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# Calculating the Bulk Modulus of a Fluid

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ThermophyiscalData:-Property will compute the properties of fluids; these properties include density, enthalpy, viscosity and more.

However, some  properties are not computable out-of-the box; these include the isothermal bulk modulus a fluid. Bulk modulus is defined as So to compute the bulk modulus we need to calculate the

 • fluid density
 • and the numeric derivative of pressure with respect to density (at constant temperature).

This procedure accepts a temperature, pressure and fluid, and calculates the bulk modulus. Numerical derivatives are computed with fdiff .

 > > BulkModulus := proc(temp, press, fluid)    local rho:    uses ThermophysicalData:    rho:=Property(density, temperature = temp, pressure = press, fluid);    return rho*fdiff(Property(P, density = D, temperature = temp, fluid), D = rho); end proc:

Hence the bulk modulus of water at 20°C and 1 atm is

 >  (1)

This value closely matches that given by miniREFPROP , as illustrated in the screengrab below This plot demonstrates that the bulk modulus of water is at a maximum when the temperature is about 320 K

 > > 