Transport phenomena

This report talks about the recent advancement of transport phenomena in nano-scale, applications of transport processes posed tremendous new challenges in the last part of 20th century in emerging areas like electronic cooling and MEMS (and NEMS) devices where heat, species and fluid flows are involved within very small dimensions, challenging the established paradigms of transport processes. This has given courage to the area of Nano-scale transport. Additionally, extending micro/Nano scale technologies to health sciences through Bio-MEMS and micro-Nano fluidic devices, bringing the concept of lab-on-chip in biological sciences have emerged as the latest important initiatives in this field. This has propelled the rise to inter-disciplinary research where engineering concepts are used to address the problems at smaller scales required for the problems related to fundamental sciences and their applications. This report on Nano Scale Transport phenomena highlight some of the scientific innovation that are been invented by researchers in the field of nanotechnology.

A generic “system on a plate” modular multicompartmental bioreactor array which enables microwell protocols to be transferred directly to the bioreactor modules, without redesign of cell culture experiments or protocols is described. The modular bioreactors are simple to assemble and use and can be easily compared with standard controls since cell numbers and medium volumes are quite similar. Starting from fluid dynamic and mass transport considerations, a modular bioreactor chamber was first modeled and then fabricated using “milli-molding,” a technique adapted from soft lithography. After confirming that the shear stress was extremely low in the system in the range of useful flow rates, the bioreactor chambers were tested using hepatocytes. The results show that the bioreactor chambers can increase or maintain cell viability and function when the flow rates are below 500 µL/min, corresponding to wall shear stresses of 10−5 Pa or less at the cell culture surface. Biotechnol. Bioeng. 2010; 106: 127–137. © 2010 Wiley Periodicals, Inc.

The results of a numerical simulation of the current distribution of a three-dimensional, tubular shaped, proton exchange membrane fuel cell model are presented. An integrated flow and current density model to predict current density distributions in two dimensions along the membrane has been developed. The numerical model has a cylindrical geometry that includes diffusion layers on the anode and cathode side, the anode being the inner most electrode, and solves the same primary flow related variables along the channels and the diffusion layers. The simulation was performed with commercial flow solver software where a control volume approach was used and source term equations that characterize the electrochemical aspects of the fuel cell have been added.

"The purpose of this checklist is to identify the stages and potential problems associated with the scale up of fixed bed reactors from the drawing board to the full scale plant, and to determine how they should be checked.

The checking can be done using various methods. These are:

•  Literature data.

•  Lab testing.

•  Calculation.

•  Modeling.

•  Semi-tech testing.

•  Piloting or Side-stream testing.


Identifying the stages that need to be addressed for a particular catalyst/reactor development will help in estimating the time needed for the development of the reactor.
"
#Fundamentals; #New Preparations and New Active Materials; #Synthesis and Characterization of Catalysts; #Characterization of Catalyst in its Working State; #Catalyst Deactivation; #Reaction Kinetics; #Reactor Modeling; #Reactor Design, Control and Optimization; #Novel Reactors and Process Developments;

This guide covers the reaction kinetics and diffusional aspects of solid catalyzed reactions. It does not deal with either the fluid dynamics or the mechanical design of reactors for solid Catalyzed reactions.

#Fundamentals; #New Preparations and New Active Materials; #Synthesis and Characterization of Catalysts; #Characterization of Catalyst in its Working State; #Catalyst Deactivation; #Reaction Kinetics; #Reactor Modeling; #Reactor Design, Control and Optimization; #Novel Reactors and Process Developments;

Gravity drainage systems occur frequently on chemical plants. Typical examples are:

(a) the condensate off-take from a condenser;

(b) the liquid off-take from the base of an absorption column;

(c) the emergency overflow from an atmospheric pressure storage tank.

Gas entrained in a liquid flowing by gravity from a vessel will reduce the volume of liquid flowing through the pipe and could cause surging flows.

This guide recommends methods for the estimation of pressure drop for the steady state flow of single phase Newtonian liquids and compressible fluids (gases and vapors) in pipe systems. It covers most of the geometries likely to be encountered in normal design cases.

This document is one of a series on fluid flow produced by GBH Enterprises.

If a rapid change is made to the flowrate of a liquid in a piping system, for example by the operation of a valve, a transient pressure change will be propagated through the system. This transient pressure may be significantly greater than either the initial pressure or the final steady state pressure which the system reaches. This may cause damage to the piping system; either by exceeding the design pressure of the piping system with consequent risk of rupture, or by producing out of balance forces which are greater than can be sustained by the pipe supports. The phenomenon known as 'water hammer' is a special case of 'pressure surge'.

1. What length of time is required to heat a 2.5 cm diameter, 5 cm long copper cylinder (k = 380 W/mK) from 16 o C to 93 o C in a furnace whose temperature is 315 o C ? The value of h at the cylinder surface is 204 KJ/hm2K and its thermal diffusivity is 0.186 m 2 /s. 2. A cylindrical steel shaft 10 cm. in diameter and 2.4 m long is heat treated to give it desired physical properties. It is heated to a uniform temperature of 600C and then plunged into an oil bath which maintains the surface temperature at 150 o C. Calculate the radial temperature profile at 2 min and at 3 min after immersion 3. A large sheet of glass 50 cm thick is initially at 150°C throughout. It is plunged into a stream of running water having a temperature of 15°C. How long will it take to cool the glass to an average temperature of 38°C? For glass: K= 0.70 W/mK; ρ= 2480 kg/m3, Cp = 0.84 kJ/kgK 4. A flat slab of rubber, 2.54cm thick initially at 21.1°C is to be placed between two heated steel plates maintained at 137.78°C. The heating is to be discontinued when the temperature at the mid plane of the slab is 132.22°C. The rubber has a thermal conductivity of 0.15912 W/m 2 (°C/m) and thermal diffusivity of 8.671x10-6 m 2 /s. Thermal resistance from metal to rubber may be neglected. 5. A slab of meat 25.4 mm thick originally at a uniform temperature of 10 o C is to be cooked from both sides until the center reaches 121 o C in an oven at 177 o C. The convection coefficient can be assumed constant at 25.6 W/m 2-K. Neglect any latent heat changes and calculate the time required. The thermal conductivity is 0.69 W/m-K and the thermal diffusivity 5.85x10-4 m 2 /h. Use the Heisler Chart. 6. A wall made of concrete, 0.305 m thick is insulated on the rear side. The wall was at a uniform temperature of 10°C and was exposed on the front side to a gas at 843°C at time zero. The convection coefficient is 28.4 W/m2.K. The thermal diffusivity of the wall is 1.74x10-3 m2/h and the thermal conductivity is 0.935 W/m K. 6.a. calculate the time for the temperature at the insulated face to reach 232°C, 6.b.at this time calculate the temperature at a point 0.152 m below the surface 7. Cooling a Steel Rod. A long steel rod 0.305 m in diameter is initially at a temperature of 588 K. It is immersed in an oil bath maintained at 311 K. The surface convective coefficient is 125 W/ m 2 ·K. Calculate the temperature at the center of the rod after 1 h. The average physical properties of the steel are k = 38 W/m·K and α = 0.0381 m2/h. 8. An ordinary egg can be approximated as a 5-cm-diameter sphere (Fig. 4–21). The egg is initially at a uniform temperature of 5C and is dropped into boiling water at 95C. Taking the convection heat transfer coefficient to be h =1200 W/m2 · C, determine how long it will take for the center of the egg to reach 70C. An egg is cooked in boiling water. The cooking time of the egg is to be determined. Assumptions 1 The egg is spherical in shape with a radius of ro =2.5 cm. 2 Heat conduction in the egg is one-dimensional because of thermal symmetry about the midpoint. 3 The thermal properties of the egg and the heat transfer coefficient are constant. 4 The Fourier number is = 0.2 so that the one-term approximate solutions are applicable. 9. A large slab 1m thick is initially at a uniform temperature of 150 o C. Suddenly its front face is exposed to a fluid maintained at 250oC, but its rear face remained insulated. The fluid has a convective coefficient of 40W/m 2 K. Assume the solid has a thermal diffusivity of 0.000025 m 2 / s and a thermal conductivity of 20W/mK. Using a numerical finite difference method with M=5 and 4 slices, construct a table for the temperature profile of the slab up to a time of 4000 sec.

Boiler Water Circulation Pumps

1 SCOPE

2 CHOICE OF TYPE AND NUMBER OF PUMPS

2.1 Need for Continuous Flow

2.2 Pump Reliability

3 CHOICE OF DRIVER

4 DUTY CALCULATIONS

5  CHOICE OF SEAL

5.1 Mechanical Seals

5.2 Soft-packed Glands

5.3 Construction Features

5.4 Guarding

6  CONSTRUCTION FEATURES

6.1 Vertical Glandless Wet-stator Motor Pumps

7 LAYOUT

7.1 Non-return Valves

7.2 Reducers at Pump Connections

7.3 Glandless Pumps for System Pressures
Exceeding 60 bar abs

7.4 Access round Glandless Pumps

7.5 Cooling Water Supply

8  RECOMMENDED LINE DIAGRAMS

8.1 Horizontal Pumps in Category 1

8.2 Vertical Wet-stator Motor Pumps in Category


APPENDICES

A PROPERTIES OF WATER AT THE SATURATION LINE

B ANNEX TO API 610, 6TH EDITION 1981:
VERTICAL GLANDLESS WET-STATOR MOTOR PUMPS

C ANNEX TO API 610, 6TH EDITION 1981:
HORIZONTAL BACK PULL-OUT PUMPS FOR BOILER
WATER CIRCULATION DUTY

FIGURES

3.1 NPSH CORRECTION FOR WATER

3.2 VELOCITY OF SOUND IN WATER AT 50 BAR
(NO BUBBLES)

3.3 VELOCITY OF SOUND IN WATER AT 50 BAR
(WITH 3% VAPOR CONTENT)

8.1 RECOMMENDED LINE DIAGRAM HORIZONTAL PUMPS - CATEGORY 1

8.2 RECOMMENDED LINE DIAGRAM HORIZONTAL PUMPS - SOFT PACKED GLAND INSTALLATION

8.3 RECOMMENDED LINE DIAGRAM HORIZONTAL PUMPS - MECHANICAL SEAL INSTALLATION

8.4 RECOMMENDED LINE DIAGRAM VERTICAL WET STATOR PUMPS - CATEGORY 2

BIBLIOGRAPHY

0 INTRODUCTION / PURPOSE

1 SCOPE

SECTION ONE - INTEGRATING.THE PUMP INTO THE SYSTEM

2 AVAILABILITY CONSIDERATIONS

3 CHOICE OF NUMBER OF PUMPS

4 CHOICE OF PUMP TYPE

4.1 Barske Type
4.2 Peripheral Type
4.3 Multistage Centrifugal Type
4.4 Inlet Booster Pumps

5 DRIVERS

5.1 Steam Turbines
5.2 Electric Motors
5.3 Dual Drivers

6 DUTY

6.1 Differential Head
6.2 Capacity
6.3 NPSH

7 MINIMUM FLOW THROUGH PUMP

7.1 Limit due to Instability in Head/Flow Characteristic
7.2 Minimum Flow Arrangements
7.3 Variable Speed Control

8 TRANSIENT EFFECTS

8.1 Reverse Flow upon Trip
8.2 Flashing

9 TEMPERATURE GRADIENTS IN CASINGS

10 INLET STRAINERS AND CASING PIPING CONNECTIONS

10.1 Strainers
10.2 Casing Piping Arrangements

11 SEAL COOLING

11.1 Packed Glands for Category 1 Pumps
11.2 Mechanical Seals

SECTION TWO - PUMP CONSTRUCTION FEATURES

12 MINIMUM FLOW THROUGH PUMP

12.1 Limit Due to First Stage Cavitation Damage
12.2 Limit Due to Instability in Head/Flow Characteristic

13 IMPELLER/DIFFUSER STAGE

13 .1 Local Cavitation
13.2 Labyrinth or Bushing Clearances
13.3 Clearances Affecting Hydraulic Forces
14 ROTOR

14. 1 Rotor Dynamics
14.2 Rotor Mechanical Balance
14.3 Torsional Critical Speeds
14.4 Rotor Assembly

15 GLAND ARRANGEMENTS

15.1 Guarding
15.2 Soft-Packed Glands
15.3 Mechanical Seals for Category 1 Pumps
15.4 Mechanical Seals for Category 2 Pumps

16 AXIAL HYDRAULIC THRUST BALANCE METHODS

16. 1 Opposed Impeller Configuration
16.2 Balance Disc
16.3 Balance Piston

17 CASING
17.1 Casing Type
17.2 Casing Connections

18 MATERIALS

19 DRIVER CONSIDERATIONS

This guide provides a basic introduction to the theory of gas-liquid reactions. It deals with the microscopic scale phenomena of absorption, mass transfer and chemical reaction and indicates how these are integrated with fluid flow and heat transfer to provide predictions of reactor performance. Some attention is given to the experimental determination of the relevant physicochemical parameters. Finally, guidance is offered on the selection of appropriate gas-liquid reactors for a given system.

#Fundamentals; #New Preparations and New Active Materials; #Synthesis and Characterization of Catalysts; #Characterization of Catalyst in its Working State; #Catalyst Deactivation; #Reaction Kinetics; #Reactor Modeling; #Reactor Design, Control and Optimization; #Novel Reactors and Process Developments;

Recently, the need to decrease CO2 concentration in the atmosphere has been recognized because of the role of CO2 as a greenhouse gas that contributes to global warming. Carbon Capture and Sequestration (CCS) is one of the most promising long term solutions for the reduction of CO2 in the atmosphere. To this end, injection of CO2 into saline aquifers has been proposed and investigated theoretically and experimentally in the last years. Modeling the storage of CO2 in saline aquifers on a reservoir scale is very demanding with respect to computational cost. Long-term subsurface storage of CO2 in saline aquifers may induce a range of chemical processes in response to disturbances in existing chemical equilibria that include, but are not limited to, dissolution of primary minerals and precipitation of secondary carbonates. CCS projects also can be done above the ground by injecting CO2 into designated fractures. The work presented in this thesis focuses on developing a fundamental understanding and modeling approach for 3 basic aspects of sequestration: 1) the effect of CO2 solubility on rates of geochemical reactions, 2) density of brine after dissolution of CO2, and 3) time dependent porosity variation of a single fracture due to precipitation of carbonates.
A new method is developed to determine the reaction rates of minerals, on the basis of transition state theory, in saline aquifers containing brine and a supercritical CO2 phase. A general Arrhenius-type equation that depends explicitly on the pH of brine is employed to determine the reaction rates. The dependence of pH on the amount of aqueous CO2 dissolved in brine is modeled in this study. An accurate pressure-volume-temperature-composition (PVTx) model is employed to determine the dissolution of supercritical CO2 in brine for the temperature range of 50-100°C and pressures up to 600 bar. Solubility of CO2 and dissolution rate of calcite predicted by the model are validated with experimental data available in the literature for specific thermodynamic and salinity conditions. The effects of CO2 activity on pH and reaction rates are evaluated by means of four different models for the activity coefficient of dissolved CO2. The results indicate that dissolution of CO2 decreases the pH of the system but an increase in the temperature and salinity values limits the pH reduction. The rates of reactions are found to increase with pressure and temperature. The results suggest that among the available mineral compositions in deep saline aquifers, the dissolution rate of anorthite is the rate limiting factor. The significance of the pre-exponential factor and the reaction order associated with the modified Arrhenius equation is evaluated to determine the sensitivity of the reaction rates as a function of the system pH. We find that the transition state theory can reasonably reproduce experimental data with new parameters that we are obtained in this study on the basis of sensitivity analysis. Finally, we develop a long-term geochemical modeling of CO2 storage on a designated fracture above the ground to investigate the impacts of temperature, pressure, and salinity on the reaction rates and, subsequently, the critical time of blockage due to precipitation of carbonates.
With regards to the second focus of this thesis, the effect of CO2 solubility on the density of binary H2O-CO2 and ternary H2O-CO2-NaCl solutions in saline aquifers is investigated. These solution densities as dispensable properties play pivotal roles in estimating the dynamic evolution of plume containing aqueous CO2 and brine and also affect fracture dynamics in geologic media. An improved model is proposed to predict the density of saturated binary and ternary solutions as a function of pressure, temperature, and salinity. The model is based on an extended form of the Redlich-Kwong Equation of State that yields more representative values of the molar volumes of liquid CO2. The extension involves finding new coefficients for the cubic Redlich-Kwong equation to match one of the solutions with the liquid molar volume deduced from experimentally measured density of binary solutions. The new coefficients are constrained to ensure that the solution branch corresponding to the molar volume in the gas phase remains unchanged. Due to variability in the experimentally measured density of binary solutions, an effective liquid molar volume is obtained with the help of a multi-parameter non-linear regression with respect to pressure and temperature. The proposed model is validated by comparing it with experimental data and is used to study the density-pressure-temperature-salinity relationship. It is found that the density of the saturated solution is proportional to the mole fraction of dissolved CO2. In general, solution density is found to increase with pressure but decreases with an increase in temperature within the range of 50-100_C. It is also found that the solution density decreases monotonically with an increase in salinity.
Finally, a new model is presented to simulate a reactive fluid within a fracture. Permeability of a fracture controls the path of aqueous CO2 migration, therefore aperture width of a fracture has a pivotal effect on solubility and mineral trapping of injected CO2. This study investigates the impact of the formation of precipitates within fractures on CO2 transport and storage capacity. The problem involves the flow of CO2 between finite walls that represents a single fracture. Fluid convection, diffusion, and chemical reactions inside a finite space are solved as a simplified representation of natural mineral trapping. The model is composed of direct numerical simulation of incompressible ow and transport combined with the kinetics of corresponding chemical reactions. For each time step, transport and reactions are solved by means of a finite difference method using a sequential non-iterative approach. The purpose of the current study is to show the time evolution of the aperture shrinkage caused by precipitation of calcite. The current model predicts the actual efficiency of the mineral trapping mechanism by considering the physical properties of the fluid such as its density, pH, and the characteristics of the mineral compositions. It is found that for low Peclet numbers (Pe < 100), the critical time for a fracture blockage is insensitive to the Reynolds number and increases with the Peclet number. At a high Peclet number Pe = 1000, however, the critical time generally decreases with increasing Reynolds number.