Semrau (1960, 1963) developed the contact power theory from the work of Lapple and Kamack(1955). This theory is empirical in approach and relates the total pressure loss (PT) of the system to the collection efficiency. The total pressure loss is expressed in terms of the power expended in injecting the liquid into the scrubber, plus the power needed to move the process gas through the system (USEPA-84/03, p. 9-13):