The compact brazed plate heat exchanger (CBE) is a simple concept: It brings media at different temperatures into close proximity, separated only by channel plates that enable heat from one media to be transferred to the other with high efficiency. The number, type and configuration of the channel plates can be varied to provide the thermal characteristics required. Compact brazed heat exchangers offer advantages such as high performance from minimal material and the ability to employ environmentally preferred refrigerants.
An efficient means of transferring heat, compact brazed heat exchangers employ a basic construction that enable them to utilize virtually all of their materials for heat transfer. Lifecycle cost studies show that compact brazed heat exchangers offer good performance and economy compared with rubber gasket and shell-and-tube heat exchangers.
Other advantages of compact brazed heat exchangers include their weight. The compact units are approximately 85 to 90 percent lighter and smaller than shell-and-tube heat exchangers of the same capacity. Due to the smaller size and lighter weight, shipping costs less, and the compact units often are easier to handle during installation. As previously noted, less material is used to make a compact brazed heat exchanger; moreover, up to 95 percent of that material is used to transfer heat, which maximizes material efficiency. As a result, the compact designs can offer better capacity utilization than plate-and-frame and shell-and-tube equivalents - considerably more, in the case of shell-and-tube units.
Due to the efficiency of the compact brazed heat exchanger design, thermal losses due to convection and radiation are lower than for alternative designs. The compact brazed heat exchanger holds only a small fraction of the system’s heat transfer media, so less is needed. In refrigerant systems, small hold-up volumes provide an environmental advantage. Furthermore, the high efficiency enables the mass flow of the media to be reduced. Pumps can be smaller, saving on capital and running costs and contributing to a lower overall system cost.
The flow inside a compact brazed heat exchanger is turbulent, which ensures good thermal performance and efficient operation even at temperature differences as low as 1K. The high level of turbulence also means compact brazed units are largely self-cleaning. Fouling is minimized, improving uptime and cutting costs. If the heat exchanger needs cleaning, it can be carried out using standard methods such as clean in place (CIP).
By virtue of their compact design, brazed heat exchangers embrace the “more from less” approach. For example, the plate design for some brazed units directs the cooling media around the port in a specific way, improving heat transfer in that area. Some manufacturers incorporate plate designs that improve performance and increase mechanical strength, enabling less material to be used. For instance, one manufacturer uses asymmetric technology because it increases the strength of the refrigerant channel walls while allowing them to be thinner, thereby improving heat transfer. In addition, the channels are narrower, increasing turbulence and hence efficiency.
Raw efficiency is one of the compact brazed heat exchanger’s obvious strengths, but the wider picture tells the full story. For instance, smaller envelopes and fewer raw materials ease transportation costs and deliver environmental gains - all the way from mining through refining, to use and disposal.
While modern refrigerants are better in terms of GWP and ODP, they present technical challenges. As noted previously, one advantage offered by compact brazed exchangers is the small hold-up volume, which means the refrigerant charge is minimal. As international legislation surrounding limits on refrigerant charge becomes increasingly stringent, it is important that process heat exchangers used in refrigeration applications are compliant. Some exchanger manufacturers have brazed units optimized for specific refrigerants such as R410A and R134a. This optimization can deliver a significant increase in heat flux, which saves energy. In addition, some manufacturers offer single- and dual-circuit compact brazed covering capacities to 400 kW, a range suited for evaporators in lower capacity heat pump and chiller applications.