Heat Transfer Of Supercritical CO2 Research Articles

Numerical Investigation of Conjugate Heat Transfer to Supercritical CO2 in a Vertical Tube-in-Tube Heat Exchanger

Conjugate heat transfer to supercritical CO2 in a vertical tube-in-tube heat exchanger was numerically investigated. The results demonstrate that most models considered are able to reproduce the heat transfer processes qualitatively, and the Abe, Kondoh, and Nagano model shows optimal agreement with the experimental data. The influences of hot fluid mass flux and temperature of the shell side, supercritical fluid mass flux of the tube side, flow direction, and pipe diameter on conjugate heat transfer were investigated based on velocity and turbulence fields. It is concluded that hot fluid mass flux and temperature of the shell side significantly affect heat transfer of the tube side. Mixed convection is the main heat transfer mechanism for the supercritical CO2 conjugate heat transfer process when the inner diameter of the tube is greater than 1 mm. In addition, density variation is highly significant for heat transfer of supercritical CO2 while high viscosity hinders the distortion of the flow field and reduces deterioration in heat transfer.

A numerical investigation of turbulent convective heat transfer of supercritical CO<SUB align="right">2 in vertical mini tubes

This article presents a numerical investigation on the turbulent convective heat transfer of supercritical CO2 in vertical mini tubes. For buoyancy-aided cases, buoyancy-opposed cases and buoyancy-free cases, the profiles of velocity, temperature and turbulent kinetic energy, as well as heat transfer coefficients and Nusselt numbers inside the tubes with the diameters less than 2 mm, under heating and cooling conditions, are obtained. It is found that the buoyancy is significant near the pseudocritical point due to the sharply varied properties of supercritical CO2, leading to the variations of the flow pattern, turbulent production and hence heat transfer coefficient in the tube. Detailed explanations to the physics of the complex but interesting transport phenomena are given. Furthermore, the values of the buoyancy parameter Grb/Reb2.7 are calculated, and Jackson and Hall’s criterion for assessing the buoyancy’s influence is examined for cooling flows in mini tubes.

Mixed convective flow and heat transfer of supercritical CO2 in circular tubes at various inclination angles

We performed the numerical simulations of laminar mixed convective flow and heat transfer in a 0.5mm diameter and 1000.0mm length tube. The supercritical carbon dioxide in the tube was cooled at constant wall temperature. The inclination angles were in the range of −90° (vertical downward flow) to 90° (vertical upward flow). The velocity and temperature distributions, secondary flow, friction factor and heat transfer coefficient were plotted vs. inclination angles and gravity force magnitudes. The kinetic energy of secondary flow was introduced to quantify its effect on the heat transfer. It is found that under the mixed convective flow and heat transfer conditions, the horizontal flow display the largest heat transfer coefficients. The inclined flows at α=−30° and 30° also behave better heat transfer performance among various inclination angles. The effect of inclined angles on the heat transfer is decreased with decreases in the gravity force magnitudes. The combined parameter of Gr/Reb2 was used to quantify the buoyancy force effect on the flow and heat transfer.

Numerical Investigation for Heat Transfer of Supercritical CO2 Cooled in a Vertical Circular Tube

Convective heat transfer of supercritical CO2 cooled in a vertical circular tube has been numerically investigated by using the computational fluid mechanics code FLUENT. The objectives of this paper are to predict the heat transfer coefficient and to study the supercritical convective heat transfer of CO2 under uniform heat flux. Simulation starts with four cases, including a physical model, mathematical model, mesh independency, and solution method. Based on the mesh size of 80 × 500 in the radial and axial directions with near-wall resolution of less than 1, the low Reynolds number turbulence model proposed by Lam and Bremhorst (LB) model is adopted to investigate the heat flux effect, buoyancy effect on flow direction, and buoyancy effect on fluid flow. The results show that the LB low-Reynolds-number turbulence model agrees well with the experimental data. Buoyancy effect significantly affects the fluid flow and heat transfer characteristics in turbulent flow, which enhances heat transfer in upward flow, and impairs it in downward flow.

Modified heat transfer equation for in-tube supercritical CO2 cooling

The cooling heat transfer of supercritical carbon dioxide (CO2) remains an issue unsolved, into which many experimental and formulating investigations were performed. This paper conducts a comprehensive survey and evaluation of the available experimental results and existing correlations for in-tube heat transfer of supercritical CO2 cooling. The 341 experimental heat transfer data of supercritical CO2 cooling from six papers are retrieved and assessed, among which three data sources containing 297 data are chosen for the comparative study of the existing heat transfer correlations and for the development of a new correlation and the rest three containing 44 data are put aside because they cannot be justified. The 13 existing heat transfer correlations are found, and they are evaluated with the 297 experimental data. A new correlation is developed through extensive computer tests based on the 297 experimental data and the evaluation of the existing correlations. The new one happens to be the modified form of the Fang model (X. D. Fang, Modeling and analysis of gas coolers, ACRC CR-16, Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign, 1999). It has the mean absolute relative deviation (MARD) of 8.9%, 14.6% lower than the best existing correlation.

Laminar convective heat transfer of supercritical CO2 in horizontal miniature circular and triangular tubes

Laminar mixed convective heat transfer of supercritical CO 2 in horizontal miniature tubes with circular or triangular cross section was investigated numerically. The distributions of the velocity, temperature and wall shear stress inside the circular or equilateral triangular tubes with the hydraulic diameters less than 1.0 mm under cooling condition, with and without gravity, were obtained. The effects of the sharply varied physical properties of supercritical CO 2 and the geometrical characteristics of tubes on the fluid flow and heat transfer were examined. It is found that the buoyancy is significant and enhances the heat transfer, especially near the pseudocritical point, unless the fluid and the tube wall are under the thermal equilibrium condition. More interesting transport phenomena and the detailed explanations to the physics were given. The results of this work benefit in the design and optimization of the high efficiency compact supercritical CO 2 heat exchangers. ► We model laminar flow and heat transfer of supercritical CO 2 in miniature tubes. ► We examine the flow and heat transfer behaviors in circle/triangular tubes under cooling condition. ► Buoyancy is significant that changes the flow patterns and enhances the heat transfer. ► Buoyancy depends on the variations of fluid physical properties and tube shape.

Experimental study of heat transfer characteristics of supercritical CO2 fluid in collectors of solar Rankine cycle system

Heat transfer characteristics of supercritical CO2 (S-CO2) fluid in collectors of a solar Rankine cycle system is experimentally investigated at different flow conditions. In the experiments, temperature, pressure and mass flow rate are measured, and local and average heat transfer coefficients are investigated. Study shows that the thermophysical properties of CO2 near the critical point have significant effects on the S-CO2 local heat transfer behaviors. The heat transfer of S-CO2 is also dependent on the mass flow rate, input heat flux and pressure at inlet of test section.

Numerical simulation of fluid flow and heat transfer of supercritical CO2 in micro-porous media

Abstract International attention has been considerably paid for the technology of CO 2 capture and storage (CCS) these days because of global warming. In line with the fact that carbon dioxide capture and storage (CCS) technology has been regarded as one of the most promising option to mitigate the climate change and global warming, we have started a 10-year R&D project on CO 2 storage in marine geological structure. We carried out relevant studies, which cover the initial survey of potentially suitable marine geological structure for CO 2 storage site, monitoring of the stored CO 2 behavior, basic design for CO 2 transport and storage process including onshore/offshore plant and assessment of potential environmental risk related to CO 2 leakage in storage site. The purpose of this paper is to model and simulate a CO 2 flow and its heat transfer characteristics in a storage site for more accurate evaluation of the safety of CO 2 storage process. Among CCS technologies, the prediction of CO 2 behavior in underground is very critical for CO 2 storage design with safety. As a part of the storage design, a micro pore-scale model was developed to mimic real porous structure and CFD (computational fluid dynamics) was applied to calculate the CO 2 flow and thermal fields in the micro pore-scale porous structure. Varying CO 2 injection conditions, the behavior of the CO 2 flow was calculated. Especially, physical conditions such as temperature and pressure were set up equivalent to the underground condition at which the CO 2 fluid was injected. From the results, the characteristics of the flow and thermal fields of CO 2 were scrutinized and the influence of CO 2 injection condition on the flow was investigated in the micro pore-scale porous structure.

Heat Transfer Characteristics of Supercritical CO2 Flow in Small-Channeled Structures

Carbon dioxide (CO2) has been proposed as a “natural refrigerant” for various kinds of refrigeration systems and has attracted increased attention from researchers and engineers all over the world. The heat transfer and flow characteristics of supercritical CO2 in a multi-port extruded aluminum test section, which had ten circular channels with inner diameter of 1.31 mm, were investigated experimentally. The CO2 was cooled with chilled copper blocks attached at the both sides of the test section. Local heat fluxes and temperatures at the outer surface of the test section were measured using 12 heat flux sensors and 24 K-type thermocouples, respectively. The mean temperatures of CO2 at the inlet and outlet of the test section were also measured. The higher heat transfer rates were achieved in the near-critical region, and the system pressure, mass velocity, and temperature of CO2 all were observed having significant effects on the heat transfer. An empirical correlation was then developed for forced convective heat transfer of supercritical CO2 in horizontal micro/mini channels.