Analysis of heat transfer oscillation and buoyancy effects of supercritical R1234ze(E) cooled in horizontal helically coiled tubes

2021 ◽  
pp. 1-24
Author(s):  
Yi-Ran Jiang ◽  
Peng Hu
Keyword(s):  
Heat Transfer ◽  
Radial Component ◽  
Buoyancy Effect ◽  
Absolute Deviation ◽  
Environmental Properties ◽  
Helical Tube ◽  
Sst Turbulence Model ◽  
Lower Temperature ◽  
Helical Tubes ◽  
The Heat Transfer Coefficient

Abstract The helically coiled tubes have been attracting huge attention for enhancing the heat transfer of supercritical fluids and improving energy efficiency. Moreover, the new refrigerant R1234ze(E) has excellent environmental properties and system performance, but few studies have been focused on the supercritical R1234ze(E) heat transfer. In this work, the SST turbulence model is adopted for the numerical simulation of the cooling heat transfer performance of s-R1234ze(E) in horizontal helically coiled tubes. The influences of heat flux, mass flux, coil pitch, and tube radius on the heat transfer coefficient, gravitational buoyancy effect, and centrifugal buoyancy effect are respectively investigated. Furthermore, the results reveal heat transfer oscillation occurs when, and the oscillation mechanism is analyzed. Different from that in the vertical helical tube, the angle between the radial component of gravitational buoyancy and centrifugal force changes continuously in the horizontal helical tube, resulting in the fluid with lower temperature may locate in the inner-left region or the inner-right region. Subsequently, the heat transfer piecewise correlation applicable for supercritical R1234ze(E) in horizontal helical tubes is developed. The average absolute deviation of the predicted results is 5.88%.

Flow and Heat Transfer in a Triple-Impingement Configuration for Trailing-Edge Cooling

2012 ◽  
Author(s):  
J. Liu ◽  
A. Weaver ◽  
T. I-P. Shih ◽  
J. Klinger ◽  
B. Heneveld ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Gas Temperature ◽  
Trailing Edge ◽  
Impingement Cooling ◽  
Hot Gas ◽  
Flow And Heat Transfer ◽  
Sst Turbulence Model ◽  
Cooling Passage ◽  
Turbine Airfoils ◽  
The Heat Transfer Coefficient

The trailing-edge region of turbine airfoils is difficult to cool. In this study, CFD conjugate analysis based on the shear-stress transport (SST) turbulence model is used to study the flow and heat transfer in a triple-impingement cooling configuration. Parameters studied include the pressure drop across the configuration (1, 2, 3, 4, and 5 bars), and the heat transfer coefficient on the hot-gas side (2,000, 4,000, and 6,000 W/m2-K). In all cases with conjugate analysis, the temperature of the coolant at the inlet of the cooling passage is 673 K, the external hot-gas temperature is 1,755 K, and the static pressure at the exit of cooling passage is 25 bars. Simulations were also performed in which the temperature of the cooling-passage wall is kept constant at 1,173 K. Results are generated to show the nature of the flow induced by the triple impingement and how that flow affects heat transfer to the turbine material.

Molecule Dynamics Simulation of Heat Transfer Between Argon Flow and Parallel Copper Plates

2014 ◽  
Vol 5 (3) ◽  
Author(s):  
Yong Tang ◽  
Ting Fu ◽  
Yijin Mao ◽  
Yuwen Zhang ◽  
Wei Yuan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Fluid Flow ◽  
Transfer Coefficient ◽  
Copper Plate ◽  
Dynamics Simulation ◽  
Lower Temperature ◽  
The One ◽  
Copper Wall ◽  
The Heat Transfer Coefficient

Molecular dynamics (MD) simulation aiming to investigate heat transfer between argon fluid flow and two parallel copper plates in the nanoscale is carried out by simultaneously control momentum and temperature of the simulation box. The top copper wall is kept at a constant velocity by adding an external force according to the velocity difference between on-the-fly and desired velocities. At the same time the top wall holds a higher temperature while the bottom wall is considered as physically stationary and has a lower temperature. A sample region is used in order to measure the heat flux flowing across the simulation box, and thus the heat transfer coefficient between the fluid and wall can be estimated through its definition. It is found that the heat transfer coefficient between argon fluid flow and copper plate in this scenario is lower but still in the same order magnitude in comparison with the one predicted based on the hypothesis in other reported work.

Heat Transfer Augmentation in 3D Inner Finned Helical Tube

Volume 3 ◽  
2004 ◽  
Author(s):  
Longjian Li ◽  
Wenzhi Cui ◽  
Quan Liao ◽  
Mingdao Xin ◽  
Tien-Chien Jen ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Boiling Heat Transfer ◽  
Flow Resistance ◽  
Single Phase ◽  
Flow Boiling ◽  
Phase Flow ◽  
Single Phase Flow ◽  
Helical Tube ◽  
Helical Tubes

Experiments were performed to investigate the performance enhancement of single-phase flow and boiling heat transfer in the 3D inner finned helical tubes. The tests for single-phase flow and heat transfer were carried out in the helical tubes with a curvature of 0.0663 and a length of 1.15m, the range of the Reynolds number examined varies from 1000 to 8500. In comparison to the smooth helical tube, the experimental results of two finned helical tubes with different inner fin geometry showed that the heat transfer and flow resistance in the 3D inner finned helical tube gains greater augmentation. Within the measured range of Reynolds number, the average augmentation ratio of heat transfer of the two finned tubes are 71% and 103%, compared with the smooth helical tube, and 90% and 140% for flow resistance, respectively. The tests for flow boiling heat transfer was carried out in the 3D inner finned helical tube with a curvature of 0.0605 and a length of 0.668m. Compared with that in the smooth helical tube, the boiling heat transfer coefficient in the 3D inner finned helical tube is increased by 40%∼120% under varied mass flow rate and wall heat flux conditions, meanwhile, the flow resistance coefficient increased by 18%∼119%.

Pressure Drop and Heat Transfer Characteristics of MWCNT/Heat Transfer Oil Nanofluid Flow inside Microfinned Helical Tubes with Constant Wall Temperature

2012 ◽  
Vol 622-623 ◽  
pp. 796-800 ◽  
Author(s):  
M.H. Kazemi ◽  
M.A. Akhavan-Behabadi ◽  
M. Fakoor Pakdaman
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Base Fluid ◽  
Weight Fraction ◽  
Constant Wall Temperature ◽  
Heat Transfer Augmentation ◽  
Helical Tube ◽  
Helical Tubes

Experiments are performed to investigate the single-phase flow heat transfer augmentation of MWCNT/HT-B oil in both smooth and microfinned helical tubes with constant wall temperature. The tests in laminar regime were carried out in helical tubes with three curvature ratios of 2R/d=25, 30 and 35. Flow Reynolds number varied from 170 to 1800 resulting in laminar flow regime. The effect of some parameters such as the nanoparticles concentration, the dimensionless curvature radius (2R/d) and the Reynolds number on heat transfer was investigated for the laminar flow regime. The weight fraction of nanoparticles in base fluid was less than 0.4%. within the applied range of Reynolds number; results indicated that for smooth helical tube the addition of nanoparticles to the base fluid enhanced heat transfer remarkably. However, compared to the smooth helical tube, the average heat transfer augmentation ratio due to nanoparticle addition for finned tube was small, about 17%. Also, by increasing the weight fraction of nanoparticles in microfinned helical tubes, no substantial changes were observed in the rate of heat transfer enhancement. For the pressure drop, the results show that the pressure drop of nanofluids was slightly higher than the base fluid and increase as the volume concentrations go up.

Experimental Study on Heat Transfer to Supercritical CO2 Flowing in Vertical Upward Tube at Medium Mass Flux

2017 ◽  
Author(s):  
Qian Zhang ◽  
Huixiong Li ◽  
Xiangfei Kong ◽  
Jun Zhang ◽  
Xianliang Lei ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Wall Temperature ◽  
Mass Flux ◽  
Temperature Peak ◽  
Buoyancy Effect ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Medium Mass ◽  
The Heat Transfer Coefficient

An experimental study was performed on heat transfer characteristics of supercritical pressure CO2 (SC-CO2) flowing at medium mass flux conditions in a vertically-upward tube of 16 mm inner diameter at the Heat Transfer and Flow test loop of Supercritical CO2 (HTF-SCO2) in Xi’an Jiaotong University. Experimental parameters included the pressure ranging from 7.5 to 10.5 MPa, the mass flux of 400–600 kg/m2s, and the heat flux of 20–100 kW/m2. Based on the experimental data, effects of mass flux, heat flux and operation pressure on heat transfer characteristics of SC-CO2 were thoroughly discussed. With the decrease of mass flux and increase of heat flux, heat transfer characteristics of SC-CO2 becomes worse and worse. The wall temperature rises to high levels with the occurrence of a wall temperature peak and the wall temperature peak also rises remarkably with the decrease in mass flux and increase in heat flux. Especially, effect of pressures on the heat transfer of SC-CO2 was found to be quite different from that previously reported in literature. When the heat flux is low (such as 30 kW/m2), the HTD was diminished with the increase in pressures, but when the heat flux is up to 50 kW/m2, the HTD is surprisingly intensified by the increase of pressure. The buoyancy effect was considered to explain this distinct influence of pressure on the heat transfer of SC-CO2 by employed a non-dimensional parameter Bu. With the increase of pressure, buoyancy effect was diminished owing to the decrease of density difference between fluids near the wall and the center. When heat flux was lower, the Bu was located between 5×10−6 and 10−4, where buoyancy effect impaired heat transfer, so the heat transfer coefficient increased by rising pressure. But when heat flux was larger, the Bu was above 10−4, where buoyancy effect began to enhance heat transfer, as a result, the heat transfer coefficient was reduced by weakened buoyancy effect because of the increase of pressure. (CSPE)

MODELING OF A HELICALLY COILED HFC134a EVAPORATOR

2014 ◽  
Vol 22 (03) ◽  
pp. 1450016 ◽  
Author(s):  
J. K. DABAS ◽  
SUDHIR KUMAR ◽  
A. K. DODEJA ◽  
K. S. KASANA
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Design Optimization ◽  
Performance Optimization ◽  
Computer Simulation Model ◽  
Analysis And Design ◽  
Hfc 134A ◽  
Helical Tube ◽  
Performance Analysis And Design ◽  
Helical Tubes

A computer simulation model has been developed for the performance analysis and design optimization of a helical coil and cylindrical shell type evaporator working with HFC-134a by using the appropriate empirical correlations of heat transfer coefficient and pressure drop in the helical tubes as available in the literature. This model is based on a numerical method of cell discretization of shell side and tube side of the evaporator. The local values of variables are calculated and the mass, momentum and energy balance is applied to each small cell. The whole sequential and iterative procedure to satisfy the boundary conditions has been transformed in the computer codes. The model has been validated by comparing with the actual results of an experimental study which is also a part of this work. A detailed analysis of the effects of varying input parameters of both fluids on the performance of evaporator was carried out with the help of this model. It also gives the optimum values of mass velocity of refrigerant and the helical tube diameter against the available flow conditions of refrigerant and of external fluid and the required degree of vapor superheat at the exit of evaporator. Thus it provides an easy solution in both the cases of either the performance optimization of an existing evaporator or the design optimization of a new evaporator. The inherent errors in the outcome of correlations for heat transfer, pressure drop and refrigerant properties are the limitations of this model.

Experimental investigation on thermal behavior of non-boiling slug and bubbly two phase-flow in helical tube with spiral

2021 ◽  
pp. 095440622110420
Author(s):  
Reza Rezazadeh ◽  
Samad Jafarmadar ◽  
Saleh Khorasani ◽  
Seyed Reza Amini Niaki
Keyword(s):  
Heat Transfer ◽  
Thermal Behavior ◽  
Two Phase Flow ◽  
Glass Tube ◽  
Constant Heat Flux ◽  
Phase Flow ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Helical Tube ◽  
The Heat Transfer Coefficient

The present study provides experimental results of the flow pattern and thermal behavior of a none-boiling air-water two-phase flow in a helical tube with a turbulator. In order to evaluate the thermal behavior, a glass tube was put under constant heat flux. The inlet, outlet, and surface temperature of the helical tube were measured to calculate the heat transfer coefficient. The results showed that the addition of the turbulator in the helical tube leads to a rapid conversion from bubble flow to slug flow. Also, the formed bubbles are much smaller and spread radially throughout the pipe. Findings showed that the turbulator significantly improved the heat transfer of the two-phase flow, in which ratios of heat transfer enhancement with and without turbulator is 28% and 19%, respectively. Finally, cost-to-benefit ratio (C.B.R) analysis confirmed that when air-water two-phase flow transits through the helical tube are not affected by the presence or absence of turbulator.

scholarly journals Numerical Evaluation of Heat Transfer and Entropy Generation of Helical Tubes with Various Cross-sections under Constant Heat Flux Condition

2018 ◽  
Vol 225 ◽  
pp. 03017 ◽  
Author(s):  
Jundika Candra Kurnia ◽  
Agus Pulung Sasmito
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Entropy Generation ◽  
Cross Sections ◽  
Transfer Rate ◽  
Transport Processes ◽  
Second Law ◽  
Straight Tube ◽  
Helical Tube ◽  
Helical Tubes

The presence of curvature-induced secondary flow in helical pipe which create complex transport phenomena and higher transfer rate has attracted significant attention from both academic and industry. Flow behavior and transport processes in helical tube have been intensively investigated. Nevertheless, most studies were focused on the performance based on first law of thermodynamics with limited studies concerning the performance based on second law of thermodynamics. The objective of this study is to investigate the heat transfer performance of helical tube according to both first and second law. The heat transfer rate and entropy generation of helical tubes with various cross-sections, i.e. circular, ellipse and square, subjected to constant wall heat flux conditions are numerically evaluated by utilizing computational fluid dynamics (CFD) approach. Their performances are compared to those of straight tube with identical cross-section. The results indicate that helical tube provides higher heat transfer at the cost of higher pressure. Moreover, it was found that entropy generation in helical tubes is considerably lower as compared to that in straight tube. Among the studied cross-sections, square has the highest heat transfer albeit having the highest pressure drop and entropy generation for both straight and helical tubes.

Evaporation of lignin-lean black liquor

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 441-450
Author(s):  
HENRIK WALLMO, ◽  
ULF ANDERSSON ◽  
MATHIAS GOURDON ◽  
MARTIN WIMBY
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Black Liquor ◽  
Salt Content ◽  
Solubility Limit ◽  
Lignin Removal ◽  
Kraft Black Liquor ◽  
Black Liquors ◽  
The Heat Transfer Coefficient

Many of the pulp mill biorefinery concepts recently presented include removal of lignin from black liquor. In this work, the aim was to study how the change in liquor chemistry affected the evaporation of kraft black liquor when lignin was removed using the LignoBoost process. Lignin was removed from a softwood kraft black liquor and four different black liquors were studied: one reference black liquor (with no lignin extracted); two ligninlean black liquors with a lignin removal rate of 5.5% and 21%, respectively; and one liquor with maximum lignin removal of 60%. Evaporation tests were carried out at the research evaporator in Chalmers University of Technology. Studied parameters were liquor viscosity, boiling point rise, heat transfer coefficient, scaling propensity, changes in liquor chemical composition, and tube incrustation. It was found that the solubility limit for incrustation changed towards lower dry solids for the lignin-lean black liquors due to an increased salt content. The scaling obtained on the tubes was easily cleaned with thin liquor at 105°C. It was also shown that the liquor viscosity decreased exponentially with increased lignin outtake and hence, the heat transfer coefficient increased with increased lignin outtake. Long term tests, operated about 6 percentage dry solids units above the solubility limit for incrustation for all liquors, showed that the heat transfer coefficient increased from 650 W/m2K for the reference liquor to 1500 W/m2K for the liquor with highest lignin separation degree, 60%.

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