annular Flow was that of Muller-Steinhagen and Heck. For intermittent Flow and stratified-wavy Flow, the best method in both cases was that of Gronnerud. It was observed that the peak in the two-phase frictional pressure gradient at high vapor qualities coincided with the onset of dryout in the Annular Flow Regime.
R N Christensen - One of the best experts on this subject based on the ideXlab platform.
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a condensation heat transfer correlation for millimeter scale tubing with Flow Regime transition
Experimental Thermal and Fluid Science, 2002Co-Authors: Weiwen William Wang, Thomas D Radcliff, R N ChristensenAbstract:This study documents local convection heat transfer and Flow Regime measurements for HFC-134a condensing inside a horizontal rectangular multi-port aluminum condenser tube of 1.46 mm hydraulic diameter. The data is compared with condensation heat transfer correlations and Flow Regime maps from the literature. Existing correlations are found to overpredict both heat transfer and the stratified-to-Annular Flow Regime transition velocity. Results of the experiments suggest that liquid drawn into the corners of the tube alter the phase distribution in the Annular Flow Regime as well as stabilizing the Annular Flow Regime at lower vapor velocities. To predict the heat transfer data, two correlations, each representing the physics of the specific phase distributions, are developed. A boundary layer analysis is applied for Annular Flow, in which the friction multiplier and dimensionless boundary layer temperature are evaluated specifically for this tube configuration. For stratified Flow, documented film condensation and single-phase forced convection correlations are combined with straightforward void fraction weighting. Finally, a weighting correlation is successfully proposed to account for the all data regardless of the mix of Flow Regimes experienced. This weighting applies the result of a modified Flow Regime map developed from the Flow visualizations. The final result is a practical correlation for the design of a condenser with millimeter-scale tubes.
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a condensation heat transfer correlation for millimeter scale tubing with Flow Regime transition
Experimental Thermal and Fluid Science, 2002Co-Authors: Weiwen William Wang, Thomas D Radcliff, R N ChristensenAbstract:This study documents local convection heat transfer and Flow Regime measurements for HFC-134a condensing inside a horizontal rectangular multi-port aluminum condenser tube of 1.46 mm hydraulic diameter. The data is compared with condensation heat transfer correlations and Flow Regime maps from the literature. Existing correlations are found to overpredict both heat transfer and the stratified-to-Annular Flow Regime transition velocity. Results of the experiments suggest that liquid drawn into the corners of the tube alter the phase distribution in the Annular Flow Regime as well as stabilizing the Annular Flow Regime at lower vapor velocities. To predict the heat transfer data, two correlations, each representing the physics of the specific phase distributions, are developed. A boundary layer analysis is applied for Annular Flow, in which the friction multiplier and dimensionless boundary layer temperature are evaluated specifically for this tube configuration. For stratified Flow, documented film condensation and single-phase forced convection correlations are combined with straightforward void fraction weighting. Finally, a weighting correlation is successfully proposed to account for the all data regardless of the mix of Flow Regimes experienced. This weighting applies the result of a modified Flow Regime map developed from the Flow visualizations. The final result is a practical correlation for the design of a condenser with millimeter-scale tubes.
Issam Mudawar - One of the best experts on this subject based on the ideXlab platform.
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enhanced model for Annular Flow in micro channel heat sinks including effects of droplet entrainment deposition and core turbulence
International Journal of Heat and Mass Transfer, 2019Co-Authors: Seunghyun Lee, Issam MudawarAbstract:Abstract This study investigates pressured drop and heat transfer characteristics for saturated Flow boiling in a micro-channel heat sink specific to the Annular Flow Regime. A theoretical control-volume-based model is presented, which relies on new relations for liquid droplet entrainment and deposition. While prior models have been attempted for Annular Flow, these models were based on simplified depictions of the vapor core based on average velocity. On the other hand, the present model provides detailed assessment of turbulence effects in the core, enabling the development of detailed cross-sectional profiles for momentum diffusivity, velocity, and shear stress. Predictive accuracy of the model is assessed against experimental data for R134a using a 609.6-mm long and 203.2-mm wide micro-channel heat sink containing 100 of 1 × 1-mm2 Flow channels. The model shows good accuracy against 69 experimental pressure drop data points, with mean absolute error (MAE) of 16.22%, and 97.10% and 100.0% of the data predicted within 30% and 50%, respectively. It also shows very good accuracy against 388 data points for local two-phase heat transfer coefficient, evidenced by a MAE of 8.35%, and with 98.45% and 99.74% of the data predicted within 30% and 50%, respectively.
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Flow boiling heat transfer in two phase micro channel heat sinks i experimental investigation and assessment of correlation methods
International Journal of Heat and Mass Transfer, 2003Co-Authors: Issam MudawarAbstract:Abstract This paper is the first of a two-part study concerning measurement and prediction of saturated Flow boiling heat transfer in a water-cooled micro-channel heat sink. In this paper, new experimental results are discussed which provide new physical insight into the unique nature of Flow boiling in narrow rectangular micro-channels. The micro-channel heat sink contained 21 parallel channels having a 231×713 μ m cross-section. Tests were performed with deionized water over a mass velocity range of 135–402 kg/m 2 s, inlet temperatures of 30 and 60 °C, and an outlet pressure of 1.17 bar. Results indicate an abrupt transition to Annular Flow near the point of zero thermodynamic equilibrium quality, and reveal the dominant heat transfer mechanism is forced convective boiling corresponding to Annular Flow. Contrary to macro-channel trends, the heat transfer coefficient is shown to decrease with increasing thermodynamic equilibrium quality. This unique trend is attributed to appreciable droplet entrainment at the onset of Annular Flow Regime development, and the increase in mass Flow rate of the Annular film by droplet deposition downstream. Eleven previous empirical correlations are assessed and deemed unable to predict the correct trend of heat transfer coefficient with quality because of the unique nature of Flow boiling in micro-channels, and the operating conditions of water-cooled micro-channel heat sinks falling outside the recommended application range for most correlations. Part II of this study will introduce a new Annular Flow model as an alternative approach to heat transfer coefficient prediction for micro-channels.
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Flow boiling heat transfer in two phase micro channel heat sinks ii Annular two phase Flow model
International Journal of Heat and Mass Transfer, 2003Co-Authors: Issam MudawarAbstract:This paper is Part II of a two-part study devoted to measurement and prediction of the saturated Flow boiling heat transfer coefficient in water-cooled micro-channel heat sinks. Part I discussed the experimental findings from the study, and identified unique aspects of Flow boiling in micro-channels such as abrupt transition to the Annular Flow Regime near the point of zero thermodynamic equilibrium quality, and the decrease in heat transfer coefficient with increasing quality. The operating conditions of water-cooled micro-channels fell outside the recommended range for most prior empirical correlations. In this paper, an Annular Flow model is developed to predict the saturated Flow boiling heat transfer coefficient. Features unique to two-phase micro-channel Flow, such as laminar liquid and vapor Flow, smooth interface, and strong droplet entrainment and deposition effects, are identified and incorporated into the model. The model correctly captures the unique overall trend of decreasing heat transfer coefficient with increasing vapor quality in the low vapor quality region of micro-channels. Good agreement is achieved between the model predictions and heat transfer coefficient data over broad ranges of Flow rate and heat flux. 2003 Elsevier Science Ltd. All rights reserved.
Chen Li - One of the best experts on this subject based on the ideXlab platform.
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Flow boiling phenomena in a single Annular Flow Regime in microchannels ii reduced pressure drop and enhanced critical heat flux
International Journal of Heat and Mass Transfer, 2014Co-Authors: Fanghao Yang, Yoav Peles, Ping Cheng, Jamil A Khan, Chen LiAbstract:In Part II of this study, we report that pressure drop was reduced by approximately 48% and critical heat flux (CHF) was increased by approximately 300% in SiNW microchannels compared to these in smooth wall microchannels. The hydraulic characteristics of the single Annular Flow were systematically investigated to reveal the mechanisms responsible for the reduced pressure drop and enhanced CHF. In the single Annular Regime, the liquid and vapor Flows were nearly fully separated during the entire Flow boiling process (i.e., from the onset of nucleate boiling to the CHF conditions). Moreover, the entrainment droplets were reduced by flattening the profile of the liquid–vapor interfaces using the high capillary pressure generated by SiNWs. These two factors, i.e., Flow separation and reduced entrainment droplets, lead to a dramatic reduction of frictional pressure drop. The separation of liquid and vapor Flows as well as the improved global and local liquid supply result in a significant CHF enhancement without using inlet restrictors (IR). Reynolds number based the vapor Flow at the exit ranged from 0.1 to 2100.