> Quick answer: The diffusion coefficient of water vapour through typical IP65 gasket materials at 25 °C and 60 °C cannot be directly quantified from available sources [1][9][17][22]. However, Fickian diffusion governs this process, with higher temperatures increasing diffusion rates.
While the exact diffusion coefficients for water vapour through typical IP65 gasket materials at 25 °C and 60 °C are not provided in the available sources [1][9][17][22], understanding how Fickian diffusion limits long-term moisture ingress is critical. This article delves into the mechanisms behind water vapour transport through gaskets, the impact of temperature on this process, and practical insights for maintaining solar lamp reliability.
Understanding Vapour Diffusion
The core mechanism governing water vapour diffusion through IP65-rated gasket materials is Fick’s first law of diffusion [3][7]. This law states that the vapour flux (the amount of vapour moving across a surface over time) is proportional to the concentration gradient and the diffusion coefficient. In steady-state conditions, this can be likened to heat conduction through a material thickness [2][13].
Key Factors Influencing Vapour Diffusion
- Temperature: Higher temperatures increase the diffusion coefficients of water vapour in materials. For instance, studies on polyurethane encapsulation have shown that moisture penetration is deeper at higher temperatures (85 °C vs 50 °C), indicating a higher effective diffusion coefficient [3][8].
- Material Properties: The permeability coefficient (PM) combines solubility and diffusivity and is often used to describe vapour transmission in polymers [10]. Materials with lower PM values resist vapour transmission more effectively.
- Pore Size: Smaller pores can resist higher hydrostatic pressures, which implies that gasket materials with smaller pores or lower permeability will limit vapour diffusion more effectively [1][15].
Temperature and Moisture Ingress
The sources indicate a general trend where diffusion increases with temperature. For example:
- A study on polyurethane encapsulation found higher moisture penetration at 85 °C compared to 50 °C, suggesting elevated temperatures accelerate moisture ingress [3][8].
- In hygrothermal tests on composite materials, specimens were aged at 70 °C to induce moisture saturation, further supporting the idea that higher temperatures enhance diffusion rates [18].
Comparison Table: Permeability Coefficients
| Material | Permeability (kg/m/s/Pa) |
|––––––|–––––––––|
| Brick | 11.5 × 10⁻¹² |
| Wood | 6 × 10⁻¹² |
This table illustrates the range of permeability values in porous solids, suggesting that IP65 gasket materials with similar or lower permeability would significantly impede vapour diffusion.
Design and Material Selection
Material selection and design are crucial for limiting moisture ingress. Silicone encapsulants have demonstrated excellent resistance to moisture under harsh conditions [17][22]. In solar lamps, venting systems allow controlled vapour escape while preventing liquid water entry [9][15].
Thermal Cycling Effects
Thermal cycling can enhance vapour diffusion by creating transient gradients that drive moisture inward. Even if the average temperature is moderate, temperature fluctuations between day and night in outdoor environments create pressure differences that drive diffusion.
Key Takeaways
- Fickian Diffusion: Governs water vapour transport through gasket materials.
- Temperature Influence: Higher temperatures increase diffusion rates.
- Material Permeability: Critical for limiting moisture ingress; lower permeability resists vapour transmission more effectively.
Frequently Asked Questions
[{„q”: „How does temperature affect the diffusion of water vapor in solar lamp gaskets?”, „a”: „Higher temperatures increase the diffusion coefficients, leading to deeper moisture penetration. For example, polyurethane encapsulation showed higher moisture ingress at 85 °C compared to 50 °C [3][8].”},
{„q”: „What role do pore sizes play in limiting vapour diffusion?”, „a”: „Smaller pores resist higher hydrostatic pressures and limit vapour diffusion more effectively. PTFE membranes, for instance, have tuned pore sizes that allow vapour transmission while blocking liquid water [1][15].”},
{„q”: „How can design mitigate moisture ingress in solar lamps?”, „a”: „Effective design includes venting systems to control vapour escape and prevent liquid water entry [9][15], ensuring long-term reliability.”}]
References
- [1] US4237526A_-_Battery_operated_device_having_a_waterproof_housing__4018fa31 — patent
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of the aperture 44 may determine the effective area of exposure to the atmosphere by diffusion member 46. The area of effective exposure and the number and size of pore of diffusion member 46 will largely control the rate of gas diffusion from the housing 12. The diffusion rate should be at least substantially equal to or greater than the rate of evolution for the unwanted hydrogen gas so as not to permit internal total pressure to rise much above atmospheric pressure and to prevent accumulation of more than about 10 percent of hydrogen by volume and preferably no more than about 5 percent by volume. Although for purposes of the present invention a device is characterized as "waterproof" if it passes the 3 foot water immersion test for one hour without leakage as mentioned previously, some devices may need to withstand greater depths of immersion. Fortunately, suitable venting membranes are commercially available in a series of different pore sizes corresponding to various depths. This relationship is illustrated in the following table for a 0.002 inch thick microporous membrane of polytetrafluoroethylene. ______________________________________ DEPTH OF WATER IMMERSION NOMINAL SIZE OF (IN FEET) REQUIRED TO PORE (INCHES) EFFECT WATER PENETRATION ______________________________________ 0.00004 14 0.00002 40 0.000008 80 0.0000008 600 ______________________________________ The hydrogen diffusion rate or gas permeability does of course lessen with decreasing pore size; however, eve
- [2] Computational Fluid Dynamics_ Fundamentals and Applications — book
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vapour resistance factor. It should be noted that in small pores close to the size of water molecules, capillary effect is also an essential factor, when the vapour is condensed, that should not be neglected. Interested readers are encouraged to read [10]. Back to a vapour transport in the stagnant condition, we can apply the mass conservation equation for vapour in the non‐hygroscopic materials when there is no vapour condensation, evaporation, or sublimations (source/sink term is zero and Ψ0 is constant) in an isothermal condition as: (5.41) In a steady‐state condition, we can simplify Eq. (5.41) to: (5.42) In isothermal conditions, δa is a constant number and, thus, one can find the pressure as a straight line (Pv(x) = Ax + B) in any layer of the porous materials similar to the temperature distribution due to the conduction. This implies that we can find the vapour mass flux as: (5.43) In a non‐isothermal steady‐state condition, nonetheless, we know from the heat diffusion equation that the temperature is linearly changing through a material (without a sink and source). Therefore, δa in Eq. (5.42) becomes dependent of temperature (δa(T(x))), which is changing in a 1D material with a length of d with two ends’ temperatures of T1 and T2 as: (5.44) After integration of Eq. (5.42) over a 1D thickness, we obtain: (5.45) Here, with understating of δa(T(x)) from experiments, we can solve the above integration and find the pressure distribution in the materials. Nevertheless, it i
- [3] Materials Science and Engineering_ An Introduction — book
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indicative of the rate of atomic motion and depends on both host and diffusing species as well as on temperature. • The diffusion coefficient is a function of temperature according to Equation 5.8. • The two heat treatments that are used to diffuse impurities into silicon during inte- grated circuit fabrication are predeposition and drive-in. During predeposition, impurity atoms are diffused into the silicon, often from a gas phase, the partial pressure of which is maintained constant. For the drive-in step, impurity atoms are transported deeper into the silicon so as to provide a more suitable concentration distribution without increasing the overall impurity content. • Integrated circuit interconnects are normally made of aluminum—instead of metals such as copper, silver, and gold that have higher electrical conductivities—on the basis of diffusion considerations. During high-temperature heat treatments, interconnect metal atoms diffuse into the silicon; appreciable concentrations will compromise the chip’s functionality. Fick’s First Law Fick’s Second Law— Nonsteady-State Diffusion Factors That Influence Diffusion Diffusion in Semiconducting Materials Equation Summary Equation Number Equation Solving For 5.1 J = M At Diffusion flux 5.2 J = −D dC dx Fick’s first law 5.4b ∂C ∂t = D ∂2C ∂x2 Fick’s second law 5.5 Cx −C0 Cs −C0 = 1 −erf( x 2√Dt) Solution to Fick’s second law—for constant surface composition 5.8 D = D0 exp(−Qd RT) Temperature dependence of diffusion coefficient
- [7] Materials Science and Engineering_ An Introduction — book
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linear, as depicted in Figure 5.3b, and concentration gradient = dC dx = ΔC Δx = CA −CB xA −xB (5.3) For diffusion problems, it is sometimes convenient to express concentration in terms of mass of diffusing species per unit volume of solid (kg/m3 or g/cm3).1 Fick’s first law diffusion coefficient steady-state diffusion concentration profile concentration gradient Figure 5.3 (a) Steady- state diffusion across a thin plate. (b) A linear concentration profile for the diffusion situation in (a). xA xB Position, x Concentration of diffusing species, C CA CB Thin metal plate Area, A Direction of diffusion of gaseous species Gas at pressure PB Gas at pressure PA PA > PB and constant (a) (b) 1Conversion of concentration from weight percent to mass per unit volume (kg/m3) is possible using Equation 4.9. 126 • Chapter 5 / Diffusion EXAMPLE PROBLEM 5.1 Diffusion Flux Computation A plate of iron is exposed to a carburizing (carbon-rich) atmosphere on one side and a decarbur- izing (carbon-deficient) atmosphere on the other side at 700°C (1300°F). If a condition of steady state is achieved, calculate the diffusion flux of carbon through the plate if the concentrations of carbon at positions of 5 and 10 mm (5 × 10−3 and 10−2 m) beneath the carburizing surface are 1.2 and 0.8 kg/m3, respectively. Assume a diffusion coefficient of 3 × 10−11 m2/s at this temperature. Solution Fick’s first law, Equation 5.2, is used to determine the diffusion flux. Substitution of the values just given into th
- [8] Inverters_and_power_modules_are_key_in_energy_management_-_PV_Tech__2a128211 — authority
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their chemical decomposition. The usual test conditions for lifetime predictions (e.g. T=85 degrees Celsius, F=85% rH) lead to over-testing of the components and to non-representative failures, especially in DC capacitors with the design shown above. For well-founded lifetime predictions, the test conditions must be adapted and further correlated with field data. Moisture ingress Thermally coupled permeation simulations were carried out to visualise the moisture ingress numerically and to provide a base for simulated lifetime estimation. The analytical results show that the moisture ingress starts from the top of the capacitor in the area of the plastic cap. Therefore, the material characteristics of the polyurethane encapsulation and the foil stack were determined experimentally at T=50 degrees Celsius and T=85 degrees Celsius with F=85% rH in each case and the resulting time-dependent moisture distribution in the capacitor was simulated (Figure 4). The results after t=~500 hours initially show a distribution of moisture in the PU above the metallisation. After t=~5,000 hours, the distribution of moisture in the PU has progressed, with the higher diffusion coefficient at T=85 degrees Celsius becoming apparent by the deeper penetration. After ~10,000 hours, the moisture has also diffused into the films. The higher diffusion coefficient of the films at T=85 degrees Celsius is also reflected in the simulation results. In summary, it can be concluded that the accelerated tests f
- [9] AU5922498A_-_System_for_reducing_condensation_in_enclosed__9aa83edc — patent
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specified time period for a specified environmental condition, while resisting (i.e., protecting against) the entry of liquid water and other contamination into the housing. The size of the water vapor permeable area of the condensation vent required to rapidly remove water vapor from a tamp housing at normal ambient conditions is greater than that taught in conventional pressure venting systems. Thus, the relationship between the surface area of water vapor permeable materials covering a vent opening and water vapor transfer has been unexplored in the conventional art as a means of reducing and eliminating condensation from vehicle lamps. As used herein, the "vent opening" shall be defined as the total cross-sectional area of one or more openings that are covered by the water vapor permeable material of the condensation vent. The cross-sectional area is calculated based on the area of the opening immediately adjacent to the water vapor permeable material. The one or more openings may be present in any part of the lamp housing. In a preferred embodiment of the present invention, the novel condensation venting systems comprise water vapor permeable materials covering venting opening areas greater than 132 mm2, which accelerate the removal of condensation from vehicle lamps while providing protection from entry of foreign materials and liquid water. The novel optimized surface areas of the water vapor permeable materials permit rapid removal of condensation from the vehicle lam
- [10] Materials Science and Engineering_ An Introduction — book
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foreign substances diffuse into the material. Penetration of these foreign substances can lead to swelling and/or chemical reactions with the polymer molecules and often a degradation of the material’s mechanical and physical properties (Section 17.11). Rates of diffusion are greater through amorphous regions than through crystalline regions; the structure of amorphous material is more “open.” This diffusion mechanism may be considered analogous to interstitial diffusion in metals—that is, in polymers, diffusive movements occur through small voids between polymer chains from one open amorphous region to an adjacent open one. Foreign molecule size also affects the diffusion rate: Smaller molecules diffuse faster than larger ones. Furthermore, diffusion is more rapid for foreign molecules that are chemically inert than for those that interact with the polymer. One step in diffusion through a polymer membrane is the dissolution of the molecu- lar species in the membrane material. This dissolution is a time-dependent process, and, if slower than the diffusive motion, may limit the overall rate of diffusion. Consequently, the diffusion properties of polymers are often characterized in terms of a permeability coefficient (denoted by PM), where for the case of steady-state diffusion through a poly- mer membrane, Fick’s first law (Equation 5.2), is modified as J = −PM ΔP Δx (14.9) In this expression, J is the diffusion flux of gas through the membrane [(cm3 STP)/ (cm2·s)], PM is the
- [13] Computational Fluid Dynamics_ Fundamentals and Applications — book
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the isothermal air diffusivity for an open‐pore. Equation (5.35) resembles the heat diffusion equation and represents air flux through permeable building materials. Likewise, the steady state solution results in a straight line for the pressure across the materials. Similar to U‐value, we can also define air resistance of the assembly. In general, the air diffusion in buildings’ material is very small in comparison with the infiltration and flow through openings (see Chapter 8) as open pore materials are barely used that can be neglected in most of the scenarios. If permeable materials are employed, the time‐dependent term has a huge response as Da is large and thus we can assume the process to be steady state, which implies that we can rewrite Eq. (5.31) as: (5.36) So, the pressure across the preamble material is changed linearly similar to the heat conduction while is defined as the air resistance. 5.4.5 Vapour Transport Through Pores Pores’ dimensions play a significant role in the moisture transfer throughout buildings’ materials, which is a similar analogy as the previous section, and can help to define the transfer of vapour through the porosity. It should be noted that the vapour permeability of air is very small throughout the pores and can be neglected. Obviously, the analogy is not a binary mixture anymore while there is no opposite direction (porosity does not move), and thus the stagnant condition of the moist air presented in Eq. (5.29) can be applied: (5.37) whe
- [15] US4237526A_-_Battery_operated_device_having_a_waterproof_housing__4018fa31 — patent
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or housing for the lamp is considered to be "waterproof” if the interior of the lamp remains dry after the lamp has been submerged in water to a depth of at least three feet for a period of at least one hour. It is common practice to employ a gasket under compression to seal the housing of the electrical lamp to satisfy the waterproof requirement. – a dry galvanic cell develops gas during the normal course of storage and discharge reactions within the cell. – the volume of gas generated by a dry cell with respect to time is dependent upon the selected electrochemical system for the cell, the chemistry of the source materials, and the conditions of storage and use of the cell. – the type of sealing arrangement used for the cell container will determine the rate and extent to which generated gas will escape the cell container and outer finish into the surrounding housing. – primary dry cells based on manganese dioxide and zinc electrodes relatively moderate to heavy gassing of H 2 and CO 2 is an inherent characteristic. – commercially available Leclanche and zinc chloride primary dry cells are usually vented. Accordingly, evolved hydrogen and CO 2 readily escape from such cells. – the present invention is, in general, most useful in devices containing a vented primary dry cell based on a manganese dioxide and zinc electrode system. – Devices of the subject invention are designed to contain and operate on a given number of unit cells of a specific size or alternatively a multice
- [17] US8847063B2_-_Encapsulation_of_solar_cells_-_Google_Patents__afa4ee8d — patent
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% of diallylmaleate cure inhibitor, 0.11 weight % of platinum catalyst and 0.38 weight % of dimethylhydrogen siloxy terminated trifluoropropyl silsesquioxane. The encapsulant was applied onto the module manually and after levelling, was cured in a standard oven at a temperature of 120° C. for 20 mins. The electrical capabilities were measured before and after the 10 day aging process set down in the Humidity Freeze test described in IEC 1646, which comprised 10 cycles of 24 hours with the temperature varying from −40° C. to 85° C. in 85% relative Humidity (RH) and the results are provided in Table 4 below None of the samples tested showed any discoloration or delamination and all samples passed the standard wet leakage current test as defined in the IEC 1646 after the conditioning period. In accordance with the requirements of IEC 1646 after conditioning a sample should not show any open circuit or leakage current, any visual defect and any decrease in maximum power should not be greater than 5% all of which the thin film modules of the present invention using the encapsulant alone (i.e. no adhesive layer required). These findings are totally contrary to the expectations of the industry and use of a silicone encapsulant as hereinbefore described is able to provide the level of protection suitable for solar or photovoltaic module. With the exception that the glass was washed with ethanol instead of acetone and that a different type of commercially available solar cell was used
- [18] Composite Materials Engineering — book
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were stabilized and then immersed in water bath at the temperature of 70 °C until moisture saturation, defined as aged specimen; and (c) drying condition: the saturated specimens were dried in an oven at the temperature of 70 °C until reaching equilibrium, defined as dried specimen. Hygrothermal Test Water absorbed specimens were prepared according to the following procedure. Prior to absorption experiment, all specimens were dried in a heating oven at 70 °C until their weights became stable. Specimens were immersed in a water bath at 70 °C until reaching the limit of saturation. The water gain percentage, Mi was determined from the equation (1), Mi =(Gi-G0)/ G0×100% (1) Where Gi is the wet weight of specimen (g), and G0 is the dry weight of specimen (g). In drying test, the saturated specimens were dried in a heating oven at 70 °C until there was no change in their weights. The specimens were then removed from the oven and were cooled down to room temperature for further testing. Mechanical Property Test The effects of hygrothermal and drying conditions on the tensile strength in laminates with three different porosities levels ranged from 0.33% to 1.50% were investigated. Five rectangular specimens had the dimensions of 230 mm×25 mm×4.5 mm were tested to determine the average tensile strength. The tensile tests were performed in an Instron 5582 mechanical test machine, and the loading rate is 2mm/min. Results and discussion Moisture Absorption Fig. 1 shows that moisture con
- [22] US8847063B2_-_Encapsulation_of_solar_cells_-_Google_Patents__afa4ee8d — patent
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after application by a curtain coater the adhesive was cured in the module in a Mid IR oven having a temperature profile of 120° C. and a speed of 0.5 m per minute for a length of 5 m. The electrical capabilities were measured before and after the 10 day aging process set down in the Humidity Freeze test described in IEC 1215, which comprised 10 cycles of 24 hours with the temperature varying from −40° C. to 85° C. in 85% relative Humidity (RH) Sample Characterization: Electrical characterization of the specimen has been done before and after conditioning, results are summarized in table 6 below None of the samples were showing discoloration or delamination and were passing the wet leakage current test as described in the IEC 1215 after the conditioning. In accordance with the requirements of IEC 1215 after conditioning a sample should not show any open circuit or leakage current, any visual defect and any decrease in maximum power should not be greater than 5% all of which the thin film modules of the present invention using the encapsulant alone (i.e. no adhesive layer required). These findings are totally contrary to the expectations of the industry and use of a silicone encapsulant as hereinbefore described is able to provide the level of protection suitable for solar or photovoltaic module of a polycrystalline Silicon wafer type. In this case the only difference from example 8 was the change in the solar cells used. The adhesive and encapsulant compositions were as descr
of the aperture 44 may determine the effective area of exposure to the atmosphere by diffusion member 46. The area of effective exposure and the number and size of pore of diffusion member 46 will largely control the rate of gas diffusion from the housing 12. The diffusion rate should be at least substantially equal to or greater than the rate of evolution for the unwanted hydrogen gas so as not to permit internal total pressure to rise much above atmospheric pressure and to prevent accumulation of more than about 10 percent of hydrogen by volume and preferably no more than about 5 percent by volume. Although for purposes of the present invention a device is characterized as "waterproof" if it passes the 3 foot water immersion test for one hour without leakage as mentioned previously, some devices may need to withstand greater depths of immersion. Fortunately, suitable venting membranes are commercially available in a series of different pore sizes corresponding to various depths. This relationship is illustrated in the following table for a 0.002 inch thick microporous membrane of polytetrafluoroethylene. ______________________________________ DEPTH OF WATER IMMERSION NOMINAL SIZE OF (IN FEET) REQUIRED TO PORE (INCHES) EFFECT WATER PENETRATION ______________________________________ 0.00004 14 0.00002 40 0.000008 80 0.0000008 600 ______________________________________ The hydrogen diffusion rate or gas permeability does of course lessen with decreasing pore size; however, eve
vapour resistance factor. It should be noted that in small pores close to the size of water molecules, capillary effect is also an essential factor, when the vapour is condensed, that should not be neglected. Interested readers are encouraged to read [10]. Back to a vapour transport in the stagnant condition, we can apply the mass conservation equation for vapour in the non‐hygroscopic materials when there is no vapour condensation, evaporation, or sublimations (source/sink term is zero and Ψ0 is constant) in an isothermal condition as: (5.41) In a steady‐state condition, we can simplify Eq. (5.41) to: (5.42) In isothermal conditions, δa is a constant number and, thus, one can find the pressure as a straight line (Pv(x) = Ax + B) in any layer of the porous materials similar to the temperature distribution due to the conduction. This implies that we can find the vapour mass flux as: (5.43) In a non‐isothermal steady‐state condition, nonetheless, we know from the heat diffusion equation that the temperature is linearly changing through a material (without a sink and source). Therefore, δa in Eq. (5.42) becomes dependent of temperature (δa(T(x))), which is changing in a 1D material with a length of d with two ends’ temperatures of T1 and T2 as: (5.44) After integration of Eq. (5.42) over a 1D thickness, we obtain: (5.45) Here, with understating of δa(T(x)) from experiments, we can solve the above integration and find the pressure distribution in the materials. Nevertheless, it i
indicative of the rate of atomic motion and depends on both host and diffusing species as well as on temperature. • The diffusion coefficient is a function of temperature according to Equation 5.8. • The two heat treatments that are used to diffuse impurities into silicon during inte- grated circuit fabrication are predeposition and drive-in. During predeposition, impurity atoms are diffused into the silicon, often from a gas phase, the partial pressure of which is maintained constant. For the drive-in step, impurity atoms are transported deeper into the silicon so as to provide a more suitable concentration distribution without increasing the overall impurity content. • Integrated circuit interconnects are normally made of aluminum—instead of metals such as copper, silver, and gold that have higher electrical conductivities—on the basis of diffusion considerations. During high-temperature heat treatments, interconnect metal atoms diffuse into the silicon; appreciable concentrations will compromise the chip’s functionality. Fick’s First Law Fick’s Second Law— Nonsteady-State Diffusion Factors That Influence Diffusion Diffusion in Semiconducting Materials Equation Summary Equation Number Equation Solving For 5.1 J = M At Diffusion flux 5.2 J = −D dC dx Fick’s first law 5.4b ∂C ∂t = D ∂2C ∂x2 Fick’s second law 5.5 Cx −C0 Cs −C0 = 1 −erf( x 2√Dt) Solution to Fick’s second law—for constant surface composition 5.8 D = D0 exp(−Qd RT) Temperature dependence of diffusion coefficient
linear, as depicted in Figure 5.3b, and concentration gradient = dC dx = ΔC Δx = CA −CB xA −xB (5.3) For diffusion problems, it is sometimes convenient to express concentration in terms of mass of diffusing species per unit volume of solid (kg/m3 or g/cm3).1 Fick’s first law diffusion coefficient steady-state diffusion concentration profile concentration gradient Figure 5.3 (a) Steady- state diffusion across a thin plate. (b) A linear concentration profile for the diffusion situation in (a). xA xB Position, x Concentration of diffusing species, C CA CB Thin metal plate Area, A Direction of diffusion of gaseous species Gas at pressure PB Gas at pressure PA PA > PB and constant (a) (b) 1Conversion of concentration from weight percent to mass per unit volume (kg/m3) is possible using Equation 4.9. 126 • Chapter 5 / Diffusion EXAMPLE PROBLEM 5.1 Diffusion Flux Computation A plate of iron is exposed to a carburizing (carbon-rich) atmosphere on one side and a decarbur- izing (carbon-deficient) atmosphere on the other side at 700°C (1300°F). If a condition of steady state is achieved, calculate the diffusion flux of carbon through the plate if the concentrations of carbon at positions of 5 and 10 mm (5 × 10−3 and 10−2 m) beneath the carburizing surface are 1.2 and 0.8 kg/m3, respectively. Assume a diffusion coefficient of 3 × 10−11 m2/s at this temperature. Solution Fick’s first law, Equation 5.2, is used to determine the diffusion flux. Substitution of the values just given into th
their chemical decomposition. The usual test conditions for lifetime predictions (e.g. T=85 degrees Celsius, F=85% rH) lead to over-testing of the components and to non-representative failures, especially in DC capacitors with the design shown above. For well-founded lifetime predictions, the test conditions must be adapted and further correlated with field data. Moisture ingress Thermally coupled permeation simulations were carried out to visualise the moisture ingress numerically and to provide a base for simulated lifetime estimation. The analytical results show that the moisture ingress starts from the top of the capacitor in the area of the plastic cap. Therefore, the material characteristics of the polyurethane encapsulation and the foil stack were determined experimentally at T=50 degrees Celsius and T=85 degrees Celsius with F=85% rH in each case and the resulting time-dependent moisture distribution in the capacitor was simulated (Figure 4). The results after t=~500 hours initially show a distribution of moisture in the PU above the metallisation. After t=~5,000 hours, the distribution of moisture in the PU has progressed, with the higher diffusion coefficient at T=85 degrees Celsius becoming apparent by the deeper penetration. After ~10,000 hours, the moisture has also diffused into the films. The higher diffusion coefficient of the films at T=85 degrees Celsius is also reflected in the simulation results. In summary, it can be concluded that the accelerated tests f
specified time period for a specified environmental condition, while resisting (i.e., protecting against) the entry of liquid water and other contamination into the housing. The size of the water vapor permeable area of the condensation vent required to rapidly remove water vapor from a tamp housing at normal ambient conditions is greater than that taught in conventional pressure venting systems. Thus, the relationship between the surface area of water vapor permeable materials covering a vent opening and water vapor transfer has been unexplored in the conventional art as a means of reducing and eliminating condensation from vehicle lamps. As used herein, the "vent opening" shall be defined as the total cross-sectional area of one or more openings that are covered by the water vapor permeable material of the condensation vent. The cross-sectional area is calculated based on the area of the opening immediately adjacent to the water vapor permeable material. The one or more openings may be present in any part of the lamp housing. In a preferred embodiment of the present invention, the novel condensation venting systems comprise water vapor permeable materials covering venting opening areas greater than 132 mm2, which accelerate the removal of condensation from vehicle lamps while providing protection from entry of foreign materials and liquid water. The novel optimized surface areas of the water vapor permeable materials permit rapid removal of condensation from the vehicle lam
foreign substances diffuse into the material. Penetration of these foreign substances can lead to swelling and/or chemical reactions with the polymer molecules and often a degradation of the material’s mechanical and physical properties (Section 17.11). Rates of diffusion are greater through amorphous regions than through crystalline regions; the structure of amorphous material is more “open.” This diffusion mechanism may be considered analogous to interstitial diffusion in metals—that is, in polymers, diffusive movements occur through small voids between polymer chains from one open amorphous region to an adjacent open one. Foreign molecule size also affects the diffusion rate: Smaller molecules diffuse faster than larger ones. Furthermore, diffusion is more rapid for foreign molecules that are chemically inert than for those that interact with the polymer. One step in diffusion through a polymer membrane is the dissolution of the molecu- lar species in the membrane material. This dissolution is a time-dependent process, and, if slower than the diffusive motion, may limit the overall rate of diffusion. Consequently, the diffusion properties of polymers are often characterized in terms of a permeability coefficient (denoted by PM), where for the case of steady-state diffusion through a poly- mer membrane, Fick’s first law (Equation 5.2), is modified as J = −PM ΔP Δx (14.9) In this expression, J is the diffusion flux of gas through the membrane [(cm3 STP)/ (cm2·s)], PM is the
the isothermal air diffusivity for an open‐pore. Equation (5.35) resembles the heat diffusion equation and represents air flux through permeable building materials. Likewise, the steady state solution results in a straight line for the pressure across the materials. Similar to U‐value, we can also define air resistance of the assembly. In general, the air diffusion in buildings’ material is very small in comparison with the infiltration and flow through openings (see Chapter 8) as open pore materials are barely used that can be neglected in most of the scenarios. If permeable materials are employed, the time‐dependent term has a huge response as Da is large and thus we can assume the process to be steady state, which implies that we can rewrite Eq. (5.31) as: (5.36) So, the pressure across the preamble material is changed linearly similar to the heat conduction while is defined as the air resistance. 5.4.5 Vapour Transport Through Pores Pores’ dimensions play a significant role in the moisture transfer throughout buildings’ materials, which is a similar analogy as the previous section, and can help to define the transfer of vapour through the porosity. It should be noted that the vapour permeability of air is very small throughout the pores and can be neglected. Obviously, the analogy is not a binary mixture anymore while there is no opposite direction (porosity does not move), and thus the stagnant condition of the moist air presented in Eq. (5.29) can be applied: (5.37) whe
or housing for the lamp is considered to be "waterproof” if the interior of the lamp remains dry after the lamp has been submerged in water to a depth of at least three feet for a period of at least one hour. It is common practice to employ a gasket under compression to seal the housing of the electrical lamp to satisfy the waterproof requirement. – a dry galvanic cell develops gas during the normal course of storage and discharge reactions within the cell. – the volume of gas generated by a dry cell with respect to time is dependent upon the selected electrochemical system for the cell, the chemistry of the source materials, and the conditions of storage and use of the cell. – the type of sealing arrangement used for the cell container will determine the rate and extent to which generated gas will escape the cell container and outer finish into the surrounding housing. – primary dry cells based on manganese dioxide and zinc electrodes relatively moderate to heavy gassing of H 2 and CO 2 is an inherent characteristic. – commercially available Leclanche and zinc chloride primary dry cells are usually vented. Accordingly, evolved hydrogen and CO 2 readily escape from such cells. – the present invention is, in general, most useful in devices containing a vented primary dry cell based on a manganese dioxide and zinc electrode system. – Devices of the subject invention are designed to contain and operate on a given number of unit cells of a specific size or alternatively a multice
% of diallylmaleate cure inhibitor, 0.11 weight % of platinum catalyst and 0.38 weight % of dimethylhydrogen siloxy terminated trifluoropropyl silsesquioxane. The encapsulant was applied onto the module manually and after levelling, was cured in a standard oven at a temperature of 120° C. for 20 mins. The electrical capabilities were measured before and after the 10 day aging process set down in the Humidity Freeze test described in IEC 1646, which comprised 10 cycles of 24 hours with the temperature varying from −40° C. to 85° C. in 85% relative Humidity (RH) and the results are provided in Table 4 below None of the samples tested showed any discoloration or delamination and all samples passed the standard wet leakage current test as defined in the IEC 1646 after the conditioning period. In accordance with the requirements of IEC 1646 after conditioning a sample should not show any open circuit or leakage current, any visual defect and any decrease in maximum power should not be greater than 5% all of which the thin film modules of the present invention using the encapsulant alone (i.e. no adhesive layer required). These findings are totally contrary to the expectations of the industry and use of a silicone encapsulant as hereinbefore described is able to provide the level of protection suitable for solar or photovoltaic module. With the exception that the glass was washed with ethanol instead of acetone and that a different type of commercially available solar cell was used
were stabilized and then immersed in water bath at the temperature of 70 °C until moisture saturation, defined as aged specimen; and (c) drying condition: the saturated specimens were dried in an oven at the temperature of 70 °C until reaching equilibrium, defined as dried specimen. Hygrothermal Test Water absorbed specimens were prepared according to the following procedure. Prior to absorption experiment, all specimens were dried in a heating oven at 70 °C until their weights became stable. Specimens were immersed in a water bath at 70 °C until reaching the limit of saturation. The water gain percentage, Mi was determined from the equation (1), Mi =(Gi-G0)/ G0×100% (1) Where Gi is the wet weight of specimen (g), and G0 is the dry weight of specimen (g). In drying test, the saturated specimens were dried in a heating oven at 70 °C until there was no change in their weights. The specimens were then removed from the oven and were cooled down to room temperature for further testing. Mechanical Property Test The effects of hygrothermal and drying conditions on the tensile strength in laminates with three different porosities levels ranged from 0.33% to 1.50% were investigated. Five rectangular specimens had the dimensions of 230 mm×25 mm×4.5 mm were tested to determine the average tensile strength. The tensile tests were performed in an Instron 5582 mechanical test machine, and the loading rate is 2mm/min. Results and discussion Moisture Absorption Fig. 1 shows that moisture con
after application by a curtain coater the adhesive was cured in the module in a Mid IR oven having a temperature profile of 120° C. and a speed of 0.5 m per minute for a length of 5 m. The electrical capabilities were measured before and after the 10 day aging process set down in the Humidity Freeze test described in IEC 1215, which comprised 10 cycles of 24 hours with the temperature varying from −40° C. to 85° C. in 85% relative Humidity (RH) Sample Characterization: Electrical characterization of the specimen has been done before and after conditioning, results are summarized in table 6 below None of the samples were showing discoloration or delamination and were passing the wet leakage current test as described in the IEC 1215 after the conditioning. In accordance with the requirements of IEC 1215 after conditioning a sample should not show any open circuit or leakage current, any visual defect and any decrease in maximum power should not be greater than 5% all of which the thin film modules of the present invention using the encapsulant alone (i.e. no adhesive layer required). These findings are totally contrary to the expectations of the industry and use of a silicone encapsulant as hereinbefore described is able to provide the level of protection suitable for solar or photovoltaic module of a polycrystalline Silicon wafer type. In this case the only difference from example 8 was the change in the solar cells used. The adhesive and encapsulant compositions were as descr