Experimental Analysis and Design Improvements on Combined Viper Expansion Work Recovery Turbine and Flow Phase Separation Device Applied in R410A Heat Pump

In light of recent trends towards energy efficiency and environmental consciousness, the heating, ventilation, air conditioning and refrigeration (HVAC&R) industry has been pushing for technological developments to meet both of these needs. As such, several solutions for harnessing the energy released from refrigerants during the expansion process of a conventional vapor-compression cycle have been developed to increase overall cycle efficiency. The study presented in this paper focuses on investigating the potential impact of installing an energy recovery expansion device known as the Viper Expander into an R410A heat pump. The Viper Expander operates by using a nozzle to accelerate the high pressure R410A into a high velocity jet of fluid impinging on a micro-turbine impeller. The impeller is coupled to a generator, which harvests the kinetic energy of the refrigerant by converting it into electrical energy that can be fed back into one of the system components, such as a fan or compressor motor. Previous Viper Expander iterations have not met performance expectations and thus, a major redesign was pursued. To improve the Viper Expander design, flow visualization of the two-phase refrigerant leaving the nozzle has been performed. Additionally, a housing redesign that will allow the Viper Expander to act as both an expansion work recovery device as well as a flash tank economizer has been proposed and modeled as a system solution

Numerical Analysis of Active Flow Boiling Regime Management Using a Vapor-Compression Cycle Applied to Electronic Processor Cooling

As computing power continues to grow at a rapid rate, the thermal load generated from electronic devices follows. Furthermore, reduced size requirements for electronic devices have driven engineers to produce this increased computing power in smaller packaging than ever before. The combination of these two trends results in high heat flux processors that require innovative cooling techniques. Industry and academia alike have anticipated this trend and have developed several general families of solutions to cooling high-heat flux processors. This work proposes the use of flow boiling in a vapor compression cycle and a spreader to distribute the heat from a high-heat flux source to the evaporator. Specifically, the balance between cycle performance and achievable heat flux is assessed, and operating conditions where the ability of the cycle to control evaporator heat flux and simultaneously achieve a high cycle efficiency are identified. A numerical flow boiling correlation is applied and a microchannel evaporator design model is proposed. Geometric parameters and performance limitations of this technique are analyzed and both quantitative and qualitative results along with future work are presented

Modeling of S-RAM Energy Recover Compressor Integration in a Transcritical Carbon Dioxide Cycle for Application in Electronics Cooling in Varying Gravity

As electronics in military aircraft become increasingly complicated, additional cooling is necessary to enable efficient and high computing performance. Additionally, the varying forces that a military aircraft endure during maneuvering and inverted flight introduce unique design constraints to the electronics cooling systems. Because this cooling system will be in an aircraft, the capacity and unique design constraints must all be met with a design that is as lightweight as possible. This paper presents a study comparing the coefficient of performance (COP) of several cycle architectures with both R134a and carbon dioxide ( ). Cycles with single-stage and two-stage compression with intercooling are compared, and both are modeled with suction-to-liquid line heat exchangers. The cycles utilizing are transcritical in order to reach the required temperatures for heat rejection from the gas cooler. Additionally, cycles with expansion work recovery and an ejector are compared. The cooling requirements are up to 150 kW with a heat source temperature as low as and a heat sink temperature of up to . The purpose of this analysis is to understand which of the above cycles performs with the highest efficiency for the given electronics cooling application

Theoretical Analysis of the Impact of an Energy Recovery Expansion Device in a CO2 Refrigeration System

Carbon dioxide (CO2) is being widely used as a refrigerant in HVAR&R applications due to its low Global Warming Potential (GWP). There are many aspects of CO2 systems that make it unique to other traditional refrigerants in that it has higher pressure levels and typically operates at transcritical levels. These higher pressure levels make CO2 systems ideal for installing an energy recovery expansion device that consists of a nozzle, micro-turbine and a generator. The expander functions by using a nozzle to convert the pressure of the refrigerant into a high speed jet that is directed into the impeller of the micro-turbine. The turbine impeller then spins a shaft that is coupled with a generator to generator electrical energy. This energy recovery expansion device is to replace the passive thermostatic expansion valve (TXV). Experimental testing of this device with R410A indicates that the device is more suitable for systems of higher pressure levels and with lower density refrigerants. For these reasons, the implementation of this energy recovery device in a CO2 refrigeration system for marine transportation has been investigated. The results of this paper quantifies the potential impact that this device could have in the system in terms of theoretical recoverable power. This recovered power has then been used to understand the impact on other various system parameters like COP, SEER and HSPF. This paper aims to present whether or not pursuing further experimental research on installing this energy recovery device into a CO2 system is of interest.

Experimental Comparison of Cycle Modifications to a Multi-Stage Two-Evaporator Transcritical CO2 Refrigeration Cycle

With increasing awareness of the adverse effects of carbon emissions on the environment, researchers within the heating, ventilation, air conditioning, and refrigeration (HVAC&R) community have been pushing for lower global warming potential (GWP) and natural working fluids as well as systems that are more efficient than the higher-GWP systems they replace. One such working fluid is carbon dioxide (CO2). While CO2 has the advantages of being low-cost, non-flammable, and possessing a high volumetric heat capacity, it has a high critical pressure associated with a low critical temperature, thus often necessitating transcritical operation that requires significant compressor input power. As such, numerous cycle modifications have been proposed that enable the transcritical CO2 cycle to match, and in some cases surpass, the coefficient of performance (COP) of existing hydrofluorocarbon (HFC) cycles under the same operating conditions. This work provides an experimental comparison of four cycle architectures that utilize the same compressors and heat exchangers. This enables a meaningful comparison of these modifications, consisting of open economization with an evaporator bypass, as well as both electronic expansion valve (EXV) and ejector expansion strategies, along with a pump applied between the gas cooler outlet and the ejector motive nozzle inlet for control and increased recoverable pressure differential. Experimental parametric studies were conducted, and comparisons of architecture costs and benefits are presented. Design recommendations are provided along with future work