Steam Download Rate Keeps Dropping To 0
Lester Chiaramonte
while dropping cards and selling them means $$$ for steam, buying games and selling cards means more $$$. considering many people buy games just for their card drops, it's not really good idea for steam to accept refunds for those games. so they'll either terminate the refund program or make drop rates longer. i don't know about you but i liked the refund system. devs started to actually work on their games already instead of saying "tough luck bruh." (see: batman arkham knight).
In recent weeks, leading up to the end of the month, indices like the S&P500 and metals like silver and gold began to run out of steam. The impetus for the decline in stock and precious metal prices was recent Fed comments regarding higher interest rates in the foreseeable future.
A heat exchanger manufacturer will design equipment to give a certain heat output. To achieve this heat output, a certain saturated steam temperature will be required at the heat transfer surface (such as the inside of a heating coil in a shell and tube heat exchanger). With saturated steam, temperature and pressure are strictly related; therefore controlling the steam pressure easily regulates the temperature.
Consider an application where steam at 10 bar g is supplied to a control valve, and a given mass flow of steam passes through the valve to a heat exchanger. The valve is held fully open (see Figure 6.4.1).
When the pressure drop across a valve is greater than critical, noise can be generated by the large instantaneous exchange from kinetic energy to heat energy in the low pressure region, sometimes exacerbated by the presence of supersonic steam.
Valve outlet velocity, noise, erosion, drying and superheating effect
Noise can be an important consideration when sizing control valves, not only because it creates increased sound levels but because its associated vibration can damage valve internals. Special noise-reducing valve trims are available but, sometimes, a less expensive solution is to fit a larger valve body than required. Complicated equations are required to calculate noise emitted from control valves and these are difficult to use manually. It is usually considered that the control valve will produce unacceptable noise if the velocity of dry saturated steam in the control valve outlet is greater than 0.3 Mach. The speed of sound in steam will depend upon the steam temperature and the quality of the steam, but can be calculated from Equation 6.4.2 if the conditions are known (Mach 1 = speed of sound).
A less accurate but useful method to estimate whether noise will be a problem is by calculating the velocity in the valve outlet port. In simplistic terms and for dry saturated steam, if this is greater than 150 m/s, there is a chance that the valve body is too small (even though the valve trim size suits the required capacity). Higher velocities also cause erosion in the downstream valve body, especially if the steam is wet at this point. It is recommended that the maximum exit velocity for wet steam is 40 m/s in the outlet port.
Another result of dropping steam pressure across a control valve is to dry or superheat the steam, depending upon its condition as it enters the valve. Large degrees of superheat are usually unwanted in heating processes, and so it is useful to be able to determine if this will occur. Superheated steam (and dry gas) velocities, however, may be allowed to reach 0.5 Mach in the outlet port; whereas, at the other end of the scale, liquids might be restricted to a maximum outlet velocity of 10 m/s.
Example 6.4.1 The valve outlet velocity and drying/superheating effect
The DN32 bodied valve will be suitable because the outlet velocity is less than 0.5 Mach allowed for superheated steam.
The same procedure can be used to determine the conditions of the downstream steam for other upstream conditions. For instance, if the upstream steam is known to be wet, the downstream condition might be wet, dry saturated or superheated, depending on the pressure drop. The allowable outlet velocity will depend on the downstream steam condition as previously outlined in this section, and observed in Example 6.4.2.
Another problem is the possibility of erosion in the valve body caused by excessive velocity in the valve outlet. In Example 6.4.1, due to the drying and superheating effect of the pressure drop from 12 bar g to 4 bar g, the steam is in a dry gaseous state containing absolutely no moisture, and erosion should not be an issue.
Simplistically, if it can be guaranteed that the steam leaving a control valve is superheated, then 250 m/s is an appropriate limit to place on the outlet velocity.
Sometimes, when saturated steam is supplied to a control valve, it will be carrying a certain amount of water and the steam may be, for example, 97% or 98% dry. If it has just passed through a properly designed separator it will be close to 100% dry, as in Example 6.4.1.
With anything more than a small pressure drop and wet steam, the steam will probably be dried to saturation point or even slightly superheated.
If the supply steam is dry and/or the valve encounters quite a large pressure drop, (as in Example 6.4.1), the steam will be more superheated.
Plate heat exchangers are a useful alternative; being relatively small and light, they have a small mass and are extremely quick to respond to changes in heat load.
When properly designed, they tend not to foul, but if they do, they are easily disassembled, cleaned and recommissioned. Compared to shell-and-tube exchangers, they can operate at lower pressures for the same duty, but because of their high heat transfer characteristics, and a lower requirement for oversizing, they are still smaller and less expensive than a comparable shell-and-tube exchanger.
Plate heat exchangers (when properly engineered to use steam) are therefore more economically suited to high pressure drops across control valves than their shell-and-tube counterparts. This can give the advantage of smaller and less expensive control valves, whilst minimising the cost of the heat exchanger itself. Generally, it is better to design the system so that the plate exchanger operates with critical pressure drop (or the highest possible pressure drop) across the control valve at full load.
It must be stressed that not all plate heat exchangers are suitable for steam use. It is very easy to buy a heat exchanger designed for liquid use and wrongly assume that it will perform perfectly when heated with steam. Correct selection for steam is not just a matter of pressure/temperature compatibility. Proper expertise is available from bona fide manufacturers, and this should always be sought when steam is the prime energy source.
Steam sizing examples using charts
16. Pressure drops, sizes of valve body and noise level are related and should be considered. It is good practice to keep the downstream steam velocity in the valve body typically below 150 m/s for saturated steam and 250 m/s for superheated steam. This can be achieved by increasing the valve body size, which will also reduce the velocity in the valve outlet and the likelihood of excess noise. It is possible to consider a saturated steam exit velocity of 150 m/s to 200 m/s if the steam is always guaranteed to be dry saturated at the valve inlet. This is because, under these circumstances, the steam leaving the control valve will be superheated due to the superheating effect of reducing the pressure of dry saturated steam. Please note that these are general figures, different standards will quote different guidelines.
17. Leakage and isolation. Control valves are meant to control flowrate rather than isolate the supply, and are likely to leak slightly when fully shut. Control valves will be manufactured to a standard relating to shut-off tightness. Generally, the better the shut-off, the higher the cost of the valve. For steam control valves, a leakage rate of 0.01% is perfectly adequate for most applications.
18. Turndown. Usually expressed as a ratio of the application maximum expected flow to the minimum controllable flow through a control valve.
19. Rangeability. Usually expressed as a ratio of the valve maximum controllable flow to the minimum controllable flow, between which the characteristics of the control valve are maintained. Typically, a rangeability of 50:1 is acceptable for steam applications.
20. It would be wrong to end this Module on control valves without mentioning cost. The type of valve, its materials of construction, variations in design and special requirements will inevitably result in cost variations. For optimum economy the selected valve should be correct for that application and not over-specified.
The National Association of Realtors expects mortgage rates will average 7.5% in the first quarter of 2024, dropping to 6.9% in the second quarter, according to its latest Quarterly U.S. Economic Forecast. The trade association predicts that rates will continue to fall to 6.3% by the end of the year.
While mortgage rates can influence market conditions in the immediate term, there's still a seasonality to home sales trends. Housing activity tends to pick up in the spring and summer months, losing steam in the fall and winter. Although mortgage rates are still likely to remain high through the end of the year, home sales prices tend to be lower during the off-season.
With the Fed skipping rate hikes across three consecutive meetings and hinting at rate cuts in 2024, refinance activity may gain steam fueled by borrowers who purchased homes when rates were hovering near 8%.
So how can we get enough steam in the oven to keep those loaves rising? There are indeed methods abound, and each person has a different approach, but arguably the most popular choice at the moment, and the one I started with, is baking bread in a Dutch oven (see my guide on how to bake bread in a Dutch oven if you're not familiar). However, there comes a time when you might want to bake two (or more) loaves at a time, or perhaps your loaves are scaled more substantial than your Dutch oven can comfortably hold. An alternative is to bake directly on stones and generate sufficient steam in your home oven by some other clever means.
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