Boiling Heat Transfer Coefficients in a Falling Film Helical Coil Heat Exchanger for the NH3–LiNO3 Mixture

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
J. A. Hernández-Magallanes ◽  
W. Rivera
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Boiling Heat Transfer ◽  
Helical Coil ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Heat Transfer Coefficients ◽  
Mass Flow Rates

This paper reports the experimental data of boiling heat transfer coefficients for the ammonia–lithium nitrate mixture in a laminar falling film. The analyzed heat exchanger consists of a shell with an internal helical coil. More than one hundred test runs were carried out in steady-state conditions to determine the boiling heat transfer coefficients at generation temperatures, concentrations, and mass flow rates typical of absorption cooling systems of capacities between 5 and 10 kW. Ammonia vapor was produced at generation temperatures between 80 °C and 105 °C obtaining boiling heat transfer coefficients between 85 and 340 W/m2K. Semi-empirical correlations were used by diverse authors to correlate the experimental data. A new correlation was proposed with which the best adjustments were obtained. Also, the influence of the heat flux, the refrigerant solution mass flow rates, and the exit vapor qualities were analyzed in the boiling heat transfer coefficients.

scholarly journals Numerical and experimental investigation of heat transfer of ZnO/Water nanofluid in the concentric tube and plate heat exchangers

2011 ◽  
Vol 15 (1) ◽  
pp. 183-194 ◽  
Author(s):  
Fard Haghshenas ◽  
Mohammad Talaie ◽  
Somaye Nasr
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Rate ◽  
Heat Exchangers ◽  
Transfer Rate ◽  
Transfer Coefficients ◽  
Flow Rates ◽  
Plate Heat ◽  
Heat Transfer Coefficients ◽  
Mass Flow Rates

The plate and concentric tube heat exchangers are tested by using the water-water and nanofluid-water streams. The ZnO/Water (0.5%v/v) nanofluid has been used as the hot stream. The heat transfer rate omitted of hot stream and overall heat transfer coefficients in both heat exchangers are measured as a function of hot and cold streams mass flow rates. The experimental results show that the heat transfer rate and heat transfer coefficients of the nanofluid in both of the heat exchangers is higher than that of the base liquid (i.e., water) and the efficiency of plate heat exchange is higher than concentric tube heat exchanger. In the plate heat exchanger the heat transfer coefficient of nanofluid at mcold = mhot = 10 gr/sec is about 20% higher than base fluid and under the same conditions in the concentric heat exchanger is 14% higher than base fluid. The heat transfer rate and heat transfer coefficients increases with increase in mass flow rates of hot and cold streams. Also the CFD1 code is used to simulate the performance of the mentioned heat exchangers. The CFD results are compared to the experimental data and showed good agreement. It is shown that the CFD is a reliable tool for investigation of heat transfer of nanofluids in the various heat exchangers.

The Correlation of Heat Transfer Coefficients for the Laminar Natural Convection in a Circular Finned-Tube Heat Exchanger

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Hie Chan Kang ◽  
Se-Myong Chang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nusselt Number ◽  
Natural Convection ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Finned Tube ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Laminar Natural Convection

This study proposes an empirical correlation for laminar natural convection applicable to external circular finned-tube heat exchangers with wide range of configuration parameters. The transient temperature response of the heat exchangers was used to obtain the heat transfer coefficient, and the experimental data with their characteristic lengths are discussed. The data lie in the range from 1 to 1000 for Rayleigh numbers based on the fin spacing: the ratio of fin height to tube diameter ranges from 0.1 to 0.9, and the ratio of fin pitch to height ranges from 0.13 to 2.6. Sixteen sets of finned-tube electroplated with nickel–chrome were tested. The convective heat transfer coefficients on the heat exchangers were measured by elimination of the thermal radiation effect from the heat exchanger surfaces. The Nusselt number was correlated with a newly suggested composite curve formula, which converges to the quarter power of the Rayleigh number for a single cylinder case. The proposed characteristic length for the Rayleigh number is the fin pitch while that for the Nusselt number is mean flow length, defined as half the perimeter of the mean radial position inside the flow region bounded by the tube surface and two adjacent fins. The flow is regarded as laminar, which covers heat exchangers from a single horizontal cylinder to infinite parallel disks. Consequently, the result of curve fitting for the experimental data shows the reasonable physical interpretation as well as the good quantitative agreement with the correction factors.

Analysis of a Load-Side Heat Exchanger for a Solar Domestic Hot Water Heating System

1998 ◽  
Vol 120 (4) ◽  
pp. 270-274 ◽  
Author(s):  
T. R. Smith ◽  
P. J. Burns ◽  
D. C. Hittle
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Exchanger ◽  
Heating System ◽  
Hot Water ◽  
Transfer Coefficients ◽  
Adequate Model ◽  
Domestic Hot Water ◽  
Heat Transfer Coefficients ◽  
Convective Heat Transfer Coefficients

Testing is done of an unpressurized drainback system with a load-side heat exchanger. Analytical calculations for the heat exchanger effectiveness and three models for convective heat transfer coefficients from correlations are compared against the experimental data. TRNSYS simulations were performed using the average effectiveness of 0.78 (the calculated effectiveness varies from 0.68 to 0.95); the results compare favorably with experimental results, indicating that a constant effectiveness is an adequate model for the system.

Nucleate Boiling in Thermally Developing and Fully Developed Laminar Falling Water Films

1988 ◽  
Vol 110 (1) ◽  
pp. 221-228 ◽  
Author(s):  
M. Cerza ◽  
V. Sernas
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Nucleate Boiling ◽  
Heat Transfer Correlation ◽  
Transfer Coefficients ◽  
Number Range ◽  
Flow Rates ◽  
Entry Length ◽  
Heat Transfer Coefficients ◽  
Water Films

This paper reports an experimental investigation of nucleate boiling in thin water films falling down the outside of a cylindrical heated tube. A mathematical model for the convective (nonboiling) heat transfer coefficient in the laminar thermal entry length was developed and used as a comparison to the experimental boiling heat transfer coefficients. A heat transfer correlation based on mechanistic arguments is presented and is shown to represent the experimental data fairly well. The experimental data were also compared with existing heat transfer data in the literature. The flow rates utilized in this study corresponded to a Reynolds number range from 670 and 4300 and the heat flux range was 6 to 70 kW/m2.

scholarly journals Convection Heat Transfer Coefficients in Thermoacoustic Heat Exchangers: An Experimental Investigation

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4525 ◽  
Author(s):  
Piccolo ◽  
Sapienza ◽  
Guglielmino
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boundary Layer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Coefficients ◽  
Oscillating Flows ◽  
Heat Transfer Coefficients

This paper investigates the thermal performance of thermoacoustic heat exchangers subjected to acoustically oscillating flows. The analysis is carried out by experimental measurements of the heat fluxes sustained by the ambient heat exchanger of a prime mover of the standing wave type. A home-made parallel-plate heat exchanger is considered for the study. The gas-side convection heat transfer coefficients expressed as Nusselt numbers are determined over a wide range of velocity amplitudes of the oscillating flow. The experimental results are then compared to the predictions of a number of theoretical models currently applied in thermoacoustics such as the time-average steady-flow equivalent (TASFE) model, the root mean square Reynolds number (RMS-Re) model, and the boundary layer conduction model. The comparison suggests that the boundary layer model performs better than the rms-Re and TASFE models in predicting the heat transfer coefficients in oscillating flows. The relative difference between the model predictions and the experimental data amounts to 19%. A new correlation law, based on regression of the experimental data, is also proposed.

Forced Convection Film Boiling Heat Transfer From Single Horizontal Cylinders in Saturated and Subcooled Liquids: Part 2—Experimental Data for Subcooled Liquids and Its Correlation

2009 ◽  
Author(s):  
Qiusheng Liu ◽  
Masahiro Shiotsu ◽  
Akira Sakurai ◽  
Katsuya Fukuda
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Forced Convection ◽  
Boiling Heat Transfer ◽  
Film Boiling ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
System Pressure ◽  
Horizontal Cylinders ◽  
Flow Velocities

Forced convection film boiling heat transfer from a horizontal cylinder in water and Freon-113 flowing upward perpendicular to the cylinder under subcooled conditions was measured for the flow velocities from 0 to 1 m/s at the system pressures ranging from 100 to 500 kPa: the platinum horizontal cylinders with diameters ranging from 0.7 to 5 mm were used as the test heaters. The film boiling heat transfer coefficients were obtained for the surface superheats from about 800 K for water and from about 400 K for Freon-113 down to minimum film boiling surface superheats. These heat transfer coefficients increase with the increase in flow velocity, liquid subcooling, system pressure, and with the decrease in cylinder diameter. A correlation for subcooled forced convection film boiling heat transfer was presented, which can describe the experimental data obtained within ±20% for the flow velocities below 0.7 m/s, and within −30% to +20% for the higher flow velocities. The correlation also predicted well the data by Shigechi (1983), Motte and Bromley (1957), and Sankaran and Witte (1990) obtained for the larger diameter cylinders and higher flow velocities in various liquids at the pressures of near atmospheric. The Shigechi’s data were in the range from about −20% to +15%, the data of Motte and Bromley were about ±30%, and the data of Sankaran and Witte were within +20% of the curves given by the corresponding predicted values.

Effect of Surface Roughness on Pool Boiling Heat Transfer of Water on a Superhydrophilic Aluminum Surface

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
Jinsub Kim ◽  
Seongchul Jun ◽  
Jungho Lee ◽  
Juan Godinez ◽  
Seung M. You
Keyword(s):  
Heat Transfer ◽  
Surface Roughness ◽  
Boiling Heat Transfer ◽  
Aluminum Surface ◽  
Transfer Coefficients ◽  
Copper Surfaces ◽  
Heat Transfer Coefficients ◽  
Superhydrophilic Surface ◽  
Aluminum Surfaces ◽  
Effect Of Surface

The effect of surface roughness on the pool boiling heat transfer of water was investigated on superhydrophilic aluminum surfaces. The formation of nanoscale protrusions on the aluminum surface was confirmed after immersing it in boiling water, which modified surface wettability to form a superhydrophilic surface. The effect of surface roughness was examined at different average roughness (Ra) values ranging from 0.11 to 2.93 μm. The boiling heat transfer coefficients increased with an increase in roughness owing to the increased number of cavities. However, the superhydrophilic aluminum surfaces exhibited degradation of the heat transfer coefficients when compared with copper surfaces owing to the flooding of promising cavities. The superhydrophilic aluminum surfaces exhibited a higher critical heat flux (CHF) than the copper surfaces. The CHF was 1650 kW/m2 for Ra = 0.11 μm, and it increased to 2150 kW/m2 for Ra = 0.35 μm. Surface roughness is considered to affect CHF as it improves the capillary wicking on the superhydrophilic surface. However, further increase in surface roughness above 0.35 μm did not augment the CHF, even at Ra = 2.93 μm. This upper limit of the CHF appears to result from the hydrodynamic limit on the superhydrophilic surface, because the roughest surface with Ra = 2.93 μm still showed a faster liquid spreading speed.

Sign in / Sign up

Export Citation Format

Share Document