The Method of Constructal Design in Heat Exchangers

This dissertation documents the usefulness of applying the Constructal design methodology of heat exchangers to the thermal and flow performance of such architectures. Based on the method of Constructal design, the system performance can be enhanced by providing its architecture or configuration more freedom to morph. Throughout this dissertation, each chapter deals with different design aspects that are relevant to heat exchangers.

Chapter 2 documents the joint performance of heat pumps that are served by a common loop (heat exchanger) buried in the ground, and which operate simultaneously: one heat pump absorbs heat from the buried loop whereas the other one rejects heat. The findings show that the flow and thermal performance are affected by the way in which the two heat pumps are connected to the buried loop.

Chapter 3 illustrates the free search for the optimal geometry of flow channel cross-sections that meet two objectives simultaneously: reduced resistances for heat transfer and fluid flow. Two elemental cross-sections are considered, squared and equilateral triangular. The results show that the two objectives are best met when the solid wall thickness is uniform, i.e., when the wetted perimeters are square and triangular, respectively. Arrays of square elements and triangular elements are also considered, and the results show that the array of triangular elements meets the two objectives better than the array of square elements.

In chapter 4, the relation between the efficiency of a power plant and its size is determined by relying on thermodynamics. The results show that the power plant efficiency should increase nonlinearly with the size, with a concave profile, i.e. with diminishing returns.

Chapter 5 shows numerically how the freedom in morphing a one stream cooling system embedded in a squared plate influence the thermal performance. Several configurations are considered in order to establish the evolutionary direction in which the thermal performance of the cooling system is improving. Examples are serpentine shapes, with various number of meanders, and loops cooling configurations (square, circular and clover leaf). The minimum peak temperature within the heated plate is achieved with the clover leaf designs.

To summarize, a primary feature of this dissertation is the ability to predict how the heat exchanger performance changes with morphing its flow configuration, varying the flow cross-sectional shape, and scaling up and scaling down the size of the flow design.