Simple Heater

From SysCAD Documentation

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General Description

The simple heater is generic "heat exchanger" model without regards to its heating media or heater size. It is only designed to give estimates of

1) Heater duty required by specifying the stream outlet temperature or

2) Stream Outlet temperature by specifying the heater duty.

Note: The Boiler & Combustion Project, which is distributed with SysCAD in the Examples folder, demonstrates the use of this model.

Diagram

The diagram shows the default drawing of the Simple Heater, with the required connecting streams. The unit will not operate unless all of the above streams are connected.

The physical location of the connections is not important; the user may connect the streams to any position on the drawing.

Inputs and Outputs

Label	Input / Output	No. of Connections		Description
		Min	Max.
Input	In	1	1	Input stream to heater.
Output	Out	1	1	Output stream from heater.

Model Theory

Heater Duty or Final Temperature:

The Simple heater uses the following equation to calculate the duty required or the final temperature of the stream.

(1) $\mathbf{\mathit{Q=\dot{m}\int Cp\boldsymbol{\Delta}T}}$

Simple Heater Design Calcs:

The simple Heater also contains some side calculations for HTC, area or LMTD. These calculations are for user information only, thus they have no affect on the mass and energy balance of the model. The basic equation used for these calculations is:

(2) $\mathbf{\mathit{Q=UA\boldsymbol{\Delta}T_{LM}}}$

NOTE: These side calculations can be based on either the actual duty of the simple heater or a design duty specified by the user.

Assumptions and Limitations

The simple heater cannot handle phase changes. Thus, it will not be suitable for steam condensing calculations.
The simple heater has only one inlet and one outlet, if multiple stream inlet/outlets are required, the user will have to add in tie unit operations for mixing and splitting.
No reactions are allowed in the heater.

Data Sections

The default access window consists of several sections,

The first tab contains general information relating to the unit.
HSC, the second tab allows the user to set design data for the unit.
The Info section, contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents. This is fully described in Common Data Sections.
Links tab, only visible in SysCAD 9.2, contains a summary table for all the input and output streams.
Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

Class: SimpleHeater-1 - The first tab page in the access window will have this name.

Tag / Symbol	Input / Calc	Description/Calculated Variables / Options
Common First Data Section
Requirements
On	Tick Box	If this option is deselected, the heater will not be operational and thus inlet conditions = outlet conditions.
DutyMethod	FixedDuty	This allows the user to specify the heater duty. The outlet temperature will be calculated from this. Note a negative duty can be used for cooling.
	ProductTemp	This allows the user to specify the required outlet temperature. The heater duty is calculated from this.
	DutyTag	This allows the user to set a tag that the unit will 'read' to set the duty. This is used to transfer energy from another unit operation.
DutyRqd	Input	The required duty. Visible if the FixedDuty method is selected.
TRqd	Input	The required temperature. Visible if the ProductTemp method is selected.
DutyTag(kW)	Input	The required SysCAD Tag for the transferred duty, e.g. Boiler.HeatRqd1 (kW) or P1.EHX.HeatFlow (kW). Visible if the DutyTag Method is selected.
DutyFactor	Input	The duty factor. To change from heating to cooling or vice versa, use -1. Visible if the DutyTag method is selected.
Results
Duty	Calc	The actual Duty of the Heater
Qm	Calc	The mass flow rate.
Ti	Calc	The inlet temperature.
To	Calc	The outlet temperature.
Pi	Calc	The inlet pressure.
dP	Calc	The change in pressure.
Po	Calc	The outlet pressure.
Vfi	Calc	The inlet Vapour fraction.
dP	Calc	The change in vapour fraction.
Vf	Calc	The outlet Vapour fraction.

Second Section - HSC

Tag / Symbol	Input / Calc	Description/Calculated Variables / Options
Heater Sizing Calculations These simple calculations do not take into account any heater type and are independent of the actual heater performance.
ModelDuty	Calc	This is the actual duty for the simple heater (thus duty calculated in the first tab page). It is displayed here merely for comparison purposes.
SizeCalc Method	None	No estimates will be provided.
	Duty	This allows the user to calculate a duty by specifying Heat Transfer Coefficient (HTC), Heat transfer Area (Area) and Log Mean Temperature Difference (LMTD).
	HTC - Design Duty	This allows the user to calculate the required HTC by specifying Duty, Area and LMTD.
	Area - Design Duty	This allows the user to calculate the required Area by specifying Duty, HTC and LMTD.
	LMTD - Design Duty	This allows the user to calculate the required LMTD by specifying Duty, HTC and Area.
	HTC - Model Duty	This allows the user to calculate the required HTC based on Actual Heater Duty and specifying Area and LMTD.
	Area - Model Duty	This allows the user to calculate the required Area based on Actual Heater Duty and specifying HTC and LMTD.
	LMTD - Model Duty	This allows the user to calculate the required LMTD based on Actual Heater Duty and specifying HTC and Area.
DesignDuty	Input	The Duty for Heater Sizing Calculation only. Note: This is only available with certain methods and this is independent to the actual heater performance.

Duty	Calc	The duty calculated based on heater sizing parameters.
HTC	Input/Calc	Heat Transfer Coefficient - This field can be input / or calculated variable based on method selected.
Area	Input/Calc	Heat Transfer Area - This field can be input / or calculated variable based on method selected.
U*A	Calc	HTC x Area
LMTD	Input/Calc	Log Mean Temperature Difference - This field can be input / or calculated variable based on method selected.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

	DLL:	HeatXch1.dll	→	Units/Links	→	Heat Transfer: Simple Heater
or	Group:	Energy Transfer	→	Units/Links	→	Heat Transfer: Simple Heater

See Project Configuration for more information on adding models to the configuration file.

Insert into Project

Insert Unit

→

Heat Transfer

→

Simple Heater

See Insert Unit for general information on inserting units.

Simple Heater

From SysCAD Documentation

Contents

General Description

Diagram

Inputs and Outputs

Model Theory

Assumptions and Limitations

Data Sections

Requirements

Results

Second Section - HSC

Adding this Model to a Project

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