scholarly journals Condensate retention as a function of condensate flow rate on horizontal enhanced pin-fin tubes

2019 ◽  
Vol 23 (6 Part B) ◽  
pp. 3887-3892 ◽  
Author(s):  
Hafiz Ali ◽  
Hassan Ali ◽  
Muhammad Abubaker ◽  
Ahmed Saieed ◽  
William Pao ◽  
...  
Keyword(s):  
Surface Tension ◽  
Ethylene Glycol ◽  
Flow Rate ◽  
Density Ratio ◽  
Test Tube ◽  
Pin Fin ◽  
Fin Tubes

The extent of condensate flooding as a function of condensate flow rate is measured on six horizontal pin-fin tubes (varying in circumferential pin-spacing) via simulated experimentation. Surface tension to density ratio is tested using three fluids namely water, ethylene glycol and R-141b. Results show that flooding was strongly effected by changing the condensate flow rate. An increase in flow rate caused a marginal decrease in flooding angle (an angle extracted from top of the test tube to the fully flooded flank). Similarly, circumferential pin-spacing also effected the retention angle and the effect goes on increasing by decreasing the surface tension to density ratio.

Enhanced Condensation of Ethylene Glycol on Single Pin-Fin Tubes: Effect of Pin Geometry

2011 ◽  
Vol 134 (1) ◽  
Author(s):  
Hafiz Muhammad Ali ◽  
Adrian Briggs
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Ethylene Glycol ◽  
Heat Transfer Enhancement ◽  
Surface Area ◽  
Two Dimensional ◽  
Transfer Enhancement ◽  
Pin Fin ◽  
Fin Tube ◽  
Fin Tubes

This paper presents a fundamental study into the underlying mechanisms influencing heat transfer during condensation on enhanced surfaces. New experimental data are reported for condensation of ethylene glycol at near atmospheric pressure and low velocity on 11 different 3-dimensional pin-fin tubes tested individually. Enhancements of the vapor-side, heat-transfer coefficients were found between 3 and 5.5 when compared to a plain tube at the same vapor-side temperature difference. Heat-transfer enhancement was found to be strongly dependent on the active surface area of the tubes, i.e., on the surface area of the parts of the tube and pin surface not covered by condensate retained by surface tension. For all the tubes, vapor-side, heat-transfer enhancements were found to be approximately twice the corresponding active-area enhancements. The best performing pin-fin tube gave a heat-transfer enhancement of 5.5; 17% higher than obtained from “optimised” two-dimensional fin-tubes reported in the literature and about 24% higher than the “equivalent” two-dimensional integral-fin tube (i.e., with the same fin-root diameter, longitudinal fin spacing and thickness, and fin height). The effects of surface area and surface tension induced enhancement and retention are discussed in the light of the new data and those of previous investigations.

EFFECT OF CONDENSATE FLOW RATE AND VAPOR VELOCITY ON CONDENSATE RETENTION FOR PIN-FIN TUBES

2019 ◽  
Vol 26 (6) ◽  
pp. 619-630
Author(s):  
Hassan Ali ◽  
Nasir Rafique ◽  
Amjad Hussain ◽  
Muazzam Ali ◽  
Haroon Farooq
Keyword(s):  
Flow Rate ◽  
Vapor Velocity ◽  
Pin Fin ◽  
Fin Tubes

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

2018 ◽  
Vol 22 (1 Part B) ◽  
pp. 435-441 ◽  
Author(s):  
Hafiz Ali ◽  
Hassan Ali ◽  
Muhammad Ali ◽  
Shahid Imran ◽  
Muhammad Kamran ◽  
...  
Keyword(s):  
Surface Tension ◽  
Flow Rate ◽  
Density Ratio ◽  
Root Diameter ◽  
Critical Flow ◽  
Critical Flow Rate ◽  
Finned Tubes ◽  
Fin Spacing ◽  
Zero Flow ◽  
Good Agreement

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

Enhanced Condensation of Ethylene Glycol on Three-Dimensional Pin-Fin Tubes

2010 ◽  
Author(s):  
Hafiz Muhammad Ali ◽  
Hassan Ali ◽  
Adrian Briggs
Keyword(s):  
Heat Transfer ◽  
Ethylene Glycol ◽  
Heat Transfer Enhancement ◽  
Three Dimensional ◽  
Active Surface Area ◽  
Two Dimensional ◽  
Transfer Enhancement ◽  
Pin Fin ◽  
Fin Tube ◽  
Fin Tubes

New experimental data are reported for condensation of ethylene glycol at near atmospheric pressure and low velocity on six three-dimensional pin-fin tubes. Enhancements of the vapour-side, heat-transfer coefficients were found between 3 to 5.5 when compared to a plain tube at the same vapour-side temperature difference. Heat-transfer enhancement was found to be strongly dependent on the active surface area i.e. on the proportion of the tube and pin surface not covered by condensate retained by surface tension. For all the tubes, vapour-side, heat-transfer enhancements were found to be approximately 3 times the corresponding active-area enhancements. The best performing pin-fin tube gave a heat-transfer enhancement of up to 5.5; 17% higher than those obtained from ‘optimised’ two-dimensional fin-tubes reported in the literature and about 24% higher than the ‘equivalent’ two-dimensional integral-fin tube (i.e. with same fin root diameter, longitudinal fin spacing and thickness and fin height).

scholarly journals Effect of a newly developed pastille on the salivary flow rate in subjects with dry mouth symptoms: a randomized, controlled, monocentric clinical study

2021 ◽  
Vol 21 (1) ◽  
Author(s):  
S. Bielfeldt ◽  
D. Wilhelm ◽  
C. Neumeister ◽  
U. Schwantes ◽  
K. -P. Wilhelm
Keyword(s):  
Surface Tension ◽  
Flow Rate ◽  
Gum Arabic ◽  
Salivary Flow ◽  
Salivary Flow Rate ◽  
Dry Mouth ◽  
Main Ingredient ◽  
Control Product ◽  
Swallowing Problems ◽  
The Mean

Abstract Background Xerostomia is associated with several diseases and is a side effect of certain drugs, resulting from reduced saliva secretion. Often, aged and sometimes younger people suffer from (idiopathic) xerostomia. Chewing gum and sucking pastilles may relieve symptoms of xerostomia by increasing the salivary flow rate due to the mechanical effect of sucking and gustatory stimulation. Swallowing problems and the urge to cough or experiencing a tickling sensation in the throat might be alleviated through a reduction in dry mouth symptoms. We investigated whether a pastille containing four polysaccharides increased the salivary flow rate and relieved the symptoms of dry mouth. Methods Participating subjects with xerostomia were randomized into two equally balanced treatment groups. Subjects received the pastille on Day 1 and a control product (Parafilm®) on Day 3, or vice versa. Unstimulated saliva was collected every 2.5 min for 0–10 min. Stimulated saliva was collected after subjects sucked the pastille or the control product. The salivary flow rate was determined gravimetrically, and, in parallel, the feeling of dry mouth was assessed using a visual analog scale. Saliva surface tension was measured in pooled saliva samples (0–5 min of sampling). Additionally, in stimulated saliva from six subjects who sucked the pastille, the presence of the main ingredient—gum arabic—was examined by Raman spectroscopy. Results Chewing the pastille significantly increased the mean salivary flow rate by 8.03 g/10 min compared to the mean changes after chewing the control product (+ 3.71 g/10 min; p < 0.0001). The mean score of dry mouth was significantly alleviated by the pastille (− 19.9 ± 17.9 mm) compared to the control product (− 3.3 ± 18.1 mm). No difference between the two products was seen regarding the saliva surface tension. Gum arabic was present in the saliva of all investigated subjects for up to 10 min after sucking the pastille. Conclusions The pastille was well tolerated and effective in increasing the salivary flow rate and reducing mouth dryness after sucking. These results were in line with the detection of the main ingredient, gum arabic, in saliva for up to 10 min after sucking the pastille. Trial registration German Register Clinical Trials (Deutsches Register Klinische Studien, DRKS) DRKS-ID: DRKS00017393, Registered 29 May 2019, https://www.drks.de/drks_web/navigate.do?navigationId=trial. HTML&TRIAL_ID = DRKS00017393.

Study on C–S and P–R EOS in pseudo-potential lattice Boltzmann model for two-phase flows

2017 ◽  
Vol 28 (09) ◽  
pp. 1750120 ◽  
Author(s):  
Yong Peng ◽  
Yun Fei Mao ◽  
Bo Wang ◽  
Bo Xie
Keyword(s):  
Surface Tension ◽  
Lattice Boltzmann ◽  
Equations Of State ◽  
Density Ratio ◽  
Maximum Density ◽  
Lattice Boltzmann Model ◽  
Two Phase Flows ◽  
Two Phase ◽  
Spurious Currents ◽  
Pseudo Potential

Equations of State (EOS) is crucial in simulating multiphase flows by the pseudo-potential lattice Boltzmann method (LBM). In the present study, the Peng and Robinson (P–R) and Carnahan and Starling (C–S) EOS in the pseudo-potential LBM with Exact Difference Method (EDM) scheme for two-phase flows have been compared. Both of P–R and C–S EOS have been used to study the two-phase separation, surface tension, the maximum two-phase density ratio and spurious currents. The study shows that both of P–R and C–S EOS agree with the analytical solutions although P–R EOS may perform better. The prediction of liquid phase by P–R EOS is more accurate than that of air phase and the contrary is true for C–S EOS. Predictions by both of EOS conform with the Laplace’s law. Besides, adjustment of surface tension is achieved by adjusting [Formula: see text]. The P–R EOS can achieve larger maximum density ratio than C–S EOS under the same [Formula: see text]. Besides, no matter the C–S EOS or the P–R EOS, if [Formula: see text] tends to 0.5, the computation is prone to numerical instability. The maximum spurious current for P–R is larger than that of C–S. The multiple-relaxation-time LBM still can improve obviously the numerical stability and can achieve larger maximum density ratio.

Prediction of the Condensation Coefficient on Horizontal Integral-Fin Tubes

1985 ◽  
Vol 107 (2) ◽  
pp. 369-376 ◽  
Author(s):  
R. L. Webb ◽  
T. M. Rudy ◽  
M. A. Kedzierski
Keyword(s):  
Surface Tension ◽  
Theoretical Model ◽  
Surface Tension Force ◽  
Tension Force ◽  
Condensation Coefficient ◽  
Film Drainage ◽  
Predicted Values ◽  
Experimental Values ◽  
Fin Tubes

A theoretical model is developed for prediction of the condensation coefficient on horizontal integral-fin tubes for both high and low surface tension fluids. The model includes the effects of surface tension on film drainage and on condensate retention between the fins. First, the fraction of the tube circumference that is flooded with condensate is calculated. Typically, the condensation coefficient in the flooded region is negligible compared to that of the unflooded region. Then the condensation coefficient on the unflooded portion is calculated, assuming that surface tension force drains the condensate from the fins. The model is used to predict the R-11 condensation coefficient on horizontal, integral-fin tubes having 748, 1024, and 1378 fpm. The predicted values are within ±20 percent of the experimental values.

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