Figure 1. Positive pressure duct type air leakage test device<\/figcaption><\/figure>\n\n\n\nStandard orifice plate with corner connection shall be used. Orifice plate \u03b2 The distance between the orifice plate and the straight pipe section of the front and rear rectifying grids should be greater than or equal to 10 times and 5 times the diameter of the air duct respectively.<\/p>\n\n\n\n
The connecting air duct shall be smooth round. Within the range of orifice plate to 2 times of air duct diameter upstream, the allowable roundness deviation shall be 0.3%, and 2% downstream.<\/p>\n\n\n\n
The orifice plate shall be connected with the air duct, and the allowable deviation of perpendicularity between the front end and the pipe axis shall be 1\u00b0; The allowable deviation of concentricity between the orifice plate and duct shall be 1.5% of duct diameter.<\/p>\n\n\n\n
After the first rectifier gate, all connection parts should be tight.<\/p>\n\n\n\n
The air leakage shall be calculated according to the following formula:<\/p>\n\n\n\n
Q=3600\u03b5\u00d7\u03b1\u00d7An<\/sub>\u221a(2\u2206P\/\u03c1)<\/p>\n\n\n\nWhere: Q — air leakage (m3<\/sup>\uff0f h)\uff1bn<\/sub> — opening area of orifice plate (m2<\/sup>);3<\/sup>)\uff1bThe discharge coefficient of the orifice plate and its application \u03b2 The relationship between values should be determined according to figure 2, and the following conditions should be met:<\/p>\n\n\n\n
Firstly, when 1.0 \u00d7 105\uff1cRe\uff1c2.0 \u00d7 106, 0.05\uff1c \u03b2 49, 50 mm \uff1c D \u2264 1000 mm, the influence of pipe roughness on flow coefficient is not considered;<\/p>\n\n\n\n
Secondly, when re is less than 1.0 \u00d7 The flow coefficient should be calculated according to the relevant provisions of the current national standard “measurement of full pipe fluid flow by differential pressure device installed in circular cross-section pipe” GB \/ T 2624 \u03b1.<\/p>\n\n\n\n Figure 2. Orifice discharge coefficient diagram<\/figcaption><\/figure>\n\n\n\nThe expansion coefficient of air beam in orifice plate \u03b5 The values can be determined according to figure 3.<\/p>\n\n\n\n \u03b22<\/sup>-P1<\/sub>\/P2<\/sub><\/td>1.00<\/td> 0.98<\/td> 0.96<\/td> 0.94<\/td> 0.92<\/td> 0.90<\/td> 0.85<\/td> 0.80<\/td> 0.75<\/td><\/tr> 0.08<\/td> 1.0000<\/td> 0.9930<\/td> 0.9866<\/td> 0.9803<\/td> 0.9742<\/td> 0.9681<\/td> 0.9531<\/td> 0.9381<\/td> 0.9232<\/td><\/tr> 0.10<\/td> 1.0000<\/td> 0.9924<\/td> 0.9854<\/td> 0.9787<\/td> 0.9720<\/td> 0.9654<\/td> 0.9491<\/td> 0.9328<\/td> 0.9166<\/td><\/tr> 0.20<\/td> 1.0000<\/td> 0.9918<\/td> 0.9843<\/td> 0.9770<\/td> 0.9689<\/td> 0.9627<\/td> 0.9450<\/td> 0.9275<\/td> 0.9100<\/td><\/tr> 0.30<\/td> 1.0000<\/td> 0.9912<\/td> 0.9831<\/td> 0.9753<\/td> 0.9676<\/td> 0.9599<\/td> 0.9410<\/td> 0.9222<\/td> 0.9034<\/td><\/tr><\/tbody><\/table>Figure 3. The expansion coefficient of the standard orifice with angle connection \u03b5 Value (k = 1.4)2<\/sub> \/ P1<\/sub> is the ratio of the total pressure behind the orifice to that in front of the orifice<\/figcaption><\/figure>\n\n\n\nFor the air leakage test device under negative pressure, the suction port of the fan should be connected with the throttle and orifice flow measurement section phase by phase, and the front 10d rectifier grid of the orifice should be placed at the windward end to form a complete device. Then it should be connected with the air duct or equipment to be measured through the soft interface (Fig. 4).<\/p>\n\n\n\n Figure 4. Negative pressure air duct type air leakage test device<\/figcaption><\/figure>\n\n\n\n\nThe air leakage test device of air chamber type shall meet the following requirements:<\/li>\n<\/ul>\n\n\n\nThe chamber-type air leakage test device shall be composed of the fan, connecting duct, pressure measuring instrument, flow equalizing plate, throttle, chamber, diaphragm, and nozzle (Fig. 5).<\/p>\n\n\n\n
In order to use the nozzle to measure the air volume, the diaphragm should divide the air chamber into two cavities, and the measuring nozzle should be installed on the diaphragm. According to the needs of the test air volume, nozzles with different diameters and numbers can be used. In order to ensure the stability of the airflow at the nozzle inlet and the correctness of the flow rate, the center distance between the two nozzles should not be less than 3 times the throat diameter of the large-diameter nozzle; <\/p>\n\n\n\n
The distance between the center of any nozzle and the nearest sidewall of the air chamber shall not be less than 1.5 times of the throat diameter of the nozzle. The distance between the installation position of the equalizing plate at the inlet end of the metering nozzle and the diaphragm shall not be less than 1.5 times of the large diameter nozzle, and the distance between the installation position of the equalizing plate at the outlet end and the diaphragm shall not be less than 2.5 times of the large diameter nozzle. The air outlet of the fan shall be connected with the test device (Fig. 5). <\/p>\n\n\n\n
When the standard long diameter nozzle is selected as the metering element type after the diameter is determined, the neck length should be 0.6 times of the diameter, the nozzle big mouth should not be less than 2 times of the diameter, and the length of the expansion part should be equal to the diameter; The nozzle end shall be planed and 1 \/ 3 thick and 10 mm thick \u00b0 Tilt (Fig. 6).<\/p>\n\n\n\nFigure 5. Positive pressure chamber type air leakage test device<\/figcaption><\/figure>\n\n\n\n Figure 6. Standard long neck nozzle<\/figcaption><\/figure>\n\n\n\nThe air chamber is a sealed box with connecting joints at both ends. The cross-sectional area of the air passage should be according to the maximum test air volume. When passing, the average air velocity should be less than or equal to 0.75m\/s. The air outlet of the fan shall be connected with the interface of the throttle and nozzle inlet direction, and the other end shall be connected with the air pipe or equipment to be measured through the soft interface (Fig. 5).<\/p>\n\n\n\n
The static pressure taps at both ends of the nozzle in the air chamber should be multiple and evenly distributed on the four walls. The distance between the static pressure tap and the nozzle baffle shall not be greater than 1.5 times the minimum nozzle throat diameter. Multiple static pressure interfaces should be connected in parallel to form a static pressure ring, and then connected with the pressure measuring instrument.<\/p>\n\n\n\n
When the device is used to measure the air leakage, the flow rate through the nozzle throat should be controlled in the range of 15m \/ s ~ 35m \/ s.<\/p>\n\n\n\n
All the connecting parts behind the nozzle clapboard in the air chamber shall be tight without leakage.<\/p>\n\n\n\n
The air volume of a single nozzle shall be calculated as follows:<\/p>\n\n\n\n
Q=3600Cd\u00d7Ad\u221a(2\u2206P\/\u03c1)<\/p>\n\n\n\n
Where: Q — air leakage of the single nozzle (m3<\/sup>\uff0f h)\uff1bd<\/sub> — flow coefficient of the nozzle (0.99 for diameter 127 mm and above, and 0.99 for diameter less than 127 mm can be obtained according to table c.2.7 or figure c.2.7-3);d<\/sub> — throat area of the nozzle (m2<\/sup>);Re<\/sub><\/td>Cd<\/sub><\/td>Re<\/sub><\/td>Cd<\/sub><\/td>Re<\/sub><\/td>Cd<\/sub><\/td>Re<\/sub><\/td>Cd<\/sub><\/td><\/tr>12000<\/td> 0.950<\/td> 40000<\/td> 0.9730<\/td> 80000<\/td> 0.9830<\/td> 200000<\/td> 0.9910<\/td><\/tr> 16000<\/td> 0.956<\/td> 50000<\/td> 0.9770<\/td> 90000<\/td> 0.9840<\/td> 250000<\/td> 0.9930<\/td><\/tr> 20000<\/td> 0.961<\/td> 60000<\/td> 0.9790<\/td> 100000<\/td> 0.9850<\/td> 300000<\/td> 0.9940<\/td><\/tr> 30000<\/td> 0.969<\/td> 70000<\/td> 0.9810<\/td> 150000<\/td> 0.9890<\/td> 350000<\/td> 0.9940<\/td><\/tr><\/tbody><\/table>Figure 7. Nozzle flow coefficient tableThe air volume of multiple nozzles shall be calculated according to the following formula:<\/p>\n\n\n\n
Q=\u2211Qn<\/sub><\/p>\n\n\n\nFor the air leakage test device under negative pressure, the suction port of the fan shall be connected with the opposite interface of the throttle and the nozzle inlet of the air chamber box, and the other end shall be connected with the air pipe or equipment to be measured through the soft interface (Fig. 9).<\/p>\n\n\n\n Figure 8. Calculation of nozzle flow coefficientFigure 9. Negative pressure chamber type air leakage test device<\/figcaption><\/figure>\n\n\n\nAir leakage test<\/strong><\/h2>\n\n\n\nThe air leakage test of the system air duct and equipment should be divided into positive pressure test and negative pressure test. It should be determined according to the working state of the tested air duct, and it can also be checked by a positive pressure test.<\/p>\n\n\n\n
The air leakage test of the system air duct can be carried out in whole or in sections, and all openings of the tested system shall be closed without air leakage.<\/p>\n\n\n\n
When the air leakage of the air duct of the tested system exceeds the requirements of the design and this specification, the air leakage position (which can be detected by listening, touching, ribbon, water film, or smoke) shall be found out and marked; After the repair is completed, it shall be retested until it is qualified.<\/p>\n\n\n\n
The measurement of air leakage should generally be the measured value under the specified working pressure (maximum operating pressure) of the system. Under special conditions, it can also be replaced by the test under the pressure close to or greater than the specified pressure. The air leakage can be calculated according to the following formula:<\/p>\n\n\n\n
Q0<\/sub>=(P0<\/sub>\/P)0.65<\/sup><\/p>\n\n\n\nWhere: Q0<\/sub> — air leakage under specified pressure [m3<\/sup>\uff0f( h\u00b7\u33a1)]\uff1b3<\/sup>\uff0f( h\u00b7\u33a1)]\uff1b0<\/sub> — the specified working pressure (PA) of air duct system test;In a word, measuring the airtightness of the air duct has a positive effect on the installation and final commissioning of the air duct.<\/p>\n","protected":false},"excerpt":{"rendered":"
Air Duct With the progress of society and the gradual improvement of human requirements for various infrastructure facilities, air duct<\/p>","protected":false},"author":1,"featured_media":11541,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[200],"tags":[210,213,211,212],"class_list":["post-11518","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-ventilation-duct","tag-air-duct","tag-air-leakage","tag-airtightness","tag-fan"],"jetpack_featured_media_url":"https:\/\/duct.harsle.com\/wp-content\/uploads\/2021\/07\/How-to-Test-Air-tightness-of-Air-Duct-14.jpg","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/posts\/11518","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/comments?post=11518"}],"version-history":[{"count":0,"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/posts\/11518\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/media\/11541"}],"wp:attachment":[{"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/media?parent=11518"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/categories?post=11518"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/duct.harsle.com\/cs\/wp-json\/wp\/v2\/tags?post=11518"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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