Study on Distribution of Flow Rates and Flow Stabilities in Parallel Long Evaporators

Akagawa, Koji; Kono, Makoto; Sakaguchi, Tadashi; Nishimura, Masaharu

doi:10.1299/jsme1958.14.837

Cited by 55 publications

(37 citation statements)

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“…From (30) of Appendix A, a = −s in N 2 + DSD T will be +∞, and a − f S 1 f T is therefore always positive. Our stability criterion (7) is consistent with the criterion reported in [21], which is a special case of our result.…”

Section: Stability Analysis Of Parallel Channels With Inlet Pressure supporting

confidence: 92%

“…Experimental, analytical, and simulation studies have been reported to establish stability criteria [7,20,21,22,23,24] With the simplified parallelpipe flow analysis by [25], a control procedure was proposed in [8] to regulate the individual pipe flow rates with a desired pipe exit quality through a set of inlet control valves. To suppress the two-phase flow instability in microchannels, the methods of inlet control valve [8], inlet restrictors [26] and inlet seed bubble generators [27] were proposed.…”

Section: Introductionmentioning

confidence: 99%

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Stability analysis and maldistribution control of two-phase flow in parallel evaporating channels

Zhang

Wen

Julius

et al. 2011

International Journal of Heat and Mass Transfer

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Parallel channel heat transfer system is an attractive means to enhance heat transfer by increasing the total surface area in the heat exchanger. Uniform distribution of flow in the channels is an important operation attribute in order to avoid channel dryout and the subsequent hot spots and possible device failure. For the system operating in the single-phase regime, uniform flow distribution is a stable equilibrium. However, in the two-phase boiling regime, stable equilibrium bifurcates -the uniform distribution becomes unstable, and new stable or unstable non-uniform distributions, or maldistributions, equilibria emerge. As a result, parallel channel heat exchangers typically operate in the single phase regime to avoid such "maldistribution instability." This paper presents a stability analysis and active flow and temperature control of a parallel channel evaporator in a pumped two-phase boiling heat transfer loop. We show that for identical channels, the system is uncontrollable with the pump alone and unobservable from the overall flow rate measurement. A conventional solution involves introducing additional valve-induced pressure drop, but the drawback is a resulting higher pumping power. We present a new, somewhat surprising, result that if the channel characteristics are all distinct, the system actually becomes controllable from * Corresponding author: TieJun Zhang, Tel.: +1-518-276-2125, Fax: +1-518-276-4897, E-mail: tjzhrpi@gmail.com the pump and observable from the total loop flow rate. For non-identical parallel systems, we show a controller design approach and demonstrate its efficacy through a simulation example.

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Section: Stability Analysis Of Parallel Channels With Inlet Pressure supporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Stability analysis and maldistribution control of two-phase flow in parallel evaporating channels

Zhang

Wen

Julius

et al. 2011

International Journal of Heat and Mass Transfer

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“…Flow distribution predictions based on this general approach have been successfully validated experimentally in the literature [27,30,31,33].…”

Section: Dynamic Flow Network Equationsmentioning

confidence: 94%

“…Flow rate distribution among parallel evaporator tubes has been studied by Akagawa et al [27]. They experimentally obtained channel load curves for individual tubes experiencing flow boiling, which displayed the N-shape as in Figure 1.…”

Section: Literature Reviewmentioning

confidence: 99%

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Predicting two-phase flow distribution and stability in systems with many parallel heated channels

Oevelen

Weibel

Garimella

2017

International Journal of Heat and Mass Transfer

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Two-phase heat exchangers are used in a variety of industrial processes in which the boiling fluid flows through a network of parallel channels. In some situations, the fluid may not be uniformly distributed through all the channels, causing a degradation in the thermal performance of the system. A methodology for modeling two-phase flow distributions in parallel-channel systems is developed. The methodology combines a pressure-drop model for individual parallel channels with a pump curve into a system flow network. Due to the non-monotonicity of the pressure drop as a function of flow rate for boiling channels, many steady-state solutions exist for the system flow equations. A new numerical approach is proposed to analyze the stability of these solutions, based on a generalized eigenvalue problem. The method is specifically designed for analyzing systems with hundreds of identical parallel channels.The method is first applied to analyze the flow distribution and stability behavior in two-channel and five-channel systems. The asymptotic behavior of the flow stability is then analyzed for increasing numbers of channels, and it is shown that the stability behavior of a system with a constant flow-rate pump curve simplifies to the stability behavior for a constant pressure-drop pump curve. A parametric study is conducted to assess the influence of inlet temperature, heat flux, and flow rate on the stability of the uniform flow distribution solution as well as on the severity of flow maldistribution. Below some critical inlet subcooling, uniform flow distribution is always stable and maldistribution does not occur, regardless of heat flux and flow rate. Above this critical inlet subcooling, there is a range of operating parameters for which uniform flow distribution is unstable. With increasing inlet subcooling, this range broadens and the severity of the associated maldistribution increases.

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Prediction of two‐phase flow distribution in parallel pipes using stability analysis

2006

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Study on Distribution of Flow Rates and Flow Stabilities in Parallel Long Evaporators

Cited by 55 publications

References 0 publications

Stability analysis and maldistribution control of two-phase flow in parallel evaporating channels

Stability analysis and maldistribution control of two-phase flow in parallel evaporating channels

Predicting two-phase flow distribution and stability in systems with many parallel heated channels

Prediction of two‐phase flow distribution in parallel pipes using stability analysis

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