Measurement and Modeling of Condensation Heat Transfer Coefficients in Circular Microchannels

2006 ◽  
Vol 128 (10) ◽  
pp. 1050-1059 ◽  
Author(s):  
Todd M. Bandhauer ◽  
Akhil Agarwal ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Transfer Model ◽  
Condensation Heat Transfer ◽  
Low Flow ◽  
Transfer Model ◽  
Shear Stresses ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Circular Microchannels

A model for predicting heat transfer during condensation of refrigerant R134a in horizontal microchannels is presented. The thermal amplification technique is used to measure condensation heat transfer coefficients accurately over small increments of refrigerant quality across the vapor-liquid dome (0<x<1). A combination of a high flow rate closed loop primary coolant and a low flow rate open loop secondary coolant ensures the accurate measurement of the small heat duties in these microchannels and the deduction of condensation heat transfer coefficients from measured UA values. Measurements were conducted for three circular microchannels (0.506<Dh<1.524mm) over the mass flux range 150<G<750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The heat transfer model is based on the approach originally developed by Traviss, D. P., Rohsenow, W. M., and Baron, A. B., 1973, “Forced-Convection Condensation Inside Tubes: A Heat Transfer Equation For Condenser Design,” ASHRAE Trans., 79(1), pp. 157–165 and Moser, K. W., Webb, R. L., and Na, B., 1998, “A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes,” ASME, J. Heat Transfer, 120(2), pp. 410–417. The multiple-flow-regime model of Garimella, S., Agarwal, A., and Killion, J. D., 2005, “Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3), pp. 1–8 for predicting condensation pressure drops in microchannels is used to predict the pertinent interfacial shear stresses required in this heat transfer model. The resulting heat transfer model predicts 86% of the data within ±20%.

Heat Transfer Model for Condensation in Non-Circular Microchannels

2007 ◽  
Author(s):  
Akhil Agarwal ◽  
Todd M. Bandhauer ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Acute Angle ◽  
Heat Transfer Model ◽  
The Other ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Tube Shape ◽  
Flow Mechanisms ◽  
Circular Microchannels

A model for predicting heat transfer during condensation of refrigerant R134a in horizontal noncircular microchannels is presented. The thermal amplification technique developed and reported in earlier work by the authors is used to measure condensation heat transfer coefficients for six non-circular microchannels (0.424 < Dh < 0.839 mm) of different shapes over the mass flux range 150 < G < 750 kg/m2-s. The channels included barrel-shaped, N-shaped, rectangular, square, and triangular extruded tubes, and a channel with a W-shaped corrugated insert that yielded triangular microchannels. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The effect of tube shape was also considered in deciding the applicable flow regime. A modified version of the annular flow based heat transfer model proposed recently by the authors for circular microchannels, with the required shear stress being calculated from a noncircular microchannel pressure drop model also reported earlier was found to best correlate the present data for square, rectangular and barrel-shaped microchannels. For the other microchannel shapes with sharp acute-angle corners, a mist flow based model from the literature on larger tubes was found to suffice for the prediction of the heat transfer data. These models predict the data significantly better than the other available correlations in the literature.

Channel Size Based Measurement Techniques for Condensation Heat Transfer Coefficients in Mini- and Micro-Channels

2005 ◽  
Author(s):  
Srinivas Garimella ◽  
Akhil Agarwal ◽  
Todd M. Bandhauer
Keyword(s):  
Heat Transfer ◽  
Thermal Resistance ◽  
Flow Rate ◽  
Test Section ◽  
High Flow ◽  
High Flow Rate ◽  
Condensation Heat Transfer ◽  
Large Temperature ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A set of techniques for the measurement of condensation heat transfer coefficients for circular and noncircular channels with 5 mm &gt; Dh &gt; 100 μm is presented. For the larger range of Dh (5 &gt; Dh &gt; 0.4 mm), single tubes or multiple parallel extruded channels are used as test sections. The test section is cooled using water at a high flow rate to ensure that the condensation side presents the governing thermal resistance. Heat exchange with a secondary cooling water stream at a much lower flow rate is used to obtain a large temperature difference, which is used to measure the condensation duty. Condensation heat transfer coefficients are measured in small quality increments for 0 &lt; x &lt; 1 over the mass flux range 150 &lt; G &lt; 750 kg/m2-s with uncertainties typically less than 20%. For 200 &gt; Dh &gt; 100 μm, channels are fabricated on a copper substrate by electroforming copper onto a mask patterned by X-ray lithography, and sealed by diffusion bonding. Subcooled liquid is electrically heated to the desired quality, followed by condensation in the test section. Downstream of the test section, another electric heater is used to heat the refrigerant to a superheated state. Energy balances on the pre-and post-heaters establish the refrigerant inlet and outlet states at the test section. Water at a high flow rate serves as the test section coolant to ensure that the condensation side presents the governing thermal resistance. Heat transfer coefficients are measured for 200 &lt; G &lt; 800 kg/m2-s for 0 &lt; x &lt; 1. It is demonstrated that uncertainties as low as 6% can be achieved in the measurement of condensation heat transfer coefficients.

Measurement of Condensation Heat Transfer Coefficients in Microchannel Tubes

2001 ◽  
Author(s):  
Srinivas Garimella ◽  
Todd M. Bandhauer
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Test Section ◽  
Condensation Heat Transfer ◽  
Large Temperature ◽  
Liquid Region ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Heat Transfer Coefficients ◽  
Small Increments

Abstract A technique for the measurement of condensation heat transfer coefficients in microchannels is reported. The high heat transfer coefficients and low mass flow rates in microchannels make it difficult to accurately measure these coefficients. The requirements for accurate heat duty measurement are in direct conflict with the requirements for deducing the heat transfer coefficients from measured temperatures and flow rates. In addition, measurement of local condensation heat transfer coefficients in small increments of quality is difficult to accomplish due to the low heat transfer rates for such quality changes. The present work reports a technique that addresses these requirements. The inlet and outlet qualities to a microchannel test section are measured through energy balances on a pre- and post-condenser. The test section is cooled using water at a high flow rate to ensure that the condensation side presents the governing thermal resistance. Heat exchange with a secondary cooling water stream at a much lower flow rate is used to obtain a large temperature difference, which is in turn used to measure the condensation duty. Local heat transfer coefficients are therefore measured in small increments for the entire saturated vapor-liquid region. This technique is demonstrated using a square microchannel geometry with a hydraulic diameter of 0.76 mm. Heat transfer coefficients for the condensation of refrigerant R134a in this geometry range from 2,110–10,640 W/m2–K over the mass flux range 150 &lt; G &lt; 750 kg/m2–s.

Condensation in a Vertical Tube Bundle Operating in Passive Condensation Mode

2009 ◽  
Author(s):  
Gavin Henderson ◽  
Wenzhong Zhou ◽  
Shripad T. Revankar
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Cooling System ◽  
Tube Bundle ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Transfer Rates ◽  
Single Tube ◽  
Heat Transfer Coefficients ◽  
Condensation Mode

Passive condenser systems are used in a number of industrial heat transfer systems. Passive containment cooling system (PCCS) which is composed of a number of vertical heat exchanger serves as an engineered safety system in an advanced boiling water reactor. The PCCS condenser must be able to remove sufficient energy from the reactor containment to prevent containment from exceeding its design pressure. Experiments were designed to simulate the PCCS condensation with a tube bundle. Scaling analysis was performed to scale down the prototype PCCS with a tube bundle consisting of four tubes. The tubes in the bundle were of prototype height (1.8 m) and diameter (52.5 mm) and the operating conditions and boundary conditions such as the operating pressure, secondary cooling system were designed to represent prototype conditions. Steam condensation tests were carried out in complete condensation mode where all the steam entering the condenser bundle is completely condensed. Condensation heat transfer coefficients (HTC) were obtained for various steam flow rate. The condensation pressure depended on the inlet steam flow rate which happens to be the maximum condensation rate for the given test pressure. Data on condensation heat transfer were obtained for primary pressure raging from 110–270 kPa. The tube bundle condensation heat transfer rates were compared with single tube heat transfer rates from previous work. The results showed that the condensation heat transfer coefficient for the tube in bundle was comparable with single tube, however the secondary side heat transfer coefficients for the tubes in bundle was higher than for the single tube. Condensation heat transfer for tube in bundle ranged from 7500 W/ m2K to 20,000 W/ m2K for the range of pressure studied. A heat and mass analogy model was developed and the condensation heat transfer prediction from the model was compared with experimental data.

scholarly journals Heat Transfer in Rotating Serpentine Passages With Trips Normal to the Flow

1992 ◽  
Vol 114 (4) ◽  
pp. 847-857 ◽  
Author(s):  
J. H. Wagner ◽  
B. V. Johnson ◽  
R. A. Graziani ◽  
F. C. Yeh
Keyword(s):  
Heat Transfer ◽  
Turbine Blade ◽  
Large Scale ◽  
Flow Direction ◽  
Operating Conditions ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Flow Equations ◽  
Turbine Blade Cooling ◽  
Heat Transfer Coefficients

Experiments were conducted to determine the effects of buoyancy and Coriolis forces on heat transfer in turbine blade internal coolant passages. The experiments were conducted with a large-scale, multipass, heat transfer model with both radially inward and outward flow. Trip strips on the leading and trailing surfaces of the radial coolant passages were used to produce the rough walls. An analysis of the governing flow equations showed that four parameters influence the heat transfer in rotating passages: coolant-to-wall temperature ratio, Rossby number, Reynolds number, and radius-to-passage hydraulic diameter ratio. The first three of these four parameters were varied over ranges that are typical of advanced gas turbine engine operating conditions. Results were correlated and compared to previous results from stationary and rotating similar models with trip strips. The heat transfer coefficients on surfaces, where the heat transfer increased with rotation and buoyancy, varied by as much as a factor of four. Maximum values of the heat transfer coefficients with high rotation were only slightly above the highest levels obtained with the smooth wall model. The heat transfer coefficients on surfaces where the heat transfer decreased with rotation, varied by as much as a factor of three due to rotation and buoyancy. It was concluded that both Coriolis and buoyancy effects must be considered in turbine blade cooling designs with trip strips and that the effects of rotation were markedly different depending upon the flow direction.

Experimental Investigation of Heat Transfer in Impingement Air Cooled Plate Fin Heat Sinks

2005 ◽  
Vol 128 (4) ◽  
pp. 412-418 ◽  
Author(s):  
Zhipeng Duan ◽  
Y. S. Muzychka
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Heat Transfer Model ◽  
Heat Sinks ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Developing Flow ◽  
Rectangular Channels

Impingement cooling of plate fin heat sinks is examined. Experimental measurements of thermal performance were performed with four heat sinks of various impingement inlet widths, fin spacings, fin heights, and airflow velocities. The percent uncertainty in the measured thermal resistance was a maximum of 2.6% in the validation tests. Using a simple thermal resistance model based on developing laminar flow in rectangular channels, the actual mean heat transfer coefficients are obtained in order to develop a simple heat transfer model for the impingement plate fin heat sink system. The experimental results are combined into a dimensionless correlation for channel average Nusselt number Nu∼f(L*,Pr). We use a dimensionless thermal developing flow length, L*=(L∕2)∕(DhRePr), as the independent parameter. Results show that Nu∼1∕L*, similar to developing flow in parallel channels. The heat transfer model covers the practical operating range of most heat sinks, 0.01<L*<0.18. The accuracy of the heat transfer model was found to be within 11% of the experimental data taken on four heat sinks and other experimental data from the published literature at channel Reynolds numbers less than 1200. The proposed heat transfer model may be used to predict the thermal performance of impingement air cooled plate fin heat sinks for design purposes.

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