Heat Exchanger Model

andrey_rushin · November 16, 2011, 08:09

I try to use the Heat Exchanger Model of FLUENT and detect, that using of more then one HX produces wrong temperature difference between in- and outflow on one of used HX. Determination of one HX only in system deliveres correct temperature values...

Does somebody know something about this problem?
Thanks!

andrey_rushin · November 17, 2011, 05:38

you are right, I give too much information

Easiest way to establish communication is to discribe one example. Please imagine to have in your system two heat exchangers - radiator and condenser. For each HX you define in FLUENT a table that consits of heat rejections with coolant flow and air massflow. So far ok.
Regarding to actual flow field conditions one appropriate combination of heat rejection, coolant massflow and air massflow will be extracted from given table. As a result I expect one HX inlet temperature, which corresponds to formula:

Tin = Tamb + Q/(e*Cp*Mp)

where:
Tin - coolant inlet temperature (predicted)
Tamb - environment temperature
Q - actual heat rejection
e - effectiveness
Cp - heat capacity of air
Mp - massflow air

If I use in system only one HX, the solved Tin is exactly one like solved using the formula. Two HX in same system deliver wrong Tin...

I am sorry for broken english

November 16, 2011, 08:09	Heat Exchanger Model	#1
andrey_rushin New Member andrey rushin Join Date: Feb 2010 Posts: 3 Rep Power: 16	I try to use the Heat Exchanger Model of FLUENT and detect, that using of more then one HX produces wrong temperature difference between in- and outflow on one of used HX. Determination of one HX only in system deliveres correct temperature values... Does somebody know something about this problem? Thanks!

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November 17, 2011, 05:38		#2
andrey_rushin New Member andrey rushin Join Date: Feb 2010 Posts: 3 Rep Power: 16	you are right, I give too much information Easiest way to establish communication is to discribe one example. Please imagine to have in your system two heat exchangers - radiator and condenser. For each HX you define in FLUENT a table that consits of heat rejections with coolant flow and air massflow. So far ok. Regarding to actual flow field conditions one appropriate combination of heat rejection, coolant massflow and air massflow will be extracted from given table. As a result I expect one HX inlet temperature, which corresponds to formula: Tin = Tamb + Q/(eCpMp) where: Tin - coolant inlet temperature (predicted) Tamb - environment temperature Q - actual heat rejection e - effectiveness Cp - heat capacity of air Mp - massflow air If I use in system only one HX, the solved Tin is exactly one like solved using the formula. Two HX in same system deliver wrong Tin... I am sorry for broken english