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C lassroom experiments on atmospheric pressure focus largely on demonstrating its existence, often in a most impressive way. A series of amusing physics demonstrations is widely known and practiced by educators teaching the topic. However, measuring the value of atmospheric pressure (P atm ) is generally done in a rather mundane way, simply by reading some commercially produced meter. Even though students building a 35-ft high water barometer 1,2 is definitely instructive, as is the measurement of P atm with much smaller gas-filled devices, 3,4 there exist hardly any physics lab exercises focused on the measurement of atmospheric pressure. This paper describes a modification of a well-known physics demonstration into an experiment that allows one to estimate atmospheric pressure quite accurately. Our simple and inexpensive apparatus can be used in lecture demonstrations or as a tool in an educational laboratory setting. The Classic DemonstrationThe demonstration upon which our method is based is the well-known one in which a drinking glass nearly full of water is covered with a piece of cardboard and then inverted while holding the cardboard in place. When the cardboard is released, no water spills out. The explanation is straightforward. Forced by gravity to slip downward slightly, the column of water acts like a piston, reducing the air pressure P inside the glass until equilibrium is a)Fig. 1. Schematic representation of the experiment: (a) initial position, the cover is pressed by hand against the opening of the partially filled, inverted bottle; (b) water is gradually released from the bottle; (c) equilibrium is achieved. 493achieved. The slip distance ∆s is small (less than a millimeter) and so the cardboard is displaced only very slightly from the glass. The surface tension of the water is sufficient to prevent it from seeping out through the tiny gap. The demonstration works reliably with a short cylindrical container but can often fail when using a tall cylinder or partly filled bottle. 5,6 It turns out in these cases that the slip distance depends strongly on the amount of water in the container. Weltin 7 has derived a formula for determining ∆s for a column of liquid in an inverted cylindrical container. The slip distance is always very small if the container is nearly full or almost empty. However, it's possible for ∆s to be rather large-6 mm for a half-full cylinder 50-cm high. And even larger values of ∆s occur if the container has a narrow opening as in the case of a glass bottle. Such a large displacement of the water column results in the cardboard being pushed completely away from the container opening and the water spilling out. Our MethodWe start with a glass bottle that is nearly full of water and hold a small piece of cardboard firmly against the top as we invert the bottle [Fig 1(a)]. If the cardboard were now simply released, the column of water would slip so far downward that it would push the cardboard away from the opening and all the water would spill out. Instead, we hold the cardboar...

Oil treatment at field stabilization units allows preparing oil for storage and transportation, including by reducing the RVP and hydrogen sulfide content in oil. However, the use of direct fire heating of oil in pipe stills to maintain the thermal regime in the stabilization column may cause the formation of secondary hydrogen sulfide as a result of the thermal decomposition of heavy sulfur-containing hydrocarbons, which leads to additional financial losses for bringing the stabilized oil to the requirements of the current regulatory documents. A way to reduce the amount of secondary hydrogen sulfide is the transition from direct fire heating of oil to heating through an intermediate high-temperature coolant. In this case, the thermal regime of the stabilization column operation is maintained by heating in the reboiler, while it remains possible to use the existing unit columns and stills without their significant retrofitting.

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The operation of most chemical processes is accompanied by the cooling of various production streams over a wide temperature range using various refrigerants. At cooling temperatures of process streams up to 25 °C, the most common refrigerant is water prepared in circulating water supply systems of petrochemical plants equipped with fan cooling towers, the work of which is considered in the article. Operation of open cooling towers in single-circuit cooling systems is characterized by high economic efficiency with a wide range of thermal capacities. However, drip entrainment of circulating water, entry of production products into the atmosphere, enrichment of circulating water with oxygen followed by growth of microorganisms in water requires a transition to two-circuit systems in which cooling is carried out by a closed-cycle refrigerant cooled by open-cycle water passing through cooling towers. But such changes in cooling systems reduce the economic efficiency of these systems. The analysis of the equipment operation in the open and closed circuits of the cooling system, provided that a number of system parameters are constant (heat load, quality of purification of recuperation heat exchangers of the cooling system, etc.), made it possible to formulate optimization (minimization) of operating costs for water cooling. Taking into account the previously obtained models of pollution growth in recuperation heat exchangers and considering the vector of control parameters of the optimization problem, the main parameter of optimization (mimimization) of operating costs for cooling, which is the cooling temperature of cooling water, was identified. The results of the analysis of the influence of ambient air parameters on the temperature of the produced cooling water in the open cooling towers are also presented, and the calculation of the economic efficiency of the cooling system operation is carried out taking into account seasonal changes in ambient air parameters.