Energy Procedia 17 ( 2012 ) 741 – 749
1876-6102 © 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Hainan University. doi: 10.1016/j.egypro.2012.02.166
2012 International Conference on Future Electrical Power and Energy Systems
Experimental Investigation of Heat Transfer and Flowing
Resistance for Air Flow Cross over Spiral Finned Tube Heat
Exchanger
He FaJiang
1,2, Cao WeiWu
2, Yan Ping
21 School of Energy and Power Engineering,
University of Shanghai for Science and Technology, Shanghai 200093, China
2 College of Mechanical Engineering
Shanghai University of Engineering Science, Shanghai 201620, China
Abstract
In order to study heat transfer and flowing resistance characteristics for air flow cross over spiral finned tube heat exchanger, 13 spiral finned tube bundles heat exchangers are experimental investigated, the specimens have constant outer diameter of base tube (d=32mm), different fin pitch (t/d=0.22~0.5), fin height (h/d=0.22~0.5), transverse tube pitch (S1/d=2~3.3125), longitudinal tube pitch (S2/d=2~3.3125), the experiments are done within the range of fluid
flowing Re number (Re=5×103~5.5×104). Experiments obtain heat transfer Nusselt number correlation and flowing resistance Euler number correlation with fluid flowing Re number, fin pitch t, fin height h, transverse tube pitch S1,
and longitudinal tube pitch S2.
© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [name organizer] Keywords: Spiral finned tube; heat transfer; flow resistance; experimental investigation
1. Introduction
Spiral finned tube is a kind of high efficiency and extended surface enhanced heat transfer parts, spiral finned tube heat exchanger has characteristic of compact structure, it can efficiently enlarge heat transfer surface area, enhance heat transfer, improve economics and efficient of heat exchanger, and has been widely used in petroleum, metallurgy, chemical and power etc. industry fields.
© 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Hainan University.
Open access under CC BY-NC-ND license.
Jameson[1] experimental studied heat transfer characteristics of staggered layout spiral finned tubes in the range of fluid flowing Re number (Re=4×103~6×104), specimen parameters are d/t=1.03~2.45, h/t=1.5~3, S1/d=1.9~3.5, S2/d=1.03~2.45, heat transfer calculation figures and tables are obtained.
Fastovskiy and Retrovskiy[2] experimental studied heat transfer and flowing resistance characteristics of staggered layout spiral finned tubes in the range of fluid flowing Re number(Re<1×104), tube material is copper, fin material is aluminum, the row number of tube is 6, specimen parameters are t/d=0.17~0.27, h/d=0.31~0.51, S1/d=1.6~2.2, S2/d=1.4~1.9, cool air flow outside of tube and steam flow inside of tube,
heat transfer correlation is obtained by experiment.
Yudin and Tokhtarova[3,4] analyzed affection of structure and layout of spiral finned tubes to heat transfer, made heat transfer and flowing resistance characteristics experiments with 17 staggered and in-line layout spiral finned tubes in the range of fluid flowing Re number(Re=1×104~5×104), specimen parameters are d=32mm, h=9mm, t=6mm, S1/d=1.7~3
,
S2/d=1.2~3, experiment result is that heat transferof staggered layout spiral finned tubes is mainly effected by transverse tube pitch, and in-line layout spiral finned tubes is mainly effected by longitudinal tube pitch under the constant Re number
,
heat transfer of spiral finned tubes is also related to the structure of fin tube, heat transfer increases with the increasing of fin height.
D. E. Briggs and E. M. Young[5] experimental studied total rolling spiral finned tubes
,
heat transfer correlation of constant tube pitch is obtained.
Z. Mirkovic[6] experimental studied heat transfer characteristics of 13 staggered layout spiral finned tubes within the range of fluid flowing Re number calculated by hydraulic diameter (Re=1.6×103~3.1×104), the row number of tube is 5, specimen parameters are d=25.4~50.8mm, h/d˙ 0.18~0.67, t/d=0.083~0.17, S1/d=4~4.75, S2/d=2.37~3.14, heat transfer Nu number correlation and
flowing resistance Eu number correlations are obtained.
Ma QiLiang[7] experimental st
udied
heat transfer characteristics of staggered layout spiral finned tubes within the range of fluid flowing Re number(Re=6.1×103~5.3×104), the row number of tube is 5, specimen parameters are d=60mm, h˙17.7mm, t =5mm, S1/d=2.783, S2/d=2.5, heat transfer Nu numberand flowing resistance Eu number correlations are obtained.
Cao JiaShen[8] experimental studied heat transfer characteristics of 9 staggered layout spiral finned tubes, the row number of tube is 7, specimens have constant outer diameter of tube (d=29mm), various fin height, fin pitch, transverse tube pitch and longitudinal tube pitch, heat transfer Nu number and flowing resistance Eu number correlations are obtained.
Because structure and size of spiral finned tube heat exchangers and operating conditions of experiments are different, fluid flow is complicated, when fluid flows across over spiral finned tube, various calculation methods result to different results, therefore further investigation about heat transfer and flow resistance characteristics of spiral finned tube heat exchanger is necessary. According to studying on affection of structure of spiral finned tube on heat transfer and resistance investigations[9], in order to analyze effect of different structure layout and size of spiral finned tubes to heat transfer and flowing resistance characteristics, experimental investigations of spiral finned tube heat exchanger with various fin height, fin pitch, transverse tube pitch and longitudinal tube pitch will be made.
2. Experimental Principle
(a) Structure (b) Layout
Figure 1. Structure and layout of spiral finned tube
According to basic principle of heat transfer[10], quantity of heat convection of outer fin part of spiral finned tube is calculated as:
f f o o F f t t dF Q f ( )
³
D (1) Where˖Ff — fin surface area, m2 tf — fin surface temperature, ć to — outer fluid temperature, ć
Įo — heat transfer coefficient of tube outside, J/m2ć
Define fin efficiency˖
f wo o o f f o o F f t t F dF t t f ) ( ) (
³
D D K (2) Where˖two — outer surface temperature of tube, ć Substitution formula (2) to formula (1) and obtain:
f f o w o o f t t F Q D ( )K (3)
Quantity of heat convection of outer surface of tube˖
b wo o o b t t F Q D ( ) (4) Where˖
Fb — outer surface area of tube, m2
Therefore total heat quantity of spiral finned tube:
) )( (o wo f f b o b f Q t t F F Q Q D K (5) Namely˖ ) ( 1 b f f o wo o F F Q t t K D (6)
Heat conduction of tube:
w w w wi wo F Q t t O G (7) S1 S2 h d ¥ t
Where˖
twi — inner surface temperature of tube, ć įw — thickness of tube, m
Ȝw — conductivity efficiency of tube, J/mć Fw — average surface area of tube, m2
Convection heat transfer of inside surface of tube˖
2 1 F Q t t i i wi D (8) Where˖
F2 — inside surface area of tube, m2 ti — inside fluid temperature, ć
Įi — heat transfer coefficient of tube inside, J/m2ć Add Formula (6)-(8) and obtain:
2 1 ) ( 1 F F F F Q t t i w w w b f f o i o D O G K D (9) Namely˖ ) ( 1 1 2 b f f i w w w i o o F F F F Q t t » ¼ º « ¬ ª K D O G D (10)
3. Specimen and Experimental Method
3.1 Specimens
Specimens are made by high frequency welding technology. In order to experimental investigate heat transfer and flowing resistance characteristics of spiral finned tube, 13 specimens with different fin height, fin pitch, transverse tube pitch and longitudinal tube pitch are made, structure parameters of 13 spiral finned tubes are as flowing Table 1.
TABLE I. STRUCTURE PARAMETERS OF SPIRAL FINNEDTUBE
No. Tube Dia. d(mm) Fin Pitch t(mm) Fin Thk. ¥(mm) Fin Height h(mm) Trans. Tube Pitch S1(mm) Long. Tube Pitch S2(mm) 1 32 7 1.5 13 80 80 2 32 10 1.5 13 80 80 3 32 13 1.5 13 80 80 4 32 16 1.5 13 80 80 5 32 13 1.5 7 80 80 6 32 13 1.5 10 80 80 7 32 13 1.5 16 80 80 8 32 13 1.5 10 64 80 9 32 13 1.5 10 92 80 10 32 13 1.5 10 106 80 11 32 13 1.5 13 80 64 12 32 13 1.5 13 80 92 13 32 13 1.5 13 80 106
Specimens are staggered layout; longitudinal tube number of specimens is 9. Because of limitation of test section size, in order to eliminate the affection of fluid flow at wall area to heat transfer and flowing resistance characteristics, specimens are arranged half spiral finned tube according to different transverse distance S1.
3.2 Experimental system
Experiments are made in the wind tunnel of Shanghai University of Engineering Science. Experimental system is as following Figure 2.
1 Water tank 2 Water flow control valve 3 Water pump 4 Air blower 5 Heater 6 Air flow valve 7 Specimen
Figure 2. Experiment system of heat transfer wind tunnel
Experimental system is composed of air cycling system and cooling water cycling system. Air is pressured by blower 4, heated in electric heater 5, flows to test section, cooled by water in heat exchanger, flows back to blower 4 and forms cycling, air flow is adjusted by the valve 6. Water flows from the high water tank 1, pressured by pump 3, heated in the test section, flows back to water tank and form cycling, water flow is adjusted by the valve 2, cooling water flows inside of spiral finned tube, hot air flows outside of spiral finned tube. Air average temperature, outer diameter of tube is used as calculating parameters in the experimental data process.
4. Experimental Results
4.1 Relations of heat transfer and flowing resistance with fin pitch
Heat transfer Nu number and flowing resistance Eu number relations with Re number (Re=5×103~5.5×104) and fin pitch t under constant tube diameter (d=32mm), fin thickness (¥=1.5mm), fin height (h=13mm), transverse tube pitch S1=80mm(S1/d=2.5), longitudinal tube pitch S2=80mm
(S2/d=2.5) are as following Figure 3 and Figure 4. 1 2 3 4 5 6 7 P2 T T P V T T V
5H 1X W PP WG W PP WG W PP WG W PP WG
Figure 3. Nu number relations with Re and fin pitch t
5H (X W PP WG W PP WG W PP WG W PP WG
Figure 4. Eu number relations with Re and fin pitch t
4.2 Relations of heat transfer and flowing resistance with fin height
Heat transfer Nu number and flowing resistance Eu number relations with Re number (Re=5×103~5.5×104) and fin height h under constant tube diameter (d=32mm), fin thickness (¥=1.5mm), fin pitch (t=13mm), transverse tube pitch S1=80mm(S1/d=2.5), longitudinal tube pitch S2=80mm(S2/d=2.5)
are as following Figure 5 and Figure 6.
5H 1X K PP KG K PP KG K PP KG K PP KG Figure 5. Nu number relations with Re and fin height h
5H (X K PP KG K PP KG K PP KG K PP KG Figure 6. Eu number relations with Re and fin height h
4.3 Relations of heat transfer and flowing resistance with transverse tube pitch
Heat transfer Nu number and flowing resistance Eu number relations with Re number (Re=5×103~5.5×104) and transverse tube pitch S1 under constant tube diameter (d=32mm), fin thickness
(¥=1.5mm), fin pitch (t=13mm), pitch height (h=10mm), longitudinal tube pitch S2=80mm (S2/d=2.5)
are as following Figure7 and Figure 8.
5H 1X V PP VG V PP VG V PP VG V PP VG Figure 7. Nu number relations with Re and transverse tube pitch S1
5H EX V PP VG V PP VG V PP VG V PP VG
4.4 Relations of heat transfer and flowing resistance with longitudinal tube pitch
Heat transfer Nu number and flowing resistance Eu number relations with Re number (Re=5×103~5.5×104) and longitudinal tube pitch S2 under constant tube diameter (d=32mm), fin thickness
(¥=1.5mm), fin pitch (t=13mm), pitch height (h=10mm), transverse tube pitch S1=80mm (S1/d=2.5) are as
following Figure 9 and Figure 10.
5H 1X V PP VG V PP VG V PP VG V PP VG Figure 9. Nu number relations withRe and longitudinal tube pitch S2
5H (X V PP VG V PP VG V PP VG V PP VG Figure 10. Eu number relations withRe and longitudinal tube pitch S2
5. Conclusions
Heat transfer Nu number correlation with fluid flowing Re number, fin pitch t, fin height h, transverse tube pitch S1, longitudinal tube pitch S2 is experimentally derived as:
33 . 0 68 . 0 132 . 0 -168 . 0 194 . 0 -2 263 . 0 1 Pr Re × ) ( × ) ( × ) ( × ) ( × 138 . 0 = d h d t d S d S Nu
The correlation is suitable for: S1/d=2~3.3125, S2/d= 2~3.3125, t/d=0.22~0.5, h/d=0.22~0.5, Re=5×103~5.5×104.
Heat transfer Nu number increases with the increasing of fluid flowing Re number, transverse tube pitchS1 and fin pitch t; decreases with the increasing of transverse tube pitchS2 and fin pitch h.
Flowing resistance Eu number correlation with fluid flowing Re number, fin pitch t, fin height h, transverse tube pitch S1, longitudinal tube pitch S2 is experimentally derived as:
228 . 0 212 . 0 325 . 0 138 . 0 2 475 . 0 1 Re × ) ( × ) ( × ) ( × ) ( × 926 . 2 = d h d t d S d S Eu
The correlation is suitable for: S1/d=2~3.3125, S2/d= 2~3.3125, t/d=0.22~0.5, h/d=0.22~0.5, Re=5×103~5.5×104.
Flowing resistance Eu number decreases with the increasing of fluid flowing Re number, transverse tube pitch S1, longitudinal tube pitch S2and fin pitch t, Eu number increases with the increasing of fin
height h.
References
[1]S. L. Jameson, “Tube spacing in finned tube banks,” Trans. ASME, vol. 67, pp. 633–642, 1945. [2]V. G. Fastovskiy and Y. V. Petrovskiy, Modern effective heat exchangers, Moscow: GEI Press, 1962.
[3]V. F. Yudin and L. S Tokhtarova, “Investigation of heat transfer and drag of finned staggered bundles with different fin shapes,” Energomashinostroyeniye, vol. 12, pp. 352-365, 1964.
[4]V. F. Yudin and L. S. Tokhtrarova, “Heat transfer and drag of finned staggered bundles with different heights and pitches of fins,” Yrudy TsKTI(Polzunov boiler and turbine institute), vol.73, pp. 276-285, 1966.
[5]D. E. Briggs and E. H Young, “Convection heat transfer and pressure drop of air flowing across triangular pitch bands of finned tubes,” Chemical Engineering Progress Symposium Series, vol. 59, pp. 1-10, 1963.
[6]Z. Mirkovic, Heat transfer and flow resistance correlation for helically finned and staggered tube banks in cross-flow, heat exchangers: Design and theory source book, edited by N. Afgan and E.U. Schlunder, New York: Scripta book company, pp. 559-584, 1974.
[7]Ma QiLiang, Zhuo Ning, and Zhang CongXian, “The investigation on the heat transfer and pressure drop in the cross Air flow over high-frequency welded helically finned tube banks,” Journal of University of Shanghai For Science and Technology, vol. 5, pp. 15-28, 1983.
[8]Cao JiaShen, “Heat transfer and resistance properties for high frequency helically welding finned tube,” Dongfang Electric Review, vol. 8, pp. 78-81, 1994.
[9]He FaJiang and Cao WeiWu, “Research on influences of structure of spiral finned tube on characteristics of economizer,” Journal of Shanghai University of Engineering Science, vol. 16, pp. 1-5, 2002.
