Vapor Mass Flow Rate Research Articles

Experimental analysis of ammonia–water rectification in absorption systems with the 10 mm metal Pall ring packing

In this paper, the mass transfer performance of the 10 mm metal Pall ring packing for ammonia rectification in ammonia–water absorption refrigeration systems (AARS) is investigated. The experimental setup is described and the experimental procedure and data reduction method are explained. Experimental results of the top vapour temperature, concentration and mass flow rate are presented for different operating conditions, including reflux ratio values from 0.4 to 1 (total reflux conditions). Vapour phase mass transfer coefficients are calculated from the measured data and the results are compared with different mass transfer correlations found in the open literature. In this paper, a correlation is proposed for the packing analysed which was fitted from the experimental data. Finally, a comparison is made between the actual packing height used in the experimental setup and the height required to obtain the same ammonia rectification in AARS with the first generation packings: ½″ ceramic Berl saddles, 15 mm glass Raschig rings and ½″ ceramic Novalox saddles. It was found that a packing height reduction between a factor of 2.5 and 3 is attained with 10 mm metal Pall rings.

Evaluation of tunable diode laser absorption spectroscopy for in‐process water vapor mass flux measurements during freeze drying

The goal of this work was to demonstrate the use of Tunable Diode Laser Absorption Spectroscopy (TDLAS) as a noninvasive method to continuously measure the water vapor concentration and the vapor flow velocity in the spool connecting a freeze-dryer chamber and condenser. The instantaneous measurements were used to determine the water vapor mass flow rate (g/s). The mass flow determinations provided a continuous measurement of the total amount of water removed. Full load runs of pure water at different pressure and shelf temperature settings and a 5% (w/w) mannitol product run were performed in both laboratory and pilot scale freeze dryers. The ratio of "gravimetric/TDLAS" measurements of water removed was 1.02 +/- 0.06. A theoretical heat transfer model was used to predict the mass flow rate and the model results were compared to both the gravimetric and TDLAS data. Good agreement was also observed in the "gravimetric/TDLAS" ratio for the 5% mannitol runs dried in both freeze dryers. The endpoints of primary and secondary drying for the product runs were clearly identified. Comparison of the velocity and mass flux profiles between the laboratory and pilot dryers indicated a higher restriction to mass flow for the lab scale freeze dryer.

Development of a numerical analysis methodology for the multi-dimensional and multi-phase phenomena of a sodium–water reaction in an SFR steam generator

A numerical approach on the exothermic sodium–water reaction (SWR) in a SFR steam generator is carried out by using a commercial computational fluid dynamics (CFD) code. The applicability of the analysis models and the physical limitations of some codes was investigated to select the most powerful CFD code to simulate a chemically reacting flow with various phases and components. In order to model the phenomena, among the several chemical reaction models studied, the eddy dissipation model (EDM) was employed because the EDM is the proper one when the reaction rate is sufficiently high when compared to the flow transport time. Based on the basic understandings for the characteristics of the SWR phenomena and the capabilities of the CFD codes, the numerical analysis methodology for a SWR was developed and transient analyses up to 0.05 s and 0.1 s with a time step of 0.0001–0.0005 s were carried out with a consideration of the geometric effect. The vapor mass flow rate and the corresponding hydrogen production rate were also calculated and compared with the conventional one-dimensional analysis results. As a result, it was found that the multi-dimensional approach underestimates the hydrogen production rate by 17% when compared to the theoretical values, and the difference is mainly caused by a multi-dimensional effect of the chemical reaction. The analysis performed in this study presents detailed information on each phase and the components of the SWR process and it also reflects the realistic SWR phenomena well. In order to confirm the applicability of the methodology, a multi-dimensional analysis was also carried out for the 49 tube bundle condition, and it was found that the results of the analysis were satisfactory.

Advanced Distillation Curve Measurement with a Model Predictive Temperature Controller

In previous work, several significant improvements in the measurement of distillation curves for complex fluids were introduced. The modifications to the classical measurement provide for (1) temperature and volume measurement(s) of low uncertainty, and most important, (2) a composition-explicit data channel in addition to the usual temperature–volume relationship. This latter modification is achieved with a new sampling approach that allows precise qualitative as well as quantitative analyses of each fraction, on the fly. In the new approach, the distillation temperature is measured in two locations. The temperature is measured in the usual location, at the bottom of the take-off in the distillation head, but it is also measured directly in the fluid. We have further modified our developmental instrument to incorporate a model predictive temperature controller. In response to either an equation-of-state calculation or a previous distillation curve, the programmable temperature controller increases the fluid temperature to achieve a constant mass flow rate of vapor through the distillation head. This approach eliminates the aberrations that one typically encounters in the data due to fluctuations in distillation rate, often referred to as hesitation. Thus, we can collect data from two temperature channels: one a true state point measurement (measured directly in the fluid) and the other comparable to previous data (measured in the head).

Modeling and experimental investigation of accumulators for automotive air conditioning systems

A stream analysis model was developed to simulate the behavior of accumulators and their influence on the automotive air conditioning (A/C) systems. It allows a comprehensive steady state simulation with a set of input conditions such as refrigerant vapor mass flow rate and pressure at the inlet of an accumulator. In this study, the refrigerant/oil mixture is R134a/PAG oil which are totally miscible, but could be any air conditioning refrigerant/oil, including carbon dioxide (CO 2)/oil. The model accounts for all major effects inside the accumulator, such as friction, bends, sudden expansion, sudden contraction and heat exchange. The outputs are vapor quality, pressure and temperature at various positions of accumulator. In order to verify the mathematical model, experiments are performed in an experimental setup made up of real size automotive air conditioning components. The simulated results agree well with the experimental data. The simulation and experimental results show an important function of accumulators that is to determine the vapor quality into compressor, and thus has influence on the performance of whole automotive A/C systems.

Vapor quality and performance of an automotive air conditioning system

This paper reports the results of a study on the performance of an automotive air conditioning system with measuring the vapor quality. To quantitatively measure the vapor quality (two-phase flow) at outlet of the accumulator, a large diameter tube is inserted between the accumulator and the compressor to separate refrigerant vapor from the miscible mixture of liquid refrigerant and lubrication oil. The coefficient of performance, evaporator cooling capacity, compressor power consumption, total mass flow rate, vapor mass flow rate, liquid mass flow rate and oil in circulation, pressures and temperatures of refrigerant at every component (inlets and outlets) are measured and analyzed with the variation of the outside temperatures at the evaporator and condenser, the speed of the compressor, refrigerant charge and oil charge. The systematical experimental results obtained from this real-size test system depict the relations between the above parameters in an automotive air conditioning system, which constitute a useful source for automotive air conditioning systems design and analysis. The vapor quality (two-phase flow) measurements realized in this work provide an extremely important tool for diagnosing the system performances.

Experimental Research on In-Tube Condensation under Steady-State and Transient Conditions

In this research study, in-tube condensation in the presence of air was investigated experimentally at a heat exchanger of countercurrent type for different operating conditions. The test matrix for the steady-state condition covers the range of pressures P = 1.8 to 5.5 bars, vapor Reynolds numbers Rev = 45 000 to 94 000, and inlet air mass fraction values Xi = 0 to 52%. The effect of air manifests itself by a reduction in the local heat flux and the local heat transfer coefficient. The local heat transfer coefficient is inversely proportional to the local air mass fraction. Both the local heat flux and the heat transfer coefficient vary with the system pressure and vapor mass flow rate. There is no effect of inlet superheating on the local heat flux. The film Reynolds number lies in the range of the turbulent region. Two experiments simulating loss of coolant to the secondary side of the condenser were performed, for pure steam and for an air/steam mixture. These transients show that the vapor suction rate, effective condensation length, and overall heat transfer rate are a function of the coolant boiloff rate and the air mass fraction.

Effects of inlet conditions on film evaporation along an inclined plate

The evaporation of falling water liquid film in air flow is used in different solar energy applications as drying, distillation and desalination, and desiccant systems. The good understanding of the hydrodynamics and heat exchange in falling liquid film and gas flow, with interfacial heat and mass transfer, can be applied in improving solar systems performance. The solar system performance is dependent on the operating conditions, system conception and related to several physical parameters, where the effects of some of these parameters are not completely clarified. In the present numerical study, we examine the effects of inlet conditions on the evaporation processes along the gas–liquid interface. The liquid film streams over an inclined plate subjected to different thermal conditions. Liquid and gas flows are approached by two coupled laminar boundary-layers. The numerical solution is obtained by utilizing an implicit finite-difference box method. In this analysis an air–water system is considered and the coupled effects of inclination, inlet liquid mass flow rate and gas velocity are examined. The results show that, for imposed heat flux or uniform wall temperature, the effect of inclination is highly dependent on the liquid mass flow rate and gas velocity. An increase in the liquid mass flow rate causes an enhancement of the effect of inclination on the heat and mass transfer. The inclination affects the heat and mass transfer, especially at lower gas velocities. In the range of inclination angles of 0–10°, an increase in the inclination improves the evaporation by increasing the vapor mass flow rate. The maximum effect of inclination is nearly achieved at an inclination angle of 10°.

Effects of inlet conditions on film evaporation along an inclined plate

The evaporation of falling water liquid film in air flow is used in different solar energy applications as drying, distillation and desalination, and desiccant systems. The good understanding of the hydrodynamics and heat exchange in falling liquid film and gas flow, with interfacial heat and mass transfer, can be applied in improving solar systems performance. The solar system performance is dependent on the operating conditions, system conception and related to several physical parameters, where the effects of some of these parameters are not completely clarified. In the present numerical study, we examine the effects of inlet conditions on the evaporation processes along the gas–liquid interface. The liquid film streams over an inclined plate subjected to different thermal conditions. Liquid and gas flows are approached by two coupled laminar boundary-layers. The numerical solution is obtained by utilizing an implicit finite-difference box method. In this analysis an air–water system is considered and the coupled effects of inclination, inlet liquid mass flow rate and gas velocity are examined. The results show that, for imposed heat flux or uniform wall temperature, the effect of inclination is highly dependent on the liquid mass flow rate and gas velocity. An increase in the liquid mass flow rate causes an enhancement of the effect of inclination on the heat and mass transfer. The inclination affects the heat and mass transfer, especially at lower gas velocities. In the range of inclination angles of 0–10°, an increase in the inclination improves the evaporation by increasing the vapor mass flow rate. The maximum effect of inclination is nearly achieved at an inclination angle of 10°.

Investigation on condensation in presence of a noncondensable gas for a wide range of Reynolds number

A theoretical model has been developed to study the local heat transfer coefficient of a condensing vapour in the presence of a noncondensable gas, where the gas/vapour mixture is flowing downward inside a vertical tube. The two-phase heat transfer is analysed using an annular flow pattern with a liquid film at the tube wall and a turbulent gas/vapour core. The gas/vapour core is modeled using the analogy between heat and mass transfer. The model incorporates Nusselt equation with McAdams modifier and Blangetti model for calculating the film heat transfer coefficient, Moody and Wallis correlations to account for film waviness effect on gas/vapour boundary layer. The suction effect due to condensation, developing flow and property variation of the gas phase is also considered. A comparative study of heat transfer coefficient and vapour mass flow rate has been made with various models to account for condensate film resistance and condensate film roughness. Results show that for very high Reynolds number, the condensation heat transfer coefficient is higher than the film heat transfer coefficient.

Film condensation between two vertical plates

SYNOPSIS A mathematical model of the condensation process from a vapour flowing downwards between two vertical plates of constant wall temperature is presented. With this model it is possible to calculate the condensate film thickness, condensate mass flow, vapour pressure difference, vapour mass flow and condenser heat rate. The case where all the vapour condenses is also considered. It is shown in both cases that as the distance between the plates increases the condenser heat rate decreases.

Numerical simulation of two-phase Helium II stratified flow in cryogenic units of TESLA

Numerical simulation has been carried out for two-phase Helium II stratified flow in 12 horizontal or declining cryogenic units each with a length of about 2.5 Km for the proposed 500 GeV TESLA (TeV Superconducting Linear Accelerator). The simulation predicts the He II level, the vapor mass flow rate in the two-phase tube, and the pressure profile through the gas return pipe of all units as well. Based on the numerical results the flow pattern and the stability of He II/vapor two-phase flow are discussed.

Experimental analysis of a transfer function for an air cooled evaporator

A transfer function to model a direct expansion air cooled evaporator, inserted in a vapor compression refrigeration plant, is deduced by means of experimental analysis. For inlet air temperatures onto the evaporator and refrigerant mass flow rate variable in appropriate ranges, the evaporator dynamic behavior is simulated by a linear model with delay. The results of transfer function are compared with experimental data, obtained by applying both step inputs and periodic changes to the refrigerant mass flow rate. The influence of the hunting, typical of a thermostatic expansion valve, is also estimated experimentally and then validated by the transfer function, obtaining a good agreement. These results could be applied to obtain a control algorithm for the refrigerant mass flow rate feeding the evaporator, by varying the speed of the compressor motor.

Melt crystallization by controlled evaporative cooling. The caprolactam–water system in batch operation

An adiabatic evaporative cooling crystallization process was developed, in which cooling is achieved by evaporating a cooling agent under a reduced pressure. In this way, the actual cooling is achieved in a condenser, without a solid phase being present. It is shown that the optimum operating strategy can be determined from the phase diagram. Caprolactam was crystallized from caprolactam–water mixtures by evaporating water. For this system the optimum process conditions are at 5 wt% water, a temperature of 53°C, and a pressure of 4.2 kPa. The temperature is controlled adequately by controlling the vapor mass flow rate instead of the pressure, which leads to an excellent and easy control system and therefore a reproducible batch crystallization process. The permeability is high and it is shown that it is possible, after the first heterogeneous nucleation event, to suppress or even avoid nucleation during the outgrowth of these nuclei. The permeability increases with the increasing crystal mass content. Therefore, a certain target permeability is attained most quickly at the highest allowable cooling rate.

Determination of the void fraction and drift velocity in a two-phase flow with a boiling solar collector

This paper presents an approach to determine the void fraction and the drift velocity in a two-phase flow with a boiling solar collector using easily obtained experimental data. The solar collector operates in a thermal siphon circuit, where the working fluid absorbs solar radiation mostly while boiling. The vapor bubbles release their latent heat in a condenser, while heating up a flow of water–glycol. Two numerical procedures are developed to calculate the void fraction because its experimental values cannot be easily measured. The use of a flow meter causes an additional pressure drop in the thermal siphon circuit and, consequently, changes the circulated mass flow rate. The first numerical procedure is based on a force balance in the thermal siphon loop and is used to estimate the total mass flow rate and the void fraction in the circuit. The second uses a drift flux correlation to estimate the void fraction and the drift velocity. Both procedures use the experimental values for the vapor mass flow rate, which is determined by an energy balance in the condenser. The volumetric flow rate of the water–glycol mixture and its temperature difference across the condenser are experimentally measured. The pipe length of the two-phase flow in the solar collector is experimentally determined using 44 thermocouples attached to the back of flow channels in the absorber plate. The results show that the two numerical models compare well and that either one can be used to estimate the void fraction in the two-phase flow solar circuit.

Heat and mass transfer processes in two phase He II/vapor

Modeling heat and mass transfer characteristics of two phase He II is discussed. The case considered assumes that the channel flow is one-dimensional and stratified, with mass exchange between the two phases. Two specific examples are considered in some detail. The first is the heat and mass transfer characteristics for small liquid flow rate. Use of several simplifying assumptions allows the problem to be reduced to solution of a one-dimensional ordinary differential equation. The result is a non-dimensional expression for the liquid level or void fraction along the channel. A set of dimensionless parameters are defined that establish the relative contributions of vapor mass transport and counterflow in the He II. The model also predicts the temperature profile and vapor mass flow rate. The second case concerns the flow of liquid under nearly isothermal conditions with relatively small vapor mass flow rate. Under these conditions, the flow may be modeled using classical hydrodynamics taking into consideration the unique characteristics of the He II. Results of these models are compared to experimental data for heat and mass transfer in a two phase He II/vapor flow.

Vaporisation of a Pyrophoric Substance: Borane Triethyl

A flow-through system is proposed for studying the evaporation rate of a pyrophoric liquid, borane triethyl (BTE), under various conditions of pressure and volume flow of inert (nitrogen). First, some basic aspects of the problem are presented. It is shown that the BTE partial pressure tends to a limit ing value that is lower than the saturated vapor pressure that can be obtained in closed box system, and that is a function of pressure and volume flow of inert. When this limiting pressure is reached, the mass flow rate of BTE vapor leaving the flow-through system is constant and equal to the evaporation rate. Therefore, such a procedure can be used for generation of controlled and stabilized BTE vapor-inert mixtures. Next, some experiments, conducted using strict precau tions, are presented. They allow for the determination of an evaporation constant for different initial masses of BTE liquid, and for different pressures and volume flows of inert.

A New Method for Measuring Vapor Emissions

An approach for measuring point-source emissions of volatile organic compounds (VOCs), acidic vapors, and other species is presented. The amount emitted is determined by directly measuring the actual weight gain of an adsorbent bed over a period of time, which is a cumulative rather than a grabbed sample. As a result, wide fluctuations of concentration and erratic flow behavior during sampling are accommodated with no apparent effect on the accuracy of the measured emission rate. The emission rate is determined by a mass balance including the mass change of the sorbent, as well as the influent and effluent humidities. Validation tests used a known mass flow rate of vapor in a carrier gas, which was compared with the amount measured. The vapor was a single VOC, a mixture of VOCs, or a mixture of a VOC with water. Conditions studied were the compound or mixture of compounds, concentration, carrier gas, flow rate, and adsorbent. In some tests the VOC was admitted intermittently. The VOCs included n-hexane, acetone, toluene, vinyl acetate, and 1,1,1 trichloroethane. For 105 tests, the average absolute discrepancy of the delivered and measured emission rates was 6.8% and the standard deviation was 3.4%.

Growth and properties of diamond-like films deposited from cyclohexane-argon mixtures in low-temperature plasma

The deposition of diamond-like films on polymer substrates from low-temperature cyclohexane-argon plasma was studied. The deposition rate was found to be proportional to the mass flow rate of cyclohexane vapor and independent of the mass flow rate of argon. The microhardness of the films and the light absorption coefficient in the blue spectral region depend on the ratio between the deposition rate and ion current density.

Pipe Flow and Pressure Oscillation due to Vapor Condensation in Pool Water.

An experimental study of pressure oscillation in a single vent tube due to vapor condensation into pool water was performed. The objectives of the work are to establish the character of the dominant frequency and the progression of the pressure wave in the condensation oscillation (CO) -chugging transition region, and to confirm the relationship between vapor velocity and pressure oscillation in chugging. In CO region, most of the pressure wave component had progressive character, and some, a stationary character of resonance in vent tube. In the CO-chugging transition region, the dominant frequency of the progressive wave component increased with vapor mass flow rate and water subcooling temperature. The effects of these parameters on the dominant frequency was explained well by a cylindrical bubble model. In chugging, the maximum vapor velocity was lower than that expected from a simulation model, and the pressure wave had no progressive component.