CN100424502C - Detecting method for convection heat exchange coefficient and its convection heat coefficient sonsor - Google Patents

Abstract

The present invention discloses a sensor for directly measuring the coefficient of convective heat transfer of a heat convection surface. The sensor is provided with a shell body, wherein a heating film, a heat insulator, a first heat couple and a temperature measuring wafer are arranged on the top part of the shell body to form a cover plate of the shell body; a heating film is coated on the bottom surface of the temperature measuring wafer; a heating lead wire is connected with the heating film, and the other end of the heating lead wire is connected with a measuring instrument; a heat insulator is filled between the heating film and the bottom of the shell body; the temperature measuring end of the first heat couple contacts the temperature measuring wafer, and a positive electrode terminal of the first heat couple is connected with a positive electrode terminal of a second heat couple; a negative electrode terminal of the first heat couple is connected with the measuring instrument; the negative electrode terminal of the second heat couple is connected with the measuring instrument, and the temperature measuring end of the second heat couple contacts fluid. The sensor of the present invention is a sensor of the coefficient of convective heat transfer is designed on the basis of the basic theory of heat transfer theory. The sensor can directly obtain the data of the coefficient of convective heat transfer of the surface of a measured object, and can also be used for measuring a heat convection heat flow of the heat convection surface. The sensor can be widely used for industrial production.

Description

A kind of method of testing of convection transfer rate and convection transfer rate sensor thereof

Technical field

The present invention relates to a kind of sensor, particularly, be meant and a kind ofly can directly measure the sensor of convection heat transfer surface convection transfer rate and a kind of method of testing of calculating convection transfer rate is provided.

Background technology

Convection transfer rate is an important parameter of weighing the convection heat transfer power, also is the master data of calculating the convection heat transfer problem.In current thermal conduction study field and production practices relevant with heat power, if the convection transfer rate data owner obtains by experiment indirectly, but for some specific occasions (as the convection heat transfer problem in the engine turbine blade), it also is very difficult obtaining convection transfer rate indirectly.

Summary of the invention

The object of the present invention is to provide a kind of based on thermal conduction study basic theories and the convection transfer rate sensor that designs, it can directly obtain the convection transfer rate data on testee surface, also can be used to measure the convection heat transfer hot-fluid on convection heat transfer surface.

Another object of the present invention provides a kind of test computing method to convection transfer rate, and this method has improved the measuring accuracy of surface coefficient of heat transfer effectively.

A kind of method of testing that can directly measure the heat of convection heat transfer surface convection transfer rate of the present invention, when sensor is installed on measured surface, and after the thermometric disk transient heating to sensor, convection transfer rate alpha test formula is

$\mathrm{\α}=\frac{\mathrm{\ρcV}}{({\mathrm{\τ}}_2-{\mathrm{\τ}}_1)F}\ln \frac{t_1-t_{\∞}}{t_2-t_{\∞}}$

Its first thermopair 5 and second thermopair 6 are at τ ₁The disk that constantly records and the temperature difference of fluid are t ₁-t _∞, at the next one constantly disk that records of first thermopair 5 and second thermopair 6 and the temperature difference t of fluid ₂-t _∞Satisfy

t ₂-t _∞＝0.33(t ₁-t _∞)

The time (this moment the moment be τ ₂) convection transfer rate error minimum, for

$\frac{\mathrm{\δ\α}}{\mathrm{\α}}=4.07\left(\frac{\mathrm{\δt}}{t_1-t_{\∞}}\right)$

A kind of sensor that can directly measure convection heat transfer surface convection transfer rate of the present invention, comprise measurement instrument 8, at least be provided with power supply in the measurement instrument 8, it also comprises housing 1, thermometric disk 2, heating film 3, heat guard 4, first thermopair 5, second thermopair 6, anodal heating lead-in wire 701 and negative pole heating lead-in wire 702, heating film 3, heat guard 4, first thermopair 5 are installed in the housing 1, and thermometric disk 2 is installed in the cover plate that housing 1 top constitutes housing 1; The back side of thermometric disk 2 is coated with heating film 3, is connected with anodal heating lead-in wire 701 and negative pole heating lead-in wire 702 on the two ends of heating film 3, and the other end of anodal heating lead-in wire 701 and negative pole heating lead-in wire 702 is connected on the power supply of measurement instrument 8; Be filled with heat guard 4 between heating film 3 and housing 1 bottom; The thermometric end of first thermopair 5 contacts with thermometric disk 2, the positive terminal of first thermopair 5 is connected with the positive terminal of second thermopair 6, the negative terminals of first thermopair 5 is connected with measurement instrument 8, the negative terminals of second thermopair 6 is connected with measurement instrument 8, and the thermometric end of second thermopair 6 contacts with fluid.

Described convection heat transfer sensor, its first thermopair 5 and second thermopair 6 constitute the temperature difference heat galvanic couple, and its temperature difference is measured by measurement instrument 8.

Described convection transfer rate sensor, its thermometric disk 2 are less than 1mm thick copper sheet or stainless steel.

Described convection transfer rate sensor, its heating film 3 can be photoetching stainless steel heating plate or electroplating film.

Sensor of the present invention can solve the especially problems of measurement of complex surface convection transfer rate of convection heat transfer surface, can directly obtain the convection transfer rate on convection heat transfer surface, and needn't carry out loaded down with trivial details temperature field measurement.

Description of drawings

Fig. 1 is the structural representation of sensor of the present invention.

Fig. 2 is the process flow diagram of sensor computing method of the present invention.

Among the figure: 1. housing 2. thermometric disks 3. heating films 4. heat guards 5. first thermopairs 6. second thermopairs 701. anodal heating lead-in wire 702. negative poles heat lead-in wire 8. measurement instruments

Embodiment

The present invention is described in further detail below in conjunction with accompanying drawing.

In the present invention, sensor is the lumped-parameter method principle according to thermal conduction study unstable state heat conduction.See also shown in Figure 1ly, suppose the copper or the stainless steel thermometric disk 2 of one very thin (thickness is less than 1mm), thermometric disk 2 is t with temperature _∞Fluid generation convection heat transfer, " U " shape that housing 1 is made for stainless steel material, thermometric disk 2 is installed in the cover plate that housing 1 top constitutes housing 1, thus the surface heat exchanging that fluid and thermometric disk 2 contact with fluid, its not heat exchange of excess-three face.Set heat interchanging area and be expressed as F, the volume of disk is expressed as V, and thermometric disk 2 density meters are shown ρ, and thermometric disk 2 specific heats are expressed as c.After thermometric disk 2 was heated, its temperature must raise; After heating stops, owing to be subjected to the cooling of fluid convection heat exchange, the temperature of thermometric disk 2 will reduce gradually.Because thermometric disk 2 is very thin, temperature is equal substantially everywhere in the thermometric disk 2, also just equals the temperature on thermometric disk 2 surfaces.τ at a time ₁The temperature difference that records disk and fluid is t ₁-t _∞, after after a while, at τ ₂The temperature difference that constantly records disk and fluid is t ₂-t _∞, and the convection transfer rate of establishing thermometric disk 2 and fluid is α.More than each amount have a following relation:

$\frac{t_1-t_{\∞}}{t_2-t_{\∞}}=e^{\frac{\mathrm{\αF}}{\mathrm{\ρcV}}({\mathrm{\τ}}_2-{\mathrm{\τ}}_1)}---\left(1\right)$

Then

$\mathrm{\α}=\frac{\mathrm{\ρcV}}{({\mathrm{\τ}}_2-{\mathrm{\τ}}_1)F}\ln \frac{t_1-t_{\∞}}{t_2-t_{\∞}}---\left(2\right)$

(2) formula of utilization can be measured the convection transfer rate α on fluid and thermometric disk 2 surfaces.As the temperature measurement error with first thermopair 5 and second thermopair, 6 composition temperature difference heat galvanic couples is δ t, can draw by error analysis, when satisfying:

t ₂-t _∞＝0.33(t ₁-t _∞) (3)

The time, the convection transfer rate error minimum that records, its method error is:

$\frac{\mathrm{\δ\α}}{\mathrm{\α}}=4.07\left(\frac{\mathrm{\δt}}{t_1-t_{\∞}}\right)---\left(4\right)$

Therefore, reducing by first thermopair 5 and second thermopair 6 forms the measuring error of temperature difference heat galvanic couple and improves t ₁-t _∞Can improve the measuring accuracy of convection transfer rate α.

Example: establish 0.1 ℃ of the measuring error that first thermopair 5 and second thermopair 6 are formed the temperature difference heat galvanic couples, at moment τ ₁The time to record the temperature difference be t ₁-t _∞=50 ℃, at t ₂-t _∞When=50 ℃ * 0.33=16.5 ℃ (calculating with formula (3)), the time of measuring this moment is τ ₂, utilize formula (2) can obtain convection transfer rate α under this operating mode, the α error minimum of this moment, relative error is $4.07\×\frac{0.1}{50}=0.814\%$ 。

The symbolic representation of above-mentioned formula is:

t _∞Fluid temperature (F.T.) (actual temperature of fluid generally about room temperature to 400 ℃, is measured with second thermopair 6)

F heat interchanging area (referring to that thermometric disk 2 and fluid contact surfaces are long-pending)

C specific heat (specific heat that refers to thermometric disk 2 materials)

V thermometric disk 2 volumes

ρ density (density value that refers to thermometric disk 2 materials)

The α convection transfer rate

The temperature measurement error of δ t temperature difference heat galvanic couple (absolute value that refers to the measuring error of first thermopair 5 and second thermopair, 6 composition temperature difference heat galvanic couples)

τ ₁Time (refer to temperature difference heat galvanic couple measure the moment of the temperature difference for the first time)

τ ₂Time (refer to temperature difference heat galvanic couple measure the moment of the temperature difference for the second time)

See also shown in Figure 1, of the present inventionly a kind ofly can directly measure convection heat transfer surface convection transfer rate sensor, by housing 1 (making " U " shape), thermometric disk 2 with stainless steel material (than book, general copper sheet or the stainless steel substrates processing of using thickness less than 1mm), heating film 3, heat guard 4, first thermopair 5, second thermopair 6, heating lead-in wire 7 and measurement instrument 8 constitute, heating film 3, heat guard 4, first thermopair 5 are installed in the housing 1, and thermometric disk 2 is installed in the cover plate that housing 1 top constitutes housing 1.The back side of thermometric disk 2 is provided with heating film 3, and the two ends of heating film 3 are connected with anodal heating lead-in wire 701 and negative pole heating lead-in wire 702, and the anodal heating lead-in wire 701 and negative pole heating lead-in wire 702 other ends are connected on the measurement instrument 8.Be filled with heat guard 4 between heating film 3 and housing 1 bottom.The thermometric end of first thermopair 5 contacts with thermometric disk 2, the positive terminal of first thermopair 5 is connected with the positive terminal of second thermopair 6, the negative terminals of first thermopair 5 is connected with measurement instrument 8, the negative terminals of second thermopair 6 is connected with measurement instrument 8, and the thermometric end of second thermopair 6 contacts with fluid.At least be provided with power supply in the measurement instrument 8, power supply can be that dry cell also can be the power supply chip that is connected with external power source, as long as can export 4V～6V voltage.For measurement instrument 8, also can adopt computer data acquiring to finish.

In the present invention, the mode that the positive pole of first thermopair 5 and second thermopair 6 links to each other constitutes the temperature difference heat galvanic couple, and its temperature difference is measured by measurement instrument 8.

In the present invention, the thermometric end of second thermopair 6 contacts with fluid, the thermometric end of first thermopair 5 with add thermometric disk 2 and contact.When working sensor, heat heating diaphragm moment energising by the heating power supply that is arranged in the measurement instrument, this heating process was generally finished with interior at 1 second.After heating finished, instrument 8 began to measure the disk that recorded by first thermopair 5 and second thermopair 6 and the temperature difference t of fluid ₁-t _∞, and the moment of record this moment be τ ₁, when the temperature difference of measuring the disk that recorded by first thermopair 5 and second thermopair 6 and fluid when instrument 8 satisfied (3) formula, the moment of record this moment was τ ₂, and export to measurement instrument 8 interior test formula (2) and calculate, promptly obtain being shown in the data of the convection transfer rate on the measurement instrument 8, and then carry out next one test.See also shown in Figure 2.For in test process, formula (3), formula (4) are through the inventor's derivation of present patent application and the optimum measurement method and the result of demonstration, the requirement of (3) is by formula measured, the convection transfer rate error minimum of gained, and formula (3) is set in measurement instrument 8 inside.When second thermopair 6 and first thermopair 5 were surveyed institute data transmission and gone in the measurement instrument 8, measurement instrument 8 just carried out calculating the convection transfer rate of output by the order of setting, computation rule.

Sensor of the present invention can be widely used in the commercial production, solve effectively on complex environment (as the engine turbine blade interior) the convection heat transfer surface especially problems of measurement of complex surface convection transfer rate, the convection transfer rate on convection heat transfer surface can be directly obtained, and loaded down with trivial details temperature field measurement needn't be carried out.

Claims (7)

1. the method for testing that can directly measure convection heat transfer surface convection transfer rate is characterized in that: when sensor is installed on measured surface, and after thermometric disk (2) transient heating to sensor, convection transfer rate alpha test formula is

$\mathrm{\α}=\frac{\mathrm{\ρcV}}{({\mathrm{\τ}}_2-{\mathrm{\τ}}_1)F}\ln \frac{t_1-t_{\∞}}{t_2-t_{\∞}}$

Its first thermopair (5) and second thermopair (6) are at τ ₁The thermometric disk (2) that constantly records and the temperature difference of fluid are t ₁-t _∞, at another moment τ ₂The thermometric disk (2) that first thermopair (5) and second thermopair (6) record and the temperature difference t of fluid ₂-t _∞Satisfy

t ₂-t _∞＝0.33(t ₁-t _∞)

The time, convection transfer rate error minimum, for

$\frac{\mathrm{\δ\α}}{\mathrm{\α}}=4.07\left(\frac{\mathrm{\δt}}{t_1-t_{\∞}}\right)$

In the formula, α refers to convection transfer rate, and ρ refers to the density value of thermometric disk (2) material, and c refers to the specific heat of thermometric disk (2) material, and V refers to thermometric disk (2) volume, and F refers to that thermometric disk (2) and fluid contact surfaces are long-pending, t _∞Refer to fluid temperature (F.T.), τ ₁Refer to the moment that the temperature difference heat galvanic couple is measured the temperature difference for the first time, τ ₂Refer to the moment that the temperature difference heat galvanic couple is measured the temperature difference for the second time, δ t refers to the absolute value of the measuring error of first thermopair (5) and second thermopair (6) composition temperature difference heat galvanic couple.

2. convection transfer rate method of testing according to claim 1 is characterized in that: the temperature difference heat galvanic couple that described first thermopair (5) and second thermopair (6) are formed is at τ ₁With τ ₂The time interval be 5 seconds～60 seconds.

3. convection transfer rate method of testing according to claim 1, the thermometric disk (2) that records when first thermopair (5) and second thermopair (6) and the temperature difference t of fluid ₂-t _∞Satisfy t ₂-t _∞=0.33 (t ₁-t _∞) time, measurement instrument (8) record moment τ at this moment ₂The sensor that is used for directly measuring convection heat transfer surface convection transfer rate comprises measurement instrument (8), measurement instrument is provided with power supply in (8) at least, it is characterized in that: also comprise housing (1), thermometric disk (2), heating film (3), heat guard (4), first thermopair (5), second thermopair (6), anodal heating lead-in wire (701) and negative pole heating lead-in wire (702), heating film (3), heat guard (4), first thermopair (5) are installed in the housing (1), and thermometric disk (2) is installed in the cover plate that housing (1) top constitutes housing (1); The back side of thermometric disk (2) is coated with heating film (3), be connected with anodal heating lead-in wire (701) and negative pole heating lead-in wire (702) on the two ends of heating film (3), the other end of anodal heating lead-in wire (701) and negative pole heating lead-in wire (702) is connected on the power supply of measurement instrument (8); Be filled with heat guard (4) between heating film (3) and housing (1) bottom; The thermometric end of first thermopair (5) contacts with thermometric disk (2), the positive terminal of first thermopair (5) is connected with the positive terminal of second thermopair (6), the negative terminals of first thermopair (5) is connected with measurement instrument (8), the negative terminals of second thermopair (6) is connected with measurement instrument (8), and the thermometric end of second thermopair (6) contacts with fluid.

4. convection transfer rate method of testing according to claim 3 is characterized in that: described first thermopair (5) and second thermopair (6) constitute the temperature difference heat galvanic couple, and its temperature difference is measured by measurement instrument (8).

5. convection transfer rate method of testing according to claim 3 is characterized in that: described thermometric disk (2) is less than 1mm thick copper sheet or stainless steel.

6. convection transfer rate method of testing according to claim 3 is characterized in that: described heating film (3) is photoetching stainless steel heating plate or electroplating film.

7. convection transfer rate method of testing according to claim 3 is characterized in that: described housing (1) is " U " shape, makes with stainless steel material.

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