)igure 1 Schematic of %rmfield HT10 ..................................................................3 )igure ! "hart of Solid S-here .............................................................................4 )igure / Biot number for Brass "ylinder .................................................................8 )igure 4 Biot number for Stainless steel cylinder .......................................................9 )igure Biot number for brass s-here ..................................................................10
2lot 1 Tem-erature +s Time .................................................................................7
2age 3 1
Shiyas Basheer "onduction
D10119909
$nsteady Heat
%BST,%"T This lab in+estigated the transient heat transfer due to conduction through a brass cylinder a stainless steel cylinder and a brass s-here5 The heat transfer coefficient 6h7 +alue for the s-here 8as calculated to be 05/;m !< 8hilst the h +alue for the cylinder 8as calculated to be !05//;m !<5 The e.-erimental thermal conducti+ity 6=7 +alue for stainless steel 8as determined to be /05>1;m< com-ared to a referenced +alue of 1;m<5 It also sho8s heat transfer change 8ith time5
2age 3 !
Shiyas Basheer "onduction
D10119909
$nsteady Heat
(B?'"TI@' To in+estigate and obser+e unsteady state heat conduction of t8o different solid geometries 8hen a ste- change is a--lied to the tem-erature at the surface of the sha-e5 The three -ieces 8hich 8ere tested includes: • •
% brass cylinder and stainless steel cylinder % brass s-here
(f the t8o geometries the brass cylinder and brass solid s-here 8ill be used to determine the h +alue for each geometries5 This 8ill be then used to determine the = +alue for stainless steel cylinder5
INT,(D$"TI(N This e.-eriment 8as carried out using an %rmfield e.-erimental a--aratus HT1> and a measurement unit HT10 8hich can be seen in figure 15
Figure 1 Schematic of Armfield HT10X
;ith the su--lied three sim-le sha-es such as solid cylinder solid s-here of 1 mm radius and the rectangular brass s-here of !mm radius three test 8ere carried out5 #easurements ta=en on a sha-e in one material can be used to confirm the conducti+ity of a similar sha-e constructed from a different material5 TransientAtem-erature heat flo8 charts are su--lied for each of the sha-es5
2age 3 /
Shiyas Basheer "onduction
D10119909
$nsteady Heat
The a--aratus consists of a /0 litres +olume insulated 8ater bath5 %t the end of the bath is an electric heater controlled by a thermostat so that a constant bath tem-erature can be obtained5 % small -um- is located near the side of the 8ater bath and is used to circulate the 8ater inside the bath5 The -um- s-eed is controlled by setting the +oltage 60A!4 @7 on the HTA10 control console5 The circulation of the 8ater in the bath ensures that the tem-erature of the 8ater in the +icinity of the test s-ecimen is constant5 The 8ater tem-erature is controlled by a rotary s8itch located on the front of the bath5 The tem-erature of the 8ater in the bath is indicated by a thermocou-le5 %nother thermocou-le measures the tem-erature embedded in the centre of the test s-ecimen 1C5
TH'(, Heat transfer often occurs in an unsteady state conditions or a transient state5 It sim-ly means a function of time and the analytical solution are a+ailable for the tem-erature distribution and heat flo8 of +arious solid sha-es 8hich are sub*ected to sudden con+ection 8ith a fluid at a constant tem-erature5 Sol+ing these ty-es of -roblems often in+ol+es using unsteady heat transfer charts such as the one sho8n in )igure ! for a long cylinder of radius b 8here the 8hole surface is sub*ected to a change in tem-erature:
Figure 2 Chart of Solid Sphere
The horiEontal a.is F re-resents the )ourier number or dimensionless time the +ertical a.is is dimensionless tem-erature G and the slanted lines re-resents the in+erse of the Biot number 6Bi75 'ach can be identified by a formulae as follo8s: 2age 3 4
Shiyas Basheer "onduction
θ=
$nsteady Heat
T ( r , t )−T ∞ T i− T ∞
Bi =
τ =
D10119909
hb k
αt 2
b
;here: k
Thermal conducti+ity
6;mA1"A17
α The thermal diffusi+ity
6m!sA17
h
6;mA!"A17
The heat transfer coefficient
t Time ste-
6s7
T60t7 Tem-erature at the centre of the cylinder
6"7
Ti Initial tem-erature of the cylinder
6"7
b ,adius of the cylinder
6m7
T ∞ Tem-erature of the 8ater bath
6"7
The follo8ing 8ere gi+en: α for brass /5>.10 A m!sA1 α for stainless steel 05.10A m!sA1
= for brass 1!1;m A!"A1
#'TH(D The follo8ing -rocedures 8ere done to conduct this e.-eriment: •
The 8ater heater 8as first chec=ed to be filled 8ith 8ater and then the electrical su--ly 8as turned on to heat the 8ater5
2age 3
Shiyas Basheer "onduction •
• • •
D10119909
$nsteady Heat
The red light 8as chec=ed to ensure that the electrical -o8er 8as connected to the unit and the thermostat on the 8ater heater 8as set to -osition 45 The +oltage 8as set to 1!@ for the circulating -um-5 The tem-erature of the 8ater 8as allo8ed to stabiliEe bet8een 0A90"5 The tem-erature of the geometry 8as obtained and allo8ed to stabiliEe at room
•
tem-erature before being immersed in the 8ater bath5 The initial tem-erature of the 8ater bath and the center of the geometry 8as recorded The sha-e 8as then immersed into the 8ater bath The tem-erature 8as then obtained for e+ery second inter+al till the center reached
•
0"5 This 8as then re-eated for the other geometries and materials
• •
,'S$&TS The results obtained from the e.-eriment can be seen in Table 1 J Table ! and a -lot of the tem-erature against time for all three materials can be seen in 2lot 1:
It can be seen from the table abo+e that the = +alue of Stainless steel cylinder is significantly smaller than that of brass cylinder that also has a similar geometry5 It can also be seen that the Stainless steel cylinder too= the longest to reach the target tem-erature of 0 o"5 These differences might be due to the fact that the Stainless steel has lo8 thermal conducti+ity than that of brass5 It can also be noted that the brass S-here has a high heat transfer coefficient than that of brass cylinder and also it ta=es longer to reach the target tem-erature of 0 o"5 This could be due to the s-here ha+ing a lo8er surface area than the cylinder5 )rom 2lot 1 earlier in the results section it can be seen that the gra-h doesnMt ha+e liner lines but cur+ed ones 8hich sho8s that the unsteady state conditions e.ists5 Ho8e+er there is a considerable difference bet8een the e.-erimental thermal conducti+ity of stainless steel cylinder of /05>1 ;m< and the referenced thermal conducti+ity of 1 ;m< 1C5 This error might be due to the follo8ing reasons: • • • • •
'rror in measurement of tem-erature and time 'Kui-ment error Inaccuracies in using the chart Human error The stainless steel used in the a--aratus might ha+e a different com-osition to the one used to calculate the referenced = +alue5
"(N"&$SI(N The e.-eriment demonstrated unsteady or transient heat transfer5 Based on the results the follo8ing can be concluded: •
$nsteady heat transfer e.ists and it de-ends on both the geometry and the material used 2age 3 1!
Shiyas Basheer "onduction
D10119909
$nsteady Heat
•
Same material 8ith different geometries ha+e different heat transfer coefficient under
• •
same conditions Different materials 8ith same geometry beha+e differently under the same conditions The e.-erimental = +alue for stainless steel 8as determined to be /05>1;m<
•
com-ared to a referenced +alue of 1;m<5 $nsteady heat transfer changes 8ith time and is nonlinear
