Condensation heat transfer and pressure drop characteristics of R-600a in horizontal smooth and helically dimpled tubes

Abstract

In the present study, condensation heat transfer and frictional pressure drops of refrigerant R-600a (iso-butane) inside a helically dimpled tube and a plain tube of internal diameter 8.3 mm were measured and analyzed. All tests were performed at different vapor qualities up to 0.82 and average saturation temperatures ranging between 38 and 42℃. Refrigerant mass fluxes varied in the range of 114-368 kg/m 2 s. The inner surface of the helically dimpled tube has been designed and reshaped through three-dimensional material surface modifications consists of both shallow and deep protrusions which are placed evenly in helical directions on the tube wall. The experimental results show that the heat transfer coefficients of the dimpled tube are 1.2-2 times of those in smooth tube with a pressure drop penalty just ranging between 58% and 195%. The highest heat transfer coefficient is occurred at vapor quality of 0.53 and mass flow rate of 368 kg/m 2 s. On the other hand, the maximum increase of pressure drop takes place at vapor quality of 0.55 and mass flow rate of 368 kg/m 2 s. Nomenclature ݉ሶ mass flow rate (kg/s) A C p surface area (m ଶ ) specific heat (kJ/kg k)

Heat transfer analysis of plain and dimpled tubes with different spacings

“…A similar study with dimples and protrusions in microchannels using Al 2 O 3 ‐Water nanofluids was conducted by Li and colleagues, Dimpled vortex generators in lattice cooling channels showed superior heat transfer capabilities due to increases in surface area . Several other similar studies on enhanced tubes with dimples in channels and tubes were performed by various researchers as reported in the literature …”

“…20 Several other similar studies on enhanced tubes with dimples in channels and tubes were performed by various researchers as reported in the literature. [21][22][23][24][25][26] At this stage, it is important to study heat transfer behavior with different spacings between the tubes, because no such study has yet been performed. Hence, with this motivation, an experimental study is reported in this article to address the heat transfer enhancement at different spacings of the tubes.…”

Comparison of the Evaporation and Condensation Heat Transfer Coefficients on the External Surface of Tubes in the Annulus of a Tube-in-Tube Heat Exchanger

“…The results showed that the dimpled tube with the largest depth provided the highest heat transfer coefficient, as well as the largest pressure drop penalty (an unexpected pressure drop increase up to 892% higher than that of the smooth tube was reported). Sarmadian et al [14] measured and analyzed the condensation heat transfer coefficient and frictional pressure drop of R600a in a helically dimpled tube. Their experimental results indicated that the heat transfer coefficients of the dimpled tube were 1.2-2 times higher than those found in an equivalent smooth tube with a pressure drop penalty ranging from 58% to 195% (when compared to smooth tubes).…”

Pressure loss and performance assessment of horizontal spiral coil inserted pipes during forced convective evaporation of R-600a

“…In another empirical study performed by Shafaee et al [17] on boiling of R-600a in plain and rough pipes, it was demonstrated that heat transfer rate and pressure drops in dimpled pipes are larger than those obtained in smooth pipes. To illustrate the impacts of operational conditions and pipe surface roughness on the magnitude of heat transfer coefficient and pressure loss obtained during condensation of R-600a, Sarmadian et al [18] evaluated a two-phase flow heat-exchanger. According to the observations, increasing the vapor quality and mass flux gives rise to the rate of transferred heat and pressure loss.…”