Documentation

# Interface (TL-IL)

Junction between thermal liquid and isothermal liquid networks

• Library:
• Simscape / Fluids / Fluid Network Interfaces

## Description

The Interface (TL-IL) block represents a cross-domain junction between thermal liquid and hydraulic (isothermal liquid) networks. The interface behaves as a moving membrane, allowing fluid networks to exchange mass and momentum while preventing the respective fluids from mixing.

Use this block as a modeling convenience when thermal effects matter in parts of a system but not in others. You can model the thermal effects using Thermal Liquid blocks and interface the resulting physical network with a Hydraulic model based on a constant-temperature assumption.

Pressure and mass flow rate are held constant across the interface. Temperature is free to fluctuate on the thermal liquid side of the interface but fixed at a constant value on the hydraulic side. Fluid properties are network-specific and do not extend across the interface.

### Mass Flow Rate

Mass is conserved at the interface. The interface wall is assumed rigid and the fluid dynamic compressibility ignored. With these assumptions, the mass accumulation rate inside the interface reduces to zero. Noting that the mass flow rate in the Hydraulic domain is computed from volumetric flow rate data:

`${\stackrel{˙}{m}}_{A}+{q}_{\text{B}}{\rho }_{\text{B}}=0,$`

where:

• ${\stackrel{˙}{m}}_{A}$ is the mass flow rate into the interface through port A.

• qB is the volumetric flow rate into the interface through port B.

• ρB is the hydraulic (isothermal liquid) density at port B.

### Pressure

Momentum is conserved at the interface. Viscous friction, fluid dynamic compressibility, and fluid inertia are ignored. With these assumptions, the momentum balance reduces to an equality statement between the pressures at port A and port B. Noting that pressure in the Thermal Liquid domain is absolute while that in the Hydraulic domain is gauge:

`${p}_{\text{A}}={p}_{\text{B}}+1\text{​}\text{\hspace{0.17em}}\text{atm,}$`

where:

• pA is the thermal liquid absolute pressure at port A.

• pB is the hydraulic (isothermal liquid) gauge pressure at port B.

### Temperature

The Simscape™ Hydraulic domain has no concept of temperature. The block computes the heat transfer rate between the thermal liquid port and the interface interior only. The temperature inside the interface is assumed to be held constant at a specified value:

`${T}_{\text{I}}={\text{T}}_{\text{Hyd}},$`

where:

• TI is the thermal liquid temperature inside the interface.

• THyd is the Hydraulic fluid temperature block parameter.

The temperature at the thermal liquid port is a function of the convective and conductive heat flow rates inside the interface. The conductive heat flow rate becomes significant only at mass flow rate approaching zero.

### Assumptions

• Viscous friction, fluid inertia, and dynamic compressibility are assumed negligible.

• The interface walls are assumed rigid.

## Ports

### Conserving

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Thermal liquid conserving port representing a passage point through the interface. Connect this port to a block network built on the Simscape Thermal Liquid domain.

Hydraulic (isothermal liquid) conserving port representing a passage point through the interface. Connect this port to a block network built on the Simscape Hydraulic domain.

## Parameters

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Temperature in the hydraulic (isothermal liquid) network. The block uses this parameter to calculate the heat transfer rate across the interface. If the isothermal liquid network contains a Hydraulic Fluid block, ensure that the specified temperature matches the System temperature (C) parameter in that block.

Area normal to the direction of flow at port A. The block uses this parameter to calculate the heat transfer rate across the interface. Ensure that the specified area matches the cross-sectional areas of the adjacent component inlets.