Pressurized Carbon Dioxide as Heat Transfer Fluid: Influence of Radiation on Turbulent Flow Characteristics in Pipe

International audienceThe influence of radiative heat transfer in a CO2 pipe flow is numerically investigated at different pressures. Coupled heat and mass transfer, including radiation transport, are modeled. The physical models and the high temperature and high pressure radiative properties method of computation are presented. Simulations are conducted for pure CO2 flows in a high temperature pipe at 1100 K (with radius 2 cm) with a fixed velocity (1 m.s −1) and for different operating pressures, 0.1, 1, 5 and 20 MPa (supercritical CO2). The coupling between the temperature and velocity fields is discussed and it is found that the influence of radiation absorption is important at low pressure and as the operating pressure increases above 5 MPa the influence of radiation becomes weaker due to an increase of CO2 optical thickness

Comparison Between New Carbon Nanostructures Produced by Plasma with Industrial Carbon Black Grades

Among the large number of processes parameters in Carbon Black (CB) manufacturing, temperature is certainly one of the most important. Whatever the process and the feedstock are, all the processes have in common a limited temperature, as a result of the feedstock energy contain. In the first part of this paper, we establish relationships between temperature and texture of the blacks, based on the analysis of different CB grades. In a second step, we,try to give explanations of some possible relationships between processes parameters and applicative properties of the blacks. Then, we present a new plasma technology for CB production from hydrocarbons cracking. The original technology will allow to investigate, at a pilot scale, a wide range of temperatures. Preliminary results obtained with the pilot are presented.

Dense suspension of solid particles as a new heat transfer fluid for concentrated solar thermal plants: on-sun proof of concept

This paper demonstrates the capacity of dense suspensions of solid particles to transfer concentrated solar power from a tubular receiver to an energy conversion process by acting as a heat transfer fluid. Contrary to a circulating fluidized bed, the dense suspension of particles’ flows operates at low gas velocity and large solid fraction. A single-tube solar receiver was tested with 64 µm mean diameter silicon carbide particles for solar flux densities in the range 200–250 kW/m2, resulting in a solid particle temperature increase ranging between 50 °C and 150 °C. The mean wall-to-suspension heat transfer coefficient was calculated from experimental data. It is very sensitive to the particle volume fraction of the suspension, which was varied from 26 to 35%, and to the mean particle velocity. Heat transfer coefficients ranging from 140 W/m2 K to 500 W/m2 K have been obtained, thus corresponding to a 400 W/m2 K mean value for standard operating conditions (high solid fraction) at low temperature. A higher heat transfer coefficient may be expected at high temperatures because the wall-to-suspension heat transfer coefficient increases drastically with temperature. The suspension has a heat capacity similar to a liquid heat transfer fluid, with no temperature limitation but the working temperature limit of the receiver tube. Suspension temperatures of up to 750 °C are expected for metallic tubes, thus opening new opportunities for high efficiency thermodynamic cycles such as supercritical steam and supercritical carbon dioxide

Numerical Simulation of Spouted Bed Reactors using Process Engineering Models: Application to Coal Gasification

A spouted bed reactor operating at high temperature has been modelled using one dimensional models based on process engineering concepts. The process of coal gasification has been selected to demonstrate the models achievements and predictions have been compared to previous spouted bed reactor experimental results

High solar flux heating of upflow bubbling fluidized bed circulating in opaque vertical tube - 3d numerical simulation

Current solar Heat Transfer Fluids (HTF) have a limited working temperature (\u3c 600 °C) and present operational risks. We proposed to use air-fluidized Dense Particle Suspensions (DPS), also called Upflow Bubbling Fluidized Bed (UBFB), in tubes as a new HTF and storage medium in the frame of the so-called CSP2 FP7 European project (http://www.csp2-project.eu/). UBFB can operate up to the solid sintering temperature, thus improving the plant efficiency, it has no lower temperature limitation and is riskless. The DPS capacity to extract heat from a tube absorber exposed to concentrated solar radiation was demonstrated on a single-tube experimental receiver that was tested at the focus of the CNRS 1 MW solar furnace in Odeillo. The DPS flowed upward through the absorber tube (i.d. 3.6 cm) that passed through a 50 cm high cavity where it was exposed to concentrated solar flux that heated the DPS. The tube wall-to-DPS Heat Transfer Coefficient (HTC) first values were calculated by Flamant et al. (1). A stable outlet temperature of 750 °C was reached with a metallic tube and a particle reflux in the near tube wall region was evidenced by Benoit et al. (2). In this paper, the UBFB behavior is studied using the multiphase flow code NEPTUNE_CFD (3). Hydrodynamics of SiC Geldart A-type particles (40 µm Sauter diameter) and heat transfer imposed by a thermal flux at the wall are coupled in 3D numerical simulations. The convective/diffusive heat transfer between the gas and dispersed phase, and the inter-particle radiative transfer (Rosseland approximation) are accounted for. The numerical and experimental results are compared in order to validate the model. The heat exchange between the particles close to the tube wall and those in the tube center is characterized. Please click Additional Files below to see the full abstract

Experimental investigation of the impact of room/system design on mixed convection heat transfer

Night cooling attracts growing interest. However, architects and engineers still hesitate to apply night cooling because of the important but hard-to-predict convective heat transfer by night. Obviously, this heat transfer mechanism depends on the driving force, fluid motion and heat transfer surface and, thus, on the room and system design. Unfortunately, studies addressing this are scarce. In response, underlying experimental effort intends to instigate global parametric analyses of night cooling at room level. To this end, this study, held in a PASLINK cell, investigates how the ventilative cooling rate, thermal mass and the supply/exhaust configuration affect the convective heat transfer. The analysis is based on airflow data, such as temperature and velocity, and the related convective heat flux. The results indicate the need for an integrated room/system design. After all, the position of the supply relative to thermally massive elements predominates the night cooling performance

Experimental analysis of the impact of room/system design on night ventilation performance

Night cooling attracts growing interest. However, building designers still hesitate to apply night cooling because of the important but hard-to-predict convective heat transfer by night. This heat transfer mechanism depends on the driving force, fluid motion and heat transfer surface and, thus, on the room/system design. Unfortunately, studies addressing this for night cooling regimes are scarce. In response, this study, held in a PASLINK cell, investigates how the ventilative cooling rate, thermal mass and the supply/exhaust configuration affect the convective heat transfer. The analysis is based on airflow data, such as temperature and velocity, and the related convective heat flux. The results indicate the air supply/exhaust configuration is particularly important in case of heterogeneously distributed thermal mass. Next to it, correlations should not be used when the setup and the convection regime differ a lot from those of the corresponding experiments

3D numerical simulation of upflow bubbling fluidized bed in opaque tube under high flux solar heating

Current solar Heat Transfer Fluids (HTF) only work below 600°C. We proposed to use air-fluidized Dense Particle Suspensions (DPS), also called Upflow Bubbling Fluidized Bed (UBFB), in tubes as a new HTF and storage medium in the frame of the so-called CSP2 FP7 European project. UBFB can operate up to the solid sintering temperature (1400 °C for SiC particles), thus improving the plant efficiency and cost of produced kWh. The DPS capacity to extract heat from a tube absorber exposed to concentrated solar radiation was demonstrated and the first values of the tube wall-to-DPS heat transfer coefficient were measured. A stable outlet temperature of 750 °C was reached with a metallic tube, and a particle reflux in the near tube wall region was evidenced. In this paper, the UBFB behavior is studied using the multiphase flow code NEPTUNE_CFD. Hydrodynamics of SiC Geldart A-type particles and heat transfer imposed by a thermal flux at the wall are coupled in 3D numerical simulations. The convective/diffusive heat transfer between the gas and dispersed phase, and the inter-particle radiative transfer (Rosseland approximation) are accounted for. Simulations and experiments are compared. The temperature influence on the DPS flow is analyzed

Hydrodynamics of Dense Fluidized Beds for Application in Concentrated Solar Energy Conversion

In the frame of the call for projects of the European Commission which aims to find alternative HTF in order to extend working temperature and to decrease environmental impact of standard Heat Transfer Fluid (HTF) used in concentrating solar power(CSP) plants, we proposed to use Dense Particle Suspensions -DPS- fluidized with air (approximately 50% of solid) in tubes as new HTF. DPS will enable operating temperature over 1 000°C which corresponds to the sintering temperatures of the solid against 560°C for the most efficient molten salts, thus increasing the plant efficiency and decreasing the cost per kWh produced, have no lower limitation of temperature and are riskless. A cold mockup of receiver using DPS has been built for the preliminary study of the concept. The operation of the mockup has shown the possibility to ensure a regular and adaptable upward flow of solid in the range 10 to 65 kg/h per tube. This paper compares the experimental results of the cold mockup running with the predictions of a multi-fluid approach 3D numerical code

A new heat transfer fluid for concentrating solar systems: Particle flow in tubes

This paper demonstrates a new concept of heat transfer fluid (HTF) for CSP applications, developed in the frame of both a National and a European project (CSP2 FP7 project). It involves a dense suspension of small solid particles. This innovation is currently. The dense suspension of particles receiver (DSPR) consists in creating the upward circulation of a dense suspension of particles (solid fraction in the range 30%-40%) in vertical absorbing tubes submitted to concentrated solar energy. So the suspension acts as a heat transfer fluid with a heat capacity similar to a liquid HTF but only limited in temperature by the working temperature limit of the receiver tubes. Suspension temperatures up to 750°C are expected for metallic tubes, thus opening new opportunities for high efficiency thermodynamic cycles such as supercritical steam and carbon dioxide. First experimental results were obtained during on-sun testing with CNRS solar facility of a single tube DSPR for an outlet temperature lower than 300°C. In this lab-scale experimental setup, the solar absorber is a single opaque metallic tube, containing upward solid circulation, located inside a cylindrical cavity dug in a receiver made of refractory, and submitted to the concentrated solar radiation through a 0.10m x 0.50m slot. The absorber is a 42.4 mm o.d. stainless steel tube. SiC was used because of its thermal properties, availability and rather low cost. The 63.9 μm particle mean diameter permits a good fluidization with almost no bubbles, for very low air velocities. Solar flux densities in the range 200-250 kW/m2 were tested resulting in solid temperature increase ranging between 50 and 150°C. The mean wall-to-suspension heat transfer coefficient (h) was calculated from experimental data. It is very sensitive to the solid fraction of the solid suspension, which was varied from 27% to 36%. These latter values are one order of magnitude larger than the solid fraction in circulating fluidized beds operating at much higher air velocity. Heat transfer coefficients ranging from 140 to 500 W/m2.K have been obtained; i.e. 400 W/m2.K mean value for standard operating conditions at low temperature