# CHT

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 March 26, 2008, 06:17 CHT #1 skarp Guest   Posts: n/a Hi I am using CHT to simulate heat transfer of convection and conduction. Consider a L shaped pipe. Considered flow as fluid domain and wall(8mm thick)considered as solid domain in steady state. Flow boundary condition is In -opening-static pressure entrain- pressure 1.36 bar and temperature 800C Out -opening-static pressure entrain- pressure 0.35 bar and temperature areaAve(T)@REGION:Out Solid domain Cast iron-pure substance,CHT and particle solid. Heat transfer-Thermal energy for both,Turbulence k-eplison Inferface-conservative interface flux and wall-adiabatic After solving Imbalance are less than 0.05% convergence up to 1e-4 for heat transfer,turb,momentum In cfx post The heat transfer to the wall is 797C. The heat loss from flow to wall is only 3C which is not acceptable. Kindly tell me what is wrong in my simulation

 March 26, 2008, 09:14 Re: CHT #2 andy2O Guest   Posts: n/a Adiabatic = perfectly insulated. So it seems from your description (if I've understood it correctly) that the outer wall of the pipe is perfectly insulated. So the heat cannot escape from the outer surface of the pipe wall. Therefore the pipe will be close to thermal equilibrium with the fluid. Therefore heat fluxes in the pipe wall are small - probably just a small heat flux along the length of the pipe. Therefore little heat is being transferred from the fluid to the pipe. Therefore temperature differences between the fluid and the pipe wall will be small. If you want to study heat loss from your pipe then you need to choose the outer boundary condition on the pipe to carefully model your actual scenario. Probably you need a heat transfer coefficient boundary condition, derived from an empirical correlation or from a separate CFD study. Adiabatic boundary conditions are unlikely to be a good choice. Regards, andy NB: Heat transfer / heat loss is usually measured in terms of energy loss per unit time i.e. Watts (W), or frequently Watts per unit area (e.g. W/m^2). It is not measured as a temperature in C... so make sure you're looking at the right data.

 March 26, 2008, 10:46 Re: CHT #3 skarp Guest   Posts: n/a Thanks andy I know only the surrounding temperature of air near the pipe outer wall. It is 170C.Can I give pipe outer wall temperature as 170C or I have simulate a convection of air near the pipe wall I have completed a simulation by giving pipe outer wall temperature as 170C and run at steady state. I have observed the temperature distribution on the outer wall of pipe is 170C. The temperature from inside to outside is 800C-170C drop. In real condition , whatever may be the case, whether the temperature of the object outer is equally to air temperature surrounded by it.

 March 27, 2008, 21:43 Re: CHT #5 Rogerio Fernandes Brito Guest   Posts: n/a how about choosing this? As boundary conditions, u can put that all the faces of the tube are submitted to a constant convection heat transfer coefficient (h = 25 W/mēK). The temperature of external enviromment could be this one: Tinfinite = 298 K

 March 28, 2008, 01:19 Re: CHT #6 skarp Guest   Posts: n/a Dear andy Can u kindly provide me the detail how to get the heat transfer co-efficient for the pipe outer wall through cfd. the pipe material is Cast Iron.

 March 28, 2008, 04:25 Re: CHT #7 andy2O Guest   Posts: n/a Where on Earth have you got those numbers from? - Why 298K when skarp has already said surrounding air is at 170 C = 443 K? - What correlation are you using to get h=25 W/m^2/K? Without evidence to back them up these numbers are *completely* meaningless. Any customer / professor / reviewer would (and should) simply throw the report of this study away if these numbers are used without supporting evidence to show they are valid.

 March 29, 2008, 04:17 Re: CHT #9 skarp Guest   Posts: n/a Thanks andy. I have got new idea from u.I will implement it and tell u within a week. Hats off for valuable info. regards skarp

 April 11, 2008, 12:29 Re: CHT #10 skarp Guest   Posts: n/a Hi andy 1.Is there any need to create a subdomain to defined the source as given in heating coil example? 2.If i model a pipe with BC inlet(opening condition) and outlet(opening).The pipe is placed inside a big box in which box has inlet and outlet(opening). pipe - water flow box - Air flow CHT simulation The flow of air in the box is towards the entry of pipe inlet (opening condition). In this case whether air enter into water under specified condition. If the pipe has in and out opening condition and air flow on the Box

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