.TransiEnt.Producer.Gas.BiogasPlant.HeatTransfer.FreeConvection.FreeConvectionHeatTransfer_Gas

Information

1. Purpose of model

This is a model of linear heat convection, e.g., the heat transfer between a plate and the surrounding air; see also: ConvectiveResistor. It may be used for complicated solid geometries and fluid flow over the solid by determining the convective thermal conductance Gc by measurements.

2. Level of detail, physical effects considered, and physical insight

(Description)

3. Limits of validity

(Description)

4. Interfaces

HeatPort_a: heat_solid

HeatPort_b: heat_fluid

5. Nomenclature

(no elements)

6. Governing Equations

The basic constitutive equation for convection is

Q_flow = A * alpha *(solid.T - fluid.T);

Q_flow: Heat flow rate from connector 'solid' (e.g., a plate)

to connector 'fluid' (e.g., the surrounding air)

A: Convection area (e.g., perimeter*length of a box)

alpha: Heat transfer coefficient

where the heat transfer coefficient alpha is calculated from properties of the fluid flowing over the solid. Examples:

Heat transfer by Free convection: External Flows (acording to W.Kast, et al.: VDI Heat Atlas, 2nd english edition, Springerl, 2010, p.667):

alpha = Nu*lamda/l;

Nu = f(Ra, Pr, Geometry)

where

alpha : Heat transfer coefficient

Nu : = alpha*l/lambda (Nusselt number)

Ra : = g*l^3*beta*dT (Rayleigh number)

Pr : = cp*eta/lambda (Prandtl number)

g : = Accelaration of gravity

l : characteristic length

height: height (characteristic lenght of vertical cylinder)

D : diameter of cylinder

rho : density of fluid (material constant)

eta : dynamic viscosity of fluid (material constant)

cp : specific heat capacity of fluid (material constant)

lambda : thermal conductivity of fluid (material constant)

7. Remarks for Usage

(none)

8. Validation

(no validation or testing necessary)

9. References

[1] W.Kast, et al.: VDI Heat Atlas, 2nd english edition, Springerl, 2010, p.667

10. Version History

Model created by Philipp Jahneke (philipp.koziol@tuhh.de), August 2018