Lab Experiments
 

 

Energy losses in pipes
Centre of pressure
Density and SG
Capillarity
Static Pressure
Flume experiments
Pipe friction loss
Pelton Wheel

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City College made a large investment in the provision of laboratory equipment for Construction and Civil Engineering students.  This equipment is used for practical demonstrations and experimental work carried out by the students.

Most of the equipment we use is developed and manufactured by Armfield .  It  is self-contained and semi portable  and  requires the minimum of preparation time, allowing more 'hands-on' student work to be achieved within a typical laboratory period.

Without a doubt, students develop a higher level of interest and improved understanding, if practical work can be seen to relate to textbook theory.

HYDRODYNAMICS

A lot of the experiments are carried out on the basic hydraulics bench.

It is a portable and self-contained service module of lightweight construction from corrosion resistant materials with quick release pipe couplings to speed the assembly of accessories.

Each accessory we use is complete, needing only connection to the bench.
F1-10 Basic Hydraulics Bench

The bench top incorporates an open channel with side channels to support the accessory on test.  Volumetric measurement is integral and has been chosen in preference to other methods of flow measurement for its ease of use, accuracy and safety in use (no heavy weights for students to drop).

The volumetric measuring tank is stepped to accommodate low or high flow rates.  A stilling baffle reduces turbulence and a remote sight tube with scale gives an instantaneous indication of water level.

The sight tube is evident to the left of the On/Off switch and circuit breaker.

 

 

 

 

 

 

 

 

A measuring cylinder is also available for measurement of very small flow rates.

A dump valve in the base of the volumetric tank is operated by a remote actuator. Opening the dump valve returns the measured volume of water to the sump in the base of the bench for recycling.   An overflow in the volumetric tank avoids possible flooding.

Water is drawn from the sump tank by a centrifugal pump and a panel mounted control valve regulates the flow.  An easy-to-use quick release pipe connector situated in the bench top allows for the rapid exchange of accessories without the need for hand tools.

TECHNICAL DETAILS
Pump: ...................................... centrifugal type max. head 21m H2O max. flow 1.35 litres/sec

Motor rating: ............................ 0.37kW

Sump tank capacity: ............... 250 litres

High flow volumetric tank: ...... 40 litres

Low flow volumetric tank: ....... 6 litres

Height of working surface: ..... 1 metre above floor level

 

HYDROSTATICS

 

The Hydrostatics Bench is designed to demonstrate the properties of fluids and their behaviour under hydrostatic conditions (fluid at rest).  This allows students to develop an understanding and knowledge of a wide range of fundamental principles and techniques, before studying fluids in motion.

The experiments and demonstrations which can be carried out on this piece of apparatus includes the following:

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determining the density, specific gravity and viscosity of different liquids

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observing the effects of capillarity

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Understanding the effects of static pressure

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demonstrating that the free surface of a static liquid is horizontal

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studying the effect of flow on a free surface

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measuring changes in liquid level

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studying the relationship between intensity of liquid pressure and depths

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determining the position of the centre of pressure on a plane surface

Studying the operation and application of pressure gauges and manometers:

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using a direct reading Mercury barometer (Mercury not supplied)

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measuring air and water pressure using manometers

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comparing results obtained from various devices

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calibrating a Bourdon-type pressure gauge using a dead weight pressure gauge calibrator

Investigating the buoyancy force and stability of floating bodies:

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verifying Archimedes' principle

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determining metacentric height

The equipment is mounted on a steel-framed bench fitted with castors allowing it to be stored away when not in use.  This is particularly useful as the laboratory is also used for other class activities and it is not unknown for small pieces of apparatus to go missing via someone's pocket or bag. 

A variety of measuring devices is incorporated, either fastened to the back of the bench or freestanding.  Water is stored in a polythene tank situated on the lower shelf of the bench.  The water can be transferred by two positive displacement hand pumps either to an elevated open storage tank connected to a number of glass tubes for free surface studies, or to a plastic sink recessed into the working surface so that bench top experiments may be conducted without spillage.  All excess water is returned to the storage tank via the sink drain.

 

OPEN CHANNEL FLOW

The Armfield  self-contained flume as shown below, is currently used.

 

It is a  small cross-section open channel comprising a clear acrylic working section with GRP inlet and discharge tanks mounted on a rigid framework.  The flume can be tilted by use of a calibrated screw jack which allows accurate slope adjustment of the channel.
Bed pressure tappings and fixing points for models are provided.  A longitudinal scale positioned at the top of the channel allows depth gauges and Pitot-static tubes to be positioned along the channel length.

The flume is available in two standard lengths of 2.5m and 5.0m.  We chose the 5m flume to provide a greater scope experiments.

The water supply and flow measuring system is provided from a service module. similar to the basic hydraulics bench.  Water is drawn from a sump tank by a submersible pump and delivered via a shunt type flow-meter and flow control valve into the inlet tank.  A suitable stilling arrangement diffuses the water flow prior to entry into the channel, ensuring smooth, uniform flow.

The level in the working section of the flume may be controlled by an overshot weir arrangement.  Flow-rates can be measured either by using the volumetric tank (maximum flow-rate 1.2 l/sec), a set of notched weirs or by the direct reading flow-meter.

The flume was supplied with the following basic equipment:

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Venturi flume

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Sharp and broad crested weirs

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3 vernier level gauges

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Crump weir

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Adjustable undershot weir

In addition to the basic equipment, we purchased the following extras:

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Pitot tube and manometer board

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Free overflow spillway section complete with ski jump, sloping apron and blended reverse curvature attachments

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Syphon spillway and air regulated syphon

 

FRICTION LOSS APPARATUS

 

The Armfield Fluid Friction Measurements unit provides facilities for the detailed study of fluid friction head losses which occur when an incompressible fluid flows through pipes, fittings and flow metering devices.  The unit is designed for use with the Armfield F1-10 Hydraulics bench as shown above.

A wide range of measurements, demonstrations and training exercises are possible with the equipment:

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confirming the relationship between head loss due to fluid friction and velocity for flow of water

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determining the head loss associated with flow through a variety of standard pipe fittings

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determining the relationship between pipe friction coefficients and Reynolds' number for flow through a pipe with roughened bore

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demonstrating the application of differential head devices in the measurement of flow rate and velocity

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providing practical training of pressure measurement techniques

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enhancing understanding of the hydraulic principles involved through the use of complementary computer software.

Pipe friction is one of the classic laboratory experiments and has always found a place in the practical teaching of fluid mechanics. 

With this unit from Armfield,  friction head losses in straight pipes of different diameters can be investigated over a range of Reynolds' numbers from 103 to nearly 105, thereby covering the laminar, transitional and turbulent flow regimes in smooth pipes.  In addition an artificially roughened pipe is supplied which, at the higher Reynolds' numbers, shows a clear departure from the typical smooth bore pipe characteristics.

In addition to the equipment for the study of losses in straight pipes, a wide range of accessories are standard including pipe fittings and control valves, a Venturi tube, an orifice plate assembly and a Pitot tube.

An arrangement of six pipes provides facilities for testing the following:

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4 smooth-bore pipes of different diameters

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artificially roughened pipe

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90 bends (large & small radii)

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90 elbow

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90 mitre

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45 elbow

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45Y

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90T

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sudden enlargement

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sudden contraction

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gate valve

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globe valve

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ball valve

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inline strainer

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Perspex Venturi

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Perspex orifice meter

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Perspex pipe section with a Pitot tube & static tapping

 

LAMINAR FLOW TABLE

 

The Armfield Laminar Flow Table has been designed to simulate ideal fluid flow and give clear visualisation of the flow patterns created using water as the working fluid.  This enables a comprehensive investigation into the principles of potential flow and allows modelling of appropriate physical systems. 

The Laminar Flow Table is an improved version of the classical Hele-Shaw apparatus with the addition of sinks and sources.  It consists of two closely spaced sheets of laminated glass, arranged horizontally on a glass fibre moulding. An inlet tank and a discharge tank are incorporated in the moulding which is supported on a floor standing, metal frame. Three adjustable feet allow rapid levelling of the flow table. 

Eight miniature tapings which may be used as sinks or sources are arranged about the centreline of the lower glass plate in a cruciform configuration.  A doublet (a sink and source in close proximity) is located at the centre of the pattern.  A system of pipes, valves and manifolds enables any combination of the sinks and sources to be used.  A row of control valves mounted above the flow table is used to adjust the flow through each individual source. 

C10 Schematic for one sink and source

A row of hypodermic needles attached to a manifold is positioned between the glass plates at the inlet edge. To visualise the flow of water between the glass plates, dye is injected through the equally spaced needles. The position of each streamline is clearly indicated by the dye which is supplied from a reservoir fitted with a flow control valve.  A black graticule (A grid or pattern used to establish scale or position) on a white background is printed on the underside of the lower glass plate to aid visualisation of the streamlines.

The patterns created by the potential flow may be recorded by tracing on the top glass sheet or by photography if required.

A diffuser in the inlet tank and an adjustable weir plate in the discharge tank help to promote a uniform flow of water.  Valves are incorporated in the base of these tanks to aid draining.  The flow of water is controlled by an inlet flow control valve.  A pressure regulator reduces the mains water pressure and helps to minimise variations in flow.

The top glass plate may be raised at the front edge and retained in this position to allow models to be placed in the working section.   

A set of models are supplied for basic flow studies.  These models are manufactured from plastic sheet and are trapped in the required position when the top glass plate is lowered.  Alternative models can be fabricated from any convenient material and used to investigate the associated flow patterns.  

Two-dimensional laminar flow is created between the two glass plates by the combination of low fluid velocity and the narrow gap between the plates.  The resulting flow is free from turbulence and gives a close approximation to the behaviour of an ideal fluid.  Since the flow is controlled by potential, the flow table can be used to model any physical system which obeys Laplace's Law.  For example, two-dimensional steady heat flow through conductor of varying cross section can be simulated.  In this instance the heat flow is represented by the flow of water and the temperature difference in the system is represented by the fluid pressure potential.

Similarly, the sinks and sources may be used in combination with the flow of water between the plates to simulate a variety of flow situations.  For example, the patterns of flow in the vicinity of wells which draw water from underground supplies (aquifers) may be represented using one or more of the tapings as sinks.  The effect of recharging the underground supply may be represented by utilising one or more of the tapings as sources.

Streamline patterns

 

   A Cylinder

 

            An Aerofoil

 

CENTRIFUGAL PUMPS

Centrifugal pumps are often used together to enhance either the flow rate or the delivery pressure beyond that available from the single pump.

The unit is designed to demonstrate the operational advantages of parallel or series operation, depending on the required duty. 

Two motor driven centrifugal pumps, mounted on a stainless steel plinth with a water reservoir and pipe work for continuous circulation.  The pumps can be configured for single pump operation, two pumps in parallel or two pumps in series by using manually operated ball valves.  Similarly, manual valves are used to control the flow and facilitate the study of suction effects, including demonstration of air release (cavitation). 

In parallel operation the two pumps draw from a shared inlet pipe of a wider diameter than the pump inlet, reflecting a typical industrial configuration of parallel pumping.  Each pump has impellers that can be easily accessed and replaced without tools.  The FM51 is delivered with three impellers in total, one with forward curved blades and two with backward curved blades, allowing the students to investigate the effects of impeller characteristics.

Electronic sensors measure the pump outlet pressure of each pump, the shared pump inlet pressure, the flow rate and the water temperature.

The pump speed of the first pump is accurately controlled by an advanced electronic inverter within the IFD7 (an essential accessory) and can be varied over the full range.  The inverter also calculates the torque produced at the motor drive shaft, allowing the power used by the pump to be derived.  The second pump runs at inherent motor speed.  This combination of control facilities allows a wide range of different configurations to be investigated.

The IFD7 also provides the conditioning electronics for the sensors and allows their readings to be displayed on computer software.  

Connections to the IFD7 are a single multi-way connector for the sensors and a connector for the pump motor drive.

The equipment is provided with advanced education and data logging software.  

 With this equipment, you can carry out a:

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Demonstration of either series, parallel or single pump operation

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Measurement of constant-speed pump performance, including production
of characteristic curves (one pump)

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Comparison of head-flow characteristics with single pump operation, at inherent speed

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Investigation of impeller styles

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Comparison of student calculations with computer results

 

 

 

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Last Edited :  10 March 2015 13:35:02