Many designers have attempted to use plate heat exchangers as direct expansion evaporators. Direct expansion type of evaporator is desirable for a low cost system design with the lowest amount of refrigerant charge. This is more important when ammonia is used as a refrigerant. There are two major obstacles that limit the use of these exchangers for large duty chillers. The distribution of two phase refrigerant through the inlet port of plate heat exchanger and the availability of proper expansion devise. Many heat exchanger manufacturers have tried different types of distributor tubes. This author has not seen a successful installation above 600 TR (2100 KWR) using direct expansion plate and frame evaporators. A research will be presented on existing literature on actual installations or theoretical designs of such DX evaporators. The paper will concentrate the work done with Ammonia evaporators. A new idea which was patented recently for a specially designed Plate and Frame heat exchanger will be presented. This design includes a special feeding tube for each Welded Pair (Cassette). The idea is to reduce the pressure drop taken at the expansion valve and there by reduce the amount of flash gas entering the port. The design and performance of a 1000 TR (3500 KW) system recently installed at a Chemical plant will be discussed. The Author believes that this is the first Chiller of this size designed with Ammonia DX evaporator. Discussions in the meeting will reveal if others have done such a large chiller using DX evaporator.
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