A numerical investigation into conjugate heat transfer for a double-tube heat exchanger in mini-scale was conducted, with an asynchronous intermittent laminar flow imposed at the inlets. As a basic component of the micro recuperator for a micro swing engine, a mini double-tube exchanger under the same flow conditions was chosen as the physical model with consideration of variable fluid properties. Results indicate that, for the asynchronous intermittent pulsed flow, the axial wall heat conduction is much more serious and the periodic fluctuation of the solid wall temperature further worsens the heat transfer efficiency. Two dimensionless numbers R* and (C) over bar* are proposed to evaluate the two adverse effects. Then, two key parameters involved in the design of the micro recuperator for the micro swing engine are studied, namely, wall thickness ratio delta/D-c and flow frequency. For certain flow frequencies, as the value of delta/D-c increases, the axial heat conduction is enhanced while the wall temperature fluctuation is reduced. For a given delta/D-c, the flow frequency dually affects the heat exchanger efficiency and the optimum frequency exists. The optimal value increases with the wall thickness ratio. These results lay a good foundation of the micro recuperator design for the micro swing engine. (C) 2019 Elsevier Ltd. All rights reserved.