Radia Eldeeb’s research while affiliated with University of Maryland, College Park and other places

Plate heat exchangers (PHXs) are compact with small approach temperature, and desirable thermal-hydraulic characteristics. It is greatly desirable to create novel PHX designs that utilize less material and less volume while attaining similar heat transfer performance and thus contribute significantly to energy conservation while lowering the environmental impact as well. Pillow Plate Heat Exchanger (PPHX) is a type of PHX with a complex wavy structure with desirable thermal-hydraulic characteristics, but yet an economical manufacturing process especially when compared to corrugated Chevron PHX (CPHX) which requires a special die for each design. PPHX has great design flexibility allowing novel designs to be created in a simpler and less costly process which provides them with a good potential to outperform other types of PHXs. PPHXs are more commonly used in chemical and process industry with limited research in Heating, Ventilating, Air Conditioning, and Refrigeration (HVAC&R) applications. In this study, the optimization of PPHXs in order to maximize their thermal-hydraulic performance, including weld shape optimization using novel weld shapes created using Non-Uniform Rational B-Splines (NURBS), is studied. Sensitivity analysis is conducted on the optimal designs to provide insights into factors affecting their performance. The potential enhancement is up to 36% improvement in heat transfer coefficient and 67% reduction in pressure drop as compared to a selected PPHX baseline design with circular spot welds. The optimal designs are compared to optimal CPHX designs from literature showing a potential improvement of 38% for heat transfer coefficient, and a reduction of 72% in pressure drop.

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. © 2016 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.

The environmental impact of high global warming potential (GWP) refrigerants pushed the HVAC&R industry to investigate alternative refrigerants. R410A is a common refrigerant for air conditioning and heat pumping applications, but has a GWP of 2088. Drop-in tests of three R410A low-GWP alternative refrigerants (R32, D2Y60 and L41a) in a 10.55 kW capacity split heat pump unit were performed. The results show that R32 and L41a are good replacement candidates for R410A. A finite volume heat exchanger model and component based vapor compression system simulation tools were validated against the experimental data. Most of the predicted COP and capacity results of R32 experiments lie within 5% of the measured values, which is in good agreement with the experiments. Further investigation was carried out by varying the size of the compressor and adding a suction line heat exchanger to the system to match the capacity to that of R410A.

With the increased regulations to move towards lower GWP refrigerants, natural fluids and their blends are becoming more favorable. Plate heat exchangers are being used in air-conditioning and refrigeration applications as well as a wide variety of other applications including food processing, chemical industry, and energy generation systems. Plate heat exchangers are favored because of their compactness, close approach temperature pure counter-flow operation, and enhanced heat transfer performance. Plate heat exchangers are increasingly utilized in two-phase flow operations due to their desirable characteristics. In order to achieve a better understanding of the current research status of two-phase flow in plate heat exchangers, this paper presents a literature review of available correlations for heat transfer and pressure drop calculations during evaporation in plate heat exchangers. Generally, research on evaporation heat transfer performance in plate heat exchangers is limited. Correlations on natural refrigerant mixtures are scarce. One recent correlationis proposed in literature for ammonia/water mixtures with specific conditions and mixture concentrations. A comparative evaluation of some of the existing correlations is presented in the light of their applicability to natural refrigerants. Overall, there is a significant gap in the literature regarding evaporation heat transfer and fluid flow characteristics of these types of exchangers.