CN1769877A - Nano fluid heat conductivity tester - Google Patents

Abstract

The invention discloses an apparatus for detecting nano fluid heat conductivity which comprises: on base being placed four calorimeters which having a clamping cap on upper end and being fixed with compressor bolt and locking nut; the calorimeters having sample chamber, on the sample chamber's upper end being placed upper end cap and collar seal, on its lower end being placed lower end cap and collar seal; on the upper end cap having two connectors on which having lead-out wire; by fine copper wires, the lower end of connector being connected with platinum wire which enwinds on mica sheet. The inventive apparatus has the advantages of having cramped construction, of being easy to operate and high efficiency.

Description

Nano fluid heat conductivity tester

Technical field

The present invention relates to new material basal heat physical property measurement field, relate in particular to a kind of nano fluid heat conductivity tester.

Background technology

Nano-fluid, promptly nanoscale (0.1～100nm) metal, compound or non-metal simple-substance are distributed in traditional heat transferring mediums such as water, ethylene glycol, machine oil with share in a certain way, form a class evenly, the novel heat eliminating medium of stable, the high capacity of heat transmission.Compare with neat liquid, nano-fluid can significantly increase temperature conductivity, and because the small-size effect of nano particle, its behavior is near molecule, the Brownian movement of fluid molecule makes nano particle can keep stable suspersion, thereby is difficult for producing in pipeline wearing and tearing and latch up phenomenon.Since nineteen ninety-five Choi proposed the notion of " nano-fluid ", nano-fluid made it in the augmentation of heat transfer field wide application prospect be arranged because of its good heat-conducting, had caused the extensive concern that global academia and engineering are used.Of common occurrence to the nano fluid heat transferring The Characteristic Study in recent years, in fundamental research and applied research, all have and obtained certain progress.

Temperature conductivity is one of indispensable parameter of research nano-fluid heat conductivility.Because the research of nano-fluid still is in the elementary step, the many physical parameters that comprise temperature conductivity all do not have experimental formula to examine, and many temperature conductivity formula about micron/millimetre-sized solidliquid mixture are not suitable for nano level solidliquid mixture, be because the HEAT TRANSFER LAW of micron/millimeter grade particle and nano particle existence than big-difference.The temperature conductivity of nano-fluid is all multifactor relevant with granule density, grain diameter, temperature, dispersant concentration etc., and this just needs lot of data to come relation between the qualitative analysis factor, so that form the experimental formula that a cover is fit to nano fluid heat conductivity; And the nano particle in the nano-fluid and the combination of base fluid are varied, and temperature conductivity separately is also different, therefore, need a cover efficiently, device is tested the temperature conductivity of nano-fluid fast.

How the main difficulty of accurately measuring the liquid thermal conductivity rate is the heat conduction of liquid is isolated from convection heat transfer, and as long as there is thermograde in fluid inside, will inevitably cause natural convection, so realize that in liquid pure conduction process is very difficult.Be the error of avoiding fluid natural convection to cause, adopt the transient state method usually.

Summary of the invention

The purpose of this invention is to provide a kind of efficient rapid nano fluid heat conductivity tester.

4 calorimeters are installed on base, and the calorimeter upper end is provided with friction top, and fixes with clamping screw, tight split nut; Calorimeter has sampling receptacle, be provided with upper end cover, upper end cover O-ring seal in the sampling receptacle upper end, be provided with bottom end cover, bottom end cover O-ring seal in the sampling receptacle lower end, upper end cover is provided with two binding posts, the binding post upper end is connected to draws lead, the binding post lower end joins through thin copper wire and platinum filament, and platinum filament is wrapped on the mica sheet.

The present invention utilizes Wheatstone bridge as test circuit.During test whole device is placed thermostatic oil bath, records the voltage difference of two platinum filaments with precise data collector, according to liquid thermal conductivity rate formula, get final product the temperature conductivity of nano-fluid.This apparatus structure compactness is sturdy, easy to operate, and efficient is the twice of general device.

Description of drawings

Fig. 1 is efficient rapid nano fluid heat conductivity tester structural representation;

Fig. 2 is upper end cover of the present invention, friction top and ring structure synoptic diagram;

Fig. 3 is bottom end cover of the present invention, base and ring structure synoptic diagram;

Fig. 4 is a test circuit schematic diagram of the present invention.

Among the figure: draw lead 1, friction top 2, upper end cover O-ring seal 3, thermostatic oil bath 4, sampling receptacle 5, thin copper wire 6, copper wire platinum filament solder joint 7, platinum filament 8, mica sheet 9, base 10, bottom end cover O-ring seal 11, bottom end cover 12, clamping screw 13, binding post 15, upper end cover 16, tight split nut 17.

Embodiment

4 calorimeters of the present invention, pressure 10bar is born in design, and working temperature can reach 200 ℃.Can adopt the transient state dual hot-wire method to test 2 groups of samples simultaneously, also can utilize the single heat-pole method of transient state to test 4 groups of samples simultaneously.

The present invention adopts the transient state dual hot-wire method, can eliminate the consumes power influence of circuit internal resistance and fluid conduction institute, and absorb a certain amount of heat except the platinum filament end leads in the test, nano-fluid is a conductor, sampling receptacles etc. all are metals, and these all can absorb certain heat.Adopt dual hot-wire method can eliminate the error that these losses bring equally.

Nano fluid heat conductivity tester is equipped with 4 calorimeters on base 10, the calorimeter upper end is provided with friction top 2, and fixes with clamping screw 13, tight split nut 17; Calorimeter has sampling receptacle 5, be provided with upper end cover 16, upper end cover O-ring seal 3 in the sampling receptacle upper end, be provided with bottom end cover 12, bottom end cover O-ring seal 11 in sampling receptacle 5 lower ends, upper end cover 16 is provided with two binding posts 15, the binding post upper end is connected to draws lead 1, the binding post lower end joins through thin copper wire 6 and platinum filament 8, and platinum filament 8 is wrapped on the mica sheet 9.The material of described sampling receptacle 5 is a copper, and the material of upper end cover 16 is a teflon.Among the present invention:

1) material: base and last friction top are stainless steel; Sample receiver is a brass, and temperature conductivity is big, can comparatively fast reach temperature balance; Container cover is a teflon, and electrically insulating material is avoided binding post and container cover conduction; Binding post is a stainless steel; Clamping screw is a cast iron.

2) sealing: sampling receptacle is by the sealing of the rubber seal on upper and lower two end caps (seeing accompanying drawing 2 and accompanying drawing 3), and the sealing at binding post place is by the rubber sheet gasket sealing, and clamping screw guarantees the reliability of sealing, and preventing to be immersed in has oil seepage to advance in the container in the oil bath.

3) platinum filament: long and short two root platinum filament places two sampling receptacles respectively, and platinum filament from top to bottom is wrapped on the mica sheet, and the upper end is connected with copper wire spot welding, and copper wire is connected with binding post again.Mica-sheet insulation and temperature conductivity are low, are desirable platinum filament supporters.

4) sampling receptacle: sampling receptacle is designed to two copper pipes that are port up and down, takes off the convenient cleaning in back from upper and lower end cap, has avoided the sample cross pollution.

As shown in Figure 4, test circuit of the present invention is: wheatstone bridge circuits, and by constant-current supply power supply, R ₀Be 0.01 grade of precision resistance, R ₁And R ₂Be variable resistor, R ₃And R ₄Be 0.01 grade of precision resistance, R _LBe expressed as long platinum filament, Rs is expressed as short platinum filament.Adopt precise data collector to measure the voltage difference of length platinum filament, thereby calculate the temperature conductivity of nano-fluid according to formula.

The fundamental formular of thermal transient collimation method test liquid coefficient of heat conductivity:

$\mathrm{\λ}=\frac{q}{4\mathrm{\π}}\·{\left(\frac{\mathrm{dT}}{d\left(\ln t\right)}\right)}^{-1}---\left(1\right)$

The heat that platinum filament absorbs is:

$q=4\mathrm{\π\λ}\·\frac{\mathrm{dT}}{d\left(\ln t\right)}---\left(2\right)$

Consideration in test process because the heat conduction and the radiation-induced thermal loss of container, lead, because the situation of two calorimeters is identical, unique difference is platinum filament length, but the thermal loss that is caused by this difference is very little, so approximate think that two calorimeter thermal loss Δ q are identical in the test, so to long platinum filament R _L,

$q_L=q-\mathrm{\Δq}=I^2{R}_L-\mathrm{\Δq}=4\mathrm{\π\λL}\·\frac{d{T}_L}{d\left(\ln t\right)}---\left(3\right)$

To short platinum filament R _S,

$q_S=q-\mathrm{\Δq}=I^2{R}_S-\mathrm{\Δq}=4\mathrm{\π\λS}\·\frac{d{T}_S}{d\left(\ln t\right)}---\left(4\right)$

3,4 formulas are asked poor:

$I^2(R_L-R_S)=4\mathrm{\π\λ}(L-S)\frac{d{T}_L-d{T}_S}{d\left(\ln t\right)}---\left(5\right)$

$I^{2}R=4\mathrm{\π\λl}\frac{\mathrm{dT}}{d\left(\ln t\right)}---\left(6\right)$

Put in order,

$\mathrm{\λ}=\frac{I^{2}R}{4\mathrm{\πl}}{\left(\frac{\mathrm{dT}}{d\left(\ln t\right)}\right)}^{-1}---\left(7\right)$

$\mathrm{\λ}=\frac{I^{2}R}{4\mathrm{\πL}}\·\frac{\mathrm{dV}}{\mathrm{dT}}\·{\left(\frac{\mathrm{dV}}{d\left(\ln t\right)}\right)}^{-1}=\frac{I^{3}R}{4\mathrm{\πl}}\·\frac{\mathrm{dR}}{\mathrm{dT}}\·{\left(\frac{\mathrm{dV}}{d\left(\ln t\right)}\right)}^{-1}---\left(8\right)$

In the formula,

The electric current of I---platinum filament, A;

R---length hot line resistance is poor, Ω;

V---platinum filament pressure drop difference, v;

L---long platinum filament length, m;

S---short platinum filament length, m;

L---platinum filament length difference, m;

Δ q---thermal loss, W;

λ---liquid thermal conductivity rate, W/ (m.k);

T---conduction time, s.

Testing procedure of the present invention

1) twine two platinum filaments that length is different respectively on two killinite sheets, length difference is about 150mm, and weld with copper wire at the platinum filament two ends, and the copper wire two ends are connected to the binding post on the upper end cover.Detect binding post two ends resistance with multimeter, confirm to connect good;

2) according to the length of platinum filament, pour highly different testing samples in sampling receptacle, the height of sample is the best just to flood platinum filament, and the heat that can guarantee platinum filament so all is used for heated sample; Upper end cover, friction top are installed;

3) connect wheatstone bridge circuits, and be connected to the binding post on the upper end cover, detect entire circuit with multimeter, it is errorless to guarantee that circuit connects;

4) connect the data acquisition unit measuring point to the Wheatstone bridge relevant position testing the voltage difference dV of two platinum filaments, and on PC the installation data capture program, be connected to testing tool;

5) open data acquisition unit, to circuit, regulator potentiometer makes dV=0, bridge balance from constant-current supply input 4mA electric current;

6) input one steady current (about 30mA) is gathered voltage difference dV, powered-down behind about 6s, end of test (EOT);

7) relation curve of drafting dV and d (lnt) is chosen one section good slope calculations of the linearity

And data are brought into the temperature conductivity λ of calculation sample in the formula (8).

Test case of the present invention

Example 1: measured distilled water (DW), ethylene glycol (EG), the coefficient of heat conductivity of glycerine under 25 ℃, compared with literature value, relative error is within 2.31%, and is as shown in the table.

Sample	Test value	Literature value	Relative error
				The distilled water glycol glycerin	0.613 0.254 0.294	0.605 0.260 0.288	1.32％ -2.31％ 2.08％

Example 2: prepared following 5 kinds of nano-fluids, with its temperature conductivity of this device to test, as shown in the table.

Sample	CuO-DW	Al 2O 3-DW	Cu-DW	Al-DW	AlN-DW
						Temperature conductivity	0.6835	0.6612	0.7260	0.6352	0.6907

* temperature conductivity unit is W/ (m.K) in the above example.

Claims (2)

1. a nano fluid heat conductivity tester is characterized in that, 4 calorimeters are installed on base (10), and the calorimeter upper end is provided with friction top (2), and fixes with clamping screw (13), tight split nut (17); Calorimeter is equipped with sampling receptacle (5), be provided with upper end cover (16), upper end cover O-ring seal (3) in the sampling receptacle upper end, be provided with bottom end cover (12), bottom end cover O-ring seal (11) in sampling receptacle (5) lower end, upper end cover (16) is provided with two binding posts (15), the binding post upper end is connected to draws lead (1), the binding post lower end joins through thin copper wire (6) and platinum filament (8), and platinum filament (8) is wrapped on the mica sheet (9).

2. according to described a kind of nano fluid heat conductivity tester of claim 1, it is characterized in that the material of described sampling receptacle (5) is a copper, the material of upper end cover (16) is a teflon.

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