Data Loading...
Fluent_HeatTransfer_O1_Optional_SolarLoad Flipbook PDF
Fluent_HeatTransfer_O1_Optional_SolarLoad
112 Views
83 Downloads
FLIP PDF 1.69MB
18.2 Release
Optional Lecture 1: Solar Load Model Heat Transfer Modeling using ANSYS Fluent
1
© 2017 ANSYS, Inc.
April 13, 2020
Outline • Introduction • Setting Up Cases Using the Solar Load Model • Practical examples • Automotive cabin • Indoor ventilation of ANSYS office in Sheffield UK
• Advantages and limitations
2
© 2017 ANSYS, Inc.
April 13, 2020
Introduction • The Solar Load Model is not a stand-alone radiation model. • Calculates radiation effects from the Sun’s rays entering the computational domain. • Only available for 3D cases. • Available for both steady and unsteady cases. • Typical applications : • Automotive climate control. • Human comfort modeling in buildings.
• Two options are available • Solar ray tracing using a tracing algorithm • Discrete ordinates (DO) irradiation, providing a means to apply solar loads directly into the DO model.
3
© 2017 ANSYS, Inc.
April 13, 2020
DO Irradiation Option • Available only in combination with the Discrete Ordinates (DO) radiation model. • Provides a means of applying radiation flux to semi-transparent walls. • The radiation heat transfer is derived from the solution of the DO radiation transfer equation
4
© 2017 ANSYS, Inc.
April 13, 2020
Solar Ray Tracing • Only adds the effects of an external radiation source to the thermal energy equation. • Models collimated beams of radiation entering in a particular direction through selected semi-transparent walls. • Uses a ray-tracing type algorithm to find where the beams pass. • Where the beams hit opaque walls, they dump their energy into those wall faces.
5
© 2017 ANSYS, Inc.
April 13, 2020
Activating the Solar Load Model • Select the ‘Solar Load Model’ in the ‘Radiation Model’ panel • Solar load parameters panel allows the user to set : • The position of the sun. (Not beam direction as in DO-Model) • The Direct and Diffuse Solar Irradiation values
6
© 2017 ANSYS, Inc.
April 13, 2020
Solar Calculator • The Solar Calculator panel allows the user to set the position of the sun by prescribing: • The global location and orientation of the object • The date and time of day
7
© 2017 ANSYS, Inc.
April 13, 2020
Boundary Conditions • Once the Solar Load Model is selected and set up, the user must specify: • Any semi-transparent walls • Opaque walls • Optical properties of each zone
8
© 2017 ANSYS, Inc.
April 13, 2020
Source Term Position • The solar load model calculates energy sources for every face subjected to solar load. • By default this energy will be sourced into the adjacent cells in the following order: • Shell conduction cells • Solid cells • Fluid cells
Heat Source Positioned in Solid Cells 9
© 2017 ANSYS, Inc.
April 13, 2020
Heat Source Positioned in Fluid Cells
Other Parameters • Other parameters are available in the TUI. • define/models/radiation/solar-parameters/… • ground-reflectivity •
Set the amount of radiation reflected from the ground and add in the total diffuse background radiation.
• Scattering-fraction •
Set the amount of direct radiation that has been reflected from opaque surfaces (after entering through the transparent surfaces) that will be considered to remain inside the domain.
• Sol-adjacent-fluidcells •
10
Apply solar loads to adjacent fluid cells only, even if solid or shell conduction zones are present
© 2017 ANSYS, Inc.
April 13, 2020
Advantages and Disadvantages • Solar load modeling is a useful approach for many climate control applications. •
Advantages • • • • •
•
Disadvantages • • •
11
Once the solar loads are calculated, exhibits low cost per iteration. Simple and quick to implement. Low memory and data file storage requirements Accurate prediction of “hot spots.” Can be used in conjunction with other radiation models. Often too simple as there is no internal radiation calculated. Reflection, absorption, and scattering effects are not considered. Only one beam direction is permitted.
© 2017 ANSYS, Inc.
April 13, 2020
Case Study – Automotive Passenger Cabin North
Semi-Transparent
West
East Solid Zones Opaque
Geometry
South
9:30 AM
Solar Heat Flux (w/m2)
Courtesy National Renewable Energy Laboratory
9:15 AM
Temperature (Celsius) 12
© 2017 ANSYS, Inc.
April 13, 2020
Case Study – Automotive Passenger Cabin • Modeled the interior of an automobile using 160,000 hexahedral cells • • •
Experimental data for 11 hours of soaking from NREL experiment is available. Ran a CFD simulation of the first 4 hours. Calculated natural convection flow and heat transfer
Semi-Transparent
• Solar Load Model to compute the heat fluxes due to solar radiation • •
Sun position updated every 5 minutes and heat fluxes are recalculated Serial solver has been run ahead only to compute the partial data files with solar flux
• DO Radiation model used for internal re-radiation of the energy • Parallel solver used to solve flow, turbulence, and DO equations, while reading intermediate data files automatically.
13
© 2017 ANSYS, Inc.
April 13, 2020
Solid Zones Opaque
Courtesy National Renewable Energy Laboratory
Case Study – Automotive Passenger Cabin
Courtesy National Renewable Energy Laboratory 14
© 2017 ANSYS, Inc.
April 13, 2020
Case Study – Automotive Passenger Cabin NREL Interior Cabin - Soaking under Solar Load: Air Volume Average Temperature
60
50
Celsius
40
30
20
10
0 5:15:00
6:15:00
7:15:00
8:15:00
9:15:00
10:15:00
time Experimental Total Air Average FLUENT 6.2 SLM+DO Volume Average in Air Zone
15
© 2017 ANSYS, Inc.
April 13, 2020
Case Study: ANSYS Sheffield‘s Office HVAC Analysis • Goal is to analyze the HVAC requirements in the reception area of ANSYS office in Sheffield, UK. • Fully glazed front wall • Small glazed area on roof. • A/C system behind the reception desk.
• 270,000 tetrahedral cell mesh without boundary layer mesh. • Natural/forced convection flow • Radiative heat transfer calculation (DO or S2S model) • Solar load model used to calculate solar heat fluxes on a normal day in the middle of summer. 16
© 2017 ANSYS, Inc.
April 13, 2020
Case Study: ANSYS Sheffield‘s Office HVAC Analysis Glass Walls
A/C system
17
© 2017 ANSYS, Inc.
April 13, 2020
Case Study: ANSYS Sheffield‘s Office HVAC Analysis
• Solar heat sources on June 21 at 1:00 pm of a typical year. • Source terms positioned in adjacent fluid cells
18
© 2017 ANSYS, Inc.
April 13, 2020
Case Study: ANSYS Sheffield‘s Office HVAC Analysis
Temperature Contours on Opaque Walls (Temperatures in Degrees C) 19
© 2017 ANSYS, Inc.
April 13, 2020
Case Study: ANSYS Sheffield‘s Office HVAC Analysis
Temperature Contours on Interior Surfaces (Temperatures in Degrees C) 20
© 2017 ANSYS, Inc.
April 13, 2020
Case Study: ANSYS Sheffield‘s Office HVAC Analysis
Temperature Contours on Interior Surfaces (Temperatures in Degrees C) 21
© 2017 ANSYS, Inc.
April 13, 2020
References
22
•
J.F Sacadura (1993) “Initiation aux transferts thermiques”, Lavoisier Tec & Doc
•
F. P. Incropera and D.P. DeWitt, Fundamentals of Heat and Mass Transfer, Wiley
•
J.S. Darrozès and C. François (1996), “Mechanique des Fluides Incompressibles,” ENSTA.
•
J.S. Turner, “Buoyancy Effects in Fluids.”
•
R. Hendes, F. van der Flugt, and C. Hoogendorn (1991), “Natural Convection Flow in a Square Cavity Calculated with Low Reynolds Number Turbulence Models,” Int. J. Heat and Mass Transfer, Vol. 34, pp. 1543-1557. © 2017 ANSYS, Inc.
April 13, 2020