Brian S. Haynes

Flow boiling heat transfer of Freon R11 and HCFC123 in narrow passages

Flow boiling heat transfer coefficients for Freon R11 and HCFC123 in a smooth copper tube with an inner diameter of 1.95 mm have been experimentally investigated. The parameter ranges examined are: heat fluxes from 5 to 200 kW m−2; mass fluxes from 50 to 1800 kg m−2 s−1; vapour quality from 0 to 0.9; system pressures from 200 to 500 kPa; and experimental heat transfer coefficients from 1 to 18 kW m−2 K−1. It was found that the heat transfer coefficients are a strong function of the heat flux and the system pressure, while the effects of mass flux and vapour quality are very small in the range examined. This suggests that the heat transfer is mainly via nucleate boiling. The present experimental data were compared with some existing correlations and recommendations on their use is made.

A CFD based combustion model of an entrained flow biomass gasifier

This paper contains the description of a detailed Computational Fluid Dynamics (CFD) model developed to simulate the flow and reaction in an entrained flow biomass gasifier. The model is based on the CFX package and represents a powerful tool which can be used in gasifier design and analysis. Biomass particulate is modelled via a Lagrangian approach as it enters the gasifier, releases its volatiles and finally undergoes gasification. Transport equations are solved for the concentration of CH4, H2, CO, CO2, H2O and O2 and heterogeneous reactions between fixed carbon and O2, CO2 and H2O are modelled. The model provides detailed information on the gas composition and temperature at the outlet and allows different operating scenarios to be examined in an efficient manner.

Kinetic and Thermodynamic Sensitivity Analysis of the NO-Sensitised Oxidation of Methane

Abstract Thermodynamic parameters such as species heats of formation and entropies may have a significant impact on the output of detailed kinetic models, but attention is generally only given to considering kinetic parameters in model development and optimisation. In this paper, a method for comparing the impact of uncertainties in both kinetic and thermodynamic parameters on the predictions of detailed kinetic models is described. This method employs kinetic and thermodynamic sensitivity analysis to define an impact factor for all parameters under consideration as the product of the sensitivity of a particular model output to the parameter and the uncertainty in the value of that parameter. Kinetic and thermodynamic impact factor analysis has been applied to the results of an experimental study of the interaction between NOx (ca. 0-200 ppm)and methane (ca. 40-1300 ppm) in the presence of oxygen (ca. 0-1%) in an atmospheric pressure flow reactor, for temperatures ranging from 500 to 700 C. A detailed che...

Biocrude yield and productivity from the hydrothermal liquefaction of marine and freshwater green macroalgae

Six species of marine and freshwater green macroalgae were cultivated in outdoor tanks and subsequently converted to biocrude through hydrothermal liquefaction (HTL) in a batch reactor. The influence of the biochemical composition of biomass on biocrude yield and composition was assessed. The freshwater macroalgae Oedogonium afforded the highest biocrude yield of all six species at 26.2%, dry weight (dw). Derbesia (19.7%dw) produced the highest biocrude yield for the marine species followed by Ulva (18.7%dw). In contrast to significantly different yields across species, the biocrudes elemental profiles were remarkably similar with higher heating values of 33-34MJkg(-1). Biocrude productivity was highest for marine Derbesia (2.4gm(-2)d(-1)) and Ulva (2.1gm(-2)d(-1)), and for freshwater Oedogonium (1.3gm(-2)d(-1)). These species were therefore identified as suitable feedstocks for scale-up and further HTL studies based on biocrude productivity, as a function of biomass productivity and the yield of biomass conversion to biocrude.

Taylor Flow in Microchannels: A Review of Experimental and Computational Work:

Over the past few decades an enormous interest in two-phase flow in microchannels has developed because of their application in a wide range of new technologies, ranging from lab-on-a-chip devices used in medical and pharmaceutical applications to micro-structured process equipment used in many modern chemical plants. Taylor flow, in which gas bubbles are surrounded by a liquid film and separated by liquid plugs, is the most common flow regime encountered in such applications. This review introduces the important attributes of two phase flow in microchannels and then focuses on the Taylor flow regime. The existing knowledge from both experimental and computational studies is presented. Finally, perspectives for future work are suggested.

A turnover model for carbon reactivity I. development

Abstract Recent studies of the carbon-oxygen reaction have increasingly identified the importance of the role of surface complexes in the reaction mechanism. The observation that the complexes can be characterized by their activation energy for thermal decomposition (which lies in the range 160–420 kJ mol−1) provides the basis for a stochastic description of the behavior of these complexes and their processes of formation and gasification. From independent studies of the kinetics of complex formation (R1b) , of thermal decomposition (R2) , and of reaction with oxygen (R3) , an overall model for the oxidation of carbon has been developed. (R1b) C (_)+ O 2 →…. C ( O )+ CO (R2) C ( O )….→ C (_)+ CO , CO 2 (R3) C ( O )+ O 2 → C ( O )+ CO , CO 2 The broad range of types of complex, characterized by their activation energies for thermal decomposition gives rise to a wide diversity of behavior under any given reaction conditions. The combination of these provides a very accurate model of the observed reaction rate of a model carbon.

An experimental study of gas–liquid flow in a narrow conduit

Abstract This paper reports an experimental study of non-boiling air–water flows in a narrow conduit (diameter 1.95 mm). Results are presented for pressure drop characteristics and for local heat transfer coefficients over a wide range of gas superficial velocity (0.1–50 m s−1), liquid superficial velocity (0.08–0.5 m s−1) and wall heat flux (3–58 kW m−2). For a given liquid flow rate, the data exhibit sudden changes in pressure drop and, to a lesser extent, in heat transfer characteristics as the gas flow is increased. These events are believed to correspond to flow transitions, from bubbly, to intermittent slug, to annular flow. Overall, the pressure drops in these diabatic non-boiling two-phase flows can be estimated with good accuracy using correlations developed for adiabatic conditions. The heat transfer results are, on average, reasonably well described by the two-phase convective heat transfer components of flow-boiling correlations but there is considerable scatter in some cases.

An experimental investigation of the mutually sensitised oxidation of nitric oxide and n-butane

The interaction between NO (0.01 to 200 ppm) and n-butane (50 to 600 ppm) in air has been investigated in a flow reactor at atmospheric pressure and temperatures from 330° C to 450° C (600 K to 720 K). Low concentrations of NO in n-butane/air systems promote the oxidation of the n-butane; conversely, low concentrations of n-butane in air promote the oxidation of NO to NO2. For given [NO]/[n-butane] ratio and reaction time, there is a critical sharply-defined ‘crossover’ temperature at which the system goes from being unreactive to reactive, with 100% conversion NO→NO2 occurring at T>Tcrossover. The crossover temperature increases, and becomes less sharply defined, with increasing [NO]/[n-butane] ratio. The conversion NO→NO2 is accompanied by the consumption of n-butane and the formation of CH3CHO, CO, HCHO, (CH3)2CO, various butenes, and propene. The extent of n-butane consumption depends in a complex manner on the experimental conditions especially on the relationship of the experiment temperature to the characteristic turnover temperature which marks the onset of the region of negative temperature coefficient (NTC) for n-butane/air reaction (≈380° C or 650 K). Trace quantities (as little as 0.02 ppm) of NO have a profound promoting effect on n-butane consumption in the vicinity of the turnover temperature by virtue of the ability of NO to convert unreactive HO2 radicals into reactive OH: HO2+NO→NO2+OH Other reactions of NO believed to be important in this system are RO2+NO→RO+NO2 and NO+OH+M→HONO+M The mutual sensitisation of the oxidation of n-butane and NO has implications for emissions of NO2 from combustion appliances and for hydrocarbon ignition phenomena in the presence of NO, such as occurs in engines.

Formate species in the low-temperature oxidation of dimethyl ether

The oxidation of dimethyl ether (DME, 340 ppm in 10% O2) has been studied experimentally in an atmospheric pressure laminar flow reactor in the temperature range from 240 degrees C to 700 degrees C for residence times in the range 2-4 s. The influence of nitric oxide additions up to 620 ppm to the feed gases has also been investigated. Products of reaction were determined by FTIR. In the absence of NO, reaction is first detected at about 260 degrees C. The products in the low-temperature region include formaldehyde (HCHO), and formic acid (HCOOH). The addition of NO leads to the appearance of methyl formate (CH3OCHO). While the overall behaviour of the system can be explained qualitatively in terms of typical low-temperature hydrocarbon ignition, recently published chemical kinetic models for DME ignition do not allow for the formation of these formate species. We find no experimental evidence for the formation of hydroperoxymethyl formate (HPMF, HOOCH2OCHO) which is predicted by the models to be a significant stable intermediate at temperatures below 350 degrees C. Since both formic acid and methyl formate have potentially harmful health effects, these observations may have significant implications for use of DME as a diesel fuel.

Soot surface growth at active sites

Abstract It is proposed that soot surface growth occurs by reaction and deposition of acetylene at specific mobile sites on the surface of soot particles. These sites are regenerated in the growth reaction and surface growth rates resulting are independent of the surface area of the soot aerosol.