{"id":"529121e1-7caa-42e4-8ab3-43c9d8d4b432","arxiv_id":"2411.16524","paper_version":3,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"A new deposition-on-crater impact regime is proposed in which the cold drop deposits at the crater base while only the heated wall film forms the corona and secondary drops.","lead":"High-speed video and infrared imaging of a cold silicone-oil drop hitting a hot silicone-oil film show that the cooled spot at the substrate stays much smaller than the splashing corona. The authors propose a new deposition-on-crater regime in which the drop stays in the crater and only the hot film splashes, which could improve spray cooling models.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The regime claim equates the maximum IR cold-spot diameter with the drop's deposited footprint; no tracer or compositional measurement verifies that the corona and secondary drops contain only wall-film liquid.","rationale":"The reader's weakest assumption is exactly the load-bearing point: the IR cold-spot diameter is used as a proxy for the drop's deposited footprint without direct fluid-origin verification. I agree with that assessment. A direct tracer experiment would settle whether the corona and secondary drops contain drop liquid, and until that test is done the strong compositional claim in the abstract is not established. Other issues, such as the fitted constant in the time-delay model and the missing contact-temperature model, affect auxiliary modeling claims but do not determine whether the deposition-on-crater regime itself exists. Since the reader already assigned a CONDITIONAL verdict, this concern does not move the verdict; it confirms that the condition should be a direct liquid-tracing test.","tokens_in":12191,"tokens_out":5101,"duration_ms":54286,"concrete_test":"Repeat at least the conditions of Figs. 4a and 4b with a fluorescent or color tracer added only to the cold drop liquid (same silicone oil). Use high-speed fluorescence or color imaging of the side view and image or collect the secondary drops. If tracer is detected in the corona sheet or in any secondary drop, the deposition-on-crater regime as stated is falsified. If tracer remains confined to a region matching the cold-spot footprint and is absent from all secondary drops, the claim is confirmed. This directly tests the footprint proxy that Eq. (26) only assumes.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim requires that the cold drop liquid remains at the crater floor and never enters the corona. The only evidence offered is that the maximum cold-spot diameter d_cold,max is close to the model spreading diameter D_spread (Eq. 26) and much smaller than the corona base. This is an indirect proxy. The IR camera measures the temperature of the graphite coating, not the location of drop-liquid material. A cold drop that is entrained into the corona and ejected upward would not necessarily cool the substrate outside the crater floor, so a small cold spot is compatible with drop liquid participating in the corona and in secondary drops. Moreover, drop and film are the same silicone oil at different temperatures, so side-view shadowgraphy cannot distinguish fluid origin. Section IV's statement that 'the secondary drops consist exclusively of the wall film liquid' therefore goes beyond what the measurements establish. This gap is load-bearing because the abstract's novelty and the spray-cooling efficiency conclusion depend on it. The time-delay model uses a fitted constant, but that is secondary; the compositional claim is the main unsupported step.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports an experimental study of a silicone-oil drop impacting a heated, pre-wetted sapphire wall, using simultaneous high-speed shadowgraphy (side view) and high-speed infrared thermography (bottom view through the IR-transparent substrate). The authors observe that the infrared cold spot at the substrate is much smaller than the corona base, persists after corona collapse, and reaches a maximum diameter close to a model prediction for the drop spreading diameter. From this, they propose a new impact regime, 'deposition-on-crater', in which the impacting cold drop deposits at the crater floor while only the heated wall film feeds the corona and the secondary splash droplets. They further develop boundary-layer models for the contact temperature, the time delay of the cold-spot appearance, and the spreading diameter, and discuss implications for spray cooling.","tokens_in":12376,"tokens_out":3903,"duration_ms":39146,"significance":"If the central compositional claim is correct, the paper identifies a previously unreported impact regime that is directly relevant to spray-cooling efficiency, since it implies that the cold drop mass is fully deposited while only the heated film is lost to splash. The experimental setup is a strength: the simultaneous side-view and calibrated bottom-view IR measurements provide a direct, quantitative view of substrate cooling during impact, and the cold-spot persistence is an interesting observation. However, the paper's main claim rests on an indirect proxy (IR cold-spot diameter) rather than on direct measurement of liquid origin, and the quantitative 'validation' of the models involves fitted constants. The work is therefore a promising contribution that currently overstates the certainty of its central conclusion.","major_comments":[{"comment":"The central claim that the drop deposits at the crater base and does not enter the corona or secondary drops rests entirely on identifying the maximum IR cold-spot diameter d_cold,max with the drop's deposited footprint. This proxy is asserted in Section IV ('This result confirms our assumption that the cold spot ... is associated with the deposited liquid drop') but is never checked against a direct tracer such as dye or fluorescence. Since the drop and film are the same silicone oil at different temperatures, side-view shadowgraphy cannot distinguish fluid origin. A cold drop that is entrained into the corona and ejected upward would not necessarily cool the substrate outside the crater, so the observed small cold spot is compatible with drop liquid participating in the corona. Consequently, the abstract's claims that 'only the wall film produces the corona and splashes' and that 'secondary drops consist only of the heated material of the wall film' go beyond what the measurements establish. This is load-bearing because the claimed novelty and the spray-cooling efficiency conclusion depend on it.","section":"Section IV, Figs. 10 and 11"},{"comment":"The 'validated' prediction for the time delay t_delay contains an ad hoc fitting parameter c=0.36 (with standard error 0.0086), and the spreading diameter D_spread in Eq. (26) uses the empirical constant A0=0.55 fitted in the authors' own reference [9]. As a result, the agreement between d_cold,max and D_spread in Fig. 11 is partly by construction: both sides of the comparison incorporate fitted numbers. The authors should either determine these constants independently from first principles or explicitly frame the comparisons as consistency checks with fitted parameters rather than as parameter-free predictions. This also affects the abstract's phrase 'validated models'.","section":"Section III C, Eq. (23), and Eq. (26)"},{"comment":"The supplementary evidence from the residual-film radius r_res being smaller than the maximum corona radius r_max is qualitative and comes from a single case (S10, H_film=52 µm) that appears to involve corona detachment rather than the deposition-on-crater regime studied in Figs. 4 and 10. It is not clear how this observation supports the claim that the drop does not enter the corona in the main experiments. A quantitative comparison between r_res and the expected drop-spreading diameter for that detachment case, or a dye-tracer experiment, would strengthen the argument.","section":"Section IV, Fig. 13"}],"minor_comments":[{"comment":"The calibration procedure uses a thermocouple placed 'close to the surface', but the exact position, the thermal contact with the graphite coating, and the uncertainty propagation into the temperature maps are not described. Please clarify how the ±1°C thermocouple accuracy and the NETD of 0.05°C translate into the reported temperature fields.","section":"Section II A"},{"comment":"The caption states that side-view and bottom-view images are 'scaled identically', but the two cameras have different fields of view (23×23 mm versus 23×18 mm). Please specify the scaling procedure and confirm that the comparison of diameters is unaffected by optical distortion.","section":"Fig. 4 caption"},{"comment":"The outer cold-spot diameter d_cold,2 is defined by a dimensionless temperature threshold of 0.08, but the choice of threshold and its sensitivity to the results are not discussed. Please state how the threshold was selected and whether the conclusions in Figs. 10 and 11 are robust to reasonable variations of this threshold.","section":"Section IV"},{"comment":"The range of the dimensionless parameter chi is narrow (0.1 to 0.25), and the claimed monotonic increase of d_cold,max/D_spread with chi could be within experimental scatter. Please include error bars and, if possible, a least-squares fit with confidence intervals to assess the trend.","section":"Fig. 11"},{"comment":"The distinction between the proposed deposition-on-crater regime and the previously reported double-corona regime (Fig. 2a) should be clarified. If the double corona is a wall-film-dominant corona, how does it differ from the new regime in terms of the liquid-origin composition of the corona? The current text leaves this ambiguity.","section":"Introduction and Section IV"},{"comment":"The statement that 'conventional theories suggest that the corona-forming liquid jet comprises material from the impacting drop and wall film' is attributed to the Yarin-Weiss kinematic discontinuity model, which does not explicitly address the composition of the jet. A more specific reference to the origin-composition assumption would help the reader evaluate the novelty claim.","section":"Introduction, ref. [5]"},{"comment":"There is a typographical issue in Eq. (16): the integral notation is unclear (the dummy variable is not distinguished), and the derivative with respect to r is missing a factor. Please revise the equation to the standard form u_z = -(1/r) ∂/∂r ∫_0^z r u_r(r,z') dz'.","section":"Section III C, Eq. (16)"}],"recommendation":"major_revision","confidential_remarks":"The acknowledgment thanks reviewers of Physical Review Letters and Journal of Fluid Mechanics, which suggests prior submissions; the referee should be mindful that the novelty claim may have been revised in response to prior reviews. The core observation is valuable and the experimental setup is careful, but the central compositional claim needs direct experimental support (e.g., dye or fluorescent tracer in the drop, or compositional analysis of secondary drops) or a substantial softening of the abstract's claims. With such an addition or reframing, the paper could become a solid contribution to the drop-impact and spray-cooling literature."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThe headline: this paper has a genuinely new experimental observation, and one big inference that goes beyond the data. The observation is that when a cold drop hits a heated thin film, the IR cold spot on the substrate is much smaller than the corona base and persists long after the corona collapses. That is direct, calibrated IR imaging, and it holds across several viscosity and temperature conditions. The deposition-on-crater regime they name is a reasonable interpretation, not a proven fact.\n\nWhat is well done: the experimental setup is careful. In-situ IR calibration, NETD around 0.05°C, confocal film thickness measurement, and a parameter range that lets them vary film viscosity and temperature. The comparison of d_cold,max with the model D_spread (Eq. 26) is suggestive, and the collapse in Fig. 11 is decent. The literature context is honest, including their own earlier corona-detachment work.\n\nThe soft spots are real. First and most important: the claim that secondary drops consist exclusively of the wall film liquid is not measured. Drop and film are the same silicone oil at different temperatures, so shadowgraphy cannot tell the liquid origin. The IR signal only tells you where the substrate is cold. A drop that is entrained upward into the corona would leave the substrate outside the crater hot regardless. So the small cold spot is consistent with the deposit-on-crater story, but it does not prove the corona is pure film liquid. A dye or fluorescent tracer in the drop, like their earlier double-corona work, would settle it. Second, the validated models are partly circular: the time delay uses a fitted c=0.36, and D_spread inherits A0=0.55 from their own fitted reference. So Figs. 8 and 11 are consistency checks, not independent predictions. Third, the abstract promises a contact-temperature model that never appears in the body. That overclaim should be cut or the model added.\n\nThe central physical picture is plausible and the observation is solid. The inference about corona composition is the load-bearing part of the novelty, and it is currently under-supported. With direct tracing, error bars on the fitted constants, and a toned-down abstract, this becomes a solid contribution to drop impact and spray cooling.\n\nRecommendation: send to peer review, but expect major revision on the compositional claim and the model validation. A serious referee will get value from the data even if they push back on the interpretation.","headline":"A genuinely new IR observation with a plausible but under-supported compositional claim; deserves refereeing after the overclaims are trimmed.","tokens_in":12900,"tokens_out":2737,"would_cite":false,"duration_ms":26451,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Impact drop deposits on the crater while only the wall film splashes.","keywords":["drop impact","wall film","corona splash","deposition-on-crater regime","spray cooling","infrared thermography","boundary layer analysis","silicone oils"],"falsifier":"Repeat a deposition-on-crater impact with a small amount of dye or fluorescent tracer added to the cold drop and inspect the corona and secondary droplets; any tracer signal in either would show that drop material leaves the crater, contradicting the regime.","tokens_in":11993,"feed_emoji":"💧","tokens_out":17059,"duration_ms":131429,"temperature":0.7,"pith_summary":"This paper aims to establish a new splash regime for a drop impacting a heated wall covered by a thin liquid film at high Reynolds and Weber numbers under the specific conditions studied here. In this regime, called deposition-on-crater, the cold impacting drop spreads and settles at the bottom of the crater it carves in the film, while the corona jet and any secondary droplets are produced entirely from the heated wall film. The evidence comes from simultaneous high-speed imaging and infrared thermography: the cold spot on the substrate is much smaller than the corona base, persists after the corona collapses, and its maximum diameter matches the theoretically predicted spreading diameter of the drop. If true, this finding matters for spray cooling because the entire cold drop mass deposits and contributes to wall cooling instead of being lost to splash.","feed_headline":"Impact drop deposits on the crater while only the wall film splashes","feed_subtitle":"In impacts on heated films, the cold drop fully deposits while the corona and droplets are just the hot wall film.","key_machinery":"The argument rests on a boundary-layer description of the spreading drop on a thin wall film, combined with a thermal-boundary-layer model for the substrate cooling. The lamella flow is described by a similarity solution with radial velocity $u_r = r/(t+\\tau)$ and thickness decaying as $t^{-2}$; the residual thickness of the combined layers is $h_{\\mathrm{res}} = A(\\delta) D \\mathrm{Re}^{-2/5}$, with $A$ built from the film influence parameter $\\chi = \\delta^{1/5}\\omega/[(1+3.86\\omega)\\kappa^{1/10}]$. From mass balance, the drop's maximum spreading diameter becomes $D_{\\mathrm{spread}} \\approx 1.1 D \\mathrm{Re}^{1/5}$, which is identified with the maximum cold-spot diameter. The matching of $d_{\\mathrm{cold,max}}$ to $D_{\\mathrm{spread}}$ is the key comparison that assigns the cold spot to the deposited drop rather than to the corona region; because this diameter is much smaller than the corona base, the drop liquid is confined to the crater floor. The thermal delay before substrate cooling appears is modeled by equating the thermal boundary layer thickness $\\sqrt{\\alpha_{\\mathrm{film}} t}/c$ to the evolving film thickness, yielding a validated formula for the delay time.","core_discovery":"The central discovery is that under the studied conditions (silicone oil drops and films, Reynolds numbers 130--350, Weber numbers 880--1030, film thickness below 30% of the drop diameter, heated film), the impacting drop never becomes part of the corona. The drop spreads along the floor of the crater it forms in the film, depositing there, while the kinematic-discontinuity corona is created only from the wall film. This is shown by infrared images in which the cold spot left by the drop has a diameter close to the predicted spreading diameter $D_{\\mathrm{spread}} \\approx 1.1 D \\mathrm{Re}^{1/5}$, much smaller than the corona base, and by the delayed appearance of cooling that matches a thermal boundary layer crossing the residual film. The paper validates models for the cold-spot diameter, the delay time before the cooling signal reaches the substrate, and the contact temperature, and argues that this deposition-on-crater regime is the most favorable for spray cooling, since the cold drop avoids splashing and the secondary drops carry only already-hot film liquid.","pith_inferences":["The regime boundary is left open in the paper; a natural criterion is that deposition-on-crater holds whenever the predicted spreading diameter $D_{\\mathrm{spread}}$ stays below the corona base diameter, which could be expressed as a condition on $\\mathrm{Re}$, $\\mathrm{We}$, and the dimensionless film thickness $\\delta$ using existing corona-growth laws.","The cold-spot measurement could be validated as a non-invasive footprint diagnostic by repeating the experiments with a fluorescing species in the drop; if it holds, it would let researchers map drop deposition in sprays without adding tracers.","If the same regime occurs in water-based sprays at practical temperatures, spray-cooling models would need to count the deposited cold drop mass as wall heat extraction and treat corona splash as pure film loss, changing the predicted heat flux.","The persistence of the cold spot long after the corona collapses suggests a slow, post-corona cooling phase on the crater floor that the present models do not explicitly describe."],"forward_implications":["In the deposition-on-crater regime, the full mass of the cold drop lands on the wall, so spray cooling efficiency is higher than in a drop-dominant corona where cold drops are lost to splash.","The cold spot's maximum diameter is predictable from $D_{\\mathrm{spread}} \\approx 1.1 D \\mathrm{Re}^{1/5}$, giving an estimate of the cooled surface area per individual drop.","The delay between impact and substrate cooling is set by the time a thermal boundary layer takes to cross the residual film, so the model can be used to estimate contact temperature and heat flux in spray-cooling simulations.","Because the corona and secondary drops in this regime contain only wall-film liquid, their material and temperature differ from the drop's, so models that mix drop and film contributions in the corona need revision."],"supporting_citations":[{"why":"Establishes the kinematic-discontinuity mechanism and the scaling for corona base diameter and lamella thickness used throughout the analysis.","marker":"[5]"},{"why":"Provides the similarity solution for a viscous spreading drop whose residual thickness and spreading diameter set the predicted cold-spot size.","marker":"[30]"},{"why":"Supplies the forced-film spreading and heat-transfer similarity solution used for the drop spreading and thermal analysis.","marker":"[31]"},{"why":"Gives the wall-film flow model, the residual film thickness formula, and the coefficient $A_0$ from which the spreading diameter and film thickness evolution are computed.","marker":"[9]"},{"why":"Documents corona detachment from the wall film and a residual film smaller than the corona, supporting the deposition-on-crater geometry.","marker":"[14]"},{"why":"Provides the double-corona observations of a wall-film-dominant regime against which the new regime is contrasted.","marker":"[8]"}],"fun_headline_variants":["Heated film splash: drop deposits, only wall film flies","Cold drop stays put as hot film splashes in new regime","Deposition-on-crater regime: drop sinks, film splashes","In hot-film impacts, drop deposits while film splashes","New regime: drop deposits at crater, film makes the splash"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The regime classification assumes that the maximum diameter of the infrared cold spot equals the footprint of the drop liquid on the crater floor; if thermal smearing or lateral conduction shrinks or blurs the cold spot, the drop could spread wider than the cold spot indicates and even feed the corona without being detected.","fun_headline_variants_meta":{"raw":{"variants":["Heated film splash: drop deposits, only wall film flies","Cold drop stays put as hot film splashes in new regime","Deposition-on-crater regime: drop sinks, film splashes","In hot-film impacts, drop deposits while film splashes","New regime: drop deposits at crater, film makes the splash"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000459,"raw_usage":{"total_tokens":2314,"prompt_tokens":971,"completion_tokens":1343,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":587,"completion_tokens_details":{"reasoning_tokens":1256}},"tokens_in":587,"tokens_out":1343,"duration_ms":8500,"temperature":1.0,"reasoning_tokens":1256,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T13:01:32.602650+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Repeat a deposition-on-crater impact with a small amount of dye or fluorescent tracer added to the cold drop and inspect the corona and secondary droplets; any tracer signal in either would show that drop material leaves the crater, contradicting the regime.","supporting_citations":[{"cited_title":"Ricci , author R","cited_arxiv_id":null,"evidence_quote":"Provides the similarity solution for a viscous spreading drop whose residual thickness and spreading diameter set the predicted cold-spot size."},{"cited_title":"Roberts , author A","cited_arxiv_id":null,"evidence_quote":"Supplies the forced-film spreading and heat-transfer similarity solution used for the drop spreading and thermal analysis."},{"cited_title":"Stumpf , author J","cited_arxiv_id":null,"evidence_quote":"Documents corona detachment from the wall film and a residual film smaller than the corona, supporting the deposition-on-crater geometry."},{"cited_title":"Liang \\ and\\ author I","cited_arxiv_id":null,"evidence_quote":"Provides the double-corona observations of a wall-film-dominant regime against which the new regime is contrasted."}],"review_version":1}