Free and Forced Convection

HT6

FREE AND FORCED CONVECTION

HEAT TRANSFER

HT6

ISSUE 11

MARCH 1998

ARMFIELD LIMITED

OPERATING INSTRUCTIONS AND EXPERIMENTS

HT6

SAI-ETY

INT'RODUCTION

REC'EIPT OF EQUIPMENT

DEE,CRIPTION

INSTALLATION REQUIREMENTS

COI@NECTION TO SERVICES

C014MISSIONING

ROIJTINE MAINTENANCE

IND,EX TO EXPERIMENTS

GE@@RAL SAFETY RULES

PAGE NO.

SAFETY IN THE USE OF EQUIPMENT SUPPLIED BY ARMFIELD

Befiz)re proceeding to install, commission or operate the equipment described in this instruction manual we wish to alert you to potential hazards so that they may be avoided.

Alt]4ough designed for safe operation, any laboratory equipment may inv@Dlve processes or procedures which are potentially hazardous. The major potential hazards associated with this particular equipment are listed below.

INJURY THROUGH MISUSE

INJURY FROM ELECTRIC SHOCK

INJURY FROM ROTATTNG COMPONENTS

BURNS FROM COMPONENTS AT HIGH TEMPERATURES

Accidents can be avoided provided that equipment -@s regularly maintained and staff and students are made aware of potential hazards. A list of general safety rules is included in this manual, to assist staff and students in this regard. The list is not intended to be fully comprehensive but for guidance only.

Pleikse refer to the notes overleaf regarding the Control of Substances Hai,,ardous to Health Regulations.

The COSHII Regulations

The Control (1988)

of Substances

Hazardous

to Health

Regulations

The COSHH regulations impose a duty on employers to protect employees and others from substances used at work which may be hazardous to health. The regulations require you to make an assessment of all operations which are liable to expose any person to hazardous solids, liquids, dusts, vapours, gases or micro-organisms. You are also required to introduce suitable procedures for handling these substances and keep appropriate records.

Since the equipment supplied by Armfield Limited may involve the use of substances which can be hazardous (for example, cleaning fluids used for maintenance or chemicals used for particular demonstrations) it is essential that the laboratory supervisor or some other person in authority is responsible for implementing the COSHH regulations.

Part of the above regulations are to ensure that the relevant Health and Safety Data Sheets are available for all hazardous substances used in the laboratory. Any person using a hazardous substance must be informed of the following:

Physical data about the substance

Any hazard from fire or explosion

Any hazard to health

Appropriate First Aid treatment

Any hazard from reaction with other substances How to clean/dispose of spillage

Appropriate protective measures

Appropriate storage and handling

Although these regulations may not be applicable in your country, it is strongly recommended that a similar approach is adopted for the protection of the students operating the equipment. Local regulations must also be considered.

USE OF RESIDUAL SAFETY DEVICE

CURRENT

DEVICE

ELECTRICAL

The equipment described in this Instruction Manual operates from a mains voltage electrical supply. The equipment is designed and manufactured in accordance with appropriate regulations relating to the use of electricity. Similarly, it is assumed that regulations applying to the operation of electrical equipment are observed by the end user.

However, it is recommended that the Residual Current Device (RCD) supplied alternatively called an Earth Leakage Circuit Breaker - ELCB) be fitted to this equipment. If through misuse or accident the equipment becomes E!Iectrically dangerous, an RCD will switch off the electrical supply and redu(,e the severity of any electric shock received by an operator to a level which, under normal circumstances, will not cause injury to that person.

If the electrical supply to the laboratory already incorporates an RCD, then the device supplied with the equipment need no@-be used. If the electrical supply does not incorporate such protection then the loose RCD supplied by ArmfiE!ld Ltd should be fitted by a competent electrician either in the supply tc, the laboratory or in the supply to the individual item of equipment. Drawing Number BM20491 gives full installation instructions.

Note: If any doubt exists whether the electrical supply incorporates a deirice then the RCD supplied should be fitted.

At least once each month, check that the RCD is operating correctly by pressing the TEST button. The circuit breaker MUST trip when the button is pressed. Failure to trip means that the operator is not protected and the equipment must be checked and repaired by a competent electrician before it is used.

INTRODIJCTION

Heat transfer by simultaneous conduction and convection, whether free or forced, forms the basis of most industrial heat exchangers and related equipment. The measurement and prediction of heat transfer coefficients for such circumstances is achieved in the Armfield apparatus by studying the temperature profiles and heat flux in an air duct with associated flat and extended transfer surfaces. The vertical duct is so constructed that the air temperature and velocity can be readily measured, and a variety of /'plug-in" modules of heated solid surfaces of known dimensions can be presented to the air stream for detailed study. A fan situated at the top of the duct provides the air stream for forced convection experiments.

An independent bench mounted console contains temperature measurement, power control, and fan speed control circuits with appropriate instrumentation. Temperature measurement, to a resolution of 0.1'C is effected using thermistor sensors with direct digital read-out in oc.

Air velocity is measured with a portable anemometer mounted on the duct.

The power control circuit provides a continuously variable, electrical output of 0-100 watts with a direct read-out in watts.

Using the instrumentation provided, free and forced convective heat transfer characteristics may be determined for:-

1. 2. 3.

A flat surface

An array of cylinders (pinned heat sink) A@n array of fins (finned heat sink)

Each module may be used independently on the bench, to demonstrate free convection in a horizontal mode.

The apparatus is fully self-contained

RECE:-IPT OF EQUIPMENT

SALES IN THE LINITED KINGDOM

The a- paratus should be carefully unpacked and the components checked .P

again-it the Advice Note. A copy of the Advice Note is supplied with this instruction manual for reference.

Any omissions or breakages should be notified to Armfield Ltd within three,days of receipt.

SALES OVERSEAS

The apparatus should be carefully unpacked and the components checked against the Advice Note. A copy of the Advice Note is supplied with this instruction manual for reference.

Any c)missions or breakages should be notified immediately to the Insurance Agent stated on the Insurance Certificate if the goods were insured by Armfield Ltd.

Your own insurers should be notified immediately if insurance was arranged by yourselves.

DESCRIPTION

Ali numerical references relate to the diagram on page 9.

The apparatus consists of a vertical rectangular duct supported by a bench mounted stand (1). A flat plate (3) pinned (4) or finned (5) exchanger may bE! installed in the duct and secured by a quick-release catch (18) on each side. Each exchanger incorporates an electric heating element with thermostatic protection against overheating. The temperature at the base of each exchanger is monitored by a thermistor sensor (19) with connecting lead (7).

The exchanger in use may be viewed through an acrylic window (14) in the wall of the duct.

A@n upward flow of air may be generated in the duct with a variable speed fan (21) mounted at the top.

A:ir velocity in the duct, whether natural or forced, is indicated on a portable anemometer (2) held in a bracket (15) on the duct wall. The anemometer sensor (16) is inserted through the wall of the duct.

A therrnistor probe (6) permits measurement of the in-going and out- going air temperatures together with surface temperatures of exchanger pins and fins.

These temperatures are determined by inserting the probe through access holes (20) in the duct wall.

An electric console (8) incorporates a variable auto-transformer with a digital readout to control and indicate power supplied to the exchanger on test. The exchanger is connected to a terminal box (11) mounted on the vertical duct which in turn is connected to the console via the supply lead (10). A variable low voltage DC supply is provided for the fan via the supply lead (17). A digital readout indicates the temperature using a therrnistor probe connected to a flexible lead (6).

Power is supplied to the equipment via a supply lead (9) connected to the rear of the console.

INSTALLATION

REQUIREMENTS

ELECTROMAGNETIC COMPATIBILITY

This apparatus is classified as Education and Training Equipment under the Electromagnetic Compatibility (Amendment) Regulations 1994. Use of the apparatus outside the classroom, laboratory or similar such place invalidates conformity with the protection requirements of the Electromagnetic Compatibility Directive (89/336/EEC) and could lead to prosecution.

FACILMES REQUIRED

The equipment should be installed on a firm, level work surface. A single phase electrical supply will be required.

No other services are necessary.

CONNE(@PTION TO SERVICES

ELECTRICAL SUPPLY FOR VERSION HT6-A

The equipment requires connection to a single phase, fused electrical supply. The standard electrical supply for this equipment is 220/24OV, 5OHz. Check that the voltage and frequency of the electrical supply agree with the label attached to the supply cable on the equipment. Connection should b(? made to the supply cable as follows:-

GREEN/YELLOW - BROWN

BLUE

Fuse Rating

EARTH LIVE (HOT) NEUTRAL I AMP

ELECTRICAL SUPPLY FOR VERSION HT6-B:

The equipment requires connection to a single phase, fused electrical supply. The standard electrical supply for thi@- equipment is 12OV, 6OHz. Check that the voltage and frequency of the electrical supply agree with the label attached to the supply cable on the equipment. Connection should be made to,the supply cable as follows:-

GREEN/YELLOW - BROWN

BLUE

Fuse Rating

EARTH LIVE (HOT) NEUTRAL 2 AM]?

ELECTRI'CAL SUPPLY FOR VERSION HT6-G,

The equipment requires connection to a single phase, fused electrical supply. 'The standard electrical supply for this equipment is ??0/24OV, 6OHz. Check that the voltage and frequency of the electrical supply agree with the label attached to the supply cable on the equipment. Connection should be made to the supply cable as follows:-

GREEN/YELLOW - BROWN

BLUE

Fuse Rating

EARTH LIVE (HOT) NEUTRAL I AMP

CONIMISSIONING

Having connected the apparatus to the electrical supply, (page 11) correct operation should be checked as follows:-

Turn the heater power control (A) and fan speed control (B) fully anti- clockwise.

Connect the fan supply lead (17) at the base of the duct to the socket (C) beneath the fan speed control on the instrument console.

Connect the thermistor probe lead (6) to the socket (D) beneath the temperature meter on the instrument console.

Connect the heater supply lead (10) to the socket (E) beneath the power control knob on the instrument console.

Clamp the flat plate heat exchanger (3) into the duct using the two toggle clamps (18) and connect the supply lead to the socket on the cover.

Connect the exchanger temperature lead (7) to the socket (F) on the heat exchanger.

Install the four 'AA' Alkaline Manganese batteries in the anemometer (2) as shown on the battery holder.

To check the condition of the batteries in the anemometer, set the switch to 'Velocity' and observe the battery low' LED. If the LED remains illuminated the batteries should be changed before using the instrument.

To set the anemometer to the zero position, slide the protective cover forward over the probe head to isolate it from any air movement. Set the switch to 'Velocity' and adjust the knurled wheel marked 'Zero' until the pointer is aligned with the zero on the scale.

Carefully slide the protective cover rearwards to expose the probe head then locate the probe (16) into the bush fitted to the duct. Place the meter into the bracket (15) situated on the side of the duct.

Ensure that the arrow on the tip of the probe is aligned with the direction of the airflow when inserting the probe through the wall of the duct. Set the switch to 'off' when the anernorneter is not being used.

Switch the equipment on by depressing the ON/OFF switch on the left hand side of the console.

Check that the LED temperature meter and wattmeter are illuminated

Check that the temperature meter indicates ambient temperature.

Increase the heater power in the exchanger by rotating the power control knob clockwise. The power supplied to the exchanger should be shown in watts on the meter.

NOTE:

The wattmeter is calibrated to read in the range 0 to 99.9 watts. Depending on the supply voltage it may be possible to exceed the maximum reading on the wattmeter if the power control knob is turned fully clockwise. This will not cause damage to the wattmeter but readings in excess of 99.9 watts will commence again at 0 watts. As the suggested experiments do not exceed 80 watts this characteristic will not affect the operation of the equipment.

Switch on the fan and increase the speed by rotating the fan speed control knob (B) clockwise.

Set the switch to 'Velocity' on the anemometer and observe that the air velocity is indicated on the meter scale. -T-

Connect the exchanger temperature lead (7) to the socket (D) on the console. Check that the temperature meter indicates the increasing temperature of the heat exchanger metalwork.

Set the heater power control knob and fan speed control knob to minimum (anti-clockwise).

Set the ON/OFF switch on the console to the OFF position.

Commissioning of the equipment is now complete.

ROUTINE MAINTENANCE

To preserve the life and efficient operation of the equipment it is important that the equipment is properly maintained. Regular servicing/maintenance of the equipment is the responsibility of the end user and must be performed by qualified personnel who understand the operation of the equipment.

In addition to regular maintenance the following notes should be observed:-

The equipment should be disconnected from the electrical supply when not in use.

The exterior of the equipment should be periodically cleaned. DO NOT use abrasives or solvents.

T'he Digital Wattmeter is protected by a fuse which is located in a holder on the rear panel of the electrical console. If replacement is necessary the fuse should be rated 250 niA, 20mm x 5mm, Quick Blow (F), ceramic.