Falling Film Evaporation of Water on Horizontal Configured Tube Bundles

2010 ◽  
Author(s):  
Wei Li ◽  
Xiaoyu Wu ◽  
Zhong Luo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Inlet Temperature ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Film Evaporation ◽  
Tube Bundles ◽  
Falling Film Evaporation

This paper reports an experimental study on falling film evaporation of water on 6-row horizontal configured tube bundles in a vacuum. Three types of configured tubes, Turbo-CAB-19fpi and −26fpi, Korodense, including smooth tubes for reference, were tested in a range of film Reynolds number from about 10 to 110. Results show that as the falling film Reynolds number increases, falling film evaporation goes from tubes partial dryout regime to fully wet regime; the mean heat transfer coefficients reach peak values in the transition point. Turbo-CAB tubes have the best heat transfer enhancement of falling film evaporation in both regimes, but Korodense tubes’ overall performances are better when tubes are fully wet. The inlet temperature of heating water has hardly any effects on the heat transfer, but the evaporation pressure has controversial effects. A correlation with errors within 10% was also developed to predict the heat transfer enhancement capacity.

scholarly journals Heat Transfer Enhancement of Falling Film Evaporation on a Horizontal Tube by Thermal Spray Coating

2020 ◽  
Vol 10 (5) ◽  
pp. 1632 ◽  
Author(s):  
Tsutomu Ubara ◽  
Hitoshi Asano ◽  
Katsumi Sugimoto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Enhancement ◽  
Spray Coating ◽  
Horizontal Tube ◽  
Thermal Spray Coating ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Film Evaporation ◽  
Falling Film Evaporation

Falling film evaporators are gaining popularity as substitutes to typical flooded evaporators because of their low refrigerant charge. It is important to form and keep a thin liquid film on the heat transfer surface to ensure their high heat transfer performance. In this study, as a heat transfer enhancement surface, a fine porous surface processed using thermal spray coating was applied to a smooth copper tube with an outer diameter of 19.05 mm. Heat transfer coefficients of falling film evaporation on a single horizontal tube were experimentally evaluated using the HFC-134a refrigerant. The experiments were performed at a saturation temperature of 20 °C with the heat flux ranging from 10 to 85 kW·m−2 and for film Reynolds numbers up to 673. The study aimed to clarify the effect of the coating on the heat transfer characteristics of falling film evaporation. The results revealed that the coating could suppress partial dry out and enhance nucleate boiling in the falling film. The maximum heat transfer enhancement factor was 5.2 in the experimental range. It was further noted that the effect of the coating was especially strong under a low heat flux condition.

scholarly journals Effect of Integrating Metal Wire Mesh with Spray Injection for Liquid Piston Gas Compression

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3723
Author(s):  
Barah Ahn ◽  
Vikram C. Patil ◽  
Paul I. Ro
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Metal Wire ◽  
Wire Mesh ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Gas Compression ◽  
Liquid Piston

Heat transfer enhancement techniques used in liquid piston gas compression can contribute to improving the efficiency of compressed air energy storage systems by achieving a near-isothermal compression process. This work examines the effectiveness of a simultaneous use of two proven heat transfer enhancement techniques, metal wire mesh inserts and spray injection methods, in liquid piston gas compression. By varying the dimension of the inserts and the pressure of the spray, a comparative study was performed to explore the plausibility of additional improvement. The addition of an insert can help abating the temperature rise when the insert does not take much space or when the spray flowrate is low. At higher pressure, however, the addition of spacious inserts can lead to less efficient temperature abatement. This is because inserts can distract the free-fall of droplets and hinder their speed. In order to analytically account for the compromised cooling effects of droplets, Reynolds number, Nusselt number, and heat transfer coefficients of droplets are estimated under the test conditions. Reynolds number of a free-falling droplet can be more than 1000 times that of a stationary droplet, which results in 3.95 to 4.22 times differences in heat transfer coefficients.

Numerical Simulation of the Liquid Flowing and Heat-Transfer outside the Tube of the Horizontal-Tube Falling Film Evaporator

2012 ◽  
Vol 614-615 ◽  
pp. 296-300 ◽  
Author(s):  
Wei Kang Hu ◽  
Li Yang ◽  
Lei Hong Guo
Keyword(s):  
Heat Transfer ◽  
Horizontal Tube ◽  
Water Desalination ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Film Evaporation ◽  
Film Evaporator ◽  
Spray Density ◽  
Performance Of Heat Transfer ◽  
Falling Film Evaporation

This paper mainly studies the falling film evaporator in the field of water desalination. Using the method of fluent simulates the process of the liquid flowing and heat-transfer on the horizontal-tube falling film evaporation. The author analyses the distribution of the liquid film, and obtain the rule that spray density, evaporation temperature, temperature difference and pipe diameter affect the performance of heat-transfer in a certain range. So the paper plays a guiding role in heat transfer enhancement in the falling film evaporator.

Heat Transfer Enhancement in Square Ducts With V-Shaped Ribs of Various Angles

2002 ◽  
Author(s):  
Rongguang Jia ◽  
Arash Saidi ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Experimental Studies ◽  
Eddy Diffusivity ◽  
Heat Fluxes ◽  
Secondary Flows ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients

Experimental studies have revealed that both downstream and upstream pointing V-shaped ribs result in better heat transfer enhancement than transverse straight ribs of the same geometry. Secondary flows induced by the angled ribs are believed to be responsible for this higher heat transfer enhancement. Further investigations are needed to understand this. In the present study, the heat and fluid flow in V-shaped-ribbed ducts is numerically simulated by a multi-block 3D solver, which is based on solving the Navier-Stokes and energy equations in conjunction with a low-Reynolds number k-ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM), while turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Firstly, the simulation results of transverse straight ribs are validated against the experimental data, for both velocity and heat transfer coefficients. Then, the results of different rib angles (45° and 90°) and Reynolds number (15,000–30,000) are compared to determine the goodness of different rib orientations. Detailed velocity and thermal field results have been used to explain the effects of the inclined ribs and the mechanisms of heat transfer enhancement.

Regional Heat Transfer and Pressure Drop in Two-Pass and Three-Pass Flow Passages With 180-Degree Sharp Turns

1989 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient ◽  
Single Turn

The heat transfer distributions for flow passing through a two-pass (one-turn) and a three-pass (two-turn) passages with 180-degree sharp turns are studied by using the analogous naphthalene mass transfer technique. Both passages have square cross-section and length-to-height ratio of 8. The passage surface, including top wall, side walls and partition walls, is divided into 26 segments for the two-pass passage and 40 segments for the three-pass passage. Mass transfer results are presented for each segment along with regional and overall averages. The very non-uniform mass transfer coefficients measured around a sharp 180-degree turn exhibit the effects of flow separation, reattachment and impingement, in addition to secondary flows. Results of the three-pass passage indicate that heat transfer characteristics around the second turn is virtually the same as that around the first turn. This may imply that, in a multiple-pass passage, heat transfer at the first turn has already reached the thermally developed (periodic) condition. Over the entire two-pass passage, the heat transfer enhancement induced by the single-turn is about 45% to 65% of the fully developed values in a straight channel. Such a heat transfer enhancement decreases with an increase in Reynolds number. In addition, overall heat transfer of the three-pass passage is approximately 15% higher than that of the two-pass one. This 15% increase appears to be Reynolds number independent. The pressure loss induced by the sharp turns is found to be very significant. Within the present testing range, the pressure loss coefficient for both passages varies significantly with the Reynolds number.

Investigation of Condensation Heat Transfer on a Tube With Wavy Fins

2019 ◽  
Author(s):  
Tailian Chen
Keyword(s):  
Heat Transfer ◽  
Condensation Heat Transfer ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Film Evaporation ◽  
Transfer Capability ◽  
Falling Film Evaporation ◽  
Insight Into ◽  
Good Agreement

Abstract In this work, heat transfer coefficient during condensation of a refrigerant on the outside surface of a copper tube with wavy fins was experimentally investigated. To fully characterize the condensation heat transfer, the experiments were conducted under two conditions: no refrigerant overfeed and subject to various degree inundation. The results under the condition of no overfeed are compared with the Beatty and Katz model. While the trend of degradation with increasing subcooling was in good agreement with the model (within 5%), the condensation heat transfer coefficients from the wavy fins were 11–15% higher. Based on the Nusselt model, the surface tension effect is not taken into account in the Beatty and Katz model, which plays an important role in condensation on a surface with fins. The photographs taken during the experiments showed that the condensate dripping columns have a pitch is in agreement with that proposed by Yung et al. [24] for falling film evaporation applications. The second part of the experiments under the various degree of inundation provides further insight into the heat transfer capability of the surface with wavy fins.

Channel Height Effect on Heat Transfer and Friction in a Dimpled Passage

1999 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Entry Length ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer enhancement in cooling passages with dimpled (concavity imprinted) surface can be effective for use in heat exchangers and various hot section components (nozzle, blade, combustor liner, etc.), as it provides comparable heat transfer coefficients with considerably less pressure loss relative to protruding ribs. Heat transfer coefficients and friction factors were experimentally investigated in rectangular channels which had concavities (dimples) on one wall. The heat transfer coefficients were measured using a transient thermochromic liquid crystal technique. Relative channel heights (H/d) of 0.37, 0.74, 1.11 and 1.49 were investigated in a Reynolds number range from 12000 to 60000. The heat transfer enhancement (NuHD) on the dimpled wall was approximately constant at a value of 2.1 times that (Nusm) of a smooth channel over 0.37≤H/d≤1.49 in the thermally developed region. The heat transfer enhancement ratio Nu¯HD/Nusm was invariant with Reynolds number. The friction factors (f) in the aerodynamically fully developed region were consistently measured to be around 0.0412 (only 1.6 to 2.0 times that of a smooth channel). The aerodynamic entry length was comparable to that of a typical turbulent flow (Xo/Dh = 20), unlike the thermal entry length on dimpled surface which was much shorter (xo /Dh<9.8). The thermal performance Nu¯HD/Nusm/f/fsm1/3≅1.75 of dimpled surface was superior to that 1.16<Nu¯HD/Nusm/f/fsm1/3<1.60 of continuous ribs, demonstrating that the heat transfer enhancement with concavities can be achieved with a relatively low-pressure penalty. Neither the heat transfer coefficient distribution nor the friction factor exhibited a detectable effect of the channel height within the studied relative height range (0.37≤H/d≤1.49).

Falling Water Film Evaporation on Horizontal Finned Tube Arrays at Low Pressure

2011 ◽  
Author(s):  
Xiao-Yu Wu ◽  
Wei Li ◽  
Zhong Luo
Keyword(s):  
Heat Transfer ◽  
Experimental Studies ◽  
Water Film ◽  
Finned Tube ◽  
Heat Fluxes ◽  
Falling Film ◽  
Transfer Coefficients ◽  
Finned Tubes ◽  
Film Evaporation ◽  
Falling Film Evaporation

Experimental studies have been done on falling film evaporation of water on four types of finned tubes arrays at the pressure of 1000 Pa. The Reynolds numbers are in the laminar range of about 10 to 110. Results show that the finned tubes that can distribute liquid longitudinally have the best performances in the partial dryout regime, and those with high fins could enhance heat transfer most in the fully wet regime. High heat fluxes will make more liquid evaporate, but also generate more dry patches on the tubes. Additionally, the inner enhancement of the tubes will also improve the overall heat transfer coefficients. And four heat transfer enhancement methods of falling film evaporation are summarized in the paper.

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