# Tag Info

107

There are two main reasons why glass is still preferred over say PMMA. The first is durability. As long as it isn't broken, the glass in a window can easily last for hundreds of years in good condition. In particular it is a lot more resistant to scratches than comparable plastics and isn't really subject to much in the way of environmental degradation. ...

44

Here is a plastic (most likely PMMA) window, in a boat, after only 37 years. In addition to the obvious scratches, the outer surface has developed a cloudiness : possibly from degradation due to UV light, and (towards the LH end) you can see a cubelike pattern of stress cracks, rather like a toughened glass windscreen after a pebble hit it. You really ...

30

What are the requirements for window glass? Resistance to moisture Resistance to UV radiation Resistance to cleaning agents Very high transmission in the visible spectrum (There are many more, from an engineering point of view) Most transparent plastics are not resistant enough. Plexiglas is one example which fulfills the requirements enough to be used ...

14

According to Wikipedia: It [Sabatier reaction ] involves the reaction of hydrogen with carbon dioxide at elevated temperatures (optimally 300–400 °C) and pressures in the presence of a nickel catalyst to produce methane and water. $$CO_2 + 4H_2 \rightarrow CH_4 + H_2O + \text{Energy}$$ as you can see from the previous chemical reaction, to obtain 1 ...

14

I actually did make windows out of plexiglas for an outbuilding. I could work them to the shape I wanted and they were lightweight. However, I discovered that they indeed scratch easily: just trying to get the protective paper off I both scraped and melted the plastic. We want hard windows for houses and primary buildings. So what you describe would be ...

10

R134a..Here "a" is used to denote that it is an isomer. R134 and R134a have same chemical formula and atomic weight but different chemical structures. R134 has NBP of about -19 C whereas R134a has a NBP of about -26C. And dont use capital 'A' in R134a …. "A" denotes that the refrigerant is non -azeotropic. ResearchGate

9

After some research, we are using glass windows as it was used traditionally. Actually plastic windows exists. Though it may take time for most of us to adapt to it. While the reasons to consider glass windows are: Up to 80% of all recycled glass can be reclaimed. Recycled glass uses 40% less energy than manufacturing new glass. Recycling doesn’t ...

7

One of the problems that plagued older rechargeable batteries (e.g. Nickel Cadmium ($\text{NiCad}$) and Nickel Metal Hydride ($\text{NiMH}$)) was the memory effect. The memory effect occurs when a rechargeable battery is not fully discharged. It then "forgets" that it has a greater capacity than it thinks it has, and so in the future it discharges less. A ...

7

My first thought was to use a small amount of chromium and then another metal (gold). This is how its done for electronics structures on glass. The chromium does react with the silicium-oxid and hence has strong bonding. I've done this only with layers of very small thickness (sub µm), and only via a PVD-technique. But, as you can read on this Wikipedia ...

6

Another issue is that the coefficient of thermal expansion of many plastics is higher than that of window glass. Frames for plastic windows would have to be able to accommodate more expansion / contraction than those for glass windows. http://www.eplastics.com/Plastic/plastics_library/Coefficients-of-Thermal-Expansions-of-Plexiglass http://www.sdplastics....

6

For a combustible mixture to ignite, it must be within its flammability limits. This forum provides an anecdotal explanation for gasoline's inflammability in an automobile tank: ...when the tank is empty the vapor level is above the HEL or UEL (upper explosive limit). If the flammable vapors are higher in concentration than this level it will not ignite. We ...

5

Measuring the conductivity of water is actually one of the standard ways of measuring its salinity. The figure below (taken from this University of British Columbia page) shows that the relationship over many orders of magnitude is $$\sigma\propto S,$$ where $\sigma$ is the conductivity and $S$ is the salinity. They further note that the conductivity ...

5

As far as I understand your question you are looking for a way to diffuse/mix two gases into each other. The process is very hard to simulate "correctly" because of the characteristics of the equations. However, it is quite unlikely that you will have a worse mixing than predicted because the models usually underestimate the turbulent mixing processes. Your ...

5

If you get complete combustion of any hydrocarbon fuel, your products will be primarily $CO_2$ and $H_2O$. Other products will be present in quantities too small to be relevant to the heat losses that you're looking at. These two gases will change the heat capacity, conductivity and density of the flame and your exhaust gases. So heat heat transfer ...

5

The easy question Do any of the components above have higher costs to society than CO2 per same unit of measure (e.g. gram, kilogram, or ton)? Yes, absolutely. This should come as no surprise given the composition of the exhaust—it's mostly inert gases. Water vapor, CO2 and nitrogen gas are all products of the various reactions taking place in the vehicle'...

5

Chuck is right that there could be some galvanic action contributing to your issue. One other possibility is that your aluminum has been contaminated with steel particles at some point. Your second picture does seem to clearly show rust, which wouldn't be happening if the metal was all aluminum. It's less clear what the issue is in the first picture, but it ...

5

$\frac{1}{22.4}\frac{\mathrm{mol}}{\mathrm{L}}$ is only valid for standard conditions. Use the ideal gas law to calculate the concentration for your conditions. $s \equiv$ standard conditions $2 \equiv$ your conditions $p_s V_s = n_s R T_s$ $\frac{p_s V_s}{n_s T_s} = R = const = \frac{p_2 V_2}{n_2 T_2}$ $\frac{n_2}{V_2} = \frac{p_2 T_s n_s}{p_s T_2 V_s}$...

5

Bottled air is used for SCUBA because it is simple, reliable and relatively inexpensive and an open circuit system with a demand valve is pretty safe to use. There are closed circuit systems (rebreathers) which use bottled pure oxygen and CO2 scrubbers, which give greatly extended endurance per weight, but they are significantly more complex than gas-mix ...

5

Nylons are a class of polymers formed from di-acid and di-amine monomers. The amine groups bond with the acid groups to form amide groups, end to end. The resulting amide groups have a positive charge at the amine hydrogen, and negative charge at the acid double-bond oxygen. The result is a polymer with periodic polar moments across the chain. The polar ...

5

This is an instrument symbol, they are read in the following way, ISA Symbology The symbology of the instrument it is placed in a circle of 7/16 “or 12 mm (see below), was in the top there is the functional identification (of the instrument or device) composed with max 5 letters, and in the bottom there is identification of the loop (measurement and/...

4

Pu238 is not usually isotopically separated from spent nuclear fuel for exactly the reason you pointed out, it would be very difficult. Instead most of what we have comes from one of two different processes. The first is bombardment of Np237 (also made in a nuclear reactor) with neutrons. It will become Np238 and then undergo a beta emission (fancy way of ...

4

One advantage these chemical systems may have over compressed tanks is how well they are suited for intermittent use and long-term storage (as opposed to regular, continuous operation). The US FAA Aviation Maintenance Technician Handbook points out this advantage on page 16-5: Sodium chlorate chemical oxygen generators also have a long shelf life, ...

4

From personal experience of refuge systems, oxygen generating systems are preferred over medical oxygen gas tanks because of space requirements, portability and the ease of relocation. When emergency refuge systems are designed and installed, either underground, in mines or tunnelling projects or at industrial plants like oil refineries and chemical plants, ...

4

Preliminary results I added a conical structure before the choking point to separate the flow. Basically cutting the fluid. This cone is attached with 4 supports. This configuration increased mixing by a ridiculous amount. I achieved a near linear product distribution. However, I have not run temperature or structural analysis on this cone to validate ...

4

Usually what is implied by low flowrate and high viscosity is that we are dealing with a so-called low Reynolds number flow. The Reynolds number is dimensionless number which is the ratio of inertial forces ($\rho U U$) and viscous force ($\mu U/L$): $$\mathrm{Re}=\frac{\rho U U}{\mu U/L}=\frac{\rho U L}{\mu}$$ For low $\mathrm{Re}$ viscous forces dominate (...

4

The Richardson number $\mathrm{Ri} = \frac{\mathrm{Gr}}{\mathrm{Re}^2} = \frac{\text{buoyancy term}}{\text{flow gradient term}}$ (1) can be used to determine if forced or natural convenction dominate in thermal convection. $\mathrm{Re}$ = Reynolds number $\mathrm{Gr}$ = Grashof number You can neglect natural convection for $\mathrm{Ri} < 0.1$ and ...

4

I found the average of the inlet and outlet pressure and temperature in the hydrocarbon stream and then used those values in the ideal gas equation to find the densities of each hydrocarbon Why would you find the density of each hydrocarbon? you now have a mixture flow and you need to find the thermal properties of this mixture for your heat transfer ...

4

The process of encasing electronics in a material is called potting. Various resin materials can be used, such as polyester resin or epoxy. Discussion of the types of resin can be found in this article on Potting Compound Types. Several sources have recommended epoxy as the easiest material to begin with, but it is much more expensive than polyester ...

Only top voted, non community-wiki answers of a minimum length are eligible