## Continue your professional development with Scribd

Exclusive 60 day trial to the world's largest digital library.

Join 1+ million members and get unlimited* access to books, audiobooks.

Cancel anytime.

Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our User Agreement and Privacy Policy.

Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our Privacy Policy and User Agreement for details.

Successfully reported this slideshow.

Like this document? Why not share!

- Plate type heat exchanger by Pankaj Nishant 25195 views
- Design Considerations for Plate Typ... by Arun Sarasan 11352 views
- Gasketed plate heat exchanger by Mohammed Hamza, M... 3571 views
- Plate heat exchangers by tst34 12053 views
- HEAT EXCHANGERS by Akshay Kumar Mishra 18833 views
- Heat exchangers by Ammar Ashraf 68721 views

Just added to SlideShare
##
Continue your professional development with Scribd

Exclusive 60 day trial to the world's largest digital library.

Join 1+ million members and get unlimited* access to books, audiobooks.

Cancel anytime.

This design project aims to propose a plate type heat exchanger that can meet given heat duty and find the number of plates required. Plate type heat exchanger uses metal plates to transfer heat between two fluids. Starting point of this design is to define given properties

No Downloads

Total views

10,983

On SlideShare

0

From Embeds

0

Number of Embeds

19

Shares

0

Downloads

582

Comments

0

Likes

20

No notes for slide

- 1. 1 REPORT TO DEPARTMENT OF CHEMICAL ENGINEERING MIDDLE EAST TECHNICAL UNIVERSITY FOR COURSE: CHE-327 HEAT AND MASS TRANSFER OPERATIONS PLATE TYPE HEAT EXCHANGER DESIGN GROUP MEMBERS: ALARA MELISA AYDIN COŞKU MOLER RESKY SAPUTRA METU (25.05.2016) Ankara, TURKEY
- 2. 2 ABSTRACT This design project aims to propose a plate type heat exchanger that can meet given heat duty and find the number of plates required. Plate type heat exchanger uses metal plates to transfer heat between two fluids. Starting point of this design is to define given properties. It is asked us to cool the inlet fluid which is waste stream from 65 oCto 40 oCusing cooling water at 15 oC.Several information of the inlet and outlet streams are given such as the inlet and outlet temperature of waste stream, mass flow rate of inlet stream, physical properties of waste and other constructional data for the similar heat exchanger; vertical, horizontal distances, plate thickness, length, effective channel width, enlargement factor, chevron angle etc. Several calculations are done in 2 parts. The first one is geometry analysis used in order to find the required number of plates. The second one is heat transfer analysis in order to find the required heat duty for both streams and actual heat duties for clean and fouled involving trial-error solution. Some correlations is needed such as heat transfer coefficient calculation, correlation of Nusselt number and Reynold number in which the empirical equation needed. Assumptions are regarded at the beginning of the design. Finally, the required heat duty for cold and hot streams are found 1.47 x 107 W and the actual heat duties for clean and fouled are 2.62 x 107 W and 2.32 x 107 W, respectively. The total required number of plates are also found as 105 plates.
- 3. 3 TABLE OF CONTENT TABLE OF CONTENTS NOMENCLATURE…………………………………………………………………………1 1. INTRODUCTION …………………………………………………………………..3 1.1. Problem Statement……………………………………………………………...4 1.2. The Calculation Method………………………………………………………..5 1.3. Assumptions……………………………………………………………………..8 2. SAMPLE CALCULATIONS…………………………………………………………10 2.1. Geometry Analysis………………………………………………………………10 2.2. Heat Transfer Analysis………………………………………………………….11 3. RESULT AND DISCUSSIONS……………………………………………………….14 4. CONCLUSIONS……………………………………………………………………….16 5. REFERENCES…………………………………………………………………………17
- 4. 4 NOMENCLATURE Thi : inlet hot stream temperature 0c Tho : outlet hot stream temperature 0c Tci : inlet cold stream temperature 0c Tco : outlet cold stream temperature 0c mc : cold stream mass flow rate kg/s mh : hot stream mass flow rate kg/s Gc : The cold channel mass velocity kg/m2s Gh : The hot channel mass velocity kg/m2s Ch : steam heat capacity J/kg.K Cc : ipa-water mixture heat capacity J/kg.K Qc : Amount of heat transfer under clean condition W Qf : Amount of heat transfer under fouled condition W Uf : Fouled overall heat transfer coefficient W/m2K Uc : overall heat transfer coefficient W/m2K Ae : Actual effective area m2 A1 : Single plate efective area m2 A1p : Single plate projected area m2 Nt : total number of plates Ne : The effective number of plates Np : Number of passes Ncp : the total number of channels per pass Lv : Vertical distance m
- 5. 5 Lh : Horizontal distance m t : Plate thickness m Lc : Plate pack length m Lw : Effective channel width m p : The plate pitch m b : the mean channel spacing m Dh : The hydraulic diameter of the channel m ∅ : The enlargement factor 𝛽 : Chevron angle o µh : viscocity of hot fluid N.s/m2 µc : viscocity of cold fluid N.s/m2 Pr : prandalt number Re : reynolds number Nu : nusselt number hc : convective heat transfer coefficient on clod fluid W.m2/K hh : convective heat transfer coefficient on hot fluid W.m2/K 𝑅𝑓ℎ : fouling factor for hot fluid m2.K/W 𝑅𝑓𝑐 : fouling factor for cold fluid m2.K/W kw : thermal conductivity of the plate material W/m.K
- 6. 6 1. INTRODUCTION Plate heat exchanger is a type of Heat Exchanger which consists of many corrugated stainless-steel sheets separated by polymer gaskets and clamped into a steel frame. It transfers heat by placing thin, corrugated metal sheets side by side and connecting them by gaskets. Flow of the substances to be heated and cooled takes place between alternating sheets allowing heat to transfer through the metal sheets. Figure 1: Plate type heat exchanger Some advantages using plate heat exchanger are high heat transfer area, high heat transfer coefficient, having lower floor space requirements, multiple duties can be performed by a single unit, most suitable type heat exchanger for lower flow rates and heat sensitive substances. Moreover, area of heat transfer of plate heat exchanger can be increased by increasing the number of the plates.
- 7. 7 1.1. Problem Statement In this problem, a plate heat exchanger is needed to be designed for a specific purpose. This heat exchanger should be able to cool a waste from 65°C to 40°C using cooling water which enters the heat exchanger at 15°C. The mass flow rate of the waste stream is 140 kg/s and its properties may be approximated as follows: ρ = 985 kg/m3 μ = 510 x 10-6 kg/m.s k = 0.650 W/m.K Pr = 3.3 Cp = 4200 J/kg.K Fouling resistance ≡ Fouling resistance of water= 0.0000069 m2.K/W (taken from Heat Exchanger: Selection, Rating and Thermal Design, table 10.4) Moreover, we are going to propose a plate type heat exchanger that can meet this heat duty and find the number of plats required for the heat exchanger. Some constructional data for a similar heat exchanger are given as follows: Total effective area (Ae)= 110 m2 Vertical distance (Lv) = 1.55 m Horizontal distance (Lh)= 0.43 m Plate thickness (t)= 0.6 mm Plate pack length (Lc)= 0.38 m Effective channel width (Lw)= 0.63 m Enlargement factor (∅)= 1.25 Chevron angle (𝛽 )= 45°
- 8. 8 Plates are stainless steel (kw = 16.5 W/m.K, taken from heat exchangers selection, Rating and thermal design, table 10.1) Figure 2: Main dimensions of a chevron plate and and developed and projected dimensions of a chevron plate cross section normal to to the direction troughs. 1.2. The Calculation Method; Calculation of this problem design are separated by 2 analysis. The first one is geometry analysis. The channels increase the surface area of the plate as compared to the original flat area. To express the increase of the developed length in relation to the projected length, a surface enlargement factor,∅, is the defined as the ratio of the developed length to the flat or projected length ∅ = 𝐷𝑒𝑣𝑒𝑙𝑜𝑝𝑒𝑑 𝑙𝑒𝑛𝑔𝑡ℎ 𝑃𝑟𝑜𝑗𝑒𝑐𝑡𝑒𝑑 𝑙𝑒𝑛𝑔𝑡ℎ = 𝐴𝑐𝑡𝑢𝑎𝑙 𝑒𝑓𝑓𝑒𝑐𝑡𝑖𝑣𝑒 𝑎𝑟𝑒𝑎 𝑝𝑟𝑜𝑗𝑒𝑐𝑡𝑒𝑑 𝑝𝑙𝑎𝑡𝑒 𝑎𝑟𝑒𝑎 =A1/A1p (1.1)
- 9. 9 Where Actual effective area can be calculated as (1.2) Actual effective area (Ae) = Lp * Lw (1.2) Or actual effective area can be calculated as Ae = A1 * Ne Where the effective number of plates. Ne,can be estimated as Ne = Nt – 2 Also Lp and Lw can be estimated from the port distance Lv and Lh and port diameter Dp as Lp ≈ Lv - Dp (1.3) Lw ≈ Lh + Dp (1.4) The value of enlargement factor is calculated the effective flow path. From (1.3 and 1.4) we can make a new equation to find Lp. Lp = Lv – Lw + Lh (1.5) Flow channel is the conduit formed by two adjacent plates between the gaskets. The cross section of a corrugated surface being very complex, the mean channel spacing, b, is defined as (1.6) b = p –t (1.6) The plate pitch (p) can be determined from the compressed plate pack length (Lc), which usually specified. p = Lc / Nt (1.7) Where Nt is the total number of plates. The hydraulic diameter of the channel (Dh) can be estimated as (1.8) Dh ≈ 2b / ∅ (1.8) Finding the total number of channels per pass (Ncp) is obtained from (1.9) Ncp = (Nt – 1) / 2 *Np (1.9) Where Nt is total number of plates and Np is the number of passes.
- 10. 10 From those correlations we can find total number of plates required. With plate type heat exchangers, heat transfer is enhanced. The heat transfer enhancement will strongly depend on the chevron inclination angle (𝛽) relative to flow direction. Moreover, the performance of a chevron plate will also depend upon the surface enlargement factor (∅), the channel profile, the mean channel spacing (b), the temperature dependent physical properties, and especially the variable viscosity effects. The second one is heat transfer analysis. In order to find heat transfer coefficient (h), correlation of Nusselt number (Nu) and Reynold number (Re) is needed. The Reynolds number based on channel mass velocity and the hydraulic diameter of the channel is defined as (1.10) Re = Gc * Dh / 𝜇 (1.10) Where the channel mass velocity is given by (1.11) Gc = mch / Ncp * b * Lw (1.11) Correlation empirical equation is needed. The correlation in the form of (1.12) are proposed by Kumar and the values of constants Ch and n are given in table 1.1 (Heat exchangers:Selection, Rating and Thermal design 2nded, p. 395) Nu = Ch * Ren * Pr * ( 𝜇 𝜇 𝑤 )0.17 (1.12) Table 1.1. Constants for single-phase heat transfer and pressure loss calculation in gasketed-plate heat exchanger (Heat exchangers:Selection, Rating and Thermal design 2nded, p. 394).
- 11. 11 Overall heat transfer coefficient under fouling conditions is calculated as (1.13) 1 𝑈 𝑓 = 1 ℎℎ + 1 ℎ 𝑐 + 𝑡 𝑘 𝑤 + 𝑅𝑓ℎ + 𝑅𝑓𝑐 (1.13) The required heat duty (Qr) for cold and hot streams is defined as (1.14) Qr = (𝑚̇ ∗ 𝐶𝑝)c *(Tc2 – Tc1) = (𝑚̇ ∗ 𝐶𝑝)h * (Th1 – Th2) (1.14) On the other hand, the actually obtained heat duty (Qf) for fouled conditions is defined as (1.15) Qf = U*Ae*F*∆𝑇𝑙𝑚 (1.15) In order to find ∆𝑇𝑙𝑚, equation (1.16) is defined as ∆𝑇𝑙𝑚 = ( 𝑇ℎ,𝑖𝑛 −𝑇𝑐,𝑜𝑢𝑡)−(𝑇ℎ ,𝑜𝑢𝑡−𝑇 𝐶,𝑖𝑛 ) ln( ( 𝑇ℎ,𝑖𝑛−𝑇 𝑐,𝑜𝑢𝑡 ) (𝑇ℎ,𝑜𝑢𝑡−𝑇 𝐶,𝑖𝑛) (1.16) For heat transfer analysis we are not given 𝑇𝑐,𝑜𝑢𝑡. So that physical properties of water cannot be decided. Hereby trial-error solution is needed to find the correct 𝑇𝑐,𝑜𝑢𝑡 . To determine the correct one we need to check both the required heat of hot and cold fluid. From energy balance analysis, the required heat of hot and cold fluid must be same. The calculation for trial-error solution stops until it reaches the equality of the required heat of hot and cold fluid. 1.3. Assumptions; Physical properties are constant at 1 atm Heat loses to or from the surrounding are negligible. The kinetic and potential energy changes are negligible. The heat exchanger operates at steady-state conditions. No phase changes in the fluid streams. Wall thermal resistances are distributed uniformly. The velocity and temperature at the inlet of the heat exchanger on each fluid side are uniform. The heat transfer area (A) is distributed uniformly on each fluid side.
- 12. 12 The cold and hot stream mass flow rate are same Number of passes is one pass
- 13. 13 2. SAMPLE CALCULATIONS 2.1 Geometry Analysis The projected plate area Single plate heat transfer area The effective number of plates Total number of plates The plate pitch the mean channel flow gap The one channel flow area The channel hydraulic Ae 110m 2 Lv 1.55m Lh 0.43m t 0.0006m Lc 0.38m Lw 0.63m kw 16.5 W m K Np 1 Lp Lv Lw Lh 1.35m A1p Lp Lw 0.851m 2 A1 A1p 1.063m 2 Ne Ae A1 103.469 Nt Ne 2 105.469 p Lc Nt 3.603 10 3 m b p t 3.003 10 3 m Ach b Lw 1.892 10 3 m 2 Dh 2 b 4.805 10 3 m
- 14. 14 2.2 Heat Transfer Analysis Total number pf channel per pass (Trial-error method) water properties at 313/288 = 300.5 K waste properties The mass flow rate per channel for hot fluid for cold fluid Ncp Nt 1 2 Np 52.234 assume 8.410 4 Pa s k 0.611 W m K mc 140 kg s Pr Cpc k 5.748 Rfwater 0.0000069 m 2 K W Cpwaste 4200 J kg K kwaste 0.650 W m K Prwaste 3.3 waste 51010 6 Pa s Rfwaste Rfwater 6.9 10 6 s 3 K kg mh mc 140 kg s mch mc Ncp 2.68 kg s Gch mch Ach 1.417 10 3 kg s m 2 Gcc Gch 1.417 10 3 kg s m 2 Reh Gch Dh waste 1.335 10 4 Rec Gcc Dh 8.103 10 3 Cpc 4185.847 J kg K Tco 40 273 313K Tci 15 273 288K Thi 65 273 338K Tho 40 273 313K
- 15. 15 Since Qrh and Qrc is almost same, then Tco assumption is acceptable Table 10.6 or hhot= 3.283x104 W/m2K or hcold=2.669x104 W/m2K The clean overall heat transfer coefficient or W/m2K The fouled overall heat transfer coefficient for counter current flow the actual heat duties for clean and fouled surfaces The required heat 45 0 Reh 100 Rec 100 ch 0.3 n 0.663 hhot kwaste Dh ch Reh n Prwaste 1 3 3.283 10 4 kg s 3 K hcold k Dh ch Rec n Pr 1 3 2.668 10 4 kg s 3 K Uc 1 1 hcold 1 hhot t kw 9.587 10 3 kg s 3 K 9.587 10 3 Uf 1 1 Uc Rfwaste Rfwater 8.467 10 3 kg s 3 K T2 Tho Tci 25K T1 Thi Tco 25K LMT D 25K Qc Uc Ae LMTD 2.636 10 7 W Qf Uf Ae LMTD 2.328 10 7 W Qrh mh Cpwaste Thi Tho( ) 1.47 10 7 W Qrc mc Cpc Tco Tci( ) 1.465 10 7 W
- 16. 16 The safety factor The precent over surface design The cleanliness factor Cs Qf Qrh 1.584 OS 100Uc Rfwaste Rfwater( ) 13.23 CF Uf Uc 0.883
- 17. 17 3 RESULTS AND DISCUSSONS Objective of this project was to design a proper plate type heat exchanger. Several assumptions were made while making the calculations. These assumptions are constant physical properties at 1 atm, negligible heat losses through the surroundings, negligible kinetic and potential energy changes, operating at steady state, no phase changes, same mass flow rates and, uniform temperature and velocity at the inlet of the heat exchanger. Calculation of this problem design are separated by 2 analysis. The first one is geometry analysis and the second one is heat transfer analysis. Geometry is analyzed by the given datas and calculations were made according to these given datas. First of all projected length was calculated as 1.35 m and then projected area was determined as 0.851 𝑚2 , by using this value single plate heat transfer area was calculated by enlargement factor times projected area, enlargement factor,∅, is the defined as the ratio of the developed length to the flat or projected length and found as 1.25. Up to here effective area and single plate heat transfer area was calculated number of effective plates was found as 103.469 by dividing effective area by single plate heat transfer area. Then total number of plates were found as 105.469. After that plate pitch was determined as 3.603 ∗ 10−3 𝑚 and mean flow channel gap was found by using that one as 3.003 ∗ 10−3 𝑚. The one channel flow area was determined by using mean flow channel gap and found as 1.892 ∗ 10−3 𝑚2 hydraulic diameter was calculated by 2 mean flow channel gap divided by enlargement factor and found as 4.805 ∗ 10−3 𝑚. Lastly total number pf channel per pass was found as 52.234 and the geometry calculations were done. In the heat transfer analyses in order to find heat transfer coefficient (h), correlation of Nusselt number (Nu) and Reynold number (Re) is needed. The Reynolds number based on channel mass velocity and the hydraulic diameter of the channel is defined as Re for hot fluid was determined as 1.335 ∗ 104 and 8.303 ∗ 103 for the cold fluid. Where the channel mass velocity is given by Gc 1.417 ∗ 103 𝑘𝑔 𝑚2 ∗𝑠 for both hot and cold fluid. In calculation of Nusselt number Correlation empirical equation is needed. The correlation in the form of (1.12) are proposed by Kumar and the values of constants Ch and n are given in table 1.1. This correlation gave us the heat transfer coefficients directly by using Nusselt number as 3.283 ∗ 104 𝑊 𝑚2∗𝐾 for hot 2.668 ∗ 104 𝑊 𝑚2∗𝐾 for cold fluid. By using these heat transfer coefficients, the overall heat transfer coefficient for hot clean and fouled heat exchangers were found 9.587 ∗ 103 𝑊 𝑚2 ∗𝐾 , 8.467 ∗ 103 𝑊 𝑚2 ∗𝐾 respectively.
- 18. 18 In the determination of Qr and Qf ∆𝑇𝑙𝑚 is required and for heat transfer analysis we are not given 𝑇𝑐,𝑜𝑢𝑡 . So that physical properties of water cannot be decided. Therefore trial-error solution is needed to find the correct 𝑇𝑐,𝑜𝑢𝑡 . To determine the correct one we need to check both the required heat of hot and cold fluid. From energy balance analysis, the required heat of hot and cold fluid must be same. The calculation for trial-error solution goes until it reaches the equality of the required heat of hot and cold fluid. To be sure of the 𝑇𝑐,𝑜𝑢𝑡 value was acceptable Qrh and Qrc was determined and found as 1.47 ∗ 107 𝑊 and 1.465 ∗ 107 𝑊 which is really close to each other so that Tcout value that choosen is acceptable. After calculation of ∆𝑇𝑙𝑚 Qr and Qf was calculated as 2.637 ∗ 107 𝑊, 2.328 ∗ 107 𝑊 respectively. Lastly the safety factor was calculated by dividing Qf to Qrh and found as 1.584 and cleanless factor as 0.883. According to the literature Process heat transfer, 1950, typical design are based on safety factor of 1.6 which is closer to 1.58. Moreover, based on Heat Exchanger: Selection, Rating, and Thermal Design, 2nd , Typical designs are based upon a cleanliness factor of 0.85 which is quite closer with our value.
- 19. 19 4 CONCLUSION After performing the required equations which are given in calculation part, it is seen that each plate is corrugated to increase the surface area and maximize heat transfer. Within a plate heat exchanger, the fluid paths alternate between plates allowing the two fluids to interact, but not mix, several times in a small area. The data from the similar heat exchanger is used in order to define the heat exchanger that is used in the project. The goal of the project is to understand the characteristics and design of a plate heat exchanger. By geometry and heat transfer analysis, the total number of plates, the actual with fouled surface and required heat duty are found as 105 plates, 2.63 x 107 W and 2.32 x 107 W, respectively. It is considered that no heat loss to surroundings however in reality there should be heat loss, therefore, error due to this assumption must be considered in real life applications.
- 20. 20 5 REFERENCES Incropera, F. (2012). Principles of heat and mass transfer (7th ed.). Singapore: John Wiley & Sons Singapore Pte. Leib, T., & Pereira, C. (2008). Perry's chemical engineers' handbook (8th ed.). New York: McGraw-Hill. Kakaç. S. (Sadik). Heal exchangers : selection, rating. and thermal design / Sadik Kakaç, Hongtan Liu.-. 2nd ed Kern,“Processheattransfer”,McGraw Hill,1950

No public clipboards found for this slide

Be the first to comment