Steam Flow Condensation on Superhydrophobic Surfaces in a High Aspect Ratio Microchannel

2020 ◽  
Author(s):  
Mirvahid Mohammadpour Chehrghani ◽  
Taher Abbasiasl ◽  
Ghazaleh Gharib ◽  
Ali Kosar ◽  
Abdolali Khalili Sadaghiani
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Superhydrophobic Surfaces ◽  
Steam Flow ◽  
Hydrophobic Surfaces ◽  
Highly Hydrophobic ◽  
Flow Condensation ◽  
Condensation Heat Transfer Coefficient

Abstract Steam flow condensation has a wide range of applications in the industry such as in air conditioning, refrigeration, and thermal power plants. Condensation of steam on highly hydrophobic surfaces has resulted in notable heat transfer improvement compared to conventional hydrophilic surfaces. Dropwise condensation and increased droplet mobility are the main reason for thermal performance enhancement of superhydrophobic surfaces. Although there are considerable reports of enhanced thermal transport behavior of highly hydrophobic surfaces on steam condensation, the literature lacks sufficient investigation on flow condensation of steam, such as the effect of average vapor quality change on heat transfer rate. Unlike gravity-driven droplet departure in quiescent dropwise condensation, droplet departure sizes in flow condensation are governed by flow-droplet shear forces and droplet-surface adhesive forces. This work experimentally investigates steam flow condensation on nanotextured highly hydrophobic and slightly hydrophobic surfaces. The experimental setup consists of a reservoir, boiler, superheater, condensation chamber (test section), pre-condenser (to adjust the inlet quality), a post condenser, and a pump. A high aspect ratio microchannel was used as the test section. Different mass fluxes and inlet vapor qualities were used for the experimentations. Visualization studies were performed to analyze droplet dynamics such as droplet departure and coalescence in flow condensation. It is shown that for both surfaces increase condensation heat transfer coefficient were a function of both average quality and mass flux. Increase in mass flux from G = 8 kg/m2s to G = 14 kg/m2s, resulted in 65% and 60% enhancement in condensation heat transfer coefficient of slightly hydrophobic and highly hydrophobic surfaces respectively.

Steam Flow Condensation on Superhydrophobic Surfaces in a High Aspect Ratio Microchannel

2021 ◽  
Author(s):  
Mirvahid Mohammadpour Chehrghani ◽  
Taher Abbasiasl ◽  
Ghazaleh Gharib ◽  
Abdolali Khalili Sadaghiani ◽  
Ali Kosar
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Superhydrophobic Surfaces ◽  
Steam Flow ◽  
Flow Condensation

Steam Flow Condensation on Superhydrophobic Surfaces in a High Aspect Ratio Microchannel

2021 ◽  
Author(s):  
Mirvahid Mohammadpour Chehrghani ◽  
Taher Abbasiasl ◽  
Ghazaleh Gharib ◽  
Abdolali Khalili Sadaghiani ◽  
Ali Kosar
Keyword(s):  
Aspect Ratio ◽  
High Aspect Ratio ◽  
Superhydrophobic Surfaces ◽  
Steam Flow ◽  
Flow Condensation

Experiment study on condensation heat transfer and pressure drop of steam flow inside rectangular tube with different aspect ratio

2020 ◽  
pp. 095765092097222
Author(s):  
Yan Yan ◽  
Jixian Dong ◽  
Tong Ren ◽  
Shiyu Feng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Condensation Heat Transfer ◽  
Aspect Ratios ◽  
Rectangular Tubes ◽  
Condensation Heat Transfer Coefficient

In this study, the condensation heat transfer coefficient and pressure drop of steam are obtained in small rectangular tubes with different aspect ratios. The experiments were carried out on three rectangular tubes with aspect ratios of 1:2, 1:3 and 1:5, with mass flux between 25 and 45 kg/m2s, and vapor qualities between 0.1 and 0.8. The experimental data were analyzed to determine the effect of vapor quality, mass flux, and aspect ratio on the heat transfer coefficient and pressure drop. The results showed that the effect of aspect ratio on condensation heat transfer coefficient appears to be dependent on the flow pattern. For stratified flow, the condensation heat transfer coefficient increases as the mass flux increases. For annular flow, the condensation heat transfer coefficient hardly changed. The pressure drop always increases as the aspect ratio increases. Previous studies on round tube heat transfer and pressure drop correlations have not successfully predicted the small rectangular tube data; therefore, modified Shah correlation and Lockhart & Martinelli correlation are proposed, which predict the data with 20% and 23% RMS error, respectively.

Impact of Turbulator Design on the Heat Transfer in a High Aspect Ratio Passage of a Turbine Blade

2014 ◽  
Author(s):  
S. Naik ◽  
S. Retzko ◽  
M. Gritsch ◽  
A. Sedlov
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
High Aspect Ratio ◽  
Transfer Coefficients ◽  
Average Heat ◽  
Heat Transfer Coefficients ◽  
Trailing Edges

The trailing edge region of gas turbine blades is generally subjected to extremely high external heat loads due to the combined effects of high mach numbers and gas temperatures. In order to maintain the metal temperatures of these trailing edges to a level, which fulfils both the part mechanical integrity and turbine performance, highly efficient and reliable cooling of the trailing edges is required without increasing the coolant consumption. In this paper, the heat transfer and pressure drop characteristic of three different turbulator designs in a very high aspect ratio passage have been investigated. The turbulator designs included angled and tapered ribs, broken discrete ribs and V-shaped small chevrons ribs. The heat transfer and pressure drop characteristics of all the turbulator configurations was initially investigated via numerical predictions and subsequently in a scaled experimental perspex model. The experimental study was conducted for a range of operational Reynolds numbers and the TLC (thermochromic liquid crystal) method was used to measure the detailed heat transfer coefficients on all surfaces of the passage. Pressure taps were located at several locations within the perspex model and both the local and average heat transfer coefficients and pressure loss coefficients were determined. The measured and predicted results show, that for all cases investigated, the local internal heat transfer coefficient, which is driven by the highly three dimensional passage flows, is highly non-uniformly within the passage. The highest overall average heat transfer was obtained for the angled and tapered turbulator. Although the average heat transfer coefficient of the discrete broken turbulator and the small chevron turbulator were slightly lower than the baseline case, they had much higher pressure losses. In terms of the overall non-dimensional performance index, which incorporates both the heat transfer and the pressure drop, it was found that the angled and tapered turbulator gave the best overall performance.

Heat Transfer in Multiple Parallel High Aspect Ratio Ducts With Triangular Trench Enhancement Features

2013 ◽  
Author(s):  
Justin Lamont ◽  
Krishnashis Chatterjee ◽  
Srinath V. Ekkad ◽  
Gustavo Ledezma ◽  
Christopher Kaminski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Aspect Ratio ◽  
Transfer Coefficient ◽  
High Aspect Ratio ◽  
Flow Direction ◽  
Numerical Approach ◽  
Experimental Results ◽  
Navier Stokes ◽  
Nusselt Number Correlation

Detailed heat transfer coefficient distributions and pressure drop have been obtained for high aspect ratio (AR = Width/Height = 12.5) ducts with triangular trench enhancement features oriented normal to the coolant flow direction. Numerical and experimental approaches analyze the performance of triangular trenches for six geometrically identical ducts branching from a common plenum. The numerical approach is based on a Reynolds Averaged Navier Stokes (RANS) turbulence model with an unstructured mesh. A transient liquid crystal (TLC) technique is used to experimentally calculate Nu on the ducts surfaces. Reynolds number (Re = 7080, 14800, and 22400, with respect to the duct hydraulic diameter are explored. As Computational Fluid Dynamics (CFD) and TLC results are both detailed, qualitative and quantitative comparisons are made. Experimental results show the closest and furthest ducts from the entrance of the plenum are considerably affected, as recirculation zones develop which partially choke the inlet the respective ducts. Results from the experiments are compared to CFD predictions from Duct 4. In addition, the experimental data are recalculated with the maximum bias in TLC temperature to indicate an improved matching between CFD and experimental methods to demonstrate that CFD captures the wall heat transfer coefficient trends similar to experimental results. The triangular trenches enhance heat transfer in the ducts two-fold compared to smooth wall Dittus-Boelter Nusselt number correlation for flow in tubes.

Sign in / Sign up

Export Citation Format

Share Document