Sweating Guarded Hotplate Status Quo

At present, sweating guarded hotplate you can see in foreign market are mainly from these two companies SGHP in NTNW and M259B in SDL ATLAS. They both entered Chinese market in the early stage and had wide application in some large institutes or labs; besides, they made some contributions to thermal and water vapor resistance test principle and methods.

NW SGHP sweating guarded hotplate adopts separation design structure thus the control box, water supplying tank and test unit are separated respectively; part of the sensor is external style. We should place test unit into the environment tank when testing, leaving water supplying tank and control box outside. Water and circular connection should be through the environment tank; the height of both test stand and water supplying tank can be adjusted manually. Ventilating system is equipped with 3 fans side structure so that wind velocity can be adjusted, but the 3 fans speed will also influence wind velocity stability. NW SGHP sweating guarded hotplate seems like a set of homemade test fixture for lab rather than a test device. It meets ISO11092 and ASTM F1868.

sweating guarded hotplate

SDL ATLAS M2598 adopts integral structure thus the test unit, control box, water flowing route and environment tank are like an integral machine. Test plate is copper grain structure, easy to be oxidized thus difficult to clean; according to customers’ response, when testing thin fabrics, the result sometimes appears negative data which is quite wrong to the actual situation; Wear made of these materials is much cold than wearing nothing. M2598 test speed is low and it takes at least 2 hours to test thick fabrics. The integral structure brings some problems such as the wind speed limited to 1m/s and environment temperature higher than 20 degree, so M2598 can only meet ISO11092 standard rather than ASTM F1868. 

QINSUN sweating guarded hotplate

Sweating guarded hotplate structure is complicated and requires high accuracy, thus manufacturing it needs difficult technology and higher cost, that’s why it is expensive, especially SGHP in NW whose price is too high for general entrepreneurs.

The above problems are main frustration of sweating guarded hotplate propaganda in China.

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How to Calculate Sweating Guarded Hotplate Testing Result

Sweating guarded hotplate testing result calculation formula:

Thermal Resistance:  Rct = (Tm-Ta) .A / (H- Hc) - Rct0

Dampness:  Ret = (Ps-Pa) .A / (H- He) - Ret0

If necessary, you can calculate other parameters according to the following formula:

Insulation rate: Wr = (1-b / a)%

ASTM F 1868A Rcf = Rct-Rcpb

ASTM F 1868B Ref = Ret-Repb

Breathable index: im = 0.060 Rcf / Ref

Water vapor transmission rate: Wd = 1 / Ret.ΦTm

When Tm = 35 ℃ when, ΦTm = 0.627W.h / g.

Crow value: clo = Rct /0.155 = 6.451 Rct

Thermal conductivity: k = 10-5.d / Rct

Wherein d is the thickness of the material (mm)

                                                        sweating guarded hotplate

Other related symbols and is defined as:

Rct resistance, m2.K / W

Ret dampness, m2.Pa / W

imt breathable index, dimensionless

Rct0 for the determination of the thermal resistance Rct determined instrument constant, m2.K / W

Ret0 for the determination of moisture resistance Ret determined instrument constant, m2.Pa / W

Rcpb bare-board thermal resistance, with Rct0

Repb bare board dampness, with Ret0

Wd water vapor transmission rate, g / m2hPa

ΦTm test plate surface temperature of saturated steam latent heat Tm when, Wh / g

A test board area, m2 sweating guardedhotplate formula

Ta climate chamber air temperature, ℃

Temperature Tm test plate, ℃

Ts hot grommet temperature, ℃

Pa water vapor pressure (in a climate chamber when the temperature Ta), Pa

Pm saturated water vapor pressure (when the surface temperature of the test plate when Tm), Pa

va test sample over the surface of the air velocity, m / s

sv standard deviation of flow velocity va, m / s

Relative humidity R.H.,%

H provided to the test panel heating power, W

                                                     sweating guarded hotplate testing

△ Hc measurement of thermal resistance Rct heating correction amount of power

△ He dampness Ret correction amount determination heated power

α △ Hc calculation of the amount of slope correction

β △ He corrected the calculation of the amount of slope

k Thermal conductivity, W / m.K

d material thickness, mm

Wr Insulation rate

plus a empty plate heat (J / Cm2.S)

b have the test sample plus heat (J / Cm2.S)

clo CLO value, the thermal resistance of a representation unit. At a temperature of 21 ° C, the air flow does not exceed 0.1m / s environmental conditions, meditation (whose basal metabolism of 58 W / m2) feel comfortable when they wear clothing insulation value of 1 Crow (clo) value.

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Textile Products Sweating Guarded Hotplate Testing Principle Analysis

Sweating guarded hotplate testing is commonly used testing method in clothing and apparatus industry for textile products heating or humidity resistance performance. Textile features testing plays quite practical and significant role in textile industry. 

Textile products sweating guarded hotplate testing principle: 
Sample is placed on electronic heating experiment board, at the same time, experiment board and the protecting board at bottom should be kept with the same temperature so that heating loss of electronic heating experiment board only due to sample itself; the wet air can flow parallel in the surface. After the experiment environment is being stable, we can calculate the sample heating resistance by way of its heating flow. 

For wet resistance, we should cover electronic heating experiment board with film which is permeable to air rather than water. The water goes through film in the form of steam after evaporated and thus there is no liquid water contacting samples. After the sample is placed on the film and under the condition that the heating of electronic heating board needed is ensured, we can test the heating flow sample wet resistance together with the exerted steam pressure.

 

For more sweating guarded hotplate or textile testing instruments information, QINSUN Instruments are ready for help.

The Comparison of New and Old Sweating Guarded Hotplate Testing Standards

In China textile industry, the earliest sweating guarded hotplate testing standard is GB/T11048-1989 which uses flat plate heat insulation device for insulation test. This method played positive role but it has following defects because of the technical limitations.

                                        sweating guarded hotplate

1.      The insulation rate is so different from that used by the international standard that the testing result couldn’t be exchanged.

2.      The concept of“insulation”has huge limitations, while thermal resistance can express textile heat transferring performance which is quite close to human physical comfort. 

3.      There are huge differences of insulation rate and thermal resistance in windless and windy environments. Thermal resistance reduces when there is wind, while the insulation rate rises which turns out to be opposite to the actual situation. Thus insulation rate is meaningful only in a certain situation.

                                                sweating guarded hotplate testing

The earliest sweating guarded hotplate testing method is ISO11092 which was formulated on the basis of flat plate tester developed by German scientists. It was released in 1993 and has been used today. ASTM F1868 is similar to it and there are several differences on testing environment and specifications.

China lately sweating guarded hotplate testing method is GB/T 11048-2008 and the main testing method A is the same as ISO11092; while method B-flat plate testing standard was used in some special situation.

 For more textile testing instruments information, please visit QINSUN Instruments-China professional textile testing equipment manufacturer. We are ready for help.