Solar collectors especially Linear Fresnel Reflectors are one of the main implements to utilize the energy of sun light. The receiver cavity of the collector is recognized as an important component of each concentrating solar power plant. In this study, the heat transfer rate and heat loss in a trapezoidal cavity of the linear Fresnel reflector are analyzed. The calculations are performed for steady-state, laminar model in which temperature-dependent density is assumed for the air inside the cavity. The effects of the cavity angle and the effect of the tube size are evaluated, in various models. DTRM radiation model is employed for the simulation, while considering radiation, conduction and convection heat transfers are as the boundary conditions. Finally, it will be observed that by increasing the cavity angle, the total value for heat transfer rate is increased, but the heat absorbed by each tube is decreased. The results also show that the tube size is less effective on heat transfer rate compared to the cavity angle. (C) 2018 Elsevier Ltd. All rights reserved.