Condensation Surface Temperature Research Articles

Biomimetic fractal pillars for the thermal–hydraulic enhancement of a vapor chamber

Owing to their remarkable thermal–hydraulic performance, vapor chambers have diverse applications, especially for cooling electronic devices. However, the performances of circular and noncircular pillars throughout the entire vapor chamber under identical wick volume conditions have been compared in very few studies. In this study, a series of noncircular pillar arrays featuring biomimetic tree-like fractal networks is introduced. The incorporation of fractal pillars significantly enhances the thermal–hydraulic performance of the vapor chamber because the gas–liquid interface area is extended. Compared to a vapor chamber with circular pillars, the maximum condensation surface temperature difference, total thermal resistance, and liquid pressure drop of this vapor chamber with fractal pillars are reduced by up to 57.8 %, 13.8 %, and 10.9 %, respectively. In particular, with large branch levels and pillar diameters, the fractal structure is pivotal for boosting the overall performance. When the number of pillars is increased, the fractal structure's impact on the thermal performance reaches a limit, whereas its boosting effect on the flow performance weakens. This study is a pioneering exploration of the application of stretched geometries in pillar-type vapor chambers, with fractal pillars utilized in showcase demonstrations.

Corrosion at Top-of-the-Line in High Pressure and Dense CO2 Environments

This study presents unique data on top-of-the-line corrosion (TLC) occurring in high-pressure environments where CO2 was in the gaseous, liquid, or supercritical state. While CO2 is traditionally in a gaseous phase, this form of degradation is referred to as TLC. In this study, similar phenomena with different mechanisms were observed in liquid CO2 and supercritical states all of which are referred to as TLC due to the location of specimens and ease of comprehension. Experiments were conducted to investigate the effect of CO2 partial pressure (ranging from 20 bar to 100 bar) with temperatures (30°C to 50°C) relating to different water condensation rates (0.001 mL/m2/s to 0.1 mL/m2/s). Uniform and localized TLC rates increased with a higher water condensation rate and surface temperature. As long as CO2 remained gaseous, its partial pressure (pCO2) showed a negligible influence on both uniform and localized TLC rates. At the highest gaseous CO2 content tested, the formation of a protective iron carbonate (FeCO3) layer decreased the TLC rate, with this effect being more pronounced at lower water condensation rates. The risk of localized corrosion for specimens exposed to this environment at high and medium water condensation rates remained an issue. In the dense phase CO2 environment, the difference in temperature between the bulk environment and the specimen’s surface caused a similar phenomenon to water condensation, termed water drop-out, which resulted in corrosion. The rate of water drop-out could not be measured experimentally or estimated theoretically but is a complex function of temperature, pCO2, and CO2 physical state. The interplay between high pCO2 and low pH of the dropped-out water led to elevated uniform and localized corrosion rates. The depth of localized corrosion, at the high and medium water drop-out conditions, reached its maximum at the surface temperature of ca. 45°C. At a lower surface temperature of ca. 25°C and a higher surface temperature of ca. 65°C, the maximum penetration rate was decreased due to slower kinetics of reactions and the formation of a more protective FeCO3 layer, respectively. The results presented in this study highlight the significant difference between corrosion rates, especially in the form of localized damage, in gaseous and dense-phase CO2 environments.

Investigation of conical passive solar still by incorporating energy metrics, efficiency, and sensitivity analyses for sustainable solar distillation

The application of solar energy technology to solve the freshwater scarcity problem of society will contribute to the sustainable development goal of the United Nations. It will also recede the dependency on fossil fuels. This paper deals with the investigation of conical passive solar still (CPSS) by incorporating energy metrics, efficiency, and sensitivity analyses. Fundamental equations have been obtained from the thermal modelling of CPSS followed by experimental validation. The coefficient of correlation for water temperature is about 0.96, for condensing surface temperature is about 0.99 and for freshwater yield is also 0.99. The present work involves diverse monthly weather conditions for the performance analysis of CPSS. In the present work, a MATLAB-based computational code is used to compute hourly freshwater output, exergy, and energy assessment for their yearly results. Afterward, energy metrics and different efficiencies were computed, and the outcomes were compared with recent investigations. Finally, the energy payback time has been lowered by 161.40%. The energy production factor and life cycle conversion efficiency for CPSS were improved by 61.71% and 28.20%, respectively, compared with the conventional solar still. The comparative study of daily thermal efficiency reveals that the efficiency of CPSS is higher by 51.47% than V-type solar still.

Experimental study to improve the performance of solar still desalination by hydrophobic condensation surface using cold plasma technology

Improvement of solar still desalination performance has become the agenda of researchers in recent years to be able to make the most of the development of such systems in times of crisis and water scarcity. In the current experimental study, using two solar still desalination systems, the effect of cold plasma coat using Dielectric Barrier Discharge (DBD) on the condensation surface is investigated. To achieve this goal, two still solar systems are tested under the same climatic conditions to demonstrate the effects of the cold plasma coating on the condensation surface wettability and hydrophobicity. Additionally, influence of plasma layer on the internal condensing surface temperature and freshwater production rate is examined. Experimental results show that the contact angle between water droplets and glass cover after using plasma coating will increase, which increases the surface hydrophobicity. Results reveal that the amount of produced fresh water in the uncoated surface desalination system equivalent to 485 ml, while in the system with cold plasma, the maximum productivity with the maximum average solar radiation of 1000 W/m2 and the absorber wall temperature of 70.1 °C, and surface angle of 35° in the experiment day is about 610 mL. Additionally, calculations represent that the produced freshwater using plasma coating increases by 25.7% compared to the uncoated system. The quality of lab-prepared saltwater samples was analyzed before and after desalination, and the results comply with the World Health Organization guidelines for drinking water quality.

An Experimental Investigation of Top-of-Line Corrosion in a Static CO2 Environment

This paper presents an experimental and theoretical investigation into water condensation and corrosion under noncorrosion product forming conditions at the top of the line in a static, CO2 environment. An experimental test cell is developed to measure droplet lifetimes, condensation rates, as well as in situ and integrated corrosion rates (using miniature electrodes and mass loss specimens, respectively) as a function of the surface and gas temperatures when the gas flow is dominated by natural convection. Experimental results show clearly that the water condensation rate is not very influential on the corrosion rate at low surface temperatures (Ts) (particularly below 25°C) but becomes much more important at higher surface temperatures (>40°C). These findings are summarized in a new empirical correlation for the top-of-line corrosion rate as a function of the condensation rate and surface temperature. A model for condensation at the top of line for static, buoyancy-driven conditions is also presented and is shown to predict dropwise condensation rates accurately for a range of experimental conditions. The developed miniature electrodes for in situ electrochemical measurement are shown to provide an accurate interpretation of the transient response in general corrosion behavior by giving real-time corrosion rates to complement the mass loss measurement.

Influence of temperature difference (water-cover surface) on the performance of a compact hemispherical solar still

The study investigated the influence of temperature difference (ΔT) between evaporative and condensing surface temperature on water productivity of hemispherical solar still. The still was developed, tested and evaluated under the climatic conditions of Ile-Ife, Nigeria, to obtain an average distillate yield per hour per day for different combination of basin temperature, water temperature, transparent cover temperature, ambient temperature and solar intensity. Results indicated a decrease in the hourly water yield as (ΔT) increases. Regression analysis revealed that ΔT has no significant influence on the hourly water yield (P > 0.05). Maximum water productivity was obtained for a low condensing surface temperature and a high evaporative surface temperature. The study concluded that the improvement on water productivity of solar still can be achieved by enhancing the evaporative and condensing surface temperature. Methods for obtaining higher evaporating temperature should be sought in order to boost water productivity of solar stills.
 Keywords: Temperature difference, Evaporative surface, Condensing surface, Hourly water yield, Heat losses.

Condensation of KCl(g) under varied temperature gradient

Homogenous nucleation or heterogeneous condensation of gaseous alkali salts commonly occurs in biomass-fired power plants, and is mainly responsible for forming fine particles and triggering deposition or corrosion on tubes. This work aims to investigate the influence of surface temperature and exposure time on the initial condensation characteristics of KCl(g) in air atmosphere. It includes both experiment and simulation calculation to qualitatively and quantitatively study the condensation and gas-to-solid conversion of KCl(g) under different temperature gradients. Experiments were carried out in an electrically heated vertical tubular furnace, in which a defined evaporating source of KCl(g) was designed. A sampling probe equipped with a temperature controlled Fe-Cr-Ni alloy condensation surface, was inserted into the furnace to capture KCl(g). For each case, the morphology of condensed salt on the probe surface was analyzed via using Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM-EDS). The results showed significant differences in morphologies of the condensed salts which were respectively observed at the condensation surface temperature of Fe-Cr-Ni alloy of 673.15, 793.15 and 873.15 K. At the same tubular furnace temperature, due to the appearance of dendritic structure, the condensation rate of KCl(g) of 3.28 × 10−6 kg/m2·s at the surface temperature of 793.15 K was greater than that obtained at 673.15 K. The calculation of gas-to-solid conversion found that condensed KCl particles whose diameter is larger than 1 μm could not be formed only relying on the mechanism of nucleation and coagulation, when the gas temperature decreased from 1073.15 K to 673.15/793.15/873.15 K, respectively. The faster the cooling rate is, the smaller the size of formed particles is, and the more the number concentration of ultra-fine particles is. In addition, severe corrosion and cracks of surface material of the condensation surface were clearly observed at 793.15/873.15 K, which may be induced by couple attacks of condensed salts, thermal stress and molecular oxygen.

Experimental and mathematical study of air gap membrane distillation for aqueous HCl azeotropic separation

AbstractBACKGROUNDIn the present study, the feasibility of air gap membrane distillation (AGMD) process is investigated for breaking an azeotropic mixture. A test cell AGMD module with hydrophobic PTFE membrane was fabricated and HCl/H2O azeotrope (20.2 wt% HCl) was taken as feed. A mathematical model based on Stefan diffusion multicomponent molecular‐Knudsen mass transfer approach has been developed and validated with experimental data. The effects of different process parameters on total permeate flux, on selectivity and on breaking an HCl/H2O azeotrope mixture also have been studied. The feed side membrane surface temperature and membrane side condensing surface temperature were estimated by CFD modelling.RESULTSThe HCl selectivity obtained in the permeate was <1, which indicates that permeate flux is leveraged with water and a higher HCl concentration in the retentate was achieved relative to the permeate. The permeate flux decreased from 36 to 17 kg m−2 h−1 upon increasing the air gap from 3 mm to 11 mm at 50 °C feed temperature. The permeate flux increased from 4 to 28.5 kg m−2 h−1 upon increasing the feed temperature from 30 to 50 °C at 5 mm air gap.CONCLUSIONWith azeotropic feed, the maximum concentration of HCl achieved in the retentate was 30.8 wt% HCl (i.e. a hyperazeotropic solution) and in permeate was found to be 15.29 wt% HCl (i.e. hypoazeotropic solution). This indicates a strong possibility of using AGMD for azeotropic mixture separation. It also was observed that the permeate flux is affected mainly by feed temperature and air gap width. © 2018 Society of Chemical Industry

Condensation Surface Temperature as a Means for Studying Film Formation Mechanisms

A rise in the condensation surface temperature during film growth is a result of energy dissipation on the condensation surface. An example of energy dissipation is the dissipation of chemical reaction heat, which releases during film deposition by reactive magnetron sputtering. The monitoring of the surface temperature during TiN film deposition by reactive (Ti–in–N2) and nonreactive (TiN–in–Ar or TiN–in–N2) sputtering methods has shown that this temperature is higher in the reactive case and decreases in the (TiN–in–Ar)–(TiN–in–N2) sequence of nonreactive sputtering modifications. It has been found that the composition and crystal structure of TiN films do not depend on the growth method and are identical to those of bulk titanium nitride. Based on these results, a formation mechanism of films obtained by the above methods has been suggested. In the case of reactive sputtering, the film was supposed to grow on the condensation surface through a reaction between titanium and nitrogen atoms. In the cases of nonreactive sputtering, the film forms from TiN molecules.

An investigation into the effect on the productivity of cascade-type solar distillation systems with varying cover thicknesses and still orientations under tropical Caribbean climatic conditions

Previous investigative work related to solar stills focuses mainly on issues relating to the temperature gradient between the brine and the condensing surface. It is common practice when calculating the efficiencies of solar stills to use the temperature of the outer glass as the condensing surface temperature rather than the temperature of the actual condensing surface. This practice is done due to the fact that the outer glass surface temperature is easily measurable and on the assumption that there is little or no drop in temperature across the thickness of the cover. These conventions in turn create room for misleading results owing to temperature losses across the cover thickness. The main objectives of this research work are to investigate the effect of using different glass cover thicknesses and different solar still orientations on the productivity of cascade-type solar stills tested under tropical Caribbean climatic conditions. In the investigation, three identical units fitted with glass covers of thicknesses 3.18, 4.76 and 6.35mm are used. Each unit comprised two identical solar stills: one oriented to face north and the other to face south. Results were gathered at the University of the West Indies in St. Augustine, Trinidad and comparative analyses were conducted. The results indicate that the solar still with the glass cover thickness of 4.76mm facing south produced the highest yield.

The glazing temperature measurement in solar stills – Errors and implications on performance evaluation

Although the brine temperature measurement in solar stills would be more or less conventional, the precise condensing surface temperature measurement, appears to present a significant difficulty to measure. In the present investigation, an analysis is developed aiming to underline the parameters affecting the glazing surface temperature measurement and a series of field measurements are presented, aiming to identify and evaluate the errors associated to the measurement of this crucial physical quantity. It is derived that among other reasons the surface temperature measurement accuracy may strongly be degraded owing to the sensor tip overheating due to the radiation absorption, as well as to the development of poor bond conductance between sensor bead and glazing surface. It may also be degraded owing to the temperature drop across the glazing thickness and the non-uniform temperature distribution over the entire condensing surface area, something that makes the selection of the appropriate location of the particular temperature transducer necessary. Based on the derived measurements, an order of magnitude analysis is employed for the approximate evaluation of error range in the condensing surface temperature measurement. This, which depending on specific conditions was found to vary between about 1 and 2 °C, was employed to demonstrate the implications and approximate conditions under which its effect could become excessively high in ordinary solar still investigations.

Assessment of the impact of collection temperature and sampler design on the measurement of exhaled breath condensate pH in healthy horses

The pH measurement of exhaled breath condensate (EBC) may provide a non-invasive method of assessing the lower airways of horses but the methodology used may influence findings. The aim of this study was to investigate the effect of two sampling devices and three methods of condensation surface cooling (ethanol slush, -100°C; dry ice, -75°C; water ice, 0°C) on EBC pH. Each method was tested 30 times using six healthy ponies. Sample pH was determined before and after de-aeration with argon for 10 min. Sampler design was found to significantly affect pH. Samples collected as a liquid had a significantly higher pH than samples frozen during collection (P<0.05). De-aeration resulted in significantly higher pH (P<0.05) with less variation. This study has shown that device design and condensation surface temperature will influence EBC pH, which will prevent a direct comparison of results when different methodologies are used.

Internal Condensing Flows inside a Vertical Pipe: Experimental/Computational Investigations of the Effects of Specified and Unspecified (Free) Conditions at Exit

Reported experimental and computational results confirm that both the flow features and heat-transfer rates inside a condenser depend on the specification of inlet, wall, and exit conditions. The results show that the commonly occurring condensing flows’ special sensitivity to changes in exit conditions (i.e., changes in exit pressure) arises from the ease with which these changes alter the vapor flow field in the interior. When, at a fixed steady mass flow rate, the exit pressure is changed from one steady value to another, the changes required of the interior vapor flow toward achieving a new steady duct flow are such that they do not demand a removal of the new exit pressure imposition back to the original steady value—as is the case for incompressible single phase duct flows with an original and “required” exit pressure. Instead, new steady flows may be achieved through appropriate changes in the vapor/liquid interfacial configurations and associated changes in interfacial mass, heat-transfer rates (both local and overall), and other flow variables. This special feature of these flows has been investigated here for the commonly occurring large heat sink situations, for which the condensing surface temperature (not heat flux) remains approximately the same for any given set of inlet conditions while the exit-condition changes. In this paper’s context of flows of a pure vapor that experience film condensation on the inside walls of a vertical tube, the reported results provide an important quantitative and qualitative understanding and support an exit-condition-based categorization of the flows. Experimental results and selected relevant computational results that are presented here reinforce the fact that there exist multiple steady solutions (with different heat-transfer rates) for multiple steady prescriptions of the exit condition—even though the other boundary conditions do not change. However, for some situations that do not fix any specific value for the exit condition (say, exit pressure) but allow the flow the freedom to choose any exit pressure value within a certain range, experiments confirm the computational results that, given enough time, there typically exists, under normal gravity conditions, a self-selected “natural” steady flow with a natural exit condition. This happens if the vapor flow is seeking (or is attracted to) a specific exit condition and the conditions downstream of the condenser allow the vapor flow a range of exit conditions that includes the specific natural exit condition of choice. However, for some unspecified exit-condition cases involving partial condensation, even if computations predict that a natural exit-condition choice exists, the experimental arrangement employed here does not allow the flow to approach its steady natural exit-condition value. Instead, it only allows oscillatory exit conditions leading to an oscillatory flow. For the reported experiments, these oscillatory pressures are induced and imposed by the instabilities in the system components downstream of the condenser.

Parametric studies on a double-exposure single-basin solar still

SYNOPSIS A parametric study on a double-exposure single-basin solar still is presented. Explicit expressions have been derived for water and condensing surface temperature, temperature differential between water and condensing surface, instantaneous distillate output and instantaneous efficiency together with the overall distillate output and overall efficiency of the system. The effects of water mass, absorptivity, reflectivity and bottom heat loss coefficient on the performance of the system have been investigated comprehensively. Numerical calculations were made for quantitative assessment of the analytical results. Performance of the system has been compared with a conventional single-basin solar still. The productivity of the double-exposure single-basin solar still is found to be enhanced significantly over the conventional single basin solar still.

Phase separation and formation of the self-organised layered nanostructure in C/Cr coatings in conditions of high ion irradiation

The paper discusses the effect of ion irradiation on a new type of nanoscale multilayer structure in C/Cr PVD coatings formed by a self-organisation mechanism. C/Cr coatings were deposited by the combined steered cathodic arc/unbalanced magnetron sputtering technique, at wide range of bias voltages, U b from − 65 to − 550 V. Plasma diagnostics carried out by electrostatic probe measurements revealed that C/Cr films grow under conditions of intensive ion bombardment with ion-to-neutral ratio exceeding J i/ J n = 6. Under these conditions the high diffusion mobility and the reactivity of the C leads to distinct changes in the coatings microstructure and phase composition. Raman spectroscopy and XPS (X-ray photoelectron spectrometer) analysis of the chemical bonding in the films showed that the phase composition of the films gradually transforms from more graphite like (sp 2 C–C bonded) to more Me-carbon (Cr–C bonded), where the content of the carbide phase increases with increase of the bias voltage to U b = − 350 V and higher. In parallel HRTEM (high-resolution transmission electron microscopy) employing HAADF (high-angle annular dark field) imaging revealed that the microstructure evolved from columnar with carbon accumulated at the column boundaries ( U b = − 65 V, − 95 V) to a structure dominated by onion like C–Cr clusters ( U b = − 120 V), which than converts to a distinct nanoscale layered structure ( U b = − 350 V, − 450 V), finally transforming to a uniform fine grain structure at U b = − 550 V. The new nanoscale layered structure forms via ion irradiation induced self-organisation mechanism. It is characterized by an abnormally large values for the bi-layer thickness of 20 nm and 25 nm, which are not related to substrate rotation, for films grown at U b = − 350 V and U b = − 450 V, respectively. ADF (annular dark field) STEM (scanning TEM) imaging and quantitative EELS (electron-energy loss spectroscopy) analysis showed that the nanoscale multilayer structure comprises of alternating layers of Me-carbide phase (48%C, 52%Cr) and almost pure C (91.34%C), where the bias voltage defines the bi-layer thickness. A coating growth model is proposed accounting for the irradiation-induced ion mixing, re-sputtering, condensation surface temperature effects, nucleation and kinetic segregation process, as well as the diffusivity of the coating elements to explain the phase separation and formation of the self-organised layered nanostructure observed in C/Cr coatings.

Structural Nonuniformity and Internal Stress in Chromium Films Deposited by Magnetron Sputtering

Using high-resolution transmission electron microscopy, selected area electron diffraction and X-ray diffraction methods, the microstructures and lattice parameters of different parts of Cr films deposited by magnetron sputtering under different deposition conditions have been studied. It was revealed that the microstructure and lattice parameter of the films deposited onto nonheated substrates vary in the film thickness direction. Lattice parameter a has a maximal value in the film-substrate interface region and gradually decreases towards the conventional value in the middle and upper film parts. In accordance with this, the internal tensile stress decreases, while the grain size increases in the direction from the substrate to the film surface. Elevation of the substrate temperature results in smoothing of nonuniformity of the film microstructure and stress distribution along the thickness. At a certain combination of a substrate temperature and bias voltage, unstressed large-grained films with uniform microstructure have been deposited. The model proposed for explanation of the obtained results is based on the supposition of dynamic elevation of condensation surface temperature during film growth that promotes the formation of the film with structure and stress nonuniformly distributed in the thickness direction.

Electrical, microphysical and dynamical observations in summer monsoon clouds

Electrical, microphysical and dynamical conditions in ground-based clouds were studied using the observations carried out at Mahabaleshwar (17°56′N, 73°40′E; 1382 m ASL), a hill station, during the summer monsoon season of 1977. There is a significant correlation between the rain intensity and the corresponding atmospheric electric potential gradient. The diurnal curves of rainfall and negative electric potential gradient exhibited two peaks. The peak in rainfall during the morning hours and the afternoon peak in electric potential gradient were statistically significant. The early morning peak in rainfall was attributed to the enhanced convergence caused by the radiational imbalance in the cloud and cloud-free regions during active monsoon conditions. The afternoon peak in the electric potential gradient was attributed to the cloud formation due to convection. The atmospheric electric potential gradient showed sign reversal from its normal fair weather positive to negative at the time of the onset of rain. The reversal of the electrical potential gradient and the incidence of positively charged raindrops at the surface were almost simultaneous. Positive raindrop charges were recorded 1–2 minutes prior to the occurrence of negative electric potential gradient showing a steep increase during heavy rain spells. The raindrop charges were predominantly positive. The possible physical mechanisms for electrification of monsoon clouds have been discussed. The cloud condensation nuclei and surface temperature also showed peaks during the morning hours. The microphysical observations suggest that the rain formation takes place in monsoon clouds both by the collision-coalescence and ice crystal processes. A simple 1-D model was used to compute different cloud physical parameters. For a cloud with its top at 9 km the precipitation efficiency is in the range 60–70% of the adiabatic liquid water content. It has an average rainfall rate of 15 mm hr −1, vertical velocity of 3–5 m s −1 and average life time of 30 minutes.

Direct use of solar energy for water desalination

Solar energy utilization in three different types of solar desalination systems is considered. The overall efficiency of a typical basin type solar desalination plant is 30 per cent or lower. The major design factors affecting energy utilization are basin temperature, condensing surface temperature and ambient air temperature. Basic reflection and thermal radiation from the evaporating surface and transparent cover are the major sources of heat energy loss in a solar still. The efficiency of a solar desalination plant can be improved by controlling radiation from the plant basin and by the reuse of the latent heat of condensation.

Influence of the condensation surface temperature on the microstructure and intrinsic stress in evaporated chromium films

Chromium was evaporated onto die cast zinc at a pressure of better than 10 −3 Pa (10 −5 Torr). The deposition rate was varied between 0.1 μm min −1 and 0.6 μm min −1. The films were found to have a b.c.c. structure and to consist of needle-like crystallites, with fine needles for low deposition rates and coarse needles for high deposition rates. A rapid growth of the crystallites occured for a deposition rate of 0.2−0.3 μm min −1. During deposition the films were found to crack because of intrinsic stresses developed in the films. There was a strong dependence of the mean distance between cracks on the deposition rate with a maximum at about 0.25 μm min −1 for a substrate temperature of 323 K (50°C). The relation of the root mean square microstrain to the deposition rate is the inverse of the relation between the mean distance between cracks and deposition rate. A model is proposed that separates the experimentally obtained root mean square strain into two parts, one due to distortions at the grain boundaries and one due to defects in the crystallites. The results given by the model for the two strain components explain the obtained Vickers hardness dependence upon deposition rate.

3.4 Influence of condensation surface temperature on macrostructure in evaporated chromium films

Chromium, with a Vickers diamond hardness of up to 1200 has been vapor deposited on die cast zinc substrates. In each coating cycle up to six specimens with equal initial condition but different thicknesses could be made. A macrostructure of cracks was found in the films. It is very like the cracking network obtained in electrodeposited chromium. The cracks are caused by intrinsic stress in the films. The ‘mean distance between cracks’ was measured as a function of film thickness, deposition rate and bulk substrate temperature. The hardness is given as a function of ‘mean distance between cracks’. The condensation surface is defined and its temperature dependence on deposition parameters is discussed. Using the concept of condensation surface temperature and the linear expansion coefficient of the film material an atomic model is given to explain the ‘mean distance between cracks’ dependence on the deposition parameters.