Constant Pressure Processes Research Articles

Effects of additives on continuous hydrate-based flue gas separation

CO2 capture from fossil fuel power plants is the main method of CO2 storage. Hydrate-based gas separation is regarded as a potential method for CO2 capture from flue gas. In this study, hydrate-based gas separation (HBGS) was used to capture CO2 from flue gas (19.96 mol% CO2 and 80.04 mol% N2), and the continuous experimental process was monitored using magnetic resonance imaging (MRI). The effects of two additives (5 wt% TBAB + 5 wt% THF and 19 wt% THF), two gas injection methods (constant pressure and constant flow rate processes), and of different pressures and flow rates on the hydrate saturation and solution movement were investigated. The results show that both additives effectively promote hydrate formation. The constant pressure process was superior to the constant flow rate process for hydrate formation. Furthermore, the flow rate had little influence on the hydrate saturation. The process was most efficient when a hydrate formation stage time of approximately 80 min was used. The solution movement resulting from the continuous multiple cycles tended to decrease during subsequent cycles. Moreover, the addition of 19 wt% THF had a more obvious effect on the solution movement than 5 wt% TBAB + 5 wt% THF. Solution concentration phenomena were observed in the presence of 19 wt% THF at 285.15 K; these phenomena may have been affected by the formation and dissociation of hydrates. Due to solution movement during the continuous industrial hydrate-based gas separation process, the solution might need to be replenished. Finally, in terms of the resulting the hydrate saturation, the use of 5 wt% TBAB + 5 wt% THF was found to be more suitable in this study, while the 19 wt% THF was more suitable for a higher experimental temperature.

Grout Spread and Injection Period of Silica Solution and Cement Mix in Rock Fractures

A systematic presentation of the analytic relations of grout spread to the time period is established. They are divided following the nature of the flow, the property of the mix and the driving process. This includes channel flow between parallel plates and radial flow between parallel discs, nonlinear Newtonian fluids like silica solution, polyurethane and epoxy, and Bingham material like cement-based grout, and three grouting processes at a constant flow rate, constant pressure and constant energy. The analytic relations for the constant energy process are new and complete the relations of the constant flow rate and constant pressure processes. The well-known statement that refusal cannot be obtained during finite time for any injected material at a constant flow rate or constant injection pressure is extended to include the energy process. The term refusal pressure or energy cannot be supported for stop criteria. Stop criteria have to be defined considering confirmed relation of the spread to the time period and of the flow rate to the pressure and spread. It is shown that it is always possible to select a grouting process along which the work will exceed any predefined energy, the consequence of which is that jacking is related to the applied forces and not to the injected energy. Furthermore, a clarification is undertaken concerning the radial flow rate of a Bingham material since there are two different formulations. Their difference is explained and quantified. Finally, it is shown that the applied Lugeon theory is not supported by the analytic relations and needs to be substantially modified.

Mechanical Disturbances Arising from Thermal Power Deposition in a Gas

Systematic asymptotic methods are used to formulate a mathematical model for the response of an inert gas to time-resolved, spatially distributed, thermal energy addition. A primary objective is to identify how thermal energy is converted to kinetic energy to predict the distribution of induced fluid motion and the presence of mechanical disturbances. The gas response to heating is found to depend on two independent parameters, one related to the amount of energy deposited into the volume relative to the initial internal energy present there and the other related to the deposition time scale relative to the characteristic acoustic time in the volume. Results are given for relatively fast (slow), high (low) intensity energy deposition into a wide range of volumes to quantify conditions leading to either near constant volume heating or those leading to near constant pressure processes. In each case, the local expansion Mach number is the fundamental source of mechanical disturbances, via the “piston effect.”

Comparative analysis between constant pressure and constant temperature absorption processes for an intermittent solar refrigerator

This paper presents a detailed comparative analysis between constant pressure and constant temperature aqua-ammonia absorption processes for an intermittent solar refrigerator. The results of the analysis indicate that constant pressure processes results in as high as 20% increase in coefficient of performance compared to constant temperature processes. Also, the results indicate that there is a critical temperature below which both the constant pressure and constant temperature processes exhibit the same performance. Furthermore, it has been observed that the optimum generator temperature for constant pressure processes is approximately 12% higher than constant temperature processes. Finally, the effect of maintaining a constant temperature or constant pressure absorption processes on the heat duties of both, the absorber and the evaporator, is addressed in the paper.

Destruction of availability (exergy) due to combustion processes: A parametric study

An analytical examination of the destruction of availability was completed for constant pressure, constant volume, and constant temperature combustion processes for isooctane vapour and air mixtures. The variation of the percentage destruction of availability was determined as a function of temperature, pressure, and equivalence ratio. The percentage destruction of availability decreased with increasing reactant temperatures (from ∼30 per cent at 300 K to ∼5 per cent at 4500 K for constant pressure and constant volume combustion processes). The effect of the reactant pressure on the percentage availability destroyed was less pronounced - for example, for a 500 K initial temperature, a change from 50 to 5000 kPa changed the percentage availability destroyed from 26 per cent to 22 per cent for constant pressure adiabatic combustion. For changes in the equivalence ratio, the lowest destruction of availability was for mixtures near stoichiometric. In addition, the contribution of the various components (e.g. chemical and thermo-mechanical) of the mixture availability to the total availability was quantified for a range of conditions. Also, the effect of the decomposition of the reactant species for high reactant temperatures (greater than 3000 K) was determined.

The Regenerative Criteria of an Irreversible Brayton Heat Engine and its General Optimum Performance Characteristics

An irreversible cycle model of the Brayton heat engine is established, in which the irreversibilities resulting from the internal dissipation of the working substance in the adiabatic compression and expansion processes and the finite-rate heat transfer in the regenerative and constant-pressure processes are taken into account. The power output and efficiency of the cycle are expressed as functions of temperatures of the working substance and the heat sources, heat transfer coefficients, pressure ratio, regenerator effectiveness, and total heat transfer area including the heat transfer areas of the regenerator and other heat exchangers. The regenerative criteria are given. The power output is optimized for a given efficiency. The general optimal performance characteristics of the cycle are revealed. The optimal performance of the Brayton heat engines with and without regeneration is compared quantitatively. The advantages of using the regenerator are expounded. Some important parameters of an irreversible regenerative Brayton heat engine, such as the temperatures of the working substance at different states, pressure ratio, maximum value of the pressure ratio, regenerator effectiveness and ratios of the various heat transfer areas to the total heat transfer area of the cycle, are further optimized. The optimal relations between these parameters and the efficiency of the cycle are presented by a set of characteristic curves for some assumed compression and expansion efficiencies. The results obtained may be helpful to the comprehensive understanding of the optimal performance of the Brayton heat engines with and without regeneration and play a theoretical instructive role for the optimal design of a regenerative Brayton heat engine.

The Influence of Quantum Degeneracy on the Performance of a Fermi Brayton Engine

The influence of quantum degeneracy on the performance of a Brayton engine using an ideal Fermi gas as the working substance is investigated, based on the theory of statistical mechanics. The general expressions of the efficiency and work output of the engine cycle are derived. The maximum work output and the corresponding efficiency are calculated. The bound of the pressure ratio of the two constant-pressure processes that the Brayton engine cycle can be operated normally is determined. Some important characteristic curves of the cycle, such as the work output versus pressure ratio curves, the efficiency versus pressure ratio curves, the maximum work output ratio versus temperature of the heat reservoirs curves, and so on, are presented. Three special cases are discussed in detail. The results obtained may reveal the general performance characteristics of a Brayton engine working with an ideal Fermi gas.

The Performance Analysis of a Quantum Brayton Refrigeration Cycle with an Ideal Bose Gas

A Brayton refrigeration cycle using an ideal Bose gas as the working substance is simply referred to as a quantum Brayton refrigeration cycle, which consists of two constant-pressure and two adiabatic processes. The influence of quantum degeneracy on the performance of the cycle is investigated, based on the correction equation of state of an ideal Bose gas. The general expressions of the coefficient of performance, refrigeration load and work input of the cycle are calculated. The lowest temperature of the working substance and the minimum pressure ratio of the two constant-pressure processes for a quantum Brayton refrigeration cycle are determined. The variations of the relative refrigeration load with the temperature of the cooled space and the pressure of the low constant-pressure process are discussed for three special cases. Some curves related to the important performance parameters are given. The results obtained here are compared with those of a classical Brayton refrigeration cycle using an ideal gas as the working substance. Some significant conclusions are obtained.

Refrigeration systems realizing L 4; low pollution, low cost, low loss, and long life

The present work describes a refrigeration system which satisfies the criteria of L 4: low pollution, low cost, low loss, and long life. The design closely models the Ericsson ideal gas cycle which consists of two isothermal and two constant pressure processes. The working fluid is Helium which does not change phase during the cycle. The present design uses a high frequency bellows pumping system where one bellows compartment is capable of producing 40W of cooling power. The number of compartments in the bellows pump can be customized according to the amount of power needed.

The Uncatalyzed Partial Oxidation of Methane for the Production of Hydrogen With Recirculation

The combustion of rich mixtures of methane representing natural gas in air or oxygenated air involving the uncatalyzed partial oxidation of methane is examined analytically with the view of hydrogen and/or synthesis gas (carbon monoxide and hydrogen) production from natural gas. This is carried out in turn for isothermal, constant pressure and constant volume combustion processes over the feed temperature range of 800–2000K and equivalence ratio of up to 3.5. The role of various operating parameters in establishing the yield of hydrogen is presented and discussed. The effectiveness of the controlled recirculation of combustion gases to the feed for enhancing the reaction and conversion rates of methane into hydrogen is examined. It is shown that there are some conditions that can be employed for such recirculation to yield significant increases in the conversion rate.

Pressure measurements in chemically reacting powder mixtures with the Bauer piezoelectric polymer gauge

The response of highly porous powder compacts and powder mixtures to high pressure shock compression loading is of considerable interest for synthesis and processing of metals, ceramics and superhard materials. This technical note reports the first successful use of the Bauer piezoelectric polymer stress-rate gauge for measurements of shock wave velocity and stress-wave profiles in porous powder compacts. A powder mixture of 5Ti+3Si shows strong chemical reaction at a pressure of 2.5 GPa, while a powder mixture of 3Ni+Al shows no evidence for reaction at 4.7 GPa. A measurement of compaction of a powder compact of rutile at 5.5 GPa shows that it is not compacted to the solid density state. Although pressure increases due to chemical reaction products in condensed phases are modest and difficult to detect, shock wave velocities provide a sensitive measure of the existence of chemical reaction. The increase in shock speed can be described in terms of constant pressure processes which are descriptive of “ballotechnic” reactions, i.e. shock-induced reactions in heterogeneous material mixtures.

A kinetic investigation of the partial oxidation of methane for the production of hydrogen

Abstract The combustion of rich mixtures of methane representing natural gas in air or oxygenated air, involving the uncatalyzed partial oxidation of methane is examined analytically. A detailed chemical kinetic scheme for the oxidation of methane, made up of 108 simultaneous reaction steps with 28 reactive species, was employed. The role of various operating parameters in establishing the yield of hydrogen is presented and discussed. The results are considered over the temperature range 800–2000 K, pressures up to 50 atm and equivalence ratios of up to 3.4. This analysis is carried out in turn for isothermal, constant pressure and constant volume combustion processes. An assessment of the effectiveness of the controlled recirculation of combustion and exhaust gases to the feed or the early stages of the reaction in enhancing the reaction and conversion rates of the methane into hydrogen was also made. There are optimum conditions which can be employed for such recirculation to yield a significant increase in the conversion rates.

Generalized ideal reference cycle for regenerative refrigeration: part 1 isothermal systems

A generalized ideal reference cycle for regenerative refrigeration systems is discussed. The cycle has isothermal processes of compression and expansion for heat addition to and heat rejection from the cycle. The regenerative processes are assumed to be partly constant volume and partly constant pressure processes. Equations are developed for cycle work, heat lifted, coefficient of performance and the pressure ratio: mean effective/maximum cycle pressures. Various special cases are deduced from the generalized analysis including the Stirling and Ericsson cycles.

Sensitivity of premixed compression-initiated supersonic combustion to small perturbations in inlet flow variables

An analysis of the sensitivity of a scramjet combustor to small perturbations in the inlet flow variables is presented. The analysis is limited to a combustor having perfectly premixed fuel and air at the inlet with combustion being.initiated with a compression process, a shock wave for example. Flow in the combustor is taken to be inviscid, one dimensional, and adiabatic with the fuel being hydrogen gas in stoichiometri c proportions. Both constant pressure and constant area combustion processes are considered. Numerical results are presented for combustor inlet conditions corresponding to a wide range of flight conditions. The major conclusion is that the combustion process can be quite sensitive to small perturbations in the inlet flow variables.