THE EFFECT OF USING SMALL CYLINDRICAL ALUMINUM PIECES AS A PACKING MATERIAL ON THE DOUBLE PIPE HEAT EXCHANGER PERFORMANCE

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 13, December 2018, pp , Article ID: IJMET_09_ Available online at aeme.com/ijmet/issues.asp?jtype=ijmet&vtype= =9&IType=13 ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed THE EFFECT OF USING SMALL CYLINDRICAL ALUMINUM PIECES AS A PACKING MATERIAL ON THE DOUBLE PIPE HEAT EXCHANGER PERFORMANCE Shereen E. Kaska Assistant Lecturer, Fuel &Energy Department /Technical College Kirkuk Mahmood H. Khaleel Assistant Lecturer, Mechanical Department /Technical Institute Kirkuk Northern Technical University Rafeq A. Khalefa Assistant Prof, Fuel &Energy Department /Technical Collegee Kirkuk ABSTRACT: This paper aims to study experimentally the effects of using small cylindrical aluminum pieces (tube) whose geometry (12.5mm diameter x12.5mm length) as a porosity filling (random packing) materials between the tube and the shell of a double pipe heat exchanger, both configurations (Parallel and Counter) flow were tested for different heat capacity ratios. A small boiler with a temperature controller was used for heating the hot fluid, the inlet and outlet temperatures were measured by using digital thermocouples, the tests were performed with different flow rates of cold fluid. Finally comparing the results of the packing case with one of without packing show a positive effects by increasing{(heat Transfer Rate(10-12)%, Effectiveness(1-17)%, Number of Transferr Units (6-50)%, Overall Heat Transfer Coefficient (20-28)% and reduces Exergy Loss about (50-75)%)}in some cases according to flow configuration and packing materials (shape and geometry). Keywords: Heat Exchangers, Packing, Performance Improving, Double Pipe Heat Exchanger, Exergy Loss editor@iaeme.com

2 The Effect of Using Small Cylindrical Aluminum Pieces As A Packing Material On The Double Pipe Heat Exchanger Performance Cite this Article: Shereen E. Kaska, Mahmood H. Khaleel and Rafeq A. Khalefa, The Effect of Using Small Cylindrical Aluminum Pieces As A Packing Material On The Double Pipe Heat Exchanger Performance, International Journal of Mechanical Engineering and Technology, 9(13), 2018, pp INTRODUCTION Heat exchangers are devices that facilitate the exchange of heat between two fluids that are at different temperatures while keeping them from mixing each other. Heat exchanger is an important device for all thermal systems (condensers and evaporators) and commonly used in practice in a wide range of applications [1], the more significant technical properties of the double pipe heat exchanger is the suitability of it when used with high pressure applications (oil refinery and other large chemical processes) and a lot of investigations and methods were conducted and applied by researchers and engineers for analyzing and developing the performance of the heat exchangers in order to reduce the size and cost with increasing the efficiency and performance. The first method (active techniques) in which the external power was needed for instance surface vibration and electrostatic fields such as pulsation which was used by[2], pipe rotation used by[3] and air injection (bubble generation) by [4&5]. Experimental investigation was done by [6] and some parameters were studied for observing their effects on exergy loss. In the second method that was widely used for developing and improving the performance and efficiency is the well known as (passive techniques) in which the external power is not required such as using (nano-fluids) [7], propellers [8], fins [9], swirl generation [10], helical wires [11], internal spring [12], and porous substrate was used by [13]. The present research is aimed to study the performance of the double pipe heat exchanger under effect of using different packing material specified by shape and size (aluminum pieces) on the shell side with applying both configurations (parallel and counter) flow, the application of this method is suitable among some of the others (passive techniques) due to its simplicity with no requirement for applying external forces. In this research three types of a small cylindrical aluminum pieces ( one solid and two hollow tubes) used as a porosity packing (random) between the tube and the shell. The specific objective of this research paper is to develop an enhanced method for developing the double pipe heat exchanger performance by increasing it's efficiency and decreasing it's size and bulky. Theoretical Analysis In the double pipe heat exchangers the heat transfer rate can be calculated by using the following relations [1]: = or = (1) and Q ave = Where = h!, = #!!, and $ h # # h h $! #! fluids respectively and T h, =hot fluid temperature T c = the cold fluid temperature. The subscripts ( i) and (o) represent the inlet and outlet hot and cold temperature respectively. The overall heat transfer coefficient can be calculated experimentally from:[14] (2) editor@iaeme.com

3 Shereen E. Kaska, Mahmood H. Khaleel and Rafeq A. Khalefa U exp = %&' (3) ( * +,-. Where A is the surface area of the tube and /0*1 = 2*,345 6*, *,89 6*,89 /: -,345 ;-,345 -,89 ;-,89 for parallel flow (4) and /0*1 = 2*,89 6*, *,345 6*,89 /: -,89 ;-,345 -,345 ;-,89 for counter flow (5) Effectiveness NTU method is the versatile and powerful method for designing and analyzing the heat exchangers and can be calculated by: [1& 5] < # =$ = > =?@A?B D?@C G?HGAG IEEJBC D?@C (6) and maximum possible heat transfer rate = G?H = (ṁc) min (T h,in -T c,in ) (7) where (ṁc) min = the lesser value of (ṁ h Cp h ) or (ṁ c Cp c ) NTU= (number of transfer units) is indicative of the size of the heat exchanger and it is evaluated by: KL = ( M ṁo P89 (8) Where A is the heat transfer area (m 2 ) and U is the overall heat transfer coefficient (W/m 2 C) The porosity of the system can be calculated by using: [15] = S6 T S (9) Where U is the total volume of the annular (shell side space) of the heat exchanger, And V is the volume of the solid packing pieces. Exergy Analysis The exergy can be defined as the maximum theoretical work which extracted from a given entity when it is brought to equilibrium with its environment. The pressure drop and temperature gradient are the main sources of exergy losses in heat exchangers. The exergy [E] for a given control volume can be calculated as[1&5]: < = < - < IDXA@ (10) Where Ei = inlet exergy, Eo = outlet exergy.and < IDXA@ = $ YZ[!#! $ h #$ =. Despite the perfect thermally insulting of the outer surfaces of the outer tube and their joints, there was heat transfer as a (heat flux) from the shell surface (outer wall surface) of the vertical heat exchanger used in this research due to less adequateness of the insulation therefore the heat transfer from the outer surfaces is taken to be[12%] which means that the heat losses from the hot fluid (Q h ) and that gained by the cold fluid (Q c ) are not equal.[13] or Q c Q h where Q c = ṁ c Cp c ΔT c and Q h = ṁ h Cp h ΔT h (11) editor@iaeme.com

4 The Effect of Using Small Cylindrical Aluminum Pieces As A Packing Material On The Double Pipe Heat Exchanger Performance exergy loss of a double pipe heat exchanger under steady state conditions, can be calculated by using: [13] E =E h +E c (12) where E h = hot fluid exergy change and E c =cold fluid exergy change, and can be expressed mathematically as [1,6]: E h =Te[ṁ h (S ho -S hi )] and E c = Te [ṁ c (S eo S ei )] (13) Where Te is the environment temperature. By taking into account the entropy change that caused by temperature difference and neglecting the loss due to frictional pressure drop (due to short length of the heat exchanger [1,5] can be evaluated as : S o S i = Cp ln (T o /T i ) (14) Where S o and S i represent the outlet and inlet specific entropy of mass fluxes. By substituting equations (13) in equation (12) the exergy loss can be obtained as: [1,5] E = Te[ṁ h Cp h ln (T ho /T hi ) + ṁ c Cp c ln(t co /T ci )] (15) Where T hi, T ho and T ci,t co represent the inlet and outlet temperatures of the hot and cold fluids respectively and Te is the environment temperature. 2. EXPERIMENTAL PROCEDURE AND INSTRUMENTATION The first step of this research was to designing and making a double pipe heat exchanger (table (1) shows the technical specification of the heat exchanger). The second step was preparing and selecting the packing materials (Aluminum) in different geometries and sizes table (2) shows the specifications and dimensions of the packing material, and figure (1) shows the packing method with samples of materials. The test rig consists of a small boiler with a hot fluid and cold fluid mass flow rates controllers and temperature indicators (the system that used in this work was from TQuepment), a thick layer of glass wool was used for insulating the shell (outer tube) to prevent and reduce the heat losses to surrounding. The system was completed as in figure (2).In all experiments performed in this work the hot water temperature and mass flow rate is kept constant at (61.1 o C) and ( kg/sec) respectively, while the cold water mass flow rate adjusted for achieving the heat capacity ratio of (0.25) at the first step where the cold water mass flow rate is equal to ( kg/sec), the data has been recorded after enough time at which the steady state conditions were achieved. The same procedure repeated for heat capacity ratios of (0.5,0.75 and 1) and the two cases of the operation (1-no packing 2-with packing) specified as in figure (1) and table (1) using (AA and AB) with both configurations (parallel flow and counter flow). Table (1) Technical Specification of the Heat Exchanger Heat Exchanger Length Shell Diameter Tube Diameter Tube Thickness 60Cm 14Cm 2.85Cm Cm editor@iaeme.com

5 Shereen E. Kaska, Mahmood H. Khaleel and Rafeq A. Khalefa Table (2) Packing material specification and dimensions Type of Packing Packing Material (Diameter Geometry *Length) mm Total Weight (g) Porosity % AA No Packing AB Cylindrical tube 12.5 * Aluminum pieces AB Figure (1) Aluminum pieces and Packing Method Figure (2) Test Rig Apparatus 3. RESULTS AND DISCUSSION The following figures represent the effects of packing the shell space with different cylindrical aluminum pieces (solid and tubes) for both configuration of double pipe heat exchanger (parallel flow and counter flow). Figure (3) represents the relationship between the heat capacity ratio and actual heat transfer rate for both configurations (parallel and counter) flow of the heat exchanger at packing cases of (AA= no packing and AB = packing with (12.5*12.5) cylindrical tubes ). It is observed that the packing method increases the heat transfer rate especially at the case (AB) for parallel flow and counter flow at some capacity ratios, from this fact packing method editor@iaeme.com

6 The Effect of Using Small Cylindrical Aluminum Pieces As A Packing Material On The Double Pipe Heat Exchanger Performance with selecting of a suitable material (high conductivity) and geometry ( maximum surface area) has significant positive effect on the heat transfer rate also one more reason of this increasing is the variation in the flow type from laminar to turbulent because the packing pieces changes the velocity and direction of the fluid during its motion through the heat exchanger. Figure (3) The Effect of Packing on the Actual heat Transfer at Different heat Capacity Ratios. Figure (4) represents the relationship between the heat capacity ratio and effectiveness for both configurations (parallel and counter) flows of the heat exchanger at cases of using packing types of (AA and AB).It is observed that the packing of the heat exchanger (shell side) with packing type {(AB) whose technical specification in table (2)}increase the effectiveness for both (parallel configuration 17%) and (counter configuration(1-16)%) at all cases of heat capacity ratios and this increasing of effectiveness is due to increase in actual heat transfer which indicates the enhancement of the packing method for performance improvement editor@iaeme.com

7 Shereen E. Kaska, Mahmood H. Khaleel and Rafeq A. Khalefa Figure (4) The relationship between heat capacity and effectiveness using different packing Figure (5) represents the relationship between heat capacity ratio and number of transfer units for both configurations (parallel and counter) flow at cases of using packing types of (AA and AB).It is observed that the NTU increases with packing the shell side of the heat exchanger especially in the case of using packing type {(AB) technical specification in table (2)} for both configurations (parallel flow (20-50)% and counter flow (6-28)% ) comparing with (AA= no packing case) editor@iaeme.com

8 The Effect of Using Small Cylindrical Aluminum Pieces As A Packing Material On The Double Pipe Heat Exchanger Performance Figure (5) The relationship between heat capacity and effectiveness using different packing Fig.(6) represents the relationship between heat capacity ratio and overall heat transfer coefficient for both configurations (parallel and counter)flow at cases of using packing types of (AA and AB).It is observed that the packing type of (AB) records maximum overall heat transfer coefficient at all cases of heat capacity ratio and flow type configurations. A great role and positive effect of the packing method is clearly denoted which increases the overall heat transfer coefficient about (20-28)% comparing with case (AA= without packing) editor@iaeme.com

9 Shereen E. Kaska, Mahmood H. Khaleel and Rafeq A. Khalefa Figure (6) The relationship between overall heat transfer coefficient an heat capacity ratio using different packing Figure (7) represents the relationship between heat capacity ratio and exergy loss for both configurations (parallel and counter) flow at cases of using packing types of (AA and AB). It is observed that the exergy loss (in case of parallel flow) records minimum value at packing type of (AB), and type (AA= without packing) shows maximum value of exergy loss at capacity ratios of (0.5 and 0.75), from this fact the selecting of packing type can be done after taking to account the flow configuration (parallel or counter) and the heat capacity ratio of the fluids

10 The Effect of Using Small Cylindrical Aluminum Pieces As A Packing Material On The Double Pipe Heat Exchanger Performance Figure (7) The relationship between exergy and heat capacity ratio using different packing 4. CONCLUSION The present work investigates experimentally the effect of packing the shell side of the double pipe heat exchanger. The effect of different packing material in size and shape are evaluated and compared with no-packing case of the heat exchanger. It was observed that the packing method increases some performance parameters which lead to improving of the double pipe heat exchanger performance.the actual heat transfer is affected strongly by using packing type of (AB) at cold water flow rates of ( kg/sec or C=0.5, kg/sec or C=0.75 and kg/sec or C=1) for parallel flow and counter flow comparing with no-packed heat exchanger.the effectiveness,ntu and U are significantly affected (increase) by using the packing method (AB) for both configurations (parallel and counter) flow comparing with nopacked heat exchanger. Minimum exergy loss achieved with using packing type of (AB) for editor@iaeme.com

11 Shereen E. Kaska, Mahmood H. Khaleel and Rafeq A. Khalefa parallel flow heat exchanger and all values of heat capacity ratios. The results achieved in this work indicates that the packing method is simple, low cost and the type (shape and size) has a significant effects on the heat exchanger performance which leads to selecting a suitable packing type according to required purpose. REFERENCES [1] Behabadi M.A.A. et. al. "Experimental Investigation on the Convective Heat Transfer of Nanofluids Flow Inside vertical helically Coiled Tubes Under Uniform Wall Temperature Condition " Int. Cmmun. Heat Mass Transfer,39,(2012),Pp [2] Guo L. et. al., "Transient Convective Heat Transfer in a Helical Coiled Tube with Pulsatile Fully Developed Turbulent Flow ", Int. Jour. of Heat Mass Transfer.41, 2867,(1988). [3] Yildiz C. et. al., "Heat Transfers and Pressure Drops in a Rotating Helical Pipes" Appl. Energy.50, 85, (1995). [4] Legendre D. et. al. "Thermal and Dynamic Evaluation of a Spheres Bubble Moving Steadily in a Superheated or Sub cooled Liquid" Physics of Fluids, 10, 1256, (1998). [5] H. H. Habeeb, R. A. Khalefa and S.E. Kaska "Performance Enhancement of the Vertical Double Pipe Heat Exchanger by Applying of Bubbling Generation on the Shell Side" Kirkuk University Journal /Scientific Studies (KUJSS),Vol.13, Issue 1, March 2018, pp. ( ) [6] Dhir V. "Boiling Heat Transfer "Annual Review of Fluid Mechanics,30, 1998, Pp [7] Aly W.I.A. "Numerical Study on Turbulent Heat Transfer and Pressure Drop of nanofluids in Coiled Tube in Tube Heat Exchanger " Energy Con. Manage. 86,2014,Pp [8] Yildiz C. et. al. "Influence of Fluid Rotation on Heat Transfer and Pressure Drop in Double Pipe Heat Exchangers" Appl. Energy,54,,1,1996,Pp [9] Nphon P. "Thermal Performance and Pressure Drop of the Helical Coil Heat Exchangers with and without helically Crimped fins "Int. Commun. Heat Mass Transfer. 34,2007,Pp [10] Akpinar E. and Bicer Y. "Investigation of Heat Transfer and Exergy Loss in a Concentric Double Pipe Heat Exchanger Equipped with Swirl Generators" Int.J. Ther. Sci. 44. (2005) Pp [11] Akpinar E. K. "Evaluation of Heat Transfer and Exergy Loss in a Concentric Double Pipe Heat Exchanger Equipped with Helical Wires" Energy Conver. Manage. 47,2006, Pp [12] Yildiz C. et. al. "Heat Transfer and Pressure Drop in a Heat Exchanger with a Helical Pipe Containing Inside Springs " Energy Conserv. Manage. 38,6,1997,Pp [13] M. K. Alkan and M. A. Al-Nimn "Improving the Performance of Double Pipe Heat Exchanger by Using Porous substrates " Int. Jour. of Heat and Mass Transfer, Vol.42, No.19, 1999,Pp [14] Sadighi H. Dizaji et. al. "The Effect of Flow, Thermodynamic and Geometrical Characteristics on Exergy Loss in Shell and Coiled Tube Heat Exchangers" Energy,91, 2015,Pp [15] Bejan A. Convection Heat Transfer Text Book, John Wiley & Sons, New Yourk (1984) editor@iaeme.com