Numerical Study of Transient Conjugate Heat Transfer in a Long Two-Phase Pipeline

2000 ◽  
Author(s):  
Yuri V. Fairuzov ◽  
Hector Arvizu Dal Piaz
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Conjugate Heat Transfer ◽  
Pipe Wall ◽  
Numerical Study ◽  
Electrical Heating ◽  
Practical Significance ◽  
Local Thermal Equilibrium ◽  
Working Fluid ◽  
Two Phase

Abstract A growing number of multiphase technology applications stimulate the development of reliable methods for modeling transient processes in two-phase systems in which the temperature field in the moving fluid and the temperature field in the bounding walls are directly dependent on each other. This situation presents a conjugate heat-transfer problem since the heat-transfer rate at the wall-fluid interface and local fluid conditions are not known a priori, and therefore need to be simultaneously calculated. Examples of such processes include the direct heating of multiphase pipelines, a change of heat load in evaporators of two-phase thermal control systems, startup or shutdown of systems with a two-phase working fluid. In this paper, direct electrical heating of a long two-phase pipeline has been modeled. The modeling of transient two-phase flow and heat transfer in the pipeline is based on two different mathematical formulations. In the first formulation, the transient heat conduction and the forced convection effects are rigorously taken into account. The second formulation assumes that the pipe wall and the fluid are in local thermal equilibrium. The effect of the thermal capacity of the pipe wall is taken into account by an additional term in the energy equation for the fluid flow. Such an approach allows significant simplifying the problem and reducing the computer running time. Numerical simulation of the sudden heat input to the pipe wall has been performed using both formulations of field equations. The practical significance of the results obtained is discussed.

A Study of Transient Heat Transfer in a Vertical Two-Phase Flow During Blowdown of a Pipeline

2001 ◽  
Author(s):  
S. Bautista-Fragoso ◽  
Yuri V. Fairuzov
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Conjugate Heat Transfer ◽  
Two Phase Flow ◽  
Pipe Wall ◽  
Mathematical Formulation ◽  
Local Thermal Equilibrium ◽  
Phase Flow ◽  
Two Phase ◽  
Drift Flux Model

Abstract A numerical model of transient two-phase flow and conjugate heat transfer in a vertical pipeline is presented in the present paper. The drift-flux model is used to describe the fluid flow in the pipeline. The modeling of transient conjugate heat transfer is based on a mathematical formulation in which the pipe wall and the fluid are assumed to be in local thermal equilibrium. The effect of the thermal capacity of the pipe wall is taken into account by an additional term in the energy equation for the fluid flow. Such an approach allows significant simplifying the problem and reducing the computer running time. Numerical simulations of blowdown of a pipeline/riser system were performed. The effect of the pipe wall on the flow behavior was investigated.

A Numerical Model of a Reciprocating-Mechanism Driven Heat Loop for Two-Phase High Heat Flux Cooling

2016 ◽  
Vol 8 (4) ◽  
Author(s):  
Olubunmi Popoola ◽  
Ayobami Bamgbade ◽  
Yiding Cao
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Model ◽  
Performance Optimization ◽  
Numerical Study ◽  
High Heat ◽  
Working Fluid ◽  
High Heat Flux ◽  
Two Phase ◽  
Transfer Device

An effective design option for a cooling system is to use a two-phase pumped cooling loop to simultaneously satisfy the temperature uniformity and high heat flux requirements. A reciprocating-mechanism driven heat loop (RMDHL) is a novel heat transfer device that could attain a high heat transfer rate through a reciprocating flow of the two-phase working fluid inside the heat transfer device. Although the device has been tested and validated experimentally, analytical or numerical study has not been undertaken to understand its working mechanism and provide guidance for the device design. The objective of this paper is to develop a numerical model for the RMDHL to predict its operational performance under different working conditions. The developed numerical model has been successfully validated by the existing experimental data and will provide a powerful tool for the design and performance optimization of future RMDHLs. The study also reveals that the maximum velocity in the flow occurs near the wall rather than at the center of the pipe, as in the case of unidirectional steady flow. This higher velocity near the wall may help to explain the enhanced heat transfer of an RMDHL.

scholarly journals Conjugate heat transfer numerical study of the ejector by means of SU2 solver

2021 ◽  
Vol 2088 (1) ◽  
pp. 012004
Author(s):  
D V Brezgin ◽  
K E Aronson ◽  
F Mazzelli ◽  
A Milazzo
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Conduction ◽  
Conjugate Heat Transfer ◽  
Numerical Study ◽  
Working Fluid ◽  
Static Pressure Distribution ◽  
Flow Parameters ◽  
Permeable Walls ◽  
Solid Bodies

Abstract In this paper, the test supersonic ejector with conjugate heat transfer in solid bodies has been studied numerically. An extensive numerical campaign by means of open-source SU2 solver is performed to analyze the fluid dynamics of the ejector flowfield accounting for the heat conduction in solids. The fluid domain simulation is carried out by employing compressible RANS treatment whilst the heat distribution in solids is predicted by simultaneous solving the steady heat conduction equation. The working fluid is R245fa and all simulations are performed accounting for real gas properties of the refrigerant. Experimental data against numerical results comparison showed close agreement both in terms mass flow rates and static pressure distribution along the walls. Within the CFD trials, the most valuable flow parameters at a wall vicinity are compared: distribution across the boundary layer of the temperature and the turbulent kinetic energy specific dissipation rate, boundary layer displacement and momentum thicknesses. A comprehensive analysis of the simulation results cases with adiabatic walls against cases with heat permeable walls revealed the actual differences of the flow properties in the wall vicinity. However, the ejector performance has not changed noticeably while accounting for the heat conduction in solids.

Complete Transient Two-Dimensional Analysis of Two-Phase Closed Thermosyphons Including the Falling Condensate Film

1994 ◽  
Vol 116 (2) ◽  
pp. 418-426 ◽  
Author(s):  
C. Harley ◽  
A. Faghri
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Conjugate Heat Transfer ◽  
Pipe Wall ◽  
Vapor Flow ◽  
Two Dimensional ◽  
Type Solution ◽  
Two Phase ◽  
Condensate Film ◽  
Good Agreement

A transient two-dimensional thermosyphon model is presented that accounts for conjugate heat transfer through the wall and the falling condensate film. The complete transient two-dimensional conservation equations are solved for the vapor flow and pipe wall, and the liquid film is modeled using a quasi-steady Nusselt-type solution. The model is verified by comparison with existing experimental data for a low-temperature thermosyphon with good agreement. A typical high-temperature thermosyphon was then simulated to examine the effects of vapor compressibility and conjugate heat transfer.

scholarly journals A Hybrid Numerical Methodology Based on CFD and Porous Medium for Thermal Performance Evaluation of Gas to Gas Micro Heat Exchanger

Micromachines ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 218 ◽  
Author(s):  
Danish Rehman ◽  
Jojomon Joseph ◽  
Gian Luca Morini ◽  
Michel Delanaye ◽  
Juergen Brandner
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Heat Exchanger ◽  
Conjugate Heat Transfer ◽  
Numerical Study ◽  
Computational Cost ◽  
Heat Transfer Analysis ◽  
Working Fluid ◽  
Micro Heat Exchanger ◽  
Parallel Microchannels

In micro heat exchangers, due to the presence of distributing and collecting manifolds as well as hundreds of parallel microchannels, a complete conjugate heat transfer analysis requires a large amount of computational power. Therefore in this study, a novel methodology is developed to model the microchannels as a porous medium where a compressible gas is used as a working fluid. With the help of such a reduced model, a detailed flow analysis through individual microchannels can be avoided by studying the device as a whole at a considerably less computational cost. A micro heat exchanger with 133 parallel microchannels (average hydraulic diameter of 200 μ m) in both cocurrent and counterflow configurations is investigated in the current study. Hot and cold streams are separated by a stainless-steel partition foil having a thickness of 100 μ m. Microchannels have a rectangular cross section of 200 μ m × 200 μ m with a wall thickness of 100 μ m in between. As a first step, a numerical study for conjugate heat transfer analysis of microchannels only, without distributing and collecting manifolds is performed. Mass flow inside hot and cold fluid domains is increased such that inlet Reynolds number for both domains remains within the laminar regime. Inertial and viscous coefficients extracted from this study are then utilized to model pressure and temperature trends within the porous medium model. To cater for the density dependence of inertial and viscous coefficients due to the compressible nature of gas flow in microchannels, a modified formulation of Darcy–Forschheimer law is adopted. A complete model of a double layer micro heat exchanger with collecting and distributing manifolds where microchannels are modeled as the porous medium is finally developed and used to estimate the overall heat exchanger effectiveness of the investigated micro heat exchanger. A comparison of computational results using proposed hybrid methodology with previously published experimental results of the same micro heat exchanger showed that adopted methodology can predict the heat exchanger effectiveness within the experimental uncertainty for both cocurrent and counterflow configurations.

AN EXPERIMENTAL AND NUMERICAL STUDY OF HEAT TRANSFER IN A SIMULATED COLLECTOR FOR A SOLAR DRYER

1993 ◽  
Vol 17 (2) ◽  
pp. 145-160
Author(s):  
P.H. Oosthuizen ◽  
A. Sheriff
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Local Heat Transfer ◽  
Lower Surface ◽  
Local Heat ◽  
Electrical Heating ◽  
Temperature Profiles ◽  
Measured Temperature ◽  
Transfer Rates ◽  
Thermocouple Probe

Indirect passive solar crop dryers have the potential to considerably reduce the losses that presently occur during drying of some crops in many parts of the “developing” world. The performance so far achieved with such dryers has, however, not proved to be very satisfactory. If this performance is to be improved it is necessary to have an accurate computer model of such dryers to assist in their design. An important element is any dryer model is an accurate equation for the convective heat transfer in the collector. To assist in the development of such an equation, an experimental and numerical study of the collector heat transfer has been undertaken. In the experimental study, the collector was simulated by a 1m long by 1m wide channel with a gap of 4 cm between the upper and lower surfaces. The lower surface of the channel consisted of an aluminium plate with an electrical heating element, simulating the solar heating, bonded to its lower surface. Air was blown through this channel at a measured rate and the temperature profiles at various points along the channel were measured using a shielded thermocouple probe. Local heat transfer rates were then determined from these measured temperature profiles. In the numerical study, the parabolic forms of the governing equations were solved by a forward-marching finite difference procedure.

Numerical Study on the Erosion Characteristics of U-Type Bend for Gas Solid Flow

2017 ◽  
Author(s):  
Yu Wang ◽  
Qi He ◽  
Ming Liu ◽  
Weixiong Chen ◽  
Junjie Yan
Keyword(s):  
Particle Size ◽  
Erosion Rate ◽  
Loading Rate ◽  
Pipe Wall ◽  
Numerical Study ◽  
Pulverized Coal ◽  
Mass Loading ◽  
Two Phase ◽  
Inlet Velocity ◽  
Pipe System

In pulverized coal-fired plant, the U-type bend is commonly used in flue gas and pulverized coal pipe system to due to the constraints of outer space. And gas-solid two-phase flow exists in these pipelines. The erosion of the pipe has significant effect on the safety and reliability of pipelines. In present paper, the erosion characteristics of U-type bend were investigated through CFD (Computational Fluid Dynamics) method. The wear distribution on the pipe wall was obtained. And the particle flow characteristics in U-type bend were analyzed. The influence of inlet velocity, mass loading rate and particle size on the erosion rate was studied as well. Result suggested that the maximum erosion rate increases exponentially with the increase of inlet velocity. And maximum erosion rate increases linearly with the increasing mass loading rate. Increasing particle size can aggravate the wear on the pipe wall.

A Loop Thermosyphon With Hydrophobic Spots Evaporator Surface

2018 ◽  
Author(s):  
Hongbin He ◽  
Biao Shen ◽  
Sumitomo Hidaka ◽  
Koji Takahashi ◽  
Yasuyuki Takata
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Nucleate Boiling ◽  
Working Fluid ◽  
Immersion Method ◽  
Two Phase ◽  
Coating Materials ◽  
High Heat Transfer ◽  
Coated Surface

Heat transfer characteristic of a closed two-phase thermosyphon with enhanced boiling surface is studied and compared with that of a copper mirror surface. Two-phase cooling improves heat transfer coefficient (HTC) a lot compared to single-phase liquid cooling. The evaporator surfaces, coated with a pattern of hydrophobic circle spots (non-electroplating Ni-PTFE, 0.5∼2 mm in diameter and 1.5–3 mm in pitch) on Cu substrates, achieve very high heat transfer coefficient and lower the incipience temperature overshoot using water as the working fluid. Sub-atmospheric boiling on the hydrophobic spot-coated surface shows a much better heat transfer performance. Tests with heat loads (30 W to 260 W) reveals the coated surfaces enhance nucleate boiling performance by increasing the bubbles nucleation sites density. Hydrophobic circle spots coated surface with diameter 1 mm, pitch 1.5 mm achieves the maximal heat transfer enhancement with the minimum boiling thermal resistance as low as 0.03 K/W. The comparison of three evaporator surfaces with same spot parameters but different coating materials is carried out experimentally. Ni-PTFE coated surface with immersion method performs the optimal performance of the thermosyphon.

Experimental Study of Condensation Flow Inside Horizontal Smooth, Herringbone and Three Enhanced Surface Tubes

2017 ◽  
Author(s):  
Xiaolong Yan ◽  
Wei Li ◽  
Weiyu Tang ◽  
Hua Zhu ◽  
Zhijian Sun ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Saturation Temperature ◽  
Horizontal Tube ◽  
Working Fluid ◽  
Experimental Investigations ◽  
Enhancement Effect ◽  
Two Phase ◽  
Inner Diameter ◽  
Enhanced Surface

Enhanced condensation heat transfer of two-phase flow on the horizontal tube side receives more and more concerns for its fundamentality and importance. Experimental investigations on convective condensation were performed respectively in different horizontal tubes: (i) a smooth tube (11.43 mm, inner diameter); (ii) a herringbone tube (11.43 mm, fin root diameter); and (iii) three enhanced surface (EHT) tubes (11.5 mm, equivalent inner diameter): 1EHT tube, 2EHT-1 tube and 2EHT-2 tubes. The surface of EHT tubes is enhanced by arrays of dimples with the background of petal arrays. Experiments were conducted at a saturation temperature of approximately 320 K; 0.8 inlet quality; and 0.2 outlet quality; 72–181 kg·m−2·s−1 mass flux using R22, R32 and R410A as the working fluid. The refrigerant R32 presents great heat transfer performance than R410A and R22 at low mass flux due to its higher latent heat of vaporization and larger thermal conductivity. The heat enhancement ratio of the herringbone tube is 2.72–2.82, rated number one. The primary dimples on the EHT tube increase turbulence and flow separation, and the secondary petal pattern produce boundary layer disruption to many smaller scale eddies. The 2EHT tubes are inferior to the 1EHT tube. A performance factor is used to evaluate the enhancement effect except of the contribution of area increase.

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