Icing Tolerant Cryogenic Heat Exchanger System for Refrigerated Vehicles
Publication Date: 2014-Jul-24
The IP.com Prior Art Database
Within a refrigeration system of the “indirect” type (CTI), condensation of water vapour creating snow or ice on the heat exchanger can develop to an extent where the performance of the heat exchanger is inadequate either in terms of cooling power, or in terms of the efficient use of cryogen. The heat exchanger should be fit for purpose, compact, cost effective, and ideally fabricated from materials with a low scrap value to reduce the likelihood of theft from the vehicle.
It is proposed below a heat exchanger capable of building up snow and ice in such a manner that the refrigerating power and efficiency of the heat exchanger remains adequate for the needs of the vehicle cooling process.
It is known in the existing art that the copper helix heat exchanger is an effective means of transferring heat in the above mentioned type of utilization. However, it is not a particularly compact configuration, and it uses a relatively large mass of copper per m² of heat exchanger area. With high copper costs, a vehicle can include a substantial scrap value of copper in a fairly accessible location for prospective thieves. The exchanger does have a major advantage in that the natural vibrations in the vehicle can be used to assist a de-icing cycle.
A traditional finned tube heat exchanger can be configured with larger than typical gaps between the tubes and fins that allow for increased ice build up before the heat exchanger becomes inadequate for the cooling demand. For a given refrigeration capacity, an icing tolerant finned tube heat exchanger has to be substantially larger than an equivalent one that would be used in non-icing conditions.
For cryogenic applications as the volume of incoming fluid, such as liquid nitrogen is converted to much higher volumes of gas, typically up to nearly a factor of 700. Heat exchangers that increase their cross sectional area to reduce flow restrictions due to this volume increase are beneficial to manage the fluid flows. When using typical finned tube exchangers, the complexity of construction to produce multiple routes for the vaporized gas flow can be costly, resulting in the use of less than optimum configurations.
Since snow and ice build up on heat exchangers varies with several factors, one of the major ones being the operating temperature of the exchanger. With the heat exchanger surface very much colder than the air, low density snow like icing occurs which does not adhere strongly to the surface. As the heat exchanger surface approaches 0°C the icing of the surfaces is much denser and much more adhesive to the exchanger surface.
The use of multiple heat exchangers in large scale food freezing applications can be set up so that heat exchangers can be isolated from the freezing system and defrosted, while other heat exchangers continue to operate. In compact vehicle refrigeration systems such a facility would be desirable, but space...