Shell and Tube Heat Exchanger

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1 Sell and Tube Heat Excanger MECH595 Introduction to Heat Transfer Professor M. Zenouzi Prepared by: Andrew Demedeiros, Ryan Ferguson, Bradford Powers November 19,

2 Abstract 2

3 Contents Discussion of Teory:... 4 Experimental Apparatus and Procedure... 7 Experimental Data... 8 Results Discussion of Results

4 Discussion of Teory: A eat excanger is a device tat is used to transfer energy in te form of eat from one fluid to anoter. Tey take two input fluids of different temperatures and as te two fluids run near eac oter te fluids transfer eat between eac oter. Te eat excanger looks like a large pipe tat consists of 37 small tubes. Tey are used in various configurations for all sorts of applications suc as space eating, refrigeration, air conditioning, power plants, cemical plants, and petrocemical plants. Heat excangers can be used in two different configurations parallel flow, Figure 1, or counter flow, Figure 2. Figure 1 ~ Cocurrent flow Figure 2 ~ Counter current flow 4

Te eat excanger looks like a large pipe tat consists of 37 small tubes.

5 Eac configuration refers to ow te fluid moves troug teir respective flow passages relative to eac oter. If eac fluid is flowing in te same direction suc as in figure 1 it is termed a parallel flow. On te oter and if te fluids flow in opposite directions as in figure 2 it is termed counter flow. Parallel flow in eat excangers appens wen bot fluids enter te eat excanger at teir largest temperature difference. Te temperature difference becomes less over te lengt of te eat excanger. In te counter flow eat excanger, te fluids enter at opposite ends and terefore at different ends of te temperature scale Figure 2. As te fluids move troug te excanger, tey bot warm up or cool down at rougly te same rate. Te temperature differential between te two fluids is relatively constant over te lengt of te excanger. Te eat transfer process wic occurs in any basic eat excanger can be summarized by te following equations. Q = m c Qc = m cc F Q = R p pc T T ( LMTD) T c = F( UA)( LMTD) Were in te last equation F is te correction factor wic equals 1 for tis experiment. LMTD is te Log Mean Temperature Difference wic is described latter in tis section. Q is te eat transferred between te ot water and cold water. Te overall resistances can be calculated using: R = R + R + R T f w cf 5

Parallel flow in eat excangers appens wen bot fluids enter te eat excanger at teir largest temperature difference. Te temperature difference becomes less over te lengt of te eat excanger.

6 Were R R R f w cf 1 = A 1 [ D D ] ln 2 = 2πLk 1 = A c and from te above equations can be found using te appropriate Nusselt number for ot and cold water. For te ot water (fluid inner tubes) 2 c w 1 Nu K = Nu D = 0.023Re 0.8 Pr 0.3 For Cooling For te cold water K c c = Nu c D c 0.55 Nu = 0.36 Re Pr c c 0.33 c For Heating Te log-mean temperature difference is given by te following equation were a and b represent te ends of te eat excanger. Te LMTD is used because te eat must pass troug four resistances te ot tube to te cold water. Tm = ( Ta Tb ) ln( T T ) a b 6

7 Heat excanger effectiveness is defined as te ratio of te actual eat transfer rate of te praticlar eat excanger to te maximum possible eat transfer rate for te same unit. ε = Q Q max Q max = C min ( ) T i T ci Were C min is equal to eiter C c or C, wicever is smaller and are defined as, C = m c p and C c = m c c pc. C ε = C min ( Ti To ) ( T T ) i ci Experimental Apparatus and Procedure For tis experiment a HT30X Heat excanger services unit was used along wit an HT33 sell and tube eat excanger. Tis device included four K-type termocouples at te ot and cold inlet and outlets. Te excanger consisted of seven stainless steel tubes 6.35 mm in diameter wit a 0.6 mm wall tickness. Te outer annulus was constructed from clear acrylic tubing 39.0 mm inner diameter wit a 3.0 mm wall tickness. Te lengt of te tube bundle is 144 mm giving a total eat transfer area of 20,000 m 2. Te procedure for te laboratory is listed below. 1. Set te cold water pressure regulator. Adjust te knob until a flow rate of 3.00 liters per minute is establised. Lock down tis setting. 2. Prime te ot water circuit. Switc on te ot water circulating pump and expel any air bubbles. Do not let te water level fall below te eigt of te priming vessel to prevent air from entering te system. 7

C ε = C min ( Ti To ) ( T T ) i ci Experimental Apparatus and Procedure For tis experiment a HT30X Heat excanger services unit was used along wit an HT33 sell and tube eat excanger.

8 3. Set te computer software to countercurrent flow and maintain a ot water temperature of 60 F. Experimental Data Te results of te experiment are displayed in te tables below. Sample Calculations: Calculating ot water eat rate: m_cw m-t T in T out Tc in Tc out RUN l/s l/s C C C C Table 1 ~ Parallel flow temperature data m_cw m-t T in T out Tc in Tc out RUN l/s l/s C C C C Table 2 ~ Counter current flow temperature data Calculating cold water eat rate: 8

5 22.9 4 2.5 3 60.5 53.7 14.8 21.3 5 3 3 60.5 53.8 14.3 20.5 Table 1 ~ Parallel flow temperature data m_cw m-t T in T out Tc in Tc out RUN l/s l/s C C C C 1 1 3 61.3 56.6 15.1 28.

9 Calculating Reynolds Number: Calculating Nusselt Number: Calculating eat transfer coefficient: Calculating overall eat transfer coefficient: Calculating Log-Mean Temperature Difference: 9

10 Calculating eat transfer rate: Calculating maximum eat transfer: Calculating Efficiency: Results Hot Water Heat Rate Cold Water Heat Rate Run Q Run Q c W W W W W W W W W W Table 3 ~ Cocurrent Heat Rates 10

52.03833 W 1 56.99436 W 2 65.66742 W 2 61.9504 W 3 70.62345 W 3 69.

11 Hot Water Heat Rate Cold Water Heat Rate Run Q Run Q c W W W W W W W W W W Table 4 ~ Counter Current Heat Rates Total Termal Resistance (K/m) Total Resistance Cold Water Flow Rate (kg/s) Figure 3 ~ Total Termal Resistance 11

14544 W Table 4 ~ Counter Current Heat Rates 1.8 1.6 Total Termal Resistance (K/m) 1.4 1.2 1 0.8 0.

12 Heat Rate (W) Hot Water Heat Rate(Cocurrent) Hot Water Heat Rate (Concurrent) Cold Water Flow Rate (kg/s) Figure 4 ~ Hot Water Heat Rate Heat Rate (W) Heat Rate Cold Water (Cocurrent) Heat Rate Cold Water (Concurrent) Cold Water Flow Rate (kg/s) Figure 5 ~ Cold Water Heat Rate 12

5 Cold Water Flow Rate (kg/s) Figure 4 ~ Hot Water Heat Rate Heat Rate (W) 90 80 70 60 50 40 30

13 Heat Rate (W) Total Heat Rate (Cocurrent) Total Heat Rate (Concurrent) Cold Water Flow Rate (kg/s) Figure 6 ~ Total Heat Rate Efficiency Cocurrent Efficiency Concurrent Efficiency Cold Water Flow Rate (kg/s) Figure 7 ~ Excanger Efficiency 13

5 Cold Water Flow Rate (kg/s) Figure 6 ~ Total Heat Rate 8 7 6 Efficiency 5 4 3 2

14 Discussion of Results Te results of tis laboratory sow tat te effectiveness of te eat excanger is related to te cold-water flow rate. Tis is due to te decrease of termal resistance decreases wit increased cold water flow. Eac trend in te Figures 4 troug 7 above increases wit flow rate. Tere was no noticeable advantage to using counter current versus concurrent flow in te data. For eac run te data collected for eat transfer rate did not vary greatly. Conclusions Te data presented in tis report sows tat eat excanger performance increase linearly wit increasing cold water flow rate. Tis follows logically since more cold water is delivered to carry away eat per unit of time. Additionally increased flow rate results in more turbulent flow. Tis also increases te eat transfer rate. Contrary to eat excanger teory owever, tere was no noticeable difference in te eat transfer rate between parallel flow and counter current flow. Te counter current flow sould sow enanced eat transfer ability. 14

Tere was no noticeable advantage to using counter current versus concurrent flow in te data. For eac run te data collected for eat transfer rate did not vary greatly.

Heat Exchangers. Heat Exchanger Types. Heat Exchanger Types. Applied Heat Transfer Part Two. Topics of This chapter

Heat Exchangers. Heat Exchanger Types. Heat Exchanger Types. Applied Heat Transfer Part Two. Topics of This chapter Applied Heat Transfer Part Two Heat Excangers Dr. Amad RAMAZANI S.A. Associate Professor Sarif University of Tecnology انتقال حرارت کاربردی احمد رمضانی سعادت ا بادی Autumn, 1385 (2006) Ramazani, Heat Excangers