Generic Heat Exchanger Component

Description

The Generic Heat Exchanger (GHX) requires that the heat exchanger performance is known. There are several options to specify the performance such as: temperature change, thermal duty, NTU, effectiveness, and the Hs parameter.

Generic Heat Exchanger can be used in Compressible and Incompressible (hydraulic and non-hydraulic) simulations. Only a simple phase change is available, and it should be used with caution. The component has four fluid connections, and it models heat exchange between two streams in a network. Heat Exchangers in Flow Simulator come with 4 hidden chambers representing the 4 sides of a heat exchanger. The Generic Heat Exchanger uses Orifice or Effective Area elements (Compressible or Incompressible) in the backend to model restrictions losses (pressure loss) of both flow paths based on user defined loss parameters and characteristic flow area. The Heat addition/removal is calculated based on user inputs for Heat Exchanger Performance curves in Generic Hx module and Q (Heat Addition/Removal) is supplied to Orifice or Effective Area Elements to predict temperatures of the exiting fluids.

Some of the important modeling aspects to be taken care while using heat exchanger components are:

The Hot Side circuit must get connected to Line 1 (Indicated by Red Color part of Component Image) and Cold Side circuit get connected to Line 2 (Indicated with Blue Color part of Component Image) as shown in the image below.

Figure 3.
You can choose to model additional inlet and outlet losses using the separate Discrete Loss/Tube Element upstream and downstream of heat exchanger respectively.
The Hot/Cold Side circuit line must be connected with either compressible or Incompressible set of elements. Mixing of elements sets for a Hot/Cold side circuit line is not allowed. Below Table represents some modeling/allowable scenarios.


Modeling/Allowable Scenarios	Flow Simulator Network
Hot Side: Compressible Gases Cold Side: Compressible Gases Example: Air to Air Heat Exchanger
Hot Side : Incompressible Liquids Cold Side : Incompressible Liquids Example: Fuel Cooled Oil Cooler (FCOC)
Hot Side: Incompressible Liquids Cold Side: Compressible Gases Example: Air Cooled Oil Cooler (ACOC)
Hot Side: Compressible Gases Cold Side: Incompressible Liquids Example: Air to Liquid Heat Exchanger

GHX components can also be arranged in a matrix to discretize temperature changes and boundary conditions. For example, a vehicle radiator can be modeled with a 20 by 20 array of GHX components to show how coolant temperatures change through the system.

Flow Simulator can also be used for Heat Exchanger design. For heat exchanger design a detailed representation of the heat exchanger is required. The example below shows flow elements representing the cold and hot side with thermal network resistors connecting the sides. Heat exchanger performance can be predicted from such a model.

Generic Heat Exchanger Element Inputs

Table of the inputs for the Generic Heat Exchanger Component.


Element Specific Generic Heat Exchanger Component Input Variables
Index	UI Name (.flo label)	Description
2,10	Geometric Input Type (CS_SHAPE_COLD, CS_SHAPE_HOT)	Type of geometry information: 0. Enter Pipe Area only (assume Hydraulic Diameter from assumed circular shape). 1. Enter Pipe Area and Hydraulic Diameter.
3,11	Cross Sectional Area (AREA_COLD, AREA_HOT)	Flow area for hot and cold side fluids.
4,12	Hydraulic Diameter (HYD_DIA_COLD, HYD_DIA_HOT)	Hydraulic Diameter for hot and cold side fluids.
5,13	Pressure Loss Options (PLOSS_COLD, PLOSS_HOT)	Options to specify type of pressure loss modeling: 0. No Loss 1. Fixed Loss Coefficient 2. Fixed Total Pressure Drop 3. Flow vs. Delta.P (PTIN - PSEX) 4. Velocity vs. Delta.P (PTIN - PSEX) 5. Loss Coefficient vs. Reynolds Number 16. Flow vs. Delta P vs. Temperature
6,14	Loss Coefficient (KLOSS_COLD, KLOSS_HOT)	Incompressible Loss Coefficient
7,15	Delta Total Pressure (DELTA_PT_COLD, DELTA_PT_HOT)	Total pressure drop across a flow path.
8,16	Mass or Volume (MASS_VOL_COLD, MASS_VOL_HOT)	Type of flow input for PLOSS = 3 and 16 0. Flow in lbm/sec 1. Flow in gallons per minute
9,17	Mass or Volume (NPRCD_COLD, NPRCD_HOT)	Number of values in PLOSS tables
18-24		Not used
25	Heat Transfer Options (HOPT)	Options for modeling Heat Transfer between Hot and Cold side fluids: 1. Thermal Duty: Heat Input 2. Hot Fluid Delta.T 3. Cold Fluid Delta.T 4. Effectiveness 5. Effectiveness vs. Flow_Rate_Cold vs. Flow_Rate_Hot 8. Effectiveness vs. NTU vs. Heat Capacity Ratio 9. Nusselt Number vs. RE_Cold vs. RE_Hot 10. Constant hA coefficient value 12. Fixed Hot Fluid Exit T 13. Fixed Cold Fluid Exit T 14. Hs Constant 15. Hs vs Flow_Rate_Cold vs. Flow_Rate_Hot 16. Hot Fluid Exit Quality 17. Cold Fluid Exit Quality 18. NTU Constant
26	Heat Input (QIN)	Heat Addition or Quality at the exit of the hot or cold stream. Quality is the mass fraction of vapor in the fluid. A quality of 0 is all liquid and 1 is all vapor.
27	Fluid Delta.T (DELT_T)	Delta Total Temperature for Hot (or Cold) Side fluid
28	Effectiveness (EFFECTIVENESS)	Effectiveness of Heat Exchanger
29	Type of Configurations (CONFIG_TYPE)	Heat Exchangers Flow Configurations 0. Parallel Flow 1. Counter Flow 2. Shell and Tube 3. Cross flow both flows unmixed Cross flow One fluid mixed
30	Number of Shell Passes (NUM_SHELL_PASS)	No. of Shell Passes for Shell and Tube Hx Configurations
31	Primary hA coefficient (PRI_HA)	Htc*Area Coefficient of Primary side fluid
32	Secondary hA coefficient (SEC_HA)	Htc*Area Coefficient of Secondary side fluid
33,34		Not used
35	Mass or Volume (MASS_OR_VOL)	Type of flow input for HOPT = 5 and 15 0. Flow in lbm/sec 1. Flow in gallon per minute
36	Overall HTC (HTC_OPT)	Type of HTC input for HOPT=8 1. Fixed Overall HTC 2. Nusselt Number vs. Re Cold and Hot
37	Overall Heat Transfer Coefficient (OVERALL_HTC)	Overall Heat Transfer Coefficient Input
38,39,43,44,45	(NHT, NHT_1, NHT_2, NHT_3, NHT_4)	Table sizes
40	Select Mixed Flow (MIXED_FLOW)	4. Mixed Flow side of HX for Cross flow one side mixed option. 1=Primary, 2=Secondary
41	HX Area (HX_AREA)	The total heat exchanger area to be used with the Hs performance parameter
42	Hs Parameter (HS_PARAMETER)	A Heat Exchanger Performance Parameter
46	NTU Constant (NTU)	The Number of transfer units for the “NTU Constant” heat transfer option.
47	Part of HX Matrix (MATRIX_MODE)	Indicates if this GHX is a standalone heat exchanger or is being modeled as part of a matrix. 0) No 1) Yes, but not master. 2) Yes, and this GHX is the master.
48	Master GHX for Matrix (MTX_MASTER_ID)	The component ID of the GHX that is considered the master for the matrix. The master contains all the flow and heat transfer inputs.
49	Discretize Mode (DIS_OPTION)	The method used to take the overall heat transfer performance information from the matrix master and apply it to all GHX components in the matrix. 0) NTU scaling 1) Evenly distribute Q
T1, T2, T3, T4	Flow vs Delta P (COLD_DELTA-P, COLD_FLOW, HOT_DELTA-P, HOT_FLOW)	User-defined curve for Flow vs. Delta.P. Delta-P table is the difference between the upstream driving total pressure and downstream sink static pressure.
T1, T2, T3, T4	Fluid Velocity vs Delta P (COLD_DELTA-P, COLD_VEL, HOT_DELTA-P, HOT_VEL)	User-defined curve for Fluid Velocity vs. Delta.P. Delta-P table is the difference between the upstream driving total pressure and downstream sink static pressure.
T1, T2, T3, T4	Loss Coefficient vs Reynolds Number (COLD_KLOSS, COLD_REYN, HOT_ KLOSS, HOT_REYN)	User-defined curve for Loss Coefficient vs. Reynolds Number. $R e y n o l d s N u m b e r = (4.0 * W / (P E R I M * μ))$ Where: $μ = D y n a m i c V i s c o s i t y$ $W = M a s s F l o w R a t e$ $P E R I M = P e r i m e t e r = U s e r I n p u t$ If Hydraulic Diameter is provided, then: $P e r i m e t e r = 4.0 * A / H Y D D I A M$ If Hydraulic Diameter or Perimeter is not Provided, Reynolds number is calculated based on Orifice Area: $P e r i m e t e r = \sqrt{(4.0 * D P I * A)}$
T5, T6, T7	Effectiveness vs. Flow_Rate_Cold vs. Flow_Rate_Hot (FLOWRATE_COLD, FLOW_HOT.., EFFECTIVENESS)	3D Table for Effectiveness vs. Flow_Rate_Cold vs Flow_Rate_Hot
T5, T6, T7	Effectiveness vs. NTU vs Heat Capacity Ratio (NTU, ..HEAT_RATIO, EFFECTIVENESS)	3D Table for Effectiveness vs. NTU vs Heat Capacity Ratio
T8, T9, T10	Nusselt Number vs. RE_Cold vs. RE_Hot (NusseltNumber, ReynoldsCold, ReynoldsHot)	3D Nusselt Number vs. RE_Cold vs RE_Hot
T1, T2, T11	Cold Flow vs. Delta P vs. T (COLD_DELTA-P, COLD_FLOW, COLD_FLOW_T)	3D Table for Cold Flow vs. Delta P vs. T
T3, T4, T12	Hot Flow vs. Delta P vs. T (HOT_DELTA-P, HOT_FLOW, HOT_FLOW_T)	3D Table for Hot Flow vs. Delta P vs. T

Generic Heat Exchanger Theory Manual


Nomenclature:
$W$ : Mass flow rate	C: Heat Capacity
$ρ$ : Density	Q: Heat Addition/Rejection
$C p$ : Specific Heat	Tt: Total Temperature
NTU: Number of Transfer Units
Subscripts:
in, up, 1: Upstream station	C: Cold
ex, dn, 2: Downstream station	H: Hot

Pressure Loss Calculations

There are six different options through which pressure loss across a Hot or Cold stream can be modeled. They are:

0. No Loss
1. Fixed Loss Coefficient
2. Fixed Total Pressure Drop
3. Flow vs Delta.P (PTIN – PSEX)
4. Velocity vs Delta.P (PTIN – PSEX)
5. Loss Coefficient vs Reynolds Number
6. Flow vs Delta P vs Delta T

As discussed above, Generic Heat Exchanger uses Orifice or Effective Area elements (Compressible or Incompressible) in the backend to model restrictions losses (pressure loss). The “No Loss” option uses a Link element. This can be the fastest run time option for GHX matrix models when pressure loss is not important.

To get more details on pressure drop calculation for:

Fixed Loss Coefficient and Fixed Pressure Drop input refer to the Orifice Documentation.
Curve based inputs (3-6) mentioned above refer to the Effective-Area Orifice Documentation

Heat Transfer Calculations

Heat Input (Qin)
$T_{t, e x, C o l d} = T_{t, i n, C o l d} + \frac{Q i n}{W_{C o l d} * C p_{a v g, C o l d}}$
$T_{t, e x, H o t} = T_{t, i n, H o t} - \frac{Q i n}{W_{H o t} * C p_{a v g, H o t}}$
Hot Fluid Delta.T
$Q = W_{H o t} * C p_{a v g, H o t} (T_{t, i n, H o t} - T_{t, e x, H o t})$
$T_{t, e x, C o l d} = T_{t, i n, C o l d} + \frac{Q}{W_{C o l d} * C p_{a v g, C o l d}}$
Cold Fluid Delta.T
$Q = W_{C o l d} * C p_{a v g, C o l d t} (T_{t, e x, C o l d} - T_{t, i n, C o l d})$
$T_{t, e x, H o t} = T_{t, i n, H o t} - \frac{Q}{W_{H o t} * C p_{a v g, H o t}}$
Effectiveness
$C_{H o t} = A B S (W_{H o t}) * C p_{a v g, H o t}$
$C_{C o l d} = A B S (W_{C o l d}) * C p_{a v g, C o l d}$
$C_{m i n} = m i n (C_{H o t}, C_{C o l d})$
$Q_{M a x} = C_{m i n} * (T_{h, i n} - T_{c, i n})$
$Q = Q_{M a x} * E f f e c t i v e n e s s$
$T_{t, e x, C o l d} = T_{t, i n, C o l d} + \frac{Q}{W_{C o l d} * C p_{a v g, C o l d}}$
$T_{t, e x, H o t} = T_{t, i n, H o t} - \frac{Q}{W_{H o t} * C p_{a v g, H o t}}$
Effectiveness vs Flow_Rate_Cold vs Flow_Rate_Hot
Effectiveness is obtained from User Defined Input for Effectiveness as function Flow_Rate_Cold and Flow_Rate_Hot.
$C_{H o t} = A B S (W_{H o t}) * C p_{a v g, H o t}$
$C_{C o l d} = A B S (W_{C o l d}) * C p_{a v g, C o l d}$
$C_{m i n} = m i n (C_{H o t}, C_{C o l d})$
$Q_{M a x} = C_{m i n} * (T_{h, i n} - T_{c, i n})$
$Q = Q_{M a x} * E f f e c t i v e n e s s$
$T_{t, e x, C o l d} = T_{t, i n, C o l d} + \frac{Q}{W_{C o l d} * C p_{a v g, C o l d}}$
$T_{t, e x, H o t} = T_{t, i n, H o t} - \frac{Q}{W_{H o t} * C p_{a v g, H o t}}$
Effectiveness vs NTU vs Heat Capacity Ratio
Effectiveness is obtained from User Defined Input for Effectiveness as function NTU and Heat Capacity Ratio.
$N T U = \frac{U A}{C_{m i n}}$
$C_{R a t i o} = \frac{C_{m i n}}{C_{m a x}}$
UA is calculated from Constant user input or from curve specified for Nusselt Number as function of Reynolds Number Cold and Reynolds Number Hot
$U A = \frac{N u s s e l t_N u m b e r * K}{D h}$
$E f f e c t i v e n e s s = f (N T U, C_{r a t i o}, C o n f i g u r a t i o n)$
$C_{H o t} = A B S (W_{H o t}) * C p_{a v g, H o t}$
$C_{C o l d} = A B S (W_{C o l d}) * C p_{a v g, C o l d}$
$C_{m i n} = m i n (C_{H o t}, C_{C o l d})$
$Q_{M a x} = C_{m i n} * (T_{h, i n} - T_{c, i n})$
$Q = Q_{M a x} * E f f e c t i v e n e s s$
$T_{t, e x, C o l d} = T_{t, i n, C o l d} + \frac{Q}{W_{C o l d} * C p_{a v g, C o l d}}$
$T_{t, e x, H o t} = T_{t, i n, H o t} - \frac{Q}{W_{H o t} * C p_{a v g, H o t}}$
Nusselt Number vs RE_Cold vs RE_Hot
Nusselt Number is obtained from User Defined Input for Nusselt Number as function of Reynolds Number Cold and Reynolds Number Hot
$U A = \frac{N u s s e l t_N u m b e r * K}{D h}$
$N T U = \frac{U A}{C_{m i n}}$
$E f f e c t i v e n e s s = f (N T U, C_{r a t i o}, C o n f i g u r a t i o n)$
$C_{H o t} = A B S (W_{H o t}) * C p_{a v g, H o t}$
$C_{C o l d} = A B S (W_{C o l d}) * C p_{a v g, C o l d}$
$C_{m i n} = m i n (C_{H o t}, C_{C o l d})$
$Q_{M a x} = C_{m i n} * (T_{h, i n} - T_{c, i n})$
$Q = Q_{M a x} * E f f e c t i v e n e s s$
$T_{t, e x, C o l d} = T_{t, i n, C o l d} + \frac{Q}{W_{C o l d} * C p_{a v g, C o l d}}$
$T_{t, e x, H o t} = T_{t, i n, H o t} - \frac{Q}{W_{H o t} * C p_{a v g, H o t}}$
Constant hA Coefficient value
$C_{H o t} = A B S (W_{H o t}) * C p_{a v g, H o t}$
$C_{C o l d} = A B S (W_{C o l d}) * C p_{a v g, C o l d}$
$C_{m i n} = m i n (C_{H o t}, C_{C o l d})$
$\frac{1}{U A} = {(\frac{1}{h * A})}_{C o l d} + {(\frac{1}{h * A})}_{H o t}$
NTU Effectiveness Methods:
1. Cross Flow Unmixed
  $E f f e c t i v e n e s s = 1 - e^{((\frac{1}{C_{R a t i o}}) N T U^{0.22} e^{(- C_{R a t i o} N T U^{0.78} - 1)})}$
2. Counter Flow
  $E f f e c t i v e n e s s = \frac{1 - e^{- N T U (1 - C_{R a t i o})}}{1 - C_{R a t i o} e^{- N T U (1 - C_{R a t i o})}}$
3. Parallel Flow
  $E f f e c t i v e n e s s = \frac{1 - e^{- N T U (1 + C_{R a t i o})}}{1 + C_{R a t i o}}$
4. Cross Flow Both Side Mixed
  $E f f e c t i v e n e s s = \frac{1}{\frac{1}{(1 - e^{_N T U})} + \frac{C_{R a t i o}}{1 - e^{- C_{R a t i o} N T U}} - \frac{1}{N T U}}$
5. Cross Flow One Side Mixed
  Cmin is mixed: $E f f e c t i v e n e s s = 1 - e^{- (\frac{1}{C_{R a t i o}}) (1 - e^{- C_{R a t i o} N T U})}$
  Cmax is mixed: $E f f e c t i v e n e s s = (\frac{1}{C_{R a t i o}}) (1 - e^{- (C_{R a t i o} (1 - e^{_N T U}))})$
  $Q_{M a x} = C_{m i n} * (T_{h, i n} - T_{c, i n})$
  $Q = Q_{M a x} * E f f e c t i v e n e s s$
  $T_{t, e x, C o l d} = T_{t, i n, C o l d} + \frac{Q}{W_{C o l d} * C p_{a v g, C o l d}}$
  $T_{t, e x, H o t} = T_{t, i n, H o t} - \frac{Q}{W_{H o t} * C p_{a v g, H o t}}$
Hs Parameter Methods (Constant and vs Hot and Cold Flowrates)
The Hs parameter is typically used to describe radiators where the hot side is a liquid coolant, and the cold side is air.
$H_{s} = \frac{A B S (W_{H o t}) * C p_{a v g, H o t} * (T_{h, i n} - T_{h, e x})}{H X_{A r e a} * (T_{h, i n} - T_{c, i n})}$
$H_{s} * H X_{A r e a} * (T_{h, i n} - T_{c, i n}) = A B S (W_{H o t}) * C p_{a v g, H o t} * (T_{h, i n} - T_{h, e x}) = Q$
A heat exchanger effectiveness can be calculated using the Hs parameter.
$E f f e c t i v e n e s s = Q / Q_{M a x}$
$Q_{M a x} = C_{m i n} * (T_{h, i n} - T_{c, i n})$
$E f f e c t i v e n e s s = \frac{H_{s} * H X_{A r e a} * (T_{h, i n} - T_{c, i n})}{C_{m i n} * (T_{h, i n} - T_{c, i n})} = \frac{H_{s} * H X_{A r e a}}{C_{m i n}}$
Q is found using the effectiveness Qmax. The Q is applied to the fluid streams to get the exit temperatures.
$T_{t, e x, C o l d} = T_{t, i n, C o l d} + \frac{Q}{W_{C o l d} * C p_{a v g, C o l d}}$
$T_{t, e x, H o t} = T_{t, i n, H o t} - \frac{Q}{W_{H o t} * C p_{a v g, H o t}}$
Fixed Hot (or Cold) Fluid Exit Temperature
Specify the temperature at the exit of the heat exchanger for the hot or cold stream. The heat flow (Q) is calculated for a hot (or cold) stream and applied to both streams.
$Q = W_{H o t} * C p_{a v g, H o t} (T_{t, i n, H o t} - T_{t, e x, H o t}) o r Q = W_{C o l d} * C p_{a v g, C o l d} (T_{t, i n, C o l d} - T_{t, e x, c o l d})$
$T_{t, e x, H o t} o r T_{t, e x, C o l d}$ are specificed as inputs.
Hot (or Cold) Fluid Exit Quality
Specify the fluid quality at the exit of the heat exchanger for the hot or cold stream. The heat flow (Q) is calculated for a hot (or cold) stream and applied to both streams. The solver calculates the Q from the enthalpy change required to change the quality to the target exit value. The source of the fluid properties must be Coolprop for this option. Also, the energy balance option must be “enthalpy based energy balance”. The energy balance option is found in Solution Panel > Working Fluid.
NTU Constant
Specify the NTU for the heat exchanger. The NTU, hat capacity ratio, and HX configuration are used to calculate the heat flow (Q).
$E f f e c t i v e n e s s = f (N T U, C_{r a t i o}, C o n f i g u r a t i o n)$
$Q_{m a x} = C_{m i n} * (T_{h, i n} - T_{c, i n})$
$Q = Q_{M a x} * E f f e c t i v e n e s s$

Generic Heat Exchanger Matrix

Any number of GHX components can be added to a matrix to discretize the pressure loss and thermal results. One of the GHX components in the matrix must be declared the matrix master. It does not matter which component is declared the master. The master is given the overall pressure loss and heat transfer performance for the entire heat exchanger. All the other GHX components in the matrix use the number of the master components to identify all components that are part of the matrix. The pressure loss is distributed evenly between all GHX components in the series. The heat transfer is discretized using two methods:

NTU scaling.
$N T U_{l o c a l G H X} = \frac{N T U_{f u l l}}{N u m b e r o f G H X i n m a t r i x} * \frac{C_{m i n, t o t a l}}{C_{m i n, l o c a l}}$
Evenly distribute Q.
Q is calculated for the total HX and distributed evenly to each.

Note: Bi-Linear interpolation is employed between the values in the table to determine Y Values. If X-Value is less than its first value entry in the table, the first Y-Value entry is used. If the X-Value is greater than its last value entry in the table, the last Y-Value entry is used. Flow Simulator does not do any extrapolation if the values are outside the prescribed input limits.

Generic Heat Exchanger Outputs

The following listing provides details about Generic Heat Exchanger Component output variables.


Name	Description	Units
PS	Static pressure	psia, MPa
PT	Total pressure	psia, MPa
TT	Total temperature of fluid	deg F, deg K
RE	Reynold Number	(None)
Rho	Density	lbm/ft^3, Kg/m^3
CP	Specific Heat	Btu/(Lbm R), kJ/Kg.K
K	Thermal Conductivity	Btu/(hr ft R), W/m.K
DVISC	Dynamic Viscosity	Lbm/(hr ft), N s/m^2
Area	Flow Area	In2, m2
Heat Mode	Heat Mode Options (An echo of the user input).	(None)
Pri/cold_side_ploss_opt	Options specified for Pressure Loss Modeling for Pri/Cold side. (An echo of the user input).	(None)
Sec/hot_side_ploss_opt	Options specified for Pressure Loss Modeling for Sec/Hot side. (An echo of the user input).	(None)
Q	Heat Transferred between Heat Exchanger fluids	BTU/sec, W
Effectiveness	Effectiveness of Heat Exchanger	(None)
Pri/cold_side_delta.p	Delta.PT on Pri/Cold side flow	psia, MPa
Sec/hot_side_delta.p	Delta.PT on Sec/Hot side flow	psia, MPa
Mdot	Mass Flow Rate	Lbm/s, kg/s
Flow configuration	Heat Exchangers Flow Configurations. (An echo of the user input).	(None)
Overall conductance(UA)	Overall Thermal Resistance	BTU/hr.F, W/K
NTU	No of Transfer Units	(None)
Pri_hA_out	Pri/Cold side flow hA Coefficient value	BTU/hr.F, W/K
Sec_hA_out	Sec/Hot side flow hA Coefficient value	BTU/hr.F, W/K
Virtual Element	The element number created at run time for the two flow streams. The virtual element calculates the flow and pressure loss information so that it can be viewed in the .res file for additional details.	(None)
Heat Capacity	Mass flow rate x Fluid Specific Heat	BTU/sec/degF, W/degK
Heat Capacity Ratio	The minimum heat capacity over the maximum heat capacity.	(None)