Integral-fin Tubes Research Articles

OPTIMALIZATION OF INTEGRAL FIN TUBE IN OUTSIDE CONDENSATION BASED ON FLOODING ANGLE

Increasing heat transfer in condensation for low surface tension fluid is dominated by using extended area (fin). One of the extended area on pipe is integral fin tube. Designing of integral fin tube should be conducted due to generate optimal condition such as designing fin spacing. Fin spacing has significantly impacted to heat transfer enhancement. Whereas the material of pipe is copper since has higher heat conductivity than others and fluid working is methanol. To predict optimal geometry of integral fin tube is conducted by using mathematical simulation by dividing area into flooded and unflooded. The active area or unflooded area represents the heat transfer area adn enhancement. In this experiment is found that the optimum fin spasing is 1 mm

Effects of Sloshing Motions on Condensation Heat Transfer Characteristics of Integral-Fin Tubes Under Sea Conditions

Abstract Integral-fin tubes with high heat transfer capability are a promising solution for improving the compactness of condensers used in the exploitation of offshore natural gas at sea, and the sloshing motions including rolling and pitching would inevitably affect the performance of tubes. For applying integral-fin tubes offshore, the effects of rolling and pitching motions on condensation heat transfer characteristics of integral-fin tubes should be known. In this study, the condensation heat transfer characteristics of integral-fin tubes under rolling and pitching motions are experimentally investigated and the effects of motion angle and frequency are quantitatively analyzed. The results show that the sloshing motions have both positive and negative effects on the heat transfer of integral-fin tubes during a period, and the pitching motion has a greater influence than the rolling motion. As the sloshing angle increases from 0 deg to 12 deg, the maximum increase and reduction rates of the ratio of local wall subcooling temperature under pitching motion to that under static conditions are 10.9% and 12.5%, respectively, and the time-averaged condensation heat transfer coefficient (HTC) increases by 3.5% maximally. As the sloshing frequency increases from 0 to 0.25 Hz, the maximum increase and reduction rates of the ratio of local wall subcooling temperature under pitching motion to that under static conditions are 7.7% and 15.2%, respectively, and the increase rate of the time-averaged condensation HTC remains about 2%.

Optimization of Condensation Heat Transfer on enhanced and integral fin tubes by Functionalized-Graphene Layers

Optimization of Condensation Heat Transfer on enhanced and integral fin tubes by Functionalized-Graphene Layers

Experimental study on R410A flow boiling heat transfer outside three enhanced tubes with different fin structures

In order to further explore the influence of the outer fin structure on flow boiling heat transfer, the refrigerant R410A was used to conduct flow boiling heat transfer experiments outside three kinds of enhanced tubes with different outer fin structures (including micro-porous, integral-fin, and independent small bosses structures). The outer diameter of the tubes is 19.05 mm with a mass flux range of 50 kg/m2 s–80 kg/m2 s, and the inlet and outlet vapor quality is maintained at 0.2 and 0.8, respectively. The micro-porous tube showed the best heat transfer performance in the test conditions (the heat transfer coefficient is about 2.52–2.64 times of that of the smooth tube), and the next is the integral-fin tube. Due to local evaporation to dryness, the performance of the independent small bosses tube is inferior to that of the smooth tube. In addition, the heat transfer characteristics of the micro-porous tube under different average vapor qualities were tested and analyzed. Finally, the heat transfer coefficient of the tested tubes can be accurately predicted by modified correlations in the deviation of ±10%.

PRACTICAL STUDY TO IMPROVEMENT THE PERFORMANCE OF HEAT EXCHANGER USING PASSIVE TECHNIQUES

The aim of this study to improve the performance of heat exchanger by using the medium integral fins on the cross flow heat exchanger practically, so, two the heat exchangers from copper were manufactures with eight passes for comparison under different boundary conditions. The water flow rate flow inner the tubes with (2, 3, 4, 5, 6) L/min with inlet temperatures (50, 60, 70) oC, as for the air flow rate were passed outer the tubes by speeds (1, 1.7, 2.3) m/sec. The results show that the medium integral finned tube gives more improvement the heat transfer than the smooth tube about 203.97% and 205.1% was enhancement factor. Motivation: The aim is improvement the heat transfer coefficient for cross flow heat exchanger by using medium integral finned tube. Study the effect of various water stream rate, air speed and inlet water temperature on heat transfer coefficient for them, Finding the cases which enhanced heat transfer for various ranges of air and water as well as inlet temperatures and the speed at the entrance. Develop the empirical correlations for (Nua) of smooth and medium integral finned tubes as function of (Pra) and (Rea).

Experimental investigation of vapor condensation of R-600a over horizontal three-dimensional integral-fin tubes

In this study, condensation heat transfer coefficients (HTCs) of refrigerant R-600a (iso-butane) over horizontal 3-Dimensional integral-fin tubes were determined at vapor temperature of 312 K with wall sub-cooling temperatures of 3–9 K under heat flux of 33–87 kW/m2. Further, our experimental results were validated by comparing them with modified Wilson plot technique. Modified Wilson plot technique underpredicts experimental heat flux by 15–35%.

Heat Transfer Characteristics and Energy Efficiency Analysis of Finned Tube Heat Exchangers

Flow and heat transfer characteristics of the integral finned tube heat exchanger are studied by the numerical simulation method in the present paper. The energy efficiency levels of two types of finned tube heat exchangers (aligned finned tube and staggered finned tube) are evaluated by PEC method. The heat transfer intensity of different finned tube heat exchangers was evaluated by the field synergy principle. When the tube spacing ratio (S1/S2=1) is small, the field synergy of staggered finned tube is similar to the aligned finned tube, and the PEC index is less than 1; when the spacing ratio (S1/S2=3) is large, the field synergy of the staggered finned tube get much stronger than the aligned finned tube, and the PEC index is larger than 1 as the Re≥8×104. Considering both the change of heat transfer intensity and the increase of resistance, it is recommended to evaluate the energy efficiency level of finned tube heat exchanger by PEC method.

Numerical and experimental investigation on the condensing heat transfer of R134a outside plain and integral-fin tubes

Condensing heat transfer of R134a on horizontal single plain and integral-fin tubes was investigated by both computational and experimental methods. The VOF model and Lee condensation model were utilized in the simulation. Validation of the model was performed with two different refrigerants. Condensing heat transfer coefficient for plain and integral-fin tubes were calculated in comparison with the experimental data and Nusselt analytical solution. Instantaneous film flow characteristics of condensation on horizontal single plain and integral-fin tubes were discussed respectively. Contours of liquid volume fraction for the plain tube and condensing heat transfer coefficient for the plain tube at different time with Tw = 303 K are presented. For integral-fin tubes, contours show that the thickness of liquid film at lateral fin surface is much smaller than that at root fin surface. Comparison between R134a and R11 were made and it was found that different surface tension could lead to different liquid film distribution which could result in different heat transfer performance. Experiments involving the same fin structure were also conducted to verify the theoretical model and a satisfactory agreement between simulation and experimental results was found.

Condensate retention of water-ethanol mixture on horizontal enhanced condensing tubes

Condensate retention has been found an important parameter for heat transfer on horizontal enhanced condensing tubes. In this research, five pin-fin (varying in circumferential pin spacing) and three integral-fin horizontal tubes are investigated for condensate retention angle (which is measured from the top of tooth to the fully flooded flank) using water-ethanol mixture. An attempt was made to find the optimum concentration of ethanol in water for maximum retention angle. Concentration of ethanol was varied in between 0.5% to 1.5% by weight. Data revealed the importance of integral-fin tube over pin-fin tube as significant increase in retention angle was observed for integral-fin tube ((having same longitudinal spacing, tooth thickness, tooth height, inner and outer diameter) while retention angle for pin-fin tubes remain unchanged. Optimum ethanol concentration was observed to be 0.75%.

Effect of condensate flow rate on retention angle on horizontal low-finned tubes

The paper reports experimental results using simulated condensation on eight hor?izontal integral finned tubes with different fin spacing but same root diameter. Condensation was simulated with low approaching zero vapor velocity of condensate using three liquids (water, ethylene glycol, and R141b) supplied to the tube via small holes between the fins along the top of the tubes. Controlling parameters of the investigation were fin spacing of condensation tubes, flow rate of condensate and surface tension to density ratio of the condensate. The results indicate that the retention angle (measured from the top of the tube to the position where the inter-fin space is completely filled with liquid) increases with the increase in fin spacing. Also, retention angle increases as the density of the condensate increases but retention angle decreases with increase in surface tension. Interesting finding is seen as retention angle remains constant with increase in condensate flow rate, starting from very low (nearly zero) flow rate to the flow rate at which the tube gets fully flooded. The critical flow rate for eight tubes of defined fin density against three working fluids is measured. Results obtained from simulated condensation for almost zero condensate velocity are in good agreement with earlier data and theoretical model for retention angle on such tubes

Heat transfer enhancement of ammonia pool boiling with an integral-fin tube

Ammonia has been and is used as refrigerant in many industrial refrigeration systems. Flooded shell-and-tube evaporators are normally employed in such systems. However, it is crucial to reduce the size and refrigerant charge of these evaporators, which can be achieved by improving their heat transfer performance using tubes with enhanced surfaces.Tests were performed to analyse the enhancement achieved with a commercial integral-fin (32 f.p.i., 1260 f.p.m.) titanium tube, if compared to a plain tube of the same nominal external diameter, under pool boiling and using ammonia. The test conditions were those than can be found in water chillers and heat transfer coefficients were determined both in increasing and decreasing heat flux order to analyse nucleation hysteresis.The average enhancement factor achieved with this tube was of 1.2 (maximum 1.3). Hysteresis on nucleation occurred and should not be neglected, particularly with the integral-fin tube. An experimental correlation is proposed for both the plain and the enhanced tubes and it predicts the experimental results within 5.5%.

Effect of circumferential pin thickness on condensate retention as a function of vapor velocity on horizontal pin-fin tubes

This paper reports the effect of circumferential pin thickness on retention angle as a function of vapor velocity on four pin-fin tubes (varying in circumferential pin thickness from 0.5 mm to 2.0 mm). Three fluids (namely water, ethylene glycol and R-141b) with high, intermediate and low surface tension to density ratios were tested. Experimentation was performed by providing downward air (to simulate vapor) through a vertical wind tunnel with velocities from 0 to 18 m/s. By providing small holes on the upper side of tube a continuous flow of condensate was ensured along the circumference of the test tubes. At low approaching zero vapor velocity; an increase in circumferential pin thickness caused a decrease in retention angle (an angle measured from top of test tube to the point of flooded flank in circumferential direction) in case of pin-fin tubes for all fluids tested. At high vapor velocity; the role of vapor shear was less effective on the upper half of pin-fin tubes when compared to the equivalent integral-fin tube (i.e. with same longitudinal fin spacing, tooth thickness, tooth height, inner and outer diameter as that of pin-fin tubes). This less effective role of vapor shear on the upper half of pin-fin tubes, when compared with integral-fin tube is thought to be due to the presence of trapped condensate in between the horizontal cuts (circumferential pin spacing) available on pin-fin tubes, which tends to resist the downward motion of the condensate. On the lower half of test tubes (as in case of test fluid R-141b) vapor velocity showed no effect on retention angle for all pin-fin tubes while for the case of equivalent integral-fin tube, retention angle was decreased with the increase of vapor velocity.

Experimental investigation during condensation of R-600a vapor over single horizontal integral-fin tubes

In this study, condensation heat transfer coefficients (HTCs) of refrigerant R-600a (iso-butane) over a horizontal smooth tube of outer diameter 19mm and five integral fin tubes of different fin-densities (945, 1024, 1102, 1181, and 1260fpm) were determined at vapor temperature of 39±0.5°C with different wall sub-cooling temperatures in a range of 3–12°C. Like other refrigerants, condensation heat transfer coefficients of R-600a showed the same trend with wall sub-cooling where condensation HTCs decrease with the rise in wall sub cooling temperatures. The heat flux was 11–20kW/m2 for the plain tube and 28–82kW/m2 for integral fin tubes. Based upon the data taken in this study, different graphs were plotted varying different parameters to show their dependency on other parameters. The experimental data were also validated by comparing them against different models.

Nucleate pool boiling and filmwise condensation heat transfer of R134a on the same horizontal tubes

Pool boiling and condensing heat transfer of R134a on one plain and three enhanced surfaces are experimentally investigated. The saturation temperature in pool boiling is 6°C and condensing is 40°C. The heat flux ranges from 8 to 86kW/m2. The enhanced tubes include integral-fin, pyramid and re-entrant cavity surface. The outside diameter of test tubes is 19mm and the length of test section for boiling is 1100mm and condensing is 1800mm. Integral-fin tube has lower heat transfer coefficient in boiling and condensing. The deviations of experiment result and Owen or Webb models are within ±10% for integral-fin tube in condensing. Pyramid surface provides quite close heat transfer coefficient with re-entrant cavity surface in pool boiling and condensing at heat flux greater than 70kW/m2. The heat transfer performances of re-entrant cavity surface tube is the highest among the three enhanced tubes in either pool boiling or condensing at not high heat flux. The heat transfer coefficients can be 1.9–4.8 and 14.8–19.3 times those of a plain tube in pool boiling and condensing respectively. The decreasing rate of heat transfer coefficient for re-entrant cavity surface is also higher than pyramid surface in condensing. Literature survey on nucleate pool boiling and filmwise condensation is also conducted.

PERSONAL REFLECTIONS ON FIFTY YEARS OF CONDENSATION HEAT TRANSFER RESEARCH

This paper discusses some of the experimental and theoretical work on condensation heat transfer with which I have been involved over many years. The explosion in publications in recent years precludes a comprehensive survey of the general field. The paper is based on an unpublished presentation I gave at the 8th Experimental Heat Transfer, Fluid Mechanics and Thermodynamics Conference (ExHFT-8) held in Lisbon, Portugal, in 2013. It focuses on the topics of dropwise condensation, which has recently again become fashionable after many years, and condensation of metals. In both of these fields the interface temperature discontinuity plays a crucial role. Also discussed is work on condensation on integral finned tubes, in microchannels, and finally on Marangoni condensation of mixtures.

Effect of vapour velocity on condensate retention on horizontal pin-fin tubes

New experimental data for condensate retention angle as a function of vapour velocity (0–19m/s) are reported on six horizontal pin-fin tubes and an equivalent integral-fin tube (i.e. with same longitudinal fin spacing, tooth thickness, tooth height, inner and outer diameter as that of pin-fin tubes) using water, ethylene glycol and R-141b. Only geometric parameter varied was the circumferential pin spacing. For all tubes tested, an increase in vapour velocity causes an increase in condensate retention angle for the cases when retention angle was less than 90° at low approaching zero vapour velocity. For the cases when the retention angle was greater than 90° at low approaching zero vapour velocity, vapour velocity shows negligible effect on retention angle for all pin-fin tubes, while for the case of integral-fin tube (i.e. using R-141b as a test fluid where retention angle is greater than 90° at low approaching zero vapour velocity) retention angle decreased with increasing vapour velocity.

Measurements and semi-empirical correlation for condensate retention on horizontal integral-fin tubes: Effect of vapour velocity

Present study is based on simulated condensation using three fluids (water, ethylene glycol and R-141b) on integral-fin tubes, horizontally oriented in a vertical wind tunnel. Eight tubes of different dimensions were used with fixed fin root diameter and internal diameter of tubes which were kept 12.7 mm and 8.0 mm respectively. Fluid, from a tank mounted above the tube at considerable height flows through the small drilled holes in between the fins. Each tube was tested with a constant flow rate of fluid i.e. the flow rate was adjusted to a minimum value that was just sufficient to produce a smooth film of condensate. Air was used to simulate vapour with a variable velocity from 0 to 19 m/s. A hot wire anemometer was mounted just above the tube into the wind tunnel to measure the air velocity. Observation windows were available on both sides of test section to visualize the condensate retention on integral-fin tubes. Two digital cameras were mounted on both sides of test section to capture the photographs of retention angle on tubes. Condensate retention showed identical behavior on both sides of tube over the tested range of vapour Reynolds number. Retention angle is found to be a strong function of vapour Reynolds number, as retention angle increases with increasing vapour Reynolds number for fluids which have higher value of surface tension to density ratio, however, retention angle decreases with increasing vapour Reynolds number for fluids which have lower value of surface tension to density ratio (i.e. refrigerants). A semi-empirical correlation accounting for the effect of vapour velocity on retention angle is developed that predicts most of the present and earlier experimental data to within ±15% (for water and ethylene glycol) and to within ±5% (for refrigerants).

An investigation of condensate retention on pin-fin tubes

Retention angle measurements on 15 rectangular pin-fin tubes are made under static conditions (without condensation) using water, ethylene glycol and R-113. Condensate retention angles found to be considerably larger than the equivalent integral-fin tubes (i.e. with the same fin height, root diameter and longitudinal pin thickness and spacing) in a range of 5%–60%. An expression for condensate retention angle on pin-fin tubes was proposed and found to agree with the measured retention angles to within 15%.

Element by element prediction model of condensation heat transfer on a horizontal integral finned tube

The paper presents an analytical model to calculate the condensation heat transfer coefficient on an integral finned tube. The model depends on elemental calculations by dividing the tube wall into small annular elements. It takes into consideration the local temperature distribution on the outside surface of the finned tube, the local heat transfer rate and the height of condensate in the channel between fins. The model is able to predict the heat transfer for different fin profiles. Gravity force and surface tension forces are included in the model, where for the latter a linear pressure distribution over the fin is assumed. For the verification of the present model, experimental data for a copper standard finned tube with 1, 1, 1, 2-tetrafluoroethane (R134a) and propane (R290) from our experimental work were used. Within this work, experiments were performed for a steel standard finned tube with R290. For tubes having more than 40 fins per inch (FPI), it could be shown that the channel between fins can be approximated to be trapezoidal or rectangular. This approximation is also applicable for the condensation on tubes having 26 FPI or larger if the subcooling between the saturated vapour and the tube wall is larger than a certain value depending on the working fluid. In comparison to previous analytical models, the present model agrees well with the experimental data and predicts these data with a mean absolute percentage deviation of 4.7%.

Enhanced film condensation of steam on a horizontal finned tube

A heat transfer experimental setup was designed and fabricated to simulate the performance of steam condensers of the multistage flash process. The test section consists of a horizontal single tube shell and tube steam condenser. The experimental study was devised to evaluate the impact of using fin-tubes rather than plain tubes to augment the heat transfer rate during the condensation of steam. Three integral finned tubes of three different materials namely Cu/Ni 90/10, Cu/Ni 70/30, and Al/Br, were tested for heat transfer performance of steam. For each material, three tubes with fin densities of 11, 13, and 15 fins per inch (FPI) were tested. The heat transfer coefficient of the smooth plain tubes was used as a baseline for comparing the heat transfer performance of the high performance enhanced tubes. For the three tested materials, tubes of fin density 11 FPI consistently produced the highest heat transfer enhancement factor followed by 15 and 13 FPI tubes, respectively. For seawater velocity of 2.5 m/s, Al–Br finned tubes yielded the maximum enhancement level followed by Cu–Ni 70/30 and Cu–Ni 90/10, respectively.