Ö Ercan Ataer

Comparative study of irreversibilities in an aqua-ammonia absorption refrigeration system

Abstract Irreversibilities in components of an aqua-ammonia absorption refrigeratio system (ARS) have been determined by second law analysis. The components of the ARS are as follows: condenser, evaporator, absorber, generator, pump, expansion valves, mixture heat exchanger and refrigerant heat exchanger. It is assumed that the ammonia concentration at the generator exit is, independent of the other parameters, equal to 0.999 and at the evaporator exit the gas is saturated vapour. Pressrre losses between the generator and condenser, and the evaporator and absorber are taken into consideration. In the results the dimensionless exergy loss of each component, the exergetic coefficient of performance, the coefficient of performance and the circulation ratio are given graphically for each different generator, evaporator, condenser and absorber temperature.

Numerical analysis of regenerators of free-piston type Stirling engines using Lagrangian formulation

Abstract The circular duct between the cylinder and displacer serves as a regenerator in free-piston Stirling engines. The cylinder wall is fixed and the displacer wall is in reciprocating motion during the steady operation of the engine. The basic equations of the working fluid and regenerative duct are derived using the Lagrangian method in terms of the displacement of the displacer, so that time does not appear in the equations. A relation is derived between the cylinder and displacer wall temperatures to obtain the initial wall temperature distributions. A computer program is written in fortran and the governing equations, which include the pressure fluctuations due to the flow reversals, are solved numerically using a finite difference method. The results and discussion are presented.

Numerical solution of boundary layer equations in compressible cross-flow to a cylinder

Abstract Two-dimensional, steady-state, compressible boundary layer and energy equations are solved numerically using finite difference method in cylindrical coordinates. The heat transfer from and to an isolated cylinder for cross-flow is calculated up to the separation point iteratively. The velocity and temperature profiles, and local Nusselt numbers around the cylinder are obtained for the constant wall temperature boundary condition at different oncoming velocities. The results are obtained for compressible and incompressible flow and given in diagrams.

Numerical analysis of laminar film-wise condensation

Abstract A numerical method is presented for the analysis of laminar film-wise condensation of vapour flowing downwards on a horizontal tube. The governing equations of condensate flow include the pressure gradient, inertia and convective terms in addition to gravity and viscous terms. The effect of vapour shear on condensation is determined by simultaneous computation of the condensate and vapour flow fields using compatible interfacial conditions. Results obtained from the analysis are given in diagrams and compared with the results given in literature.

An approach to the analysis of regenerators of stirling-cycle machines

Abstract The governing equations of the regenerator of Stirling-cycle machines are derived by using the Lagrangian method in terms of the displacement of the displacer, so that time does not appear in the equations. A simplifying assumption is made that the heat transfer coefficient, based on the displacement of the displacer rather than time, is reasonably constant. As an approximation the pressure of the system and the mass of the gas in the expansion and compression volumes are assumed to be sawtooth functions of the displacement of the displacer. The governing equations of the regenerator are non-dimensionalized and a simplified iterative method is developed to solve the equations within certain assumptions. The equations, which include the pressure fluctuations due to flow reversals and longitudinal conduction, are solved numerically by a digital computer using a finite difference method and the results are presented.