Enhancement of Convective Heat Transfer in Internal Viscous Flows by Inserting Motionless Mixers

2009 ◽  
Author(s):  
Ramin K. Rahmani ◽  
Anahita Ayasoufi ◽  
Theo G. Keith
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Turbulent Flows ◽  
Heat Exchangers ◽  
Convection Heat Transfer ◽  
Viscous Fluids ◽  
High Rate ◽  
Working Fluid ◽  
Static Mixer ◽  
Shell And Tube

In chemical processing industries, heating, cooling and other thermal processing of viscous fluids are an integral part of the unit operations. Enhancement of the natural and forced convection heat transfer rates has been the subject of numerous academic and industrial studies. Motionless mixers, also known as static mixers, are often used in continuous mixing, heat transfer, and chemical reactions applications. These mixers have low maintenance and operating costs, low space requirements, and have no moving parts. Heat exchangers equipped with mixing elements are especially well suited for heating or cooling highly viscous fluids. Shell and tube heat exchangers incorporate static mixing elements in the tubes to produce a heat transfer rate significantly higher than that of conventional heat exchangers. The mixing elements continuously create a new interface between the working fluid and tube wall, thereby producing a uniform heat history in the fluid. It is desired to employ motionless mixers in heat transfer applications to provide a high rate of heat transfer from a thermally homogenous fluid with low pressure drop. In the past, laboratory experimentation has been a fundamental part of the design process of a new static mixer for a given application as well as the selection of an existing static mixer. It is possible to use powerful computational fluid dynamics (CFD) tools to study the performance of these mixers without resorting to experimentation. In this paper, which is an extension to the previous work of the authors, the enhancement of performance of shell and tube heat exchangers by inserting motionless mixers (SMX and helical) is studied for creeping, laminar, and low-Re turbulent flows. It is shown that the studied mixers produced similar flow histories for the working fluid considered. Both SMX and helical mixers are able to increase thermal performance of heat exchangers. The SMX mixer manifests a higher performance in temperature blending and in heat transfer enhancement compared to the helical mixer. However, the pressure drop created by SMX elements, and consequently the required energy to maintain the flow in tube, is significantly higher.

Single-Phase Heat Transfer and Pressure Drop of Water Cooled Inside Horizontal Smooth Tubes in the Transitional Flow Regime

2010 ◽  
Author(s):  
Josua P. Meyer ◽  
Leon Liebenberg ◽  
Jonathan A. Olivier
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Transition Region ◽  
Heat Exchangers ◽  
Operating Conditions ◽  
Transitional Flow ◽  
Working Fluid ◽  
Tube Heat Exchanger ◽  
Smooth Tubes

Heat exchangers are usually designed in such a way that they do not operate in the transition region. This is usually due to a lack of information in this region. However, due to design constraints, energy efficiency requirements or change of operating conditions, heat exchangers are often forced to operate in this region. It is also well known that entrance disturbances influence where transition occurs. The purpose of this paper is to present experimental heat transfer and pressure drop data in the transition region for fully developed and developing flows inside smooth tubes using water as the working fluid. The use of different inlet disturbances were used to investigate its effect on transition. A tube-in-tube heat exchanger was used to perform the experiments, which ranged in Reynolds numbers from 1 000 to 20 000, with Prandtl numbers being between 4 and 6 while Grashof numbers were in the order of 105. Results showed that the type of inlet disturbance could delay transition to a Reynolds number as high as 7 000, while other inlets expedited it, confirming results of others. For heat transfer, though, it was found that transition was independent of the inlet disturbance and all commenced at the same Reynolds number, 2 000–3 000, which was attributed to secondary flow effects.

CFD Aided Design of Heat Transfer Plates for Gasketed Plate Heat Exchangers

2014 ◽  
Author(s):  
Ece Özkaya ◽  
Selin Aradag ◽  
Sadik Kakac
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Three Dimensional ◽  
Separate Flow ◽  
Working Fluid ◽  
Number Range ◽  
Plate Heat ◽  
Pressure Distributions ◽  
Cfd Analyses

In this study, three-dimensional computational fluid dynamics (CFD) analyses are performed to assess the thermal-hydraulic characteristics of a commercial Gasketed Plate Heat Exchangers (GPHEx) with 30 degrees of chevron angle (Plate1). The results of CFD analyses are compared with a computer program (ETU HEX) previously developed based on experimental results. Heat transfer plate is scanned using photogrammetric scan method to model GPHEx. CFD model is created as two separate flow zones, one for each of hot and cold domains with a virtual plate. Mass flow inlet and pressure outlet boundary conditions are applied. The working fluid is water. Temperature and pressure distributions are obtained for a Reynolds number range of 700–3400 and total temperature difference and pressure drop values are compared with ETU HEX. A new plate (Plate2) with corrugation pattern using smaller amplitude is designed and analyzed. The thermal properties are in good agreement with experimental data for the commercial plate. For the new plate, the decrease of the amplitude leads to a smaller enlargement factor which causes a low heat transfer rate while the pressure drop remains almost constant.

scholarly journals Heat transfer and pressure drop evaluation of different triangular baffle placement angles in cross-corrugated triangular channels

2020 ◽  
Vol 24 (1 Part A) ◽  
pp. 355-365
Author(s):  
Koray Karabulut
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Navier Stokes ◽  
Working Fluid ◽  
Inlet Temperature ◽  
Ansys Fluent ◽  
Number Range ◽  
Plate Heat ◽  
Corrugated Channel

Plate heat exchangers have a widespread usage and the simplest parallel plate channel structures. Cross-corrugated ducts are basic channel geometries used in the plate heat exchangers. In this study, the increasing of heat transfer from the cross-corrugated triangular ducts by inserting triangular baffles with different placement angles into the channel upper side and pressure drop have been numerically investigated. Numerical calculations have been carried out to solve Navier-Stokes and energy equations by employing k-? turbulence model as 3-D and steady with ANSYS-FLUENT program. While inlet temperature of the air used as working fluid is 293 K, constant surface temperature values of the the lower corrugated channel walls are 373 K. The height of the baffle and apex angle of the corrugated duct have been taken constant as 0.5 H and 60?, respectively. Investigated Reynolds number range is 1000-6000 while the baffle placement angles are 30?, 45?, 60?, and 90?. Numerical results of this study are within 3.53% deviation with experimental study existed in literature. The obtained results have been presented as mean Nusselt number temperature and pressure variations of the fluid for each baffle angle. The temperature and velocity vector contour distributions have been also assessed for different Reynolds numbers and baffle angles. The value of the Num for the corrugated channel with 60? baffle angle is 8.2% higher than that of the 90? for the Re = 4000. Besides, for Re = 1000 the value of the pressure drop is 39% lower in the channel with 60? baffle angle than that of 90?.

scholarly journals Modelling of Polymeric Shell and Tube Heat Exchangers for Low-Medium Temperature Geothermal Applications

Energies ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2737
Author(s):  
Francesca Ceglia ◽  
Adriano Macaluso ◽  
Elisa Marrasso ◽  
Maurizio Sasso ◽  
Laura Vanoli
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Power Plants ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Working Fluid ◽  
Heat Transfer Area ◽  
Geothermal Fluid ◽  
Shell And Tube

Improvements in using geothermal sources can be attained through the installation of power plants taking advantage of low and medium enthalpy available in poorly exploited geothermal sites. Geothermal fluids at medium and low temperature could be considered to feed binary cycle power plants using organic fluids for electricity “production” or in cogeneration configuration. The improvement in the use of geothermal aquifers at low-medium enthalpy in small deep sites favours the reduction of drilling well costs, and in addition, it allows the exploitation of local resources in the energy districts. The heat exchanger evaporator enables the thermal heat exchange between the working fluid (which is commonly an organic fluid for an Organic Rankine Cycle) and the geothermal fluid (supplied by the aquifer). Thus, it has to be realised taking into account the thermodynamic proprieties and chemical composition of the geothermal field. The geothermal fluid is typically very aggressive, and it leads to the corrosion of steel traditionally used in the heat exchangers. This paper analyses the possibility of using plastic material in the constructions of the evaporator installed in an Organic Rankine Cycle plant in order to overcome the problems of corrosion and the increase of heat exchanger thermal resistance due to the fouling effect. A comparison among heat exchangers made of commonly used materials, such as carbon, steel, and titanium, with alternative polymeric materials has been carried out. This analysis has been built in a mathematical approach using the correlation referred to in the literature about heat transfer in single-phase and two-phase fluids in a tube and/or in the shell side. The outcomes provide the heat transfer area for the shell and tube heat exchanger with a fixed thermal power size. The results have demonstrated that the plastic evaporator shows an increase of 47.0% of the heat transfer area but an economic installation cost saving of 48.0% over the titanium evaporator.

Mesochannel Compact Heat Exchangers for Automotive Air Conditioning Applications

2008 ◽  
Author(s):  
Amir Jokar ◽  
Mohammad H. Hosni ◽  
Steven J. Eckels
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Air Conditioning ◽  
Working Fluid ◽  
Empirical Correlations ◽  
Transfer Coefficients ◽  
Compact Heat Exchangers ◽  
Automotive Air Conditioning ◽  
Uncertainty Estimates

Experimental study of the single-phase heat transfer and fluid flow in mesochannels, i.e., between microchannels and minichannels, has received continued interest by researchers in recent years. The studies have resulted in empirical correlations for various geometries ranging from simple circular pipes to complicated enhanced non-circular channels. In spite of these extensive studies, it is still unclear whether the theories and correlations developed for conventional macrochannels are directly applicable for use in microchannels (Dh = 10–200 μm) and minichannels (Dh = 200 μm–3 mm) with heat exchanger applications. A few researchers have agreed that similar results maybe obtained for the laminar flow regime regardless of the channel size; however, no general agreement has been reached for the transitional and turbulent flow regimes yet. In this study, different mesochannel air-liquid compact heat exchangers were evaluated and the experimental results were compared with published empirical correlations. These compact heat exchangers were used in the secondary fluid loops of an automotive air conditioning system that used refrigerant R134a as the working fluid. A modified Wilson plot technique was applied to obtain the heat transfer coefficients, and the Fanning equation was used to calculate the pressure drop friction factors. The uncertainty estimates for the measured and calculated parameters were calculated. The results of this study showed that the well established heat transfer and pressure drop correlations for the macrochannels are not directly applicable for use in the compact heat exchangers with mesochannels.

Investigation on Shell-Side Performance of Heat Exchanger With Axially Staggered Overlap Helical Baffles

2010 ◽  
Author(s):  
Shui Ji ◽  
Wenjing Du ◽  
Lin Cheng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Low Cost ◽  
Convection Heat Transfer ◽  
Working Fluid ◽  
Shell Side ◽  
Open Issue

Since its appearance in the 80’s of the 20th century, the heat exchanger with helical baffles (HEHBs) has attracted lots of attention. Benefiting from its relatively simple manufacture procedure and low cost, the heat exchanger with overlapped helical baffles receives much concern. However, there are few reports on the influence of the specific overlap size of helical baffles on the shell-side heat transfer performance and fluid friction property. In this paper, numerical investigation on this open issue is carried out by means of numerical method. The emphasis is laid on the relationship between the overlap size of helical baffles and the shell-side performance. Baffles with the shape of a quarter-ellipse are simulated and the heat-transfer oil is selected as the working fluid. Results show that in the condition of same helix angles and same flow rates, 10% increase of the specific overlap size brings an increase of 23–42% on the pressure drop and an increase of 2–8% on the convection heat transfer coefficient; hence the corresponding heat transfer coefficient pre unit pressure drop is decreased by 11–22%. Compared with the continuously overlap configuration, the axially staggered overlap helical baffles can improve the comprehensive performance of HEHBs on the condition of an identical helical pitch, and hence it is favorable for the situation with strict constrain on pressure drop.

scholarly journals Design and Analysis of double- stacked Heat Exchanger for Brewery Application

2020 ◽  
Vol 9 (1) ◽  
pp. 1793-1798
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Transfer Rate ◽  
Flow Rate ◽  
Transfer Rate ◽  
Working Fluid ◽  
Support Weight ◽  
Tube Heat Exchanger ◽  
Shell And Tube

A heat exchanger is a device intensively used for enhancing the transfer of heat energy between two or more working fluids at different temperature, which are in thermal contact. The optimal design and efficient operation of heat exchanger and heat transfer network are of a great significance in any of the process industry. The heat transfer efficiency depends on both design of heat exchanger and property of working fluid. From various types of heat exchanger, the double stacked shell and tube heat exchanger with straight tube and single pass is to be under study. Here the redesign of heat exchanger takes place with the key objectives of optimizing the pressure drop, optimizing the heat transfer rate and reducing the saddle support weight used for cooling purpose in brewery application. The design calculations are carried out using the Kerns and Bell Delwar method and other important parameters dealing with material selection and geometries are also taken into consideration. FEA analysis for optimizing the saddle support weight is carried out using Dassault systeme’s Solidworks while the CFD analysis for optimizing pressure drop and heat transfer rate is carried out using Dassault systeme’s Solidworks analysis software and the design and working of Shell and tube heat exchanger is determined in terms of variables such as pressure ,temperature ,mass flow rate ,flow rate ,energy input output that are of particular interest in Shell and tube heat exchanger analysis.

Experimental Study and Genetic-Algorithm-Based Correlation on Shell-Side Heat Transfer and Flow Performance of Three Different Types of Shell-and-Tube Heat Exchangers

2006 ◽  
Vol 129 (9) ◽  
pp. 1277-1285 ◽  
Author(s):  
Qiu-wang Wang ◽  
Gong-nan Xie ◽  
Bo-tao Peng ◽  
Min Zeng
Keyword(s):  
Heat Transfer ◽  
Genetic Algorithm ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Transfer Coefficients ◽  
Shell Side ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
Shell And Tube

The heat transfer and pressure drop of three types of shell-and-tube heat exchangers, one with conventional segmental baffles and the other two with continuous helical baffles, were experimentally measured with water flowing in the tube side and oil flowing in the shell side. The genetic algorithm has been used to determine the coefficients of correlations. It is shown that under the identical mass flow, a heat exchanger with continuous helical baffles offers higher heat transfer coefficients and pressure drop than that of a heat exchanger with segmental baffles, while the shell structure of the side-in-side-out model offers better performance than that of the middle-in-middle-out model. The predicted heat transfer rates and friction factors by means of the genetic algorithm provide a closer fit to experimental data than those determined by regression analysis. The predicted corrections of heat transfer and flow performance in the shell sides may be used in engineering applications and comprehensive study. It is recommended that the genetic algorithm can be used to handle more complicated problems and to obtain the optimal correlations.

Techno-economic analysis of nitrogen-doped graphene/water nanofluid in various heat exchangers (A unified analysis)

2021 ◽  
pp. 095765092110521
Author(s):  
Yousif M Alkhulaifi ◽  
Shahzada Zaman Shuja ◽  
Bekir Sami Yilbas
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Working Fluid ◽  
Heat Transfer Area ◽  
Plate Heat ◽  
Nitrogen Doped ◽  
Nitrogen Doped Graphene ◽  
Doped Graphene ◽  
Shell And Tube ◽  
Double Pipe

Nitrogen-doped graphene (NDG)/water nanofluid is one of the emerging working fluids toward achieving high heating rates in heat transfer devices. In the present study, thermal performance improvement and techno-economic analysis of a double pipe, shell and tube, and plate heat exchangers are presented while incorporating NDG/water nanofluid as a working fluid. The variable properties of NDG nanofluid are incorporated and the influence of nanoparticle concentrations and mass flow rates on the device thermal performance and related costs are evaluated. The findings demonstrate that device heat transfer area and costs are adversely affected by using NDG/water nanofluid in all types of heat exchanging devices considered. An increase in heat transfer area is associated with the decrease of the specific heat capacity of the working fluid. The increase of heat transfer area can be as high as 58.5%, 45.1%, and 67.0% for double pipe, shell and tube, and plate heat exchangers, respectively. In addition, area increase becomes persistent with other types of nanoparticles used in the carrier fluid.

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