[spf101]

If a liquid is placed under pressure (1500 psi) in a fixed vessel and the vessel is full, containing only the liquid, will a temperature increase change the volume in density asit relates to specific gravity by means of thermal expansion or would that happen only when the pressure is released.

[Borek]

It is mostly a question about how stiff is the container.

[fledarmus]

If your vessel has no headspace, the thermal expansion should relate directly to the compressibility. You could consider a two step process, where you use thermal expansion to increase the volume at constant pressure, then isothermal compression to decrease the volume at constant temperature and calculate the resulting pressure.

[Enthalpy]

In common hydraulic cylinders the fluid's compressibility accounts for more volume variation (or absorption) than the metal, but by a moderate factor.

Typical liquid "bulk modulus" are like 0.7GPa (silicone), 1.xGPa (mineral oil), 2GPa (water), 2.xGPa (polyglycol) near 100b - it's not linear and depends strongly on residual bubbles. You can also find a "compressibility factor", the reciprocal. Sound speed is more easily found and its square equals the modulus divided by the density (all in consistent units, do it as you can with your Btu/ft/°F*in*Cd*Bq) - but this is the bulk modulus at room pressure, far smaller than at 100b.