Food Transport Refrigeration with Engine Exhaust and Metal Hydride Reactors

Title: Food Transport Refrigeration with Engine Exhaust and Metal Hydride Reactors. Abstract: Conventionally, food transport refrigeration is driven by the vehicle’s engine itself or by a diesel genset; the refrigeration cycle almost universally used is the vapour compression system (VCS), with the working fluid usually a HFC (eg R404a) with a relatively high global warming potential. VCS needs electrical power, which increases vehicle fuel consumption, and CO2, NOx and PM emissions, significantly. In the face of higher fuel costs (reductions in the tax rebate on the “red” diesel used in gensets are anticipated) and increasingly strict regulations on NOx and PM emissions, particularly in urban areas, a more efficient, lower emissions food transport refrigeration system is therefore needed. In this feasibility study, a new, largely heat driven refrigeration technology will be designed, simulated and optimised, for prototype development manufacture and tests in the next stage. As the efficiency of the diesel genset is about 30%, about 50% of the waste heat will meet the typical semi-trailer refrigeration demand. The technology is a metal hydride system (MHS), with two pairs of metal hydride (MH) reactors, one pair with high temperature hydride and the other with low temperature hydride. The MHS operates in two half cycles. In each, heat from the genset or vehicle engine exhaust heats one of the high temperature MH reactors, which desorbs hydrogen (H2) from the hydride, at high pressure and temperature. The H2 flows to one of the low temperature reactors, where it is absorbed at lower pressure and temperature, and heat is released to ambient. Meanwhile, heat is absorbed from the refrigerated space by the second low temperature reactor to produce coolth, and H2 is desorbed at low pressure and temperature. The desorbed hydrogen is then absorbed by the second high temperature reactor at reduced pressure and medium temperature, and releases heat to the ambient. In the second half cycle the roles of each reactor are reversed, and continuous refrigeration is produced on a 10-20 minute cycle. Compared to the VCS, the MHS will reduce fuel consumption and the associated CO2, NOx and PM emissions by a targetted minimum of 50%, use a low global warming potential 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 challenges of developing a commercially viable MHS include choice of metal hydride, low heat transfer coefficients during metal hydration and dehydration processes, and complicated controls for continuous system operation. These challenges will be addressed in this project, particularly by the use of metal additive manufacture (MAM) in the design and close integration of the reactor components, including heat pipes for the high temperature reactors, and in the optimisation of geometries and dimensions of the heat transfer components. . Some essential design and operating conditions for conventional food transport refrigeration will be obtained from industrial partners so that the prototype to be developed in Phase 2 can be applied in practice. With the support from industrial partners, the product route to market will be defined and demonstrated