Dimensioning of Spiral Heat Exchangers to Give Minimum Costs

1984 ◽  
Vol 106 (3) ◽  
pp. 633-637 ◽  
Author(s):  
A. B. Jarze˛bski
Keyword(s):  
Fluid Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Input Data ◽  
Heating Surface ◽  
Working Fluid ◽  
Spiral Flow ◽  
Flow Rates ◽  
Process Fluid ◽  
Minimum Costs

Simple expressions are presented for calculating approximate dimensions of spiral heat exchangers to give minimum annual cost of heating surface plus energy required to pump the fluids. The case of spiral–spiral flow is considered. Equations are derived for exchangers with and without distance holders between plate strips and for two sets of input data: (i) both volumetric fluid flow rates V1, V2 and all inlet and appropriate outlet temperatures are given; (ii) the flow rate of the process fluid V1 and the effectiveness e1 are imposed, while the flow rate of the working fluid V2 is an additional variable subject to optimization. For the latter case, appropriate optimum values of V2 can readily be found from the graphs provided.

scholarly journals The effect of the intermediate fluid flow rate on the system performance in the closed circuit applications of the solar collector

2019 ◽  
pp. 472-472 ◽  
Author(s):  
Hasan Yildizhan ◽  
Taqi Cheema ◽  
Mecit Sivrioğlu
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Flow Rate ◽  
Solar Collector ◽  
Closed Loop ◽  
Closed Circuit ◽  
Working Fluid ◽  
Solar Collectors ◽  
Flow Rates ◽  
Energy And Exergy

Solar collector water heating system use solar thermal energy to provide hot water for domestic and industrial use. These systems are operated either as open-loop or closed-loop flow circuit. The former loop systems are not recommended for the cold climates having water freezing problem. Although previous studies on solar collectors have used closed-loop operation with water as the working fluid; however, it must have high boiling and low freezing points for the colder regions and thus arises the need for antifreeze mixtures of water. Another solution to the same problem is the use of heat transfer oil as intermediate working fluids. In the present study, the energy and exergy analysis of a boiler supported vacuum tube solar collector system working with closed-loop in different working fluid flow rates have been performed and evaluated. Heat transfer oil has been used as an intermediate working fluid in the closed loop system at different flow rates of 0.277 kg/s, 0.383 kg/s, 0.494 kg/s. The results show that the collector temperature difference as well as the outlet temperature decrease; however, the collector inlet temperature increases by increasing the flow rate. Moreover, with the increase in flow rate, it was ascertained that the energy and exergy efficiency of the system and the collectors increase. The main finding of the present study is that the intermediate fluid used in the closed-circuit operation of the solar collectors has a direct effect on the energy and exergy efficiency of the system.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

Study on the effect of pore-scale heterogeneity and flow rate during repetitive two-phase fluid flow in microfluidic porous media

2021 ◽  
pp. petgeo2020-062
Author(s):  
Jingtao Zhang ◽  
Haipeng Zhang ◽  
Donghee Lee ◽  
Sangjin Ryu ◽  
Seunghee Kim
Keyword(s):  
Porous Media ◽  
Fluid Flow ◽  
Flow Rate ◽  
Sweep Efficiency ◽  
Residual Saturation ◽  
Flow Rates ◽  
Content Type ◽  
Lower Flow ◽  
Supplementary Material ◽  
Lower Flow Rate

Various energy recovery, storage, conversion, and environmental operations may involve repetitive fluid injection and, thus, cyclic drainage-imbibition processes. We conducted an experimental study for which polydimethylsiloxane (PDMS)-based micromodels were fabricated with three different levels of pore-space heterogeneity (coefficient of variation, where COV = 0, 0.25, and 0.5) to represent consolidated and/or partially consolidated sandstones. A total of ten injection-withdrawal cycles were applied to each micromodel at two different flow rates (0.01 and 0.1 mL/min). The experimental results were analyzed in terms of flow morphology, sweep efficiency, residual saturation, the connection of fluids, and the pressure gradient. The pattern of the invasion and displacement of nonwetting fluid converged more readily in the homogeneous model (COV = 0) as the repetitive drainage-imbibition process continued. The overall sweep efficiency converged between 0.4 and 0.6 at all tested flow rates, regardless of different flow rates and COV in this study. In contrast, the effective sweep efficiency was observed to increase with higher COV at the lower flow rate, while that trend became the opposite at the higher flow rate. Similarly, the residual saturation of the nonwetting fluid was largest at COV = 0 for the lower flow rate, but it was the opposite for the higher flow rate case. However, the Minkowski functionals for the boundary length and connectedness of the nonwetting fluid remained quite constant during repetitive fluid flow. Implications of the study results for porous media-compressed air energy storage (PM-CAES) are discussed as a complementary analysis at the end of this manuscript.Supplementary material: Figures S1 and S2 https://doi.org/10.6084/m9.figshare.c.5276814.Thematic collection: This article is part of the Energy Geoscience Series collection available at: https://www.lyellcollection.org/cc/energy-geoscience-series

scholarly journals Learning The Fluid/Flow Properties Using Microfluidics

2019 ◽  
Vol 215 ◽  
pp. 10002
Author(s):  
Pooria Hadikhani ◽  
Navid Borhani ◽  
S. Mohammad H. Hashemi ◽  
Demetri Psaltis
Keyword(s):  
Neural Networks ◽  
Fluid Flow ◽  
Microfluidic Device ◽  
Flow Rate ◽  
Deep Neural Networks ◽  
Good Accuracy ◽  
Flow Properties ◽  
Flow Rates

Deep neural networks (DNN) are employed to measure the flow rate and the concentration of the liquid using the images of the droplets in a microfluidic device. The trained networks are able to measure flow rates and concentrations with good accuracy.

Experimental analysis on thermal and friction factor characteristics of fluid flow in tube with novel double strip helical screw tape

2019 ◽  
Vol 234 (6) ◽  
pp. 874-886
Author(s):  
Shashank R Chaurasia ◽  
RM Sarviya
Keyword(s):  
Nusselt Number ◽  
Fluid Flow ◽  
Friction Factor ◽  
Experimental Analysis ◽  
Flow Characteristics ◽  
Performance Ratio ◽  
Working Fluid ◽  
Flow Rates ◽  
Twist Ratio ◽  
Single Strip

An experimental analysis has been carried out to investigate the thermal and friction factor characteristics of fluid flow in a tube with double strip helical screw tape (DS-HST) inserts with different values of twist ratio and compared with single strip helical screw tape inserts and plain tube. Water is used as a working fluid at different flow rates with constant heat flux conditions. CFD analysis is also carried out to visualize thermal and fluid flow characteristics of fluid flow in tube with inserts. Experimental results have showed that Nusselt number and friction factor have attained excellent enhancement with double strip helical screw tape inserts in the range of flow rates than single strip helical screw tape inserts at the value of twist ratio 1.5. Correlation is also developed for Nusselt number with a range of Reynolds number, twist ratio and number of strips. Moreover, the performance ratio has attained maximum value at twist ratio of 2.5 with high values of flow rate. It is concluded that DS-HST is able to attain enhancement in the efficiency of heat exchanger, causing a reduction in size for thermal applications.

Flow Losses in Stirling Engine Heat Exchangers

1988 ◽  
Vol 110 (1) ◽  
pp. 58-62 ◽  
Author(s):  
J. D. Jones
Keyword(s):  
Closed Form ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Pressure Variation ◽  
Working Fluid ◽  
Design Work ◽  
Flow Losses ◽  
The Difference ◽  
Flow Velocities

Closed-form expressions are sought which will allow the rapid and accurate calculation of pressure variation, flow velocities, and flow friction losses in crank-driven Stirling cycle machines. The compression and expansion spaces of the Stirling machine are assumed to be isothermal and their volumes are assumed to vary sinusoidally. It is further assumed that the cyclic pressure variation of the working fluid and the flow velocities within the passages of the machine can be represented by sinusoids. Closed-form expressions are deduced for the amplitude and phase of these variations. Using the expressions so deduced, formulae are derived for frictional losses in the three heat exchangers, taking into account the variation in mass flow rate over the cycle and the difference in amplitude of mass flow between the two ends of the regenerator. By comparing these expressions with calculations based on the assumption of an average flow rate over the cycle, it is shown that the latter method leads to flow losses being underestimated by more than 50 percent. It is recommended that the formulae deduced here be used for first-stage design work.

STUDY OF FLOW AERODYNAMICS IN A CHANNEL WITH DUMBBELL-SHAPED DIMPLES

2016 ◽  
Vol 6 (1) ◽  
pp. 15-20
Author(s):  
Ivan Dmitrievich FEDOTENKOV ◽  
Anna Aleksandrovna TSYNAEVA
Keyword(s):  
Flow Rate ◽  
Heat Exchangers ◽  
Gas Flow ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Aerodynamic Resistance ◽  
Smooth Wall ◽  
Heat Transmission ◽  
Flow Rates ◽  
Small Flow

The paper deals with the study of aerodynamic resistance in a channel with dumbbell-shaped dimples on the surface and with smooth walls. It has been found that the hydraulic resistance of a channel with dumbbell-shaped dimples is higher than of a smooth one. The surface of the channel of the proposed design is also higher. It can be used for the intensification of heat transmission in recuperative heat exchangers of ventilation systems. The numerical study of the flow in a rectangular channel with one-sided arrangement of dimples of proposed geometry has been carried out. It has been determined that the use of such dimples at small flow rates near the inlet (1-0.5 m/s) will increase the rate of gas flow near the surface with dimples in comparison with a smooth wall to 20 %. When the flow rate near the inlet is 16.5 m/s, the areas with lower rates appear near the dimples.

scholarly journals Numerical simulation of concentrating solar collector P2CC with a small concentrating ratio

2012 ◽  
Vol 16 (suppl. 2) ◽  
pp. 471-482 ◽  
Author(s):  
Velimir Stefanovic ◽  
Sasa Pavlovic ◽  
Marko Ilic ◽  
Nenad Apostolovic ◽  
Dragan Kustrimovic
Keyword(s):  
Mathematical Model ◽  
Fluid Flow ◽  
Solar Radiation ◽  
Solar Energy ◽  
Radiation Intensity ◽  
Solar Collector ◽  
Numerical Procedure ◽  
Working Fluid ◽  
Flow Rates ◽  
Solar Radiation Intensity

Solar energy may be practically utilized directly through transformation into heat, electrical or chemical energy. A physical and mathematical model is presented, as well as a numerical procedure for predicting thermal performances of the P2CC solar concentrator. The demonstrated prototype has the reception angle of 110? at concentration ratio CR = 1.38, with the significant reception of diffuse radiation. The solar collector P2CC is designed for the area of middle temperature conversion of solar radiation into heat. The working fluid is water with laminar flow through a copper pipe surrounded by an evacuated glass layer. Based on the physical model, a mathematical model is introduced, which consists of energy balance equations for four collector components. In this paper, water temperatures in flow directions are numerically predicted, as well as temperatures of relevant P2CC collector components for various values of input temperatures and mass flow rates of the working fluid, and also for various values of direct sunlight radiation and for different collector lengths. The device which is used to transform solar energy to heat is referred to as solar collector. This paper gives numerical estimated changes of temperature in the direction of fluid flow for different flow rates, different solar radiation intensity and different inlet fluid temperatures. The increase in fluid flow reduces output temperature, while the increase in solar radiation intensity and inlet water temperature increases output temperature of water. Furthermore, the dependence on fluid output temperature is determined, along with the current efficiency by the number of nodes in the numerical calculation.

scholarly journals Four Layer Cylindrical Model of Mucus Transport in the Lung: Effect of Prolonged Cough

2019 ◽  
Vol 19 (1) ◽  
pp. 53-63
Author(s):  
Arti Saxena ◽  
Vijay Kumar ◽  
JB Shukla
Keyword(s):  
Fluid Flow ◽  
Flow Rate ◽  
Circular Tube ◽  
Medical Science ◽  
Moist Air ◽  
Serous Fluid ◽  
Mixture Flow ◽  
Flow Rates ◽  
Immotile Cilia ◽  
Laminar Condition

Background: In this paper, a four layer model of the simultaneous and coaxial flow of moist air, mucus, mixture of mucin and periciliary liquid and serous fluid (assumed to be incompressible and Newtonian fluids) in a circular tube under time dependent pressure gradient representing prolonged cough is analyzed to study the mucus transport in an airway in the presence of prolonged cough. It is assumed that air and mucus flow under quasi steady state turbulent conditions while the mixture of mucin and periciliary liquid and serous layer surrounding mixture layer flows under unsteady laminar condition in presence of immotile cilia carpet. Result: It is shown that the mucus transport increases as the viscosity of serous fluid decreases. Also the mixture and serous fluid flow rates increase as the viscosity of serous fluid decreases. It is also observed that the effect of resistance to flow by serous fluid in the cilia bed is to decrease flow rates. The flow rates of mucus and mixture of mucin and periciliary fluid increase as the viscosity of mixture decreases also air and mixture of mucus and periciliary fluid flow rates increase as the thickness of mixture increases. Conclusion: As the thickness of mucus increases its flow rate increases on the other hand the mixture flow rate, mucus and serous fluid flow rate decreases with the increase of the mixture thickness. Bangladesh Journal of Medical Science Vol.19(1) 2020 p.53-63

scholarly journals Efficiency Improvement of a Photovoltaic Thermal (PVT) System Using Nanofluids

Energies ◽  
2019 ◽  
Vol 12 (16) ◽  
pp. 3063 ◽  
Author(s):  
Joo Hee Lee ◽  
Seong Geon Hwang ◽  
Gwi Hyun Lee
Keyword(s):  
Flat Plate ◽  
Flow Rate ◽  
Thermal Efficiency ◽  
Measurement Errors ◽  
Efficiency Analysis ◽  
Working Fluid ◽  
Efficiency Improvement ◽  
Flow Rates ◽  
Electrical Efficiency ◽  
Water Based

Many studies and considerable international efforts have gone into reducing greenhouse gas emissions. This study was carried out to improve the efficiency of flat-plate photovoltaic thermal (PVT) systems, which use solar energy to produce heat and electricity simultaneously. An efficiency analysis was performed with various flow rates of water as the working fluid. The flow rate, which affects the performance of the PVT system, showed the highest efficiency at 3 L/min compared with 1, 2, and 4 L/min. Additionally, the effects of nanofluids (CuO/water, Al2O3/water) and water as working fluids on the efficiency of the PVT system were investigated. The results showed that the thermal and electrical efficiencies of the PVT system using CuO/water as a nanofluid were increased by 21.30% and 0.07% compared to the water-based system, respectively. However, the increase in electrical efficiency was not significant because this increase may be due to measurement errors. The PVT system using Al2O3/water as a nanofluid improved the thermal efficiency by 15.14%, but there was no difference in the electrical efficiency between water and Al2O3/water-based systems.

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