Experimental Model Identification and Controller Design of a Vapor Compression Cycle for Electronics Cooling

In this paper dynamic identification of the evaporator dynamics in a vapor compression cycle (VCC) subjected to imposed heat flux is studied. The imposed heat flux boundary condition at the evaporator represents a specific application of the VCC for electronics cooling. However, different models and control algorithms than traditional VCCs are required. First principle models are highly nonlinear and, hence, not practical for system control. A dynamic model identification of the refrigerant temperature at the exit of the evaporator, refrigerant pressure, and temperature of the heating element is performed by varying the expansion valve opening. It is shown that single-input single-output (SISO) identification is not sufficient to capture the dynamics of the evaporator, due to the coupling of the dynamics in the entire system. Including the effect of incoming mass flow rate into the evaporator to the model significantly improves the identification and prediction of the evaporator dynamics. Finally, a SISO controller based on the identified model, is designed and tested experimentally. The control objective is to maintain the temperature of the heating element below a set point, subjected to changes in heat flux.

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

Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C ◽

10.1115/imece2009-11500 ◽

2009 ◽

Cited By ~ 1

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.

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Model predictive control of vapor compression cycle for large transient heat flux cooling

2016 American Control Conference (ACC) ◽

10.1109/acc.2016.7524972 ◽

2016 ◽

Cited By ~ 2

Author(s):

Zehao Yang ◽

Daniel T. Pollock ◽

John T. Wen

Keyword(s):

Heat Flux ◽

Model Predictive Control ◽

Predictive Control ◽

Vapor Compression ◽

Vapor Compression Cycle ◽

Compression Cycle ◽

Transient Heat Flux

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Multivariable Control of Vapor Compression Cycle With Transient Heat Flux

Volume 8B: Heat Transfer and Thermal Engineering ◽

10.1115/imece2013-63610 ◽

2013 ◽

Cited By ~ 2

Author(s):

Zehao Yang ◽

Daniel T. Pollock ◽

John T. Wen

Keyword(s):

Heat Flux ◽

Open Loop ◽

Controller Synthesis ◽

Operating Point ◽

High Heat Flux ◽

Vapor Compression ◽

Worst Case ◽

Vapor Compression Cycle ◽

Compression Cycle ◽

Model Linearization

This paper investigates feedback control of refrigeration cycles for high heat-flux cooling applications, where large transient heat loads may be present. We apply H∞ controller synthesis for disturbance rejection, with the evaporator heat-flux treated as the disturbance input. The controller synthesis is based on model linearization about a chosen operating point. We analyze model uncertainty due to the linearization error to ensure robustness of the closed-loop systems. We use a low-order, lumped-element nonlinear model for the vapor compression cycle. We obtain linearized systems at different operating points, and quantify system nonlinearity using the H∞ norm. Controllers synthesized for the chosen nominal systems are tested for both nominal (near the operating point) and the worst-case performance in nonlinear simulations. For systems close to critical heat-flux (CHF), it is shown that a trade-off exists between the nominal performance and robust stability. For systems far away from CHF, it is shown that the open-loop system has the optimal cooling capacity. The performance of H∞ controller for systems near CHF is validated by experiment.

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Gain-scheduling control of vapor compression cycle for transient heat-flux removal

Control Engineering Practice ◽

10.1016/j.conengprac.2015.02.004 ◽

2015 ◽

Vol 39 ◽

pp. 67-89 ◽

Cited By ~ 7

Author(s):

Zehao Yang ◽

Daniel T. Pollock ◽

John T. Wen

Keyword(s):

Heat Flux ◽

Gain Scheduling ◽

Vapor Compression ◽

Vapor Compression Cycle ◽

Compression Cycle ◽

Gain Scheduling Control ◽

Transient Heat Flux

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Rechargeable Personal Air Conditioning Device

Volume 1: Biofuels, Hydrogen, Syngas, and Alternate Fuels; CHP and Hybrid Power and Energy Systems; Concentrating Solar Power; Energy Storage; Environmental, Economic, and Policy Considerations of Advanced Energy Systems; Geothermal, Ocean, and Emerging Energy Technologies; Photovoltaics; Posters; Solar Chemistry; Sustainable Building Energy Systems; Sustainable Infrastructure and Transportation; Thermodynamic Analysis of Energy Systems; Wind Energy Systems and Technologies ◽

10.1115/es2016-59253 ◽

2016 ◽

Cited By ~ 1

Author(s):

Yilin Du ◽

Jan Muehlbauer ◽

Jiazhen Ling ◽

Vikrant Aute ◽

Yunho Hwang ◽

...

Keyword(s):

Air Conditioning ◽

Cooling System ◽

Cooling Capacity ◽

Comfort Level ◽

Vapor Compression ◽

Air Conditioning System ◽

System A ◽

Single Person ◽

Vapor Compression Cycle ◽

Compression Cycle

A rechargeable personal air-conditioning (RPAC) device was developed to provide an improved thermal comfort level for individuals in inadequately cooled environments. This device is a battery powered air-conditioning system with the phase change material (PCM) for heat storage. The condenser heat is stored in the PCM during the cooling operation and is discharged while the battery is charged by using the vapor compression cycle as a thermosiphon loop. The conditioned air is discharged towards a single person through adjustable nozzle. The main focus of the current research was on the development of the cooling system. A 100 W cooling capacity prototype was designed, built, and tested. The cooling capacity of the vapor compression cycle measured was 165.6 W. The PCM was recharged in nearly 8 hours under thermosiphon mode. When this device is used in the controlled built environment, the thermostat setting can be increased so that building air conditioning energy can be saved by about 5–10%.

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