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 > Dh > 100 μm is presented. For the larger range of Dh (5 > Dh > 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 < x < 1 over the mass flux range 150 < G < 750 kg/m2-s with uncertainties typically less than 20%. For 200 > Dh > 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 < G < 800 kg/m2-s for 0 < x < 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 < G < 750 kg/m2–s.

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%.

Measurement of Heat Transfer and Pressure Drop During Condensation of Carbon Dioxide in Microscale Geometries

2010 ◽  
Author(s):  
Brian M. Fronk ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Pressure Drop ◽  
Test Section ◽  
Copper Substrate ◽  
Condensation Heat Transfer ◽  
Heat Transfer Analysis ◽  
Transfer Coefficients ◽  
Local Pressure ◽  
Heat Transfer Coefficients

Heat transfer coefficients and pressure drops during condensation of carbon dioxide (CO2) are measured in small quality increments in microchannels of 100 &lt; Dh &lt; 200 μm. Channels are fabricated on a copper substrate by electroforming copper onto a mask patterned by X-ray lithography, and sealed by diffusion bonding. The test section is cooled by chilled water circulating at a high flow rate to ensure that the thermal resistance on the condensation heat transfer side dominates. A conjugate heat transfer analysis in conjunction with local pressure drop profiles allows driving temperature differences, heat transfer rates, and condensation heat transfer coefficients to be determined accurately. Heat transfer coefficients are measured for G = 600 kg m−2 s−1 for 0 &lt; x &lt; 1 and multiple saturation temperatures. Preliminary results for a 300 × 100 μm (15 channels) test section are presented. These data are used to evaluate the applicability of correlations developed for larger hydraulic diameters and different fluids for predicting condensation heat transfer and pressure drop of CO2.

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.

Experimental Apparatus for the Determination of Condensation Heat Transfer Coefficient for R134a and R600a Flowing Inside Vertical and Horizontal Tubes Respectively

2009 ◽  
Author(s):  
Ahmet Selim Dalkilic¸ ◽  
O¨zden Ag˘ra
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Cooling Water ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Experimental Apparatus ◽  
Vertical Test

Determination of condensation heat transfer coefficients for HFC-134a in a 7 mm i.d. vertical smooth copper tube and R600a in a 4 mm i.d. horizontal smooth copper tube are experimentally investigated. The test sections are 1 m long horizontal and 0.5 m long vertical counter flow tube-in-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The experiments are performed at average qualities ranging between 0.1–0.99 for the horizontal test section and 0.67–0.99 for the vertical test section. The mass fluxes are ranging between 50–120 kg m−2s−1 and saturation temperatures are between 30–43 °C for the horizontal test section, the mass fluxes are around 29 kg m−2s−1 and saturation temperatures are between 30–36 °C for the vertical test section. The experimental apparatus are designed to capable of changing the different operating parameters such as mass flow rate and condensation temperature of refrigerant, cooling water temperature, and mass flow rate of cooling water etc and investigate their effect on heat transfer coefficients and pressure drops. The ex-proof diaphragm pump for R600a and the gear pump for R134a are used to circulate the refrigerant in these systems. The detailed description of design and development of the test apparatus, control devices, instrumentation, and the experimental procedure are reported and the study of experimental setups from the available literature survey with the existing ones are compared in this paper. The condensation heat transfer coefficients are obtained for two different test sections with various experimental conditions and compared with some well-known correlations in the literature.

Heat Removal and Thermal Stabilization of High-temperature Surfaces by a Dispersed Coolant Flow

Vestnik MEI ◽  
2021 ◽  
pp. 19-26
Author(s):  
Valentin S. Shteling ◽  
◽  
Vladimir V. Ilyin ◽  
Aleksandr T. Komov ◽  
Petr P. Shcherbakov ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flux Density ◽  
Flow Rate ◽  
Heat Flux Density ◽  
Coolant Flow ◽  
Transfer Coefficients ◽  
Stationary Heat ◽  
Heat Transfer Coefficients ◽  
Stationary Heat Transfer

The effectiveness of stabilizing the surface temperature by a dispersed coolant flow is experimentally studied on a bench simulating energy intensive elements of thermonuclear installations A test section in which the maximum heat flux density can be obtained when being subjected to high-frequency heating was developed, manufactured, and assembled. The test section was heated using a VCh-60AV HF generator with a frequency of not lower than 30 kHz. A hydraulic nozzle with a conical insert was used as the dispersing device. Techniques for carrying out an experiment on studying a stationary heat transfer regime and for calculating thermophysical quantities were developed. The experimental data were obtained in the stationary heat transfer regime with the following range of coolant operating parameters: water pressure equal to 0.38 MPa, water mass flow rate equal to 5.35 ml/s, and induction heating power equal to 6--19 kW. Based on the data obtained, the removed heat flux density and the heat transfer coefficients were calculated for each stationary heat transfer regime. The dependences of the heat transfer coefficient on the removed heat flux density and of the removed heat flux density on the temperature difference have been obtained. High values of heat transfer coefficients and heat flux density at a relatively low coolant flow rate were achieved in the experiments.

Investigation of Buoyancy Effects in Asymmetrically Heated Near-Critical Flows of Carbon Dioxide in Horizontal Microchannels Using Infrared Thermography

2021 ◽  
Author(s):  
Lindsey V. Randle ◽  
Brian M. Fronk
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Flux ◽  
Infrared Thermography ◽  
Test Section ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Parallel Microchannels

Abstract In this study, we use infrared thermography to calculate local heat transfer coefficients of top and bottom heated flows of near-critical carbon dioxide in an array of parallel microchannels. These data are used to evaluate the relative importance of buoyancy for different flow arrangements. A Joule heated thin wall made of Inconel 718 applies a uniform heat flux either above or below the horizontal flow. A Torlon PAI test section consists of three parallel microchannels with a hydraulic diameter of 923 μm. The reduced inlet temperature (TR = 1.006) and reduced pressure (PR = 1.03) are held constant. For each heater orientation, the mass flux (520 kgm−2s−2 ≤ G ≤ 800 kgm−2s−2) and heat flux (4.7 Wcm−2 ≤ q″ ≤ 11.1 Wcm−2) are varied. A 2D resistance network analysis method calculates the bulk temperatures and heat transfer coefficients. In this analysis, we divide the test section into approximately 250 segments along the stream-wise direction. We then calculate the bulk temperatures using the enthalpy from the upstream segment, the heat flux in a segment, and the pressure. To isolate the effect of buoyancy, we screen the data to omit conditions where flow acceleration may be important or where relaminarization may occur. In the developed region of the channel, there was a 10 to 15 percent reduction of the local heat transfer coefficients for the upward heating mode compared to downward heating with the same mass and heat fluxes. Thus buoyancy effects should be considered when developing correlations for these types of flow.

The Impact of Fin Deformation on Condensation Heat Transfer Coefficients in Internally Grooved Tubes

2013 ◽  
Author(s):  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Thermal Contact ◽  
Heat Pumps ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Condensing Heat Transfer ◽  
The Impact ◽  
Tube Expansion

In HVACR equipment, internally enhanced round tube (microfin) designs such as axial, cross-grooved, helical, and herringbone are commonly used to enhance the boiling and condensing performance of evaporators, condensers, and heat pumps. Typically, such tubes are mechanically expanded by a mandrel into a fin pack to create an interference fit between the tube outside surface and the fin collar to minimize the thermal contact resistance between tube and fin. However, during this expansion process, the internal enhancements undergo varying amounts of deformation, which degrades the in-tube thermal performance. Extensive data on condensing heat transfer coefficients in microfin tubes have been reported in the open literature. However, researchers have seldom used expanded tubes to acquire and report such data. Hence, it is always questionable to use such pristine tube data for designing heat exchangers and HVACR systems. Furthermore, the HVACR industry has been experiencing steeply rising copper costs, and this trend is expected to continue in coming years. So, many equipment manufacturers and suppliers are actively converting tubes from copper to aluminum. However, because of appreciable differences between the material properties of aluminum and copper, as well as other manufacturing variables, such as mandrel dimensions, lubricant used, etc., tube expansion typically deforms aluminum fins more than copper fins. Based on an analysis of the surface area changes arising from tube expansion, and an assessment of the best extant in-tube condensation heat transfer correlations, this work proposes a method of estimating the impact of tube expansion on in-tube condensation heat transfer. The analysis leads to certain interesting and useful findings correlating fin geometry and in-tube condensation thermal resistance. This method can then be applied to more realistically design HVACR heat exchangers and systems.

Sign in / Sign up

Export Citation Format

Share Document