Moving-Boundary Heat Exchanger Models With Variable Outlet Phase

2008 ◽  
Vol 130 (6) ◽  
Author(s):  
Brian D. Eldredge ◽  
Bryan P. Rasmussen ◽  
Andrew G. Alleyne
Keyword(s):  
Heat Exchanger ◽  
Moving Boundary ◽  
System Level ◽  
Phase System ◽  
Vapor Compression ◽  
Vapor Compression Cycle ◽  
Compression Cycle ◽  
Cycle Systems ◽  
Level Model ◽  
And Control

Vapor compression cycle systems using accumulators and receivers inherently operate at or near a transition point involving changes of phase at the heat exchanger outlets. This work introduces a condenser/receiver model and an evaporator/accumulator model developed in the moving-boundary framework. These models use a novel extension of physical variable definitions to account for variations in refrigerant exit phase. System-level model validation results, which demonstrate the validity of the new models, are presented. The model accuracy is improved by recognizing the sensitivity of the models to refrigerant mass flow rate. The approach developed and the validated models provide a valuable tool for dynamic analysis and control design for vapor compression cycle systems.

A Simulink Pathway for Model-Based Control of Vapor Compression Cycles

2015 ◽  
Author(s):  
Anhtuan D. Ngo ◽  
Joshua R. Cory ◽  
Brandon M. Hencey ◽  
Soumya S. Patnaik
Keyword(s):  
Control Design ◽  
Control Synthesis ◽  
Vapor Compression ◽  
Linear Quadratic ◽  
Model Based Control ◽  
Model Based ◽  
Cycle System ◽  
Vapor Compression Cycle ◽  
Compression Cycle ◽  
Transient Thermal

Current and next generation tactical aircraft face daunting thermal challenges that involve reliably maintaining thermal constraints despite large transient loads. Model-based control synthesis has the potential to improve the performance of a vapor compression cycle system during its transient operating condition, driven by intermittent and dynamic thermal loads, when compared to the current heuristic control design technique. However, the excessive labor and expertise necessary to develop models amenable to model-based control design techniques has been an impediment to widespread deployment. This paper demonstrates a Simulink pathway for model-based design via the AFRL Transient Thermal Modeling and Optimization (ATTMO) toolbox. An effective, simple linear quadratic gaussian control design is demonstrated and opens the door for widespread deployment of many advanced control techniques.

The Steady-State Modeling and Analysis of a Two-Loop Cooling System for High Heat Flux Removal

2009 ◽  
Author(s):  
Rongliang Zhou ◽  
Juan Catano ◽  
Tiejun Zhang ◽  
John T. Wen ◽  
Greg J. Michna ◽  
...  
Keyword(s):  
Heat Flux ◽  
Steady State ◽  
Heat Exchangers ◽  
Cooling System ◽  
High Heat ◽  
System Structure ◽  
High Heat Flux ◽  
Vapor Compression ◽  
Vapor Compression Cycle ◽  
Compression Cycle

Steady-state modeling and analysis of a two-loop cooling system for high heat flux removal applications are studied. The system structure proposed consists of a primary pumped loop and a vapor compression cycle (VCC) as the secondary loop to which the pumped loop rejects heat. The pumped loop consists of evaporator, condenser, pump, and bladder liquid accumulator. The pumped loop evaporator has direct contact with the heat generating device and CHF must be higher than the imposed heat fluxes to prevent device burnout. The bladder liquid accumulator adjusts the pumped loop pressure level and, hence, the subcooling of the refrigerant to avoid pump cavitation and to achieve high critical heat flux (CHF) in the pumped loop evaporator. The vapor compression cycle of the two-loop cooling system consists of evaporator, liquid accumulator, compressor, condenser and electronic expansion valve. It is coupled with the pumped loop through a fluid-to-fluid heat exchanger that serves as both the vapor compression cycle evaporator and the pumped loop condenser. The liquid accumulator of the vapor compression cycle regulates the cycle active refrigerant charge and provides saturated vapor to the compressor at steady state. The heat exchangers are modeled with the mass, momentum, and energy balance equations. Due to the projected incorporation of microchannels in the pumped loop to enhance the heat transfer in heat sinks, the momentum equation, rarely seen in previous refrigeration system modeling efforts, is included to capture the expected significant microchannel pressure drop witnessed in previous experimental investigations. Electronic expansion valve, compressor, pump, and liquid accumulators are modeled as static components due to their much faster dynamics compared with heat exchangers. The steady-state model can be used for static system design that includes determining the total refrigerant charge in the vapor compression cycle and the pumped loop to accommodate the varying heat load, sizing of various components, and parametric studies to optimize the operating conditions for a given heat load. The effect of pumped loop pressure level, heat exchangers geometries, pumped loop refrigerant selection, and placement of the pump (upstream or downstream of the evaporator) are studied. The two-loop cooling system structure shows both improved coefficient of performance (COP) and CHF overthe single loop vapor compression cycle investigated earlier by authors for high heat flux removal.

Sign in / Sign up

Export Citation Format

Share Document