Fluid Pressure Drop Research Articles

Comparative analysis of performance of different types of Tesla valves

Abstract The Tesla valve is a valve with no moving parts. Its special configuration also allows the pressure drop of fluid passing through the Tesla valve from the reverse inlet to be much greater than the pressure drop of fluid passing through the Tesla valve from the forward inlet. Therefore, the Tesla valve has a certain degree of single pilot connectivity and pressure reduction capability. This article selected 8 common types of Tesla valves, By using numerical calculation method through Fluent simulation, the differences of resistance coefficient, pressure drop and Di value of 8 types of single-stage Tesla valves under three different working conditions were compared. In order to explore the performance of 8 kinds of Tesla valves under the three working conditions. At the same time, the relationship between the flow state and the structure of each part of the fluid before and after passing through the distributary pipe is analyzed. The simulation results show that due to the different structure of various Tesla valves, the flow rate, pressure and turbulent kinetic energy of the fluid inside the valve also have different changes. At the same time, there are many similarities in the flow state of some Tesla valves with similar structural types. Finally, according to the calculation results, the advantages and disadvantages of various types of Tesla valves and their applications are analyzed.

Experimental study on the heat storage characteristics of rock bed heat storage system with different packing structure

Establishing energy storage systems can provide an effective solution to the challenges posed by the variability and intermittency of renewable energy sources. Among the available options for energy storage, rock-packed bed thermal energy storage systems are widely favored for their performance, cost-effectiveness, and reliability. The more compact the rock packing, the more adequate the heat exchange of the system; however, poorer permeability increases fluid friction losses and pressure drop, which is detrimental to heat transport within the system. The permeability and heat exchange of the system jointly determines its thermal energy storage performance. This study proposes a composite packing scheme utilizing intact rock slabs and broken rock to enhance the thermal energy storage performance of the packed bed. This approach aims to augment heat exchange efficiency and elevate energy storage density while maintaining the bed's commendable permeability. Heat injection and heat extraction experiments of rock beds were conducted to study the heat storage characteristics of the rock-packed bed thermal storage system under different packing structure. In addition, this study investigates the effect of different injection pressures on the storage and release of heat in the system. The results show that the volume of the pore space of the filled bed, serving as the primary domain for gas flow and gas-rock heat exchange, is a decisive factor affecting the packed bed's permeability and heat exchange performance. When the porosity of the packed bed increased from 5.5 % to 9.9 %, its permeability increased from 1.42 × 10−13 m2 to 3.20 × 10−13 m2, yet the thermal exchange efficiency declined from 67.2 % to 65.3 %. Reasonably arranging intact rock slabs and broken rock fill can alter the path of heat transfer within the packed bed, thereby effectively enhancing its heat storage and release performance. For the same pore volume conditions, the heat exchange efficiency of the packed bed is increased by about 10 % by increasing the number of layers of broken rock fill. Additionally, high gas injection pressures can facilitate heat storage and release processes, but it does not mean that this is more efficient. The research findings can guide the selection of packing and injection schemes in packed bed thermal energy storage systems.

Study on gas–liquid sulfonation reaction under annular flow pattern in micro-reactor: Mechanism, model and process optimization

Micro-sulfonation is a new sulfonation method with great development potential. The gas–liquid micro-sulfonation are safe, efficient and low-cost, however, limited by the research progress and application scope of micro-reactors, the development of gas–liquid micro-sulfonation technique is far from enough. The gas–liquid sulfonation reaction process under annular flow pattern in micro-reactor is experimentally studied in this paper. The maximum MESA (fatty acid methyl ester sulfonic acid) yield under the experimental conditions in this study achieves 89.771 %, which is obviously higher than that (64.1 % for gas–liquid sulfonation and 76.82 % for liquid–liquid sulfonation) in conventional reactors and should be higher if the micro-reactor structure or operating conditions being further optimized. Based on the analyses of experimental results, the effect mechanisms of mass transfer and reaction on the gas–liquid micro-sulfonation efficiency are explored, and the sulfonation efficiency models and pressure drop model of four micro-reactors are established by dimensional analysis method. On account of both the mass transfer characteristics of gas–liquid two-phase flow and the high-viscosity of sulfonation products, enhancing the local disturbance of liquid phase can significantly improve the reaction efficiency. Finally, the operating conditions of two-phase flow rates and reaction time are optimized to ensure the high sulfonation product yield meanwhile reduce the fluid pressure drop or energy consumption of sulfonation process using the improved NSGA-II algorithm.

Performance of an additive-manufactured precooler under high-temperature and negative pressure environment

This paper introduces an original plate-fin precooler designed for potential applications in extreme low-pressure environments. Utilizing additive manufacturing technology, the heat transfer plate thickness is constrained to 2.0 mm, with channel widths inside the plate achieving 0.8 mm. Through experimental methods, this study aims to assess the precooler’s performance and identify critical influencing factors. Experimental results indicate that the hot fluid inlet temperature to the precooler exceeds 1100 K, with static pressures dropping below 30 kPa. Despite these conditions, the precooler demonstrates an impressive pressure recovery coefficient exceeding 97 % and achieves a maximum temperature drop of 731.4 K for the hot fluid. Furthermore, it is observed that the overall performance of the precooler diminishes with increasing mass flow rates of the hot fluid, showing fluctuations of up to 25 % when assessed by the j/f1/3 factor. Additionally, while the hot fluid inlet velocity exceeds 90 m/s, laminar flow predominates during the heat transfer process. Moreover, regardless of whether the cooling fluid experiences a phase change within the precooler, its heat transfer performance show priority than that of the hot fluid. Thus, changes in the mass flow rate of the cooling fluid have minimal impact on the overall precooler performance. Finally, the first-stage heat exchanger plays a critical role in the heat transfer process, accounting for over 2/3 of the total temperature and pressure drop for the hot fluid. This research is expected to contribute to the design of high-efficiency, low-resistance precoolers, particularly those applied for operation under negative pressure conditions.

Pressure drop prediction for R407C fluid during flow evaporation in horizontal pipes using Kalman Filter

The estimation of pressure drop in systems involving two-phase fluids holds a substantial influence over system design, energy efficiency, heat transfer dynamics, and the overall system performance. Existing correlations in the current literature exhibit considerable errors, primarily attributable to the diverse characteristics of flow patterns inside the pipe. This work presents a discussion on the pressure drop of the R-407C fluid in horizontal pipes during two-phase flow, along with the application of the Kalman Filter to improve the estimations produced by well-known correlations. The initialization data used were obtained through equations created based on experimental data and considering the influence that diameter, mass velocity, and saturation pressure have on the pressure drop. The correlations used as a basis for the calculations were selected from the literature, considering the lowest percentage error observed in the pressure drop estimation. Experimental data of pressure drop where compared with the results the obtained by using the correlation alone and in combination with a Kalman Filter. For tubes with a diameter greater than 1.5 mm, applying the correlation together with the Kalman Filter resulted in a Mean Absolute Relative Deviation (MARD) of 15.71, whereas using the correlation alone yielded a MARD of 28.26. For tubes with diameters of 1.5 mm or less, the MARD values were 12.12 and 62.90, for the combination of correlation and the Kalman Filter and for the correlation alone, respectively. These results underscore the viability of the Kalman Filter as an effective tool for improving the accuracy of pressure drop calculations in horizontal tubes.

Study on transient prediction method of dynamic underbalanced pressure after perforation detonation in ultra-deep wells

Dynamic underbalanced pressure creates a significant transient pressure difference between the upper and lower ends of the packer and the inner and outer walls of the string below the packer, which can lead to the failure of the packer, the tubing, and the casing and is one of the main reasons for the low success rate of the perforation-acidizing-testing combined technology in ultra-deep wells. A danger caused by the dynamic underbalanced pressure is increased rapidly with an increase in the well depth. Despite the fact that researchers have a well enough understanding of the applications and benefits of the dynamic underbalanced pressure, the mechanism of the wellbore failure caused by the dynamic underbalanced pressure is inadequate. Therefore, a pressure drop model of tubing-casing annulus fluid is established, and a seepage model of reservoir rock is given. A transient prediction method of the dynamic underbalanced pressure is developed by coupling the pressure drop model and the seepage model. Then, the determining factors, key nodes of the maximum value, and derivation and propagation laws of the dynamic underbalanced pressure are revealed. An influence study focusing on an ultra-deep well is conducted. The obtained results indicated that the dynamic underbalanced pressure describes a fast drop in the annulus fluid pressure caused by the fluid flow among the annulus, the perforating guns, and the perforation tunnels since the pressures in the perforating guns and the perforation tunnels are lower than the annulus pressure after the perforation detonation. The annulus fluid pressure can slowly recover and increase due to the fluid flow between the screens and the annulus and the fluid flow between the reservoir rock and the wellbore. The main form of the wellbore failure caused by the dynamic underbalanced pressure is the casing collapse deformation. Therefore, changing perforating conditions, wellbore conditions, and reservoir rock conditions can increase the maximum for the dynamic underbalanced pressure to improve the success rate of the combined technology. The research presented in this paper can provide a new understanding and prediction method of the dynamic underbalanced pressure.

Permeability of large‐scale fractures with ununiform proppant distributions in coalbed methane development

AbstractThe coalbed methane (CBM) productivity is directly determined by the fracture permeability during hydraulic fracturing, which is regulated by the distribution of proppants. The proppant may be unevenly distributed in the fracture because of variables like the architecture of the fracture and the characteristics of the sand‐carrying fluid. This study used two types of random functions to produce different ununiform distributions of proppant clusters in large‐scale fractures, with the aim of investigating the effect of these distributions on the overall permeability of the fracture. A model of fluid‐structure coupling is proposed. The closure of large‐scale fractures under in‐situ stress is analyzed using solid mechanics and the penalty function; the CBM flowing in proppant clusters and the high‐speed channel between them is simulated using Darcy's law and the Navier–Stokes equation, respectively; and the overall permeability of fractures is computed using the fluid pressure drop throughout the fracture and the fluid flowing velocity in the fracture's outlet. Since most CBM flows along high‐speed channels between the proppant clusters, the simulated findings show that the overall permeability of fractures with an uneven distribution of proppant clusters is significantly higher than that of the proppant cluster itself. As CBM becomes more discretely distributed, the proportion of CBM flowing within the proppant cluster continuously drops. As the permeability of the proppant cluster increases, the volume ratio of proppant clusters decreases, and the distribution of proppant clusters becomes more discrete, the overall permeability of the fracture continuously increases.

Design Calculation of Three Phase Separator

This research paper investigates the intricacies of design calculations involved in the development of three-phase separators in the oil and gas industry. Efficiently separating oil, water, and gas mixtures is crucial for maximizing production and ensuring compliance with environmental regulations. The paper explores the fundamental principles and equations used in the design of three-phase separators, including determining vessel dimensions, retention times, residence times, and separation efficiencies. Various factors influencing the design calculations, such as fluid properties, flow rates, pressure drops, and temperature gradients, are thoroughly analyzed. Additionally, the paper explores the importance of computational tools and simulation techniques in optimizing the design process and predicting separator performance under different operating conditions. Practical examples and case studies are provided to illustrate the application of design calculations in the successful implementation of three-phase separators in the oil and gas industry

Experimental and numerical simulation research on fluid pressure drop inside sintered metal porous plates

Experimental and numerical simulation research on fluid pressure drop inside sintered metal porous plates

Design and dynamic characteristics of automatic vertical drilling tool

Higher performance is needed in deeper and longer horizontal wellbore drilling. In vertical drilling conditions, wellbore trajectory often be led to deviation due to objective conditions. Based on the engineering issues, this paper presents a new automatic vertical drilling tool, including the innovative design and working mechanism research. This tool working mechanism are carried out, such as the mechanics model of eccentric tube and the relationships between eccentric torque and deflection angle. The eccentric tube torque increases with the wellbore deviation angle. When wellbore deviation angle is constant, the eccentric tube torque reaches maximum value when its deflection angle is 90°. The internal flow parameters are studied by fluid field simulation, such as drilling fluid flow rate, pressure drop, and pressure distribution inside this tool during downhole drilling process. The larger the diameter of switch hole, the higher is the pressure drop around, which leads to the force on push block increasing. The drilling fluid pressure increases with higher input flow rate inside this tool. The comparison of results, the data of simulation and theoretical model calculations, verified the reliability and accuracy of research. This study has provided innovative ideas and reference for drilling tool design and wellbore trajectory control methods.

Analysis of Fluid Pressure Drop through a Globe Valve using Computational Fluid Dynamics and Statistical Techniques

Fluid mechanics plays a crucial role in everyday life, enabling the selection of accessories, materials, and various components essential for a system through which fluid flows. Pressure drop stands out as one of the most relevant factors in the design of fluid flow systems. However, analytical and experimental physical methods can increase these analyses' costs and time. Hence, in this study, statistical tools are employed to carry out specific experiments supported by numerical fluid simulation, aiming to comprehend the pressure drop behavior in a fluid as it passes through a globe valve. This valve, in turn, possesses distinct operating and manufacturing characteristics. The methods employed encompass a complete factorial system of response surface as support to construct the experimental design path through computational fluid dynamics. Among the key findings, it is demonstrated that, for systems with relatively low flow rates, the valve opening percentage does not exhibit a significant relationship with fluid pressure drop. Conversely, significant effects are observed for systems with relatively high flow rates regarding the valve opening percentage and pressure drop, reaching values of up to 73% pressure drop in this study. It can be inferred that the integration of statistical experimental design techniques and computational fluid dynamics constitutes a valuable resource for studying the pressure drop of a fluid passing through a system.

Supercritical carbon dioxide heat transfer in horizontal tube based on the Froude number analysis

The heat transfer and pressure drop (ΔP) of supercritical fluid are crucial for the safety of advanced power cycles. Here, experiments were performed for sCO2 in a horizontal tube with inner diameter (din) of 10 mm, covering in the ranges of (G): 496.7–1346.2 kg/m2, heat flux (qw): 97.4～400.3 kW/m2 and pressure (P): 7.53–23.51 MPa. Inspired by the similarity of the outer wall temperature (Tow) distributions between the sCO2 flow and those of stratified-wavy-flow in subcritical pressures, the multiphase flow theory is introduced in subcritical pressures to deal with the sCO2 heat transfer. In the two-phase-like (TPL) regime, heat transfer coefficients (HTC) and friction factors (f) of sCO2 are found to significantly deviate from the correlations based on the single-phase flow theory. Further, the vapor-like Froude number FrVL is proposed to develop new correlations for both the heat transfer and the flow resistance covering the whole data range. The present paper establishes a connection between the flow resistance and heat transfer in supercritical pressures, which is important for the design and operation of sCO2 power cycles.

Numerical investigation of melting process enhancement in shell and coil latent heat storage tanks by the simultaneous use of conical coil and conical shell

Efficient energy storage rates are crucial for latent heat energy storage units. Building on previous studies highlighting the benefits of shell and helical tube configurations, which enhance energy storage rates through increased heat exchange areas, this research introduces a novel configuration featuring a combination of conical shell and conical coil. Various geometric variations, including conical/cylindrical shells and conical coils, are explored to assess their impact on charging performance using numerical simulations based on the enthalpy-porosity method. The study investigates three different numbers of coil turns (4, 6, and 8) for each configuration. Results demonstrate that the proposed conical shell and conical coil configuration significantly accelerates the melting rate, achieving a liquid fraction of 0.897 within 160 min—an improvement of 7.6 % compared to the conventional shell and helical tube configuration with the same phase change material quantity. Additionally, increasing coil turns from 6 to 8 yields an 8.8 % rise in the liquid fraction for the simple cylindrical case, comparable to the 7.6 % increase achieved by the proposed conical configuration. The findings underscore the preference for geometry modifications over increasing coil turns, as the latter leads to greater space occupation within the tank, resulting in reduced energy storage capacity and a concomitant 30 % undesirable increase in heat transfer fluid pressure drop.

Assessing nozzle flow dynamics in fused filament fabrication through the parametric map α−λ

Polymer rheology profoundly influences the intricate dynamics of material extrusion in fused filament fabrication (FFF). This numerical study, which uses the Giesekus model fed with a full rheometric experimental dataset, meticulously examines the molten flow patterns inside the printing nozzle in FFF. Our findings reveal new insight into the interplay between elastic stresses and complex flow patterns, highlighting their substantial role in forming upstream vortices. The parametric map α–λ from the Giesekus model allowed us to sort the materials and connect the polymer rheology with the FFF nozzle flow dynamics. The identification of elastic instabilities, the characterization of flow types, and the correlation between fluid rheology and pressure drop variations mark significant advancements in understanding FFF processes. These insights pave the way for tailored nozzle designs, promising enhanced efficiency and reliability in FFF-based additive manufacturing.

AIRCRAFT HYDRAULIC DRIVE ENERGY LOSSES AND OPERATION DELAY ASSOCIATED WITH THE PIPELINE AND FITTING CONNECTIONS

Theoretical research on hydraulic processes occurring in aircraft hydraulic drives is presented in the studies. Installation of angular fitting connections in aircraft pipeline systems influences hydrodynamic processes and fluid flow characteristics analysed in the research. The provided analysis is based on a validated numerical model utilizing Navier–Stokes equations and the k-epsilon turbulence model. Fluid flow inside the aircraft hydraulic drive pipeline system was investigated with flow rates up to 100 l/min. A mesh independence study was conducted for numerical simulation of the fluid flow. The obtained results include fluid pressure drops, energy losses, and operational delays associated with fluid flow vortex formations at 45° and 90° angular fitting connections. Additionally, compared results from standard methods of calculation for angular fitting connections, including the equivalent length and equivalent length same shape methods.

Gas-liquid two-phase flow pressure drop in flattened tubes: an experimental and numerical study

Experimental, numerical and empirical research is carried out on pressure drop features of air-water two-phase flow in horizontal flattened tubes. Circular tubes of 10.5 mm I.D. made of copper were successively flattened into inner heights of 9, 8, and 6 mm (AR=1.27, 1.5, and 2.2, respectively). The experiment operation conditions were 200, 500, and 1000 kg/m2s for mass velocity, 6, 8, 10 LPM for flow rate, and 0 to 0.005 for gas quality. Also, the pressure drop for R134a and R410A was estimated numerically using ANSYS Fluent. The simulation test condi-tions were for vapor quality of 0.1 to 0.9 and saturation temperature of 40°C, while the condi-tions for mass velocity and flowrate are taken as that of the experiment test. The experimental data were examined to see how different factors affect on the pressure gradient. According to the outcomes and as compared to the circular tube, the pressure gradient was raised up to 27%, 95%, and 218% for tubes flattened with aspect ratio of 1.27, 1.5, and 2.2, respectively. More-over, the pressure drop for either air-water or refrigerant fluids is increased dramatically with increasing flow rate, but it decreases with increasing vapor quality. When compared to known circular tube correlations, a good agreement was achieved. Finally, the minimum difference between the experimental, numerical, and correlated results was less than 3% for gas quality of 0.0048 and aspect ratio of 2.2.

Investigation of heat transfer and pressure drop in flexible metal hoses with corrugated surfaces

In this study, we conducted a numerical investigation of heat transfer and pressure drop in annular corrugated and 1-, 2-, and 3-start spiral-corrugated flexible metal hoses. To validate the numerical results for pressure drop, we established an experimental setup. The pressure drop results were verified through experimental data, while the numerical heat transfer results were validated against existing correlations in the literature. The results obtained using the corrugated flexible metal hoses were compared to those of a smooth tube, and all hoses along with the smooth tube were 1 meter long. The hydraulic diameters of the annular corrugated hose and the spiral corrugated hoses were 25 mm and 26.2 mm, respectively, with a corrugation depth of 3.2 mm for all hoses. Water, at an average temperature of 25?C, was used as the fluid, with a constant surface temperature of 70?C for the test tube. Analyses were conducted for Reynolds numbers ranging from 10000 to 50000. The results indicated that the fluid outlet temperature and pressure drop values for the annular corrugated hose were generally higher than those for the spiral corrugated hoses. Among the hoses tested, the 1-start spiral corrugated hose showed the highest friction factor, 7.83 times higher than that of the smooth tube. The 3-start spiral corrugated hose achieved the highest Nusselt number, 1.4 times higher than that of the smooth tube, at a Reynolds number of 20000. The performance evaluation criteria for all hoses ranged from 0.6 to 1.

Experimental investigation on the frictional pressure drop of two-phase fluids in the shell side of LNG spiral-wound heat exchangers

The frictional pressure drop of the two-phase fluids in the shell side of spiral-wound heat exchangers (SWHEs) is essential for the safe and cost-efficient operation of SWHEs. However, the characteristics of frictional pressure drop are not entirely understood yet. To investigate the frictional pressure drop characteristics, we constructed and validated the large-scale experimental platform. This study utilized air and water as working fluids to examine the impact of the total mass flow rate and vapor quality on the frictional pressure drop. The results indicate that the frictional pressure drop increases with the total mass flow rate and vapor quality. As the total mass flow rate continues increasing, the rising mass flow rate will restrain the growth rate of the frictional pressure drop. On the contrary, the rising vapor quality will promote the growth rate of the frictional pressure drop. When vapor quality rises from 0.40 to 0.48, from 0.30 to 0.40, and from 0.19 to 0.27, the frictional pressure drop gradient increases from 40.78 Pa·m−1 to 69.75 Pa·m−1, from 25.62 Pa·m−1 to 57.23 Pa·m−1, and from 21.18 Pa·m−1 to 84.58 Pa·m−1, respectively. In addition, the present study compared the predictive frictional pressure drops of six correlations with the experimental data while also analyzing the predictability of these correlations. Moreover, this study proposed a modified correlation, and the predictive values of the modified correlation met with 95 % of the experimental data with a deviation of ±25 %.

Large Eddy Simulation of Low Reynolds Number Flow Around a NACA0015 Airfoil with Modified Trailing Edges

The flow field of a low Reynolds number regime is three-dimensional and exceedingly complicated due to numerous forms of vortical phenomena, which has triggered the interest of many researchers. This study aims to investigate the influence of various trailing edge configurations on the aerodynamic characteristics and flow structure of airfoils. Specifically, five different configurations, namely baseline, serration, comb, and comb-serration are analyzed in detail. The study seeks to identify the configuration that provides optimal aerodynamic performance, which can then inform the design of more efficient airfoils for a range of applications, including unmanned aerial vehicle (UAV), wind energy, and automotive design. A Large-eddy simulation numerical model was developed to effectively evaluate unsteady pressure fluctuations and turbulence parameters at the source. The pressure coefficient and skin friction coefficient figures reveal that modifications result in an early negative pressure zone and uneven flow along the airfoil surfaces. This study presents numerical findings on the NACA0015 airfoil at a zero angle of attack. The pressure coefficient distribution along the airfoil surface exhibits a symmetrical pattern, with the highest pressure observed at the leading edge due to flow deceleration. Analysis of the skin friction coefficient confirms the absence of separation zones on the airfoil surface, except for the tip of the trailing edge. The velocity profile demonstrates a consistent and smooth flow, indicating stable and symmetrical conditions across the airfoil. Moreover, the velocity profiles of the baseline airfoil at zero angle of attack do not indicate any signs of flow separation. Notably, the serrated, combed and comb-serrated trailing edge configurations each yield distinctive effects on fluid flow. The serrated trailing edge promotes increased fluid velocity and pressure drop, while the combed configuration induces separation at the root. Meanwhile, the comb-serrated design sustains a continuous fluid flow over the airfoil surface. Overall, these results contribute to a comprehensive understanding of the aerodynamic behavior and flow characteristics influenced by various trailing edge configurations.

Transient recovery from heat pipe dryout by power throttling

Heat pipes and vapor chambers are passive heat spreaders driven by capillary pumping of an internal working fluid via a porous wick. The capillary limit is the maximum steady-state heat input at which the fluid pressure drop can be supported by the capillary pressure head generated in the wick. However, heat pipes and vapor chambers often find application in devices where the heat input is highly transient and can exceed the capillary limit for brief time intervals. Operating heat pipes briefly above the capillary limit will not result in a dryout if the operating time interval does not exceed a characteristic time-to-dryout. Operation over a duration that exceeds this time-to-dryout can induce transient dryout and may lead to thermal hysteresis, that is, the original heat pipe thermal resistance may not be recovered even after the heat input is lowered back below the capillary limit. To fully recover the heat pipe performance after a transient dryout event, our recent experiments have shown that the heat input must be lowered (or throttled) significantly below the capillary limit. Due to the highly transient nature of power dissipation from electronic devices, it becomes imperative to characterize the throttling power level and duration required to ensure full recovery of a heat pipe from dryout under transient operations. This work experimentally characterizes recovery of heat pipes from dryout by power throttling under transient conditions, where ‘power throttling’ is the act of reducing the operating power level significantly below the capillary limit to eliminate post-dryout thermal hysteresis. We deduce from the experiments that the power must be throttled for longer than a minimum throttling time interval, defined as the time-to-rewet, in order to eliminate dryout-induced thermal hysteresis. The dependence of this time-to-rewet on the throttling power level is explored, and guidelines are presented on the need for throttling and the choice of throttling power under transient conditions.