Led by: Professor Yunting Ge, London South Bank University
The standard cooling cycle for refrigerated transport is the Vapour Compression System (VCS). Working fluids are traditionally hydrofluorocarbons (HFC) with relatively high Global Warming Potential (GWP); it is electrically powered by the vehicle’s alternator or by a diesel genset on the trailer. Both, especially the latter, significantly increase fuel consumption, and CO, NOx, PM and noise emissions. Higher fuel costs, anticipated reductions in tax rebates on “red” diesel used in gensets and stricter emissions regulations, particularly in urban areas, drive the need for more efficient, lower emissions systems.
SBRI recently funded a feasibility study – ExHAUst-heat driven cooLIng for refrigERated tranSport (HAULIERS) of a new refrigeration technology, driven largely by the heat in the vehicle engine’s exhaust gases. It combines desorption and absorption of hydrogen (H2) in two pairs of metal hydride reactors, each pair with a hot and a cold reactor. Exhaust gas (~300°C) heats the first hot reactor and desorbs H2 at high pressure and temperature (~250°C). The H2 flows to the first cold reactor, which absorbs it at lower pressure and temperature (~35°C), releasing heat to ambient (~25°C). Meanwhile, cold air from the refrigerated space (~-12°C) passes through the cold reactor of the second pair and desorbs H2. This cools the air further to ~-25°C, which passes back to the refrigerated space. Meanwhile, the H2 flows at low temperature/pressure to the second hot reactor, where it is absorbed while releasing heat to ambient.
In the cycle’s second half, the functions of each reactor pair are exchanged. The hot reactor of the first pair is now cooled by ambient air as it absorbs the H2 being desorbed from the cold reactor, which now receives and further cools the cold air from the refrigerated space. The hot reactor of the second pair is heated by the exhaust gas, while the cold reactor is cooled by ambient air. Each half cycle the roles of each pair of reactors are reversed, and continuous refrigeration is produced on a 10-20 minute cycle.
The small amounts of electrical power needed to operate valves, fans and controls can be supplied from the vehicle alternator, batteries or solar power on the trailer roof. Standby heat can be provided electrically, by storing heat excess and/or coolth, or by combusting fuel in an ultra-low emissions porous media combustor.
Compared to the VCS, the Metal Hydride System (MHS) will eliminate the trailer’s genset and its associated fuel consumption and CO, NOx, PM and noise emissions, using a low GWP working fluid (H2), have fewer moving parts and lower maintenance costs, and be lighter and smaller. H2 is stable at high temperature, non-toxic, cheap, inert to materials of construction and can be handled safely.
The feasibility study concluded that the MHS is technically and commercially viable. It is expected to proceed to the next stage to develop, manufacture and test a prototype suitable for different scales of refrigerated transport units. To achieve this target, we are applying some funding from government and industries to support this project and welcoming some industrial partners in relevant areas to collaborate.
If any industrial companies are interested in this project, please contact Professor Yunting Ge through email email@example.com to discuss it in further details.