setting heat flux inlet boundary condition

eliminator · July 27, 2015, 00:51

hi every one, can we set inlet boundary condition as heat flux or heat loss by any means like udf or anything else?

rasool motamedi · July 27, 2015, 05:39

yes
look at tutorials

Opaque · July 27, 2015, 10:04

Would you mind being more specific ? Specification of heat flux at an inlet is not a common boundary condition in the heat transfer literature (assuming is even possible)

At inlets, there is more than heat flux crossing the boundary; therefore, a flux condition should include more than just heat. What are your modeling requirements ? or what are you trying to model ?

The better the description, the higher the chances someone in the forum may pitch in.

eliminator · July 28, 2015, 01:01

Quote:

Originally Posted by Opaque

Would you mind being more specific ? Specification of heat flux at an inlet is not a common boundary condition in the heat transfer literature (assuming is even possible)

At inlets, there is more than heat flux crossing the boundary; therefore, a flux condition should include more than just heat. What are your modeling requirements ? or what are you trying to model ?

The better the description, the higher the chances someone in the forum may pitch in.

hi opaque,
actualy i am optimizing heat exchanger for mass...now i want to study, what is performance of heat exchanger if we increase or decrease heat input to heat exchanger, in that sense i want heat (watts) as input BC.

ghorrocks · July 28, 2015, 01:06

The heat input in the fluid entering the heat exchanger is from the temperature and specific heat of the fluid - so you define the temperature of the fluid entering. No need to define a heat flux, the heat flux is inherent in the specification of the temperature.

eliminator · July 28, 2015, 01:18

Quote:

Originally Posted by ghorrocks

The heat input in the fluid entering the heat exchanger is from the temperature and specific heat of the fluid - so you define the temperature of the fluid entering. No need to define a heat flux, the heat flux is inherent in the specification of the temperature.

hi ghorrocks,
thanks for reply
i have done simulation in same way u said. but heat exchanger is with large electric motor, and whole system simulation takes longer time...to reduced time, i want heat as input BC. (to get temperature at inlet, i need to run whole system and that i don't want)..Reply?

Opaque · July 28, 2015, 08:50

I understand what you are modeling now. Still your use of vocabulary is confusing. In my vocabulary, heat is due to temperature gradients (like k. grad T), or friction (irreversible work) not energy transport by fluid motion.

Have you looked at the Total Enthalpy boundary condition ? At inlets, the contribution to the energy flow (transport plus conduction) is dominated by the transport (mass flow, Cp, and Temperature); therefore, there is no need for a flux boundary condition.

July 27, 2015, 00:51	setting heat flux inlet boundary condition	#1
eliminator New Member tushar Join Date: Mar 2015 Posts: 10 Rep Power: 11	hi every one, can we set inlet boundary condition as heat flux or heat loss by any means like udf or anything else?

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July 27, 2015, 05:39		#2
rasool motamedi Member rasool Join Date: Apr 2013 Posts: 41 Rep Power: 13	yes look at tutorials

July 27, 2015, 10:04		#3
Opaque Senior Member Join Date: Jun 2009 Posts: 1,815 Rep Power: 32	Would you mind being more specific ? Specification of heat flux at an inlet is not a common boundary condition in the heat transfer literature (assuming is even possible) At inlets, there is more than heat flux crossing the boundary; therefore, a flux condition should include more than just heat. What are your modeling requirements ? or what are you trying to model ? The better the description, the higher the chances someone in the forum may pitch in.

July 28, 2015, 01:06		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,728 Rep Power: 143	The heat input in the fluid entering the heat exchanger is from the temperature and specific heat of the fluid - so you define the temperature of the fluid entering. No need to define a heat flux, the heat flux is inherent in the specification of the temperature.

July 28, 2015, 08:50		#7
Opaque Senior Member Join Date: Jun 2009 Posts: 1,815 Rep Power: 32	I understand what you are modeling now. Still your use of vocabulary is confusing. In my vocabulary, heat is due to temperature gradients (like k. grad T), or friction (irreversible work) not energy transport by fluid motion. Have you looked at the Total Enthalpy boundary condition ? At inlets, the contribution to the energy flow (transport plus conduction) is dominated by the transport (mass flow, Cp, and Temperature); therefore, there is no need for a flux boundary condition.