Carbon dioxide heat transfer coefficients and pressure drops during flow boiling: Assessment of predictive methods

2010 ◽  
Vol 33 (6) ◽  
pp. 1068-1085 ◽  
Author(s):  
R. Mastrullo ◽  
A.W. Mauro ◽  
A. Rosato ◽  
G.P. Vanoli
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Flow Boiling ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Predictive Methods

Experimental Study of Miscible and Immiscible Oil Effects on Heat Transfer Coefficients and Pressure Drop in Microchannel Gas Cooling of Supercritical CO2

2003 ◽  
Author(s):  
Guohua Kuang ◽  
Michael Ohadi ◽  
Yuan Zhao
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Vapor Compression ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Negative Effect ◽  
Gas Cooling

Carbon Dioxide (CO2) is being investigated as an alternative refrigerant for vapor compression systems. In addition to its environmental benefits, Carbon Dioxide offers certain attractive thermal characteristics such as small surface tension, small liquid viscosity and large refrigerant capacity. Furthermore, combination with microchannels provides CO2 heat exchangers that have low weight, high compaction and high heat transfer coefficient. But certain oil (e.g., lubricate oil for compressor) will be carried into the vapor compression system, which usually has negative effect on heat transfer and pressure drop. The objective of the present paper is to study the effect of oil addition on heat transfer coefficient and pressure drop in supercritical gas cooling process in microchannels. Experiments addressed effect of three different types of oil (two immiscible and one miscible) at various oil concentrations ranging from 0% (no oil) to 5% by weight. As expected, oil addition has significant negative effect on heat transfer coefficients. At higher oil concentrations the heat transfer coefficients are substantially lower and the pressure drops are higher. As far the type of oil is concerned, the immiscible oil demonstrated more negative influence on the heat transfer and pressure drops than the miscible oil.

Heat Transfer During Forced Convection Boiling of R-12 Under Swirl Flow

1986 ◽  
Vol 108 (3) ◽  
pp. 567-573 ◽  
Author(s):  
K. N. Agrawal ◽  
H. K. Varma ◽  
S. Lal
Keyword(s):  
Heat Transfer ◽  
Flow Boiling ◽  
Swirl Flow ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Heat Transfer Augmentation ◽  
Twisted Tapes ◽  
Flow Heat

This work is an experimental investigation of heat transfer augmentation in a horizontal R-12 evaporator, continuing an earlier study [1] by the authors on swirl flow pressure drops. Twisted tapes were used to create swirl motion during the flow boiling inside an evaporator tube of 10 mm i.d. Average heat transfer coefficients have been determined for 60 runs corresponding to three heat fluxes, five mass velocities, and four twist ratios. Swirl flow heat transfer coefficients have been found, in general, to be greater than the corresponding plain flow values, but the degree of enhancement varies depending on the test conditions and the twist ratio of the inserted tape. An empirical correlation which predicts the average swirl flow heat transfer coefficients within ± 30 percent of the experimentally observed values has been successfully developed.

Heat Transfer Enhancement in Triangular Ducts With an Array of Side-Entry Wall/Impinged Jets

1999 ◽  
Author(s):  
J.-J. Hwang ◽  
C.-S. Cheng ◽  
Y.-P. Tsia
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Inclined Angle

An experimental study has been performed to measure local heat transfer coefficients and static well pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right-triangular ducts of the same altitude and different apex angles of β = 30 deg (Duct A), 45 deg (Duct B) and 60 deg (Duct C) are tested for various jet Reynolds numbers (3000≦Rej≦12600) and jet spacings (s/d = 3.0 and 6.0). Results show that an increase in Rej increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Rej, the Duct C has the highest wall-averaged heat transfer because of the highest jet center velocity as well as the smallest jet inclined angle. Moreover, the distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.

Experimental Study of Evaporation Heat Transfer Characteristics and Pressure Drops of R410A and R134a in a Multiport Mini-Channel

2009 ◽  
Author(s):  
Jatuporn Kaew-On ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

The evaporation heat transfer coefficients and pressure drops of R-410A and R-134a flowing through a horizontal-aluminium rectangular multiport mini-channel having a hydraulic diameter of 3.48 mm are experimentally investigated. The test runs are done at refrigerant mass fluxes ranging between 200 and 400 kg/m2s. The heat fluxes are between 5 and 14.25 kW/m2, and refrigerant saturation temperatures are between 10 and 30 °C. The effects of the refrigerant vapour quality, mass flux, saturation temperature and imposed heat flux on the measured heat transfer coefficient and pressure drop are investigated. The experimental data show that in the same conditions, the heat transfer coefficients of R-410A are about 20–50% higher than those of R-134a, whereas the pressure drops of R-410A are around 50–100% lower than those of R-134a. The new correlations for the evaporation heat transfer coefficient and pressure drop of R-410A and R-134a in a multiport mini-channel are proposed for practical applications.

Periodically Converging-Diverging Tubes and Their Turbulent Heat Transfer, Pressure Drop, Fluid Flow, and Enhancement Characteristics

1984 ◽  
Vol 106 (1) ◽  
pp. 55-63 ◽  
Author(s):  
P. Souza Mendes ◽  
E. M. Sparrow
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Surface Area ◽  
Equal Mass ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Friction Factors

A comprehensive experimental study was performed to determine entrance region and fully developed heat transfer coefficients, pressure distributions and friction factors, and patterns of fluid flow in periodically converging and diverging tubes. The investigated tubes consisted of a succession of alternately converging and diverging conical sections (i.e., modules) placed end to end. Systematic variations were made in the Reynolds number, the taper angle of the converging and diverging modules, and the module aspect ratio. Flow visualizations were performed using the oil-lampblack technique. A performance analysis comparing periodic tubes and conventional straight tubes was made using the experimentally determined heat transfer coefficients and friction factors as input. For equal mass flow rate and equal transfer surface area, there are large enhancements of the heat transfer coefficient for periodic tubes, with accompanying large pressure drops. For equal pumping power and equal transfer surface area, enhancements in the 30–60 percent range were encountered. These findings indicate that periodic converging-diverging tubes possess favorable enhancement characteristics.

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