Research Papers

Modeling of Surge Characteristics in Turbo Heat Pumps

[+] Author and Article Information
Hye Rim Kim

Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Koreahrimkim@snu.ac.kr

Seung Jin Song

Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Koreasjsong@snu.ac.kr

To a less extent, similar temperature fluctuations have been found in the condenser (12). During the flow reversal stage, the cooling water temperature difference between the condenser outlet and inlet become negligible. This phenomenon can be understood by an explanation similar to the one given for the evaporator above.

J. Turbomach 133(4), 041015 (Apr 21, 2011) (9 pages) doi:10.1115/1.4002993 History: Received July 02, 2010; Revised July 11, 2010; Published April 21, 2011; Online April 21, 2011

This paper presents a new analytical model of surge dynamics in turbo heat pumps. Turbo heat pumps use refrigerants as the working fluid and consist of a centrifugal compressor, condenser, expansion valve, and evaporator. Compared with a gas turbine engine, the turbo heat pump system introduces additional complexities. First, the turbo heat pump forms a closed-loop system. Second, the system has two plenums, condenser and evaporator, which are coupled to each other. Third, the heat pump runs on a refrigeration cycle with two phases: vapor and liquid. Fourth, heat transfer effects of evaporation and condensation have to be considered. Fifth, unlike air, a refrigerant has strong real gas effects and thus cannot be modeled as an ideal gas. The new model addresses such additional complexities on the basis of the first principles of conservation of mass, momentum, and energy. When applied to a gas turbine system, the new model’s predictions become identical to those from the Greitzer’s model. Furthermore, comparison with the available experimental data shows that the model can also accurately predict surge behavior in actual turbo heat pumps. Finally, the effects of Greitzer’s B parameter and the ratio of evaporator and condenser volume have been examined. Parameter B influences both surge shape and frequency. Finally, surge frequency is extremely sensitive to the ratio of the two plenum volumes.

Copyright © 2011 by American Society of Mechanical Engineers
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Figure 1

Turbo heat pump: (a) schematic of turbo heat pump and (b) P-h diagram

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Figure 2

Shell-and-tube type condenser and evaporator

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Figure 3

Predictions from Greitzer’s model (11) and the new heat pump model: (a) B=0.6 and (b) B=1.58

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Figure 4

Surge predictions with experimental data: (a) transient nondimensional axial velocity and pressure rise, (b) pressure rise versus mass flow rate, (c) compressor inlet and outlet pressure, and (d) rate of heat transfer in evaporator Q̇̃L

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Figure 5

Prediction results, B=0.0256: (a) transient nondimensional mass flow rate and pressure rise and (b) pressure rise versus mass flow rate

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Figure 6

Prediction results, B=0.153: (a) transient nondimensional mass flow rate and pressure and (b) pressure rise versus mass flow rate

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Figure 7

ω2/ω1 effect on surge frequency




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