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A comprehensive experimental investigation of water cold plate with different flow configurations for electronic cooling was conducted. Serpentine, parallel and wavy channels cold plate were designed to study the hydrothermal performance of water cold plate for electronic servers cooling. Thermal resistance, pressure drop, Nusselt number, servers’ temperatures and performance evaluation criterion were measured, evaluated and compared to evaluate the hydrothermal performance of the different configurations. The results showed that the serpentine channels cold plate has a better thermal performance than both parallel and wavy channels cold plate. The serpentine channels cold plate yields a lower thermal resistance by (6.02–10.5%), (2.4–8.7%) and a higher average Nusselt number by (7.9–13.9%), (6.3–13.7%) compared to parallel and wavy channels cold plate, respectively. Also, the results indicated that the serpentine channels cold plate has a higher pressure drop and pumping power compared to parallel and wavy channels cold plates. Similarly, the results showed that the wavy channel has better thermal performance than parallel channels due to the larger flow path and the rotational flow occurred. The I-Type inlet and outlet configuration used in the wavy channel cold plate provide a lower pressure drop compared to parallel channels however the large flow path. The performance evaluation criterion showed that the wavy channels cold plate has a higher performance evaluation criterion than serpentine channels due to its lower pressure drop.

Cold plate is an important component for a liquid battery thermal management system. In order to study the transient thermal performance of the cold plate under conditions with sharply increasing heat loads, the numerical model of a battery cold plate is established. The validation experiment shows that the error between the simulation and experiment is around 2.5% to 5%. Effects of the coolant flow rate, the increase in heat flux, and the channel number are analyzed to study the transient thermal performance of the cold plate. Results show that the average temperature of the cold plate at 540 s is lowered from 28.3°C to 26.9°C when the coolant flow rate is raised from 0.065 kg/s to 0.165 kg/s. The temperature deviation is decreased when the coolant flow rate is increased from 0.065 kg/s to 0.115 kg/s; however, it is slightly increased if the coolant flow rate is further increased. Both average temperature and temperature deviation are raised if the final heat flux is increased from 11 000 W/m2 to 16 500 W/m2, which are 2 and 3 times of the initial, respectively. In addition, increasing the channel number has slightly positive effect on the average temperature of the cold plate, while the temperature deviation is increased when the channel number is increased from 3 to 11 due to the non-uniform velocity distribution between each channel. The results of this study will be helpful during the design of cold plate for battery thermal management, especially for transient conditions with sudden rising heat loads like thermal runaway.

In order to investigate the effects of three parameters of a mini-channel cold plate on the cooling performance of a U-shaped mini-channel structure, the effects of the channel length (L), width (W...

For lithium-ion battery thermal management system for electric vehicles, the insertion of metal plates with channels on both sides of a lithium-ion battery is an effective method for a high-temperature cooling. Inspired by the nature spider-web structure, we propose a cold plate with a bionic spider-web channel inside. Based on the heat generation characteristics of the pouch lithium-ion battery at an extreme discharge rate of 12 C, we used an orthogonal experimental design to study the cooling performance of the spider web-channel structure for a lithium-ion battery. Numerical simulation results showed that, among the structural parameters of the spider-web channel, the channel width had the largest influence on the cooling performance of the cold plate, while the channel angle had the smallest influence. The increase in the channel width could not indefinitely enhance the cooling performance of the cold plate. The most suitable structure was obtained at a width of 3 mm. When the channel angle was 120°, the pouch lithium-ion battery could provide the best thermal balance.

In today’s world, most data centers have multiple racks with numerous servers in each of them. The high amount of heat dissipation has become the largest server-level cooling problem for the data centers. The higher dissipation required, the higher is the total energy required to run the data center. Although still the most widely used cooling methodology, air cooling has reached its cooling capabilities especially for High-Performance Computing data centers. Liquid-cooled servers have several advantages over their air-cooled counterparts, primarily of which are high thermal mass, lower maintenance. Nano-fluids have been used in the past for improving the thermal efficiency of traditional dielectric coolants in the power electronics and automotive industry. Nanofluids have shown great promise in improving the convective heat transfer properties of the coolants due to a proven increase in thermal conductivity and specific heat capacity. The present research investigates the thermal enhancement of the performance of de-ionized water-based dielectric coolant with Copper nanoparticles for a higher heat transfer from the server cold plates. Detailed 3-D modeling of a commercial cold plate is completed and the CFD analysis is done in a commercially available CFD code ANSYS CFX. The obtained results compare the improvement in heat transfer due to improvement in coolant properties with data available in the literature.

The freezing process of supercooled water droplets on cold plates is studied experimentally and numerically. A numerical model that considers both the supercooling effect on the physical properties and the volume expansion effect on the droplet freezing profile is established to simulate the droplet freezing behaviors using the Solidification/Melting model. Experiments are conducted on both hydrophilic and hydrophobic surfaces for 5, 10, 20, 30 and 40 μL supercooled water droplets. The droplet freezing behaviors including the freezing front movement and freezing time are observed using the image recognition technology. The evolution of the freezing front calculated by the numerical model agrees better with the experimental observation than the traditional model that ignores the supercooling effect or uses the initial droplet profile. The model reduces the deviation of freezing time from about 30% to about 10% for both hydrophilic and hydrophobic surfaces. With use of the average value of the freezing times yielded by the numerical and theoretical models, a correlation is developed for predicting the freezing time. It can correlate more than 90% of the simulation data and all of the experimental points within ±25%. As the cold plate temperature, droplet volume and contact angle increase, the freezing time increases, with the plate temperature and contact angle possessing a more significant influence than the droplet volume on the freezing process.

For poor high-temperature performance of power battery utilized in electric vehicles, a battery thermal management system (BTMS) functioned as reducing battery’s temperature is indispensable. This work designs a serpentine-channel cold plate as cooling unit of fluid BTMS, and a parameterized U-tube representing a part of serpentine-channel in cold plate is created. A thermal resistance model, as well as an objection function f1 based on it, is developed to characterize thermal performance of cold plate. This study using theories of friction loss and excess loss defines a pressure loss model of cold plate based on the parameterized U-tube. After a series of simulations performed on different U-tube with varying structural parameters, combining with pressure loss model, objective function of pressure loss f2 is obtained. By calculating f1 and f2, the laws of thermal performance with pressure loss and the optimum structure of the serpentine-channel cold plate can be obtained. This work provides a simple way to design the structure of the fluid cold-plate BTMS with optimum thermal performance and minimum pressure loss.

In this paper, three liquid-cooled cold plate structure schemes of the thermal control unit for an indirect single-phase liquid-cooled server were proposed in this paper. The mesh independence was validated and thermal simulations were completed for different schemes based on the same boundary conditions, then effects of fin geometrical parameters on pressure drop and heat transfer characteristic were investigated. Furthermore, an optimization was performed with goal of reducing pressure drop and weight based on the optimal liquid-cooled cold plate with 2mm diameter circular fins, pressure drop is lower 6.1%, the weight is lower 12.2% compared with the primal model.

This paper deals with the experimental and numerical investigations of seven integrated circuit (IC) chips cooled using the water flowing inside the cold plate at different flowrates. The study includes the supply of three different heat input cases under four different flowrates (0.063 kg/s, 0.125 kg/s, 0.25 kg/s, and 0.5 kg/s) to cool the high heat-generating IC chips mounted on the SMPS board at various positions. The optimal configuration (71-11-74-76-65-24-15) for the arrangement of the 7 IC chips is considered for the analysis. The numerical simulations are carried out using the commercial software ansys fluent (R-16) to support the experiments. Both the results (IC chips temperature) agree with each other in the error band of 8–14%. The smallest chip U6 attains the maximum temperature, as its heat attenuation rate is very high. The water flowing inside the cold plate absorbs the heat from the IC chips; by increasing the flowrate (Reynolds number increases), there is an increase in the convective heat transfer coefficient of the chips (Nusselt number increases) and ultimately cools these faster. A correlation is proposed for the Nusselt number of the chips with the Reynolds number of the flow. The results suggest that the liquid cold plate plays a vital role in the cooling of the IC chips and leads to better thermal management.

One of the main goals of a pumped two-phase flow cooling system is to ensure that there is a two phase flow at the exit of the cold plate so that the heat transfer coefficient remains very high. To decrease the mass flow rate but still prevent dryout, there is a motivation to maintain the exit quality at roughly 0.6 to 0.7 for an unknown time-varying heat load. In this paper, a simple output feedback control algorithm is proposed to achieve this goal. A nonlinear model based on the conservation of mass, momentum, and energy is used. Steady state solutions and their stability are analyzed. Results from numerical simulations with R134a flow corroborate the validity of the proposed novel feedback control algorithm.

Effective thermal management is critical to the performance and durability of lithium-ion batteries for electric vehicles. As an alternative to conventional cold plates with straight channels, a new cold plate with divergent-shaped channels has been proposed to minimize the maximum temperature and pressure drop. Compared with conventional straight-shaped channels, the divergent-shaped channels exhibit enhanced performance with a higher heat dissipation capacity and lower frictional resistance. To further reduce the local flow resistance, divergent-shaped channels with two inlets and one outlet have been evaluated. This new design can successfully decrease the pressure drop by 7.2% and decrease the maximum temperature difference from 3.99 to 3.19 K. Finally, battery cooling modules with a counter-flow configuration have been constructed, which achieve a smaller maximum temperature difference. This work contributes to the development of effective and efficient battery cooling systems for electric vehicles.

To accurately control the frosting process, analyzing the influence of different factors on frosting is meaningful and challengeable, especially in the early frosting stage. According to the sensitivity analysis, the influence of different surface wettability and environmental factors on the growth of frost layer were quantitatively analyzed. Based on the experimental data on cold plate surface under forced convection conditions, new models with emphasis on the initial conditions of the frosting process are developed. Results show that supersaturation degree, supercooling degree and cold plate temperature are the key factors on the growth of frost layer, but their specific influence varies in the early frosting stage. And proportions of these three factors reach 39.42%, 35.58% and 21.15%, respectively. The coincidence rates of the new models with an error of 15% reach>90% for the whole frosting process, and 83% for the early frosting stage. Compared with previous models, the coincidence rates of the new models for the whole frosting process and the early frosting stage are increased by at least 8.86% and 15.28%, respectively. Contributions of this study are expected to predict the growth of frost layer in the early frosting stage and provide a reference for the optimal defrosting control of air source heat pumps.

In this paper, a numerical model using ANSYS Fluent for a minichannel cold plate is developed for water-cooled LiFePO4 battery. The temperature and velocity distributions are investigated using exp...

This paper designs a microchannel liquid cold plate suitable for array multi-chip cooling. The influence of aspect ratio of rectangular cross section on heat transfer and flow performance of microchannel cold plate was studied by numerical analysis. The optimal ratio of height to width of rectangular section is selected and its structure is optimized. The results show that when the equivalent diameter of rectangular cross-section is fixed, the friction coefficient f and Nusselt number Nu increase with the increase of aspect ratio of rectangular cross-section; after optimizing the structure of the channel, the microchannel cold plate exhibits good heat transfer characteristics of low pressure drop, realizing effective heat dissipation and meeting the requirements of pressure drop.

A frost model for predicting frosting behavior under cryogenic conditions was developed. The frosting behavior was visualized through numerical analysis, and the results were compared to experimental data to confirm the validity of the model. It was shown that under cryogenic temperatures, a considerably low-density frost layer was formed owing to the frosting mechanism, which was sublimation-dominant frosting, rather than conventional condensation-freezing. It was qualitatively confirmed through experiments that low-density frost formed near the frost surface, and high-density frost formed near the cryogenic cold plate. Furthermore, the frost density distribution of the interior frost was quantitatively analyzed through a numerical analysis. The surface temperature of frost was seen to rise rapidly during the initial stage of frosting. Thus, it is possible to estimate the time at which the frosting mechanism changes from sublimation to condensation-freezing.

A computational fluid dynamics (CFD)-based model to predict macroscopic and local frost behaviors on a cold plate is described. The model was validated by comparing its results with a range of experimental data. The effects upon the model of various factors that affect frost formation were studied, including the inlet velocity, relative humidity, and cold plate temperature; the numerical predictions agreed very well with experimental data, with a maximum deviation of 0.3 mm in the average frost thickness. Similarly, the modeled average frost density was in good agreement with experimental data, with an error of 10% after 60 min and a maximum error of 25% during the early stages of frost formation. The model outlined herein is able to describe the localized details of frost growth, including the distribution of frost density and the absolute humidity along the y -axis, in contrast to existing approaches.

This manuscript compiles both theoretical and experimental information on contact freezing with the aim to better understand this potentially important but still not well quantified heterogeneous freezing mode. There is no complete theory that describes contact freezing and how the energy barrier has to be overcome to nucleate an ice crystal by contact freezing. Experiments on contact freezing conducted using the cold plate technique indicate that it can initiate ice formation at warmer temperatures than immersion freezing. Additionally, a qualitative difference in the freezing temperatures between contact and immersion freezing has been found using different instrumentation and different ice nuclei. There is a lack of data on collision rates in most of the reported data, which inhibits a quantitative calculation of the freezing efficiencies. Thus, new or modified instrumentation to study contact nucleation in the laboratory and in the field are needed to identify the conditions at which contact nucleation could occur in the atmosphere. Important questions concerning contact freezing and its potential role for ice cloud formation and climate are also summarized., Atmospheric Chemistry and Physics, 13 (19), ISSN:1680-7375, ISSN:1680-7367

This study compares three different liquid cooling technologies to determine which of the three methods is able to cool the highest power density processor chips.

A compact thermal model was established to model thermal characterization of a microchannel cold plate for high temperature uniformity in multiple heat sources. Analytical calculation of the compact model was presented. Experiments were also conducted to validate the model. The comparison reveals that the measured temperatures are close to the ones predicted by the compact thermal model. The cold plate can help multiple heat sources achieve high temperature uniformity, and the maximum temperature difference among the heat sources is 1.3 °C in the present experimental cases. Moreover, a straight minichannel cold plate was designed and tested under the same flow rate. The measured results show that there exists relatively large temperature gap among the heat sources, and the maximum value is 6.7 °C.

This study examines the refrigerant distribution of a dual cold-plate system subject to the influence of heating load and inlet configurations. Three inlet configurations, namely, uniformly divided, side-entrance, and inlet inclination, are examined. For an unequal heating load for both uniformly divided and side-entrance configurations, it is found that the distribution of mass flow rate subject to the influence of heating load is strongly related to the outlet states of the two cold plates. For the condition where one of the cold plates is in a superheated state while the other is in a saturated state, the mass flow rate pertaining to a fixed heating load is lower than that of a smaller heating load, and the difference increases significantly when the heating load gets smaller. For the condition where both outlet states of cold plate are at superheated states, the mass flow rate for the fixed heating load is about the same for the uniformly divided configuration and is marginally higher than that of the...

A novel cooling design featuring a two-stage expansion process is proposed in this study. Without any help from insulation, the design can minimize or even entirely eliminate condensate formation outside the cold-plate surface even for a very low evaporation temperature. The design incorporates a double-pipe inlet/outlet and a two-container cold plate, and its performance is compared to a conventional cold plate. For the conventional cold plate, the outlet pressure/temperature hold quite steadily at a light heat load, and the outlet pressure/temperature shows a substantial rise when the refrigerant is completely evaporated. The outlet pressure/temperature of the condensate-free cold plate shows an opposite trend at a heavy heat loading. The benefit of this characteristic is that the wall surface temperature and the outlet temperature of the cold plate can be maintained comparatively more steady than the conventional cold plate.

A numerical solution of the natural convection heat transfer between two cold and hot isolated vertical plates is presented for different horizontal and vertical location ratios of an enclosure. Results show that: a) flow configurations of cold and hot plates are different; b) the increase of vertical location ratio, toward that corresponding to the enclosure middle value, is considerably diminishing the temperature differences between heating and cooling conditions; c) the effect of vertical location ratio variation is more prominent on heat transfer for cold and hot plates than that of the horizontal location ratio variation; d) the average Nusselt number, obtained from the hot isolated plate, is 20–39% larger than that of the cold plate under the same conditions when the isolated plate varies horizontally; e) for a narrow distance between the inner plate and the bounding wall, the inner plate Nusselt number is enhanced, but aside from this, the plate average Nusselt number is insensitive to the plate p...

Experimental study is performed to analyze the shear driven droplet shedding on cold substrates with different shear flow speeds typical of those in the flight conditions. Understanding the mechanism of simultaneous droplet shedding, coalescence and solidification is crucial to devise solutions for mitigating aircraft in-flight icing. To mimic this scenario experimental set up is designed to generate shear flow as high as 90 m/s. The droplet shedding at high speed is investigated on a cold surface (0 and −5 °C) of different wettabilities ranging from hydrophilic to superhydrophobic. Result analyses indicate that on a hydrophilic substrate, the droplets form a rivulet which then freezes on the cold plate. In contrast, on the superhydrophobic surface, there is no rivulet formation. Instead, droplets roll over the substrate and detach from it under the effect of high shear flow.Copyright © 2014 by ASME

A mathematical model for the optimization of ice making in a laminar falling film is presented. The model is first validated, and a series of numerical experiments are conducted to assess the effects of the mass flow rate, the inlet water temperature and the length and temperature of the cold plate on ice accumulation. The results are then correlated in a simple algebraic expression for the frequency of the intermittent freezing and removal cycle that maximizes the production of ice. Applying this calculation procedure to a commercial system, it is shown that the same amount of ice can be produced in a time interval more than six times shorter.

The subject of this paper is the presentation of a simple theoretical model of cooling of a semiconductor. The problem of the unsteady behaviour both of the semiconductor and of the cold plate that are in touch by the contact layer was studied analytically. The influence of the parameters of the materials and the cooling conditions was investigated. The results in the form of an analytical formula and graphs are presented and the heat stream is compared with the experimental results.

A mathematical model is presented to predict the frost properties and heat and mass transfer within the frost layer formed on a cold plate. The model consists of the laminar flow equations for air-side and the empirical correlation of local frost density. The correlation of local frost density used in this study is obtained from various experimental conditions by considering frosting parameters. The numerical results are compared with experimental data to validate the model, and agree well with experimental data within a maximum error of 9%.

This paper presents the results of velocity measurements of natural convection in symmetrically and asymmetrically heated vertical channels. In the first case of symmetrical flow, the two channel plates were both kept at a constant temperature higher than the ambient. In the second case of asymmetrical flow, one plate was kept at a temperature higher than the ambient temperature while the other plate was kept at a temperature lower than the ambient temperature. The velocity measurements were performed using a Laser Doppler Anemometer. In the case of symmetrical flow, the results indicate a reverse flow region located at the center of the channel close to its exit. In the case of asymmetrical flow, the results show that the flow accelerates up the hot plate and decelerates down the cold plate. The results also indicate that cooling one of the two plates below ambient influences the flow pattern significantly and results in the formation of a small reversed vortex at the center of the channel.

A drop of water deposited on a cold plate freezes into an ice drop with a pointy tip. While this phenomenon clearly finds its origin in the expansion of water upon freezing, a quantitative description of the tip singularity has remained elusive. Here we demonstrate how the geometry of the freezing front, determined by heat transfer considerations, is crucial for the tip formation. We perform systematic measurements of the angles of the conical tip, and reveal the dynamics of the solidification front in a Hele-Shaw geometry. It is found that the cone angle is independent of substrate temperature and wetting angle, suggesting a universal, self-similar mechanism that does not depend on the rate of solidification. We propose a model for the freezing front and derive resulting tip angles analytically, in good agreement with observations., Comment: Letter format, 5 pages, 3 figures. Note: authors AGM and ORE contributed equally to the paper

A compact thermal model for multiple heat sources mounted on minichannel cold plate to achieve high temperature uniformity was presented in the authors’ previous work. In this paper, based on this compact thermal model, a fractal tree-like minichannel cold plate was designed and fabricated to obtain high temperature uniformity, and its thermal performance was tested under different working conditions by experiments. The comparison reveals that the measured temperatures are close to the ones predicted by the compact thermal model. The cold plate designed based on the compact thermal model can help multiple heat sources achieve high temperature uniformity, and the maximum temperature difference among the heat sources is 1.3 °C. Moreover, a straight minichannel cold plate was designed and tested under the same conditions. The measured results show that there exists relatively large temperature gap among the heat sources, and the maximum value is 6.7°C, which is much higher than 1.3 °C in the fractal tree-like minichannel. Therefore, the fractal tree-like microchannel or minichannel cold plate has an advantage over the straight one in obtaining temperature uniformity for multiple heat sources.Copyright © 2013 by ASME

The behavior of particles under thermophoretic effect was examined experimentally by getting rid of the effect of natural convection utilizing microgravity environment. The microgravity environment was realized by using a drop tower facility. In this system, measurement fields with temperature gradient were established between two metal plates. In order to provide a steep temperature gradient within a limited experimental duration, the preheated metal plate was forced to approach the cold plate quickly after the microgravity environment was established. Temperature distribution and the behavior of individual particles were observed simultaneously. The fields in an almost steady state with monotonic temperature gradient were obtained. In these fields, no other forces than thermophoretic force which might induce the particles movement were confirmed to exist. The fields ideal for the measurement of the thermophoretic effect were obtained in our experiments. The measured thermophoretic velocities were found ...

Containerless solidification, in which the melt is confined by its own surface tension, is an important technique by which very pure materials can be produced. The form of the solidified product is sensitive to conditions at the tri-junction between the solid, the melt and the surrounding vapor. An understanding of the dynamics of tri-junctions is therefore crucial to the modelling and prediction of containerless solidification systems. We consider experimentally and analytically the simple system of a liquid droplet solidifying on a cold plate. Our experimental results provide a simple test of tri-junction conditions which can be used in theoretical analyses of more complicated systems. A new dynamical boundary condition at the tri-junction is introduced here and explains the surprising features of solidified water droplets on a cold surface.

A novel design featuring a two-stage expansion process is proposed in this study. Without any help of insulation, the design can minimize or even entirely eliminate the formation of condensate in the cold-plate surface for a typical refrigeration system. The design incorporates a double-pipe inlet outlet and a two-container cold plate. A detailed comparison is also made amid conventional cold plate and the present condensate-less cold plate. For the conventional cold plate, it is found that the refrigerant mass flowrate is almost unchanged with respect to heating load. However, a slight decrease of mass flowrate for the present condensate-less cold plate is seen due to additional expansion/contraction/friction loss occurring in the first container. In addition, the decay in mass flowrate results in a gradual decline of outlet temperature that is opposite to the conventional cold-plate design.

This study examines the refrigerant distribution of a dual cold plate system subject to the influence of heating load using a R-134a based vapor compression system with a nominal capacity ranging from 50∼250 W. The cold plate is of identical configuration. Initially, test is performed under an equal heating load for each cold plate (70 W) which then gives rise to a uniform distribution and equal outlet superheat condition. For an unequal heating load, it is found that the distribution of mass flowrate subject to the influence of heating load is strongly related to the outlet states of the two cold plates. For the condition where one of the cold plate is in superheated state while the other is in saturated state, the mass flowrate for the fixed heating load is lower than that of smaller heating load, and the difference increases when the heating load gets smaller due to the influence of accelerational pressure drop. A maximum of 17% difference is seen at a loading ratio of 0.571 (40W/70W). For the condition where both outlet states of cold plate are at superheated states, the mass flowrate for the fixed heating load is marginally higher than that of the smaller heating load, and the difference is insensitive to the rise of heating load. For this situation, the effect of accelerational pressure is negligible, and it is mainly attributed to two-phase/single-phase distribution pertaining to the effect of heating load.Copyright © 2008 by ASME

The electronic circuit simulator PSpice can provide the means of obtaining numerical nonanalytic solutions to thermal heat flow problems which would otherwise be difficult or impossible to derive. Rules for relating physical heat flow parameters to equivalent distributed lossy transmission line parameters are derived. This method for numerical evaluation of the heat dissipating performance of complicated fin structures forming cold-stacks is validated by comparison with recently published analytic solutions for double stack cold plates.

The form of the solidified product in containerless solidification is sen-sitive to conditions at the tri-junction between the solid, the melt and the surrounding vapor. We consider experimentally and analytically the simple system of a liquid droplet solidifying on a cold plate. As opposed to the one-dimensional analysis of Anderson et al. (1996), our axisymmetric boundary integral analysis shows that a simple non-dynamic condition at the tri-junction is sufficient. A simple static zero growth angle of zero along with a fluid that expands upon freezing produces a frozen drop that has an inflection point near a cusp that forms at the symmetry axis. Some dynamics of the droplet are considered with discussion of possible micro droplet ejection at the final moment of solidification.

The present paper evaluates the most important experimental thermal characterisation techniques for electronic components. Weak points are indicated in the standardised methods for the still air, cold plate and fluid bath environment. Improvements have been developed: Suitable measures determine well-controlled surface temperature profiles over the whole component surface in the double cold plate. Two impinging jets impose reproducible heat transfer coefficients in the fluid bath method. Hence, the reproducibility, the scope and the accuracy of the measurements are enhanced.

Simulation of frost formation process on cold surface is carried out based on fractal theory combined with phase change dynamics. Before frosting, the phenomena of vapor condensation, droplet growth and frozen on cold plate are successfully simulated based on phase change dynamics and then a fractal simulation of the frost formation and growth process over the frozen droplets is carried out based on diffusion limited aggregation (DLA) model. The simulation results accord well with the experimental results. The time when the condensation droplets are present and frozen on the surface during simulation process is nearly the same as the experimental result. Before the droplets are frozen, the trend that the surface contact radius of the droplet varies with condensation time is similar to actual one. The simulation results also show that the thickness of frost layer is nearly equal to the measured value. By that means, the feasibility of this method of simulating the frost formation is verified and the new attempt made to foster the combination between fractal theory and phase change dynamics is of great significance. This study also provids a foundational theory work for a more reasonable and accurate frosting process model.

We report comprehensive measurements of interfacial properties as well as observations of new behavior at the cellular interface in directionally solidifying succinonitrile. Observations of the bifurcation from the planar state in samples ≥ 100µm thick show that the initial instability occurs first along the shortest dimension of the interface. This raises questions about the applicability of many conventional descriptions of patterns that rely on two-dimensional diffusive fields. We also describe new instabilities related to wavelength selection in cells and droplet formation at their roots.

The transient heat transfer rate from a free-falling large drop of molten lead to a cold plate surface maintained at about room temperature was experimentally estimated by solving the inverse heat conduction problem, taking into account the time variation of the area covered by the drop. Furthermore, the change with time in thickness of the solidification layer formed within the drop was estimated on the basis of a few assumptions and the cooling condition required to obtained a high cooling rate was found.