An air curtain is a directed jet of air separating a controlled space from an environment of different temperature and humidity. This investigation describes the development and verification of an eddy viscosity model which accounts for the influence of the initial turbulence intensity on the transfer of heat and moisture across a recirculated air curtain. The control of the turbulence intensity at the nozzle exit of an air curtain permits control of heat and moisture transfer and therefore the energy required to operate the air curtain.
Both theoretical and experimental studies were made of the recirculated air curtain. An explicit finite difference scheme was used to solve the continuity, momentum and energy equations for an air curtain at an opening of a test chamber. Eddy viscosity values as well as the jet development length were measured and used in the computer program in order to calculate the velocity, temperature and moisture concentration distributions in the air curtain. Experimental measurements of the velocity distributions confirmed the eddy viscosity model results at various initial turbulence intensities and initial velocities.
The rate of heat transfer through the air curtain was evaluated from the difference of energy carried into the jet at the nozzle exit and its recirculation back into the return duct. Numerical integrations were carried out at corresponding cross sections of the air curtain in order to evaluate the flows of energy and moisture at the appropriate locations. Heat transfer rates were calculated for various initial turbulence intensities. Experimental data verified the calculated values both qualitatively and quantitatively.
Results from this investigation show that a decrease of the initial turbulence intensity from 14% to 1% can reduce the energy consumption for operating the air curtain by approximately 40% --Abstract, pages ii-iii
