Flow Boiling Heat Transfer Characteristics in Horizontal, Three-Dimensional Enhanced Tubes

Abstract

An experimental investigation was conducted to explore the flow boiling heat transfer characteristics of refrigerants R134A and R410A inside a smooth tube, as well as inside two newly developed surface-enhanced tubes. The internal surface structures of the two enhanced tubes are comprised of protrusions/dimples and petal-shaped bumps/cavities. The equivalent inner diameter of all tested tubes is 11.5 mm, and the tube length is 2 m. The experimental test conditions included saturation temperatures of 6 °C and 10 °C; mass velocities ranging from 70 to 200 kg/(m2s); and heat fluxes ranging from 10 to 35 kW/m2, with inlet and outlet vapor quality of 0.2 and 0.8. It was observed that the enhanced tubes exhibit excellent flow boiling heat transfer performance. This can be attributed to the complex surface patterns of dimples and petal arrays that increase the active heat transfer area; in addition, more nucleation sites are produced, and there is also an increased interfacial turbulence. Results showed that the boiling heat transfer coefficient of the enhanced surface tubes was 1.15–1.66 times that of the smooth tubing. Also, effects of the flow pattern and saturated temperature are discussed. Finally, a comparison of several existing flow boiling heat transfer models using the data from the current study is presented.

Experimental Approaches to Measurement of Vapor Quality of Two-Phase Flow Boiling

“…Although different theoretical and experimental approaches have been engaged to date to estimate heat loss during flow boiling, majority of these methods are based on the estimation of heat loss from single-phase flow [6,[9][10][11][12][13][14][15]. Indeed, single-phase experiments were conducted to estimate heat loss percentages for a range of mass fluxes and heat fluxes.…”

“…Although many experimental studies have been conducted to date to investigate the impact of local vapor quality on boiling heat transfer performance, majority of these studies have taken the similar approach to measure local vapor quality Experimental Approaches to Measurement of Vapor Quality of Two-Phase Flow Boiling DOI: http://dx.doi.org /10.5772/intechopen.94473 only at the outlet of test section mainly under uniform wall heat flux boundary conditions using electrical heating [6][7][8][9][10][11][12]. There are limited studies investigating the effect of local vapor quality for other thermal boundary conditions [13,14], while their techniques to measure local vapor quality are not reported clearly. Hence, there is a considerable gap in the literature concerning vapor quality measurement under other thermal boundary conditions (e.g.…”

Experimental Investigation of Critical Heat Flux on Different Surfaces at Low Pressure and Low Flow

“…The other group is represented by flow boiling experiments where the surface effects can be also studied but firstly, the flow parameters together with the geometry of the test section have to be set. Sun et al [7] carried out experiments on smooth and enhanced copper tubes using refrigerants as a working medium. Results obtained at a pressure of 1 MPa, mass fluxes from 70 to 200 kg/(m 2 •s) and heat fluxes in the range from 10 to 35 kW/m 2 showed higher heat transfer performance for enhanced tubes than the smooth one, which authors attributed to the complex two-layer surface structures of enhanced tubes.…”

Effects of Nozzle Exit Position on Condenser Outlet Split Ejector-Based R600a Household Refrigeration Cycle

“…Many household refrigeration cycles such as those used in refrigerators, air conditioners, dehumidifiers, and water purifiers are applied globally; consequently, several studies on improving the energy efficiency of household refrigeration cycles have been conducted [1][2][3][4][5][6][7][8][9][10]. The major irreversible losses in the household refrigeration cycle are generated by the throttling process, which requires the use of capillary tubes or an electrical expansion valve.…”