Double Pipe Heat Exchanger

PARALLEL FLOW / COUNTERFLOW HEAT EXCHANGER  A!" (a) Calculate Heat -Transfer rate by using Parallel flow & Counter flow heat exchanger. (b) Compare the alues of ! Tm & " in parallel and counter flow runs. THEOR#" Heat exchangers are deices in which heat is transferre transferred d from one fluid to another. another. The  process of exchanging heat between two .different fluid s is one of the most important and fre"uently used process found in many industries. The necessity for doing this# arises in a magnitude magnitude of industrial industrial applications. applications. Common examples of heat exchangers exchangers are the radiator of a car# the condenser at the bac$ of a refrigerator and the steam boiler of a thermal power plant. Heat exchangers are classified into three categories% . Transfer type. '. torage type. . *irect contact type. + transfer type of heat exchanger is one on which both fluids pass simultaneously through the deice and heat is transferred through separating walls. ,n practice most of  heat exchangers used are transfer type .Transfer type heat exchanger are further classified according to flow arrangement as% Parallel flow in which fluids flow in the same direction. Counter flow in which fluids flow in opposite direction. Cross flow in which fluids flow at right angles to each other.

Hot fluid out

Hot fluid in

Cold fluid in

Cold fluid out Parallel flow Heat Exchanger

Hot fluid in

Hot fluid out

Cold fluid out

Cold fluid in Counter flow Heat Exchanger

Thi

Tco Tco

Tho Cro$$ Flow Heat Exchanger

Te%&erature &rof'le$" C+-l hen a fluid at a constant temp. gies heat to a colder fluid whose temp gradually increases. C+-' hen a fluid at a constant temp. getting heated from a warmer fluid whose temp. gradually decreases. C+- hen a fluid gradually loosing heat and another fluid gradually gaining heat such system li$e water heater.

!T'

! Tm / (! T 0! T') 1 (ln ! T 1! T')

Temp. Thi

!T Tco +r 

+ simple xample of transfer type heat exchanger can be in the form of tube type arrangement in which one of the fluids is flowing through the inner tube and the other  through the annulus surroundings it . The heat transfer ta$es place across the walls of the inner tube. PROCE(URE" . Place the thermometers in position and note down their readings when they are at room temp. and no water is flowing at either side. This is re"uired to correct the temp. '. tart the flow on the hot water side. . tart the flow through annulus and the run the exchanger either as parallel flow unit. 2. Put on the geyser.

3. +d4ust the flow rate on hot water side #between the rate of .3 to 2 litre per  minute. 5. +d4ust the flow rate on cold water side #between the rate of  to 6 litre per minute. 7. 8eeping the flow rates same# wait till the steady state conditions are reached. 6. 9ecord the temps. on hot water and cold side and also the flow rates accurately. :. Ta$e the readings with different flow rates. ;. 9epeat the experiment with a counter flow under identical flow conditions. O)*ER+ATON* ,nner tube material / copper < ,* / :.3 mm# =* / '.7 mm >ength of Heat xchanger / .5 meter. (a) P+9+>>> ?>= 9@A .A. H=T +T9 ,* C=>* +T9 ,* ; ; ?low rate Thi C Tho C ?low rate Tci ;C Bh 8g1hr  Bh 8g1hr 

(b) C=@AT9 ?>= 9@A .A. H=T +T9 ,* ?low rate Thi ;C Bh 8g1hr 

;

Tho C

C=>* +T9 ,* ?low rate Tci ;C Bh 8g1hr 

Tco ;C

Tco ;C

C+>C@>+T,=A% ', Heat tran$fer rate '$ calculate- a$" "h / Heat transfer rate from hot water  / mh C ph( T hi 0 Tho)8cal1 hr. "c / Heat transfer rate from cold water  / mc C pc( T co 0 Tci)8cal1 hr. " / ("h  "c) 1 ' 8cal1hr. +ssume C ph/ C pc / 8cal1$g-Dc '',Logar'th%'c %ean te%&erature -'fference .L!T(, '$ calculate- a$  follows% >BT* / ! Tm / (! Ti 0! To) 1 ln (! Ti 1 ! To) ''', Oer all heat tran$fer coeff'c'ent can 0e calculate- 01 u$'ng2 " / @ + Tm @ / " 1 + ! Tm 8cal 1 hr-m' - ;C Calculate @ri based on +i / E di >

@ri based on +o / E do > ,) Compare the alues of ! Tm & " in the parallel flow and counter flow runs.  Aote that if experiment is conducted ery carefully then the superiority of counter flow +rrangement in terms of higher alue of Tm and excess alue of " for same flow rates conditions can be reealed. PRECAUTON*" . *uring the complete experimentation open the ales of geyser before starting it. '. ?or parallel flow open the ales F& F#and close . ales F' & F2. . ?or counter flow open the ales F'&F2and close ales F, & F.