GB2171506A

GB2171506A - Plate heat transfer apparatus

Info

Publication number: GB2171506A
Application number: GB08504548A
Authority: GB
Inventors: Michael Peter Bond
Original assignee: APV International Ltd
Current assignee: APV International Ltd
Priority date: 1985-02-21
Filing date: 1985-02-21
Publication date: 1986-08-28
Also published as: GB8504548D0; GB2171506B

Abstract

To meet this need, plate heat transfer apparatus comprises an assemblage of plates mounted together in a frame, pressure and/or temperature sensing devices and a micro-processor mounted in part, preferably a fixed head, of the frame and connected to the sensing devices and programmed to monitor the performance of the apparatus on the basis of the input data provided by them to provide performance data and/or warning signals and/or control signals on the basis of the input data. At least one of the sensing devices may be mounted on a grid mounted in the frame between passes or sections of the apparatus or at the end of such a pass or section.

Description

SPECIFICATION Plate heat transfer apparatus This invention relates to plate heat transfer apparatus.

The term plate heat transfer apparatus is intended to embrace not only plate heat exchangers of the conventional gasketed type, but also welded-up or partially welded-up heat exchangers using closely spaced face-to-face plates and plate evaporators of gasketed or welded types. The invention will be particularly described and discussed in connection with conventional gasketed plate heat exchangers, but its use is not necesarily so limited.

It is known to monitor and control the operation of plate heat transfer apparatus by means of a computer controlling the plant operation. For this purpose, the individual pieces of apparatus comprising the plant are each provided with sensors and probes connected to the remote computer and arranged to supply data via suitable highways. The plant is controlled by valves and other control gear which are remotely operated and controlled by means of signals generated manually or by the computer and transmitted either along the same highways or on dedicated cables.

It is an object of the invention to provide heat transfer apparatus which may be used to monitor its own performance and generate control or data signals accordingly.

In accordance with a first aspect of the invention, there is provided heat transfer apparatus (as hereinbefore defined) comprising an assemblage of plates mounted together in a frame and including pressure and/or temperature sensing devices and a micro-processor mounted in part of the frame and connected to the sensing devices and programmed to monitor the performance of the apparatus on the basis of the input data provided by them and provide performance data and/or warning signals and/or control signals on the basis of the input data.

The micro-processor is preferably mounted in a fixed head of the frame.

Sensing devices may also be provided for sensing other process parameters and feeding the data to the micro-processor.

At least one of the sensing devices may be mounted on a grid mounted in the frame between passes or sections of the apparatus or at the end of such a pass or section. By this means, the adapatation of plates to accept port probes would be avoided, and the data could stili be obtained from within the apparatus.

As a minimum, sensors are likely to be provided for measuring the input and output temperatures of two media in heat exchange, and for ascertaining the pressure loss in respect of each of the two media.

The micro-processor is conveniently programmed to produce and display values for the temperature changes of the media in the apparatus, and to produce and display a value for the end temperature differences between the media.

It may also be programmed to produce and display instantaneous values of the overall heat transfer coefficient (U values) and to ascertain and store the maximum values of temperature and/or pressure sensed during operation.

The micro-processor may also be programmed to apply control measures to the operation of the apparatus, and to display the fact that it had done so, in the event of particular parameters falling outside a predetermined range.

In accordance with a second aspect of the invention, there is provided a support device for sensors for use in a heat transfer apparatus according to the invention as set forth above, comprising a grid or like construction adapted to tbe mounted between passes of the apparatus or at the end of such a pass, and comprising at least one sensing device mounted on the grid or like construction.

In a practical form of heat exchanger in accordance with the invention, substantial information will need to be stored in the microprocessor for heat transfer and pressure drop correlations. The actual arrangement and the physical properties of the fluids will be required as inputs. Also, flowrates should be recorded, but if this proves too expensive, the user may be allowed to input flow values. If the user does not know the flows, default values may be calculated but will then tend to be unreliable for duties involving non-asymptotic fouling such as milk heating. The calculated values will also be less than reliable for viscous materials.

The pressure losses should be measured, including compensating for the static head, for each medium. The pressure losses may be displayed and will serve as guide to the extent of fouling. Both process and service fluid temperature changes can be displayed, and so can the end temperature differences. The latter would be of use for example in chillers and would serve as warning of incipient or attained freezing conditions.

For liquid/liquid applications, the logarithmic mean temperature difference can be calculated and the number of heat transfer units (HTU) can be displayed. The HTU can be compared with that specified for the duty by the user and any over- or under-performance noted.

The calculation program may allow for end effects and concurrency.

If the desired duty is stored in the memory, the percentage deviation from the desired duty can be displayed.

In what follows the symbol U means the overall heat transfer coefficient.

For most applications: Current HTU Current = Uc:ean X Clean HTU The value of Ucc,,cnt may therefore be computed.

The value of U,,,,,, is the instantaneous value of U in current conditions of fouling, and therefore the overall fouling resistance can be computed from the expression: 1 1 =-+fouling resistance Current Uclean The heat load may also be computed. This may be displayed and so may the deviation from original.

Since in many cases the heat exchanger will only be operated at less than full capacity, it is a generally a more practical procedure to store some information in memory before the apparatus is installed.

Such information will include known properties of both the process medium and the service medium. Such properties, for liquid/liquid heat transfer for example, are the density, the specific heat, the thermal conductivity, the inlet viscosity and the outlet viscosity.

Also to be included are basic data about the apparatus such as the number of passes and the number of passages per pass. Also the metal heat transfer coefficient should be recorded. Pre-ascertained performance details should also be included, which will enable computation of the film heat transfer coefficients.

If the flow rates are known either by calculation or measurement, then it follows that the following parameters are available for display: Pressure drops by measurement; Flows rates by measurement or calculation; Temperature changes by measurement or calculation; Temperature differences by measurement or calculation; and Number of htu's by calculation.

The heat load=mass flowXSpecific heatXtemperature change is also available for display, for liquid/liquid applications. For other duties, modified procedures may be used.

The value of Utu,,nt can now be calculated and displayed.

For the given flows, the film heat transfer coefficients can be computed in a few simple steps (provided that the accuracy required is not great). These can be summed to calculate the expected clean overall heat transfer coefficient (Uc,ean) The overall fouling resistance may then be calculated, and both the value of Uccac and the fouling resistance are available for display.

The expected clean heat load can be calculated and displayed.

The user could set a value for achieved heat load, outlet temperature, fouling resistance or the value of U to give warning that plates require cleaning. Alternatively, e.g. for ultra high temperature treatment of milk, the criterion will be a pressure drop limit. It is known that, depending on the time of the year and, therefore, the quality of the milk, the permissible run time will change because of differing rates of pressure loss build-up.

If individual pressures are measured, then a warning can be incorporated against exceeding the design pressure of the apparatus.

From the temperature measurements, a warning could be issued of any temperature excursion beyond the design value.

Such pressure and temperature excursions could be stored in memory.

One convenient arrangement for mounting the required sensors would be the use of a grid or other intermediate construction introduced between plates or at the end of the plate pack, and on which the sensors could be mounted. It is conventional practice to introduce a grid construction between plates where there is a change-over between sections or passes, and in order to provide the necessary connections, a similar grid construction could be used to carry the sensors.

Various other modifications may be made within the scope of the invention.

Claims

1. Plate heat transfer apparatus (as hereinbefore defined) comprising an assemblage of plates mounted together in a frame and including pressure and/or temperature sensing devices and a micro-processor mounted in part of the frame and connected to the sensing devices and programmed to monitor the performance of the apparatus on the basis of the input data provided by them and provide performance data and/or warning signals and/or control signals on the basis of the input data.

2. Heat transfer apparatus as claimed in claim 1, in which the micro-processor is mounted in a fixed frame member.

3. Heat transfer apparatus as claimed in claim 2, in which the micro-processor is mounted in a head of the frame.

4. Heat transfer apparatus as claimed in claim 1, 2 or 3, in which sensing devices are also provided for sensing other process parameters and feeding the data to the micro-processor.

5. Heat transfer apparatus as claimed in claim 1, 2, 3 or 4, in which at last one of the sensing devices is mounted on a grid mounted in the frame between passes or sections of the apparatus or at the end of such a pass or section.

6. Heat transfer apparatus as claimed in any of the preceding claims, in which sensors are provided for measuring the input and output temperatures of two media in heat exchange.

7. Heat transfer apparatus as claimed in any of the preceding claims, in which sensors are provided for ascertaining the pressure loss in respect of each of the two media.

8. Heat transfer apparatus as claimed in any of the preceding claims, in which the micro-processor is programmed to produce and display values for the temperature changes of the media in the apparatus.

9. Heat transfer apparatus as claimed in claim 8, in which the micro-processor is also programmed to produce and display a value for the end temperature differences between the media.

10. Heat transfer apparatus as claimed in any of the preceding claims, in which the micro-processor is programmed to produce and display instantaneous values of the overall heat transfer coefficient (U values).

11. Heat transfer apparatus as claimed in any of the preceding claims, in which the micro-processor is programmed to ascertain and store the maximum values of temperature and/or pressure sensed during operation.

12. Heat transfer apparatus as claimed in any of the preceding claims, in which the micro-processor is programmed to apply control measures to the operation of the apparatus, and to display the fact that it had done so, in the event of particular parameters falling outside a predetermined range.

13. Plate heat transfer apparatus as claimed in any of the preceding claims, substantially as hereinbefore described.

14. A support device for sensors for use in a heat transfer apparatus as claimed in any of the preceding claims, comprising a grid or like construction adapted tbe mounted at the end of or between passes or sections of the apparatus and comprising at least one sensing device mounted on the grid or like construction.