NEAR-ISOTHERMAL REGENERATOR - COMPLETE THERMAL CHARACTERIZATION

Near-isothermal analysis of thermal regenerators used in Stirling and pulse-tube refrigerators is based upon realistic assumptions for tempe ratures above 10 K. The flow passages are small compared to the conduc tive heat penetration depth in the gas and the thermal mass of the mat rix is large compared to that of the gas. The analysis shows that the oscillating now includes a thermoacoustic effect, so that the enthalpy nux is not equivalent to a heat flux leaking across a temperature dif ference. An evaluation of the entropy sources allows for splitting the enthalpy nux into a reversible component and a loss. This one-dimensi onal model, applicable to arbitrary matrix topologies, uses an empiric al convection coefficient for heat transfer. To assess its validity, r esults for a laminar, constant Nusselt number are compared with two-di mensional results for a tubular regenerator based upon the exact physi cs of transverse heat transfer. The comparison shows that empirical co nvection coefficients yield incorrect results and that the error incre ases with the pressure amplitude.