Frost Formation Research Articles

Experimental and numerical investigation of frost formation on an array of square fins under natural convection condition

The numerical and experimental processes of frost formation on square-finned tubes in natural convection are investigated in the current study. The frost growth survey on these types of finned tubes is beneficial and necessary to understand heat and humidity control phenomena due to low operating temperature. By using cooling, heating, and humidification devices, controlled conditions such as relative humidity between 50% to 70%, ambient air temperature between 20 °C to 30 °C, and an average refrigerant temperature between −20 °C to −10 °C are changed. The results include frost thickness, density, and heat transfer consequences under various ambient temperature conditions, average refrigerant temperature, and humidity. Based on empirical measurements, the frost accumulated on top of the fin is higher than the bottom, and frost is formed only on the fins' edge and blocks the flow path and short space between the fins. The computational fluid dynamics method is applied to predict the flow field and frost growth on the fins. Comparison between numerical results and experimental data shows that the current numerical method can be utilized more effectively to find out the frost behavior. According to the measurements, correlations are presented for frost growth.

Division of Frosting Type and Frosting Degree of the Air Source Heat Pump for Heating in China

The frosting type and frosting degree of the outdoor heat exchanger of air source heat pump (ASHP) in the heating season are greatly affected by the local environmental temperature and humidity. China has a vast territory, and the climate varies greatly in different regions. Therefore, when the ASHP is running in different climate zones for heating in winter, there are significant differences in the frosting type and frosting degree. In order to achieve deeper understanding of frost formation and provide more accurate guidance for the suitability application of antifrosting and defrosting technologies, a study on the division of frosting type and frosting degree was performed in this work. Based on the three-phase diagram of water and combined with the theory of phase change dynamics, the outdoor heat exchanger of the ASHP in the heating season was divided into four states: neither frosting nor condensation, condensation, condensation frosting, and sublimation frosting, and the proportion of each state in a typical city in different climate zones was calculated. The results showed that more than 80% of the heating seasons in Nanjing, Shanghai, Wuhan, Changsha, Xi’an, and Harbin had the frosting phenomenon. Sublimation frosting was the main frosting type in Xi’an, Beijing, and Harbin, while Chongqing was all condensation frosting. Moreover, a frosting model was developed and the frosting degree was divided into mild frosting, moderate frosting, and heavy frosting, according to the performance attenuation of the ASHP under frosting conditions. The proportion of each frosting degree in a typical city was achieved. About 50% of the heating seasons in Nanjing and Changsha were distributed in the heavy frost area and 100% in Chongqing.

Mathematical Model for Frost Formation on Plane Surface.(Dept.M)

Suggested model covers the necessity of calculating the effect of frost formation, on the evaporator wall in cooling storage rooms, on the heat transfer efficiency between refrigerant and wet air. In it obtained analytical relationships for temperature distribution in both wall material and frost layer, overall heat transfer coefficient and the time of frost layer formation as a function of frost layer thickness.

Recent trends in hydroclimate and groundwater levels in a region with seasonal frost cover

In cold climate, the main annual recharge event is spring snowmelt. Projections of groundwater storage hence depend on winter hydroclimate. Winter recharge is a factor of rain, melt and ground frost. Increases in winter rain and melt have already been observed. However, due to complex processes involved in ground frost formation and its natural patchy coverage, the effect of ground frost on recharge is poorly understood.The objective of the study is to improve the understanding of the connection between groundwater storage and hydroclimate in Sweden and Finland, a region with temperate and cold climate, from a seasonal frost cover perspective. In the study, annual, frost-free season and frost season temperature and precipitation trends in the climate regions are compared between one global and two regional reanalysis datasets. Effective precipitation and wet day frequency trends between 1980 and 2010 are compared to groundwater level trends for the same period. Trends are calculated using the Mann-Kendall test and Sen’s slope.The results show that the region is generally experiencing warming and increased precipitation. These trends are strongest in the frost season. Further, the global dataset systematically underestimates median temperatures and precipitation compared to the regional datasets. Effective precipitation trends are generally weak, and indicate wetting in the frost season and drying in the frost-free season. Wet day frequency trends are decreasing significantly on the regional scale in Finland, but with nearly no trends in Sweden. Groundwater levels in southern Finland and southeastern Sweden are declining significantly, while groundwater levels in southwestern Sweden are significantly rising. The results indicate that groundwater trends in southern Finland are linked to wet day frequency and effective precipitation trends in the frost-free season, and that trends in the frost season have no impact on annual groundwater level trends. In southern Sweden, groundwater level trends appear linked to annual and frost-free season trends in effective precipitation, though insignificantly. These trends may be explained by century-scale trends in precipitation drought indices identified by previous studies.

Two-dimensional simulation of frost formation on the NACA0012 airfoil under strong convection by using the p-VOF method

A newly developed frosting simulation method, p-VOF method, is applied to simulate the dynamic frost formation on the NACA0012 airfoil under strong convection. The p-VOF method is a pseudo VOF method of the multiphase flow simulation with phase change. By solving a simplified mass conservation equation explicitly instead of the original volume fraction equations in CFD software, the efficiency and robustness of calculation are greatly improved. This progress makes it possible to predict a long-time frost formation. The p-VOF method was successfully applied to the simulation of dynamic frosting on the two-dimensional NACA0012 airfoil under strong convection conditions with constant frost physical properties. The simulation result shows that the average thickness of the frost layer increases, and the frost bulges and flow separation appear earlier, when the airfoil surface temperature decreases or the air humidity increases. The frost bulges and flow separation appear earlier, when the air velocity is faster, the growth rate of the frost layer at the early stage is greater, but the final frost layer is thinner.

Dimensionless Model of Frost Roughness on Cold Flat Plate Under Forced Convection

Laboratory experiments were conducted to generate empirical dimensionless correlations for estimating surface roughness of frost formed on a cold flat plate under forced convection. Environmental variables, including wall temperature , air velocity , relative humidity , and air temperature , were considered when generating the correlations. The test conditions were chosen to simulate the environmental conditions experienced by cold-soaked fuel frost formation on the upper surface of airplane wings. Experimental conditions included wall temperatures from to , freestream temperatures from 8 to , relative humidities from 60 to 91%, and air velocities from 0.5 to . The root-mean-square height, skewness, and equivalent sand-grain roughness height of frost were correlated as functions of the Reynolds number, absolute humidity, and dimensionless temperatures. The comparison between the correlation of frost equivalent sand-grain roughness height in this study and a previous model revealed the importance of test surface geometry on frost roughness formation.

Effects of frost formation on the ice adhesion of micro-nano structure metal surface by femtosecond laser

In this work, we study the effect and evolution of frost condensation on the ice adhered micro-nano structured Ni metal surface. By measuring the ice adhesion strength to the porous-structured surface under different frosting coverage, it is found that the ice adhesion on the surface changes not only with the morphology but also with the different evolution stages of the frosting coverage. Combining the changes in surface morphology and low-temperature wettability, the reasons for the changes in the ice adhesion strength are attributed to the change of wettability of the porous-structured surface under different frosting coverage, which affects the infiltration state of the surface and results in different mechanical interlocking, air-pockets and cracks states at the ice-solid interface. Moreover, it is found that the ice adhesion strength of the hydrophobic and hydrophilic porous-structured surface tends to be the same when the surface is heavily frosted. In addition, we demonstrate that both the hydrophobic and hydrophilic columnar-structured surfaces have smaller ice adhesion strength than the original surface without any micro-nano structures regardless of whether the surface is frosted or not, and the measured lowest ice adhesion strength of the hydrophobic columnar-structured surface can be down to 30 kPa in all frosted evolution stages, which is less than one tenth of the original surface. The findings in this work suggest that the influence of frosting should be fully considered when designing the icephobic micro-nano structured metal structure, and it can further serve as an important guidance for the design of passive icephobic surfaces expected to be free from the frosting effect.

The Influence of Electroconvection on The Efficiency of Finned Air Coolers under Condition of Frost Formation.(Dept.M)

The Influence of Electroconvection on The Efficiency of Finned Air Coolers under Condition of Frost Formation.(Dept.M)

Effect of heat transfer area distribution on frosting performance of refrigerator evaporator

The present study investigates the effect of the distribution of available heat transfer area on the thermohydraulic behavior of a typical fin-and-tube type evaporator used in a domestic frost-free refrigerator. Previous studies in the literature have not explored the effect of the number of fin rows and fin pitch distribution across the fin rows on the performance of fan-supplied evaporator geometries under frosting. The present study attempts to address this by developing a thermohydraulic model of the evaporator to predict the heat transfer rate, pressure drop and frost formation. A distributed evaporator model is developed by dividing the evaporator into individual control volumes and the balance equations are applied along with a suitable semi-empirical frost growth model to predict the rate of frost formation. Experiments were performed in a purpose-built test facility to validate the numerical model. The developed model is employed to compare different heat exchanger geometries with a constant area but varying in total fin rows and fin pitch distribution. Results show that distributing the available heat transfer area among a higher number of fin rows results in longer successive defrost intervals. However, the evaporator occupies more volume. For a given heat transfer area and fin rows, longer operating time can be achieved by selecting fin pitches that provide uniform blockage ratio across the fin rows. It is observed that for a specific fin pitch at the leading row, reducing the fin pitch linearly across the fin rows resulted in uniform blockage ratio across the fin rows.

Image processing for frost thickness measurement in fin-and-tube heat exchangers

In studies addressing performance degradations owing to frost formation on heat exchangers, the frost thickness is considered an important parameter. The most commonly used method for measuring frost thickness comprises capturing and analyzing an image. However, relatively few studies have investigated the most reasonable method for deriving frost thickness by analyzing an image. In current measurement techniques, it is difficult to quantitatively determine which methods have less error relative to the true value in a complex shape. Therefore, this study attempted to recommend a more reasonable method, based on analysis of various aspects. First, the fundamental concept of image processing was described in detail. Then, the effects of thresholding algorithms, threshold application algorithms, and the determination of the number of segments on the frost thickness were investigated. Based on the results, an appropriate image processing method for measuring frost thickness was recommended. The frost thickness obtained by this method was well-measured, with an uncertainty of approximately 0.18 mm.

A CFD model of frost formation based on dynamic meshes technique via secondary development of ANSYS fluent

To simulate the non-uniform frost growth in flow direction for humid air flowing through a freezing channel, a 2D numerical frosting model based on dynamic meshes technique is developed in the current work via the secondary development of commercial ANSYS Fluent. The computation domain consists of both frost layer and humid air regions, and the local heat and vapor fluxes at the surface of frost layer are determined by numerical temperature and vapor fraction fields in the humid air region rather than by empirical correlations. The frost layer is treated as a growing packed bed with heat and mass transfer dominated by molecular diffusion, where local absorption coefficient of vapor desublimation and local vapor fraction are both determined by solving the pseudo steady vapor diffusion equation with a source term theoretically. The interface of frost layer and humid air regions is treated as two walls for the iteration of its temperature, of which the humid air side is specified with the temperature equal to the frost-side counterpart and the frost side takes the heat flux including the extra latent heat caused by vapor deposit. User-defined functions are compiled to implement the above treatments to ANSYS Fluent. Frosting experiments in the literature are simulated with the current model for validation. How the profile of frost layer evolves with time in the frosting process is explored. The contours and profiles of velocity, temperature and vapor fraction are presented to discuss the effects of heat and mass transfer on frost formation. Numerical results demonstrate that the proposed CFD model can predict the frost growth and densification with a relative deviation less than 5% compared with experiments. Besides, the computation load of current model is small due to no solution of complex multiphase flow. In addition, dynamic meshes help current model to capture the interface of frost layer and humid air regions accurately.

Impact of propylene- and ethylene glycol-based deicing materials on the environment and airports infrastructure

Snow, frost and ice formations on aircraft surfaces have a negative impact on aerodynamic and operational properties of aircraft. Ethyleneglycol and propyleneglycol are the most used components of liquids for aircraft deicing that have an environmental impact. Deicing agents are toxic and pollute the environment when they enter soil or water bodies. These substances evaporate during the treatment of aircraft and in the case of ethylene glycol have an unpleasant dizzying odor that enters the air and is carried by air currents. Deicing materials can cause problems with corrosion of maintenance materials (aircraft skin, engine blades, aerodrome coating, etc.). The article analyzes a large amount of domestic and foreign technical and regulatory information, which allowed a comprehensive comparison of physicochemical and operational properties of propylene- and ethylene glycol-containing deicing materials, as well as to investigate their impact on ecosystem components, including the humans. Comparative studies show that propylene glycol is inert to living organisms and humans. Ethylene glycol adversely affects reproductive function, metabolism, immune system and reduces haemoglobin. The LD50 (total toxicity indicator) of ethylene glycol is more than 4 times lower compared to propylene glycol, which confirms the extremely high toxicity of ethylene glycol and deicing substances containing it. Propylene glycol-based deicing fluids are more environmentally friendly due to low toxicity, increased biodegradation under the same operational requirements

휜-튜브 열교환기에서 초발수 코팅의 적용이 착제상 거동에 미치는 영향

The formation and growth of frost in refrigerating systems can cause degradation of the system’s performance. Since super-hydrophobic coating technology can delay frost growth, it has received much attention. However, only a limited number of studies have investigated effects of super-hydrophobic surfaces on frost growth. Therefore, this study investigated effects of surface characteristics on frost behavior of heat exchangers. Heat exchangers with bare, hydrophobic, and super-hydrophobic surfaces were tested. Their frost retardation capabilities were evaluated by comparing the time taken for the air flow passage to be blocked. Super-hydrophobic surfaces delayed the time by an average of 61% compared to bare surfaces. Effects of surface characteristics on heat transfer rate and pressure drop of the heat exchanger were also evaluated. Super-hydrophobic surfaces increased the average heat transfer rate by 6.73% and decreased the average pressure drop by 41.6% compared to bare surfaces. In the defrosting process, super-hydrophobic surfaces decreased the defrost energy by an average of 24.9%.

An insight into the estimation of frost thermal conductivity on parallel surface channels using kernel based GPR strategy

In heat exchange applications, frost formation on the cold surface causes a decrease in the rate of heat transfer and growth in the pressure drop. Thus, the study on the frost thermal conductivity has a significant and vital place for the engineers and researchers dealing with the heat exchangers. In the literature, there is a lack of accurate and applicable methods for determination of frost thermal conductivity. Additionally, the high cost and difficulties of experimental works clarify the importance of computational and mathematical methods. The errors in the determination of frost thermal conductivity on parallel surface channels can cause inaccuracy in estimations of frost density and thickness. The main aim of present work is suggesting Gaussian Process Regression (GPR) models based on four different kernel functions for the estimation of frost thermal conductivity in terms of time, air velocity, relative humidity, air temperature, wall temperature, and frost porosity. To achieve this purpose, a total number of 57 frost thermal conductivity values has been collected. Comparing the suggested GPR models and other available computational methods express the quality of the developed models. The best predictive tool has been selected as a GPR model, including Matern kernel function with R2 values of 0.997 and 0.994 in training and testing phases, respectively. In addition, the effectiveness of discussing variables on frost thermal conductivity has been investigated by sensitivity analysis and showed that air temperature is the most effective parameter. The present work gives engineers an insight into frost thermal conductivity and the effective parameters in its determination.The significant advantage of present work is the accurate prediction of thermal conductivity by a brief knownledge in artificial intelligence.

Superhydrophobic heat exchangers delay frost formation and enhance efficency of electric vehicle heat pumps

The number of electric vehicles has rapidly expanded as high-performance automotive lithium-ion batteries have become more affordable. However, the range of electric vehicles decreases in cold climates partly because of the additional thermal loads associated with cabin heating. One way to improve the efficiency of cabin heating is to replace resistive heating elements with an air-source heat pump system. However, to gain the full benefit of heat pumping, frost formation on the outdoor heat exchanger must be minimized. In this work, we modified the surface wettability of aluminum louvered-fin automotive heat pump evaporators and tested them under realistic operating conditions in a transcritical carbon dioxide (CO2) heat pump. Each heat exchanger underwent several consecutive frosting and defrosting cycles to understand the cyclic performance of the system. The heat exchanger with a superhydrophobic outer surface was able to delay frost formation and maintain higher heat transfer rates when compared to heat exchangers with higher surface energies (hydrophilic). The delayed frost formation resulted in a system efficiency benefit in the first few frosting cycles but diminished in later cycles due to water retention and incomplete defrosting. However, for most automotive applications the superhydrophobic heat exchanger showed substantial benefits for normal driving trips. The scalable and optimized superhydrophobic heat exchangers developed here have the potential to increase the efficiency of automotive heat pumps and consequently increase the range and reduce energy consumption of electric vehicles.

Anti-icing properties of femtosecond laser-induced nano and multiscale topographies

Surfaces covered with micro, nano and multiscale topographies are the subject of significant interest due to their ice-repellency properties in the last decade. Ultrafast laser processing is becoming a widely used clean manufacturing technique to fabricate ordered nano and multiscale topographies on metallic surfaces over relatively large areas. In this work, single-tier nano and two-tier multiscale topographies were fabricated on stainless steel surfaces with one-step femtosecond laser processing to impart anti-icing response. Droplet freezing and frost formation on laser treated surfaces were examined at −10 °C and compared with the lubricant-impregnated and superhydrophobic nanoparticle-coated ones. While the hydrophilic nanoscale topography has accelerated the droplet freezing and performed worse than untreated surfaces, their hydrophobic counterparts increased the time to freezing by nearly two times. Overall, the superhydrophobic two-tier multiscale topography has significantly delayed both the droplet freezing time and frost formation on surfaces. Furthermore, the two-tier multiscale topography has sustained its anti-icing response even after being subjected to 25 abrasion cycles, while the surfaces with only nanoscale topography and nanoparticle-coating lost their functionality in only 10 cycles. Therefore, such robust two-tier multiscale topographies devoid of any coatings can enable and underpin many industrial applications where ice accumulation on surfaces results in performance degradation, e.g. in aerospace, refrigeration, air-conditioning and energy applications.

Hydrologic performance of grass swales in cold maritime climates: Impacts of frost, rain-on-snow and snow cover on flow and volume reduction

Sustainable urban drainage solutions (SuDS) are a diverse set of design options that mitigate floods and improve water quality. Grass swales are the sole component of SuDS that transports runoff over long distances to downstream recipients. A deeper understanding of the performance of grass swales in different winter conditions is important in order for cities to achieve a greater climate resiliency. The goal of this study was to assess the impacts of frequent rain-on-snow, and freeze–thaw cycles on the hydrologic performance of grass swales. A total of 63 field synthetic runoff experiments were performed in a 5.8 m long section of a grass swale in the Urriðaholt neighborhood, Gardabaer, Iceland over 18 months. A three-fold reduction in peak flow attenuation was observed in winter (avg. 13%) compared to summer (avg. 38%) for hydraulic loadings ranging between 19 and 131 cm/h. The reduction in the performance of the swale was primarily due to frost formation and secondarily due to snow. The frequent rainfall, snowmelt, and rain-on-snow events elevated the soil water content and rendered the swale media susceptible to frost formation. The formation of pore ice within the 5 cm soil horizon led to a considerable reduction in soil porosity, which negatively affected the infiltration capacity, and shortened runoff lag times. Snow affected the performance by concentrating the flow in narrow channels, which reduced the effective area of infiltration, but also led to longer lag times and stored a portion of the runoff water within its pack. Despite the deterioration in the swale’s efficiency in winter, infiltration was observed in all synthetic runoff experiments, indicating that frost was either porous/granular, or heterogeneous in nature. The swale served its purpose to moderately reduce runoff peaks and volumes, especially for small and medium events. This research highlights the importance of effectively draining infiltration-based systems in cold climates to avoid the adverse effects of low temperatures.

Thermophysical Characterization of Cyclic Frost Formation in the Subsurface and Nominal Water Activity on Comets: Case Study of 67P/Churyumov-Gerasimenko

Abstract We use a generic thermophysical model to study in detail the formation of water-ice frost in the near-surface layers of comet 67P/Churyumov-Gerasimenko. We show that nightly frost formation is a common phenomenon. In particular, while abrupt landscapes may be conducive to frost formation, they are not a requisite condition. We show that the process of subsurface frost formation is similar to that of the condensed ice layer, or crust, underneath. The sublimation of frost produces regular, enhanced outgassing early in the morning. In the case of 67P, this activity is subordinate to and precedes the daily peak sourced from the ice-rich layers located above the diurnal skin depth. In any case, frost activity should be a nominal component of comet water activity.

How Frost Forms and Grows on Lubricated Micro- and Nanostructured Surfaces.

Frost is ubiquitously observed in nature whenever warmer and more humid air encounters colder than melting point surfaces (e.g., morning dew frosting). However, frost formation is problematic as it damages infrastructure, roads, crops, and the efficient operation of industrial equipment (i.e., heat exchangers, cooling fins). While lubricant-infused surfaces offer promising antifrosting properties, underlying mechanisms of frost formation and its consequential effect on frost-to-surface dynamics remain elusive. Here, we monitor the dynamics of condensation frosting on micro- and hierarchically structured surfaces (the latter combines micro- with nano- features) infused with lubricant, temporally and spatially resolved using laser scanning confocal microscopy. The growth dynamics of water droplets differs for micro- and hierarchically structured surfaces, by hindered drop coalescence on the hierarchical ones. However, the growth and propagation of frost dendrites follow the same scaling on both surface types. Frost propagation is accompanied by a reorganization of the lubricant thin film. We numerically quantify the experimentally observed flow profile using an asymptotic long-wave model. Our results reveal that lubricant reorganization is governed by two distinct driving mechanisms, namely: (1) frost propagation speed and (2) frost dendrite morphology. These in-depth insights into the coupling between lubricant flow and frost formation/propagation enable an improved control over frosting by adjusting the design and features of the surface.

The Distribution of Frosts on Mars: Links to Present‐Day Gully Activity

AbstractNumerous types of activity in mid latitude martian gullies have been observed over the last decade. Some activity has been constrained to occur in the coldest times of year, suggesting that surficial frosts that form seasonally and diurnally might play a key role in this activity. Here we use thermal infrared data to explore the global, spatial and temporal variation of temperatures conducive to CO2 and H2O frost formation on Mars, and assess their distribution relative to gully landforms. CO2 frost detections are observed at all latitudes and are strongly correlated with dusty, low thermal inertia regions near the equator. While it is difficult to accurately detect the formation of H2O frost, the global H2O frost point distribution generally follows water vapor column abundance, and is weakly correlated with surface pressure. Most global CO2 frost detections do not contain gullies, but 47% of all gullies, and 73% of active gullies (76% in the south, and 25% in the north) do overlap with CO2 frost detections. We predict that the conditions necessary for significant present‐day gully activity include a few centimeters of CO2 frost within loose, unconsolidated sediments (I ∼ 300 ) on relatively steep (>20°) slopes. Additionally, it could be possible for small amounts of H2O frosts to play a role in present‐day equatorial mass wasting events. However, whether present‐day gully activity is representative of gully formation is still open to debate, because it seems unlikely that frosts can erode channels into rocky substrates–even considering geologic timescales.