Experimental Study on Heat Transfer and Pressure Drop of Recuperative Heat Exchangers Using Carbon Foam

This work focuses on the development of high-effectiveness recuperative heat exchangers using solid and corrugated carbon foam blocks. Characterization tests were conducted on heat transfer and pressure drop for a single carbon foam block with different sizes. Results show that carbon foam can be an effective medium for heat transfer enhancement, and a short length in the flow direction yields a high heat transfer coefficient. The corrugation can enhance heat transfer and reduce pressure drop at the same time. A recuperative heat exchanger with carbon foam, which consists of separate blocks of carbon foams packed between thin sheets of stainless steel, was designed. The hot and cold flow paths were arranged in counterflow in the recuperator. The heat exchanger was designed in a modular manner so that it can be scaled up for a larger heat transfer requirement or a higher overall effectiveness. The anisotropic property of carbon foam was exploited to achieve higher effectiveness for one pair of foam blocks. Experiments with four pairs of carbon foams were conducted to evaluate the performance of carbon foam used in the recuperative heat exchanger. Measurements were made for both solid and corrugated foams for comparison. With four pairs of carbon foam blocks, an overall effectiveness $εtotal$ greater than 80% was achieved. This paper demonstrates an approach to reach an effectiveness $εtotal$ of 98% by placing many pairs of carbon foams in series.