## Fluids

Topics relate to Fluent, CFX, Turbogrid and more

#### Problem in Fluent, temperature destribution of solar collector

• Arash kazemian
Subscriber

Hello, I have simulated a solar thermal collecot which includes a rectangular plate (2m*1m) and collecor tubes. rectangular plate absorbs solar radiation, inside the collector there is water as working fluid, with velocity of 0.02 m/s, tube diameter is 1 cm, boundary conditions are : velocity inlet for inlet of collecot=0.02 m/s, for outlet of collector=pressure outlet of 0 pa, uniform solar radiation from the top of rectangular plate.

my quesstions are :

1. why there temperature desctribution is not uniform in right side of panel, since the length from inlet to outlet within harisontal pipes are same for all so based on bernoli equation it should have uniform temperature destribtion not right side down has highest temperature.

2. Re in this model is less than 2300, but i have selected uniform velocity inlet of 0.02 m/s, since the enrtance of collector is not long enough, fluid maybe is not fully developed, then how can i undrestand should i use laminar model or torbulence model?

3. The reseaon which temperature desribution is not uniform is it becuase I have not considere fully developed flow as inlet boundary condition?

regards

• Essence
Ansys Employee

Hello,

Could you please share the screenshot of the mesh?

Many a times, the flow may transition from laminar to turbulent. In such case, you need to use Intermittency transition model. But if the flow is laminar throughout the domain, please use laminar model only.

Also, please share the legend of the temperature contour. If the temperature of the water is high enough, you need to consider the effects of density and viscosity changes due to change in temperature.

Yes. I would suggest to account for the effect of fully developed flow. Either extend the inlet for the flow to get developed or you can also import/read the profile of the fully developed flow.

• Arash kazemian
Subscriber

Thank you for your response. I used a structured mesh throughout the entire model. Regarding the temperature legend, it ranges from 40°C to 50°C, so the temperature difference is not that high, and we can assume constant properties. I have some questions:

1. If Re is less than 2300, should I consider laminar flow or turbulence? Since the model includes some branches and not only a straight tube, how can we determine if it is laminar or turbulent? If it is turbulent, which model would be most suitable for this model - k-e, k-w, or...?

2. I used fully developed flow at the inlet, yet the temperature contour is still like the last figure. Is this contour reasonable or not?

• Arash kazemian
Subscriber

• Essence
Ansys Employee

Hello,

You can use Custom Field Functions/ Named Expressions to verify if the flow is turbulent or not. Based on that, you can choose the models.

Please refine the mesh apart from the fluid zones. Please share the screenshot of the models you used (turbulence and radiation).