THERMAL
LABORATORY-I
VIRTUAL LABORATORY
EXPERIMENTS
ASHWIN R
II-MECH-B
21BME045
1. FLOW MEASUREMENT BY ORIFICEMETER
AND VENTURIMETER
AIM:
1. To find the coefficient of discharge for venturi meter.
2. To find the coefficient of discharge for orifice meter.
THEORY:
Flow measurement is the quantification of bulk fluid movement. It
is important to know the amount of material entering and exiting the
process to control various industrial processes. Different types of
meters are used for flow measurement and it is selected based on the
applicability of the instrument on a specific problem, installed cost and
costs of operation, the range of flow rates, and its accuracy.
In the following sections we will be discussing about the venturimeter
and orifice meter, vastly used in the industries for flow measurement
of liquids and gases.
Venturimeter
Venturimeter works on the principle of head flowmeter. Venturi tube
gradually reduces the flow area, thus creating differential pressure
across it. Any changes in fluid flow rate through venture are measured
in terms of diffenential pressure across it.
It consists of convergent inlet cone (having included angle between, 19
degree to 23 degree), a uniform diameter throat (having length equal
to its diameter) and a divergent outlet cone (having included angle
between 5 degree to 15 degree).
The high pressure tap located on the convergent section while low
pressure tap is located at the middle of the throat. The manometer is
connected between these taps.
SIMULATION:
REFERENCE:
BOOKS:
[1] D. Patranabis, “Sensors and Transducers”
[2] A. K. Shawney, “A course in Mechanical Measurements and Instrumentation”
[3] Bela G. Liptak, “Instrument Engineers' Handbook: Process Measurement and
Analysis”
[4] Doeblin, “Measurement Systems Applications and Design”
2. TWO PHASE FLOW IN HORIZONTAL TUBES
AIM:
The object of this experiment is ;1. To visually observe the flow pattern of a two phase flow
2. To measure the two phase pressure drop and to compare it
the calculated value
THEORY:
Two phase gas liquid flow is important in a variety of chemical
engineering applications such as the simultaneous transport of the
gas and oil in horizontal pipelines or a vertical wells several flow
regimes can occur, depending on many factors, including the
orientation of the pipe the individual magnitudes of the liquid and gas
flow rates and physical properties such as density, surface tension
and viscosity. It hence becomes imperative to study the flow regimes
and pressure drop characteristics of two phase flow.
For horizontal pipes, there are seven principal flow regimes shown in
the figure above and which occur successively at ever increasing gas
flow rates.
1. Bubble flow in which the gas is dispersed as small bubbles
throughout the liquid which is the continuous phase
2. Plug flow which is an intermediate between bubble flow and slug
flow
Slug flow in which the individual small bubbles have started to
coalesce together in the form of slugs. The liquid phase is still
continuous.
3. Stratified flow in which the gas occupies the top half of the pipe
and liquid occupies the bottom half.
4. Wavy flow in which the increasing gas flow rate causes ripples to
form on the surface of the liquid.
5. Annular flow in which the fast moving gas stream is now a
continuous phase that encompasses central portion of the tube
with the liquid forming a relatively thin film on the tube well.
6. Mist flow in which the velocity of the continuous gas phase is so
high that it reaches as far as the tube wall and entrains the liquid
in
the
form
of
droplets.
For vertical pipes, there are five principal flow regimes shown in figure
below and which occur successively at ever increasing gas flow rates.
1. Bubble flow in which the gas is dispersed as small bubbles
throughout the liquid which is the continuous phase. Slug flow in
which the individual small bubbles have started to coalesce
together in the form of slugs. The liquid phase is still continuous.
2. Churn flow which is an intermediate between slug flow and
annular flow
3. Annular flow in which the fast moving gas stream is now a
continuous phase that encompasses central portion of the tube
with the liquid forming a relatively thin film on the tube well.
4. Wispy annular flow in which the velocity of the continuous gas
phase is so high that it reaches as far as the tube wall and entrains
the liquid in the form of droplets.
5.
PROCEDURE:
The flow rate for water and is selected by varying the valve positions.
Flow rate of water can be measured by the bucket and stopwatch
method. The air flow rate can be read from the rotameter. The flow
regime that develops in the pipe can be observed and reported. This
flow regime can be verified theoretically by studying the graph given in
the theory.
As the water and air flows a pressure drop is developed across the pipe
which is reflected in a height difference across the manometer. The
experimental pressure drop can be calculated.
A suitable correlation such as the Lockhart-Martinelli method can be
used to calculate the pressure drop theoretically. The correlation is
given in the theory.
SIMULATION:
REFERENCE:
BOOKS:
1. McCabe, W.L., Smith, J.C. and Harriott, P., "Unit Operations of
Chemical Engineering", 5th Edition, McGraw Hill International, 1993.
3. NATURE OF FLOW
AIM:
The object of this experiment is to study gas liquid absorption in an
absorption column:1. To visually observe laminar and turbulent flow patterns.
2. To determine the critical Reynolds Number for transition from
laminar to turbulent flow.
3. To determine the friction-factor and to verify the relationship
between friction factor (f) and Reynolds Number (NRe)
THEORY:
Pipe flow problems occur in the design of many types of engineering
projects. A few of these include refineries (liquid flow), gasoline plants
(gas or vapor flow), chemical plants etc. Fluid flow is an integral part of
any chemical industry and understanding the phenomena that dictate
the motion of any fluid through popes is of utmost importance to any
chemical engineer. There is always need of develop an efficient system.
To reduce wastage of energy through pipe flow, it would be beneficial
to first study the various flow regimes of fluids on a small scale.
Here are some formulae which we are using in this experiment:
NRe = ρvD/μ
NRe is a dimensionless number called Reynolds number. ρ is density of
fluid, V is velocity, D is internal diameter of pipe in which fluid flows and
μ is the viscosity of fluid. For calculation purpose all the parameters are
taken in SI units.
f= (ΔPgcD)/2Lρv2 =gΔhD/2Lv2
f is friction-factor. This formula relates friction-factor with various
parameters. Some of them we find experimentally and others are
constant. ΔP is pressure drop, D is inner diameter, L is length of pipe
and V is velocity. gc is equal to one here because we are using SI units
in given expression. Δh is the height difference of two water tanks.
There are some correlations between Reynolds number and frictionfactor. For laminar flow it’s given by:
f=16/ NRe
For turbulent two correlations exist:
f=0.046NRe-0.2
f=0.0014 +
(50000
(0.125/
NRe0.32)
<
NRe <106 )
(3000 < NRe < 3x106)
PROCEDURE:
1) Allow the water to fill the equipment and adjust the flow rate to the
lowest possible value.
2) Adjust the flow rate of the dye solution so that its flow rate is the
same as the velocity of water.
3) Measure the volumetric flow rate using a measuring vessel and a
stop watch.
4) Increase the flow rate of water in small increments and repeat the
above steps.
5) From the highest flow rate decrease the flow rate in small
decrements, and repeat the above steps.
SIMULATION
REFERENCE:
BOOKS:
1. McCabe, W.L., Smith, J.C. & Harriott, P., 2005. Unit operations of
chemical engineering, McGraw-Hill.
4.ADIABATIC CALORIMETRY
AIM:
To determine the heat of mixing of binary systems by adiabatic
calorimetry and the partial molar enthalpies of two components.
THEORY:
Calorimetry involves measurements of enthalpy changes in various
processes like mixing, dilution, dissolution, crystallization, adsorption
or in a chemical reaction. In addition, it is used for the determination
of heat capacities. Calorimetry can be of two types: adiabatic or
isothermal. In anadiabatic calorimeter no heat is exchanges with
surroundings and hence temperature change is to be monitored during
the process occuring in the calorimeter. In such a case the accuracy of
measurement of any physical property using a calorimeter depends on
the accuracy of temperature measurement and how good the
adiabatic shield is.
A vacuum ask/Dewar ask is used as an adiabatic calorimeter. However,
minute "heat leaks" are not uncommon. In order to reduce heat flow
to or from the surroundings, the Dewar ask itself should be placed in a
constant temperature container such as a large thermostat or
insulated box whose temperature should be regulated as close to the
contents of the Dewar flask as possible. Care should be taken so that
"heat leak" does not occur through either the lid of the Dewar ask or
openings in the lid. If the instrument is sensitive enough, stirring of the
contents would also be controlled and its effect should be monitored
in a blank experiment.
D = Glass Dewar Flask of capacity 100 ml, S = Polypropylene Stopper,
H = Resistance Heater, ST= Stirrer, T = Temperature Sensor
PROCEDURE:
1) Add 150 ml of water to the calorimeter. Switch on the supply of
electric current and start the timer. Note the average current value,
Voltage drop across resistor and time for which current is passed.
Calculate K using Equation 1.
2) Calculate the volumes of methanol and water required to make 150
ml of solution such that mole fraction of methanol is 0.2. Pour the
component with larger volume in the calorimeter. Note the initial
temperature. Then add the component with smaller volume and allow
the mixture to attain steady state and note the temperature.
3) Now switch on the current supply. Allow the current to pass through
the mixture till a temperature rise of about 2째C is observed. Note the
initial and final temperatures and also the ammeter reading, voltmeter
reading and time for which current is passed.
4) Repeat steps 2 and 3 for mixtures of composition 0.4, 0.6 and 0.8
mole fraction of methanol.
SIMULATION:
REFERENCE:
BOOKS:
1. Smith, J.M., Ness, H.C.V. & Abbott, M.M., 2005. Introduction to
chemical engineering thermodynamics, McGraw-Hill.
5.FLOW THROUGH FITTINGS
AIM:
The object of this experiment is:1. To measure the pressure drop in the straight section of smooth,
rough and fitting as a function of flow rate.
2. To calculate Reynolds number and fanning friction factor using
measured flow rate and pressure drop.
3. To calculate roughness parameter using calculated experimental
fanning friction factor.
4. To understand the effect of Reynolds number and roughness on
friction factor.
THEORY:
In any chemical industry, piping networks have significant importance
since they are used to manipulate the various parameters related to
flow of a fluid. For example, pipes of different diameters and valves can
be used to change flow rates of the fluid, while bends are used to
change the direction of flow of the fluid. The effect that each of this
equipment has on the flow of the fluid must be known to chemical
engineers, so that more efficient piping networks can be designed.
Valves commonly used in industries are globe valves, ball valves and
gate valves. Globe valves offer maximum precision in controlling the
flow, whereas ball valves are mainly used to either allow maximum flow
or stop the flow completely.
The common types of pumps used are centrifugal pump, positive
displacement pumps and reciprocating pumps. Centrifugal pump
convert kinetic energy of impellers into potential energy of water.
Positive displacement pumps work on the principle of trapping a fixed
amount of water and then forcing it through the discharge tube.
A rough pipe is one which has threads inside. Roughness parameter is
the ratio of the pitch of the thread to the diameter of the pipe. For
pipes of equal diameter, the friction factor and hence the pressure
drop of the rough pipe is more. In the laminar region, there is no effect
of the roughness because the layer near the walls of the pipe is
stationary and there is no lateral mixing. However in the turbulent
region, it plays an important role as there is lateral mixing and greater
the roughness parameter, greater is the resistance offered to the flow.
In this experiment we correlate the Fanning friction factor to the
Reynold’s number for various flow rates in different pipes. Finally, the
roughness parameter of the rough pipe is calculated using the
experimental value of friction factor. The Fanning friction factor is
evaluated using the equation:
Ff = ΔPD/2Lρv2 ...(1)
Where ΔP is the pressure drop, L is the length of the pipe, D is the inner
diameter, v is the velocity of the fluid and ρ is the density of the fluid.
The theoretical value of the friction factor is given by the ColebrookWhite Equation,
1 / √f = -4log[4.67 / (Re√f) + ε / D] + 2.28 ...(2)
In this equation, f is the Fanning friction factor, D is the inner diameter
and ε is the absolute roughness parameter.
PROCEDURE:
1) Ensure all valves are closed and outlet and bypass valves (see Fig. 1)
of the pipe system are open. Ensure that pressure tapings are proper
connected to the subject pipe, without air bubble.
2) Turn on the centrifugal pump and let water initially circulated back
through bypass.
3) Open the first pipe inlet valve completely and operated direct the
water flow appropriate flow meter.
4) Switch on the centrifugal pump, flow meter and pressure gauge.
5) Re ensure that there are no air bubbles in the tubes connected to
the pressure tapings, remove if any air bubbles are present.
6) Wait for one minute for the flow to reach steady state, although it
may have fluctuation, however fluctuation between constant bound.
7) Record the corresponding flow rate (liter per min) and pressure
readings (bar) (Note: If flow rate is more than 10 lpm use flow meter
1(less precise) otherwise if flow rate is below 10 lpm then use flow
meter 2(more precise)). Caution: While changing the flow meters, turn
both the flow meters on, first and then turn off with is not required. In
any case, high flow rate should not go the more precise meter.
8) Vary the flow rate by manipulating the bypass valve and record 5
such readings at various flow rates (flow rates could be altered by inlet
valves as well, however, bypass valve is to be most commonly used.)
9) Repeat the above steps for rest of the pipes.
10) For measurement of pressure drop of pipe bend, connect the
pressure taping to bend and repeated the procedure for pipe (Any inlet
valve could be kept open).
11) Once all readings are recorded, switch off centrifugal pump, flow
meter and pressure gauge and fully open the bypass valve. Inlet valve
of all the pipes are to be turned off.
SIMULATION: