Fluid, Heat and Mass Transfer in a Venlo Type Greenhouse with Variable Boundary Conditions

Abstract

Greenhouse production of crops is problematic in the United Arab Emirates due to the harsh arid climate, which produces an unfavourable micro-climate within a greenhouse. This ‘micro-climate’ is controlled to create optimal conditions to grow crops. In order to determine these conditions, we simulate a two-dimensional micro-climate to study the temperature distribution of a ventilated system with different outlet positions. Thus creating the symmetric and asymmetric models. These models are compared between two cases of fluid properties defined by nondimensional parameters such as the Reynolds number. The aim is to understand how to amend the conditions of a micro-climate to remove heat by ventilation, as well as to determine which model is ventilated better by comparing models across cases. Our objectives are to observe the behaviour of the airflow for each model by evaluating heat balances, and then analyse whether the positioning of the outlet effects heat transfers in accordance to different fluid properties. The finite-difference method is presented for the numerical solution of the Navier-Stokes equations of an incompressible Newtonian fluid, in two dimensions, a stream functionvorticity formulation. Using a uniform grid of mesh points to discretise these equations, we then derive finite difference equations which are then solved to approximate solutions. Numerical results show that the symmetric model for the set of parameters (case 2) with Reynolds number Re = 1.622 x 105 and Grashof number Gr = 6.770 x 109 as the most influential case in the distribution of temperature. Thus, overall there is a better ventilated system through the symmetric channel for case 2. This is highlighted by a total heat flux of Q = 54.90 with a ratio of averaged gradient between the ground and the roof as 6.272 : 1.