The effect of gap width between horizontal tube and twisted tape on the pressure drop in turbulent water flow (original) (raw)
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Simulation of heat transfer enhancement in tube flow with twisted tape insert
Progress in Computational Fluid Dynamics, An International Journal, 2017
Heat transfer behaviour in a tube with inserted twisted tape swirl generator is investigated numerically, for different values of the twist ratio and diameter ratio and for Reynolds numbers within the range 100-20,000. The transition-SST model is used as the turbulence model. The computational model is validated, first, on a plain tube, where a good agreement is achieved with the correlations. The subsequent analysis of the tube with twisted tape indicates that the use of twist tape enhances heat transfer generally, which is accompanied by a higher pressure drop. It is observed that an improvement of the thermal-hydraulic performance can only be observed for certain configurations and Reynolds numbers.
Swirl flow heat transfer and pressure drop with twisted-tape inserts
Advances in heat transfer, 2003
An extended review of the application of twisted-tape inserts in tubular heat exchangers and their thermal-hydraulic performance is presented. Twisted tapes promote enhanced heat transfer by generating swirl or secondary flows, increasing the flow velocity due to the tube partitioning and blockage, and providing an effectively longer helical flow length. Depending on the tape-edge to tube-wall contact, some fin effects may also be present. Their usage in both single-phase and two-phase (boiling and condensation) flows is considered, and heat transfer and pressure drop results from different investigations are presented. The characteristic features of swirl-induced heat transfer enhancement, nature of swirl flows and their scaling, and development of predictive correlations for heat transfer coefficients and friction factors (or pressure drop) are discussed. Also, some aspects of the use of geometrically modified twisted-tape inserts, as well as compound application with other enhancement techniques, are briefly discussed.
International Journal of Automotive and Mechanical Engineering, 2012
The present work shows the results obtained from experimental investigations of the augmentation of turbulent flow heat transfer in a horizontal tube by means of varying width twisted tape inserts, with air as the working fluid. In order to reduce excessive pressure drops associated with full-width twisted tape inserts, with a lower corresponding reduction in heat transfer coefficients, reduced-width twisted tapes of widths ranging from 10 mm to 22 mm are used, which are lower than the internal diameter of the tube of 27.5 mm. Experiments were carried out for plain tubes with/without twisted tape inserts at a constant wall heat flux and different mass flow rates. The twisted tapes are of three different twist ratios (3, 4 and 5), each with five different widths (26 (full-width), 22, 18, 14 and 10 mm). The Reynolds number varied from 6000 to 13500. Both the heat transfer coefficient and pressure drop are calculated, and the results are compared with those of a plain tube. It is obser...
The Effect of Twisted-Tape Width on Heat Transfer and Pressure Drop for Fully Developed Laminar Flow
Journal of Engineering for Gas Turbines and Power, 1996
A series of experiments was conducted to study the effect of twisted-tape width on the heat transfer and pressure drop with laminar flow in tubes. Data for three twisted-tape wavelengths, each with five different widths, have been collected with constant wall temperature boundary condition. Correlations for the friction factor and Nusselt number are also available. The correlations predict the experimental data to within 10 to 15 percent for the heat transfer and friction factor, respectively. The presence of the twisted tape has caused the friction factor to increase by a factor of 3 to 7 depending on Reynolds number and the twisted-tape geometry. Heat transfer results have shown an increase of 1.5 to 3 times that of plain tubes depending on the flow conditions and the twisted-tape geometry. The width shows no effect on friction factor and heat transfer in the low range of Reynolds number but has a more pronounced effect on heat transfer at the higher range of Reynolds number. It i...
Case Studies in Thermal Engineering, 2019
Twisted tubes and twisted tapes are swirl flow generators utilized for increasing thermal performance. The combined effects of twisted tubes and twisted tapes on heat transfer, pressure drop and thermal performance were experimentally investigated. Experiments were performed using a trapezoidal shaped twisted tube and twisted tapes having various twist ratios (y/w = 2.0, 3.0, 4.0 and 5.0). Water was used as the test fluid in a turbulent regime (4,500<Re<16,000). A simulation of velocity, temperature contours and local Nusselt number plots was also performed to gain information about fluid flow and heat transfer. The results of the combined devices are studied along with those of a smooth circular tube and a twisted tube alone, for comparison. The experimental results show that at a given Re, the Nusselt number (Nu), friction factor (f) and thermal performance of a
IMECE, 2019
Heat exchangers are widely used in heating and cooling devices. The primary challenge is to improve the efficiency of the heat transfer equipment. Researchers have utilized various techniques to achieve this goal. Using twisted tapes could significantly increase the heat transfer rate from a circular surface due to turbulence generated from swirl flow. To enhance the heat transfer rate by twisted tape, two types of arrangements namely: (i) plain twisted tape and (ii) altered twisted tape geometries are used. These arrangements result in swirl flows. For improving heat transfer through swirl flow, some important parameters such as Reynolds number, external surface temperature, friction factor, inlet pressure, and surface heat flux are also considered. To identify the aftereffect of the velocity of inlet water, several parameters namely: (i) external surface temperature, (ii) inlet pressure, (iii) external surface heat flux and (iv) twist ratio are varied. A numerical modelling using k-ε method is performed to evaluate the effects of turbulence from the twisted tape on the heat transfer rate. The objective is to analyze the improvement of heat transfer effectiveness due to the swirl flow. The change in the values of the resulting Reynolds number by changing the inlet fluid velocity from 0.1 ms-1 to 0.7 ms-1 and rotational speed from 200 rpm to 600 rpm is studied. It is observed that for such changes heat transfer increases by 17 percent. It is also observed that heat transfer is directly proportional to inlet pressure and inversely proportional to the increment of twist ratio. The rate of heat transfer increased from 17 percent to 19 percent when the angular velocity of the twisted tape is changed from the 0 rpm to 600 rpm while the velocity of the water inside the pipe is held constant at 0.7 ms-1. Higher heat transfer rate is observed with high inlet pressure. Likewise, higher value of the Nusselt number is observed with higher rotational speed of the twisted tape and higher velocity at the pipe inlet. In addition, it is also observed that when the twist ratio is changed from 4 to 6, the rate of heat transfer is diminished by 6 percent.
Influence of free convection on heat transfer during laminar flow in tubes with twisted tapes
Experimental Thermal and Fluid Science, 1991
• Experiments were carried out with a viscous oil flowing through a horizontal tube containing a twisted tape to understand and quantify heat transfer in the presence of free convection. Data were obtained with the constant wall heat flux boundary conditions for two tube diameters (31.7 mm and 22.8 mm) and for twist ratios varying from about 4 to 8. The Reynolds number (Re0) was varied from 35 to 1756, the Prandtl number (Pro) from 73 to 404, the Rayleigh number (Ra b) from 0.186 × 106 to 33.57 × 106, and the modified Rayleigh number (Ra~) from 5.59 × l06 to 1.96 × 109. The data points are classified into three zones: zone l, where the secondary flow due to swirl is dominant; zone 2, which is a transition zone; and zone 3, where the secondary flow due to free convection is dominant. Data in zone 1 are found to agree well with the correlation of Hang and Bergles, while data in zone 3 are correlated against the Rayleigh number and the modified Rayleigh number in the forms Nu b = C Ra~' and Nu 0 = Cl(Ra~-) rn'. In developing these correlations it is shown that the extent of transition zone 2 is small. Hence the simple generalized method recommended for all zones is to calculate the Nusselt number using the Hang and Bergles correlation and either one of the free convection correlations and then use the higher of the two values of Nusselt number obtained.
International Journal of …, 2009
Experimental investigations of heat transfer and friction factor characteristics of circular tube fitted with full length twisted tape with trapezoidal -cut were studied for the Reynolds number range of 2000-12000. The experimental data obtained from plain tube were verified with the standard correlation to ensure the validation of experimental results. The results obtained from the tube fitted with trapezoidal-cut twisted tape were compared with plain tube. The results show that there was a significant increase in heat transfer coefficient and friction factor for tape with trapezoidal-cut. The heat transfer enhancement of trapezoidal-cut twisted tape is reasonable since the performance ratio was more than unity. Subsequently an empirical correlation has been formulated to base on experimental results with ±5% variation in Nusselt number and ±6% in friction factor.
HEAT TRANSFER IN THE TRANSITIONAL FLOW REGIME INSIDE SMOOTH TUBES WITH TWISTED TAPE INSERTS
A higher heat transfer at relatively low energy cost in heat exchangers used in various engineering applications is essential towards achieving sustainable energy management in the industries. This is achievable by enhancing and operating heat exchangers in the transitional flow regime as compared with the laminar flow regime. The Nusselt number results of an experimental investigation on transition in a smooth tube equipped with twisted tape insert of twist ratio 5 are presented in this study. This experiment was performed under a constant heat flux boundary condition of 2 kW⁄m 2 , using water as working fluid over a range of 500 ≤ Re ≤ 11 000 and 3.9 ≤ Pr ≤ 6.7. In the enhanced tube transition from laminar to turbulent occurred at a range of Reynolds numbers of 750 to 2 082, while the transition in smooth tube commenced and ended at a Reynolds number of 2 700 and 3 187 respectively.