scholarly journals An Experimental Study of In-Tube Condensation and Evaporation Using Enhanced Heat Transfer (EHT) Tubes

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 867
Author(s):  
Boren Zheng ◽  
Jiacheng Wang ◽  
Yu Guo ◽  
David John Kukulka ◽  
Weiyu Tang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Surface ◽  
Phase Flow ◽  
Enhanced Heat Transfer ◽  
Two Phase ◽  
Evaporation And Condensation ◽  
Nucleation Sites ◽  
Enhanced Tubes ◽  
Enhanced Tube ◽  
Plain Tube

A study was carried out to determine in-tube evaporation and condensation performance of enhanced heat transfer tubes (EHT) using R410A, with the results being compared to a plain tube. The test tubes considered in the evaluation include: plain, herringbone (HB) and spiral (HX) microgrooves, herringbone dimple (HB/D), and hydrophobic herringbone (HB/HY). Experiments to evaluate the condensation were conducted at a saturation of 318 K, and at 279 K for evaporation. Mass flux (G) ranged between 40 to 230 kg m−2s−1. Condensed vapor mass decreased from 0.8 to 0.2; and the mass of vaporized vapor increases from 0.2 to 0.8; heat flux increased with G. Inlet and outlet two-phase flow patterns at 200 kg m−2s−1 were recorded and analyzed. Enhanced tube heat transfer condensation performance (compared to a plain tube) increased in the range from 40% to 73%. The largest heat transfer increase is produced by the herringbone–dimple tube (HB/D). In addition to providing drainage, the herringbone groove also helps to lift the accumulated condensate to wet the surrounding wall. Evaporation thermal performance of the enhanced tubes are from 4% to 46% larger than that of smooth tube with the best performance being in the hydrophobic herringbone tube (HB/HY). This enhancement can be attributed to an increase in the number of nucleation sites and a larger heat transfer surface area. Evaporation and condensation correlations for heat transfer in smooth tubes is discussed and compared.

Suppression of Flow Boiling Nucleation

1997 ◽  
Vol 119 (3) ◽  
pp. 517-524 ◽  
Author(s):  
G. E. Thorncroft ◽  
J. F. Klausner ◽  
R. Mei
Keyword(s):  
Heat Transfer ◽  
Dimensionless Parameter ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Complete Suppression ◽  
Phase Flow ◽  
Two Phase ◽  
Nucleation Sites

A simple model is presented for estimating the ratio of the maximum to minimum cavity radius required for ebullition in two-phase flow with heat transfer. The resulting dimensionless parameter, rmax/rmin, is demonstrated to correlate flow boiling nucleation site density. As the convective heat transfer associated with bulk turbulence in two-phase flow is enhanced, rmax→rmin, and the probability of finding surface cavities whose radii lie between rmaxandrmin is reduced. Thus, active nucleation sites become deactivated. A vertical flow boiling facility was fabricated in which the nucleation suppression point can be measured. Experiments conducted for mass flux ranging from 183–315 kg/m2-s and inlet quality ranging from 0–0.151, along with data available from the literature, suggest that rmax/rmin is the leading order dimensionless parameter on which the complete suppression of nucleation sites depends. Although the suppression of nucleation sites also depends, to a certain extent, on the surface/fluid combination and heat flux, it is found that complete suppression occurs for rmax/rmin ranging from 40 to 120. This is proposed as a criterion to discriminate the purely convective regime from the nucleate boiling regime.

Heat Transfer Enhancement Using Laminar Gas-Liquid Segmented Fluid Streams

2009 ◽  
Author(s):  
Y. S. Muzychka ◽  
E. J. Walsh ◽  
P. Walsh
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Liquid Fraction ◽  
Phase Flow ◽  
Fluid Circulation ◽  
Transfer Enhancement ◽  
Enhanced Heat Transfer ◽  
Two Phase ◽  
Internal Fluid ◽  
Existing Data

Heat transfer enhancement using segmented non-boiling gas-liquid streams is examined. Segmentation results in a two phase flow of liquid/gas having a constant liquid fraction, i.e. no phase change occurs. In this flow configuration, enhanced heat transfer occurs as a result of a shorter effective thermal length and internal fluid circulation in the liquid plugs. A simple theory for laminar segmented flows is developed based on Graetz theory and comparisons made with existing data from the literature and new data obtained in a companion study.

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