Numerical analysis of irreversible processes in a piston-cylinder system using LB1S turbulence model. (June 2019)

• Record Type: Journal Article
• Authors: Yusof, Siti Nurul Akmal; Asako, Yutaka; Faghri, Mohammad; Tan, Lit Ken; Sidik, Nor Azwadi bin Che; Japar, Wan Mohd Arif bin Aziz
• Is Part Of: International journal of heat and mass transfer. Volume 136(2019)
• Page Start: 730
• Page End: 739
• Publication Date: 2019-06
• Subjects: Turbulent flow -- Irreversible process -- Piston velocities -- Numerical analysis; Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2019.03.007
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Irreversible processes in a piston-cylinder system were numerically investigated by using LB1S model. Computations were performed for a single compression and cyclic compression and expansion processes. The final state values of a single compression obtained by turbulent and laminar computations agreed well when up < 10 m/s. The maximum value of the turbulent viscosity for N = 1000 rpm were lower than the dynamic viscosity. 0.29% of the compression work in each cycle was converted into the thermal energy when N = 50, 000 rpm. Abstract: A numerical analysis for the irreversible processes in an adiabatic piston-cylinder system was conducted using the Lam & Bremhorst low Reynolds number turbulence model (LB1) modified for compressible flows by Sarkar and Balakrishnan (LB1S model). Two-dimensional compressible momentum equation and energy equation which includes the substantial derivative of pressure and the viscous dissipation terms were solved numerically to obtain the state quantities of the system. The computations were performed for a single compression process with constant piston velocity, u p = - 10 m/s and for cyclic compression and expansion processes with sinusoidal velocity variation. The selected rotation speed ranges from 1000 to 50, 000 rpm. The computations were performed for 10 cycles. It was found that the sinusoidal piston velocities have effects on the state quantities of the piston-cylinder system and it experienced an irreversible process when the piston moved with a finite velocity. For the case of single compression process, the flow was laminar when the piston velocity was below 10 m/s. In the cyclic processes, the flow was turbulent when the rotation speed is in the range from 2000 to 50, 000 rpm. However, for the case of 2000 rpm, the flow was laminar only at the first cycle. This is due to the turbulent viscosity that is lower than dynamic viscosity ( 1.862 × 10 - 5 Pa s). It was found increasing the rotation speed will increase the value of the turbulent viscosity. In the cyclic processes for the cases N = 1000, 10, 000 and 50, 000 rpm, the internal energy increased by 0.003%, 0.028% and 0.289% of the compression work in each cycle, respectively.