Thermal measuring and testing – Distance or angle – Thickness – erosion – or deposition
Reexamination Certificate
1999-07-22
2002-12-31
Fulton, Christopher W. (Department: 2859)
Thermal measuring and testing
Distance or angle
Thickness, erosion, or deposition
C374S029000
Reexamination Certificate
active
06499876
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to monitoring apparatus and in particular to monitoring apparatus for use in monitoring soil build-up in a pipework system which includes a heat exchanger.
BACKGROUND OF THE INVENTION
The monitoring apparatus of the present invention is particularly though not exclusively suitable for use in processes involved with the heat treatment of milk and milk products. The soil build-up in the conduits of heat treatment equipment for milk and milk products is a serious problem, threatening the sterile operation of the equipment and reducing the efficiency of the process. Frequent cleaning is often necessary to remove deposits: often one shift in three is spent cleaning.
The use of a heat flux sensor to monitor fouling is known from a paper entitled “The use of a heat flux sensor in monitoring fouling” by A. D. Jones et al which forms part of the proceedings of a conference held at Jesus College, Cambridge, 23-25 March 1994, pages 230-241; edited by Fryer, Hasting and Jeurnink and published by the European Commission DGXII, Science, Research and Development (ISBN92-827-4360-8).
The heat flux sensor is intended to be used in processes involved with the heat treatment of milk and milk products. It was operated by attaching it to a pipe through which a milk protein solution flowed to represent the soil build-up that occurs when the milk protein solution is heated in a heat exchanger.
The heat flux sensor used by Jones et al measured heat flux alone to monitor the condition of the interior surface of the pipe. The sensor, which was a commercial heat flux sensor was used to measure a temperature difference across a known thermal resistance and from this the heat flux and heat transfer coefficient was calculated. The type of sensor used was a Rhopoint type 20450-2 and a number of points arise from the use of any such commercial type of heat flux sensor.
Firstly, a nanovoltmeter is used to measure a voltage corresponding to the temperature difference across the sensor. In the case of the sensor used by Jones et al the voltages measured were of the order of 400 to 1000 microvolts. These result in relatively low levels of sensor response, which might be feasible in a laboratory environment, but may well result in a significant noise-to-signal ratio if the sensor were to be used in a commercial environment. It can be see from the Hones et al paper that for a constant Reynolds number and bulk temperature, the heat transfer coefficient for the clean condition at time 0 varies considerably, e.g. between 0.21 and 0.31. This demonstrates the problems encountered when trying to ensure such small signals.
Secondly, it can be seen that the sensitivity of the system is limited by the heat flux element itself. Considering the Jones et al sensor arrangement, a 1 mm soil deposit would result in a theoretical reduction in the output signal of approximately 40-50%, i.e. a 2:1 attenuation. If the relative contribution of the thermal resistance of the heat flux sensor to the overall thermal resistance between the copper block and the bulk fluid is calculated, it is found that this accounts for 50-80%, i.e. the bulk of the heat transfer resistance. Thus the sensitivity of the system is limited by the heat flux element itself. Ideally, the limitation on overall heat transfer should be on the product side such that changes in the product side due to soil build-up have the maximum impact on sensor response.
Thirdly, the Jones et al paper does not take account of potential heat losses and their impact on the results obtained.
It can be seen from
FIGS. 7
a
and
7
b
that in the heat flux sensing apparatus used by Jones et al there is a potential for heat to be lost.
FIG. 7
a
shows that heat can be transferred from the copper block to the fluid conduit which by passes the heat flux element due to the heat energy taking the path of least resistance. Thus this heat loss is not considered. Another potential loss is shown in
FIG. 7
b
and occurs if the copper block does not fully contact the fluid conduit. That is to say, if there is a small air gap between the copper block and the fluid conduit, there will be flow of heat along the conduit away from the heat flux element. The heat flux calculations shown are based on one dimensional heat transfer across the sensor element. The potential for heat losses indicated above invalidates these calculations.
With the known geometry of the heat flux sensing apparatus used by Jones et al and using standard heat transfer correlations for laminar flow heat transfer together with the heat flux element data, it is possible to calculate a predicted heat transfer coefficient. The predicted value of this for the Jones et al system is 0.65 kW/m
2
□K. This is substantially higher than the value mentioned by Jones et al and may well be a result of heat from the copper block by-passing the heat flux element.
FIG. 6
shows how the heat losses from the Jones et al heat flux sensor affect the results obtained. The measured results indicate that, even taking into account some heat loss in the predicted results, there were more heat losses from the sensor than were allowed for. Thus the Jones et al sensor would not provide reliable results if used commercially.
There is therefore a need for an improved monitoring apparatus which can monitor a soil build-up on the interior of a fluid conduit adjacent to the monitoring apparatus and which is representative of the soil conditions within the conduit system.
DEFINITION OF THE INVENTION
According to a first aspect of the invention, there is provided a monitoring apparatus for monitoring soil build-up in a conduit through which fluid may flow, which apparatus includes a body located outside of the conduit and in thermal connection with it such that heat can flow between the body and the fluid flow, a heat controlling means to regulate the temperature of the body and a monitor capable of monitoring any change in power input to the heat controlling means necessary to maintain the body at the regulated temperature, whereby a change in power input to the heat controlling means is indicative of a change in heat flux between the fluid flow and the body, thereby indicating a change in soil build-up.
A second aspect of the invention provides a monitoring apparatus for monitoring soil build-up in a conduit through which fluid may flow, which apparatus includes a body in thermal connection with the conduit such that heat can flow between the body and the fluid flow; a heater for heating the body; a controller for controlling the heater; pressure measurement means to measure the fluid pressure within the conduit; and a monitor capable of monitoring the temperature of the body, the heater being controlled such that it intermittently heats the body to a predetermined temperature and the monitor being capable of monitoring the loss of heat from the body to the fluid flow, whereby a change in the rate of heat loss from the body or a change of pressure within the conduit or both is indicative of a change in soil build-up.
A third aspect of the invention provides a monitoring apparatus for monitoring soil build-up in a conduit through which fluid may flow, which apparatus includes a body in thermal connection with the conduit such that the body is at a lower temperature than the fluid flow and heat can flow from the fluid flow to the body, means for cooling the body and a monitor capable of monitoring heat flux from the fluid flow to the body whereby a change in heat flux from the fluid flow to the body is indicative of a change in soil build-up.
A fourth aspect of the invention provides a method of operating a pipework system, the method including monitoring soil build-up in the pipework system using a monitoring apparatus according to the first, second or third aspects of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The monitoring apparatus of the invention is capable of utilizing the principle of measuring the power required preferably to maintain the body at a desired temperature and fro
Baginksi Edward
Burns Ian William
Hasting Anthony Peter
Bovee Warren R.
Fulton Christopher W.
Hamilton Neil E.
Jagan Mirellys
JohnsonDiversey, Inc.
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