Documentation

Heat Exchanger (TL)

Detailed model of a heat exchanger between a thermal liquid network and a general fluid

  • Library:
  • Fluid Network Interfaces / Heat Exchangers

Description

The Heat Exchanger (TL) block models the heat transfer and fluid dynamics of a heat exchanger located between a thermal liquid network and an external fluid. The fluid properties of the thermal liquid network, specified through a Thermal Liquid Settings (TL) block, do not apply to the external fluid. The fluids do not mix nor do they change phase.

The equations underpinning the model, and therefore the available parameterizations and their required inputs, depend on the active block variant. To see the active variant or to change it, right-click the block and select Simscape > Block Choices. There are two variants with differing degrees of assumed knowledge about the component properties:

  • Simple Model — Provide tabulated data relating the mass flow rate at the inlets to the pressure drop between them and to the specific dissipation factor of the heat exchanger (a measure of its effectiveness). The heat transfer rate is determined from the value of the specific dissipation factor at the simulated operating conditions.

  • E-NTU Model — Provide detailed data on the component geometry, flow configuration, and performance properties such as the thermal resistance, pressure loss coefficient, and fouling factor. The heat transfer rate is determined in part from a calculated parameter known as the number of transfer units, or NTU.

Flow Configuration

The block dialog box provides a choice of common heat exchanger configurations. These include concentric-pipe with parallel and counter flows, shell-and-tube with one or more shell passes, and cross-flow with mixed and unmixed flows. A generic configuration lets you model other heat exchangers based on tabular effectiveness data.

Heat Exchanger Configurations

Component Structure

This block is a composite component assembled from simpler components found in the Fundamental Components library. The structural block diagram depends on the active block variant. The figures show the blocks comprising each variant and their respective connections.

In the Simple Model variant, a Specific Dissipation Heat Transfer block captures the heat transfer between the thermal liquid networks while a Simple Heat Exchanger Interface (TL) block captures the pressure drop and temperature change between the inlets.

Block Diagram for Simple Model Variant

In the E-NTU Model variant, an E-NTU Heat Transfer block captures the heat transfer between the thermal liquid networks while a Heat Exchanger Interface (TL) block captures the pressure drop and temperature change between the inlets.

Block Diagram for E-NTU Model Variant

Ports

Input

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Isobaric specific heat of the controlled fluid.

Dependencies

This port is exposed when the block variant is set to Simple Model. Right-click the block and select Simscape > Block Choices to change the active block variant.

Entrance mass flow rate of the controlled fluid. Positive values indicate flow into the heat exchanger. Negative values indicate flow out of the heat exchanger.

Dependencies

This port is exposed when the block variant is set to Simple Model. Right-click the block and select Simscape > Block Choices to change the active block variant.

Thermal capacity rate of the external fluid.

Dependencies

This port is exposed when the block variant is set to E-NTU Model. Right-click the block and select Simscape > Block Choices to change the active block variant.

Fluid-wall heat transfer coefficient for the external fluid.

Dependencies

This port is exposed when the block variant is set to E-NTU Model. Right-click the block and select Simscape > Block Choices to change the active block variant.

Conserving

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Opening through which thermal liquid can enter and exit the heat exchanger.

Opening through which thermal liquid can enter and exit the heat exchanger.

Thermal port associated with the inlet temperature of the external fluid.

Parameters

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Block Variant: Simple Model

Heat Transfer Tab

Array of mass flow rates at the thermal liquid inlet. Each value corresponds to a row in the specific dissipation lookup table. Positive values indicate flow into the heat exchanger and negative values indicate flow out of the heat exchanger.

Array of mass flow rates at the inlet for the controlled fluid. Each value corresponds to a row in the specific dissipation lookup table. Positive values indicate flow into the heat exchanger and negative values indicate flow out of the heat exchanger.

Matrix of specific dissipation values corresponding to the specified mass flow rate arrays for the thermal liquids and the controlled fluid. The block uses the tabulated data to calculate the heat transfer at the simulated operating conditions.

Option to warn if the specific dissipation falls outside the bounds of the specified tabulated data.

Thermal Liquid Tab

Array of mass flow rates at which to specify the pressure drop tabulated data.

Array of pressure drops from inlet to outlet corresponding to the tabulated mass flow rate data.

Temperature at which the tabulated pressure-drop data is specified.

Pressure at which the tabulated pressure-drop data is specified.

Mass flow rate below which to initiate a smooth flow reversal to prevent discontinuities in the simulation data.

Volume of thermal liquid occupying the heat exchanger at any given time. The initial conditions specified in the Effects and Initial Conditions tab apply to this volume. The volume is constant during simulation.

Flow area at the thermal liquid inlets. Inlets A1 and B1 are assumed to be identical in size.

Block Variant: E-NTU Model

Common Tab

Geometry of flow through the heat exchanger. Select Generic — effectiveness table to provide effectiveness data for any flow arrangements not explicitly provided.

Number of passes that the heat exchanger tube makes along the length of the shell between the fluid inlet and outlet. Increasing the number of shell passes increases the area of heat transfer between the fluids.

One- and Two-Pass Configurations

Mixing condition of each fluid. Mixing impacts the heat transfer correlations used during simulation. Each fluid mixes only with itself—in its compartment in isolation from the second fluid.

Values of the number of heat transfer units (NTU) at which to specify the tabulated effectiveness data. Each value corresponds to a row in the effectiveness lookup table. The number of transfer units is defined as:

NTU=AsUCmin,

where:

  • AS is the heat transfer surface area.

  • U is the overall heat transfer coefficient.

  • Cmin is the smallest of the thermal capacity rates of the two fluids.

Values of the thermal capacity ratio at which to specify the tabulated effectiveness data. Each value corresponds to a column in the effectiveness lookup table. The thermal capacity ratio is defined as:

Cr=CminCmax,

where Cmin is the smallest of the thermal capacity rates of the two fluids and Cmax is the largest.

Matrix with the heat exchange effectiveness values corresponding to the specified values of the number of heat transfer units and capacity ratio. The matrix rows correspond to different values of the number of heat transfer units. The matrix columns correspond to different values of the thermal capacity ratio.

Thermal resistance of the wall between the two fluids.

Thermal Liquid Tab

Aggregate flow area free of obstacles based on the smallest tube spacing or corrugation pitch.

Hydraulic diameter of the tubes or channels comprising the heat exchange interface. The hydraulic diameter is the ratio of the flow cross-sectional area to the channel perimeter.

Volume of thermal liquid occupying the heat exchanger at any given time. The initial conditions specified in the Effects and Initial Conditions tab apply to this volume. The volume is constant during simulation.

Reynolds number below which the flow is laminar. The flow transitions to turbulent above this number and it becomes fully turbulent at the number specified in the Turbulent flow lower Reynolds number limit parameter.

Reynolds number above which the flow is turbulent. The flow transitions to laminar below this number and it becomes fully laminar at the number specified in the Laminar flow upper Reynolds number limit parameter.

Parameterization of the pressure-loss calculation. The default parameterization, constant loss coefficient, provides the simplest option. Select a different parameterization if you have detailed data on the Darcy friction factor or Euler number.

Dimensionless number used to compute the pressure loss between the inlet and outlet. The pressure loss coefficient is assumed constant and the same for direct and reverse flows.

Distance traversed by the fluid from inlet to outlet.

Pressure loss due to local resistances such as bends, inlets, and fittings, expressed as the equivalent length of those resistances.

Average height of all surface defects on the internal surface of the pipe. The surface roughness enables the calculation of the friction factor in the turbulent flow regime.

Proportionality constant between convective and conductive heat transfer in the laminar regime. The shape factor encodes the effects of component geometry on the laminar friction losses.

Values of the Reynolds number at which to specify the tabulated Darcy friction factor data. The block uses this data to construct a lookup table. Each Reynolds number corresponds to an element in that table.

Tabulated Darcy friction factor data corresponding to the specified values of the Reynolds number. The block uses this vector to create a lookup table for the Darcy friction factor.

Values of the Reynolds number at which to specify the tabulated euler number data. The block uses this data to construct a lookup table. Each Reynolds number corresponds to an element in that table.

Tabulated Euler number data corresponding to the specified values of the Reynolds number. The block uses this vector to create a lookup table for the Euler number.

Parameterization used to calculate the heat transfer rate between the heat exchanger fluids.

Aggregate surface area available for heat transfer between the heat exchanger fluids.

Distance along which heat transfer takes place.

Proportionality constant between convective and conductive heat transfer in the laminar regime. This parameter enables the calculation of convective heat transfer rates in laminar flows. The appropriate value to use depends on component geometry.

Values of the Reynolds number at which to specify the tabulated Colburn factor data. The block uses this data to construct a lookup table. Each Reynolds number corresponds to an element in that table.

Tabulated Colburn factor data corresponding to the specified values of the Reynolds number. The block uses this vector to create a lookup table for the Colburn factor.

Values of the Reynolds number at which to specify the tabulated Nusselt number data. The block uses this data to construct a lookup table. Each Reynolds number corresponds to a row in that table.

Values of the Reynolds number at which to specify the tabulated Nusselt number data. The block uses this data to construct a lookup table. Each Prandtl number corresponds to a column in that table.

Tabulated Nusselt number data corresponding to the specified values of the Reynolds and Prandlt numbers. The block uses this vector to create a lookup table for the Nusselt number, with rows corresponding to different Reynolds numbers and columns corresponding to different Prandtl numbers.

Heat transfer coefficient between the thermal liquid and the heat-transfer interface.

Empirical parameter used to quantify the increased thermal resistance due to dirt deposits on the heat transfer interface.

Effects and Initial Conditions

Option to model the pressure dynamics inside the heat exchanger. Setting this parameter to Off removes the pressure derivative terms from the component energy and mass conservation equations. The pressure inside the heat exchanger is then reduced to the weighted average of the two port pressures.

Temperature of the internal volume of thermal liquid at the start of simulation.

Pressure of the internal volume of thermal liquid at the start of simulation.

Introduced in R2016a

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