Camelia Stanciu

Nonlinear Thermodynamic Analysis and Optimization of a Carnot Engine Cycle

As part of the efforts to unify the various branches of Irreversible Thermodynamics, the proposed work reconsiders the approach of the Carnot engine taking into account the finite physical dimensions (heat transfer conductances) and the finite speed of the piston. The models introduce the irreversibility of the engine by two methods involving different constraints. The first method introduces the irreversibility by a so-called irreversibility ratio in the entropy balance applied to the cycle, while in the second method it is emphasized by the entropy generation rate. Various forms of heat transfer laws are analyzed, but most of the results are given for the case of the linear law. Also, individual cases are studied and reported in order to provide a simple analytical form of the results. The engine model developed allowed a formal optimization using the calculus of variations.

Maximum Exergetic Efficiency Operation of a Solar Powered H2O-LiBr Absorption Cooling System

A solar driven cooling system consisting of a single effect H2O-LiBr absorbtion cooling module (ACS), a parabolic trough collector (PTC), and a storage tank (ST) module is analyzed during one full day operation. The pressurized water is used to transfer heat from PTC to ST and to feed the ACS desorber. The system is constrained to operate at the maximum ACS exergetic efficiency, under a time dependent cooling load computed on 15 July for a one storey house located near Bucharest, Romania. To set up the solar assembly, two commercial PTCs were selected, namely PT1-IST and PTC 1800 Solitem, and a single unit ST was initially considered. The mathematical model, relying on the energy balance equations, was coded under Engineering Equation Solver (EES) environment. The solar data were obtained from the Meteonorm database. The numerical simulations proved that the system cannot cover the imposed cooling load all day long, due to the large variation of water temperature inside the ST. By splitting the ST into two units, the results revealed that the PT1-IST collector only drives the ACS between 9 am and 4:30 pm, while the PTC 1800 one covers the entire cooling period (9 am–6 pm) for optimum ST capacities of 90 kg / 90 kg and 90 kg / 140 kg, respectively.

Concepts and fundamental equations in Thermodynamics with Finite Speed

This paper presents the basic concepts and fundamental equations of the Thermodynamics with Finite Speed (TFS) resulted by the systematically study of the thermal reciprocating machine in relation with the piston finite speed and thermal molecular speed measured in the considered thermodynamic system. These concepts are based on the idea that any propagation of the interaction in the thermodynamic systems of finite dimensions is achieved by finite speeds: (1) - piston speed, (2) - average speed of the gas molecules inside the cylinder. A specific approach (scheme of calculation) for non-equilibrium (irreversible) thermodynamic processes is developed within TFS in order to find the fundamental equations appropriate for Optimizing Efficiency or COP and Power of thermal reciprocating machines. Analytical equations for all 5 irreversible thermodynamic processes in gases (isometric, isothermal, isobaric, adiabatic, polytropic) are deduced by integration of the combined First and Second Laws equation for processes with Finite Speed. This paper is limited to Irreversible Processes with Finite Speed, without taking into account the Friction and Throttling effects. It also notes the main moments in the development of TFS that led to these concepts and fundamental equations.

Analysis of a flat plate collector for hot water domestic use - a sensitivity study

The paper presents the study of a flat plate collector (FPC) used to heat water for domestic use in stationary operation. A comparison is provided between the cases of constant and time-dependent water circuit, in clear sky conditions. Numerical results emphasize the hot water temperature obtained with a given FPC area for a certain value of the mass flow rate. Imposing both the mass flow rate and hot water temperature, the minimum required area of the FPC can be determined. The computations are based on energy and mass balance equations. Steady state is obtained after three days of continuous operation.

Performances Evaluation for a Reversed Quasi-Carnot Cycle (Refrigeration Machine) by Using the Direct Method from Finite Speed Thermodynamics

The Direct Method from Finite Speed Thermodynamics is used in order to Determine in a complete analytical format of the COP and consumed Power of a Reversed Cvasi-Carnot Cycle (Refrigeration Machine with vapor) taking into account internal irreversibility generate by: Finite Speed, Friction, Throttling and Internal Heat Loses.