The Experts below are selected from a list of 93 Experts worldwide ranked by ideXlab platform
John R Thome - One of the best experts on this subject based on the ideXlab platform.
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an experimental study on flow Boiling Pressure drop in multi microchannel evaporators with different refrigerants
Experimental Thermal and Fluid Science, 2017Co-Authors: Houxue Huang, John R ThomeAbstract:Abstract A key parameter in designing two-phase flow systems for the cooling of high heat flux electronics is the Pressure drop in microchannel evaporators. As a result, an experimental study was performed to investigate the flow Boiling Pressure drop of refrigerants in two silicon multi-microchannel evaporators. Three types of refrigerants (R1233zd(E), R245fa and R236fa) were tested under three inlet subcoolings and three nominal outlet saturation temperatures. The test section’s backside base temperatures were measured by an infrared (IR) camera. A single-phase flow validation in terms of the inlet and outlet restriction Pressure drops and the channel flow friction factor was carefully done before the Boiling tests. The operating conditions for stable flow Boiling tests were: mass fluxes from 1250 to 2750 kg m−2 s−1, heat fluxes from 20 to 64 W cm−2. The resulted maximum vapor quality at the outlet manifold was 0.51. It is found that within the present test conditions the channel Pressure drop increased with the inlet subcooling and inlet orifice width but slightly affected by the outlet saturation temperature. In addition, compared to the other two types of refrigerants, R236fa exhibited the lowest channel Pressure drop due to its smallest liquid to vapor density ratio and liquid viscosity. Based on the obtained 184 points of stable flow Boiling data, a new empirical model suitable for the high mass flux operating conditions was developed. The new Pressure drop model yielded the best prediction of the experimental data with a mean absolute error (MAE) of 27.8% and it was thus implemented to predict the local Pressure and temperature profiles, allowing a quantitative analysis to obtain highly accurate local heat transfer coefficients.
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experimental investigation on flow Boiling Pressure drop and heat transfer of r1233zd e in a multi microchannel evaporator
International Journal of Heat and Mass Transfer, 2016Co-Authors: Houxue Huang, Navid Borhani, John R ThomeAbstract:An experimental study on flow Boiling Pressure drop and heat transfer of a new environmentally friendly refrigerant R1233zd(E), in a parallel multi-microchannel evaporator was carried out. The silicon microchannels evaporator was 10 mm long and 10 mm wide, having 67 parallel channels, each 100 × 100 μm2, separated by a fin with a thickness of 50 μm. Upstream of each channel, a micro-orifice was placed to stabilize the two-phase flow and to obtain good flow distribution. The operating conditions for flow Boiling tests were: mass fluxes from 500 to 2750 kg m−2 s−1, heat fluxes from 6 to 50 W cm−2, inlet subcooling of 5.8 K, and a nominal outlet saturation temperature of 35 °C for stable flow Boiling. The test section’s backside base temperatures were measured by an infrared (IR) camera. The stable flow Boiling data without back flow was selected through flow visualization recorded by a high-speed camera coupled with a microscope. These data were then used to assess the applicability of existing two-phase Pressure drop models, and to further develop a new empirical model suitable for the high mass flux operating conditions. This new Pressure drop model was used to predict the local fluid temperature for the further heat transfer data identification. The fine-resolution local heat transfer coefficients were obtained by solving the three-dimensional inverse heat conduction problem. The experimental results showed that in the saturated flow Boiling region the local heat transfer coefficient first decreased moderately in the very low vapor quality region (x<0.05), then increased significantly but monotonically along the flow direction. The fine-resolution local heat transfer data at the saturated flow Boiling region were compared with two groups of heat transfer correlations. The first one considered the flow Boiling mechanism occurring in muliti-microchannels as a combination of nucleate Boiling and forced convection Boiling, while the other one associated this mechanism to liquid thin film evaporation, thus indicating a controversy. It is found that the flow pattern based model belonging to the second group yielded the best agreement with the experimental data, predicting 92.0% of this new database within ±30%.
Michael K Jensen - One of the best experts on this subject based on the ideXlab platform.
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Pressure drop with highly subcooled flow Boiling in small diameter tubes
Experimental Thermal and Fluid Science, 1997Co-Authors: Wei Tong, Arthur E Bergles, Michael K JensenAbstract:Abstract Pressure drop may be the most important consideration in designing heat-removal systems utilizing high-heat-flux subcooled Boiling. In this study, an experimental investigation was performed to identify the important parameters affecting Pressure drop across small-diameter tubes in highly subcooled flow Boiling. The effects of five parameters—mass flux, inlet temperature, exit Pressure, tube internal diameter, and length-to-diameter ratio—on both single- and two-phase Pressure drop were studied and evaluated. Experiments were carried out with tubes having inside diameters ranging from 1.05 to 2.44 mm. Mass fluxes ranged from 25,000 to 45,000 kg/(m2 s), exit Pressures from 4 to 16 bar, and inlet temperatures from 22 to 66°C. Two length-to-diameter ratios were tested. These conditions resulted in critical heat flux levels of 50–80 MW/m2. The experiment results indicate that mass flux, tube diameter, and length-to-diameter ratio are the major parameters that alter the Pressure-drop curves. Both single- and two-phase Pressure drops increase with increasing mass flux and length-to-diameter ratio but decrease with increasing internal diameter. Inlet temperature and exit Pressure have been shown to have significant effects on two-phase Pressure drop but very small effects on single-phase Pressure drop. These results agree well with those from other investigations under similar conditions. As a result of this study, Pressure-drop correlations are presented for predicting both single-phase and subcooled Boiling Pressure drop in small-diameter tubes under different heat-flux conditions.
Issam Mudawar - One of the best experts on this subject based on the ideXlab platform.
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machine learning algorithms to predict flow Boiling Pressure drop in mini micro channels based on universal consolidated data
International Journal of Heat and Mass Transfer, 2021Co-Authors: Yue Qiu, Deepak Garg, Sungmin Kim, Issam Mudawar, Chirag R KharangateAbstract:Abstract Two-phase flow in mini/micro-channels can meet the high heat dissipation requirements of many state-of-the-art cooling solutions. However, there is lack of accurate universal methods for predicting parameters like Pressure drop in these configurations. Conventional ways of predicting Pressure drop employ either Homogeneous Equilibrium Model (HEM) or semi-empirical correlations. This current study leverages the availability of data collected over the past few decades to build several machine learning models to demonstrate the efficacy and ease of building and deploying such models. A consolidated database of 2787 data points for flow Boiling Pressure drop in mini/micro-channels is amassed from 21 sources that includes 10 working fluid, reduced Pressures of 0.0006 –0.7766, hydraulic diameters of 0.15–5.35 mm, mass velocities of 33.1
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time averaged and transient Pressure drop for flow Boiling with saturated inlet conditions
International Journal of Heat and Mass Transfer, 2016Co-Authors: Lucas E Oneill, Chirag R Kharangate, Issam MudawarAbstract:Abstract This study explores flow Boiling Pressure drop of FC-72 in a rectangular channel subjected to single-side and double-sided heating for vertical upflow, vertical downflow, and horizontal flow with positive inlet quality. Analysis of temporal records of Pressure transducer signals is used to assess the influences of orientation, mass velocity, inlet quality, heat flux, and single-sided versus double-sided heating on magnitude of Pressure drop oscillations, while fast Fourier transforms of the same records are used to capture dominant frequencies of oscillations. Time-averaged Pressure drop results are also presented, with trends focusing on the competing influences of body force and flow inertia, and particular attention paid to the impact of vapor content at the test section inlet and the rate of vapor generation within the test section on Pressure drop. Several popular Pressure drop correlations are evaluated against the present Pressure drop database. Predictions are presented for subsets of the database corresponding to low and high ranges of inlet quality and mass velocity. The correlations are ranked based on mean absolute error, overall data trends, and data spread. While most show general success in capturing the data trends, they do so with varying degrees of accuracy.
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consolidated method to predicting Pressure drop and heat transfer coefficient for both subcooled and saturated flow Boiling in micro channel heat sinks
International Journal of Heat and Mass Transfer, 2012Co-Authors: Sungmin Kim, Issam MudawarAbstract:Published studies concerning transport phenomena in micro-channel heat sinks can be divided into those concerning saturated Boiling versus those focused on subcooled Boiling, with the vast majority related to the former. What has been lacking is a single generalized method to tackle both Boiling regimes. The primary objective of the present paper is to construct a consolidated method to predicting transport behavior of micro-channel heat sinks incurring all possible heat transfer regimes. First, a new correlation is developed for subcooled flow Boiling Pressure drop that accounts for inlet subcooling, micro-channel aspect ratio, and length-to-diameter ratio. This correlation shows excellent predictive capability against subcooled HFE 7100 Pressure drop data corresponding to four different micro-channel geometries. Next, a consolidated method is developed for Pressure drop that is capable of tackling inlet single-phase liquid, subcooled Boiling, saturated Boiling, and single-phase vapor regimes as well as inlet contraction and outlet expansion. A similar consolidated method is developed to predict the heat transfer coefficient that is capable of tackling all possible combinations of heat transfer regimes. The new consolidated method is shown to be highly effective at reproducing both data and trends for HFE 7100, water and R134a.
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experimental investigation and theoretical model for subcooled flow Boiling Pressure drop in microchannel heat sinks
Journal of Electronic Packaging, 2009Co-Authors: Jaeseon Lee, Issam MudawarAbstract:This study examines the Pressure drop characteristics of subcooled two-phase microchannel heat sinks. A new model is proposed, which depicts the subcooled flow as consisting of a homogeneous two-phase flow layer near the heated walls of the microchannel and a second subcooled bulk liquid layer. This model is intended for conditions where subcooled flow Boiling persists along the entire microchannel and the outlet fluid never reaches bulk saturation temperature. Mass, momentum, and energy control volume conservation equations are combined to predict flow characteristics for thermodynamic equilibrium qualities below zero. By incorporating a relation for apparent quality across the two-phase layer and a new criterion for bubble departure, this model enables the determination of axial variations in two-phase layer thickness and velocity as well as Pressure drop. The model predictions are compared with HFE 7100 Pressure drop data for four different microchannel sizes with hydraulic diameters of 176–416 μm, mass velocities of 670–5550 kg/m2 s, and inlet temperatures of 0°C and −30°C. The Pressure drop database is predicted with a mean absolute error of 14.9%.
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fluid flow and heat transfer characteristics of low temperature two phase micro channel heat sinks part 2 subcooled Boiling Pressure drop and heat transfer
International Journal of Heat and Mass Transfer, 2008Co-Authors: Issam MudawarAbstract:This second part of a two-part study explores the performance of a new cooling scheme in which the primary working fluid flowing through a micro-channel heat sink is indirectly cooled by a refrigeration cooling system. The objective of this part of study is to explore the Pressure drop and heat transfer characteristics of the heat sink. During single-phase cooling, Pressure drop decreased with increasing heat flux because of decreased liquid viscosity. However, Pressure drop began increasing with increasing heat flux following bubble departure. These opposite trends produced a minimum in the variation of Pressure drop with heat flux. Increasing liquid subcooling decreased two-phase Pressure drop because of decreased void fraction caused by strong condensation at bubble interfaces as well as decreased likelihood of bubble coalescence. It is shown macro-channel subcooled Boiling Pressure drop and heat transfer correlations are unsuitable for micro-channel flows. However, two new modified correlations produced good predictions of the present heat transfer data.
Marco Enrico Ricotti - One of the best experts on this subject based on the ideXlab platform.
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subcooled and saturated water flow Boiling Pressure drop in small diameter helical coils at low Pressure
Experimental Thermal and Fluid Science, 2008Co-Authors: Andrea Cioncolini, Lorenzo Santini, Marco Enrico RicottiAbstract:Experimental Pressure drop results on Boiling water flow through three helical coils of tube inner diameter of 4.03 mm and 4.98 mm and coil diameter to tube diameter ratio of 26.1, 64.1 and 93.3 are presented. Both subcooled and saturated flow Boiling are investigated, covering operating Pressures from 120 to 660 kPa, mass fluxes from 290 to 690 kg m(-2) s(-1) and heat fluxes from 50 to 440 W m(-2). Existing correlations for subcooled flow Pressure drop are found not capable to fit the present subcooled database, while the measurements in saturated flow conditions are successfully reproduced by existing correlations for both straight and coiled pipe two-phase flow. The experimental database is included in tabular form. (c) 2008 Elsevier Inc. All rights reserved.
Paulo E L Barbieri - One of the best experts on this subject based on the ideXlab platform.
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convective Boiling Pressure drop of refrigerant r 134a in horizontal smooth and microfin tubes
International Journal of Refrigeration-revue Internationale Du Froid, 2004Co-Authors: Enio Pedone Bandarra Filho, José Maria Saiz Jabardo, Paulo E L BarbieriAbstract:Abstract Present study deals with the Pressure drop of refrigerant R-134a under convective Boiling conditions in horizontal smooth and microfinned (‘grooved’) copper tubes. Experiments have been carried out in an experimental set up developed for change of phase studies with a test section made out of 7.0, 7.93, and 9.52 mm external diameter, 1.5 m long copper tubes, electrically heated by tape resistors wrapped on the external surface. Mass velocities and refrigerant qualities varied in the following ranges: 70–1100 kg s −1 m −2 and 5–95%. The annular flow pattern has been observed to occur over most of the operational conditions. For smooth tubes, the Jung and Radermacher correlation for the liquid two phase flow multiplier fits with reasonable precision the experimental data. As for grooved tubes, a correlation of the two phase flow multiplier in terms of the Martinelli's parameter has been developed which fits the data with an average absolute deviation of the order of 6.3%. The proposed correlation fits with good precision data obtained elsewhere for grooved tubes of different diameter and microfin geometry.