Abstract
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.
Highlights
Heat transfer tubes designed with passive surface enhancements can augment the thermal performance of the tube and produce only a small increase to pressure drop
Wang et al [18] investigated and compared the pool boiling characteristics of a copper surface with a micronano, bi-porous enhancement. They found that this new surface produced better heat transfer performance; this type of enhanced surface can be a significant addition to the design of an enhanced heat transfer tube under boiling conditions
Enhanced tubes with a non-composite surface structure (EHT—HX and enhanced heat transfer tubes (EHT)— Herringbone pattern (HB)) show different heat transfer coefficient (HTC), even though similar grooves make up the surface; the inside HTCs of the EHT—HB tube are higher than the values found in the EHT—HX tube
Summary
Heat transfer tubes designed with passive surface enhancements can augment the thermal performance of the tube and produce only a small increase to pressure drop. Guo et al [7] studied several enhanced tubes in order to evaluate in-tube condensation conditions using R22, R32, and R410A; they found that herringbone tubes provide a 200–300% performance increase when compared to plain tubes. Li et al [9] evaluated micro fin and 3D tubes in order to determine intube condensation characteristics They found that the HTC of a copper herringbone tube was up to 2.2 times higher than the HTC of a smooth tube; while the performance increase of the 1EHT tube was up to 1.65 times higher. Wang et al [18] investigated and compared the pool boiling characteristics of a copper surface with a micronano, bi-porous enhancement They found that this new surface produced better heat transfer performance; this type of enhanced surface can be a significant addition to the design of an enhanced heat transfer tube under boiling conditions.
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