PREFACE Materials used for thermal insulation and storage, along with other construction and building envelope components, are subjected to transient thermal conditions which can include dynamically changing temperature, moisture content, surface heat transfer, specific heat, etc. In addition, most building design and energy-related standards are based on a steady-state criterion (R-values using the apparent thermal conductivity measurements). This mismatch between the steady-state principles used in design and code requirements and the dynamic operation of buildings can result in lower thermal efficiency than achievable or higher cost (due to addition of more insulation than required). This mismatch can also lead to a gross underestimation of the performance of materials that store energy under cyclic temperature conditions, for example phase change materials (PCM). Although some experimental methods for transient analysis of building envelopes have been developed, there are no standardized testing procedures available to quantitatively characterize materials and systems under dynamic conditions. Data on dynamic material characteristics are needed to improve thermal design and analysis, whole-building simulations, and energy code-related work. This led to the development of a proposed ASTM Standard Test Method for characterizing PCM products under dynamic conditions. A series of measurements are needed to determine the enthalpy storage of a test specimen over a temperature range. First, both HFMA plates are held at the same constant temperature until steady state is achieved. Steady state is defined by the reduction in the amount of energy entering the specimen from both plates, or vice-versa, to a very small and nearly constant value. Next, both plate temperatures are changed by identical amounts and held at the new temperature until steady state is again achieved. The enthalpy absorbed or released by the specimen from the time of the temperature change until steady state is reached at the new plate temperatures is recorded. Using a series of temperature step changes of 1.5 ± 0.5°C, the cumulative enthalpy stored or released over a certain temperature range is determined. The specific heats of the solid and liquid phases are determined from the slope of the sensible enthalpy storage as a function of temperature, above and below the phase change temperature range. The proposed test method requires the measurement temperature range to begin at least 10°C below the phase change temperature range and continue till 10°C above. Since the phase change temperatures may not be known a priori, preliminary tests with coarser temperature step changes are useful in estimating the required measurement temperature range. Complete details of the test method can be found in the draft standard test method document (attached as Appendix A).

The free-piston Stirling engine ( F P S E ) is a heat driven mechanical oscillator from which power can be extracted. Linear dynamics is applied here in order to obtain: a stability criterion, a means for determining the oscillation frequency, relative amplitudes of the dynamic components, eflects of friction on starting and the locus of the roots of the system determinant. Three common configurations of these engines are investigated. NOTATION 2 LINEAR MODELReferring to Fig. 1, piston motion causes changes in working gas pressure, p , that excite motion of the dis-Dlacer which transfers working gas between the hot and The MS wus receioed on 26 June 1984 and was accepted for publication on 25 'Old 'paces thus changing p aid hence the force On March 1985. the piston. Oscillation occurs under proper conditions 91/85 0 IMechE 1985 0263-7138/85 $2.00 + .05

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