G.2.1
rising hot fluid and sinking cold fluid. Free convection only takes place in a gravitational
field [203].
Forced convection, on the other hand, is caused by a fluid flow caused by external
forces, which therefore enhance the convective heat exchange. The heat transfer depends
very much on whether the induced flow over a solid surface is laminar or turbulent. In the
case of turbulent flow, an increased heat transfer is expected with respect to the laminar
situation. This is due to an increased heat transport across the main direction of the flow.
On the contrary, in laminar flow regime, only conduction is responsible for transport in the
cross direction. For this reason, forced convection is always studied separately in the
laminar and turbulent regimes [203].
The overall convection transfer is made up of the two relative contributions from free
and forced components. The mixed convective coefficient can be obtained by taking the
cubic root of the cubes of the forced and convective coefficients [163],
Since the convective heat transfer coefficients will be different on the top and rear surfaces
of the module, the total heat transfer coefficient has to be decoupled between the top
and rear surfaces. The overall convective heat transfer will eventually be determined by
the sum of the two components.
Convective heat transfer on the top surface
Convective heat transfer has to be distinguished in free and forced components. For the
forced component we further have to distinguish between laminar and turbulent flow. We
obtain for the laminar and turbulent convective heat transfer coefficients
Re is the Reynolds number that expresses the ratio of the inertial forces to viscous forces,
where w is the wind speed at the height of the PV array, D h is the hydraulic diameter of the
module, which is used as relevant length scale, and ν is the kinematic viscosity of air. Pr is
the Prandtl number which is the ratio between the momentum diffusivity and the thermal
diffusivity. It is considered to be 0.71 for air. Finally, ρ and c air are the density and heat
capacity of air, respectively. The hydraulic diameter of a rectangle of length L and width
rising hot fluid and sinking cold fluid. Free convection only takes place in a gravitational
field [203].
Forced convection, on the other hand, is caused by a fluid flow caused by external
forces, which therefore enhance the convective heat exchange. The heat transfer depends
very much on whether the induced flow over a solid surface is laminar or turbulent. In the
case of turbulent flow, an increased heat transfer is expected with respect to the laminar
situation. This is due to an increased heat transport across the main direction of the flow.
On the contrary, in laminar flow regime, only conduction is responsible for transport in the
cross direction. For this reason, forced convection is always studied separately in the
laminar and turbulent regimes [203].
The overall convection transfer is made up of the two relative contributions from free
and forced components. The mixed convective coefficient can be obtained by taking the
cubic root of the cubes of the forced and convective coefficients [163],
Since the convective heat transfer coefficients will be different on the top and rear surfaces
of the module, the total heat transfer coefficient has to be decoupled between the top
and rear surfaces. The overall convective heat transfer will eventually be determined by
the sum of the two components.
Convective heat transfer on the top surface
Convective heat transfer has to be distinguished in free and forced components. For the
forced component we further have to distinguish between laminar and turbulent flow. We
obtain for the laminar and turbulent convective heat transfer coefficients
Re is the Reynolds number that expresses the ratio of the inertial forces to viscous forces,
where w is the wind speed at the height of the PV array, D h is the hydraulic diameter of the
module, which is used as relevant length scale, and ν is the kinematic viscosity of air. Pr is
the Prandtl number which is the ratio between the momentum diffusivity and the thermal
diffusivity. It is considered to be 0.71 for air. Finally, ρ and c air are the density and heat
capacity of air, respectively. The hydraulic diameter of a rectangle of length L and width