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Ventilation Operating Costs
Published in William Popendorf, Industrial Hygiene Control of Airborne Chemical Hazards, 2019
This cycle begins on the right side of Figure 17.4 where (like any gas or vapor) the temperature of the vapor phase of a specifically chosen refrigerant rises as it is compressed. The warm, high-pressure vapors then flow through a finned heat exchanger (depicted at the top of the figure that is typically outdoors) where it will condense and release its “heat of evaporation.” The now at least partly liquid refrigerant that leaves the condenser is cooler than the gas when it arrived (although the first law still says that it cannot be cooler than the ambient warm air (or water) into which it is dumping its heat).j Like all diatomic gases that cool when they undergo a pressure reduction (the “Joule–Thomson effect”), the refrigerant’s temperature drops upon passing through a pressure reduction and expansion valve on the left side of Figure 17.4. As the now cold refrigerant evaporates in the second heat exchanger at the bottom of Figure 17.4, it absorbs its “heat of vaporization” from the cool environment, making the cool environment colder. The now-vapor phase refrigerant is still at or above the cool environmental temperature outside the evaporator as it leaves the evaporator and returns to the compressor to repeat the cycle.
Real Gases
Published in Igor Bello, Vacuum and Ultravacuum, 2017
The detailed investigation of the Joule–Thomson effect147 on a base of the thermodynamic principles shows that the ratio ΔT/Δp is a function of p and T. At some pressures and temperatures, the temperature change is not observed, which means that the real gas behaves as the ideal gas. At these conditions, the attractive and repulsive forces are in balance. At higher pressures, the influence of larger repulsive forces results in heating of a real gas so that the ratio ΔT/Δp is negative. Therefore, this effect is called the negative Joule–Thomson effect. At lower pressures, prevalent attractive molecular forces between molecules induce cooling of real gases at their expansion and the value of ΔT/Δp is positive. We talk about the positive Joule–Thomson effect at which gas cools. However, the positive Joule–Thomson effect (cooling of gas) may be observed for any gas, but only within limited regions of temperatures and pressures. The discussed cooling phenomenon at real gas expansion can be used at gas liquefaction. Each gas, before cooling down upon its expansion, has to be below a certain temperature known as inversion temperature. Inversion temperatures for some gases can be found in different publications. For example, Wannier148 gives experimental inversion temperatures for He, H2, N2, and CO2 to be 51, 202, 621, and 1500 K, respectively.
Carbon Membranes for Natural Gas Sweetening
Published in Xuezhong He, Izumi Kumakiri, Carbon Membrane Technology, 2020
Evangelos P. Favvas, Sotirios P. Kaldis, Xuezhong He
Coker et al. [155] considered the hollow fiber membrane as a series of stages in the axial direction and developed a model taking into account pressure-dependent permeability coefficients and bore-side pressure gradients. They concluded that the existence of a boundary layer at the membrane interface (known as concentration polarization) results in the formation of pressure and concentration gradients and reduces the driving force. Scholz et al. [156] developed and validated a model taking into account concentration polarization, the Joule–Thomson effect, pressure losses and real gas behavior. They concluded that the non-ideality of a CO2 gas mixture is significant and could affect the modeling results.
Progress in research on dispersants in gas hydrate control technology
Published in Journal of Dispersion Science and Technology, 2023
Yue Qin, Liyan Shang, Rencong Song, Li Zhou, Zhenbo Lv
The temperature drop in the gas-liquid mixed system due to the Joule–Thomson effect causes the gas and liquid phases in the system to reach the low-temperature conditions necessary for the formation of hydrates,[44] which means that the thermodynamics of the system must be in the phase coexistence state.[45] When the hydration reaction system is in the form of a slurry, changes in the pressure value in the kinetic parameters have a negligible effect on the extent of hydrate formation, and this variation is difficult to analyze. However, the thermodynamic method can solve the problem of hydrate dissociation under slurry conditions. At present, most studies use the Clapeyron equation or Clausius–Clapeyron equation to calculate the enthalpy of the dissociation of hydrates.[46–49] The gas pressure and gas fraction are used directly or indirectly to obtain the dissociation enthalpy values using the two equations. Therefore, measuring specific gas state parameters, controlling the solubility of the gas in the liquid phase, and controlling the molar mass of the gas that can participate in the reaction are ways in which the dissociation enthalpy can be varied in different systems. To this end, the application of dispersant in the system is not only the most direct but also the most effective method for controlling the amount of gas that can participate in the reaction in the liquid phase. Consequently, it is crucial to study how the dispersant affects the liquid phase.
Multi response optimization of dual jet CO2+SQL in milling Inconel 718
Published in Materials and Manufacturing Processes, 2023
Nimel Sworna Ross, V. Sivaraman, M. Belsam Jeba Ananth, M. Jebaraj
The drop size and speed have an impact on the SQL stream. The investigation was conducted using olive oil with an approximate viscosity of 40 cP. It has a high viscosity index, low in volatility, and is lubricious. Oil + air droplets with sizes ranging from 0.5 to 5 µm were jetted at a 45º angle on the rake side of the insert at 2 bar pressure. The cryogenic CO2 arrangement was designed to release the liquefied gas at a 45º angle to the cutter-work material junction. In the cryogenic tank, CO2 was compressed at high pressure (57 bar). Because of the Joule – Thomson effect, the liquid CO2 turns into 40% snow and 60% gas as it exits the pipe. Without any additional energy, the cryogen is sprayed fiercely into the cutting region by the pressure inside the tank (rake face). CO2 gas is allowed to pass through the thermally insulated rubber hose at a pressure of 2.5 bar. The rake face of the cutter is outfitted with CO2 and SQL nozzles (Fig. 1). The CO2 nozzle delivers cooling, while the SQL offers lubrication. For discharging SQL and CO2 at the insert, a 2 mm nozzle exit was used.
A review on sustainable alternatives for conventional cutting fluid applications for improved machinability
Published in Machining Science and Technology, 2023
D. J. Hiran Gabriel, M. Parthiban, I. Kantharaj, N. Beemkumar
Jamil et al. conducted experimental research to compare the effects of cryogenic CO2 and hybrid nano fluid-based Minimum Quantity Lubrication (MQL) techniques for turning Ti–6Al–4V. Coated carbide inserts were employed for the process of turning. The cryogenic lubricant was applied using a nozzle with an orifice of 0.5 mm. The pressure of the cryogenic CO2 was maintained at 8 bar. The nozzle was positioned 5 cm from the zone of cutting. When the coolant is sprayed, due to the Joule–Thomson effect, a temperature drop occurs, causing the liquid CO2 to freeze into dry micro grains. These dry micro grains made an effective penetration into the zone of metal cutting and aided in the effective evacuation of heat generated during machining when compared to hybrid nanofluid–based Minimum Quantity Lubrication (MQL). The investigation showed that the cryogenic CO2-assisted turning process made parts that were of a good enough quality to be useful (Jamil et al., 2019).