Recuperative Heat Exchangers
In a storage type exchangers, both fluids flow alter-natively through the same flow passages, and hence heat transfer is intermittent. The heat transfer surface (or flow passages) is generally cellular in structure and is referred to as a matrix, or it is a permeable (porous) solid material, referred to as a packed bed. When hot gas flows over the heat transfer surface (through flow passages) the thermal energy from the hot gas is stored in the matrix wall, and thus the hot gas is being cooled during the matrix heating period.
HEAT EXCHANGERS
RECUPERATIVE HEAT EXCHANGERS IN PROCESSING:
As cold gas flows through the same passages later (i.e., during the matrix cooling period), the matrix wall gives up thermal energy, which is absorbed by the cold fluid. Thus, heat is not transferred continuously
through the wall as in a direct-transfer type exchanger (recuperator), but the corresponding thermal energy is alternately stored and released by the matrix wall. This storage type heat exchanger is also referred to as a
regenerative heat exchanger ,or simply as a regenerator. To operate continuously and within a desired temperature range, the gases, headers, or matrices are switched periodically (i.e., rotated), so that the same passage is occupied periodically by hot and cold gases are generated.
A heat exchanger is a device used to transfer heat between two or more fluids. The fluids can be single or two phase and, depending on the exchanger type, may be separated or in direct contact. Devices involving energy sources such as nuclear fuel pins or fired heaters are not normally regarded as heat exchangers although many of the principles involved in their design are the same.
In order to discuss heat exchangers it is necessary to provide some form of categorization. There are two approaches that are normally taken. The first considers the flow configuration within the heat exchanger, while the second is based on the classification of equipment type primarily by construction. Both are considered here.