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Fundamental concepts
Published in W. John Rankin, Chemical Thermodynamics, 2019
In thermodynamics, a process is said to occur when a system changes from one state of equilibrium to another, for example, an ice cube in a glass (state 1) melting to form water in the glass (state 2) or a piece of zinc reacting with sulfuric acid to form hydrogen and zinc sulfate. Processes are classified according to the conditions under which they occur as follows: An isothermal process is one that occurs at constant temperature.An adiabatic process is one that occurs with no heat exchange with the surroundings.An isobaric process is one that occurs at constant pressure.An isochoric process is one that occurs at constant volume.
Process Dynamics I — Development of Simulation Models
Published in Roger T. Haug, of Compost Engineering, 2018
Recall that heat flow in isobaric (constant pressure) processes is equal to the enthalpy change. The value of specific heat at constant pressure, cp, varies depending on the component. The following values in units of Btu/lb-°F or cal/g-°C are assumed in the simulation models: water, 1.00; solids, 0.25; dry gases, 0.24; and water vapor, 0.44. Values for water, dry gas (air), and water vapor are available in handbooks. The values chosen are applicable over the temperature range common to composting. Specific heat for composting solids is based on the work of Mears et al.5
The First Law of Thermodynamics
Published in David R. Gaskell, David E. Laughlin, Introduction to the Thermodynamics of Materials, 2017
The change in enthalpy from a to c (Figure 2.6). The enthalpy change is most simply calculated from the consideration of a path which involves an isothermal portion, over which ΔHʹ = 0, and an isobaric portion, over which ΔHʹ = qp = ∫ ncpdT. For example, consider the path a → b → c.
Exergetic port-Hamiltonian systems: modelling basics
Published in Mathematical and Computer Modelling of Dynamical Systems, 2021
Markus Lohmayer, Paul Kotyczka, Sigrid Leyendecker
We always use the word ‘energy’ in the thermodynamic sense. We use Latin letters for extensive quantities and lowercase Greek letters for intensive quantities. In particular, we use for internal energy, for entropy, for temperature, for volume, for pressure, for mass, and for chemical potential. Uppercase , , etc. denote corresponding potential functions. We use for total mass because is used for the dissipation operator in the GENERIC. A system is called closed if mass (of every type of atom) is constant. It is called isolated if no exchange of energy and mass is possible across its boundaries. A system or process is called isochoric/isothermal/isobaric if volume/temperature/pressure is constant.
Exergy and exergoeconomic analysis of a municipal waste-to-energy steam reheat power plant for Port Harcourt city
Published in International Journal of Ambient Energy, 2018
Some logical assumptions were employed to ease the complexity of the problem formulation and analysis of the plant. These assumptions include: The combustion reactions are purely Aspen HYSYS conversion reactions; thus, the incinerator is modelled as a conversion reactor in the Aspen HYSYS environment.The percentage conversion of the reactor is taken to be 75% – combustion efficiency.The combustion process is an isobaric and adiabatic process.The ambient reference properties, Po and To, are taken to be 1 bar and 27°C (Oko and Ogoloma 2011), and coincides with the reactor inlet properties such as the feed waste and excess air streams.The isentropic efficiencies of the pump and steam turbines are both 85% (Moran et al. 2003; Oko 2008).Heat losses and pressure drops due to mechanical losses and friction were neglected (Moran et al. 2003).The chemical exergy of air is taken to be zero (Nag 2008) and all fluid streams are assumed to be ideal, neglecting changes in their kinetic and potential energy and assuming a steady state condition.Recyclable or noncombustible materials such as metals and glass are sorted out of the feed waste, which is dried before the incineration process.The cost per unit exergy of waste, was assumed to be 2.0 US$/GJ (Mondal and Ghosh 2016).