{"id":842,"date":"2014-05-06T08:27:11","date_gmt":"2014-05-06T06:27:11","guid":{"rendered":"http:\/\/cadredidactice.ub.ro\/gavrilalucian\/?p=842"},"modified":"2014-05-06T08:27:11","modified_gmt":"2014-05-06T06:27:11","slug":"tema-2-fenomene-de-transfer-2014-ipa-ib-ei-ipmi","status":"publish","type":"post","link":"https:\/\/cadredidactice.ub.ro\/gavrilalucian\/2014\/05\/06\/tema-2-fenomene-de-transfer-2014-ipa-ib-ei-ipmi\/","title":{"rendered":"Tema 2 Fenomene de transfer 2014 (IPA, IB, EI, IPMI)"},"content":{"rendered":"

\u00centr-o instala\u021bie de evaporare cu multiplu efect din industria laptelui se folose\u0219te un condensator de suprafa\u021b\u0103 \u00een care are loc condensarea vaporilor de ap\u0103 proveni\u021bi din ultimul evaporator. Condensatorul este un schimb\u0103tor de c\u0103ldur\u0103 cu fascicul tubular (SCFT) orizontal, echipat cu 301 \u021bevi confec\u021bionate din o\u021bel inoxidabil [\u03bbo\u021bel<\/sub> = 17,5 W\/(m\u00d7K)] av\u00e2nd \u00d8 = 55 \u00d7 2,5 mm \u0219i L = 4 m. Prin \u021bevi circul\u0103 4255 m3<\/sup>\/h ap\u0103 de r\u0103cire care se \u00eenc\u0103lze\u0219te de la 20 la 60\u02daC. Aburul care condenseaz\u0103 (Tcondensare<\/sub> = 120\u02daC) \u00een spa\u021biul dintre \u021bevi are un coeficient individual de transfer de c\u0103ldur\u0103 de 10 kW\/(m2<\/sup>\u00d7K). \u00cen decursul func\u021bion\u0103rii, \u00een \u021bevi se depune o crust\u0103 de piatr\u0103 de cazan cu grosimea de 0,5 mm \u0219i conductivitatea termic\u0103 de 1,16 W\/(m\u00d7K).<\/p>\n

Propriet\u0103\u021bile termofizice ale apei:<\/strong><\/em><\/p>\n\n\n\n\n\n
\n

T (K)<\/strong><\/p>\n<\/td>\n

\n

\u03c1 (kg\/L)<\/strong><\/p>\n<\/td>\n

\n

\u03bc (mPa\u00d7s)<\/strong><\/p>\n<\/td>\n

\n

\u03bb [W\/(m\u00d7K)]<\/strong><\/p>\n<\/td>\n

\n

cp<\/sub> [kJ\/(kg\u00d7K)]<\/strong><\/p>\n<\/td>\n<\/tr>\n

\n

293<\/p>\n<\/td>\n

\n

1<\/p>\n<\/td>\n

\n

1,000<\/p>\n<\/td>\n

\n

0,60<\/p>\n<\/td>\n

\n

4,18<\/p>\n<\/td>\n<\/tr>\n

\n

333<\/p>\n<\/td>\n

\n

0,98<\/p>\n<\/td>\n

\n

0,470<\/p>\n<\/td>\n

\n

0,66<\/p>\n<\/td>\n

\n

4,18<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Pe baza datelor de mai sus preciza\u021bi cine se modific\u0103 semnificativ<\/strong> (cu mai mult de \u00b1 10%) \u00een urma depunerii crustelor:<\/p>\n

    \n
  1. sec\u021biunea de curgere a apei;<\/li>\n
  2. viteza de curgere a apei;<\/li>\n
  3. aria total\u0103 de transfer de c\u0103ldur\u0103 a condensatorului;<\/li>\n
  4. coeficientul global de transfer de c\u0103ldur\u0103;<\/li>\n
  5. regimul de curgere al apei;<\/li>\n
  6. fluxul termic total transferat;<\/li>\n
  7. poten\u021bialul mediu al transferului termic.<\/li>\n<\/ol>\n

    Justifica\u021bi prin calcule r\u0103spunsurile date.<\/strong><\/p>\n

    IMPORTANT!<\/strong><\/span><\/p>\n