Flow boiling in mini and microchannels has become an attractive option for many applications, such as compact and low charge heat exchangers. Microchannel heat exchangers, however, are more susceptible to maldistribution between parallel flow channels. When operating during uneven heat load conditions, the maldistribution becomes even more severe. Electrohydrodynamic (EHD) conduction pumping technology offers an innovative way to redistribute flow between parallel branches in a microchannel heat exchanger and is also being explored as a next generation mechanism of microgravity heat transport. In EHD conduction pumping, a strong electric field interacts with dissociated electrolytes in dielectric fluid to generate a net body force, and thus, a net flow, with no moving parts, no acoustical noise, lower power consumption, and the ability to operate in microgravity. An EHD conduction pump was designed, fabricated, and tested for upstream flow distribution control of a parallel microchannel evaporator in an opposing configuration. Flow redistribution capability was measured at system flowrates up to 6 ml/min. The EHD conduction pump was capable of completely blocking and reversing the flow in its branch. Recovery from near critical heat flux conditions up to a maximum heat flux of 77.5 W/cm2 was also demonstrated for the operating conditions and design of this study. This was achieved in the absence of enhanced surfaces. The working fluid is HFE 7100. The results show that EHD conduction is able to effectively control the flow distribution of the microchannel evaporator, however, its effectiveness decreases with increasing heat flux and flowrate.
{"title":"Upstream Electrohydrodynamic Conduction Pumping for Flow Distribution Control of Parallel Microchannel Evaporators","authors":"Nathaniel J. O'connor, M. Talmor, J. Yagoobi","doi":"10.1115/1.4064442","DOIUrl":"https://doi.org/10.1115/1.4064442","url":null,"abstract":"\u0000 Flow boiling in mini and microchannels has become an attractive option for many applications, such as compact and low charge heat exchangers. Microchannel heat exchangers, however, are more susceptible to maldistribution between parallel flow channels. When operating during uneven heat load conditions, the maldistribution becomes even more severe. Electrohydrodynamic (EHD) conduction pumping technology offers an innovative way to redistribute flow between parallel branches in a microchannel heat exchanger and is also being explored as a next generation mechanism of microgravity heat transport. In EHD conduction pumping, a strong electric field interacts with dissociated electrolytes in dielectric fluid to generate a net body force, and thus, a net flow, with no moving parts, no acoustical noise, lower power consumption, and the ability to operate in microgravity. An EHD conduction pump was designed, fabricated, and tested for upstream flow distribution control of a parallel microchannel evaporator in an opposing configuration. Flow redistribution capability was measured at system flowrates up to 6 ml/min. The EHD conduction pump was capable of completely blocking and reversing the flow in its branch. Recovery from near critical heat flux conditions up to a maximum heat flux of 77.5 W/cm2 was also demonstrated for the operating conditions and design of this study. This was achieved in the absence of enhanced surfaces. The working fluid is HFE 7100. The results show that EHD conduction is able to effectively control the flow distribution of the microchannel evaporator, however, its effectiveness decreases with increasing heat flux and flowrate.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139380159","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Hong-Qing Jin, Aditi Kalle, Yuheng Zhang, Sophie Wang
Mitigation of scale formation and performance degradation remains a vital challenge for falling film evaporators in various industries. In this work, an experimental study of falling film flow on a horizontal tube is conducted to investigate the effects of wettability gradients on thermal, hydraulic, and fouling behavior. It is revealed that certain hydrophobic coating patterns, such as strip, ring, and grid pattern, lead to unwetted heat transfer area, which results in decreased heat transfer compared to fully wetted plain tube. By adjusting the geometry and position of the wettability gradient, the hybrid coating demonstrates improved heat transfer performance. Based on the characteristics of horizontal tube falling film flow, impinging jet, thin film flow, and liquid retention at the tube bottom, a hybrid coating pattern is developed to improve surface wetting and mitigate the scaling coverage. It is revealed that scale deposition is regulated by wettability gradient. Crystals tend to be dense and compact in hydrophilic areas, while they appear scattered or even absent in hydrophobic regions, depending on the dimension of the hydrophobic area. While at the hydrophilic/hydrophobic boundary, a noticeable scale thickness step is observed, which raises the potential for self-cleaning. The balance of minimization of scaling layer coverage and maximization of wetting area requires an optimal design in coating dimensions, for which a systemic study of both flow dynamics and fouling characteristic on the falling film is necessary in the future.
{"title":"Effect of Wettability Gradient On the Scale Formation in Falling Film Flow","authors":"Hong-Qing Jin, Aditi Kalle, Yuheng Zhang, Sophie Wang","doi":"10.1115/1.4064445","DOIUrl":"https://doi.org/10.1115/1.4064445","url":null,"abstract":"\u0000 Mitigation of scale formation and performance degradation remains a vital challenge for falling film evaporators in various industries. In this work, an experimental study of falling film flow on a horizontal tube is conducted to investigate the effects of wettability gradients on thermal, hydraulic, and fouling behavior. It is revealed that certain hydrophobic coating patterns, such as strip, ring, and grid pattern, lead to unwetted heat transfer area, which results in decreased heat transfer compared to fully wetted plain tube. By adjusting the geometry and position of the wettability gradient, the hybrid coating demonstrates improved heat transfer performance. Based on the characteristics of horizontal tube falling film flow, impinging jet, thin film flow, and liquid retention at the tube bottom, a hybrid coating pattern is developed to improve surface wetting and mitigate the scaling coverage. It is revealed that scale deposition is regulated by wettability gradient. Crystals tend to be dense and compact in hydrophilic areas, while they appear scattered or even absent in hydrophobic regions, depending on the dimension of the hydrophobic area. While at the hydrophilic/hydrophobic boundary, a noticeable scale thickness step is observed, which raises the potential for self-cleaning. The balance of minimization of scaling layer coverage and maximization of wetting area requires an optimal design in coating dimensions, for which a systemic study of both flow dynamics and fouling characteristic on the falling film is necessary in the future.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139380287","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Axial conduction is a crucial performance deteriorating factor in miniaturized heat transfer devices, primarily due to the low fluid flow rates, high solid cross-sectional to free-flow area ratio, and use of high thermal conductivity materials. These causative factors, inherent to micro-scale systems, should be such that the axial conduction is minimum. The reciprocating flow of the convective fluid (instead of steady unidirectional flow) is proposed per se as an alternative, which directly alters the solid temperature profile, the root cause of axial conduction. An experimental setup is built as a proof of the concept. In the test rig, a double-acting reciprocating pump generates a fully reversing periodic flow of air through a flow channel carved into a steel block embedded with a heater. The experimental temperature profile in the solid at the cyclic steady state is bell-shaped, indicating a virtual adiabatic plane capable of restricting axial heat transfer. The experimental results are verified taking the help of an independent finite-element-based numerical analysis. Similarly, the non-dimensional interfacial flux ratio (?_0 ), integrally related to axial conduction, for unidirectional and reciprocating flow is significantly different. This ratio in the vicinity of the inlet is ~53% less with the reciprocating compared to the equivalent unidirectional flow. The optimal thermal performance with the reciprocating flow is correlated through a critical Strouhal number expression, Sr ≤ (pDh)/L. In thermal management applications employing reciprocating flow, the limiting relation can be used to determine flow parameters and optimum geometry design.
轴向传导是微型传热设备性能下降的一个关键因素，这主要是由于流体流速低、固体横截面与自由流动面积比高以及使用了高导热材料。这些微型系统固有的致病因素应使轴向传导最小。对流流体的往复流动（而不是稳定的单向流动）本身就是一种替代方案，它可以直接改变固体温度曲线，而这正是轴向传导的根本原因。为证明这一概念，我们建立了一个实验装置。在试验装置中，双作用往复泵产生完全反向的周期性气流，通过在嵌入加热器的钢块上开凿的流道。在循环稳定状态下，固体中的实验温度曲线呈钟形，表明虚拟绝热面能够限制轴向传热。实验结果在独立的有限元数值分析的帮助下得到了验证。同样，单向流和往复流的非维度界面通量比 (?_0 ) 与轴向传导密切相关，两者之间存在显著差异。与等效的单向流相比，往复流在入口附近的这一比率要小 53%。往复流的最佳热性能与临界斯特劳哈尔数表达式 Sr ≤ (pDh)/L 有关。在采用往复流的热管理应用中，可利用该极限关系确定流动参数和最佳几何设计。
{"title":"Experimental and Computational Evidence of Damped Axial Conduction with Reciprocating Flow","authors":"I. Mitra, Indranil Ghosh","doi":"10.1115/1.4064446","DOIUrl":"https://doi.org/10.1115/1.4064446","url":null,"abstract":"\u0000 Axial conduction is a crucial performance deteriorating factor in miniaturized heat transfer devices, primarily due to the low fluid flow rates, high solid cross-sectional to free-flow area ratio, and use of high thermal conductivity materials. These causative factors, inherent to micro-scale systems, should be such that the axial conduction is minimum. The reciprocating flow of the convective fluid (instead of steady unidirectional flow) is proposed per se as an alternative, which directly alters the solid temperature profile, the root cause of axial conduction. An experimental setup is built as a proof of the concept. In the test rig, a double-acting reciprocating pump generates a fully reversing periodic flow of air through a flow channel carved into a steel block embedded with a heater. The experimental temperature profile in the solid at the cyclic steady state is bell-shaped, indicating a virtual adiabatic plane capable of restricting axial heat transfer. The experimental results are verified taking the help of an independent finite-element-based numerical analysis. Similarly, the non-dimensional interfacial flux ratio (?_0 ), integrally related to axial conduction, for unidirectional and reciprocating flow is significantly different. This ratio in the vicinity of the inlet is ~53% less with the reciprocating compared to the equivalent unidirectional flow. The optimal thermal performance with the reciprocating flow is correlated through a critical Strouhal number expression, Sr ≤ (pDh)/L. In thermal management applications employing reciprocating flow, the limiting relation can be used to determine flow parameters and optimum geometry design.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139380833","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mini-channel heat exchanger are widely used due to their compact structures and high efficiency. Integrating heat exchangers with triply periodic minimal surfaces (TPMS) has shown great potential to optimize the flow and heat transfer performance. In this study, Gyroid (G), Diamond (D) and IWP type TPMS based heat exchangers are constructed in three dimensions. The thermal hydraulic, entropy production and flow-induced noise characteristics of TPMS based heat exchangers are numerically investigated. The results indicate that the TPMS channels with larger viscosity entropy production have smaller thermal entropy production due to the greater flow disturbance. The G-channel has the highest friction factor and the lowest sound source intensity, while the D-channel obtains the strongest sound source intensity due to frequent cross-collisions of the fluid. The sound source intensity of the IWP channel is 10% lower than the D-channel. The wall dipole sound source plays a dominant role in TPMS channels. This study provides different perspectives to evaluate the performance of a TPMS heat exchanger, and provides references for the design and optimization of TPMS heat exchangers.
{"title":"Numerical Study on Thermal Hydraulic and Flow-Induced Noise in Triply Periodic Minimal Surface (TPMS) Channels","authors":"Xinhai Gan, Jinghan Wang, Zhiyu Liu, Min Zeng, Qiuwang Wang, Zhilong Cheng","doi":"10.1115/1.4064441","DOIUrl":"https://doi.org/10.1115/1.4064441","url":null,"abstract":"\u0000 Mini-channel heat exchanger are widely used due to their compact structures and high efficiency. Integrating heat exchangers with triply periodic minimal surfaces (TPMS) has shown great potential to optimize the flow and heat transfer performance. In this study, Gyroid (G), Diamond (D) and IWP type TPMS based heat exchangers are constructed in three dimensions. The thermal hydraulic, entropy production and flow-induced noise characteristics of TPMS based heat exchangers are numerically investigated. The results indicate that the TPMS channels with larger viscosity entropy production have smaller thermal entropy production due to the greater flow disturbance. The G-channel has the highest friction factor and the lowest sound source intensity, while the D-channel obtains the strongest sound source intensity due to frequent cross-collisions of the fluid. The sound source intensity of the IWP channel is 10% lower than the D-channel. The wall dipole sound source plays a dominant role in TPMS channels. This study provides different perspectives to evaluate the performance of a TPMS heat exchanger, and provides references for the design and optimization of TPMS heat exchangers.","PeriodicalId":510895,"journal":{"name":"ASME journal of heat and mass transfer","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2024-01-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139380255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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