{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/93075"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/93075","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"Enhanced coalescence-induced jumping droplet departure","abstract":"Water vapor condensation on superhydrophobic surfaces has received much attention in recent years due to its ability to shed water droplets at length scales three decades smaller than the capillary length (~ 1mm) via coalescence induced droplet jumping. Jumping-droplet condensation has been demonstrated to enhance heat transfer, anti-icing, and self-cleaning efficiency, and is governed by the theoretical inertial-capillary scaled jumping speed (U). When two droplets coalesce, the experimentally measured jumping speed (U_exp) is fundamentally limited by the internal fluid dynamics during the coalescence process (U_exp < 0.23U). Here, we theoretically and experimentally demonstrate multi-droplet (>2) coalescence as an avenue to break the two-droplet speed limit. Using side-view and top-view high-speed imaging to study more than 1000 jumping events on a copper oxide nanostructured superhydrophobic surface, we verify that droplet jumping occurs due to three fundamentally different mechanisms: 1) coalescence between 2 droplets, 2) coalescence between more than 2 droplets (multi-drop), and 3) coalescence between 1 or more droplets on the surface and a returning droplet that has already departed (multi-hop). We measured droplet-jumping speeds for a wide range of droplet radii (5-50 µm), and demonstrated that while the two-droplet capillary-to-inertial energy conversion mechanism is not identical to that of multi-drop jumping, speeds above the theoretical two-droplet limit (> 0.23U) can be achieved. However, we discovered that multi-hop coalescence resulted in drastically reduced jumping speeds (<< 0.23U) due to adverse momentum contributions from returning droplets. To quantify the impact of enhanced jumping speed on heat transfer performance, we developed a condensation critical heat flux model to show that modest jumping speed enhancements of 50% using multi-drop jumping can enhance performance by up to 40%.","abstract_html":"Water vapor condensation on superhydrophobic surfaces has received much attention in recent years due to its ability to shed water droplets at length scales three decades smaller than the capillary length (~ 1mm) via coalescence induced droplet jumping. Jumping-droplet condensation has been demonstrated to enhance heat transfer, anti-icing, and self-cleaning efficiency, and is governed by the theoretical inertial-capillary scaled jumping speed (U). When two droplets coalesce, the experimentally measured jumping speed (U_exp) is fundamentally limited by the internal fluid dynamics during the coalescence process (U_exp &lt; 0.23U). Here, we theoretically and experimentally demonstrate multi-droplet (&gt;2) coalescence as an avenue to break the two-droplet speed limit. Using side-view and top-view high-speed imaging to study more than 1000 jumping events on a copper oxide nanostructured superhydrophobic surface, we verify that droplet jumping occurs due to three fundamentally different mechanisms: 1) coalescence between 2 droplets, 2) coalescence between more than 2 droplets (multi-drop), and 3) coalescence between 1 or more droplets on the surface and a returning droplet that has already departed (multi-hop). We measured droplet-jumping speeds for a wide range of droplet radii (5-50 µm), and demonstrated that while the two-droplet capillary-to-inertial energy conversion mechanism is not identical to that of multi-drop jumping, speeds above the theoretical two-droplet limit (&gt; 0.23U) can be achieved. However, we discovered that multi-hop coalescence resulted in drastically reduced jumping speeds (&lt;&lt; 0.23U) due to adverse momentum contributions from returning droplets. To quantify the impact of enhanced jumping speed on heat transfer performance, we developed a condensation critical heat flux model to show that modest jumping speed enhancements of 50% using multi-drop jumping can enhance performance by up to 40%.","abstract_has_math":false,"creators":["Kim, Moonkyung"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"M.S.","degree_level":"Thesis","degree_discipline":"Mechanical Engineering","degree_department":null,"school":null,"contributors":["Miljkovic, Nenad"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2016,"date_issued":"2016-11-10T18:43:16Z","date_published":"2016-11-10T18:43:16Z","updated_at":"2026-07-22T22:26:35Z","subjects":["jumping-droplet","coalescence","condensation","multi-hop","droplet","heat transfer"],"languages":["en"],"rights":["© 2016 Moonkyung Kim"],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/2142/93075","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Miljkovic, Nenad"]},{"key":"dc:creator","label":"Author","values":["Kim, Moonkyung"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2016-11-10T18:43:16Z","2018-11-11T10:15:32Z","2016-07-19","2016-08"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Mechanical Engineering"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Thesis"]},{"key":"thesis:degree_name","label":"Degree Name","values":["M.S."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["jumping-droplet","coalescence","condensation","multi-hop","droplet","heat transfer"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["© 2016 Moonkyung Kim"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/2142/93075"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Water vapor condensation on superhydrophobic surfaces has received much attention in recent years due to its ability to shed water droplets at length scales three decades smaller than the capillary length (~ 1mm) via coalescence induced droplet jumping. Jumping-droplet condensation has been demonstrated to enhance heat transfer, anti-icing, and self-cleaning efficiency, and is governed by the theoretical inertial-capillary scaled jumping speed (U). When two droplets coalesce, the experimentally measured jumping speed (U_exp) is fundamentally limited by the internal fluid dynamics during the coalescence process (U_exp < 0.23U). Here, we theoretically and experimentally demonstrate multi-droplet (>2) coalescence as an avenue to break the two-droplet speed limit. Using side-view and top-view high-speed imaging to study more than 1000 jumping events on a copper oxide nanostructured superhydrophobic surface, we verify that droplet jumping occurs due to three fundamentally different mechanisms: 1) coalescence between 2 droplets, 2) coalescence between more than 2 droplets (multi-drop), and 3) coalescence between 1 or more droplets on the surface and a returning droplet that has already departed (multi-hop). We measured droplet-jumping speeds for a wide range of droplet radii (5-50 µm), and demonstrated that while the two-droplet capillary-to-inertial energy conversion mechanism is not identical to that of multi-drop jumping, speeds above the theoretical two-droplet limit (> 0.23U) can be achieved. However, we discovered that multi-hop coalescence resulted in drastically reduced jumping speeds (<< 0.23U) due to adverse momentum contributions from returning droplets. To quantify the impact of enhanced jumping speed on heat transfer performance, we developed a condensation critical heat flux model to show that modest jumping speed enhancements of 50% using multi-drop jumping can enhance performance by up to 40%.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2018-08-01","The student, Moonkyung Kim, accepted the attached license on 2016-07-19 at 10:04.","The student, Moonkyung Kim, submitted this Thesis for approval on 2016-07-19 at 10:11.","This Thesis was approved for publication on 2016-07-19 at 15:43.","DSpace SAF Submission Ingestion Package generated from Vireo submission #9996 on 2016-11-10 at 12:27:15","Made available in DSpace on 2016-11-10T18:43:16Z (GMT). No. of bitstreams: 2 KIM-THESIS-2016.pdf: 2145602 bytes, checksum: b6e47343082a88f3f12b8c47703d1f43 (MD5) LICENSE.txt: 4210 bytes, checksum: 0ecef92e7216ac9fd49fa9fef5223b7f (MD5) Previous issue date: 2016-07-19","Embargo set by: Seth Robbins for item 95498 Lift date: 2018-11-10T18:43:22Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","U of I Only Restriction Lifted for Item 95498 on 2018-11-11T10:15:32Z."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Enhanced coalescence-induced jumping droplet departure"]}]}],"canonical_facts":{"dc:contributor":["Miljkovic, Nenad"],"dc:creator":["Kim, Moonkyung"],"dc:date":["2016-11-10T18:43:16Z","2018-11-11T10:15:32Z","2016-07-19","2016-08"],"dc:description":["Water vapor condensation on superhydrophobic surfaces has received much attention in recent years due to its ability to shed water droplets at length scales three decades smaller than the capillary length (~ 1mm) via coalescence induced droplet jumping. Jumping-droplet condensation has been demonstrated to enhance heat transfer, anti-icing, and self-cleaning efficiency, and is governed by the theoretical inertial-capillary scaled jumping speed (U). When two droplets coalesce, the experimentally measured jumping speed (U_exp) is fundamentally limited by the internal fluid dynamics during the coalescence process (U_exp < 0.23U). Here, we theoretically and experimentally demonstrate multi-droplet (>2) coalescence as an avenue to break the two-droplet speed limit. Using side-view and top-view high-speed imaging to study more than 1000 jumping events on a copper oxide nanostructured superhydrophobic surface, we verify that droplet jumping occurs due to three fundamentally different mechanisms: 1) coalescence between 2 droplets, 2) coalescence between more than 2 droplets (multi-drop), and 3) coalescence between 1 or more droplets on the surface and a returning droplet that has already departed (multi-hop). We measured droplet-jumping speeds for a wide range of droplet radii (5-50 µm), and demonstrated that while the two-droplet capillary-to-inertial energy conversion mechanism is not identical to that of multi-drop jumping, speeds above the theoretical two-droplet limit (> 0.23U) can be achieved. However, we discovered that multi-hop coalescence resulted in drastically reduced jumping speeds (<< 0.23U) due to adverse momentum contributions from returning droplets. To quantify the impact of enhanced jumping speed on heat transfer performance, we developed a condensation critical heat flux model to show that modest jumping speed enhancements of 50% using multi-drop jumping can enhance performance by up to 40%.","Submission published under a 24 month embargo labeled 'U of I Access', the embargo will last until 2018-08-01","The student, Moonkyung Kim, accepted the attached license on 2016-07-19 at 10:04.","The student, Moonkyung Kim, submitted this Thesis for approval on 2016-07-19 at 10:11.","This Thesis was approved for publication on 2016-07-19 at 15:43.","DSpace SAF Submission Ingestion Package generated from Vireo submission #9996 on 2016-11-10 at 12:27:15","Made available in DSpace on 2016-11-10T18:43:16Z (GMT). No. of bitstreams: 2 KIM-THESIS-2016.pdf: 2145602 bytes, checksum: b6e47343082a88f3f12b8c47703d1f43 (MD5) LICENSE.txt: 4210 bytes, checksum: 0ecef92e7216ac9fd49fa9fef5223b7f (MD5) Previous issue date: 2016-07-19","Embargo set by: Seth Robbins for item 95498 Lift date: 2018-11-10T18:43:22Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system","U of I Only Restriction Lifted for Item 95498 on 2018-11-11T10:15:32Z."],"dc:format":["application/pdf"],"dc:identifier":["http://hdl.handle.net/2142/93075"],"dc:language":["en"],"dc:rights":["© 2016 Moonkyung Kim"],"dc:subject":["jumping-droplet","coalescence","condensation","multi-hop","droplet","heat transfer"],"dc:title":["Enhanced coalescence-induced jumping droplet departure"],"dc:type":["text"],"thesis:degree_discipline":["Mechanical Engineering"],"thesis:degree_level":["Thesis"],"thesis:degree_name":["M.S."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:26:35Z"}