Heat Transfer Analysis of Corrugated Plate Heat Exchanger of Different Plate Geometry: A Review

Transcription

1 Heat Transfer Analysis of Corrugated Plate Heat Exchanger of Different Plate Geometry: A Review Jogi Nikhil G. 1, Assist. Prof. Lawankar Shailendra M. 2 1 M.Tech student, 2 Assistant Professor, Government College of Engineering, Amravati. Maharashtra, India Abstract Corrugated plate heat exchangers have larger heat transfer surface area and increased turbulence level due to the corrugations. In this study, experimental heat transfer data will obtained for single phase flow (water-to-water) configurations in a corrugated plate heat exchanger for symmetric 45 /45, 45 /75 chevron angle plates. The effect of variation of chevron angles with other geometric parameter on the heat transfer coefficient will be study. Reynold number ranging from 500 to 2500 and Prandtl number ranging from 3.5 to 6.5 will be taken for given experiment.based on the experimental data, a correlation will estimate for Nusselt number as a function of Reynolds number, Prandtl number and chevron angle. Keywords Chevron angle, Corrugated plate heat exchangers, Heat transfer coefficient, Nusselt number, Prandtl number, Reynolds number, Single phase flow. I. INTRODUCTION Plate Heat Exchangers have a number of applications in the pharmaceutical, petrochemical, chemical, power, dairy, food & beverage industry. Recently, plate heat exchangers are commonly used when compared to other types of heat exchangers such as shell and tube type in heat transfer processes because of their compactness, ease of production, sensitivity, easy care after set-up and efficiency.the temperature approach in a plate heat exchangers may be as low as 1 C whereas shell and tube heat exchangers require an approach of 5 C or more. A. Plate Heat Exchanger As shown in Figure 1, the plate heat exchanger is basically a series of individual plates pressed between two heavy end covers. These plates are gasketed, welded or brazed together depending on the application of the heat exchanger. The basic geometry of plates used in plate heat exchanger is shown in figure2.stainless steel is a commonly used metal for the plates because of its ability to withstand high temperatures, its strength, and its corrosion resistance. The entire assembly is held together by the tie bolts. Individual plates are hung from the top carrying bar and are guided by the bottom carrying bar. For single-pass circuiting, hot and cold side fluid connections are usually located on the fixed end cover. Multi-pass circuiting results in fluid connections on both fixed and moveable end covers. The plates are pressed to form troughs at right angles to the direction of flow of the liquid which runs through the channels in the heat exchanger. These troughs are arranged so that they interlink with the other plates which forms the channel with gaps of mm between the plates. Figure 1.Various parts of plate heat exchanger Material required for plate heat exchanger parts : Plate material stainless steel Gasket material - Nitriale Butadiene Rubber (NBR) Nozzle material stainless steel 110

2 Figure 2. Basic geometry of chevron plate [15] B. Fluid Flow in Plate Heat Exchanger Figure 2, illustrates the nature of fluid flow through the plate heat exchanger. The primary and secondary fluids flow in opposite directions on either side of the plates. Water flow and circuiting are controlled by the placement of the plate gaskets. By varying the position of the gasket, water can be channelled over a plate or past it. Gaskets are installed in such a way that a gasket failure cannot result in a mixing of the fluids. In addition, the outer circumference of all gaskets is exposed to the atmosphere. As a result, should a leak occur, a visual indication is provided. Figure 3. Fluid flow in plate heat exchanger C. Geometric Parameter Affecting Plate Heat Exchanger Chevron Angle, β: Typically varying from 20 to 65, β is the measure of softness (small β, low thermal efficiency and pressure drop) and hardness (large β, high thermal efficiency and pressure drop) of thermal and hydraulic characteristics of plates. Some authors define Π/2- β as the chevron angle. Surface Enlargement Factor, φ: φ is the ratio of developed area [based on corrugation pitch, P c,and plate pitch, p] to the projected area(viz. L w L p, L w = L h + D p and L p = L v D p ) Corrugation Depth or Mean Channel Spacing, b: b = p t, the difference between plate pitch, p and the plate thickness, t Channel Flow Area, A x : A x is the minimum flow area between plates and is estimated as product of plate corrugation depth and width of plate (i.e., A x = b L w ) Channel Hydraulic Diameter, D h : D h is defined as four times ratio of minimum flow area to wetted perimeter, D h = 2bL w /(b+l w φ).since b<<l w, D h is usually taken to be 2b/φ. D. Physical Parameters Affecting Plate Heat Exchanger The six most important parameters are as follows: The amount of heat to be transferred (heat load). The inlet and outlet temperatures on the primary and secondary sides. The maximum allowable pressure drop on the primary and secondary sides. The maximum operating temperature. The maximum operating pressure. The flow rate on the primary and secondary sides. Temperature Program: This means the inlet and outlet temperatures of both media in the heat exchanger. Heat Load: Disregarding heat losses to the atmosphere, which are negligible, the heat lost (heat load) by one side of a plate heat exchanger is equal to the heat gained by the other. The heat load (P) is expressed in kw or kcal/h. Logarithmic Mean Temperature Difference: Logarithmic mean temperature difference () is the effective driving force in the heat exchanger. Thermal Length: Thermal length (θ) is the relationship between temperature difference dt on one side and. dt 111

3 Thermal length describes how difficult a duty is from a thermal perspective. Density: Density (ρ) is the mass per unit volume and is expressed in kg/m 3 or kg/dm 3. Flow Rate: This can be expressed in two different terms, either by weight or by volume. The units of flow by weight are in kg/s or kg/h, the units of flow by volume in m 3 /h or l/min. To convert units of volume into units of weight, it is necessary to multiply the volume flow by the density. Pressure Drop: Pressure drop (Δp) is in direct relationship to the size of the plate heat exchanger. If it is possible to increase the allowable pressure drop, and incidentally accept higher pumping costs, then the heat exchanger will be smaller and less expensive. As a guide, allowable pressure drops between 20 and 100 kpa are accepted as normal for water/water duties. Specific Heat: Specific heat (c p ) is the amount of energy required to raise 1 kg of a substance by one degree centigrade. The specific heat of water at 20 C is kj/kg C or 1.0 kcal/kg C. Viscosity: Viscosity is a measure of the ease of flow of a liquid. The lower the viscosity, the more easily it flows. Viscosity is expressed in centipoises (cp) or centistokes (cst). Overall Heat Transfer Coefficient: Overall heat transfer coefficient (U) is a measure of the resistance to heat flow, made up of the resistances caused by the plate material, amount of fouling, nature of the fluids and type of exchanger used. Overall heat transfer coefficient is expressed as W/m 2 C or kcal/h, m 2 C. E. Heat Transfer Analysis Heat Load, P: p mc dt and p P h A Where, P = heat load [kw] m = mass flow rate [kg/s] c p = specific heat [kj/kg C] dt = temperature difference between inlet and outlet on one side [ C] h = heat transfer coefficient [W/m 2 C] A = heat transfer area [m 2 ] = log mean temperature difference Thermal Length [θ]: dt Logarithmic Mean Temperature Difference []: T1 T2 ln( T / T ) 1 2 Here, T1 T1 T, 4 T2 T2 T3 Where, T 1 = Temperature inlet hot side T 2 = Temperature outlet hot side T 3 = Temperature inlet cold side T 4 = Temperature outlet cold side Total Overall Heat Transfer Coefficient [U]: x R U h h k hs cs f Where, h hs =The heat transfer coefficient between the hot medium and the heat transfer surface [W/m 2 C] h cs = The heat transfer coefficient between the heat transfer surface and the cold medium[w/m 2 C] Δx = The thickness of the heat transfer surface [m] R f = The fouling factor [m 2 C/W] k = The thermal conductivity of the material separating the medias [W/m C] Heat Transfer Correlation: The heat transfer correlation for a fluid flow past a solid surface is expressed in a dimensionless form is given as: Nu Nu(Re, Pr) Where, Nu= Nusselt number Re=Reynolds number Pr =Prandtl number For fully developed laminar flows, we expected the Nusselt number Nu to be constant however for a turbulent flow it is expressed as: Nu C 1 Re Pr Where,C 1, α & β are constants. II. LATERATURE SURVEY Focke W. W. et al. [1] established that the inclination angle between plate corrugations and the overall flow direction is a major parameter in the thermo hydraulic performance of plate heat exchangers. 112

4 The observed maximum transfer rate at an angle of about 80 is explained from the observed flow patterns. At higher angles the flow pattern becomes less effective for transfer, in particular at 90 marked flow separation is observed. Mehrabian M. A. and Pouter R. [2] studies the local hydrodynamic and thermal characteristics of the flow between two identical APV SR3 plates and looks at the effect of corrugation angle on the performance when the plate spacing is fixed. The CFD calculations show that the inclination angle between the plate corrugations and the overall flow direction is a major parameter in the thermo hydraulic performance of plate heat exchangers. Metwally H. M. and Mbanglik R. M. [3] considered Laminar periodically developed forced convection in sinusoidal corrugated-plate channels with uniform wall temperature and single-phase constant property flows. The flow field is found to be strongly influenced by γ and Re, and it displays two distinct regimes: a low Re or γ undisturbed laminar-flow regime and a high Re or γ swirlflow regime. Gradeck M. et al. [4] performed experiments to study effects of hydrodynamic conditions on the enhancement of heat transfer for single phase flow. These experiments have been conducted for a wide range of Reynolds numbers, [0 < Re < 7500] in order to obtain the different regimes from steady laminar to turbulent. Finally they have pointed out a strong relation between the wall velocity gradient and the Nusselt number. Further investigations will be made on two-phase and boiling flow. Bobbili Prabhakara Rao et al. [5] carried out experimental investigation to find the flow and the pressure difference across the port to channel in plate heat exchangers for a wide range of Reynolds number In their study, low corrugation angle plates have been used for different number of channels, namely, 20 and 80. Water has been used as working fluid for both hot and cold fluids. Longo and Gasparella [6] carried out experiments using water as a working fluid in herringbone type plate heat exchanger with chevron angle of 65 and developed Nusselt number correlation. They used modified Wilson plot technique and incorporated variable fluid property effects. Garcı a Cascales J. R. et al. [7] focused on the study of heat transfer in plate heat exchangers working with R-22 and R-290, comparing different correlations for the evaluation of the heat transfer coefficient. Naphon Paisarn [8] presented the effect of relevant parameters on the heat transfer characteristics and pressure drop. 113 The corrugated plates of different corrugated tile angles 20, 40 and 60 with the height of the channel of 12.5 mm for the heat flux and the Reynolds number in the ranges of kw/m 2 and are tested. Due to the presence of recirculation zones, the corrugated surface has significant effect on the enhancement of heat transfer and pressure drop. Using the Buckingham Pi theorem, Lin J.H. et al. [9] derives dimensionless correlations to characterize the heat transfer performance of the corrugated channel in a plate heat exchanger. The experimental data are substituted into these correlations to identify the flow characteristics and channel geometry parameters with the most significant influence on the heat transfer performance. Zhi-jian Luan et al. [10] designed a new-type corrugation plate heat exchanger and carried out experimental and numerical simulations for observing heat transfer performance and effect of flow resistance of the working fluid on it. Warnakulasuriya and Worek [11] investigated heat transfer and pressure drop of a viscous absorbent salt solution in a commercial plate heat exchanger. Overall heat transfer coefficient and Nusselt number are reported to increase with Reynolds number while friction factor decreased. Based on the experimental data, correlations for Nusselt number and friction factor were proposed. Tsai Ying-Chi et al.[12] investigated the hydrodynamic characteristics and distribution of flow in two crosscorrugated channels of plate heat exchangers. The velocity, pressure and flow distribution of the fluid among the two channels of the plate heat exchanger with its local flow characteristics around the contact points have been proposed. Dovic D. et al. [13] investigated characteristics of the flow in chevron plate heat exchangers through visualization tests of channels with β = 28 and β = 61.Mathematical model is then developed with the aim of deriving correlations for prediction of f and Nu for flow in channels of arbitrary geometry [β and b/l] Durmus Aydın et al. [14] studied the effects of surface geometries of three different type heat exchangers called as PHEflat [Flat plate heat exchanger], PHE corrugated [Corrugated plate heat exchanger] and PHE asteriks [Asterisk plate heat exchanger] on heat transfer, friction factor and exergy loss. The experiments were carried out for laminar flow conditions with single pass in parallel and counter flow direction having Reynolds number and Prandtl number in the range of 50 Re 1000 and 3 Pr 7, respectively.

5 Khan T. S. et al. [15] carried out experiment for single phase flow [water-to-water] configurations in a commercial plate heat exchanger for symmetric 30 /30, 60 /60, and mixed 30 /60 chevron angle plates having Reynold number ranging from 500 to 2500 and Prandtl number from 3.5 to 6.5. Based on the experimental data, a correlation to estimate Nusselt number as a function of Reynolds number, Prandtl number and chevron angle has been proposed. Gherasim Iulian et al. [16] presented an experimental investigation of the hydrodynamic and thermal fields in a two channel chevron-type plate heat exchanger for laminar and turbulent conditions. The friction factor for a Reynolds number up to 850 and the Nusselt number for the hot channel for a Reynolds number up to 1500 are presented. III. CONCLUSION Experiments have been performed to investigate heat transfer characteristics of a commercial plate heat exchanger with different chevron angles and other geometrical parameters under turbulent flow conditions. Reynolds number is varied from about Based on the experimental data, a simplified Nusselt number correlation incorporating effects of Reynolds number, Prandtl number, viscosity variation and chevron angle trying to be propose. IV. FUTURE SCOPE Different types of plates will also be tested and investigated using the set-up constructed. Based on the experimental results obtained from the set-up and the computational fluid dynamics analysis of the same cases, new correlations can be found for the different plate geometries to be tested and analyzed. With the result of new experiments, the selection program can also be extended for new type of plate geometries. NOMENCLATURE D p Port diameter [m] β Chevron angle [⁰C] L w Plate width [m] L h Horizontal distance between centers of ports [m] P c Corrugation pitch [m] t Plate thickness [m] L v Vertical distance between centers of ports [m] L h Horizontal distance between centers of ports [m] b Corrugation depth or mean channel spacing [m] φ Surface enlargement factor A x Channel flow area [m 2 ] 114 D h Channel hydraulic diameter [m] ρ Density [kgm -3 or kgdm -3 ] Δp Pressure drop [kpa] γ aspect ratios h hs cs Hydraulic Hot Surface Cold Surface REFERENCES SUBSCRIPT [1] Focke W.W, Zachariades J., Olivier I., 1985 The effect of the corrugation inclination angle on the thermo hydraulic performance of plate heat exchangers, Int. J. Heat Mass Transfer 28 [8], pp [2] Mehrabian M.A, Poulter R., 2000 Hydrodynamics and thermal characteristics of corrugated channels: computational approach, Applied Mathematical Modelling 24,pp [3] Metwally H.M., Manglik R.M.,2004 Enhanced heat transfer due to curvature-induce lateral vortices in laminar flows in sinusoidal corrugated-plate channels, International Journal of Heat and Mass Transfer 47, pp [4] Gradeck M., Hoareau B., Lebouche M.,2005 Local analysis of heat transfer inside corrugated channel, International Journal of Heat and Mass Transfer 48,pp [5] Bobbili Prabhakara Rao, Sunden Bengt, Das Sarit K.,2006 An experimental investigation of the port flow maldistribution in small and large plate package heat exchangers, Applied Thermal Engineering 26,pp [6] Longo G.A., Gasparella A., 2007 Refrigerant R134a vaporization heat transfer and pressure drop inside a small brazed plate heat exchanger, International Journal of Refrigeration 30, pp [7] Garcı a-cascales J.R., Vera-Garcı a F., Corber an-salvador J.M., Gonz alvez- Maci a J., 2007 Assessment of boiling and condensation heat transfer correlations in the modelling of plate heat exchangers, International Journal of Refrigeration 30,pp [8] Naphon Paisarn, 2007 Laminar convective heat transfer and pressure drop in the corrugated channels, International Communications in Heat and Mass Transfer 34,pp [9] Lin J.H., Huang C.Y., Su C.C., 2007 Dimensional analysis for the heat transfer characteristics in the corrugated channels of plate heat exchangers, International Communications in Heat and Mass Transfer 34,pp [10] Zhi-jian LUAN, Guan-min ZHANG, Mao-cheng TIAN, Ming-xiu FAN,2008 Flow resistance and heat transfer characteristics of a new-type plate heat exchanger, Journal of Hydrodynamics 20,pp [11] Warnakulasuriya F.S.K, Worek W.M.,2008, Heat transfer and pressure drop properties of high viscous solutions in plate heat exchangers, International Journal of Heat and Mass Transfer 51,pp [12] Tsai Ying-Chi, Liu Fung-Bao, Shen Po-Tsun, 2009 Investigations of the pressure drop and flow distribution in a chevron-type plate heat exchanger, International Communications in Heat and Mass Transfer 36,pp

6 [13] Dovic D., Palm B., Švaic S.,2009 Generalized correlations for predicting heat transfer and pressure drop in plate heat exchanger channels of arbitrary geometry, International Journal of Heat and Mass Transfer 52,pp [14] Durmus Aydın, Benli Huseyin, Kurtbas Irfan, Gul Hasan, 2009 Investigation of heat transfer and pressure drop in plate heat exchangers having different surface profiles, International Journal of Heat and Mass Transfer 52,pp [15] Khan T.S., Khan M.S., Chyu Ming-C., Ayub Z.H.,2010 Experimental investigation of single phase convective heat transfer coefficient in a corrugated plate heat exchanger for multiple plate configurations, Applied Thermal Engineering 30,pp [16] Gherasim Iulian, Taws Matthew, Galanis a Nicolas, Nguyen Cong Tam,2011 Heat transfer and fluid flow in a plate heat exchanger part I. Experimental investigation, International Journal of Thermal Sciences 50,pp