01078 Establishment of fragmentation model of coal during combustion

01078 Establishment of fragmentation model of coal during combustion

16 Fuel science and technology (fundamental science, analysis, instrumentation) efficiencies in a composted pine bark biofilter were determined at met...

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16 Fuel science and technology (fundamental science, analysis, instrumentation) efficiencies in a composted pine bark biofilter were determined at methane concentrations ranging from 0.1 to 2.5% (v/v) and retention times of 20-400 min. Methane removal efficiencies exceeding 70%, were obtained when the biofilter was subjected to gas retention times in excess of 30 min and methane concentrations up to 0.5% (v/v). The data obtained were used to develop an empirical model that successfully described the overall removal efficiency with an R* value of 0.97. It was concluded that composted pine bark could indeed be successfully utilized in passive gas-flow biofiltration for the attenuation of methane in worked underground coal mining chambers.

04/01078 Establishment during combustion

of fragmentation

model of coal

Wu, Z.-S. et al. Ranliao Huaxue Xuebao, 2003, 31. (1), 17-21. (In Chinese) The primary fragment phenomenon of coal during combustion was introduced and a one-dimension model of single particle coal was established. The primary fragment of coal during combustion results from the accumulation of coal volatile, which leads to the production of pressure gradient in coal. This explains well the pulverization phenomenon of coal. The particle size distribution based on the primary fragment inside the combustion chamber could be predicted in the future. In the meantime, the effect of primary fragment of coal on design and operation of circulating fluidized bed combustion boiler was also demonstrated.

04101079 Evaluation of earth-to-air heat exchangers standardised method to calculate energy efficiency

with a

Pfafferott, J. Energy and Buildings, 2003, 35, (IO), 971-983. In designing an earth-to-air heat exchanger (EAHX), a decision on design goals has to be made. If the air flow is given by the ventilation system and the construction site is known, the question is: is it more important to achieve a high specific energy performance based on the surface area of an EAHX, a high adoption of air temperature to ground temperature or a very small pressure loss? This paper deals with the performance of three EAHXs for mid European office buildings in service, with the aim of characterizing their efficiency. A general method to compare EAHXs in operation will be introduced. First, the temperature behaviour is described by plots over time and characteristic lines, and compared by standardized duration curves. Second, the energy gain is illustrated by standardized graphs. Third, a parametric model is used to provide general efficiency criteria. Thermal efficiency should be defined by both the dynamic temperature behaviour and energy performance.

04/01080 Evaporation droplet due to ambient numbers

model of a single hydrocarbon fuel turbulence at intermediate Reynolds

Wu, J. -S. et al. International Journal of Heat and Mass Transfer, 2003, 46, (24), 47414745. A general evaporation model of a single liquid fuel droplet under various ambient turbulence conditions at intermediate droplet Reynolds numbers is proposed combining the current and previous experimental results. Extensive evaporation experiments of single fuel droplets are conducted at room temperature in quasi-laminar and turbulent environments at Reynolds numbers in the range of 72-333. Tested hydrocarbon fuels include by pentane, hexane, heptane, octane and decane. Flow fields, behind a perforated plate or a circular disk in a vertical low-speed wind tunnel, provide the required ambient turbulent environments for droplet evaporation experiments. The ambient turbulence intensities vary in the range of l-60% and the integral length scales in the range of 0.5-20 times of the initial droplet diameter. Results show that normalized evaporation rate (K/K,) decreases with increasing effective Damkiihler number (0.0001
04/01081 Exergy destruction due to mean flow and fluctuating motion in incompressible turbulent flows through a tube Wang, S. P. et al. Energy, 2003, 28, (8). 809.-823. The control volume method has been widely used to describe the rate of exergy destruction due to process irreversibility in a laminar fluid flow stream. This work demonstrates that when the approach is applied to turbulent flows, and the fluid properties are based on averaged values, some information may be lost. The Reynolds time average method was applied to the set of equations of exergy transfer for turbulent flows and found that the exergy destruction is mainly due to two factors, i.e. the mean flow dissipations and the fluctuating motion dissipations. As a case study, this result is used to model the incompressible turbulent flows through a duct with constant heat flux. The distributions of exergy destruction due to mean flow and fluctuating motion viscous dissipations as well as to mean flow and fluctuating motion heat transfer irreversibility in radial and in axis directions are obtained. The numerical solution of an ,example with

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Fuel

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Energy

Abstracts

March 2004

water passing through the duct is obtained and the mechanisms of irreversibility analysed. It is shown that for a given fluid, the total exergy destruction per unit length is a function of the geometrical parameters and the boundary conditions as well as the Reynolds number. It implies that the design of a thermal system can be optimized through minimizing the exergy destruction in the system.

04/01082 Experimental analysis channel-chimney systems

of asymmetrical

isoflux

Manta, 0. et al. International Journal of Thermal Sciences, 2003. 42, (9), 837-846. Air natural convection in an asymmetrically heated channel with unheated extensions has been investigated experimentally. Local and maximum wall temperatures and heat transfer coefficients are presented, for different values of the process parameters. Optimal configurations in terms of the minimum values of maximum wall temperatures are obtained. Average Nusselt numbers and maximum dimensionless wall temperatures are correlated to the Rayleigh number and to the geometrical dimensionless parameters in the 10-1.5~10~ range of the Rayleigh number times the expansion ratio. The addition of downstream unheated extensions improves the thermal performance of the channel for some configurations, the longer the extension and the lower the aspect ratio the lower the wall temperature in the channel.

04/01083 Experimental a full-scale gasification

design project

and statistical

evaluation

of

Coetzer, R. L. J. and Keyser, M. J. Fuel Processing Technology, 2003, 80, (3), 263-278. Sasol in South Africa gasifies -30 million tons of bituminous coal per year to synthesis gas, which is converted to fuels and chemicals via the Fischer-Tropsch process. Three years ago, Sasol embarked upon a unique project to optimize the gas production of the Sasol-Lurgi fixed bed dry bottom coal gasification process. Optimization of the gasification process was carried out by using the method of factorial experimental design on the process variables of interest obtained from a specifically equipped full-scale test gasifier. A response surface model in the process variables was fitted for each of the performance variables. The models developed were validated and are valid when considering different data sets. This paper discusses the application of factorial experimental design and the combination of process variables and mixture components in optimizing a production process. Of importance to optimization is the control of stone content in the coal.

04/01084 Experimental models of medium break loss of coolant accidents with and without steam generator tube rupture Marn, J. et al. International Journal of Pressure Vessels and Piping, 2003, 80, (lo), 737-744. This paper reports model experiments simulating medium break loss of coolant accidents, with and without steam generator tube rupture (SGTR), in pressurized water reactors. Apart from a significant influence on the pressure in the reactor coolant system in the early parts of the accident, SGTR generally has only a small effect on the pressures and temperatures during the accident. The initial reactor conditions are found to be more significant. Some results of preliminary numerical models are briefly presented and these are broadly in agreement with the experimental measurements.

04/01085 spectrum

Experimental study of variations of the solar of relevance to thin film solar cells

Gottschalg, R. et al. Solar Erzergy Materials and Solar Cells, 2003, 79, (4). 527-537. The influence of variations in the incident solar spectrum on solar cells is often neglected. This paper investigates the magnitude of this variation and its potential influence on the performance of thin film solar cells in a maritime climate. The investigation centres on the analysis of a large number of measurements carried out in Loughborough, UK, at 10 min intervals over a period of 30 months. The magnitude of the spectral variation is presented both on a daily and a seasonal basis. Of the different thin film materials studied, amorphous silicon is shown to be the most susceptible to changes in the spectral distribution, with the ‘useful fraction’ of the light varying in the range +6% to -9% of the annual average, with the maximum occurring in summer time.

04/01086 Flow characteristics of gas-liquid two-phase flow in plate heat exchanger (Visualization and void fraction measurement by neutron radiography) Asano, H. et al. Experimental Thermal and Fluid Science, 2004, 28, (23). 223-230. In order to clarify the gas-liquid two-phase flow characteristics in a plate heat exchanger, gas-liquid two-phase flows in simulated heat exchangers with a single channel placed in a vertical plane were visualized by a neutron radiography method. Air-water adiabatic two-