Development of digital thermal insulation value tester for jute products

Transcription

1 Indian Journal of Fibre & Texile Research Vol. 34, March 2009, pp Developmen of digial hermal insulaion value eser for jue producs Gauam Roy a, Malay Naskar & S N Ghosh Naional Insiue of Research on Jue and Allied Fibre Technology, 12 Regen Park, Kolkaa , India Received 28 January 2008; revised received and acceped 7 July 2008 A new ype of digial insrumen has been developed for measuring hermal insulaion value of various jue producs using wo-plae mehod. The insrumen is based on a microprocessor and provides auomaic resuls in og for he maerial under es. I requires no preparaion of es samples if he area of he sample is no less han 700 cm 2. The es is nondesrucive and process of sample preparaion is free from human error. Keywords: Jue, Microprocessor, Reference disc, Thermal insulaion value, Tog 1 Inroducion The hermal insulaion propery of a exile maerial is of considerable pracical imporance, paricularly when hese maerials are used as clohing, winer garmens, blanke, quil, carpe, floor coverings, room insulaion, ec. The mechanism of hermal insulaion propery includes, in case of exile maerials, he combined effec of ransmission of hea by conducion, convecion and radiaion o some exen. The hermal propery of he componens of he exile maerials, enrapped air in he srucure of he maerials and environmenal condiions play imporan roles in conribuing owards he hermal resisance value of he producs. The diversificaion of jue, he fibres, he sicks and oher bio-residues of plans demands developmen of non-convenional producs. Naional Insiue of Research on Jue and Allied Fibre Technology has been developing various value-added diversified producs from jue, using weaving, kniing and nonwoven echnology. Some of he producs are also subjeced o undergo exposure in hea. Nowadays, jue fibre is used o produce various winer garmens, blankes, carpes, quils, floor coverings, ec. eiher by weaving and kniing and/or by nonwoven echnologies. Hard boards from jue sick paricles, dus and sicks of oher plans of allied fibres are also very much under producion. Such boards are generally used as pariion wall, false ceiling, ec. I is known ha he resisance, offered by a exile maerial o he movemen of hea hrough i, is a To whom all he correspondence should be addressed. gauamroy1234@yahoo.com obviously of criical imporance o is hermal comfor. A suiable insrumen for measuring he hermal resisance or insulaion value of he aforesaid producs is very much an essenial need of he day. However, o measure he hermal properies of he producs made ou of jue and is blends, here is no single insrumen available so far. As jue fibres are very coarse, he producs made ou of i are also coarser in naure. By blending finer fibres wih jue, finer producs are also developed. An insrumen, which can accommodae boh hick and hin exile maerials and non-exile shee like producs, may need o mee he demand of he presen day. In view of he above, in he presen sudy an insrumen has been developed for a quick and reliable assessmen of hermal insulaion properies of exile and non-exile maerials. Mehods of measuring hea ransfer have been devised by several workers. Prokop 1 used ho and cold discs separaed by es samples, while Shinkai e al. 2 observed an anomalous negaive value in a similar es. This has been corroboraed by Paul and Mukhopadhyay 3, while measuring hermal insulaion value of jue fabric. Jokl and Sverak 4 deermined he hea resisance of clohing by using calorimeer. Zamolaev 5 repored a semi-auomaic device where emperaure difference was measured under a sable condiion. Sukharev and Haasse 6 repored wo insrumens, one measures differen hermal properies like conduciviy, aciviy and emperaure change, and he oher measures oal hermal resisance under convecion condiions wih a layer of air beneah he sample.

2 ROY e al.: DEVELOPMENT OF DIGITAL THERMAL INSULATION VALUE TESTER 37 In he presen insrumen, he hermal resisance of he maerial is deermined by suing disc mehod, an applicaion of Lee s disc apparaus o exiles. Following inernaionally acceped sandards 7, guarded wo plae mehod has been employed o develop he insrumen. The insrumen can be used for he producs having he hickness of wider range and under he more relaxed amospheric conrol. 2 Maerials and Mehods The hermal resisance or insulaion of a exile maerial is usually defined by he raio of he emperaure difference beween he wo faces of he maerial o he rae of flow of hea per uni area normal o he faces. I is analogous o he elecrical resisance in case of curren flow hrough elecrical conducor. Disc mehod, an applicaion of Lee s disc apparaus o exiles, was employed o develop he insrumen. In his mehod, he maerial under es is held beween wo meal discs one of which has he known hermal resisance. In seady sae condiion, he emperaure drop values across he meal disc of known hermal resisance and across he maerial under es are measured and hen used o obain he hermal resisance of he specimen by he following echniques. Le TR ref and TR samp be he hermal resisance of he known disc and he sample respecively. Le 1 be he emperaure regisered by he lower surface of known disc, 2 be he emperaure regisered by he lower surface of he sample and 3 be he emperaure regisered by he upper surface of he sample. Assuming consan rae of hea flow a seady sae condiion, he TR samp is compued using he following relaionship: = TR 3 ref TR samp, or TR samp = TR ref 2 1 The hickness of a exile fabric varies wih pressure applied on i. This is more revealed in case of samples like a raised blanke or a knied winer garmen whose pseudo-hickness increases is uiliy value. In deermining he hermal resisance propery of a exile maerial if he apparen or he pseudohickness characer is disored, i will give a hermal resisance value. To avoid such probabiliies, exile engineers prefer using he value of he hickness in gsm in idenifying he characer of a exile fabric. The insrumen is designed in such a way ha i may accommodae a maerial of a wide range of hickness under minimum fixed weigh wihou causing any palpable disorion o he srucure, bu sufficien o keep he sample smooh in beween he esing surfaces. In case of replicaion of ess of a single sample, he effec of hickness on hermal resisance propery may be ignored. Bu when he resuls of differen samples require o be compared, i is recommended o calculae he hermal insulaion value of a sample per uni gsm of he same. 2.1 Descripion of Insrumen Figure 1 shows an isomeric view of he panel board and he measuring device of he insrumen. A microprocessor-conrolled heaer (3) wih a heaer plae (3a) is placed as he hea source on which disc (1) is kep. A sample under es is placed on he disc (1) which is ermed as he reference disc. The disc (2) is placed on 3 2 Fig. 1 Isomeric view of insrumen

3 38 INDIAN J. FIBRE TEXT. RES., MARCH 2009 he sample under es. Three semiconducor emperaure sensors (T 1, T 2 and T 3 ) are fied on he heaer plae, reference plae disc (1) and disc (2) respecively o measure he source emperaure ( 1 ), he emperaure of he boom surface ( 2 ) and ha of he upper surface ( 3 ) of he sample under es. In a panel board (4) of he insrumen as shown in Fig.1, wo (5, 6) four digi seven segmen display unis are provided. In he upper display (5), he emperaures 1, 2, and 3 and in he lower display (6), he variable parameers are displayed which can be adjused as per he requiremen of he es. A fourh sensor (T 4 ) is provided o measure and indicae he ambien emperaure. A buzzer (7) is provided which generaes an alarm a every 10 min inerval. When a hermal equilibrium is reached, he hermal insulaion value of he sample under es is displayed on he lower display (5) in he uni of og and he upper display (5) is indicaed by he leers TrES. The end poin of a es is declared by a non-sop whisle of he buzzer (7) o draw he aenion of he operaor. The final resul remains frozen unil i is rese. The lower display (6) is also used o se operaing crieria of he microprocessor and conroller before saring he experimen. Third and fourh (8, 9) digial displays are provided in he panel board (4) o measure he ime elapsed under es and he ambien emperaure. In Fig. 2, a schemaic circui diagram of he insrumen has been provided. The inpus from he hree emperaure sensors (T 1, T 2, and T 3 ) are fed o a precision ype non-invering amplifier (11) hrough a 3:1 analog muliplexer (10). The oupu (O A ) of he amplifier (11) is fed o a volage frequency converer (12) where he oupu volage is convered o a frequency of square wave ype wih a predefined maximum value. The oupu digial signal of variable frequency (d svf ) is firs elecrically isolaed using an opical isolaor (13) and he oupu (d soi ) is fed o a gaed couner (14) o conver he inpu value o an equivalen 12 bi binary signal (b s ), which is fed o a microprocessor (15) hrough 12 bi daa lines and an inernal lach (17) as well as a buffer amplifier (18) circui. From he analog muliplexer (10), a 2 bi address informaion (a i ) for hree sensors (T 1, T 2, and T 3 ) is provided o he microprocessor (15). The hermal insulaion value of he sample under es is deermined a he seady sae condiion, which is deeced by a microprocessor-based program. The deails of he algorihm of he program are given in Fig. 3. Fig. 2 Schemaic diagram of circui design of insrumen Fig. 3 Flowchar of compuaion algorihm of program

4 ROY e al.: DEVELOPMENT OF DIGITAL THERMAL INSULATION VALUE TESTER 39 Though he emperaure sensors are of sandard make, hey were furher calibraed using boiling waer bah and condiioning oven and were found o be perfec. 3 Resuls and Discussion 3.1 Correcion Facor due o Conac Resisance Since he juncions of hree plaes incorporaed in he insrumen are of a finie hickness, i is quie possible ha due o conac resisance he measuremen of he emperaures of he acual surfaces on which hey are embedded may no be much precise. This conac resisance may lead o a higher hermal resisance value of he sample under es. I is, herefore, of significan imporance o deduce a correcion facor due o conac resisance. This correcion facor is o be considered for evaluaing he hermal resisance of he sample. This has been accomplished by obaining he hermal resisance value of he plaes wihou a sample. For he presen insrumen, his correcion facor is found o be as low as which is almos negligible for a hermal insulaion value up o 2 digis. 3.2 Warm up Time o Sar a Tes To obain he recommended ime o sar a es, a jue nonwoven fabric was esed for abou 200 min. All he hree emperaures ( 1, 2, and 3 ) required o compue hermal resisance were ploed agains ime (Fig. 4). I is observed ha he source emperaure ( 1 ) becomes sable afer min. The hea ransmission reaches in is seady sae afer abou 150 min for he presen es sample. However, he ime o reach seady sae condiion depends upon he Fig. 4 Plo of hree emperaures agains ime ype of maerial and is hickness. I is, herefore, recommended o sar he es soon afer he source emperaure becomes sable. So, before saring a es he insrumen should be warmed up for a leas 30 min. 3.3 Repeaabiliy Tes The insrumen is based on microprocessor, which scans consecuive hree values of emperaure o idenify he seady sae condiion. The microprocessor is programmed in such a way ha when he range of hree consecuive hermal insulaion values is less han 0.01, he hermal resisance value, hus regisered, is sen o indicae he end of he es. Table 1 shows some saisical resuls based on he 6 daa repeaedly obained a a seady sae condiion, using a jue nonwoven fabric wih 3mm of hickness. I is observed ha he variabiliy crieria, such as range and variance, are very small. The variabiliy of emperaure recorded on hree plaes ( 1, 2 and 3 ) is almos negligible. This suggess ha he sensors used in he insrumen are measuring he emperaure correcly. The very low variabiliy of he og values also indicaes ha he hermal insulaion value is almos accurae in each ime of repea es of a sample. The range of he same indicaes a maximum error of 0.01 in hermal resisance value in he repea es. 3.4 Some Advanages of New Insrumen There are following advanages of he newly developed digial hermal insulaion value eser: The insrumen requires no preparaion of es samples if he area of he sample is no less han 700 cm 2. The es is non-desrucive and process of preparaion of sample is free from human error. The insrumen can be operaed a a maximum se poin of C. I may be prese a any inermediae poin wih an incremen of C. There is a provision in he insrumen o observe he hermal resisance value a any poin of ime of es. Table 1 Saisical resuls of emperaures and hermal resisance value Saisical parameer Mean Range Variance 1, C 2, 0 C 3, o C Compued hermal resisance value, og

5 40 INDIAN J. FIBRE TEXT. RES., MARCH 2009 The insrumen displays sensor emperaure a source, inermediae disc and op disc a an inerval of 10 s. I also displays he ambien emperaure. A provision has been made o use a buzzer o whisle afer every 10 min o indicae he duraion of es, which is iner alia displayed by a imer. The end poin of a es is declared by a non-sop whisle of he buzzer o draw he aenion of he operaor. The final resul in "og" is displayed, indicaed by he leers TrES. The final resul remains frozen unil rese. The resuls are displayed digially. I operaes wih a domesic supply of 230V, 50Hz. The samples like blanke, quil, carpe, wrapper, winer garmens as well as board, laminaed produc and paper can be esed on his insrumen. The samples of a wide range of hickness can be esed. The insrumen is handy, porable and requires no exra care for insallaion. 4 Conclusions I is a universal insrumen suiable for exile and non-exile maerials. I is no only a low cos and microprocessor based precision device, bu also have he advanage of non-desrucive, emplae free operaion as well. I can accommodae sample of wider range of hickness. The audio signal end-poin indicaion is a unique feaure of he insrumen. I has also he advanage of providing he incremenal rise of emperaure o aain he seady sae condiion for deerminaion of hermal resisance value of a sample. Indusrial Imporance: In view of he growing process for diversificaion of jue o apparel, winer garmens and oher winer proecive maerials, he new insrumen will be of much use and uiliy. Maerials like paricle board, false ceiling, able op, and pariion wall are also required o be hermally insulaed which require a quick and reliable measuremen as well. I is very much needed in indusrial applicaions where hese ypes of maerials are manufacured. Acknowledgemen The auhors are indebed and graeful o Dr. S K Bhaacharyya, Direcor, NIRJAFT, for his coninuous encouragemen and direc help in carrying ou he research work successfully. References 1 Prokop J, Texile, 25 (1969) Shinkai K, Suzuki A, Ohira M M & luagaki K, Bull Res Ins Polym Tex, May (1976) Geo Paul V & Mukhopadhyay M K, Indian J Tex Res, 2 (1977) Jokl M & Sverak J, Texile, 25 (1970) Zamolaev N P, Technol Tex Ind, USSR, 2 (1972) Sukharev M I & Haase J, Tekinol Legkoi Prom, 5 (1970) Mehods for deerminaion of hermal resisance of exiles, BS 4745 (Briish Sandards Insiue, Berkshire, U K), 1974.