JPS62134508A - Method and device for measuring size of small hole of outer surface of tube, heat transfer property thereof is improved - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an evaporator tube with improved heat transfer, and more particularly to a method and a method for measuring the pore size of an evaporator tube with improved heat transfer. The present invention relates to an apparatus and a closed-loop control system for manufacturing tubes with improved external heat transfer.

BACKGROUND OF THE INVENTION In the evaporator of some types of refrigeration equipment, the fluid to be cooled is passed through a heat transfer tube, and the refrigerant in contact with the outer surface of the tube absorbs heat from the fluid inside the tube. This causes a phase change from liquid to vapor. The shape of the outer and inner surfaces of the tube is important in determining the overall heat transfer characteristics of the tube. For example, it is known that one of the most efficient ways to transfer heat from the fluid within the tube to the boiling refrigerant surrounding the tube is through the mechanism of nucleation boiling.

It is known in the art that nucleation boiling can be effected by providing vapor trapping regions, or cavities, in the heat transfer surface. According to this theory, vapor trapped in the cavity nucleates bubbles at or slightly above the saturation temperature, and the bubbles increase in volume as they are supplied with heat.
Eventually, the surface tension is overcome and the steam bubbles break and separate from the heat transfer surface. When the vapor bubble leaves the heat transfer surface, liquid enters the void area and captures the remaining vapor, forming another bubble. Heat transfer is thus improved by the continuous formation of bubbles and by the convective and boundary layer mixing effects of the bubbles moving through the boundary layer of superheated refrigerant covering the vapor trapping region. A heat exchange surface containing a large number of discrete artificial regions is disclosed in U.S. Pat. No. 3,301.
, No. 314.

It is known that the vapor trapping region, or cavity, forms a stable cylinder of foam when it is of the foam regeneration type. A regenerative bubble trapping region is defined herein as a cavity or groove in which the size of the surface pores or gaps is smaller than the subsurface cavity or groove. A regenerative grooved heat transfer tube is disclosed in U.S. Pat. No. 3,696,
No. 861 and No. 3,768,290.

It has been found that excessive flow of liquid from the periphery of the tube causes the regenerative vapor trapping zone to be enriched with liquid, impairing its effectiveness. However, a heat transfer surface that has surface pores with a certain aperture ratio, i.e., subsurface channels communicating with the circumference of the tube through small pores, provides good heat transfer, and the vapor trapping area, i.e., the subsurface It was found that this prevents the channel from overflowing with liquid.

Regarding the inner surface shape of the heat transfer tube, it is known that providing the tube with internal ribs improves the heat transfer properties of the tube by increasing the turbulence of the fluid flowing inside the ribbed tube. .

U.S. Patent No. 4, assigned to the same assignee as the applicant,
As disclosed in U.S. Pat. Tubes with communicating helical external fins (forming subsurface channels) are manufactured in a single pass process using a tube fin forming and roll rolling machine. According to this method, a mandrel with a groove is placed in an unformed tube and a tool ar 1j carrying a tool gang is rolled onto the outer surface of the tube. The unformed tube is pressed against a mandrel, thereby forming at least one internal rib on the inner surface of the tube. At the same time, at least one helical outer fin is formed on the outer surface of the tube by means of the fin-forming disk carrying the tooling gang. These helical external fins form subsurface channels between them and are pushed down into the radially outward regions of the internal ribs, i.e. the regions where the tube is pressed against the grooves of the mandrel to form the ribs. It has a part. After the external fins are formed, they are transferred onto the external surface of a smooth roller-like disc or tube carried by a tool arm. The roller-like disc curves the tips of the outer fins into contact with adjacent helical fins only in areas that are not radially outward of the inner ribs, thereby creating a closed subsurface channel. (1η). The tips of the external fins at the depressed portion located radially outward of the internal ribs are also curved, but these do not contact the adjacent helical fins, This creates pores that provide fluid communication between the liquid surrounding the tube and the subsurface channel.

The performance of such tubes is largely dependent on the improved heat transfer properties of the tube's outer surface. Therefore, it is important to maintain the subsurface channel dimensions and pore dimensions to proper values during the tube manufacturing process. However, due to tool wear, variations in the materials from which the tube is constructed, dimensional variations in tube length, machine tolerances, etc., variations occur in the dimensions of the subsurface channels and the dimensions of the stoma. To compensate for such variations and maintain proper pore size, measure the pore size of each tube produced and adjust the fin former to properly size the subsurface channels and pores. It is necessary to maintain the value at a certain value. However, the traditional method of checking the size of the small holes in the tube with improved heat transfer and adjusting the fin forming machine is labor-intensive and expensive, making it very difficult to use in the manufacturing process. It is. For example, one method has been for an operator to randomly select manufactured tubes and optically check the pore size of the selected tubes under a microscope. Another method was to take pictures of the tube and use an image analyzer to compare the area of the pores in certain selected areas with the area of the pores in the photo of the monk. Once the stoma size is determined, the operator adjusts the fin former to compensate for variations from the desired stoma size. However, these methods are time consuming and do not meet the quality and quantity of tubes required for the manufacturing process.

Thus, there is a need for a method and apparatus for measuring pore size and a control system for producing tubes with improved heat transfer properties that substantially overcome the deficiencies of the prior art. There is.

SUMMARY OF THE INVENTION A closed loop electronic control system has been developed for producing tubes with improved heat transfer. The control device includes at least one pressure quadrature transducer that measures the average size of the pores in the surface of the heat transfer tube and transmits an output signal corresponding to the size of the pores to a microcomputer. The microcomputer analyzes the signal from the pressure quadrature transducer and supplies the output signal to the programmable controller. A programmable controller controls a servo motor that adjusts the fin former to maintain the stoma size at the proper value. A pressure I transducer is a measuring device that contains a sealed chamber in contact with the surface of a tube with enhanced heat transfer properties, into which compressed air flows and a small surface of the tube with enhanced heat transfer properties. The average size of the pores on the surface of the tube that flow through the pores into the subsurface channels of the tube and exit through the exit pores around the tube to create a pressure drop across the chamber, thereby improving heat transfer. gives an indicator of The pressure drop across the surface pores of a tube is related to the dimensions of the subsurface channels and pores, and thus to the expected boiling heat transfer coefficient of the tube.

Instruments used to measure room pressure are adversely affected by changes in the air temperature, air humidity, and supply pressure of the measuring device. However, in the present invention, an orifice plate with a known resistance to air flow is provided in one leg of the measuring device, and a tube with enhanced heat transfer to be measured is provided in the other leg of the measuring device. This is used to provide a pressure-related input signal to a differential pressure transducer.

One object of the present invention is to measure the average size of the pores on the surface of a tube with improved heat transfer properties and automatically adjust the fin forming machine to maintain the pore size at the proper value. An object of the present invention is to provide a method and a control device.

Another object of the present invention is to improve heat transfer properties.
It is an object of the present invention to provide a method and control device capable of inspecting 0096 tubes and adjusting a fin forming machine to maintain the pore size of all tubes produced at appropriate values.

Yet another object of the present invention is to provide a method and control system for reducing downtime of a fin forming machine by mechanically adjusting the fin forming head.

Yet another object of the invention is to provide a measuring device configured to compensate for variations in temperature, humidity and pressure of the supplied air.

These objects of the present invention provide a novel evaporator tube configured to measure the pore size and automatically adjust the fin forming machine to maintain the pore size at a proper value in an evaporator tube with improved heat transfer. This is accomplished by a method and control device. The control device of the present invention includes at least one pressure quadrature transducer that outputs an analog electrical signal to a signal conditioning device that amplifies and linearizes the signal received by the signal conditioning device; The signal is output to the microcomputer. The microcomputer compares the input signal to a reference signal and provides an output signal to the programmable controller. The programmable controller outputs digital signals to be provided to the motion control device. The output signal of the motion controller is provided to a servo motor that drives a linear actuator to adjust the fin-forming head. Thus, in accordance with the present invention, the average pore size of the heat transfer oriented tube is measured and the fin former is adjusted to maintain the pore size at the proper value.

The measuring device for measuring pore size includes a controlled air supply connected in parallel to a constant reference orifice plate and a tube with improved heat transfer properties to be measured. The difference between the pressure drop of the air across the tube and the reference orifice plate is measured by a differential pressure transmitter, and the difference is determined by the size of the tube's apertures for improved heat transfer. Compatible. The measuring device thus measures the average pore size of the tube with improved heat transfer and compensates for changes in the pressure, temperature, or humidity of the supplied air. Additionally, the measuring device includes a test block with a sealing device that can be intimately engaged with a specific surface area of the tube with enhanced heat transfer. The surfaces of the test block, sealing device, and tube form a sealed chamber to define a flow path through which compressed air is blown into the chamber to improve heat transfer through small holes in the tube and It flows through subsurface channels, which correspond to the pressure differential between the inlet and outlet of the chamber or the area of passage through which air escapes from the chamber. This corresponding passage area represents the sum of the areas of all the holes in the area of the tube with improved heat transfer that lies below the area projected onto the plane of the chamber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention will be explained in detail below by way of example embodiments with reference to the accompanying figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Since evaporator tubes with enhanced heat transfer properties have critical dimensions that must be precisely controlled to maintain good heat transfer performance, this invention is particularly suited to improved heat transfer properties. An example used for an evaporator tube will be described. Such enhanced heat transfer tubes are designed for use in evaporators of refrigeration systems in which the fluid to be cooled flows through the tube and the refrigerant to be evaporated is placed in contact with the outer surface of the tube. Typically, several heat transfer tubes are mounted in parallel, several tubes are connected to form one fluid circuit, and a plurality of such parallel fluid circuits are provided to form a tube bundle. be done. Generally, all the tubes of the plurality of fluid circuits are housed within a shell and immersed in a refrigerant within the shell. The heat transfer capacity of an evaporator is determined primarily by the average heat transfer characteristics of the heat transfer tubes. Thus, the size of the subsurface channels and the size of the pores on the surface of the tube are important. Therefore, it is important to maintain good subsurface channel dimensions and pore dimensions during the manufacturing process of evaporator tubes with enhanced heat transfer.

FIG. 1 is an illustration of a fin forming station for producing tubes with enhanced heat transfer properties in accordance with the principles of the present invention. Fin forming station 10 includes an electronic control cabinet 12, a supply section 14, a fin forming head section 16, a discharge section 32, and a stoma measurement section 18. Electronic control cabinet 12 includes a microcomputer, a programmable controller, and an operator console 22.

The microcomputer determines whether the process is within control tolerances, and the programmable controller performs the logic operations, timing control, sequence control, and calculations to perform the fin forming process. The feed section 14 generally includes two similar parallel mandrels 24 (the two mandrels lie in substantially the same horizontal plane, so the rear mandrel is omitted in the figure). These mandrels are supported by multiple support arms 2.
6 and positioned by a piston device 28. The operator therefore loads blank tubes onto the front and rear mandrels 24 and feeds one of the mandrels, e.g. the front mandrel, to descend and move the blank tubes along the fin-forming longitudinal axis 29 into the fin-forming head section 16. Section 1
Activate 4. Once the material tube is brought into a state of improved heat transfer, the mandrel is retracted to its original position;
An ejector, such as an ejector wheel, in ejector section 32 engages the heat transfer enhanced tube and directs the tube to stoma measurement section 18 . Once the heat transfer enhanced tube has been completely fed into the stoma measurement section 18, it is engaged by a measuring device 40 for measuring the size of the stoma on its surface. A constant reference orifice device 150 provides a reference pressure drop.

When the front mandrel returns to its original position, the rear mandrel is lowered, the controller adjusts the fin former, and the fin forming process is repeated.

The fin forming head section 16 includes a fin forming head 50 having a plurality of tool arms 52 and a tube positioning device 53, as shown in FIGS. The end of the blank tube is accurately positioned within the fin forming head 50 before the process begins. Each tool arm 52 includes a tool gang structure having a plurality of fin-forming disks 54 and rollers 56 that cooperate with the mandrel 24 to form a tube with enhanced heat transfer. The fin-forming disk 54 is inclined at an angle to the fin-forming longitudinal axis 29 to move the tube with improved heat transfer through the fin-forming head section 16 to the discharge section 32. Once the blank tube is in a fully heat-enhanced condition, the fin-forming head 50 of the fin-forming head section 16 is opened. That is, the tool arm μ 52 is moved radially outwards by means of a servo motor 58 cooperating with a cam surface 59, the mandrel is retracted to its original position, and the ejection device in the ejection section 32, e.g. Engage the enhanced tube and send it to the stoma measurement section 18. Once the heat transfer enhanced tube has been fully moved into the stoma measurement section 18 and the front mandrel has been returned to its original position, the rear mandrel 24 is lowered and the process described above is repeated.

The stoma measurement section 18 will now be described in detail with reference to FIGS. 3-6. As shown in FIG. 3, the small hole ΔDI device has a substantially rectangular shape having a chamber 45 therein and a slot 43 for receiving a flexible insert 44 made of, for example, moldable urethane. block 4
2, and is adapted to engage with a part of the surface of the tube 30 with improved heat transfer properties. air population 47
and an air outlet 48 extending through the rectangular block 42 to the chamber 45.

3 and 4 also illustrate a tube 30 with enhanced heat transfer properties having subsurface channels 35 communicating with the circumference of the tube through small holes 34. FIG. The rectangular block 42 and flexible insert 44 have arcuate longitudinally extending channels that allow the flexible insert to closely engage the surface of the tube 30 for enhanced heat transfer. It is supposed to be done. In this case, the flexible insert 44 acts like a gasket against the surface of the tube with improved heat transfer. Thus, in FIG. 3 (a tube with improved heat transfer properties is shown in an exploded view 30a,
The air enters the inlet with the flexible insert 44 sealed against the surface of the heat transfer enhanced tube, as clearly shown in FIG. 47 and into the chamber 45, the air inside the chamber 45 is blown into the chamber 45, as shown by the arrow in FIG.
A small hole 3 in the surface of the tube in the projected area of 5
4, flow in the corresponding subsurface channel 35, exit around the tube through the small hole 34 outside the projected area of the chamber 45, or accumulate within the chamber 45, which means that the air It is read by a pressure gauge 39 fixed to the outlet 48.

5 and 6 show an enhanced heat transfer tube 30 supported in a channel of a support 41 below a pore measuring device 40. FIG. Air at a constant pressure is supplied to the air supply 47 by a regulator 38. Air pressure at outlet 48 is measured by a pressure gauge or manometer 39. Once the tube with enhanced heat transfer properties has been placed in the channel of the support 4, the measuring device 40 is lowered in a known manner so that the flexible insert 44 is inserted into the tube as shown in FIG. engages the surface of the Therefore, during operation, the regulator 38
A part of the pressure of the air flowing at a constant pressure through the flow path is lost across the flow control valve 36 provided in the flow path, and the pressure of the air flowing through the gauge 3 is lost.
It is read at 7. The remaining pressure, ie, the pressure not lost across the small hole 34, is read at three gauges. The difference between the pressure shown on gauge 37 and the pressure shown on gauge 39 thus indicates the pressure drop across the stoma, which is an indicator of the average size of the stoma formed in the tube. . This average pore size measurement is determined by measuring the heat transfer coefficient at boiling of the tube, where the pressure drop across the pores is known and determines the optimal pore size.

A relationship is thus established between the pressure drop across the pores and the heat transfer coefficient at the desired boiling state.

The theory involved in this invention is that the pressure drop across an orifice is a function of the area of that orifice. When a heat-enhanced tube with pores on its surface that communicate with subsurface channels is blown with compressed air through the pores, the resulting pressure drop is absorbed by the pores of the enhanced heat-transfer tube. shows the average dimensions of The pressure drop across the tube pores is related to the tube's expected boiling heat transfer efficiency.

In operation, a heat transfer enhanced tube including a continuous subsurface channel having a closed surface with small holes spaced apart along the closed surface has a passageway therein. A stomal measuring device includes a substantially rectangular fixation device having a substantially rectangular shape. A flexible sealing device having a chamber therein is secured to the passageway of the securing device. The chamber has an inlet and an outlet pressure tap into which air from an air supply is blown. A manometer is connected to the outlet pressure tap to measure the pressure in the chamber. The pressure indicated by the manometer is therefore equal to the air pressure lost due to the flow of air through the tube pores and subsurface channels divided by the population pressure.

FIG. 7 is an illustration showing the pneumatic system of the tube measuring device with improved heat transfer properties. The stoma measurement section 18 has a pneumatic circuit 157 for actuating the clamping mechanism 154.
, and a pneumatic circuit 162 for supplying air to the i'lFJ constant device 40 and the constant reference orifice device 150 for performing ostium measurements.

Compressed air, typically from a building supply conduit 156, is supplied to a solenoid valve 159 via a filter and dryer assembly 158. Once the tube with improved heat transfer is completely introduced into the stoma measuring section 18, a limit switch (not shown) is actuated and the solenoid valve 1 is activated.
59 is excited and air is supplied to the clamp mechanism 154. Clamping mechanism 154 engages measurement device 40 with the enhanced heat transfer tube as shown clearly in FIG.

When the measuring device 40 is tightly engaged with the surface of the evaporator tube, air enters the pneumatic circuit 162 for measuring the stoma.
It is supplied through. That is, compressed air from building supply conduit 156 is supplied to pneumatic circuit 162 via filter and dryer assembly 164, high pressure regulator 166, solenoid valves 16, 8, and regulator 167. When the pneumatic circuit 162 is actuated, the solenoid valve 168 opens and air flows through the precision pressure regulator 167 to the supply brenum 165. Air from the supply plenum 165 flows to each measurement device 40 and base orifice device 150. A flow control valve 172 in the flow path typically allows half of the air pressure flowing from the supply plenum 165 to the measurement device 40.
is lost as it flows across the The remainder of the air pressure is lost as it flows across the pores of the tube with enhanced heat transfer. Similarly, air from the supply brenum flows to the reference orifice device 150 so that approximately half of the air pressure is lost in flowing across the flow control valve 173 and the remainder of the air pressure is lost in flowing across the constant reference orifice device 150. Lost.

A closed loop process for producing heat transfer enhanced tubes and measuring the pore size of the heat transfer enhanced tubes in accordance with the present invention is schematically illustrated as a flowchart in FIG. This process includes a heat transfer improvement step 260 in which fins are formed on the tube, and a check step 2 in which the pore size of the tube with improved heat transfer characteristics is measured.
62, a processing step 264 that calculates data from the checking process and determines new settings for the fin forming machine, a control process 266 that controls the settings of the fin forming machine, and a programmable controller that performs sequence control of various functions. A motion ho I [both steps 268 and 258, which perform the interface between the tool A and the servo motor that actually drives the tool A, and a positioning step 258 where the tool A is positioned by the servo motor to achieve the optimum geometry of the tube. Contains.

There are scope for microcomputers to control the average pore size in the closed loop manufacturing process described above. This range is determined by the difference between the material properties and the XJ method of the raw tube used. Therefore, in the process described above, the overall average heat transfer performance of the heat transfer enhanced evaporator tube is determined to match the minimum average heat transfer performance of the heat transfer enhanced tube. In this case, the distribution of average pore size for a plurality of tubes is employed.

The closed-loop control system of the present invention for producing evaporator tubes with enhanced heat transfer provides precise control of the actuation of the fin-forming head compared to conventional mechanical adjustments for operator control, ensuring that all produced tube and automatically adjusts the position of the fin-forming head to maintain proper pore size. The closed loop control system thus requires no operator interaction.

In operation, each tube passes through the stoma measurement section 18 after it has been brought into its heat transfer enhanced condition.
In that section at least one measuring device 40 is lowered to clamp the tube. Dry compressed air is blown through the small holes and the resulting pressure is detected by a pressure quadrature transducer and read by a microcomputer. After a number of tubes have been processed, the microcomputer applies statistical process control procedures to determine whether the position of the fin-forming head needs to be changed. If the position of the fin-forming head needs to be changed, the microcomputer outputs a signal to the programmable controller indicating the desired change. Even small changes in the position of the fin-forming head, accomplished by servo motors and linear actuators, are sufficient to change the stoma size and bring the process within suitable tolerance limits.

Although the present invention has been described in detail with respect to specific embodiments above, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. will be clear to those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is an illustration of a fin forming machine for producing tubes with improved heat transfer properties in accordance with the present invention. FIG. 2 is a side view of one tool arm of the fin-forming head shown in FIG. 1, together with a cross-section of the tube fitted onto the mandrel. FIG. 3 shows a state in which the small hole measuring device of the present invention is engaged with a tube with improved heat transfer properties, and a portion of the tube indicated by a phantom line is projected onto a plane, as shown in FIG. FIG. 2 is an enlarged view of the outer surface of a tube with improved heat transfer properties produced by the illustrated fin forming machine. FIG. 4 is a longitudinal sectional view showing a portion of a tube with improved heat transfer properties and a small hole measuring device according to the present invention. FIG. 5 is a longitudinal sectional view of the small hole measuring device of the present invention. FIG. 6 is a front view of the small hole measuring device shown in FIG. 5. FIG. 7 is an illustrative diagram showing the pneumatic system of the tube measuring device with improved heat transfer performance according to the present invention. FIG. 8 is a flow chart showing the operation of the fin forming machine of the present invention. 9 is a front view showing the fin forming head of the fin forming machine shown in FIG. 1. FIG. 10... Fin forming station, 12... Electron;
L control cabinet I-,]4...f supply section 2
16...Fin formation head, 18...Small hole 1
1111 Fixed section, 22... Operator console, 24 - Mandrel, 26... Support arm, 28
...Piston device, 29...Longitudinal axis, 30...
Tube with improved heat transfer, 32... Discharge section, 34... Small hole, 35... Subsurface channel,
36...Flow rate 1lII control valve, 37...Gauge, 38
...Regulator, 3...Pressure gauge (manometer), 40...Measuring device. 41... Support body, 42... Block, 43... Slot. 44... Flexible insert, 45... Chamber, 47...
- Air inlet, 48... Air outlet, 50... Fin forming head. 52... Tool arm, 53... Tube positioning device. 54... Fin forming disk, 56... Roller, 5
8... Servo motor, 59... Cam surface, 150...
・Certain base ■ Orifice device, 154... Clamp machine I
L156... Supply conduit, 157... Pneumatic circuit, 1
58... Filter and dryer assembly, 159... Solenoid valve, 162... Pneumatic circuit, 164... Filter and dryer assembly, 165... Supply plenum, 166... High pressure regulator, 167...・Accurate pressure regulator, 168...Solenoid valve 2172
．． 173...Flow rate control valve

Claims (5)

[Claims] (1) A pressure measuring device having an inlet and an outlet connected to a fluid source of known pressure is heated by a method of measuring the average size of a plurality of small holes in the outer surface of a tube with improved heat transfer. disposing a portion of the outer surface of the tube with enhanced conductivity; and flowing the fluid at the known pressure into the pressure measuring device;
supplying a fluid of known pressure to the inlet to flow through the small hole and over a portion of the outer surface covered by the pressure measuring device; and detecting the pressure of the fluid within the pressure measuring device. determining the difference between the pressure detected in the pressure measuring device and the known pressure; and converting the determined difference into a desired small hole in the outer surface of the tube for improved heat transfer. and comparing to a predetermined pressure related to an average dimension of. (2) a first adjustable flow control valve and a first adjustable flow control valve downstream of the first adjustable flow control valve; a first pressure fluid flow path including a test housing closely engaging a portion of the surface of the heat transfer enhanced tube; a second adjustable flow control valve; a reference orifice located downstream of the possible flow control valve and having an orifice area substantially equal to the desired pore area per unit area of the tube; simultaneously supplying fluid at a constant pressure to parallel pressure fluid channels; placing the tube having the desired pore area per unit area in intimate engagement with the test housing; adjusting the first and second adjustable flow control valves until a differential pressure between downstream pressures of the first and second adjustable flow control valves reaches a predetermined value; replacing a tube having a stoma area per unit area and placed in engagement with said test housing with a tube having a stoma size to be measured; determining a differential pressure between a downstream pressure of a flow control valve; and a heat transfer in engagement with the test housing due to the difference between a predetermined value of the differential pressure and the determined differential pressure. a method comprising: determining pore size on a surface of a tube with improved properties; (3) A device for measuring the size of a small hole in a tube with improved heat transfer properties, the fixing device being configured to receive a portion of the surface of the tube with improved heat transfer properties, the fixing device comprising: a sealing device; a fixation device having an internal cavity configured to receive the sealing device, the sealing device having a cavity therein, the cavity being in fluid communication with a source of pressurized fluid exiting the flow outlet means through the cavity; and a differential pressure between the source pressure and the pressure at the outlet means, indicative of fluid bypassing the mutually engaging surfaces and exiting through the stoma to the circumference of the tube. A measuring device for measuring a certain differential pressure; (4) A pore sizing device for a tube with improved heat transfer, comprising a pressure fluid source, a first adjustable flow control valve, and a portion of the surface of the tube with improved heat transfer. fluid from said pressure fluid source flows through small holes in said heat transfer tube and around said tube, thereby increasing fluid pressure downstream of said first adjustable flow control valve. a first pressure fluid flow path including a test housing defining a passageway for reducing the flow rate; a second adjustable flow control valve; a reference orifice having a predetermined area; at least two mutually parallel pressure fluid passages connected in fluid communication with the pressure fluid source; a differential pressure transducer device for measuring a differential pressure between parallel pressure fluid flow paths, one side of the differential pressure transducer device being in fluid communication with a downstream side of the first adjustable flow control valve; connected, the other side of the differential pressure transducer device being in fluid communication with a downstream side of the second adjustable flow control valve, whereby the heat transfer enhanced tube a differential pressure transducer device that measures the difference between a pressure drop across the stoma and a pressure drop across the reference orifice. (5) A control device for the fin forming head of the fin forming machine that improves the heat transfer performance of the outer surface of the tube, and measures the size of the small holes on the outer surface of the tube with improved heat transfer performance. at least one pneumatic measuring device for generating a signal indicative of a pore size; and receiving and processing the signal indicative of the measured pore size to determine the measured pore size and a predetermined pore size. a processor for determining the difference between the fins and generating an output signal if the measured stoma size differs from the predetermined stoma size; and means for adjusting the forming head.