Automotive Adsorption Air Conditioner Powered by Exhaust Heat. Part 2: Detailed Design and Analysis

Abstract This paper presents the detailed design and analysis of an automotive adsorption air conditioner, particularly the critical components, the adsorbent canisters, or adsorbers, and the exhaust-to-oil heater. The best adsorbent-refrigerant combination is activated carbonammonia. For the adsorber shell and tubes, austenitic stainless steel 304 has sufficient fatigue strength at 300 °C and is compatible with ammonia. Annular fins and wool inside the adsorbers are nickel-plated low-carbon steel. The exhaust-to-oil heater is of ferritic stainless steel and can withstand heating beyond 400 °C. The adsorbers, oil heater, and refrigerant reservoir are sized on the basis of the cooling requirement for a subcompact car during a typical commute, as defined in Part 1. The refrigerant reservoir provides immediate cooling upon start-up of a cold engine while the exhaust system and adsorbers are heating. A thermal reservoir containing phase-change material (PCM) allows full recharging of the refrigerant reservoir after a 20 min commute. Detailed thermal, fluidic, and mechanical analyses of the adsorbers and oil heater are performed. Eliminating the mechanical compressor increases fuel mileage by 14-18 per cent for mid-size, compact, and subcompact cars, or 4.6-6.0 per cent annually, given a 4 month cooling season. The adsorption system adds ∊3.5 per cent to vehicle mass, which reduces fuel mileage by ∊2.1 per cent. Thus, the annual benefit/cost ratio in terms of fuel mileage ranges from 2.3 to 2.7.