Local measurement of flow boiling heat transfer in an array of non-uniformly heated microchannels

Ritchey, Susan N.; Weibel, Justin A.; Garimella, Suresh V.

doi:10.1016/j.ijheatmasstransfer.2013.12.012

Cited by 41 publications

(17 citation statements)

References 23 publications

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“…Flow maldistribution in parallel-channel two-phase heat sinks has been observed experimentally in various studies [8][9][10][11][12][13]. Maldistribution can have several causes: asymmetrical inlet header designs, differences in channel geometry or surface properties, non-uniform heating, and the non-monotonic nature of channel pressure drop as a function of flow rate.…”

Section: Flow Maldistributionmentioning

confidence: 99%

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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Section: Flow Maldistributionmentioning

confidence: 99%

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

Self Cite

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“…Flow maldistribution in parallel-channel two-phase heat sinks has been observed experimentally in various studies [7][8][9][10][11][12]. It can have several causes: asymmetrical inlet header designs, differences among the parallel channels in geometry or surface properties, non-uniform heating, or the non-monotonic nature of channel pressure drop as a function of flow rate.…”

Section: Introductionmentioning

confidence: 99%

The effect of lateral thermal coupling between parallel microchannels on two-phase flow distribution

Oevelen

Weibel

Garimella

2018

International Journal of Heat and Mass Transfer

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Evaporating flows in parallel channels occurring in a variety of industrial heat exchange processes can encounter nonuniform flow distribution between channels as a result of two-phase flow instabilities.Such flow maldistribution can have a negative impact on the performance, robustness and predictability of these systems. Two-phase flow modeling can assist in understanding the mechanistic behavior of this flow maldistribution, as well as determine parametric trends and identify safe operating conditions. The work described in this paper expands on prior two-phase flow distribution modeling efforts by including and assessing the effect of thermal conduction in the walls surrounding the parallel channels.This thermal conduction has a critical dampening effect on wall temperature gradients. In particular when a channel is significantly starved of flow rate and risks dryout, channel-to-channel thermal coupling can redistribute the heat load from the flow-starved channel to neighboring channels. The model is used to simulate the two-phase flow distribution in a system of two parallel channels driven by a constant flow rate pump. A comparison between thermally isolated and coupled channels indicates that thermally coupled channels are significantly less susceptible to maldistribution. Furthermore, a parametric study reveals that flow maldistribution is only possible in thermally coupled systems beyond a certain critical heat flux threshold. This threshold heat flux increases as the lateral wall conductance is increased, converging to a constant value in the limit of very high lateral conductance.

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“…Havacılık, savunma, uzay, tıp gibi yüksek teknoloji alanlarında kullanılan elektronik ekipmanların artan ısı akısı değerleri nispeten daha az yüzey sıcaklık artışının görüldüğü iki fazlı soğutma uygulamalarını cazip hale getirmektedir (Ritchey et al, 2014).…”

Section: Introductionunclassified

Flow Boiling Characteristics of Nanofluids in Microchannels

Manay¹

2017

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ÖZET: Mikrocihazlarda giderek artan ısı akısı değerleri nedeniyle geleneksel ısı transfer arttırım yöntemleri mikrosistemlerin soğutulmasında yetersiz kalmaktadır. Kaynama ile ısı transferi yüksek ısı transfer katsayılarının elde edilmesi yanında yüzey sıcaklığının neredeyse sabit olması nedeniyle yüksek ısı atımını gerektiren mikrosistem uygulamaları için önemli bir potansiyele sahiptir. Diğer yandan geleneksel akışkanlar yerine nanoakışkanların kullanımı yüksek ısıl performans için önemli bir alternatif olarak düşünülmektedir. Nanoakışkanların tek fazlı ısı transferiyle ilgili birçok çalışma olmasına rağmen mikrokanallarda kaynamalı akış durumunda nanoakışkan kullanımıyla ilgili sınırlı sayıda çalışma mevcuttur. Literatürde nanoakışkanların kaynamalı akışta kullanımının bazı çalışmalara göre uygun olup olmadığı yönünde belirsizlikler vardır. Bu nedenle nanoakışkanların kaynamalı akış şartlarında kullanılabilirliği ile ilgili daha kapsamlı çalışmalara ihtiyaç vardır. Bu çalışmada, farklı nanoakışkanlar ile yapılan deneysel çalışmalar derlenmiş ve nanoakışkanların mikrokanallarda kaynamalı akışta kullanımının avantaj ve dezavantajları belirlenmeye çalışılmıştır.Anahtar kelimeler: Kaynamalı akış, kritik ısı akısı, mikrokanal, nanoakışkan ABSTRACT: Due to the ever increasing heat flux values, traditional heat transfer enhancement methods fail to satisfy on cooling of micro systems. Flow boiling heat transfer has a great potential for the applications requiring high heat removal rates because high heat transfer coefficients are achieved in addition to surface temperature to be nearly constant. On the other hand, use of nanofluids instead of traditional fluids is thought to be an important alternative for high thermal performance. Although there are numerous study on the single phase heat transfer of nanofluids, a few number of study concerning with the flow boiling heat transfer of nanofluids in microchannels exists. In the literature, there are some conflicts on whether the use of nanofluids in flow boiling is appropriate or not. Thus, more detailed studies on the usability of nanofluids in boiling flow conditions are required. In this study, experimental studies conducted by with nanofluids were reviewed, and the advantages and disadvantages of the using nanofluids in boiling flows in microchannels were determined.

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Local measurement of flow boiling heat transfer in an array of non-uniformly heated microchannels

Cited by 41 publications

References 23 publications

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

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

The effect of lateral thermal coupling between parallel microchannels on two-phase flow distribution

Flow Boiling Characteristics of Nanofluids in Microchannels

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