Heat Transfer Enhancement during Condensation in Smooth Tubes with Helical Wire Inserts (original) (raw)
Related papers
Condensation heat transfer coefficients of enhanced tubes.
In solar power generating plants, dry cooling towers are used when there is scarcity of water. Normally, condensation of the steam occurs in dry cooling towers in tubes at inclined angles. Almost all the previous work on condensation was in horizontal and vertical tubes until recently when work was done on condensation in inclined tubes but limited to smooth tubes and one type of enhanced tube. The purpose of this paper is to continue on previous work and present heat transfer coefficients and pressure drops during the condensation of R134a in an enhanced tube of inner diameter of 8.67mm with 60 fins with height of 0.22mm spiraled at an angle of 37 o. The experiments were conducted at condensing temperatures of 30 o C and 40 o C at mass fluxes between 300 kg/m 2 s and 400 kg/m 2 s and various vapour qualities. It was found that the heat transfer coefficients and pressure drops increased with mean quality. Overall, the heat transfer enhancement factors were between 2.1 and 2.9 and the pressure drop penalty factors were between 1.2 and 1.8 with the enhancement more pronounced at lower mass fluxes. Finally, the heat transfer and pressure drops increased with decrease in condensing temperature.
Condensation heat transfer of R22 and R410A in horizontal smooth and microfin tubes
International Journal of Refrigeration-revue Internationale Du Froid, 2005
An experimental investigation of condensation heat transfer in 9.52 mm O.D. horizontal copper tubes was conducted using R22 and R410A. The test rig had a straight, horizontal test section with an active length of 0.92 m and was cooled by the heat transfer fluid (cold water) circulated in a surrounding annulus. Constant heat flux of 11.0 kW/m 2 was maintained throughout the experiment and refrigerant quality varied from 0.9 to 0.1. The condensation test results at 45 8C were reported for 40-80 kg/h mass flow rate. The local and average condensation coefficients for seven microfin tubes were presented compared to those for a smooth tube. The average condensation coefficients of R22 and R410A for the microfin tubes were 1.7-3.19 and 1.7-2.94 times larger than those in smooth tube, respectively. q
International Journal of Engineering Materials and Manufacture, 2018
This paper reports an experimental analysis to investigate the enhancement of turbulent heat transfer flow of air through one smooth tube and four different tubes with wire-coil inserts (Pitches, Pc = 12, 24, 40, and 50 mm with corresponding helix angles, α =10 0 , 20 0 , 35 0 , and 45 0 , respectively) at low Reynolds numbers ranging from 6000 to 22000. The test section of the tube was electrically heated and was cooled by fully developed turbulent air flow. The performance of the tubes was evaluated by considering the condition of maximizing heat transfer rate. From the measured data, the heat transfer characteristics such as heat transfer coefficient, effectiveness and Nusselt number, and the fluid flow behaviours such as friction factor, pressure drops and pumping power along the axial distance of the test section were analyzed at those Reynolds numbers for the tubes. The results indicated that for the tubes with wirecoil inserts at low Reynolds numbers, the turbulent heat transfer coefficient might be as much as two-folds higher, the friction factors could be as much as four-folds higher, and the effectiveness might be as much as 1.25 folds higher than those for the smooth tube with similar flow conditions. A correlation was also developed to predict the turbulent heat transfer coefficients through the tubes at low Reynolds numbers.
Heat Transfer Enhancement in a Tube using Rectangular-cut Twisted Tape Insert
Procedia Engineering, 2013
An experimental investigation was carried for measuring tube-side heat transfer coefficient, friction factor, heat transfer enhancement efficiency of water for turbulent flow in a circular tube fitted with rectangular-cut twisted tape insert. A copper tube of 26.6 mm internal diameter and 30 mm outer diameter and 900 mm test length was used. A stainless steel rectangular-cut twisted tape insert of 5.25 twist ratio was inserted into the smooth tube. The rectangular cut had 8 mm depth and 14 mm width. A uniform heat flux condition was created by wrapping nichrome wire around the test section and fiber glass over the wire. Outer surface temperatures of the tube were measured at 5 different points of the test section by T-type thermocouples. Two thermometers were used for measuring the bulk temperatures. At the outlet section the thermometer was placed in a mixing box. The Reynolds numbers were varied in the range 10000-19000 with heat flux variation 14 to 22 kW/m 2 for smooth tube, and 23 to 40 kW/m 2 for tube with insert. Nusselt numbers obtained from smooth tube were compared with Gnielinski [1] correlation and errors were found to be in the range of -6% to -25% with r.m.s. value of 20%. At comparable Reynolds number, Nusselt numbers in tube with rectangular-cut twisted tape insert were enhanced by 2.3 to 2.9 times at the cost of increase of friction factors by 1.4 to 1.8 times compared to that of smooth tube. Heat transfer enhancement efficiencies were found to be in the range of 1.9 to 2.3 and increased with the increase of Reynolds number.
Enhancement of laminar and transitional flow heat transfer in tubes by means of wire coil inserts
International Journal of Heat and Mass Transfer, 2007
This work presents an extensive experimental study on three wire coils of different pitch inserted in a smooth tube in laminar and transition regimes. Isothermal pressure drop tests and heat transfer experiments under uniform heat flux conditions have been carried out.The friction factor increases lie between 5% and 40% in the fully laminar region. The transition from laminar flow to turbulent flow is continuous, without the instabilities and the pressure drop fluctuations that a smooth tube presents.Heat transfer experiments have been performed in the flow ranges: Re=10–2500,Pr=200–700Re=10–2500,Pr=200–700 and Ra=3×106–108Ra=3×106–108. At Reynolds numbers below 200, wire coils do not enhance heat transfer with respect to a smooth tube. For Reynolds numbers between 200 and 1000, wire coils remarkably increase heat transfer. At Reynolds numbers above Re≈1000–1300Re≈1000–1300, transition from laminar to turbulent flow takes place. At Reynolds number around 1000, wire inserts increase the heat transfer coefficient up to eight times with respect to the smooth tube.A performance comparison between wire coils and twisted tape inserts has shown that wire inserts perform better than twisted tapes in the low Reynolds number range: Re=700–2500Re=700–2500.
ENHANCEMENT OF HEAT TRANSFER USING WIRE COIL INSERT IN TUBES
iaeme
This work presents an extensive experimental study on five wire coils of different pitch inserted in a smooth tube in laminar and transition regimes. Isothermal pressure drop tests and heat transfer experiments under uniform heat flux conditions have been carried out the air flow friction and heat transfer characteristics in a round tube fitted with coiled wire turbulators for the turbulent regime, Re = 2000 –10,000 and Pr = 0.7. The use of coiled circular wire causes a high pressure drop increase, which depends mainly on spring pitches and wire thickness the heat transfer in case of the conical coil is highest as compare to the plain pipe and the pipe containing the coil of different pitches. The enhancement efficiency increases with the decreasing pitches and found highest in the conical sets. The friction factor is highest around at a Reynolds number 2200- 3000
Condensation Heat Transfer on Enhanced Surface Tubes: Experimental Results and Predictive Theory
Journal of Heat Transfer, 2002
Condensation heat transfer in a bundle of horizontal enhanced surface copper tubes (Gewa C+ tubes) has been experimentally investigated, and a comparison with trapezoidal shaped fin tubes with several fin spacing has been made. These tubes have a specific surface three-dimensional geometry (notched fins) and the fluids used are either pure refrigerant (HFC134a) or binary mixtures of refrigerants (HFC23/HFC134a). For the pure fluid and a Gewa C+ single tube, the results were analyzed with a specifically developed model, taking into account both gravity and surface tension effects. For the bundle and for a pure fluid, the inundation of the lowest tubes has a strong effect on the Gewa C+ tube performances contrary to the finned tubes. For the mixture, the heat transfer coefficient decreases dramatically for the Gewa C+ tube.