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The speed of sound in various gases was measured using two different acoustic resonators. The first, a fixed-pathlength variable-frequency cylindrical resonator, was operated between 50 and 100 kHz, while the second, a spherical resonator of radius 60 mm, was operated between 2 and 15 kHz. The temperatures and pressures of the gases were accurately controlled and measured. Measurements were made on argon, xenon, helium, and 2,2-dimethylpropane at various temperatures between 250 and 340 K, and at pressures below 110 kPa. The results obtained in 2,2-dimethylpropane were used to derive values of the perfect-gas heat capacity and the second acoustic virial coefficient at temperatures between 250 and 340 K. The second acoustic virial coefficients determined using the spherical resonator have a precision of about ±0.1 per cent and have been used to calculate second virial coefficients. Measurements of the acoustic losses in the spherical resonator indicate that the vibrational relaxation time of 2,2- dimethylpropane at 298.15 K and 100 kPa is 4 ns. Detailed measurements of the speed of sound in argon indicate that a precision approaching 1 x10-6 is possible in acoustic thermometry using a spherical acoustic resonator. The second acoustic virial coefficients obtained in argon are in close agreement with values calculated from the interatomic pair-potential-energy function.

The speed of sound in a number of gases has been measured. Values were obtained from measurements of the frequencies of the radial modes of a spherical resonator. At low pressures( < 1 MPa) the speed of sound was determined using a 40 mm aluminium spherical resonator which was operable over wide ranges of temperature. Three substances were studied: ethane, tetrafluoromethane and methanol. Perfect-gas heat capacities and, second and third acoustic virial coefficients were determined from an analysis of the results. From the acoustic virial coefficients, estimates of the second and, in some instances) the third (p, Vm, T) virial coefficients were obtained. Results were compared with previous determinations. For measurements at pressures up to 10 MPa a new stainless steel resonator was constructed for which a detailed description is given. Measurements were performed over the temperature range 250 to 350 K and at pressures up to 10 MPa in the pure gases argon, nitrogen, and methane, and in the binary mixture of methane and ethane with mole fraction composition {(1 - x)CH₄ + xC₂H₆}, where x=0.15. Under such conditions the acoustic model was tested severely. The fractional precision of the results was generally better than 10 parts per million in u' for the whole temperature and pressure range. Acoustic and volumetric virial coefficients have been calculated from the results and are compared with previous determinations. For the industrially important gases, comparison of the experimental speeds of sound with those predicted from equations of state have been performed.

This thesis describes an investigation into the acoustic phenomenon in in-line tubular heat exchangers subjected to cross flow. The flow through such a heat exchanger can result in the production of very high noise levels, which occur as a result of the excitation of an acoustic standing wave in the cavity between the tube rows. This acoustic vibration can occur in large and small heat exchangers alike, resulting in drastically impared performance and working life. The phenomenon associated with such vibration is poorly understood and considerable anomalies still exist in published literature. There are several theories which attempt to describe this mechanism, however, none of these can satisfactorily account for its complex nature. The objective of the present work was to carry out an investigation to assess this acoustic phenomenon. The initial stages of this work produced an experimental rig to allow the phenomenon to be fully investigated, this included the examination of the effect of row depth and bank geometry on the acoustic resonance. The next step was to determine the role played by acoustic damping. This included making measurements of the damping under flow conditions and establishing its dependancy on velocity. A method of increasing the acoustic damping of a given bank was developed and incorporated in a tube bank. The results obtained from these experiments revealed that the acoustic system behaved in a manner which was consistent with that of a self excited system. Finally an appropriate mathematical model of the system was developed. The model,, which considers an acoustic feedback effect, was found to give quite an accurate representation of the system, and has the ability to account for all the observations made in this investiagation. This, together with the experimental results, enabled a series of guidelines to be presented as a basis for the design of such a tube bank.

No description available.

No description available.

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No description available.