Nobuo Takata

Condensation of downward-flowing HFC134a in a staggered bundle of horizontal finned tubes: effect of fin geometry

Experimental results are presented that show the effect of fin geometry on condensation of refrigerant HFC134a in a staggered bundle of horizontal finned tubes. Two types of conventional low-fin tubes and three types of three-dimensional fin tubes were tested. The refrigerant mass velocity ranged from 8 to 23 kg/m2s and the condensation temperature difference from 1.5 to 12 K. The effect of condensate inundation was more significant for the three-dimensional fin tubes than for the low-fin tubes. In most cases, the highest performance was obtained by the tube with a three-dimensional structure at the tip of low fins. In the case of high mass velocity and high condensate inundation rate, however, the highest performance was obtained by one of the low-fin tubes. The results were compared with previous results for bundles of smooth tubes and low-fin tubes.

Experimental measurements for condensation of downward-flowing R123/R134a in a staggered bundle of horizontal low-finned tubes with four fin geometries

Experiments were conducted to obtain row-by-row heat and mass transfer data during condensation of downward-flowing zeotropic mixture R123/R134a in a staggered bundle of horizontal low-finned tubes. The vapor temperature and the mass fraction of R134a at the tube bundle inlet were about 50°C and 14%, respectively. The refrigerant mass velocity ranged from 9 to 34 kg m−2 s−1, and the condensation temperature difference from 1.9 to 12 K. Four kinds of low-finned tubes with different fin geometry were tested. The highest heat transfer coefficient was obtained with a tube which showed the highest performance for R123. However, the diference among the tubes was much smaller for the mixture than for R123. The heat transfer coefficient and the vapor-phase mass transfer coefficient decreased significantly with decreasing mass velocity. The mass transfer coefficient increased with condensation temperature difference, which was due to the effect of suction associated with condensation. On the basis of the analogy between heat and mass transfer, a dimensionless correlation of the mass transfer coefficient was developed for each tube.

Vapor absorption by LiBr aqueous solution in vertical smooth tubes

Abstract Heat and mass transfer in a falling film vertical in-tube absorber was studied experimentally with LiBr aqueous solution. The presented results include the effect of solution flow rate, solution subcooling and cooling water temperature on the absorption in a smooth copper tube 16.05 mm I.D. and 400 mm long. The experimental data in the previous report for a 1200-mm-long tube was also re-examined and compared. It was demonstrated by the observation of the flow in the tube that the break down of the liquid film into rivulets leads to deterioration of heat and mass transfer at lower film Reynolds number or in longer tubes. An attempt to evaluate physically acceptable heat and mass transfer coefficients that are defined with estimated temperature and concentration at the vapor–liquid interface was also presented.

Effect of Fin Geometry on Condensation of R407C in a Staggered Bundle of Horizontal Finned Tubes

Experimental results are presented that show the effect of fin geometry on condensation of downward flowing zeotropic refrigerant mixture R407C in a staggered bundle of horizontal finned tubes. Two types of conventional low-fin tubes and three types of three-dimensional-fin tubes were tested. The refrigerant mass velocity ranged from 4 to 23 kg/m 2 s and the condensation temperature difference from 3 to 12 K. The measured condensation heat transfer coefficient was lower than the previous results for R134a, with the difference being more significant for smaller mass velocity. The effect of fin geometry on the condensation heat transfer coefficient was less significant for R407C than for R134a. The effect of condensate inundation was more significant for the three-dimensional-fin tubes than for the low-fin tubes. By using the dimensionless heat transfer correlation for the condensate film that was based on the experimental data for R134a, a superficial vapor-phase heat transfer coefficient was obtained for condensation of R407C. The vapor-phase heat transfer coefficient showed characteristics similar to the vapor-phase mass transfer coefficient that was obtained in the previous study for R123/R134a.

Comparative assessment on irreversible losses in heat pumps using R744/R32/R1234yf and R744/R32/R1234ze(E)

This article presents an experimental assessment of coefficient of performance and irreversible loss in the heat pump cycle using hydro-fluoro-olefin base ternary mixtures: YF300 (R744/R32/R1234yf; 4/44/52 mass%), YF200 (R744/R32/R1234yf; 5/28/67 mass%), ZE300 (R744/R32/R1234ze(E); 4/43/53 mass%), and ZE200 (R744/R32/R1234ze(E); 9/29/62 mass%). The smaller volumetric capacity of YF200 and ZE200 increases the irreversible loss caused by the pressure drop with increasing heat load. ZE200, which has a temperature glide of approximately 22 K, increases the irreversible loss in the condenser, evaporator, and expansion valve. The experimental results indicate that YF300 and ZE300 could be potential alternatives to R410A and R32.