Scientific Herald of the Voronezh State University of Architecture and Civil Engineering. Construction and Architecture

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1 Scienific Herald of he Voronezh Sae Universiy of Archiecure and Civil Engineering. Consrucion and Archiecure UDC : Voronezh Sae Universiy of Archiecure and Civil Engineering Ph. D. applican of Dep. of Design of Auomobile Roads and Bridges A. N. Manaenkov Russia, Voronezh, el.: 8(4732) ; A. N. Manaenkov TECHNIQUE OF ESTIMATION OF THE REFRIGERATING CAPACITY OF SELF-ACTING COOLERS The echnique of definiion of refrigeraing capaciy of self-acing cooling plans applied in areas wih a severe climae as devices lowering deph of soils freezing is described. These devices are applied in he sruggle wih ice, criical shrinkage of he arificial srucures and oher phenomena conneced wih ground hawing. The resuls of experimenal measuremens obained by emulaion of phenomena occurring in he cooling plan are given. Keywords: calculaion of cooling plan, sruggle wih ice, Gapeev s plan, deerminaion of refrigeraing capaciy, alernaive design procedure. Inroducion Erecion of reliable insallaions on permanenly frozen soils is a complicaed echnical problem. The mos familiar self-acing cooling plans are single-ube, wo-ube, muliube, hree-ube (curved), muliube and single-ube coolers of S. I. Gapeev developed in design and survey insiue Lengiprorans. These coolers use kerosene as a hea ransfer agen [1, 2]. In presen, experimenal-heoreical formula of S. I. Gapeev is used for deerminaing refrigeraing capaciy [3]: ' " ' " Q 24 Vк Vк( ) q k k, (1) where 24 is he work of he cooler in winer, degree-hour; V k is he volume of kerosene, lire; ' is he emperaure of kerosene in he beginning of he cooler opera- 72

2 Issue 1 (5), 2010 ISSN " ion; is he average elevaed emperaure of kerosene (in winer); is he coefficien of kerosene volume measuremen; q is he hea capaciy of 1 lire of kerosene, degree-hour (depends on design o he cooler), calorie; is he coefficien considering he change in specific surface of kerosene cooling in ubes compared o pilo ' plan (increases wih decrease in diameer); k is he coefficien considering he influence of wind влияние ветра, i is aken o be equal o 1 0.1, where is he " wind speed, m/seс; k is he coefficien considering he raio of volume of kerosene in he upper plan (in he air) o he volume of kerosene in he boom plan (in he ground). I is aken o be equal o Vв М г. I should be noe however, ha calculaion echnique of he coolers has hardly been developed. I is based primarily on he use of he resuls of conduced experimens and correcion coefficiens whose naure and mehods of deerminaion are no clear [4]. In presen paper we aemp o consider generalized mehod of calculaion in accordance wih environmen parameers and cooler capaciy. In he scheme wih differen diameers of he ubes circulaion is susained hrough difference in emperaure (o be more exac, in specific weighs of kerosene) in he righ and in he lef branches (Fig. 1) [5]. As will be seen from he furher consideraion, emperaure drop is raher small. Therefore, average emperaure beween poins can be found from linear law Under hese assumpions, operaional head is equal o H ( ), (2) p h h1 where is he value of change in kerosene specific weigh for change. 0 1 of emperaure Going o he deerminaion of 1 and 3, i is necessary o keep in mind ha in his case i is no allowed o use linear dependence for errors o be avoided. 73

3 Scienific Herald of he Voronezh Sae Universiy of Archiecure and Civil Engineering. Consrucion and Archiecure Fig. 1. Calculaion scheme of a cooler A fixed volume of circulaion emperaures are compued from he Shukhov (Grasgof) formula: Rearranging gives: 3 r 1 в 1 r ; a 3 в. (3) в 1 (1 ) 1 1 ( 1) 1 в а 0 ( ав) а a ( 1) в ( ) r ( 1) 3 в r ( ав) ( ав) ( ав). (4) If soil emperaure is aken o be equal o r =0, formulae become simpler: ( ав) 3 в ( aв) а 1 ; 3 1. (5) а 74

4 Issue 1 (5), 2010 ISSN In hese formulae h ( K K ) K ' в в ; (6) W c W c ; 1 where W is he number of circulaing kerosene, kg/hour; с is he hea capaciy of kerosene, kilocalorie/kg degree Celsius; 1, 3 are emperaures of kerosene in poins 1 h 1 and 3; в is he air emperaure; r is he soil emperaure a a deph of ; K 'r is he 2 oal coefficien of hea ransfer from ground o he ubes; K ' в is he oal coefficien of hea ransfer from he ubes o air. K ' r и K ' в depend on many facors. Firs of all, i depends on ube di- Coefficiens ameer. Calculaions showed ha disance beween ubes is equal o 3D ; coefficien of inerference is abou for each ube. Hence, K ' r =1.25 K r. I is known ha coefficien of hea ransfer for verical cylinder is expressed by he formula K r 2 h, 2 h n where h is he heigh of he cylinder; is he radius of he cylinder; is he hea conduciviy of he ground. Going o he deerminaion of K ' в, i is necessary o noe ha value of K ' в depends firs of all on wind speed and is deermined by he formula (for one ube) K ' в h ( K K1) ; K ; K1 1, (8) ( d) 9.4 d, kilocalorie /m hour degree Celsius, (9) where is he wind speed, m/seс. In connecion wih high hermal ineria in he ground average wind speeds in winer (during 8 monhs) should be enered ino calculaion. Muual inerference of he ubes is no aken ino consideraion when calculaing air secion because of small value of he radiaion componen. 75 (7)

5 Scienific Herald of he Voronezh Sae Universiy of Archiecure and Civil Engineering. Consrucion and Archiecure To deermine he amoun of circulaing air and, herefore, he amoun of he hea, we need o define hydraulic characerisic of he plan: ( L ). (10) d Subsequen calculaion, as well as experimenal daa of Gapeev have shown ha kerosene movemen mode in ubes is laminar (Fig. 2). Fig. 2. Design of wo-ube cooler Hence, Then 2 2 P ( L ) 2 ( h1 h) Д 2g Д. (11) 2 g p (12) 2 H ) Д Д 2 H 76

6 Issue 1 (5), 2010 ISSN The following iniial condiions were aken: calculaion plan was made from ubes of diameer 76/89, of size h=2.0 m; h 1 =4.0 m; air emperaure в = C; wind speed v = 4 m/seс; ground emperaure г = 0 0 C. We obain hea capaciy of he plan Т = kilocalorie/hour ( kilojoules). To suppor he calculaions and o sudy he processes in he cooler during is operaion, we have developed pilo plan simulaing he working secion of he single-ube cooler. The pilo plan was modeled on he basis of cylindrical conainer made of ransparen glass o observe he processes going on in i. This cylinder reconsiues par of he single-ube cooler (Fig. 3). To reconsruc circulaion in he sysem, we have made wo secions: cooling secion and freezing secion. In cooling secion, ground needed for freezing is emulaed. To simulae his siuaion, we heaed he circulaing liquid o obain emperaure difference in poins 1 and 2. In freezing secion, amospheric air is emulaed in areas wih severe climae (in winer). To simulae his siuaion, we cooled he circulaing liquid in his secion. This helps o reconsruc naural condiions of cooler operaion. To analyze emperaure characerisics in poins 1 and 2, as well as o record he daa, we used wo-channel measuring insrumen: regulaor of ТРМ 202 ype in combinaion wih inpu ransducers (emperaure ransducers). The emperaure is measured o 1 decimal place wih daa reenion on PC. The circulaion speed is measured wih moion indicaor which is moved by circulaing flows. Refrigeraing capaciy is he cooler occurs in several sages: 1. Raed circulaing volume is deermined: Q 3600 V. 2. Temperaure difference in poins 1 and 2 is deermined. 3. Speed of kerosene circulaion is deermined: L. 77

7 Scienific Herald of he Voronezh Sae Universiy of Archiecure and Civil Engineering. Consrucion and Archiecure 4. Hea capaciy of he plan is deermined: T W ( Wc Q c, where is he densiy of kerosene; с is he hea capaciy of kerosene). c Fig. 3. Design of experimenal plan 78

8 Issue 1 (5), 2010 ISSN Comparison of heoreical and experimenal daa and heir reducion o one equivalen resul in he following: hea produciviy of he sysem during firs observaion is kilocalories /hour ( kilojoules); hea produciviy of he sysem during second observaion is 194,163 kilocalories /hour ( kilojoules); hea produciviy of he sysem during hird observaion is kilocalories/hour ( kilojoules). Comparing he resuls wih raed hea produciviy obained earlier ( kilojoules) we obain daa similar o experimenal ones ( kilojoules; kilojoules; kilojoules). Small discrepancies can be aribued o he simple mehod of conversion of he single-ube experimenal sysem o he wo-ube raed one. In addiion, errors involving visual conrol of he experimenal plan are possible. Summary The echnique of esimaion of he refrigeraing capaciy of self-acing coolers was obained and proved experimenally. This echnique is proposed as an alernaive o experimenal and heoreical mehod of Gapeev. References 1. Gapeev, S. I. Use of he naural cold in road consrucion. Moscow, pp. 2. Gapeev, S. I. Recommended measures and experimenal researches on cooling of permafros soils for he purpose of heir srenghening and increase of he upper bound of bedding. Circular 22. Leningrad, pp. 3. Gapeev, S. I. Guidance on designing, consrucion and operaion of arificial srucures of highways on waerways wih ice. Мoscow, pp. 4. Gapeev, S. I. Srenghening of frozen bases by cooling. Moscow, pp. 79