Similarity criteria for estimating gas emission from scale models

Similarity, or the relationship between a model and a prototype, is an important issue when using physical modelling techniques. The objective was to investigate similarity criteria using Reynolds number (Re) and jet momentum ratio (Rm) in two scale models (SM-1 of 1:6 and SM-2 of 1:12.5) of a pig house under isothermal conditions to predict airflow and ammonia emission. Experiments were conducted using two ventilation control strategies (constant inlet opening and constant inlet velocity) in SM-1 and SM-2 by (1) keeping the same inlet Re with constant inlet opening, and (2) keeping the same Rm with constant inlet opening and constant inlet velocity. Aqueous ammonia solutions, with four different total ammoniacal nitrogen (TAN) concentrations and two different pH levels, were used as emission sources inside the scale models. Non-dimensional normalised emission rate, defined as the ratio of the measured emission rate and the reference emission rate at inlet air velocity of 1 m s−1 of the scale models, was proposed for when using Re and Rm as similarity. Rm was found to be a better scaling parameter than Re for predicting the influence of airflow on ammonia emission rate when using the non-dimensional normalised emission rate in scale models with both ventilation control strategies and ammonia solutions of different TAN and pH.

Research highlights
► Similarity criteria for estimation of gas emission from scale model studies were established.
► Normalised emission rate was proposed for similitude studies that use Reynolds Number (Re) and jet momentum ratio (Rm) as similarity criteria.
► Rm was better than Re for similarity of airflow in ammonia emission.