In this project, modelling of turbulent conjugate heat transfer within RANS frame is studied. The starting point is a four-equation transport model, developed by Craft et al. (2010). In this project, the model from Craft et al. (2010) has been tested on 1D fully-developed channel flow with heated wall at Pr=0.71 with ReÏ=150, comparing predictions against DNS data from Flageul et al. (2017) covering a range of fluid and solid thermal properties. The results showed too rapid decay of temperature variance across the solid region. This investigation makes use of the wider range of available DNS data, to advance understanding of the processes involved and identify the influential parameters. Then the Craft et al. (2010) model is made sensitive to these physical phenomena. The three main elements of the model development are a) a model of the dissipation of thermal fluctuations in the solid region based entirely on solid-domain DNS data, b) a re-optimised model of the transport equations for the thermal fluctuations and their dissipation rate within the fluid domain and c) a revised set of interface conditions for the discontinuity of the dissipation rate of thermal fluctuations across the fluid-solid boundary. This was carried out using a 1D solver written by the author of this thesis using Fortran. Since the model is developed by considering fully-developed turbulent flow, its capability for handling more complex and challenging cases needs to be investigated. The revised new model has thus been incorporated into the open source CFD package Foam-extend 4.0, which can handle numerical simulations for complicated engineering problems. Then the solver developed within Foam-extend 4.0 has been used to test the revised model for 3D conjugate heat transfer in a channel flow with a hot jet injected from the bottom. The results have been compared with those from DNS data (Wu et al. (2017)) and those from the Craft et al. (2010) model, with the present model showing generally good agreement with the DNS.