Numerical Analysis of Heat Transfer Characteristics of a Falling Film Type Plate-Fin Condenser/Reboiler

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Yuanyuan Zhou ◽  
Jianlin Yu
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Falling Film ◽  
Heat Transfer Characteristics ◽  
Allocation Ratio

Falling film type condensers/reboilers applied to cryogenic air separation units (ASUs) have drawn more attentions in recent years. This paper presents and analyzes a mathematical model for the falling film plate-fin condensers/reboilers (FPCR). In the modeling, both the laminar falling film evaporation and condensation processes, incorporating with interference of mass transfer and interfacial shear stress, are considered, and related to a plate-fin heat exchanger (PHX). The liquid film flow and heat transfer characteristics of oxygen and nitrogen fluids in the PHX are analyzed under given conditions by solving the model with a numerical iteration method. The variations of liquid film thicknesses and local heat transfer coefficients of oxygen and nitrogen as well as the total local heat transfer coefficient have been obtained. Furthermore, the effects of the inlet mass flow rate allocation ratio (i.e., the ratio of inlet mass flow rate of oxygen liquid over the base plate to that over the fin surfaces) on the wetted length of the heat transfer surfaces, the heat transfer performance, and the oxygen liquid circulation ratio (i.e., the ratio of the inlet liquid mass flow rate to the generated vapor mass flow rate) are also discussed. A proper inlet mass flow rate allocation ratio of oxygen liquid is presented. The wave effects are further considered and analyzed through the inclusion of a model for the wave factor.

Effect of Coolant Mass Flow Rate of Dirt Purge Hole on Heat Transfer and Flow Characteristics at a Turbine Blade Tip Underside

2018 ◽  
Author(s):  
Zhiqi Zhao ◽  
Lei Luo ◽  
Xun Zhou ◽  
Songtao Wang
Keyword(s):  
Heat Transfer ◽  
Mass Flow Rate ◽  
Turbine Blade ◽  
Mass Flow ◽  
Flow Rate ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Bend Channel ◽  
Blade Tip ◽  
Cooling Passage

High thermal load on the turbine blade tip surface would lead to high temperature corrosion and severe structural damage. One method to reduce blade tip high thermal stress is to use cooler fluid from the compressor, that exists dirt purge hole mounted on the tip underside, for cooling purpose. In this study, internal serpentine cooling passage is modeled as a U bend channel with a sharp 180-deg turn with the dirt purge hole arranged at the tip-wall. The effect of the layout of dirt purge hole and varying coolant mass flow rate on flow structure, heat transfer on the tip-wall and friction factor of the U bend channel are numerically studied with Reynolds number ranging from 100,000 to 440,000. The results show that the vortex pair is forced to flow near the tip-wall while the increasing shearing effect induced by the vortex pairs increases the local heat transfer. With an increase mass flow rate of the dirt purge hole, the suction effect enhances the local heat transfer performance. However, the pressure loss is also increased accordingly at all Reynolds numbers. The augmentations with Reynold analogy performance and the thermal performance for 5.8% mass flow rate case is 12.5% and 12.7%, respectively, which reaches the highest performance augmentation compared to the smooth-tip channel.

scholarly journals Local Heat Transfer in Turbine Disk-Cavities: Part I — Rotor and Stator Cooling With Hub Injection of Coolant

1990 ◽  
Author(s):  
R. S. Bunker ◽  
D. E. Metzger ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Computer Assisted ◽  
Disk Radius ◽  
Wide Range

Results are presented from an experimental study designed to obtain detailed radial heat transfer coefficient distributions applicable to the cooling of disk-cavity regions of gas turbines. An experimental apparatus has been designed to obtain local heat transfer data on both the rotating and stationary surfaces of a parallel geometry disk-cavity system. The method employed utilizes thin thermochromic liquid crystal coatings together with video system data acquisition and computer-assisted image analysis to extract heat transfer information. The color display of the liquid crystal coatings is detected through the analysis of standard video chromanance signals. The experimental technique used is an aerodynamically steady but thermally transient one which provides consistent disk-cavity thermal boundary conditions while yet being inexpensive and highly versatile. A single circular jet is used to introduce fluid from the stator into the disk-cavity by impingement normal to the rotor surface. The present study investigates hub injection of coolant over a wide range of parameters including disk rotational Reynolds numbers of 2 to 5 · 105, rotor/stator spacing-to-disk radius ratios of .025 to .15, and jet mass flow rates between .10 and .40 times the turbulent pumped flow rate of a free disk. The results are presented as radial distributions of local Nusselt numbers. Rotor heat transfer exhibits regions of impingement and rotational domination with a transition region between, while stator heat transfer shows flow reattachment and convection regions with evidence of an inner recirculation zone. The local effects of rotation, spacing, and mass flow rate are all displayed. The significant magnitude of stator heat transfer in many cases indicates the importance of proper stator modeling to rotor and disk-cavity heat transfer results.

Local Heat Transfer in Turbine Disk Cavities: Part I—Rotor and Stator Cooling With Hub Injection of Coolant

1992 ◽  
Vol 114 (1) ◽  
pp. 211-220 ◽  
Author(s):  
R. S. Bunker ◽  
D. E. Metzger ◽  
S. Wittig
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Mass Flow ◽  
Flow Rate ◽  
Gas Turbines ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Computer Assisted ◽  
Disk Radius ◽  
Wide Range

Results are presented from an experimental study designed to obtain detailed radial heat transfer coefficient distributions applicable to the cooling of disk-cavity regions of gas turbines. An experimental apparatus has been designed to obtain local heat transfer data on both the rotating and stationary surfaces of a parallel geometry disk-cavity system. The method employed utilizes thin thermochromic liquid crystal coatings together with video system data acquisition and computer-assisted image analysis to extract heat transfer information. The color display of the liquid crystal coatings is detected through the analysis of standard video chromanance signals. The experimental technique used is an aerodynamically steady but thermally transient one, which provides consistent disk-cavity thermal boundary conditions yet is inexpensive and highly versatile. A single circular jet is used to introduce fluid from the stator into the disk cavity by impingement normal to the rotor surface. The present study investigates hub injection of coolant over a wide range of parameters including disk rotational Reynolds numbers of 2 to 5 × 105, rotor/stator spacing-to-disk radius ratios of 0.025 to 0.15, and jet mass flow rates between 0.10 and 0.40 times the turbulent pumped flow rate of a free disk. The results are presented as radial distributions of local Nusselt numbers. Rotor heat transfer exhibits regions of impingement and rotational domination with a transition region between, while stator heat transfer shows flow reattachment and convection regions with evidence of an inner recirculation zone. The local effects of rotation, spacing, and mass flow rate are all displayed. The significant magnitude of stator heat transfer in many cases indicates the importance of proper stator modeling to rotor and disk-cavity heat transfer results.

The Intertube Falling Film: Part 2—Mode Effects on Sensible Heat Transfer to a Falling Liquid Film

1996 ◽  
Vol 118 (3) ◽  
pp. 626-633 ◽  
Author(s):  
X. Hu ◽  
A. M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Liquid Film ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Falling Film ◽  
Mode Effects ◽  
Nusselt Numbers ◽  
Transfer Behavior ◽  
Continuous Sheet

When a liquid film falls from one horizontal tube to another below it, the flow may take the form of discrete droplets, jets, or a continuous sheet; the mode plays an important role in the heat transfer. Experiments are reported that explore the local heat transfer behavior for each of these flow patterns, and the results are related to the important features of the flow. Spatially averaged Nusselt numbers are presented and discussed, and new mode-specific design correlations are provided. This research is part of an overall study of horizontal-tube, falling-film flow and heat transfer.

Condensation Heat Transfer and Flow Properties of R134a Refrigerant in Rectangular Minichannel: A Numerical Study

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Wei Li ◽  
Di Lyu ◽  
Jingzhi Zhang ◽  
S. A. Sherif
Keyword(s):  
Heat Transfer ◽  
Pressure Gradient ◽  
Liquid Film ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Numerical Study ◽  
Condensation Heat Transfer ◽  
Vapor Quality ◽  
Vof Model

Abstract This study numerically investigated the condensation heat transfer and flow characteristics of refrigerant R134a in a rectangular minichannel. Three-dimensional simulations were carried out at different mass fluxes, vapor qualities, and gravity conditions using the volume-of-fluid (VOF) model, a turbulence model, and a phase transition model. The effects of various parameters on the surface heat transfer coefficient and the frictional pressure gradient are investigated. The condensation process was found to be enhanced due to the increase of vapor quality and mass flow rate, while the frictional pressure gradient was found to decrease with the decrease of vapor quality and mass flow rate. Simulation results revealed that the liquid film tends to accumulate along the corner of the cross section of the minichannel. Furthermore, the thickness of the liquid film was found to increase with the decrease of mass flux and vapor quality.

scholarly journals The Effects of Gravity on the Pressure Drop and Heat Transfer Characteristics of Steam in Microchannels: An Experimental Study

Energies ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3575 ◽  
Author(s):  
Minhhung Doan ◽  
Thanhtrung Dang ◽  
Xuanvien Nguyen
Keyword(s):  
Heat Transfer ◽  
Experimental Study ◽  
Pressure Drop ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Performance Index ◽  
Gravitational Acceleration ◽  
Heat Transfer Characteristics ◽  
Vertical Microchannel

Experiments were carried out to investigate the pressure drop and heat transfer behaviors of a microchannel condenser. The effects of gravity on the condensation of steam in the microchannels were investigated for both horizontal and vertical cases. For the experimental results, the pressure drop of vertical microchannels in the condenser is lower than for horizontal microchannels. In the case of the horizontal microchannel, as the mass flow rate of steam increases from 0.01 g·s−1 to 0.06 g·s−1, the pressure drop increases from 1.5 kPa to 50 kPa, respectively. While the mass flow rate of steam in the vertical microchannel case increases from 0.01 g·s−1 to 0.06 g·s−1, the pressure drop increases from 2.0 kPa to 44 kPa, respectively. This clearly indicates that the gravitational acceleration affects the pressure drop. The pressure drop of the vertical microchannel is lower than that obtained from the horizontal microchannel. In addition, the capacity of the condenser is the same in both cases. This leads to the performance index obtained from the vertical microchannel condenser being higher than that obtained from the horizontal microchannel condenser. These results are important contributions to the research on the condensation of steam in microchannels.

scholarly journals Computational analysis of transient turbulent flow and conjugate heat transfer characteristics in a solar collector panel with internal, rectangular fins and baffles

2010 ◽  
Vol 14 (1) ◽  
pp. 221-234 ◽  
Author(s):  
Rachid Saim ◽  
Said Abboudi ◽  
Boumédiene Benyoucef
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Turbulent Flow ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Solar Collector ◽  
Computational Analysis ◽  
Heat Transfer Characteristics ◽  
Thermal Exchange

The poor thermal exchange between the absorber and the fluid in the solar air flat plate collector, gives the bad performance and the mediocre thermal efficiency. The introduction of obstacles in the dynamic air vein of the solar collector in order to obtain a turbulent flow is a technique that improves the thermal exchange by convection between the air and the absorber. This article present a computational analysis on the turbulent flow and heat transfer in solar air collector with rectangular plate fins absorber and baffles which are arranged on the bottom and top channel walls in a periodically staggered way. To this end we solved numerically, by the finite volumes method, the conservation equations of mass, momentum and energy. The low Reynolds number k-? model was adopted for the taking into account of turbulence. The velocity and pressure terms of momentum equations are solved by the SIMPLE algorithm. The parameters studied include the entrance mass flow rate of air. The influence of the mass flow rate of air on the axial velocity and the efficiency of upward type baffled solar air heaters have been investigated numerically. The results show that the flow and the heat transfer characteristics are strongly dependent on mass-flow rate of air and the presence and/or the absence of the baffles and fins in the solar collector. It was observed that increasing the Reynolds number will increase the efficiency of the solar panel, as expected.

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