Date of Award

Summer 1992

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Mechanical & Aerospace Engineering

Program/Concentration

Mechanical Engineering

Committee Director

S. K. Chaturvedi

Committee Member

A. S. Roberts

Committee Member

J. J. Singh

Committee Member

S. N. Tiwari

Abstract

The natural convective heat transfer and air movement in a Trombe wall solar passive system has been studied analytically and numerically. Three Trombe wall channel geometries including the parallel channel with axial inlet and exit, parallel channel with side vents and Trombe wall channel coupled to the room have been considered. Several models representing these Trombe wall geometries have been formulated. For the parallel channel with axial inlet and exit geometry, a momentum-integral method has been used to solve parabolic governing equations for two-dimensional laminar flow. This formulation leads to a second order ordinary differential equation for pressure defect in the Trombe wall channel. The solution of this equation leads to prediction of velocity, temperature and pressure fields, and Nusselt number correlations that are in good agreement with previously reported finite difference solution of natural convection boundary layer equations.

For the side-vented channel case, results are obtained for both two-dimensional laminar and turbulent natural convective flow regimes. Due to presence of recirculating flow patterns in this geometry, full Navier-Stokes equations in two-dimensions are employed. The turbulent flow characteristics are modeled by a two-equation (k-e) model. The governing equations for steady laminar as well as turbulent flows are solved by a finite

volume technique that uses the quadratic upwind differencing scheme to discretize nonlinear governing equations to form algebraic equations which govern physical variables at the various numerical grid points. The coupled algebraic equations are solved by a semi-implicit algorithm known as SIMPLER. Flow patterns, isotherms and heat transfer characteristics are obtained for aspect ratios of 10 and 20, and Grashof number ranging from 1 .4 x l03 to 1 .4 x l08. The effect of the free pressure boundary location of flow characteristics is also analyzed. Results show that the mass flow rates induced and net energy delivered by the system is governed by the channel Grashof number and the channel vent size. Numerical results also indicate a transitional regime as indicated with number of iterations. Correlations for average Nusselt number as a function of Grashof number and vent size are also obtained based on numerical results. The inlet and exit pressure losses for the geometry have also calculated. Results show that the total vent loss coefficient for the side-vented cavity shows a minimum at Gr = 1.4 x 104 for which the dimensionless mass flow rate also shows a maximum value.

Results are also obtained for a more comprehensive geometry in which the Trombe wall channel is coupled to the room. Both heating and ventilation modes are investigated. In the heating mode, the natural convective mass flow rate and energy delivery rate are predicted as a function of the channel width and the cooled wall temperature. Several truncated Trombe wall passive system geometries are also considered in an attempt to reduce the computational time. Results indicate that for these truncated configurations, the heat delivery rate and convective mass flow rate are within nine percent of the values obtained for the more comprehensive and full size geometry. For the ventilation mode, the effect of ventilation port position on mass flow rate and energy delivery rate is investigated.

DOI

10.25777/fn85-nm72

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