- Heat Input (Qin)
Tt,ex,Cold=Tt,in,Cold+QinWCold*Cpavg,Cold
Tt,ex,Hot=Tt,in,Hot−QinWHot*Cpavg,Hot
- Hot Fluid Delta.T
Q= WHot*Cpavg,Hot (Tt,in,Hot−Tt,ex,Hot)
Tt,ex,Cold=Tt,in,Cold+QWCold*Cpavg,Cold
- Cold Fluid Delta.T
Q= WCold*Cpavg,Coldt (Tt,ex,Cold−Tt,in,Cold)
Tt,ex,Hot=Tt,in,Hot−QWHot*Cpavg,Hot
- Effectiveness
CHot= ABS(WHot)*Cpavg,Hot
CCold= ABS(WCold)*Cpavg,Cold
Cmin=min(CHot, CCold)
QMax= Cmin*(Th,in−Tc,in)
Q= QMax*Effectiveness
Tt,ex,Cold=Tt,in,Cold+QWCold*Cpavg,Cold
Tt,ex,Hot=Tt,in,Hot−QWHot*Cpavg,Hot
- 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.
CHot= ABS(WHot)*Cpavg,Hot
CCold= ABS(WCold)*Cpavg,Cold
Cmin=min(CHot, CCold)
QMax= Cmin*(Th,in−Tc,in)
Q= QMax*Effectiveness
Tt,ex,Cold=Tt,in,Cold+QWCold*Cpavg,Cold
Tt,ex,Hot=Tt,in,Hot−QWHot*Cpavg,Hot
- Effectiveness vs NTU vs Heat Capacity Ratio
Effectiveness is
obtained from User Defined Input for Effectiveness as function NTU and
Heat Capacity Ratio.
NTU= UACmin
CRatio= CminCmax
UA is calculated from
Constant user input or from curve specified for Nusselt Number as
function of Reynolds Number Cold and Reynolds Number Hot
UA= Nusselt_Number *KDh
Effectiveness=f(NTU, Cratio, Configuration)
CHot= ABS(WHot)*Cpavg,Hot
CCold= ABS(WCold)*Cpavg,Cold
Cmin=min(CHot, CCold)
QMax= Cmin*(Th,in−Tc,in)
Q= QMax*Effectiveness
Tt,ex,Cold=Tt,in,Cold+QWCold*Cpavg,Cold
Tt,ex,Hot=Tt,in,Hot−QWHot*Cpavg,Hot
- 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
UA= Nusselt_Number *KDh
NTU= UACmin
Effectiveness=f(NTU, Cratio, Configuration)
CHot= ABS(WHot)*Cpavg,Hot
CCold= ABS(WCold)*Cpavg,Cold
Cmin=min(CHot, CCold)
QMax= Cmin*(Th,in−Tc,in)
Q= QMax*Effectiveness
Tt,ex,Cold=Tt,in,Cold+QWCold*Cpavg,Cold
Tt,ex,Hot=Tt,in,Hot−QWHot*Cpavg,Hot
- Constant hA Coefficient value
CHot= ABS(WHot)*Cpavg,Hot
CCold= ABS(WCold)*Cpavg,Cold
Cmin=min(CHot, CCold)
1UA=(1h*A)Cold+(1h*A)Hot
NTU Effectiveness
Methods:
- Cross Flow Unmixed
Effectiveness=1−e((1/CRatio)NTU0.22e(−CRatioNTU0.78−1))
- Counter Flow
Effectiveness= 1−e−NTU(1−CRatio)1−CRatioe−NTU(1−CRatio)
- Parallel Flow
Effectiveness= 1−e−NTU(1+CRatio)1+CRatio
- Cross Flow Both Side Mixed
Effectiveness= 11(1−e_NTU)+CRatio1−e−CRatioNTU−1NTU
- Cross Flow One Side Mixed
Cmin is mixed:
Effectiveness=1−e−(1/CRatio)(1−e−CRatioNTU)
Cmax is mixed:
Effectiveness= (1CRatio)(1−e−(CRatio(1−e_NTU)))
QMax= Cmin*(Th,in−Tc,in)
Q= QMax*Effectiveness
Tt,ex,Cold=Tt,in,Cold+QWCold*Cpavg,Cold
Tt,ex,Hot=Tt,in,Hot−QWHot*Cpavg,Hot
- 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.
Hs=ABS(WHot)*Cpavg,Hot*(Th,in−Th,ex)HXArea*(Th,in−Tc,in)
Hs*HXArea*(Th,in−Tc,in)=ABS(WHot)*Cpavg,Hot*(Th,in−Th,ex)=Q
A heat exchanger effectiveness can
be calculated using the Hs parameter.
Effectiveness=Q / QMax
QMax= Cmin*(Th,in−Tc,in)
Effectiveness=Hs*HXArea*(Th,in−Tc,in)Cmin*(Th,in−Tc,in)=Hs*HXAreaCmin
Q is found using the effectiveness
Qmax. The Q is applied to the fluid streams to get the exit
temperatures.
Tt,ex,Cold=Tt,in,Cold+QWCold*Cpavg,Cold
Tt,ex,Hot=Tt,in,Hot−QWHot*Cpavg,Hot
- 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= WHot*Cpavg,Hot (Tt,in,Hot−Tt,ex,Hot) or Q= WCold*Cpavg,Cold (Tt,in,Cold−Tt,ex,cold)
Tt,ex,Hot or Tt,ex,Cold
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 .
- 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).
Effectiveness=f(NTU, Cratio, Configuration)
Qmax=Cmin*(Th,in−Tc,in)
Q=QMax*Effectiveness