Abstract: Plate Heat Exchangers (PHEs) are used in a wide variety of applications including heating, ventilation, air-conditioning, and refrigeration. PHEs are characterized by compactness, flexible thermal sizing, close approach temperature, and enhanced heat transfer performance. Due to their desirable characteristics, they are increasingly utilized in two-phase flow applications. Detailed research on heat transfer and fluid flow characteristics in these types of exchangers is required to design and use plate heat exchangers in an optimal manner. This paper reviews the available literature on the correlations for heat transfer and pressure drop calculations for two-phase flow in PHEs as an initial process step in order to understand the current research status. Comparative evaluations for some of the existing correlations are presented in the light of their applicability to different refrigerants. Overall, there is a significant gap in the literature regarding two-phase heat transfer and fluid flow characteristics of these types of exchangers.

Abstract: Supercritical carbon dioxide (scCO2) is being used in many engineering applications due to the fact that, at supercritical stage, it has unique thermal properties with enhanced heat transfer and flow characteristics. The main purpose of this article is to provide an overview of the published studies that are relevant to the flow behavior and heat transfer characteristics of scCO2. The review of available works display that the heat transfer and pressure drop characteristics of heat exchangers using scCO2 as working fluid rely on many parameters such as tube shape and size, mass flux, inlet temperature and pressure, type of process (heating or cooling) etc. Moreover, application of scCO2 in cooling and heating processes and the available empirical correlations for heat transfer are also discussed. Overall it is observed that as the inlet pressure increases, the density and viscosity increases. Thus, when the temperature is higher than the critical temperature the pressure drop decreases with increasing inlet pressure. On the other hand, in heating, the heat transfer rate (View the MathML sourceQ˙) of scCO2 decreases as the inlet temperature increases above the critical temperature for all supercritical pressures. In cooling, View the MathML sourceQ˙ of scCO2 reaches peak value at near critical pressure and decreases as the inlet pressure increases. This review paper can provide information for further investigations on scCO2.

Abstract: Cost is equally important to power density or efficiency for the adoption of waste heat recovery thermoelectric generators (TEG) in many transportation and industrial energy recovery applications. In many cases, the system design that minimizes cost (e.g., the $/W value) can be very different than the design that maximizes the system’s efficiency or power density, and it is important to understand the relationship between those designs to optimize TEG performance-cost compromises. Expanding on recent cost analysis work and using more detailed system modeling, an enhanced cost scaling analysis of a waste heat recovery TEG with more detailed, coupled treatment of the heat exchangers has been performed. In this analysis, the effect of the heat lost to the environment and updated relationships between the hot-side and cold-side conductances that maximize power output are considered. This coupled thermal and thermoelectric (TE) treatment of the exhaust waste heat recovery TEG yields modified cost scaling and design optimization equations, which are now strongly dependent on the heat leakage fraction, exhaust mass flow rate, and heat exchanger effectiveness. This work shows that heat exchanger costs most often dominate the overall TE system costs, that it is extremely difficult to escape this regime, and in order to achieve TE system costs of $1/W it is necessary to achieve heat exchanger costs of $1/(W/K). Minimum TE system costs per watt generally coincide with maximum power points, but preferred TE design regimes are identified where there is little cost penalty for moving into regions of higher efficiency and slightly lower power outputs. These regimes are closely tied to previously identified low cost design regimes. This work shows that the optimum fill factor Fopt minimizing system costs decreases as heat losses increase, and increases as exhaust mass flow rate and heat exchanger effectiveness increase. These findings have profound implications on the design and operation of various TE waste heat recovery systems. This work highlights the importance of heat exchanger costs on the overall TEG system costs, quantifies the possible TEG performance-cost domain space based on heat exchanger effects, and provides a focus for future system research and development efforts.

Abstract: A novel building scale multi-section absorption heat exchanger (AHE) that is consist of a multi-section absorption heat pump and a plate heat exchanger was designed, developed and applied in district heating system to realize heat exchange from primary water to secondary water. The multi-section generating, condensing, absorbing and evaporating processes were designed to realize large external fluid inlet/outlet temperature difference in each component. The heat transfer loss can be reduced, and a low return primary water temperature can be reached to recover low grade waste heat as heat source. The performance of the prototype AHE was tested. The return primary water temperature was stable and was below 30 °C in the past two heating seasons, which was 10–15 K lower than inlet water temperature of secondary water. A temperature difference of 10 K–20 K in each component was realized. A pressure gradient from top to bottom was established to ensure stable fluid flow from top to bottom. The AHE has higher heat exchange effectiveness and better regulation performance compared with plate heat exchanger according to field test. And finally, the simulation model used to design the prototype machine was verified by the test results.

Abstract: The shell and coil heat exchangers are commonly used in heating, ventilation, nuclear industry, process plant, heat recovery and air conditioning systems. This type of recuperators benefits from simple construction, the low value of pressure drops and high heat transfer. In helical coil, centrifugal force is acting on the moving fluid due to the curvature of the tube results in the development. It has been long recognized that the heat transfer in the helical tube is much better than in the straight ones because of the occurrence of secondary flow in planes normal to the main flow inside the helical structure. Helical tubes show good performance in heat transfer enhancement, while the uniform curvature of spiral structure is inconvenient in pipe installation in heat exchangers. Authors have presented their own construction of shell and tube heat exchanger with intensified heat transfer. The purpose of this article is to assess the influence of the surface modification over the performance coefficient and effectiveness. The experiments have been performed for the steady-state heat transfer. Experimental data points were gathered for both laminar and turbulent flow, both for co currentand countercurrent flow arrangement. To find optimal heat transfer intensification on the shell-side authors applied the number of transfer units analysis.