A Bi2Te3 TEC with silica aerogel encapsulation is developed. Silica aerogel with different thicknesses is filled in the void spaces around the TE legs and started from cold-side ceramic plate. A three dimensional mathematical model for the TEC is developed. This model considers the effect air gap and silica aerogel. (Bi0.2Sb0.8)(2)Te-3 and Bi-2(Te(0.97)Sh(0.03))(3), which have temperature-dependent TE properties, are selected to be p-type and n-type TE materials. Also, an experimental test bench is built to validate the three dimensional model. The performances of non-silica aerogel encapsulated TEC with and without consideration of air gap are investigated. Meanwhile, the effects of different thicknesses of silica aerogel encapsulation under different T(a)s and V(a)s are analysed. The results show that the cold side ceramic and interconnector, and cold part of TE legs can be insulated effectively while the hot part of TE legs can be effectively dissipated using part silica encapsulation when T-h >= T-a >= T-c. The maximum Q(c) at L-aer = 0.8 mm is nearly increased by 7% as compared with that at L-aer = 0 mm when T-a = (T-c + T-h)/2. Moreover, apart from the cold side interconnector, L-aer should be about 2%, 15% and 25% of the L-leg corresponding to the maximum Q(c) condition when T-a = T-c, T-a = (T-h + T-c)/2 and T-a = T-h, respectively. The value of L-aer can be (T-a-T-c)/(T-h -T-c)L-leg corresponding to the optimum COP condition. (C) 2015 Elsevier Ltd. All rights reserved.