Читать книгу Hydraulic Fluid Power - Andrea Vacca - Страница 77

As explained in Chapter 3, the product Q · Δp represents hydraulic power. For the case of an orifice, this product represents the power dissipation introduced by the orifice itself:

(4.8)

This power dissipation mostly goes into heat generation within the fluid. In most cases, the portion of heat exchange with the external environment (through the solid walls of the components in the system, including the orifice) is minimal and negligible. The temperature increase of the fluid can be calculated from the energy balance:

(4.9)

Figure 4.5 Hydraulic symbol of two valves and equivalent orifice networks.

The Eq. (4.9) points out how the effects due to the thermal expansion of the fluid can be neglected. This is a reasonable assumption for oils, which have a thermal expansion coefficient, α, typicall of 7 · 10⁻⁴ [1/K].

Assuming common properties for mineral based oil, the value of ΔT is approximately 5 to 6 degrees Celsius per 100 bar of pressure drop.