Analytical expression of electric power was deduced in case of the large-scale thermoelectric device that consists of the multiple cylindrical tubes like roll cake exposed to two thermal fluids. The output powers of the four arrangements were mathematically solved from heat transfer theory. The maximum output power of roll-cake module was practically the largest for the system of the counter flow with a single thermoelectric tube (V I C system), but 1/4 of the ideal output power (V 111 system). The multiplication of thermoelectric tubes can shorten significantly the device length, although the output power decreases only a little. For example, the double vortical tubes (V2CC system) can generate 95.7% output power by 38.5% diameter, compared with the single tube (V1C system). (C) 2004 Elsevier B.V. All rights reserved.