Since many renewable energy technologies use low cost or free primary energy sources such as solar insolation or wind, the capital cost of conversion equipment can become the dominant factor in determining economic feasibility. A natural approach to lowering the capital cost per unit of electricity is to strive for high efficiency equipment, i.e., increase the amount of electricity produced. Another approach is to seek out low cost conversion technologies, i.e., lower the capital cost. Capital equipment costs must be significantly lower than currently available off-the-shelf technologies to make solar power generally attractive economically for small-scale electricity generation. One potential low capital cost energy conversion technology is the liquid piston Stirling engine. A necessary design component for liquid piston Stirling engines is estimation of the frictional losses in the oscillating liquid columns. While frictional losses for fully developed laminar and turbulent pipe flow are characterized quite completely, average frictional loss factors for the continually starting and stopping liquid flow in oscillating columns are less complete. Direct measurements of frictional loss using a log-decrement method are reported in the paper. Measurements were completed for a variety of piping and tubing sizes and configurations. It was found that liquid volume correlated damping coefficient data well. A comparison with an equivalent fully developed laminar flow damping coefficient is presented.

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