Compact heat exchangers, enhancement and heat pumps

In order to achieve widespread use of heat pumps across the full spectrum of potential applications, it is critical that the first cost of the units is acceptable. There are many factors influencing this cost, including the number of units manufactured, the ease of installation, the complexity of the control requirements, and the cost of the working fluid(s). A common feature of all heat pump cycles is the presence of at least one heat exchanger, indeed some heat-driven cycles are composed almost entirely of heat exchangers, each having a different but critical role to play. There are several important aspects of heat exchangers that can help to reduce first cost of these components and the system, (in addition to the possible positive impact on coefficient of performance). Two of these are discussed here — compact heat exchangers (CHEs) and heat transfer enhancement. The latter may be directly associated with CHEs but can be equally beneficial in reducing approach temperature differences in ʹconventionalʹ shell and tube heat exchangers. Both are essential features of many intensified processes, which the author argues need compatible heat pumps if the market for the latter is to flourish. In this paper, the most recent types of CHE are described, with emphasis on the benefits they can bring to heat pump first cost and performance. Heat transfer enhancement in heat pumps is also reviewed.