# Specific Dissipation Heat Exchanger (TL-TL)

Heat exchanger parameterized by specific dissipation data for systems with two thermal liquid flows

*Since R2024a*

**Libraries:**

Simscape /
Fluids /
Heat Exchangers /
Thermal Liquid

## Description

The Specific Dissipation Heat Exchanger (TL-TL) block models the complementary cooling and heating of fluids held briefly in thermal contact across a thin conductive wall. The block uses a simplified model based on the concept of specific dissipation, which is a measure of the heat transfer rate.

### Heat Transfer Model

The block heat transfer model depends on the heat transfer rate defined by the specific dissipation. Specific dissipation is a measure of the heat transfer rate observed when thermal liquid 1 and thermal liquid 2 inlet temperatures differ by one degree. Its product with the inlet temperature difference gives the expected heat transfer rate

$$Q=\xi ({T}_{\text{In,1}}-{T}_{\text{In,2}}),$$

where *ξ* is specific dissipation and
*T _{In}* is inlet temperature for
thermal liquid 1 (subscript

`1`

) or thermal liquid 2 (subscript
`2`

). The specific dissipation is a tabulated function of the
mass flow rates into the exchanger through the thermal liquid 1 and thermal liquid 2 inlets:$$\xi =f({\dot{m}}_{\text{1}},{\dot{m}}_{\text{2}})$$

To accommodate reverse flows, the tabulated data can extend over positive and negative flow rates, in which case the inlets can also be thought of as outlets.

The specific dissipation is the heat exchanger heat transfer rate divided by the difference in inlet temperatures

$$\xi =\frac{Q}{{T}_{\text{In,1}}-{T}_{\text{In,2}}}$$

The specific dissipation is also equal to the overall heat transfer coefficient defined based on inlet temperature multiplied by the heat transfer surface area or the heat capacity rate multiplied by the effectiveness factor, for whichever fluid has a smaller value.

The heat transfer model, as it relies almost entirely on tabulated data, and as that data normally derives from experiment, requires little detail about the exchanger. Flow arrangement, mixing condition, and number of shell or tube passes, if relevant to the heat exchanger modeled, are assumed to manifest entirely in the tabulated data.

See the Specific Dissipation Heat Transfer block for more detail on the heat transfer calculations.

### Composite Structure

The block is a composite component. A Specific Dissipation Heat Exchanger Interface (TL) block models the thermal liquid flow on side 1 of the heat exchanger. Another models the thermal liquid flow on side 2. A Specific Dissipation Heat Transfer block captures the heat exchanged across the wall between the flows.

## Examples

## Ports

### Conserving

## Parameters

## Extended Capabilities

## Version History

**Introduced in R2024a**