A stochastic model is proposed to describe the correlation between the
scalar fluctuations and their dissipation and the distribution of the
conditional scalar dissipation in flows characterised by 'young' scal
ar turbulence, such as the mixing layer formed between opposed jets. I
t predicts the scalar field from an ensemble of instantaneous scalar i
nterfaces of specified functional form, referred to as mixinglets, ran
domly displaced in space, and is shown to compare favourably with expe
rimental data from counterflows and direct numerical simulations of sc
alar fields characterised by short residence times. The model is initi
ally formulated to account for molecular diffusion and turbulent conve
ction and then extended to include all turbulent transport processes b
y incorporating a description for the instantaneous turbulent strain r
ates. The contribution of each mechanism to the evolution of the singl
e and joint statistics is quantified individually and the ability of t
he model to represent conditional scalar statistics with application t
o combustion modelling is addressed.