during the NALSEM operating cycle from the initial heater input to the final conversion into electric power. In this flow process, the net thermal input is the sum of the expansion work and the rejected heat (lTe + Hc), while the regenerator heat loss is defined as the difference between the coolant waste heat and the compression work (HQ —| B^l). The energy characteristics thus obtained are compared in Figs 11(a) and (b) for two distinct output power conditions. Since thermal input increased linearly with engine speed, it is obvious from the figure that the unit number of the heater (representative of a heat transfer parameter) is almost constant with engine speed. Waste heat from the cooler and the heat loss from the regenerator both increased with engine speed, with the cooler in particular absorbing a large amount of the compression energy. Net thermal input also increased remarkably for high power operations, with its value exceeding the heater input above 24 Hz. This indicated additional input energy from some source, perhaps from the displacer driving power. To solve this problem, it is necessary to independently determine the power produced in the bottom space of the displacer. Thermal efficiencies as determined from energy parameters are shown in Fig. 12 as a function of engine speed. As the engine speed increases, thermal efficiency also increases because of the rapidly increasing expansion work, yet was still below about half the predicted efficiency. This is in disagreement with a general speed dependency as would be expected in any kinematic Stirling engine operation. If no additional expansion work occurs due to displacer motion, the NALSEM engine is expected to have thermal efficiencies identical to its kinematic Stirling counterpart. Regenerator effectiveness can be determined from heat loss and the temperature difference between the hot and cold ends of the regenerator. For constant heater wall
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