AN EXPERIMENTAL STUDY OF EXERGY IN A CORRUGATED PLATE HEAT EXCHANGER

Transcription

1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 6, Issue 11, Nov 2015, pp , Article ID: IJMET_06_11_002 Available online at ISSN Print: and ISSN Online: IAEME Publication AN EXPERIMENTAL STUDY OF EXERGY IN A CORRUGATED PLATE HEAT EXCHANGER Mohd. Rehan Khan and Dr. Ajeet Kumar Rai Mechanical Engineering Department, SSET, SHIATS Allahabad , (U.P.) India. ABSTRACT In the present work an attempt has been made to investigate the performance of a 3 channel 1-1 pass, corrugated plate heat exchanger. The plates had sinusoidal wavy surfaces with corrugation angle of Hot water at different inlet temperature ranging from 40 0 C to 60 0 C was made to flow in the central channel to get cooled by water in the outer channels. For hot and cold fluid, Reynolds number was in the range of 900 < Re > Performance was measured in parallel and counter flow arrangement. Exergy loss is calculated and it is found that exergy loss is more in parallel flow arrangement than in the counter flow arrangement. Key words: Heat Exchanger, Reynolds number and loss. Cite this Article: Khan, M. R. and Dr Rai, A. K. An Experimental Study of Exergy in a Corrugated Plate Heat Exchanger. International Journal of Mechanical Engineering and Technology, 6(11), 2015, pp INTRODUCTION Heat exchanger is a most important device used to transfer heat from one fluid stream to another. They are widely used in the various engineering applications. Their design requirement is to increase the energy saving and to decrease the cost. The way to improve the global performances of plate heat exchangers is to find efficient heat transfer surfaces which do not induce much pressure loss. Corrugated plate heat exchangers are used to increase the thermal performance and higher compactness. Breaking and destabilizing in the thermal boundary layer are occurred as fluid flowing through the corrugated surfaces. Many researchers have studied on the heat transfer characteristics of the corrugated channels. Experimental and numerical studies were performed by Sunden and S.Trollheden on the heat transfer and pressure drop in the corrugated channels and the smooth tubes. It was found that the heat transfer obtained from the corrugated channel was 3.5 times higher than that from the smooth tube. The pressure drop in the corrugated channel is 5 6 times larger than that from a smooth channel. Fabbri has studied the laminar convective heat transfer in a channel 16 editor@iaeme.com

2 An Experimental Study of Exergy in a Corrugated Plate Heat Exchanger composed of the smooth and corrugated walls. The heat transfer performance of the corrugated wall channel was compared with that of a smooth wall. Hamza et al. have experimentally studied effects of the operating parameters on laminar flow forced convection heat transfer of air flowing in a channel having a V-corrugated upper plate. The experiments were performed for Reynolds number and tilting angles of channel in the ranges of , and 0 60, respectively. To determine the optimal design and operating conditions of heat exchangers, the performance of heat exchanger should be evaluated correctly. It is thus needed to develop an accurate and reliable evaluation method. Presently the evaluation criteria of the performance of heat exchangers fall into two catalogues: the entropy evaluation method and the exergy evaluation method. In the analysis and design of heat exchangers, it is necessary to evaluate the entropy generation/exergy destruction due to heat exchange and pressure drop as a function of the design variables selected for the optimization analysis. Bejan presented a method for fixed or minimum number of entropy generation units in counter flow heat exchangers for gas-to-gas applications. He also investigated a heat exchanger with heat transfer loss and frictional pressure drop in channels, and reported heat exchanger effectiveness using the entropy generation number. Boyd et al. demonstrated that it was possible to design an optimal heat exchanger based on the second law of thermodynamics to minimize the loss of available work. Sarangi and Chowdhury analyzed the entropy generation in a counter flow heat exchanger and discussed some formal mathematical consequences of entropy generation.. Sekuli estimated the quality of the heat exchange process in heat exchanger analysis using the entropy generation. Durmus et al studied experimentally forced convection heat transfer and pressure drop in plate heat exchangers having different surface profiles. The results show that the efficiency of the heat exchanger increases with increasing the fluids' contact surface, pressure drop and mass flow rates due to an enhanced heat transfer to the fluid. Pandey et al. carried out heat transfer and pressure drop studies on a sinusoidal plate heat exchanger. The results show that the results show that the average energy loss in PHE with rectangular wavy surface is about 79.53% of that with the rectangular geometry. 2. NOMENCLATURE A Cross sectional area, (m 2 ) c Specific heat at constant pressure, (J kg -1 K -1 ) C Heat capacity rate, (W K -1 ) D h Hydraulic diameter, (m) E Exergy loss, (W) h heat transfer coefficient, (W m _2 K _1 ) L length, (m) M mass flow rate, (kg s _1 ) P Pressure, (N m _2 ) Pr Prandtl number Q Heat transfer rate, (W) Re Reynolds number T Temperature, (K) V Average velocity of fluid, (m s _1 ) ρ Density of air, (kg m _3 ) 17 editor@iaeme.com

3 Mohd. Rehan Khan and Dr Ajeet Kumar Rai Suffixes c Cold e Environment, ambient h Hot I Inlet max Maximum o Outlet min Minimum 3. EXPERIMENTAL SETUP The photograph of the experimental setup, fabricated with 22 gauge GI sheets to investigate the heat transfer characteristics of the plate heat exchanger channels for same flow conditions with different inlet hot water temperatures are shown in (Figure 1). It includes a hot water loop, two coolant loop and a measurement system. The hot water loop comprises a water tank, a heater, and a water pump. The cold water loop comprises a water tank, and a water pump. A digital temperature indicator with thermocouples is used to measure temperatures at inlet and exit of the hot and cold streams. The flow rate is measured by noting down time for collection of fixed volume of the fluid. The whole system is thermally insulated to minimize the energy loss. Figure 1 Photographs of sinusoidal wavy corrugated plates used in plate heat exchanger. Figure 2 Photographs of experimental setup 18 editor@iaeme.com

4 An Experimental Study of Exergy in a Corrugated Plate Heat Exchanger 3.1. Specifications of the experimental setup Length of the test section =100 cm Width of the test section = 10 cm Height of a flow channel, i.e. gap between two successive corrugated plates = 5 cm. Chevron angle of the plate = 45 o Material of the plate is GI of 22 gauge Experimental procedure Hot water was made to flow through the central corrugated channel to maintain the channel surfaces at approximately constant temperature. Cold water is made to flow in the upper and lower channels. Thermocouples were inserted in the inlet and exit of the hot and cold streams, were used to record the corresponding fluid temperatures. Thermocouples were calibrated with ZEAL thermometer. Experiments were conducted for 40, 45, 50, 55, 60 0 C inlet temperature of hot water in parallel and counter flow arrangement. The hot and cold water flow rate is maintained constant for all inlet hot water temperatures and for both parallel and counter flow arrangements. Mass flow rate of hot fluid (water) is maintained at 0.05 kg/s and that of the cold fluid (water) is 0.16 kg/s Numerical Methodology In the present experiment, flow rates of hot and cold fluids are kept constant in parallel and counter flow arrangement. After collection of the data of temperatures at inlet and exit of the hot and cold fluid streams, exergy losses of the two heat exchanging fluids are calculated as given below. Heat lost to the surroundings = heat given by hot fluid - heat taken by cold fluid m h c h =(T hi - T ho )-m c c c (T co - T ci ) Values of heat given by hot fluid and heat absorbed by cold fluid, calculated in the present experiment showed that there was negligible loss of heat to the surroundings due to proper insulation of the heat exchanger. For such heat exchanger,w=0 and Q = 0, and exergy loss for a steady state open system can be found as a sum of those for the individual fluids, i.e., E = E h + E c The exergy changes for the two fluids are obtained as given below: For hot fluid (i.e. water), E h = T e [m h (s ho - s hi )] and for cold fluid or E h = T e [C h ln(t ho -T hi )] E c =Te[mc(s co - s ci )] or; E c = T e [C c ln(t co /T ci )] The exergy loss caused by pressure drop is not to be considered for liquids because ΔE also contains the exergy loss caused by the pressure drop. Besides the 19 editor@iaeme.com

5 Mohd. Rehan Khan and Dr Ajeet Kumar Rai Exergy (W) exergy loss, the effectiveness of the PHE is calculated from experimental observations using the following equation: Ԑ =[ C c (T co - Tc i ]/[C min (T hi - T ci )] Reynolds number is calculated based on hydraulic diameter of sinusoidal wavy PHE channel from Re =(ρvd h /µ) Where D h = 4(width x height)/2(width + height) and V = m/ρ(width x height) Physical properties, ρ and m of the fluid are evaluated at its mean Bulk temperature. 4. RESULTS AND DISCUSSION Figure 3 shows the variation of maximum possible heat transfer rate for different inlet temperature of hot water and for a given inlet temperature of cold water in both parallel and counter flow arrangements. As inlet hot water temperature increases, Q max increases. Trend is found similar in parallel and counter flow arrangements. Effectiveness in counter low is 44.5% more than parallel flow arrangement Qmax (W) Parallel Flow Counter Flow Temperature ( 0 C) Figure 3 Variation of Q max for different inlet hot water temperature Parallel Flow Counter Flow Temperature 50 0 C Figure 4 Variation of Exergy for different hot water inlet temperature 20 editor@iaeme.com

6 E/Qmax An Experimental Study of Exergy in a Corrugated Plate Heat Exchanger Temperature 0 C Parallel flow Counter flow Figure 5 Variation of E/Qmax for different inlet temperature of hot water Variation of exergy loss with hot fluid inlet temperature for a fixed cold fluid inlet temperature is given in Figure 4 for both parallel and counter flow arrangements. Exergy loss is less at low inlet hot temperature relative to the high inlet hot temperature. This observation may be attributed to increased temperature resulting in the increase in irreversibility which is responsible for increase in exergy loss. It is also observed that with rise in inlet hot water temperature, exergy loss is more in counter flow arrangement than in parallel flow arrangement, which is in accordance with the results found by Pandey et. al. [2011]. Variation of Exergy loss (E/Q max ) with inlet hot water temperature is shown in Figure 5 for a constant inlet cold water temperature. It may be seen that the (E/Q max ) is more in parallel flow arrangement than in the counter flow arrangement. CONCLUSION 1. A three channel 1-1 pass corrugated with corrugation angle 45 0 plate type heat exchanger was fabricated. 2. Performance of plate heat exchanger at different input heat load was measured in parallel and counter flow arrangement. 3. Exergy analysis was performed to find its behavior in parallel and counter flow arrangement. 4. Effectiveness in counter low is 44.5% more than parallel flow arrangement. 5. Exergy loss was found 7.2% more in parallel flow than in counter flow arrangement. REFERENCES [1] Sunden, B. and Trollheden, S. Periodic laminar flow and heat transfer in a corrugated two-dimensional channel. International Communications in Heat and Mass Transfer, 16, 1989, pp [2] Fabbri, G. Heat transfer optimization in corrugated wall channels. International Journal of Heat and Mass Transfer, 43, 2000, pp [3] Hamza, A., Ali, H. and Hanaoka, Y. Experimental study on laminar flow forcedconvection in a channel with upper V-corrugated plate heated by radiation. International Journal of Heat and Mass Transfer, 45, 2002, pp editor@iaeme.com

7 Mohd. Rehan Khan and Dr Ajeet Kumar Rai [4] Bejan, A. The concept of irreversibility in heat exchanger design: counterflow heat exchangers for gas-to-gas applications. J HeatTransfer, 99, 1977, pp [5] Bejan, A. General criterion for rating heat exchanger performance. Int.J Heat Mass Transfer, 21, 1978, pp [6] Boyd, J. M., Bluemel, V., Keil, T. H., Kucinkas, G. R. and Molinari, S. The second law of thermodynamics as a criterion for heat exchanger design. Energy, 6(7), 1981, pp [7] Sarangi, S. and Chowdhury, K. The generation of entropy in a counterflow heat exchanger. Cryogenics, 22, 1982, pp [8] Sekulic, D. P. The second law quality of energy transformation in heat exchanger. J Heat Tranfer, 112, 1990, pp [9] Durmus, A., Benli, H., Kurtbas, I. and Gul, H. Investigation of heat transfer and pressure drop in plate heat exchangers having different surface profiles. Int J Heat Mass Transf, 52, 2009, pp [10] Pandey, S. D. and Nema, V. K. Rating of an experimental plate heat exchanger. In:Proceedings of national conference: advance in management of energy efficiency and clean environment. Kanpur, India, 2010, pp [11] Mukherjee, P., Biswas, G. and Nag, P. K. Second law analysis of heat transfer in swirling through a cylindrical duct. J Heat Transfer, 109, 1987, pp [12] Ismael, O. M., Dr. Rai, A. K., Mahdi, H. F. and Sachan, V. An experimental study of heat transfer in a plate heat exchange. International Journal of Mechanical Engineering and Technology, 5(4), 2014, pp [13] Pandey, S. D. and Nema, V. K. An experimental investigation of exergy loss reduction in corrugated plate heat exchanger. Energy, 36, 2011, pp [14] Kumar, A., Dr. Rai, A. K. and Sachan, V. Experimental Study of heat transfer in a corrugated plate heat exchanger. International Journal of Mechanical Engineering and Technology, 5(9), pp editor@iaeme.com