In this paper,constructal optimization of the twice Y-shaped assemblies of fins with six freedom degrees (characteristic parameters of geometry) is performed by employing finite element method and taking dimensionless...In this paper,constructal optimization of the twice Y-shaped assemblies of fins with six freedom degrees (characteristic parameters of geometry) is performed by employing finite element method and taking dimensionless maximum thermal resistance as a performance index,and the heat transfer performance of the twice Y-shaped assemblies of fins under various conditions with different freedom degrees are analyzed. The results show that the twice assemblies can improve the heat transfer performance of Y-shaped fin remarkably,and the minimum maximum thermal resistance of the twice Y-shaped assemblies of fins decreases by 36.37% compared with that of once Y-shaped assembly of fins. It is also proved again that the larger the number of freedom degrees for evolving is,the more perfect the system performance is. The effects of different characteristic parameters of geometry on the performance of the twice Y-shaped assemblies of fins are different,one should pay different attention to these parameters in practical engineering designs. The effects of two angles on the maximum thermal resistance are larger,but the optima of the two angles are robust. The effects of two height ratios on the maximum thermal resistance are more remarkable than those of two thickness ratios.展开更多
An experimental study on R22 film condensation on single horizontal tubes(one smooth tube and two doubly enhanced ones) was conducted at the saturation temperatures of 32℃, 35℃ and 38℃ respectively. A modified Wi l...An experimental study on R22 film condensation on single horizontal tubes(one smooth tube and two doubly enhanced ones) was conducted at the saturation temperatures of 32℃, 35℃ and 38℃ respectively. A modified Wi lson plot was used to obtain the water-side and vapor-side heat transfer coeff icients. The results indicated that the experimental condensation heat transfer coefficients agreed with the Nusselt theory with ±10%. The water side heat tr ansfer coefficients of tube No.1 and tube No.2 were 2.78 and 2.99 times of t hat of smooth tube, respectively. At the same heat flux the condensation heat t ransfer coefficients of tube No.1 and tube No.2 were 8.2—18.0 times and 8. 1—12.4 times of the smooth tube, respectively. Thermal resistance analysis sh owed that the relative percentage of vapor-side thermal resistance increased wi th water velocity. When the thermal resistance values of the two sides were equ al, the water velocity of tube No.1 was 1.25 m·s-1(Re=2.41×104) and that of No.2 was 0.82 m·s-1(Re=1.54×104).For all cases, th e wall thermal resistance was less than 4 percentage. The reasons accounting fo r the superiority of tube No.1 were analyzed.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.10905093)the Program for New Century Excellent Talents in University of China(Grant No.NCET-04-1006)the Foun-dation for the Author of National Excellent Doctoral Dissertation of China(Grant No.200136)
文摘In this paper,constructal optimization of the twice Y-shaped assemblies of fins with six freedom degrees (characteristic parameters of geometry) is performed by employing finite element method and taking dimensionless maximum thermal resistance as a performance index,and the heat transfer performance of the twice Y-shaped assemblies of fins under various conditions with different freedom degrees are analyzed. The results show that the twice assemblies can improve the heat transfer performance of Y-shaped fin remarkably,and the minimum maximum thermal resistance of the twice Y-shaped assemblies of fins decreases by 36.37% compared with that of once Y-shaped assembly of fins. It is also proved again that the larger the number of freedom degrees for evolving is,the more perfect the system performance is. The effects of different characteristic parameters of geometry on the performance of the twice Y-shaped assemblies of fins are different,one should pay different attention to these parameters in practical engineering designs. The effects of two angles on the maximum thermal resistance are larger,but the optima of the two angles are robust. The effects of two height ratios on the maximum thermal resistance are more remarkable than those of two thickness ratios.
文摘An experimental study on R22 film condensation on single horizontal tubes(one smooth tube and two doubly enhanced ones) was conducted at the saturation temperatures of 32℃, 35℃ and 38℃ respectively. A modified Wi lson plot was used to obtain the water-side and vapor-side heat transfer coeff icients. The results indicated that the experimental condensation heat transfer coefficients agreed with the Nusselt theory with ±10%. The water side heat tr ansfer coefficients of tube No.1 and tube No.2 were 2.78 and 2.99 times of t hat of smooth tube, respectively. At the same heat flux the condensation heat t ransfer coefficients of tube No.1 and tube No.2 were 8.2—18.0 times and 8. 1—12.4 times of the smooth tube, respectively. Thermal resistance analysis sh owed that the relative percentage of vapor-side thermal resistance increased wi th water velocity. When the thermal resistance values of the two sides were equ al, the water velocity of tube No.1 was 1.25 m·s-1(Re=2.41×104) and that of No.2 was 0.82 m·s-1(Re=1.54×104).For all cases, th e wall thermal resistance was less than 4 percentage. The reasons accounting fo r the superiority of tube No.1 were analyzed.
