Accurate Heat Transfer Measurements for Condensation on Horizontal, Integral-Fin Tubes

1992 ◽  
Vol 114 (3) ◽  
pp. 719-726 ◽  
Author(s):  
A. Briggs ◽  
X.-L. Wen ◽  
J. W. Rose
Keyword(s):  
Heat Transfer ◽  
Significant Proportion ◽  
Theoretical Models ◽  
Experimental Investigations ◽  
Transfer Coefficients ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
Tube Wall Temperature ◽  
Overall Resistance ◽  
Fin Tubes

In most earlier experimental investigations of condensation on low-fin tubes, vapor-side heat transfer coefficients have been found from overall (vapor-to-coolant) measurements using either predetermined coolant-side correlations or “Wilson plot” methods. When the outside resistance dominates, or is a significant proportion of the overall resistance, these procedures can give satisfactory accuracy. However, for externally enhanced tubes, and particularly with high-conductivity fluids such as water, significant uncertainties may be present. In order to provide reliable, high-accuracy data, to assist in the development of theoretical models, tests have been conducted using specially constructed plain and finned tubes fitted with thermocouples to measure the tube wall temperature, and hence the vapor-side heat transfer coefficient, directly. The paper describes the technique for manufacturing the tubes and gives results of systematic heat transfer measurements covering the effects of fin height, thickness, and spacing, tube diameter, and vapor velocity. The tests were carried out with steam, ethylene glycol, and R-113, with vertical vapor downflow. The heat flux was measured using an accurately calibrated 10-junction thermopile and paying particular attention to coolant mixing and isothermal immersion of thermocouple junctions. Care was taken to avoid errors due to the presence in the vapor of noncondensing gas and the occurrence of dropwise condensation. Smooth, consistent, and repeatable results were obtained in all cases. The data are presented in easily accessible form and are compared with the results of previous investigations, where indirect methods were used to determine the vapor-side data, and with theory.

Effect of Vapour Velocity on Condensation of Ethylene Glycol on Horizontal Integral Fin Tubes: Heat Transfer and Retention Angle Measurements

2010 ◽  
Author(s):  
Claire L. Fitzgerald ◽  
Adrian Briggs ◽  
Huasheng Wang ◽  
John W. Rose
Keyword(s):  
Heat Transfer ◽  
Ethylene Glycol ◽  
Root Diameter ◽  
Transfer Coefficients ◽  
Vapor Velocity ◽  
Finned Tubes ◽  
Tube Wall Temperature ◽  
Transfer And Retention ◽  
Plain Tube ◽  
Fin Tubes

Heat-transfer data are reported for forced-convection filmwise condensation of ethylene glycol flowing vertically downward over two single, horizontal instrumented integral-fin tubes and one plain tube. Vapor-side, heat-transfer coefficients were obtained by direct measurement of the tube wall temperature using two specially manufactured, instrumented tubes with thermocouples embedded in the tube walls. Both tubes have fin height of 1.6 mm and fin root diameter and 12.7 mm, with fin thickness and spacings of 0.3 mm and 0.6 mm, respectively for one of the tubes and 0.5 mm and 1 mm, respectively for the other. Tests were performed at low pressures; 5.59kPa, 8.15kPa and 11.23kPa, at nominal vapour velocities from 13m/s to 82 m/s. All the data show that both of the finned tubes provided an increase in heat flux at the same vapour-side temperature difference with increasing vapour velocity. Visual observations were made and photographs obtained of the fluid retention angle φf at each combination of vapor velocity and pressure tested. It was observed that the curvature of the meniscus was distorted by the increase in vapor velocity and in many cases, the extent of condensate flooding decreased compared to its value in the quiescent vapor case.

An Experimental Study of R-113 Film Condensation on Horizontal Integral-Fin Tubes

1990 ◽  
Vol 112 (3) ◽  
pp. 758-767 ◽  
Author(s):  
P. J. Marto ◽  
D. Zebrowski ◽  
A. S. Wanniarachchi ◽  
J. W. Rose
Keyword(s):  
Heat Transfer ◽  
Surface Area ◽  
Theoretical Models ◽  
Smooth Tube ◽  
Film Condensation ◽  
Transfer Coefficients ◽  
Finned Tubes ◽  
Drainage Patterns ◽  
Fin Tube ◽  
Fin Tubes

Heat transfer measurements were made at near-atmospheric pressure on a smooth tube, on 24 integral-fin tubes having machined, rectangular-shaped fins, and on a commercial integral-fin tube. All tubes were made of copper. The vapor flowed vertically downward with a nominal velocity of 0.4 m/s. Vapor-side heat transfer coefficients were determined with a typical uncertainty of ± 7 percent using a “modified Wilson plot” technique. The vapor-side heat transfer coefficient of the integral-fin tubes (based upon the outside surface area of the smooth tube) was enhanced considerably more than the surface area enhancement provided by the fins. Heat transfer enhancements (for the same vapor-to-wall temperature difference) up to around 7 were measured for a corresponding area enhancement of only 3.9. The optimum fin spacing was found to lie between 0.2 and 0.5 mm, depending upon fin thickness and height. The data were compared with those of other investigations and with several existing theoretical models. Visual observations of condensate drainage patterns from the finned tubes were also made.

Condensation From Pure Steam and Steam–Air Mixtures on Integral-Fin Tubes in a Bank

2004 ◽  
Vol 127 (6) ◽  
pp. 571-580 ◽  
Author(s):  
Adrian Briggs ◽  
Sritharan Sabaratnam
Keyword(s):  
Heat Transfer ◽  
Transfer Coefficients ◽  
Vapor Velocity ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
Wide Range ◽  
Plain Tube ◽  
Reported Data ◽  
Pure Steam ◽  
Fin Tubes

Data are reported for condensation of steam with and without the presence of air on three rows of integral-fin tubes situated in a bank of plain tubes. The data cover a wide range of vapor velocities and air concentrations. Unlike previously reported data for plain tubes using the same test bank and apparatus, the heat-transfer coefficients for the finned tubes were largely unaffected by vapor velocity. When compared to a plain tube of fin-tip diameter and at the same vapor side temperature difference, heat-transfer enhancement ratios between 3.7 and 4.9 were found for the finned tubes compared to a plain tube in quiescent vapor conditions, while values between 1.9 and 3.9 were found when compared to a plain tube at the same vapor velocity. When compared to the plain tubes, the heat transfer to the finned tubes was much more susceptible to the presence of noncondensing gas (air) in the vapor, with enhancement ratios falling as low as 1.5 compared to the plain tubes when even small concentrations of air were present.

scholarly journals Condensation inside smooth horizontal tubes: Part 1. Survey of the methods of heat-exchange prediction

2015 ◽  
Vol 19 (5) ◽  
pp. 1769-1789 ◽  
Author(s):  
Volodymyr Rifert ◽  
Volodymyr Sereda
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Film Condensation ◽  
Experimental Investigations ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

Survey of the works on condensation inside smooth horizontal tubes published from 1955 to 2013 has been performed. Theoretical and experimental investigations, as well as more than 25 methods and correlations for heat transfer prediction are considered. It is shown that accuracy of this prediction depends on the accuracy of volumetric vapor content and pressure drop at the interphase. The necessity of new studies concerning both local heat transfer coefficients and film condensation along tube perimeter and length under annular, stratified and intermediate regimes of phase flow was substantiated. These characteristics being defined will allow determining more precisely the boundaries of the flow regimes and the methods of heat transfer prediction.

Prediction of Heat Transfer Coefficients in Gas Flow Normal to Finned and Smooth Tube Banks

1981 ◽  
Vol 103 (4) ◽  
pp. 705-714 ◽  
Author(s):  
J. C. Biery
Keyword(s):  
Heat Transfer ◽  
Gas Flow ◽  
Finned Tube ◽  
Smooth Tube ◽  
Transfer Coefficients ◽  
Tube Bank ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
High Reynolds ◽  
Tube Banks

A new method is presented to predict heat transfer coefficients for gas flow normal to smooth and finned tube tanks with triangular pitch. A transformation from the actual tube bank to an equivalent equilateral triangular pitch infinite smooth tube bank (ETP-I-STB) is made. A function of Ch(Ch = NSTNPR2/3NRe0.4) versus (Xt D0)Δ, ratio of transverse pitch to tube diameter for the ETP-I-STB, was developed. The Ch for the equivalent ETP-I-STP then applies to the actual tube bank. The method works with circular finned tubes, smooth tubes, continuous finned tubes, and segmented finned tubes with any triangular pitch. Also, fair predictions were made for in-line tubes with high Reynolds numbers.

Experimental Study on Characteristics of Condensation and Flow Resistance Inside Horizontal Corrugated Low Finned Tubes

2018 ◽  
Author(s):  
Bin Ren ◽  
Xiaoying Tang ◽  
Hongliang Lu ◽  
Dongliang Fu ◽  
Yannan Du ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Flow Resistance ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Finned Tubes ◽  
Heat Transfer Coefficients ◽  
Inlet Conditions

It is the simplest and most feasible method to enhance heat transfer by replacing the smooth tube with various kinds of special-shaped enhanced tubes. In this paper, the characteristics of condensation and flow resistance inside horizontal corrugated low finned tubes were studied experimentally. The effects of steam inlet conditions and condensation tubes structural parameters were analyzed. The results showed that the heat transfer performance inside corrugated low finned tubes was greater than that inside smooth tubes. Like inside smooth tubes, the heat transfer coefficients increased with the vapor quality and steam mass flux. But the enhancement rate showed the opposite trend. And the heat transfer coefficients inside corrugated low finned tubes increased with the decrease of pitch and increase of protrusion height. Meanwhile, the variation trend of pressure drop gradient changing with inlet conditions and construal parameters was consistent with trend of heat transfer coefficient. The performance evaluation criteria were used to evaluate the comprehensive performance. It was found that the maximum performance evaluation factor was acquired at the minimum vapor quality and mass flux. The maximum value was 2.24 happened in the tube with pitch of 6 mm and height of 0.7mm. Finally, both the correlation for heat transfer coefficient and correlation for pressure drop gradient were developed by fitting experimental data. And this would provide calculation foundations for the design of horizontal condensers with corrugated low finned tubes.

scholarly journals Effect of Heat Source Placement on Natural Convection from Cylindrical Surfaces

Energies ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 4334
Author(s):  
Andrej Kapjor ◽  
Peter Durcansky ◽  
Martin Vantuch
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Source ◽  
Theoretical Models ◽  
Heat Transfer Process ◽  
Heat Output ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Thermal Fields ◽  
Horizontal Cylinders

Placement of heat source can play a significant role in final heat output, or heat source effectivity. Because of this, there is a need to analyze thermal fields of the heat exchange system by natural convection, where the description by criterion equations is desired, as the net heat output from tubes can be quantified. Based on known theoretical models, numerical methods were adapted to calculate the heat output with natural air flow around tubes, where mathematical models were used to describe the heat transfer more precisely. After validation of heat transfer coefficients, the effect of wall and heat source placement was studied, and the Coanda effect was also observed. The heat source placement also has an effect at the boundary layer, which can change and therefore affect the overall heat transfer process. The optimal wall-to-cylinder distance for an array of horizontal cylinders near a wall was also expressed as a function of the Rayleigh number and number of cylinders in the array.

The Indirectly Heated Carbonate Looping Process for CO2 Capture—A Concept With Heat Pipe Heat Exchanger

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Daniel Hoeftberger ◽  
Juergen Karl
Keyword(s):  
Heat Transfer ◽  
Fluidized Bed ◽  
Power Plants ◽  
Batch Reactor ◽  
Heat Pipes ◽  
Experimental Investigations ◽  
Transfer Coefficients ◽  
Carbonation Reaction ◽  
Heat Transfer Coefficients ◽  
Bubbling Fluidized Bed

The carbonate looping process using the reversible calcination/carbonation reaction of limestone is a promising way to reduce CO2 emissions of fossil fired power plants. This paper describes the concept of an indirectly heated version of this process in which heat pipes accomplish the heat transfer from an air-blown fluidized bed combustor to a bubbling fluidized bed calciner. It defines the calciner's specific heat demand which is a pendant to the heating value of coal. The dimensioning depends on the processes inside heat pipes as well as heat transfer of immersed heating surfaces. Experimental investigations in an electrically heated batch reactor with a similar pipe grid provide heat transfer coefficients under calcination conditions.

Experimental Heat Transfer Coefficient and Pressure Drop during Condensation of R-134a and R-410A in Horizontal Micro-fin Tubes

2018 ◽  
Vol 26 (03) ◽  
pp. 1850022 ◽  
Author(s):  
Sanjeev Singh ◽  
Rajeev Kukreja
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Outer Diameter ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
R 134A ◽  
Fin Tubes

Condensation heat transfer coefficients and pressure drops of HFC refrigerants R-134a and R-410A have been investigated experimentally in smooth and micro-fin tubes (helix angles 18[Formula: see text] and 15[Formula: see text]) of outer diameter 9.52[Formula: see text]mm at mass fluxes from 200 to 600[Formula: see text]kg/m[Formula: see text]s, vapor qualities between 0.1 and 0.9 and at saturation temperatures of 35[Formula: see text]C and 40[Formula: see text]C. Results showed that the heat transfer coefficients of R-134a and R-410A inside micro-fin tubes were 1.21–1.82 and 1.15–1.47 times higher and frictional pressure drops were 2.11–2.56 and 1.62–2.12 times higher than those of smooth tubes. These experimental results are compared with the existing heat transfer and frictional pressure drop correlations proposed by different researchers. The comparison showed fairly good agreement with these existing correlations within [Formula: see text]30%. A new correlation has also been proposed for predicting heat transfer coefficient in micro-fin tubes. The oil concentrations measured for refrigerants R-134a and R-410A varied in the range of 1.3–1.5%, respectively.

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