* Corresponding author. Tel.:+34 943 037 948; fax: E-mail address:ccosta@centrostirling.com Copyright © 2012 by ISEC International Stirling Engine Committee. All right reserved. Stirling Regenerator Test Bench Design for Pressure Drop and Thermal Efficiency Measurements S. C. COSTA a * , I. BARRENO a , J. I. PRIETO b , M. A. GONZÁLEZ b and D. GARCÍA b a CS Centro Stirling S. Coop., Ave. Alava 3, 20550 Aretxabaleta, Spain, ccosta@centrostirling.com b Department of Physics, University of Oviedo, Ave. Calvo Sotelo s/n, 33007 Oviedo, Spain, jprieto@uniovi.es Keywords: Stirling engine regenerator, test bench, oscillating flow, pressure drop, thermal efficiency. Abstract A Stirling regenerator test bench was designed to analyse, evaluate and compare the pressure drop and heat transfer characteristics of different regenerators under oscillating flow conditions. The test bench operating conditions range was initially selected based on the performance of the commercial, well-known Stirling engine Whispertech-EHE. This oscillating flow test bench is based on a symmetrical design, which allows two different regenerators to be tested simultaneously under the same flow conditions. The oscillating flow is obtained by means of a linear drive motor which moves a piston in an oscillating motion. Both the frequency and the stroke of the piston can be modified to achieve different test conditions. The measurement equipment consists of pressure and differential pressure transducers, mass flow metre and thermocouples located at both ends of the regenerators. This paper describes the test bench design criteria, the testing procedure, some experimental results and preliminary conclusions about the test bench utility. Nomenclature wr A wetted area of regenerator, m 2 xr A cross-sectional area of regenerator, m 2 f C friction factor     2 ½ u L r p r hr    p c specific heat of gas at constant pressure, J/(kg·K) r c specific heat of regenerator material, J/(kg·K) V c specific heat of gas at constant volume, J/(kg·K) h convective heat transfer coefficient, W/(m 2 ·K) k thermal conductivity of the gas, W/(m·K) r k thermal conductivity of the regenerator material, W/(m·K) r L regenerator length, m m  mass flow rate, kg/s fo N Fourier number     1     ma ref hr r hr r N RT r r u   ma N Mach number =   xr ref ref pA RT m RT u   pr N Prandtl number = k c p  re N Reynolds number = xr hr hr A r m r u     4 4  st N Stanton number =     p xr p c m hA c u h    TCR N thermal capacity ratio =            1    p T c c c ref r r p r r s n engine frequency, rev/s p pressure, Pa R specific gas constant, J/(kg·K) hr r local hydraulic radius of regenerator, m C T compression space temperature, K E T expansion space temperature, K g T gas temperature, K gL T gas temperature at hot side, K 0 g T gas temperature at cold side, K ref T reference temperature at which physical properties are computed, K wr T regenerator matrix temperature, K wrL T regenerator matrix temperature at hot side, K 0 wr T regenerator matrix temperature at cold side, K t time, s u gas velocity, m/s u mean gas velocity, m/s dr V regenerator dead volume, m 3 x longitudinal coordinate along the regenerator length, m r  thermal diffusivity of regenerator material, m 2 /s  regenerator thermal efficiency  adiabatic coefficient  viscosity of gas, Pa∙s V ¶ volumetric porosity  density of gas, kg/m 3 r  density of regenerator material, kg/m 3