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Critical Heat Flux in Forced Convective Subcooled Boiling with One and More Impinging Jets
Published in John C. Chen, Yasunobu Fujita, Franz Mayinger, Ralph Nelson, Convective Flow Boiling, 2019
Boiling provides an efficient heat transfer process for applications such as the cooling of electric components(Bar-Cohen, 1991, and Mudawar and Wadsworth, 1991) and fusion components(Boyd, 1983 and Dhir and Scott, 1987). The critical heat flux(CHF), which defines the upper limit of the efficient range of boiling heat transfer, limits the maximum heat flux which may be dissipated from the components. An enhancement of the CHF becomes important to utilize the boiling heat transfer properly. An impinging liquid jet(Monde, 1991), for example, as shown in Fig.1, can be considered very simple and attractive as a means of the CHF enhancement. Grambill and Lienhard (1989) pointed out that the impinging jet is one of the potential coolings for the components with high heat fluxes.
Augmentation Techniques and External Flow Boiling
Published in Satish G. Kandlikar, Masahiro Shoji, Vijay K. Dhir, Handbook of Phase Change: Boiling and Condensation, 2019
Masanori Monde, Tatsuhiro Ueda, Yasuo Koizumi, Masanori Monde, Vijay K. Dhir
Boiling provides an efficient heat transfer mechanism for applications such as the cooling of electric components (Incropera, 1988), metal processing (Viskanta and Incropera, 1992), and fusion components (Boyd, 1983), where heat transfer coefficients commonly exceed 10,000 W/(m2K) at relatively high heat fluxes. The critical heat flux (CHF), which defines the upper limit of the efficient range of boiling heat transfer, limits the maximum heat flux that may be dissipated from the components. For enhancement of the CHF, it is important to utilize the boiling heat transfer properly and to satisfy the demands of efficient cooling processes. Jet impingement systems offer a very attractive means to enhance the CHF.
Gas–Liquid Two-Phase Flows
Published in Greg F. Naterer, Advanced Heat Transfer, 2018
The maximum heat flux (or critical heat flux; CHF) occurs at the transition between nucleate boiling and film boiling. Kutateladze (1948) presented a dimensional analysis of the dependence of the CHF on various operating parameters. Accurate prediction of the CHF is critical in various industrial systems because operations beyond the CHF may pose major safety risks. If the heat flux exceeds the CHF, then a large sudden increase in system temperature can lead to system damage, such as melting of components in a nuclear reactor, or overheating of a chemical reactor. Even operating near the CHF has safety risks due to boiling in the transition region which may cause unstable and abrupt changes in the wall heat flux.
Investigation of critical heat flux enhancement on nanoengineered surfaces in pressurized subcooled flow boiling using infrared thermometry
Published in Heat Transfer Engineering, 2023
Chi Wang, Guanyu Su, Olorunsola Akinsulire, Limiao Zhang, Md Mahamudur Rahman, Matteo Bucci
Flow boiling is used to remove heat in a variety of industrial applications, the size of which can be as small as an electronic chip, or as large as a nuclear reactor. One limiting factor for flow boiling heat transfer is the critical heat flux (CHF), defined as the heat flux at which a boiling crisis occurs. When the heat flux is below the CHF, the boiling process is in the nucleate boiling regime and discrete, non-interacting bubbles nucleate on the boiling surface. Such heat transfer regime is very effective, i.e., high heat fluxes can be removed with a relatively low surface temperature compared to single-phase forced convection. However, if the heat flux exceeds the CHF, the boiling regime changes into a film boiling regime. In film boiling, a stable vapor patch isolates the heated surface. The existence of the vapor film severely deteriorates the efficiency of the heat transfer process and may result in a catastrophic rise of the surface temperature (e.g., the surface to be cooled may melt down). As a result, the operating heat flux of industrial applications cooled by nucleate boiling is set to be much lower than the CHF limit to avoid the boiling crisis and ensure safe and continuous operation. Still, in systems where boiling is used for cooling purposes, e.g., nuclear reactors, a higher operating heat flux is often beneficial, as it leads to a better economic efficiency or a larger safety margin.
Development of a critical heat flux correlation based on an annular film dryout mechanistic model under the annular flow conditions
Published in Journal of Nuclear Science and Technology, 2023
Tadakatsu Yodo, Naoya Odaira, Daisuke Ito, Kei Ito, Yasushi Saito
Critical heat flux (CHF) is one of the most important thermal criteria for light water reactors (LWRs). In subcooled boiling conditions, the phenomenon of CHF is known as a departure from nucleate boiling (DNB), which causes the formation of a local vapor layer, resulting in a dramatic reduction of heat transfer capability. DNB generally occurs at high heat flux and low vapor quality. In saturated flow boiling, the flow pattern varies from bubbly, slug, churn, and finally to annular flow. In the annular flow, the liquid film thickness decreases along the flow direction due to the liquid evaporation and other effects, resulting in a liquid film dryout, the liquid film disappears, resulting in a rapid temperature increase in the heated rod. Such boiling transition is called liquid dryout or simply dryout [1]. The accuracy of the dryout-type CHF prediction is also essential for the thermal-hydraulic design and safety analysis of LWRs.
Heat Transfer Enhancement Using Different SiO2 Nanofluid Mixing Conditions on a Downward-Facing Heating Surface
Published in Nuclear Technology, 2022
Zhibo Zhang, Huai-En Hsieh, Yuan Gao, Shiqi Wang, Zhe Zhou
The downward-facing heating surface of boiling heat transfer has been widely used in various industrial applications, such as the in-vessel retention accident strategy of nuclear power plants, cryogenic systems, refrigeration, and heat dissipation of microelectronic equipment. The limit of heat flux that is permitted in the design of heat transfer equipment is called the critical heat flux (CHF). The heating surface changes from nucleation boiling to film boiling at this critical point. As a result, the boiling heat transfer performance deteriorates and the temperature of the heating area increases steeply. If the surface temperature exceeds the material limits, the heating surface may be destroyed, and then the entire heat transfer system will collapse. Therefore, enhancing the CHF can increase the power density of a system and improve its the economic benefits.