WO2000007000A1

WO2000007000A1 - Monitoring the heat transfer properties of a heat transferring surface

Info

Publication number: WO2000007000A1
Application number: PCT/GB1999/002428
Authority: WO
Inventors: Norman Foster Glen; Jeffery Harry Howarth; Andrew Mark Jenkins
Original assignee: National Engineering Laboratory
Priority date: 1998-07-28
Filing date: 1999-07-26
Publication date: 2000-02-10
Also published as: EP1114311A1; GB9816304D0; AU5058599A

Abstract

A method for monitoring the heat transfer properties of a heat transferring surface forming part of a containment for a flowing liquid is described. The monitoring method comprising the steps of diverting a representative fraction of the flowing liquid through a test conduit (20) selected to be an analogue of the heat transferring surface, causing a determined heat flow to pass through the wall of the test conduit between the fraction of flowing liquid passing through the test conduit and a heat source or sink means external to the test conduit, measuring the rate of flow of liquid through the test conduit, measuring selected temperatures and/or temperature differentials at selected locations, and calculating the heat transfer properties of the test conduit on the basis of the measurements to provide an analogue of the heat transferring properties of the heat transferring surface. Apparatus for the method is also described.

Description

MONITORING THE HEAT TRANSFER PROPERTIES OF A HEAT TRANSFERRING

SURFACE

This invention relates to monitoring, and relates more particularly but not exclusively to monitoring the effects of fouling in fluid-carrying thermal transfer arrangements, eg heat exchangers.

Heat exchangers containing flowing fluids are widely employed throughout industry in (for example) the food processing industries, the chemical industry, pharmaceuticals, etc. Heat exchanger surfaces in contact with liquids are liable to progressive fouling due to corrosion, biological growth, deposits, and other reasons. Notwithstanding anti-fouling measures such as mechanical cleansing of surfaces and dosing of liquids with biocides, fouling usually progresses to such an extent as seriously to degrade heat transfer through the fouled surfaces.

Fouling of heat exchangers in process plant is so ubiquitous that the fouling allowance in the calculation of heat exchanger surface area is a firmly established aspect of design. The practice of estimating the size of this allowance is, however, far from ideal, often relying on unattributed tabulated values of R_f (thermal fouling resistance). This causes unnecessary inefficiency in affected industries resulting from oversizing of plant and equipment, lost production due to scheduled and unscheduled downtime, and from energy losses due to increased thermal inefficiency and pressure drop.

Different approaches to this problem have been adopted. Some improvements have been achieved by specific organisations through the use of proprietary and in- house R_f databases, and some further published values are slowly becoming available. However, the problem of fouling remains, even in well designed plant, both for existing plant and new plant.

Another approach has involved research into mathematical modelling of fouling for the purpose of predicting the rate and cleanability of fouling, and determination of optimum cleaning schedules. Progress is hindered due to the complexities of process stream properties interacting with frequently unknown flow and surface characteristics.

Normal mitigation practices therefore rely on the use of chemicals for the control of deposition, in conjunction with on-line and off-line cleaning. The timely and effective application of even these practices is limited, however, due to a lack of knowledge about the condition of the heat transfer surfaces and of the progress of fouling. Plant instrumentation is almost invariably incapable of adequately providing the information needed to keep fouling under control and minimise downtime.

The failure of prior art approaches to the problem of fouling is highlighted by the published estimates of the cost of fouling. When added to increased capital costs from oversizing of plant, the costs of fouling to EU process industry are estimated at 5200 Mecu per annum, with equal contributions from oversizing, maintenance and cleaning, lost production and increased energy use. ("Economic aspects of heat exchanger fouling" by A M Pritchard in "Fouling von Warmeϋbertragungsflachen" , GVC-VDI-Gesellschaft fur Verfahrenstechnik und Chemieingenieurwessen, Mlinchen, 1990). Further penalties which are less easily quantified are the lost opportunities for improved efficiency due to a reluctance to adopt newer technologies such as compact exchangers, enhanced heat transfer surfaces, heat transfer intensification devices such as turbulators and new chemical mitigation regimes.

Although the use of fouling measurements in laboratory experiments using monitors or instrumented test sections is known, the application of monitors to industrial plant remains a rarity. There rightly exists a general lack of confidence in laboratory-based experience as existing systems often require considerable skill in interpreting the data.

The present invention provides a fouling monitor for use in industrial plant which overcomes many of the problems of previous devices by providing a self- contained unit with on-board data processing and an output signal directly proportional to R_f (thermal fouling resistance).

As used throughout this specification, the term "liquid" comprises true liquids and liquid-like fluent materials, eg slurries, soups, suspensions, etc. According to a first aspect of the present invention there is provided a monitoring method for monitoring the heat transfer properties of a heat transferring surface forming part of a containment for a flowing liquid, the monitoring method comprising the steps of diverting a representative fraction of the flowing liquid through a test conduit selected to be an analogue of the heat transferring surface, causing a determined heat flow to pass through the wall of the test conduit between the fraction of flowing liquid passing through the test conduit and a heat source or sink means external to the test conduit, measuring the rate of flow of liquid through the test conduit, measuring selected temperatures and/or temperature differentials at selected locations, and calculating the heat transfer properties of the test conduit on the basis of the measurements to provide an analogue of the heat transferring properties of the heat transferring surface.

The method preferably comprises the step of measuring the temperature differential in the liquid flowing through the test conduit, between liquid upstream of the heat source or sink means and liquid downstream of the heat source or sink means.

The method preferably also comprises the step of determining the temperature differential between inner surface of the wall of the test conduit and the bulk temperature of the liquid in a region of the test conduit through which the heat flow passes between the liquid and the heat source or sink means.

According to a second aspect of the present invention there is provided monitoring apparatus for monitoring the heat transfer properties of a heat transferring surface forming part of a containment for a flowing liquid, the monitoring apparatus comprising a test conduit selected to be an analogue of the heat transferring surface, diversion means for diverting a representative fraction or sidestream of the flowing liquid through the test conduit, a heat source or sink means external to the test conduit and thermally coupled thereto, flow rate measuring means for measuring the rate of flow of liquid through the test conduit, temperature measuring means for measuring selected temperatures and/or temperature differentials at selected locations, and calculating means for calculating the heat transfer properties of the test conduit on the basis of the measurements to provide an analogue of the heat transferring properties of the heat transferring surface.

The temperature measuring means preferably comprises means for determining the temperature increase or decrease of the liquid passing through the test conduit caused by operation of the heat source or sink means; the temperature differential determining means may operate either by utilising a differential measurement technique or by separately measuring the temperatures of the liquid upstream and downstream of the heat source or sink means, and subtracting one temperature from another. The temperature measuring means preferably also comprises means for determining the temperature differential between the inner surface of the wall of the test conduit and the bulk temperature of the liquid in the vicinity of the heat source or sink means; the temperature differential determining means may operate either by utilising a differential measurement technique or by separately determining the inner surface temperature and the average fluid temperature within the test conduit, and then subtracting one temperature from the other.

Embodiments of the invention will now be described with reference to the accompanying drawings wherein:

Fig 1 is an overall schematic diagram of a preferred embodiment of monitoring apparatus; and

Fig 2 is a schematic diagram of part of the apparatus of Fig 1.

Referring first to Fig 1, this is a schematic representation of a monitoring arrangement 10 installed on a pipeline 12 which is carrying a stream of liquid whose effect on a downstream heat exchanger (not shown) is to be monitored by the arrangement 10. A liquid diverter 14, which may simply be a side-branch whose bore is small relative to that of the pipeline 12, taps a small but adequate portion of the liquid flow along the pipeline 12 and diverts the tapped portion of flowing liquid into and through the monitoring arrangement 10. (Treatment of the tapped liquid within the monitoring arrangement 10 will be detailed below) . After its passage through the monitoring arrangement 10, either the tapped liquid can be returned to the pipeline 12 by means of a further side-branch 16 downstream of the diverter 12, or the tapped liquid can be jettisoned to a drain 18.

Although the portion of flowing process liquid tapped by the diverter 14 to run through the monitoring arrangement is small relative to the total flow of process liquid along the pipeline 12, the tapped portion is adequate to ensure that the tapped portion is a representative fraction of the flowing process liquid. Within the monitoring arrangement 10, the representative fraction of liquid tapped by the diverter 14 passes along a test conduit 20 formed of the same material as the downstream heat exchanger and having the same wall thickness. Thus the susceptibility of the test conduit 20 to internal fouling and the thermal transfer ability of the test conduit 20 are analogues of the downstream heat exchanger, ie the test conduit 20 models these aspects of the heat exchanger with adequate accuracy. The test conduit 20 is part of a flow module 22 contained within the monitoring arrangement 10. The flow module 22 also contains other components and sub-assemblies which will now be detailed with reference to Fig 2.

Referring to Fig 2, this schematically illustrates the arrangement within the flow module 22 of the test conduit 20 and of the other components and sub- assemblies. The latter comprise a valve or other suitable flow control device 24 for regulation of the volumetric rate of liquid flow through the test conduit 20 as measured by a flowmeter or other suitable flow measurement device 26. Surrounding part of the test conduit 20 within the flow module 22 is a block 28 of metal or other material of good thermal conductivity. Thermally coupled to the block 28 is a heat source and/or sink 30 of any suitable form. The heat source and/or sink 30 could, for example, be a coiled pipe carrying a heated or chilled fluid, an electrically powered resistive heating element, an array of Peltier units, or any other suitable means by which a controlled heat flow can be applied to the test conduit 20, ie by which heat can be supplied to or extracted from the test conduit 20 at a known rate so as to model the thermal conditions pertaining to the downstream heat exchanger. A first temperature sensor 32 is embedded in the block 28 slightly beyond the outer surface of the test conduit 20 such that the sensor 32 measures a temperature from which the inner surface temperature of the test conduit 20 can be derived at a location where the conduit 20 is surrounded by the block 28. This arrangement of the temperature sensor 32 enables the inner surface temperature of the test conduit 20 to be derived.

A second temperature sensor 34 measures the temperature of the liquid flowing through the test conduit 20, at a location immediately upstream of the block 28.

A third temperature sensor 36 measures the temperature of the liquid flowing through the test conduit 20, at a location immediately downstream of the block 28.

The temperature sensors 34 and 36 can be arranged to measure absolute temperatures, or they can be jointly arranged so to as measure the difference in liquid temperatures between upstream and downstream sides of the block 28, ie so as to measure the increase or decrease in liquid temperature brought about by operation of the heat source and/or sink 30. If a differential technique is used, an additional temperature sensor must be used to measure the absolute temperature of the liquid flowing through the test conduit 20 at a defined location between the differential measurement points (for example at the location of the upstream temperature sensor 34).

The temperature differential between the inner surface of the wall of the test conduit 20 and the bulk temperature of the liquid between upstream and downstream sides of the block 28 can be determined from the temperatures measured by the temperature sensors 32, 34 and 36. Alternatively, sensor 32 can be replaced with a differential measurement technique consisting of one sensor within the liquid and one within the test conduit wall, between the upstream and downstream sides of the block 28, from which the temperature differential can be determined.

Also contained within the monitoring arrangement 10, but outwith the flow module 22, are an instrumentation signal processing and control module 38, and a power supply module 40.

The module 38 contains a data analysis and storage unit (not shown per se) or other suitable means by which flow rate signals from the flow measurement device 26 and temperature dependent signals from the temperature sensors 32, 34 and 36 are monitored and processed to produce a calculated thermal fouling resistance R_f for the surface in contact with the liquid flowing through the test conduit 20, as well as operating the flow control device 24 to control the rate of flow of tapped process liquid through the test conduit 20, and regulating operation of the heat source and/or sink 30 to ensure a desired rate of heat flux, ie a desired rate of heat supply to or heat extraction from the test conduit 20 and the liquid flowing therethrough.

The power supply module 40 contains equipment necessary to receive mains electric power and to deliver power at the lower voltage(s) required by the instrumentation, signal processing and control module 38 and by such devices (eg the flow control device 24) as may draw power from the module 38. If the heat source and/or sink 30 is electrically operated, the necessary power must also be supplied by the module 40 under the control of the module 38.

Each of the modules 22, 38 and 40 has a respective housing which is waterproof to an appropriate standard (for example Standard "IP65"), and which can be locked shut to guard against tampering.

If the data analysis and storage unit within the module 38 registers a zero flow rate signal from the flow measuring device 26 (or an excessively low flow rate), operation of the heat source and/or sink 30 is interrupted until adequate flow is resumed. Similarly, if the data analysis and storage unit registers temperature signals from the temperature sensors 32, 34 and 36 which are excessively high or low (depending on whether the device 30 is being used as a heat source or as a heat sink), operation of the heat source and/or sink 30 is interrupted. Additionally or alternatively, there may be one or more independent devices for protection against over-temperature or under- temperature.

Operation of the monitoring arrangement 10 will now be detailed.

The following sections describe the monitoring technique, components and principle of operation required for an embodiment of general purpose process fouling monitor in accordance with the invention.

Sidestream Monitoring

Sidestream monitoring takes a side stream of a fluid from a process stream and passes it through an appropriately instrumented test section. The fluid is either returned to the process or run to drain. The monitor detects change in heat transfer in the test section subjected to an applied heat flux due to fouling, corrosion or erosion of the surface in contact with the fluid flowing through the test section.

The test section simulates the temperature and heat flux (for a heat transfer application), the geometry and fluid flow for the application under test.

The modes of operation of this technique are:

• constant surface temperature; • constant heat flux; and • zero heat flux.

In principle, the technique used can simulate heat transfer or isothermal applications, use any geometry of flow channel and test any fluid.

Test Section

The test section may consist of a single test section or multiple sections connected in series or parallel.

For each test section -

• the material of the test section may be the same as that of a specific unit in the process being tested, or not, as appropriate;

• the flow geometry consists of any flow path/channel geometry required to simulate the fluid flow of a specific unit in the process being tested (and may be, but is not limited to, cylindrical, flat or corrugated plate, spiral or extended surfaces); • a method is provided for applying or removing a quantity of heat from the fluid under test either by supplying heat by an appropriate means (including, but not limited to, electrical resistance heaters, steam or other heat transfer fluid, induction heating) or by removing heat using a cooling coil;

• mechanisms are provided for varying and controlling the heat flux or wall temperature (depending on mode of operation) and the fluid flow rate;

• sufficient sensors of appropriate resolution and accuracy are provided to measure the parameters required to determine the change in heat transfer coefficient as a function of time; and

• a method is provided for storing the output from the sensors and processing the data to produce a calculated thermal fouling resistance.

By using a modular design and, for a heating duty application, using a suitable design for applying the heat flux to the test section, it is possible to produce an intrinsically safe monitor for use in hazardous locations.

Principle of Operation

The overall heat transfer coefficient U of the test section in contact with the fluid under test is given

^{by u} = ^ (1) where Q = rate of heat flow, Ai = surface area of test section in contact with test fluid, and ΔT = mean temperature difference between fluid and wall of test section.

The deterioration in heat transfer as a function of time is determined at any given time by

¹ " 1 ⁽2⁾ R_f = ϋ ϋ ^{U U}° where R_f - thermal fouling resistance, U = heat transfer coefficient at time t, and U₀ = heat transfer coefficient at time t₀.

The rate of heat flow is determined from

Q = ΛiC_pδT (3)

where n = mass flow rate of fluid through test section, C_p = specific heat capacity of test fluid, and δT = temperature difference between fluid at inlet to and outlet from test section.

The mass flow rate of the fluid can be determined by direct measurement with a mass flow meter or calculated from the known dimensions of the test section and the density of the test fluid if a volumetric or superficial velocity flow meter is used. If an indirect measurement method is used the data analysis and storage unit shall be capable of processing the signal produced from such a meter, plus any other required signals and information (such as fluid temperature, variation of fluid density with temperature) to produce a mass flow rate.

The change in temperature of the test fluid across the test section must be measured to sufficient accuracy and with sufficient resolution to allow values of R_f to be calculated to ±lxlO^"5 square metre degree Kelvin per watt. This may be achieved either by direct measurement of the temperature difference using, for example, a differential thermocouple or thermopile assembly or indirectly by measuring the inlet and outlet fluid temperature and calculating the difference.

The mean temperature of the fluid in the test section must also be measured with sufficient accuracy to allow the data analysis and storage unit to calculate required thermophysical properties of the fluid including density, viscosity and heat capacity.

The mean temperature of the wall of the test section in contact with the test fluid must be measured with sufficient accuracy and with sufficient resolution to allow values of R_f to be calculated to ±lxlO^"5 square metre degree Kelvin per watt. Depending on the geometry of the test section multiple sensors may be required and the data storage and analysis unit may have to calculate a representative value.

If the test section is to be used in constant wall temperature mode a signal representative of the mean temperature of the wall of the test section in contact with the test fluid must be sent to the unit used to control the rate of heat flow to or from the test section. The film heat transfer coefficient _£ for the fluid in contact with the wall of the test section will be a function of temperature and fluid velocity and hence the apparent overall heat transfer coefficient U of the test section will vary even in the absence of any deterioration due to fouling, corrosion or erosion. Thus, in equation 2, U₀ must be the reference heat transfer coefficient at time t₀ corresponding to the temperature and fluid velocity conditions pertaining at time t. This can be achieved by using a function to calculate the effects of temperature and fluid velocity on the heat transfer coefficient. For forced- convection heat transfer in turbulent pipe flow, the general form of this function is

h o CReⁿPr^m ( 4 )

where Re = fluid Reynolds number, Pr = fluid Prandtl number, and C, m and n are constants.

The form of the equation (additional factors to account for viscous fluids, short flow passage correction terms etc) and the values of the constants depend on the specific application. The data analysis and storage unit must therefore be capable of processing any received signals and information (such as fluid temperature and flow rate, variation of fluid properties with temperature) to calculate an appropriate reference heat transfer coefficient U₀ using a form of equation (4) specific to the geometry, fluid and flow conditions pertaining in the test section.

The principle of operation is such that any change in heat transfer in the test section (corrected for fluid velocity effects) will be detected, whether caused by fouling, corrosion, erosion or any combination thereof. Furthermore, the technique is not specific to one particular form or mechanism of fouling but will detect any change in heat transfer in the test section caused by any fouling mechanism or combination of mechanisms.

Calibration

Each of the sensors (flow meter, temperature sensors) must be calibrated as must all parts of the signal processing assembly. In addition to individual calibration of sensors it may be necessary to calibrate complete functional groups (including, for example, the sensors used to measure the change in temperature of the test fluid across the test section).

To account for the effects of fluid temperature and flow rate variations as described by equation (4) each test section must be calibrated across the full range of conditions at which it will operate. Under clean fluid conditions a series of measurements are made at fluid velocities covering the required range. Clean heat transfer coefficients are then calculated from equations (1) and (3) and a plot of 1/U against 1/Reⁿ produced from which the reference heat transfer coefficient may then be calculated.

All the sensors and signal processing assembly must be sufficiently stable such that over the period required to detect a meaningful change in R_f sensor or instrument drift does not cause unacceptable errors in R_f.

Data Analysis/Storage

The function of the data analysis and storage unit is to take the raw data measured by the sensors (temperatures and/or temperature differences and flow rate) and process it to provide a calculated thermal fouling resistance R_f and make the value available in a convenient form. The data analysis and storage unit therefore provides -

• digital storage of all measured parameters;

• digital storage of all required calibration data, coefficients and constants;

• processing of the measured values according to the equations, calibrations and other functions required to calculate R_f;

• digital storage of all relevant processed values;

• mechanisms for retrieval and display of data; and

• analogue and/or digital output signals corresponding to any measured or processed values.

Storage of calibration data, coefficients and constants and retrieval of processed data is possible locally or remotely. It is also possible to alter, locally or remotely, the program which controls the operation of the data analysis and storage unit.

In addition to controlling the data storage and processing functions outlined above, the program controlling the operation of the data analysis and storage unit may be required to perform additional tasks including, but not limited to, periodic automation calibration to determine residual thermal offsets in δT and ΔT and storage, processing and outputting of data from additional sensors which may be incorporated into the monitor (such as pressure/differential pressure measuring devices, pH and conductivity meters, general or species-specific biological activity meters).

Use :

The monitor, in particular its output R_f signal, can be used in a number of ways, including but not limited to :-

• provision of a control signal for chemical dosing;

• provision of a control signal for on-line mechanical cleaning;

• scheduling of off-line cleaning and shutdowns;

• early warning for manual dosing/cleaning;

• process optimisation; and

• assessment of new technologies (including, for example, new heat exchanger designs, new biocides and treatment chemicals).

The fouling monitor is a sidestream monitor which uses the technique outlined above with the following specific features and optional alternatives:

• single or multiple test sections, in series or parallel;

• cylindrical bore test section(s), which may be made from the same material as the specific heat exchanger being monitored; • aqueous fluids flowing through the test section(s);

• heating or cooling duty;

• a method to smooth the applied or removed heat, using a heat dissipation block, to ensure a uniform or near uniform wall temperature throughout the test section;

• either local or remote operation of manual or automatic control of applied heat flux to provide constant heat flux or constant wall temperature of test section(s);

• either local or remote operation of manual or automatic control of fluid velocity;

• low-flow and wall over-temperature detection;

• simulation of typical aqueous fluid heat exchanger temperature and flow conditions;

• a suitable choice of sensors and data logging equipment and calibration thereof to enable the tube-side R_f due to fouling, corrosion or erosion to be obtained with a resolution of ±lxlO"⁵ square metre degree Kelvin per watt and an accuracy of ±5x10"⁵ square metre degree Kelvin per watt;

• calibration of the test section(s) to provide a velocity-independent measurement of R_f;

• any change in the heat transfer in the test section (corrected for fluid velocity effects) will be detected, whether caused by fouling (due to any mechanism or combination of mechanisms), corrosion, erosion or any combination thereof;

• an onboard data logging and processing unit with a program which controls the logging interval, stores raw data, processes the data using stored functions and calibration coefficients to provide a calculated R_f and stores all appropriate processed data;

• a mechanism for storage of the data logger control program, either locally or by telemetry;

• a mechanism for retrieval of the stored data, either locally or by telemetry; and

• an analogue output signal (current or voltage) proportional to R_f.

In the assembly embodiment, the heat exchanger was described as being downstream of the monitoring arrangements 20. However, the monitoring arrangement is not necessarily upstream of the heat exchanger since conditions of access, plant operation, or other considerations may require the monitoring arrangement to be downstream of the heat exchanger.

In the exemplary embodiment, use of a side branch 14 on the pipeline 12 as sampling diverter was described. In general, whatever sampling procedure is employed should ensure that the liquid sample is representative (even if the liquid contains particulates) , since it may in certain circumstances be necessary to sample the fluid from a sump or from the header box of a heat exchanger. In the exemplary embodiment, the test conduit 20 was formed of the same material as the downstream heat exchanger, and had the same wall thickness. However, the test conduit material is not necessarily the same as the last heat exchanger, and the wall thickness of the test conduit is irrelevant, since the technique of the invention isolates the effects of fouling on the inner surface only. While the bore of the test conduit 20 is preferably selected such that the test conduit is an analogue of the heat exchanger, it may be desirable or necessary to substitute a tube of a different bore, and then to scale the monitoring results on the basis of Reynolds number so as to give hydrodynamic equivalence.

Other modifications and variations can be adopted without departing from the scope of the invention.

Claims

1. A method for monitoring the heat transfer properties of a heat transferring surface forming part of a containment for a flowing liquid, the monitoring method comprising the steps of diverting a representative fraction of the flowing liquid through a test conduit selected to be an analogue of the heat transferring surface, causing a determined heat flow to pass through the wall of the test conduit between the fraction of flowing liquid passing through the test conduit and a heat source or sink means external to the test conduit, measuring the rate of flow of liquid through the test conduit, measuring selected temperatures and/or temperature differentials at selected locations, and calculating the heat transfer properties of the test conduit on the basis of the measurements to provide an analogue of the heat transferring properties of the heat transferring surface.

2. A method as claimed in Claim 1 which includes the step of measuring the temperature differential in the liquid flowing through the test conduit, between liquid upstream of the heat source or sink means and liquid downstream of the heat source or sink means.

3. A method as claimed in Claim 1 or Claim 2 which includes the step of determining the temperature differential between inner surface of the wall of the test conduit and the bulk temperature of the liquid in a region of the test conduit through which the heat flow passes between the liquid and the heat source or sink means.

4. Apparatus for monitoring the heat transfer properties of a heat transferring surface forming part of a containment for a flowing liquid, the monitoring apparatus comprising a test conduit selected to be an analogue of the heat transferring surface, diversion means for diverting a representative fraction or sidestream of the flowing liquid through the test conduit, a heat source or sink means external to the test conduit and thermally coupled thereto, flow rate measuring means for measuring the rate of flow of liquid through the test conduit, temperature measuring means for measuring selected temperatures and/or temperature differentials at selected locations, and calculating means for calculating the heat transfer properties of the test conduit on the basis of the measurements to provide an analogue of the heat transferring properties of the heat transferring surface.

5. Apparatus as claimed in Claim 4 wherein the temperature measuring means comprises means for determining the temperature increase or decrease of the liquid passing through the test conduit caused by operation of the heat source or sink means.

6. Apparatus as claimed in Claim 4 or Claim 5 wherein the temperature measuring means comprises means for determining the temperature differential between the inner surface of the wall of the test conduit and the bulk temperature of the liquid in the vicinity of the heat source or sink means.

7. Apparatus as claimed in Claim 5 or Claim 6 wherein the temperature means utilises a temperature differential measurement technique.

8. Apparatus as claimed in any one of Claims 4-7 wherein the temperature means is adapted to measure the temperatures of the liquid upstream and downstream of the heat source or sink means.

9. Apparatus as claimed in any one of Claims 4-8 wherein the temperature means is adapted to measure the inner surface temperature and the average fluid temperature within the test conduit.

10. Apparatus as claimed in any one of Claims 4-9 wherein the test conduit is formed of the same material as the heat transferring surface.

11. Apparatus as claimed in any one of Claims 4-10 wherein the monitoring apparatus includes a flow control device.

12. Apparatus as claimed in any one of the Claims 4-11 wherein the monitoring apparatus includes a flow measurement device.

13 Apparatus as claimed in any one of Claims 4-12 wherein a thermally conductive block surrounds at least part of the test conduit.

14. Apparatus as claimed in Claim 13 wherein a temperature sensor is located in the block.

15. Apparatus as claimed in Claim 13 or Claim 14 wherein a temperature sensor is located upstream of the block.

16. Apparatus as claimed in any one of Claims 13, 14 or 15 wherein a temperature sensor is located downstream of the block.

17. Apparatus as claimed in any one of Claims 4-16 which includes an instrumentation signal processing and control module.

18. Apparatus as claimed in any one of Claims 4-17 which includes a power supply module.

19. Apparatus as claimed in any one of Claims 4-18 wherein the test conduit has multiple test sections connected in series or parallel.

20. Apparatus as claimed in any one of Claims 4-19 wherein the calculating means provides thermal fouling resistance (Rf) data of the heat transferring surface.

21. Apparatus as claimed in any one of Claims 4-20 wherein the apparatus is adapted to store, process and relay to a remote location heat transfer properties and/or Rf data obtained thereby.

22. A method for providing thermal fouling resistance (Rf) data of a heat transferring surface forming part of a containment for a flowing liquid comprising calculating the Rf data from the heat transfer properties obtained from the method of any one of Claims 1 to 3.

23. A method for monitoring the heat transfer properties of a heat transferring surface forming part of a containment for a flowing liquid substantially as herein described and with reference to Figures 1 and 2.

4. Apparatus for monitoring the heat transfer properties of a heat transferring surface forming part of a containment for a flowing liquid substantially as herein described and with reference to Figures 1 and 2.