Heat exchanger design for thermoelectric electricity generation from low temperature flue gas streams

Abstract

An air-to-oil heat exchanger was modeled and optimized for use in a system utilizing a thermoelectric generator to convert low grade waste heat in flue gas streams to electricity. The NTU-effectiveness method, exergy, and thermoelectric relations were used to guide the modeling process. The complete system design was optimized for cost using the net present value method. A number of finned-tube compact heat exchanger designs were evaluated for high heat transfer and low pressure loss. Heat exchanger designs were found to favor either power density or exergy effectiveness to achieve optimal net present value under different conditions. The model proved capable of generating complete thermoelectric flue gas systems with positive net present values using thermoelectric material with a ZT value of 0.8 and second law efficiency of 13%. Complete systems were generated for a number of economic conditions. The best complete system achieved a first law efficiency of 1.62% from a 1500 C flue gas stream at an installed cost of $0.79 per watt.