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Technical Briefs

Experimental Validation for the dp/dt Assumption of Heat Exchangers in Vapor Compression Refrigeration Cycles

[+] Author and Article Information
Pengfei Li

 United Technologies Research Center, East Hartford, CT 06108lip1@utrc.utc.com

John E. Seem

 Building Efficiency Research Group, Johnson Controls, Inc., Milwaukee, WI 53202john.seem@gmail.com

Yaoyu Li

 Department of Mechanical Engineering, University of Texas at Dallas, Richardson, TX 75080yaoyu.li@utdallas.edu

J. Heat Transfer 134(11), 114502 (Sep 24, 2012) (6 pages) doi:10.1115/1.4006157 History: Received May 20, 2011; Revised January 08, 2012; Published September 24, 2012; Online September 24, 2012

Calculation of time derivatives of refrigerant pressures is important for dynamic simulation of heat exchangers in vapor compression cycles, i.e., typically the condenser and evaporator. This technical brief presents an experimental study on the pressure transient for the condenser and evaporator of a screw chiller with R134a, along with the analysis for the associated time derivatives. The experimental results from eight test cases suggest that the time derivatives of the condenser and evaporator pressures at their inlet are extremely close to those at the respective outlets. This observation can thus justify the key assumption of equal time derivatives of pressures in the dynamic modeling of heat exchangers, which in consequence improves the numerical efficiency and/or convergence, especially for large and complex thermal-fluid systems.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Photograph of the chiller test bench

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Figure 2

Schematic of sensor allocation and data acquisition system for dp/dt test: (a) close view and (b) distant view

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Figure 3

Photographs of the butterfly valve used in York YR chiller

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Figure 4

Cross-sectional view of water tubes in the condenser and evaporator

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Figure 5

Experimental results of case 2 where (a) and (b) are the pressures at the inlet and outlet of the condenser and evaporator, respectively, and comparison of dp/dt at their respective inlet and outlet; (c) and (d) are the normalized dp/dt difference at the condenser and evaporator sides, respectively

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Figure 6

Experimental results of case 3 where (a) and (b) are the pressures at the inlet and outlet of the condenser and evaporator, respectively, and comparison of dp/dt at their respective inlet and outlet; (c) and (d) are the normalized dp/dt difference at the condenser and evaporator sides, respectively

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Figure 7

Experimental results of case 4 where (a) and (b) are the pressures at the inlet and outlet of the condenser and evaporator, respectively, and comparison of dp/dt at their respective inlet and outlet; (c) and (d) are the normalized dp/dt difference at the condenser and evaporator sides, respectively

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