Counter-flow Heat Exchanger Research Articles

Application of computational fluid dynamics (CFD) methods to analyze energy efficiency of indirect evaporative coolers

This paper proposes a method based on computational fluid dynamics to determine pressure drop and air distribution characteristics in recuperative exchangers. The numerical calculations were performed for a representative counter-flow heat exchanger with a relatively complex structure, providing a large heat exchange surface. To verify a proposed method, the empirical calculations based on known analytical solutions for straight channels with various shapes of cross-sections were also performed. Numerical and empirical calculations were compared with certified data obtained according to standards EN 308: 1997 standards. The verification showed that the numerical methods properly predict the pressure drop in operating parameters of the exchanger, within the uncertainty of experimental data. The empirical methods calculation accuracy strongly depends on the assumptions made before.

A hybrid 3He Joule-Thomson cryocooler designed for precooling the space dilution refrigerator

Space sub-Kelvin refrigeration technology is an indispensable part of many deep space exploration missions. The dilution refrigerator (DR) is one of the sub-Kelvin refrigerators used in space missions. The space DR requires a closed-cycle design for a longer service life. The 3He Joule-Thomson (JT) cryocooler is an excellent choice among the space mechanical cryocoolers for precooling the space closed-cycle DR (CCDR) because it can provide a stable, vibration-free precooling environment. In this paper, the required cooling capacity of the CCDR's final precooling stage is calculated. The design goal of the 3He JT cryocooler is to obtain 3.6 mW of cooling power at or below 1.7 K. A third-stage counter-flow heat exchanger (CFHX3) is designed for the 3He JT cryocooler with an actual heat exchange efficiency higher than 99 %. A four-stage JT compression system consisting of two oil-free linear compressors is developed based on space compressors verified by many space missions of China. The JT expansion impedance consists of two orifices with diameters of 27 μm and 26 μm in series. Then, experiments are conducted on the coordination of the CFHX3, the JT expansion impedance, and the JT compression system. Hence, a hybrid 3He JT cryocooler is successfully designed, fabricated, and tested for the CCDR and obtains a no-load temperature of 1.40 K with a power consumption of 277 W. Furthermore, with a power consumption of 320 W, the 3He JT cryocooler attains a cooling power of 3.75 mW at 1.54 K with temperature fluctuation lower than ±0.02 K.

Enhancement of Double-Pipe Heat Exchanger Effectiveness by Using Porous Media and TiO2 Water

In this paper, the rate of heat transfer by forced convection in a counterflow heat exchanger, at turbulent flow conditions were investigated experimentally, using porous media and TiO2 Nanofluid to observe the behaviour of heat transfer with flow rate and volume concentration of nanoparticles t enhance heat transfer through it. 3 mm Steel balls (ε=39.12%) as a porous media completely filled to the inner pipe (core pipe). The cold and hot water are used as working fluids through the inner and outer pipes. Then using, the TiO2 nanofluid instead of cold water flowing through the porous pipe to enhance heat characteristics. The effects of operating parameters include flow rate (4 LPM, 6 LPM, and 8 LPM), Reynolds number between (3000 – 7000), and nanoparticle volume fraction (0.001, 0.002 and 0.003) on Convective heat transfer co-efficient and Nusselt number. Effective thermal conductivity is increased when the nanoparticle volume fraction is increased. The heat transfer coefficient increases with decreasing nanofluid temperature, but the heating fluid's temperature has no significant effect on the nanofluid's heat transfer coefficient. The results show that porous media and TiO2-based nanofluid's improve heat transfer at flow rate of 4 LPM by 35.4% and improve NTU and effectiveness at flow rate of 4LPM by 12.4%, and 24%, respectively, when compared to pure water without porous media. This improvement in thermophysical properties yielded high heat transfer of heat exchangers used in process industries.

Impact of bumpers position variation on heat exchanger performance: an experimental and predictive analysis using an artificial neural network

Experimentally and numerically, the thermal performance enhancement of counterflow twin-pipe heat exchanger with bumpers position variation was explored. A set of semicircular bumpers were positioned at varying distances from the fluid flow entrance on the annulus gap of the concentric pipe heat exchanger (10–70, 70–130, and 130–190 cm). The hot water entered the inner pipe at a constant mass flow rate of 0.0167 kg/s, whereas the cold air entered the annulus gap of a concentric pipe heat exchanger at changing mass flow rates of 2 × 10−5 to 14 × 10−5 kg/s. The numerical portion comprised simulating the efficacy of the heat exchanger with a smooth pipe and varied bumper placements using an artificial neural network (ANN) model. The experimental portion of the present work consisted of a series of tests to determine the optimal position of the bumpers for maximizing heat exchanger efficiency. At a constant fluid inlet temperature and with varied mass flow rates of the cold air, the numerical model was compared to the experimental results. When the bumpers are put at a distance of 130–190 cm, the heat exchanger has the highest thermal efficiency compared to other bumper placements and a smooth pipe. In all cases of the investigation, there is a good correlation between numerical and experimental data.

Efficiency of counter flow heat exchange in copper tube using APISN and XTRA KOOL oils

Abstract We all know that heat exchanger is one of the equipment to transfer the heat between the fluids. Heat will transfer from one side of fluid to another side of fluid. In this project we use counter flow heat exchanger. In this heat exchanger one kind of fluid will come from one side and another kind of fluid will come from another side. Both fluids will be sending inside to the tube in opposite direction. Here we are using two medium one is hot fluid and another one is APISN (American Petrol Institution of Super Natural) with B grade oil. Inside of apparatus we are using copper tube, to enhance the heat transfer. Because that copper is having higher thermal conductivity (385 W/m K). When we compared to the carbon steel (19 W/m K), copper is having more thermal conductivity. The reason for choosing copper tube is not only higher thermal conductivity; it's also having properties like corrosion resistance, max allows able stress and internal pressure. Hot fluid will be send through the way of inside of the copper tube. Over the copper tube will send APISN oil, both will be send in an opposite manner. In a setup of counter flow heat exchanger, we put two holes with some dimension. When the fluid goes inside of the tube we insert the digital thermo-meter to note down the temperature of both inlet and outlet. After taking all reading we will evaluate the counter flow heat exchanger with term of efficiency.

A design model for spiral wound heat exchangers which accounts for property variation, longitudinal heat conduction, and heat-in-leak

• A combined analytical-numerical design model for cryogenic SWHE is developed. • Analytical sizing module finds the optimum configuration of SWHE. • The effects of property variation, LHC, and heat-in-leak are investigated. • LHC impact is negligible compared to property variation and heat-in-leak. • A sensitivity analysis on the input constraint is performed. Spiral Wound Heat Exchangers (SWHEs) can be a good and reliable choice for serving as the main heat exchanger in the cryogenic gas liquefaction cycles using throttling process such as the Linde-Hampson cycle. In this application, a high pressure hot gas stream has to be cooled down via transferring heat to a low pressure cold gas in a high-effectiveness heat exchanger. Present research has been organized to develop a design model which is able to find the optimum SWHE configuration for gas liquefaction cycles. The model has to be capable of considering the important physical phenomena in the cryogenic temperature ranges, including variation of fluid properties with temperature, longitudinal heat conduction (LHC) through separating walls, and heat-in-leak. Therefore, a combined analytical-numerical design model has been developed in the present study. The design model is essentially composed of two stand-alone modules, i.e. an analytical sizing module and a numerical performance evaluation module. To develop the design model, first, the geometrical characteristics of SWHE are studied and primary geometrical parameters are recognized. Then, the analytical sizing module is developed which is able to determine the optimum values of primary geometrical parameters of SWHE minimizing the heat transfer surface area based on the input design requirements. Afterwards, a 1D finite difference numerical module is presented in which important physical phenomena can be considered in the evaluation of the thermo-hydraulic performance of all types of counter flow or parallel flow heat exchangers as well as SWHEs. Finally, the two modules are combined to construct a design model. Two examples in which the low pressure superheated vapor helium is intended to cool down the high pressure supercritical helium flowing inside the tubes are also provided to demonstrate the applicability of the proposed combined model, and also, to elucidate its sensitivity to the input constraints. It was concluded that while variations of fluid properties and the external heat fluxes due to the radiation and convection have significant influence on the performance of cryogenic SWHE, the LHC is of minor importance and can be neglected. Moreover, decreasing the shell-side allowable pressure drop from 10 kPa to 2 kPa, causes the heat exchanger length and its outside diameter to increase by 79% and 48%, respectively.

Effect of an Internal Heat Exchanger on the Performances of a Double Evaporator Ejector Refrigeration Cycle

A theoretical investigation is presented about a double evaporator ejector refrigeration cycle (DEERC). Special attention is paid to take into account the influence of the sub-cooling and superheating effects induced by an internal heat exchanger (IHX). The ejector is introduced into the baseline cycle in order to mitigate the throttling process losses and increase the compressor suction pressure. Moreover, the IHX has the structure of a concentric counter-flow type heat exchanger and is intentionally used to ensure that the fluid at the compressor inlet is vapor. To assess accurately the influence of the IHX on the DEERC performance, a mathematical model is derived in the frame of the dominant one-dimensional theory for ejectors. The model also accounts for the friction effect in the ejector mixing section. The equations of this model are solved using an Engineering Equation Solver (EES) for different fluids. These are: R134a as baseline fluid and other environment friendly refrigerants used for comparison, namely, R1234yf, R1234ze, R600, R600a, R290, R717 and R1270. The simulation results show that the DEERC with an IHX can achieve COP (the coefficient of performance) improvements from 5.2 until 10%.

IMPROVING THE THERMAL PERFORMANCE OF A CONCENTRIC-TUBE HEAT EXCHANGER SYSTEM UTILIZING A NOVEL HYBRID MAGNETIC NANOFLUID

Hybrid magnetic nanofluid is the phase involved in a suspension of a mixture of nanometer-sized particles in traditional fluids. The most conspicuous attributes of this fluid comprise improved heat characteristics, for instance, convective heat transfer coefficient, compared to the conventional fluid. Hybrid magnetic nanofluid of iron oxide and ferric oxide with a mixture proportion of 50:50 was added to distilled water (DW). The impact of forced convective heat transfer coefficient in turbulent flow was estimated by employing parallel- and counter-flow concentric-tube heat exchanger systems. The forced convective heat transfer coefficient of the hybrid magnetic nanofluids was calculated applying empirical equations corresponding to the experimental results. Furthermore, the system's performance with (Fe<sub>3</sub>O<sub>4</sub>@Fe<sub>2</sub>O<sub>3</sub>/DW) 0.5 wt.% hybrid magnetic nanofluid with (Fe<sub>3</sub>O<sub>4</sub>/DW), (Fe<sub>2</sub>O<sub>3</sub>/DW) 0.3 wt.% regular magnetic nanofluids, and distilled water was compromised. The determinations reveal notable improvement in the convective heat transfer coefficient in both parallel- and counter-flow regimes in the case of hybrid magnetic nanofluid compared to the regular ones and base fluid, the highest enhancement in the overall convective heat transfer coefficient was up to 49.8% compared to distilled water at 31,689 Reynolds number and 18.46% and 20.5% compared to Fe<sub>3</sub>O<sub>4</sub>/DW and Fe<sub>2</sub>O<sub>3</sub>/DW regular magnetic nanofluids at 36,215 Reynolds number in the parallel-flow regime. Moreover, the Nu number was improved in the case of the hybrid magnetic nanofluid reaching maximum values up to 38.1%, 13.2%, and 14.8% corresponding to distilled water and regular magnetic nanofluids, respectively. The augmentation in the heat transfer utilizing hybrid magnetic nanofluids was caused by 22.47% thermal conductivity improvement compared to base fluid.

Parameter Estimation of Hyperbolic Model of Counterflow Heat Exchanger

The aim of this paper is to estimate the parameters of a counterflow heat exchanger in the case where the dynamics are described by a system of two hyperbolic partial differential equations (PDEs). This study is performed using data collected on a laboratory test bench. First we study the practical identifiability of the system, the objective of which is to verify the possibility of determining the parameters of the system in a unique way from the available data. Next the parameter estimation is performed by a nonlinear optimization method, typically by the Levenberg-Marquardt algorithm on a set of ordinary differential equations obtained from the reduction of the original PDEs by the method of lines. Since the Levenberg-Marquardt algorithm may only converge with a reasonable estimate of the parameters, we first consider a least squares parameter estimation approach based on the global difference model. Finally, the results of this Identification are validated by using laboratory data, and by verifying some statistical properties.

Thermodynamics Analysis of the Distributed Parameter Model of Counterflow Heat Exchanger

In this paper we are interested in the thermodynamic analysis of a counterflow heat exchanger, when the dynamics are described by two hyperbolic partial differential equations (PDEs). First from the first and second law of thermodynamics we derive the different models of the heat exchanger. Next we perform an analysis of the equilibrium profiles from a certain condition on the system parameters that guarantees the existence and uniqueness of the solution of the PDEs model. In this analysis we show the importance of the thermal pinch as an energy efficiency factor. Finally we study the passivity and the asymptotic stability of the considered heat exchanger essentially basing ourselves on the entropy as a storage function, entropy production as a dissipation function, and the thermodynamic availability function as a Lyapunov function.

KINERJA GAS PENUKAR PANAS ALIRAN BALIK SHELL AND TUBE UNTUK PENGERING PERTANIAN

Abstract—One of the important post-harvest processes of rice is drying. Drying is divided into two, namely natural drying (using sunlight) and artificial drying (using tools). In this study drying utilizes heat from a biomass furnace and a configuration of heat exchanger pipes. Where the utilization of heat and the configuration of heat exchanger pipes in the design can increase thermal efficiency because the exhaust hot air mixed with smoke can still be used for drying. The configuration of the heat exchanger pipe greatly influences the expected moisture content level. The purpose of this study was carried out to determine the performance of the shell and tube counter flow heat exchanger for agricultural dryer gases with a heat source from biomass and to find the effect of the configuration of the heat exchanger pipe arrangement on the working process of the drying machine. This research is an experimental test of the performance of heat exchange pipes with a heat source from a biomass furnace. The exchange pipe performance parameters that must be known are temperature and time. The method used in this study refers to experimental and descriptive methods, namely research conducted in a systematic, factual and accurate manner. The results of this study are that the heated air flow rate affects LMTD, heated air outlet temperature, heat transfer coefficient, and efficiency, with variations in the heated air flow rate of 0.11 kg/s, 0.16 kg/s, 0.20kg/s, 0.24kg/s. Highest efficiency of 94% at a heated air flow rate of 0.24 kg/s. and the smallest efficiency of 74% is found in the value of the heated air flow rate of 0.11 kg/s.
 Keywords : dewatering, biomass, pipe configuration, heat exchanger pipe

CFD analysis of heat transfer enhancement in a concentric tube counter flow heat exchanger using nanofluids (SiO2/H2O, Al2O3/H2O, CNTs/H2O) and twisted tape turbulators

A concentric tube, counter flow heat exchanger with nanofluids under turbulent flow conditions has been examined using a computational fluid dynamics model. The proposed model consists of Twisted Tape Turbulators (TTT) on the annular side and inside the tube along with different nanofluids. Twisted Tape Turbulators produce a swirl motion within the fluids to increase heat transfer. Al2O3/H2O, SiO2/ H2O, and CNTS/ H2O nanofluids (with varying volume concentrations of 1 %, 2 %, and 3 %) with the turbulent flow (Reynold number Re = 2000 to 10000) were considered to determine three major parameters i.e., heat transfer rate (Q), overall heat transfer coefficient (U) and Nusselt number (Nu). This study resulted in 6.03 %, 16.74 %, and 6.74 % enhancement of overall heat transfer coefficient (U) with a 3 % volume concentration of CNTS/H2O nanofluid, Al2O3/H2O nanofluid, and SiO2/H2O nanofluid, respectively, when equated to without twisted tape tabulators. This analysis shows the maximum value of Nusselt number as 143,136.68 and 140.12 for CNTS/H2O, Al2O3/H2O, and SiO2/H2O, respectively, for the twisted tape tubular arrangement. It is concluded that when using twisted tape turbulator, the heat transfer rate (Q), overall heat transfer coefficient (U), and Nusselt Number (Nu) increase with increasing Reynolds number (turbulent flow conditions) and volume concentrations of nanofluid.Novelty statement: Twisted Tape Turbulators (TTT) arrangement with different concentrations and types of nanofluids combined are infrequent in the study of concentric tube heat exchanger with turbulent flow to obtain enhanced heat transfer.

Enhancement of heat transfer coefficient by using helical coil heat exchanger

In this paper to study, a numerical analysis of a helical coil (tube-in-tube) heat exchanger is carried out for various B.Cs (Boundary Conditions), and the optimal heat transfer conditions are identified for various D/d ratios. For analysis purposes, the turbulent flow model with counterflow heat exchanger is taken into consideration. For various boundary conditions, the impact of D/d ratio on heat transfer rate and pumping power is observed. The D/d ratio varies between 10 and 30 with an interval of 5-point gap. For various D/d ratios, it is possible to determine the Nu (Nusselt number), friction value, power, and LMTD variation of the inner fluid with respect to Re (Reynolds number).

Enhancement of heat transfer coefficient by using helical coil heat exchanger

In this paper to study, a numerical analysis of a helical coil (tube-in-tube) heat exchanger is carried out for various B.Cs (Boundary Conditions), and the optimal heat transfer conditions are identified for various D/d ratios. For analysis purposes, the turbulent flow model with counterflow heat exchanger is taken into consideration. For various boundary conditions, the impact of D/d ratio on heat transfer rate and pumping power is observed. The D/d ratio varies between 10 and 30 with an interval of 5-point gap. For various D/d ratios, it is possible to determine the Nu (Nusselt number), friction value, power, and LMTD variation of the inner fluid with respect to Re (Reynolds number).

Seasonal energy efficiency ratio of regenerative indirect evaporative coolers—Simplified calculation method

Evaporative-cooling technology is a promising alternative to conventional air-cooling systems that are based on using direct expansion units in terms of energy efficiency. Seasonal energy efficiency ratio (SEER) calculation methodologies and standards for these air-cooling systems remain limited. Therefore, the objective of this study is to develop a novel simplified method for calculating the SEER for regenerative indirect evaporative coolers (RIEC). Experimental tests were performed to obtain energy efficiency ratio models of four RIEC systems. Five climate zones in the Mediterranean region were considered for calculation of the SEER values. A detailed calculation method based on annual energy simulations was employed, and the results of the seasonal index were compared with those of a simplified calculation method based on the steady-state operation at four specific test points. The relative error between the SEER calculation methods was 4.6% for all the RIEC systems and climate zones. The highest SEER values of 5.8 and 5.5 were achieved for the Cairo and Madrid weather conditions, respectively. This study can serve as a reference for research on the seasonal performance and life-cycle analysis of RIEC based on an efficient counterflow heat exchanger with a wide range of airflow and cooling capacities.

Performance prediction for modified design of dew point evaporative cooler for air cooling

ABSTRACT Traditional air conditioning systems use lot of energy; thus, dew point evaporative air-cooling systems could be a good alternative. Many experts studied the impact of constructional and operating characteristics on Maisotsenko cycle (M-cycle) to improve its performance. Cooler performance is influenced by the heat exchanger. Heat exchangers were constructed using flat and corrugated plates. The present study proposes the use of geometrically modified trapezoidal corrugated plates for counter flow heat exchanger, which consists of alternate air and water flow passageways. The numerical model is developed to predict the performance under variety of inlet air conditions and channel dimensions. In the standard range of incoming air properties such as relative humidity, the performance parameters assist in making cooler recommendations. Comparison and validation of simulation results are done with published experimental data for corrugated and trapezoidal corrugated plate heat exchangers. For trapezoidal corrugated plates, simulation findings revealed 10% increase in wet bulb efficiency and 7% increase in dew point efficiency over corrugated plates. The efficiency of wet bulb and dew point decreases as channel gap widens. For trapezoidal corrugated plates, the larger channel spacing minimises pressure drop.

Thermodynamic characteristics of counter flow and cross flow plate fin heat exchanger based on distributed parameter model

The distributed parameter models of counter flow and cross flow plate fin heat exchanger (PFHE) are constructed to investigate their thermodynamic characteristics. In practical application, the cold end of PFHE may be directly connected to the cold equipment. Therefore, the effect of longitudinal heat conduction (LHC) under different thermal boundary conditions set on two ends of the separating plates (SPs) is investigated based on the model of counter flow PFHE. It is found that LHC effect transmits the effect of boundary condition on two ends of the SPs into the inner domain of PFHE. The LHC effect on the heat transfer performance of PFHE is positive when setting appropriate boundary condition on two ends of the SPs. When considering LHC, compared with the adiabatic boundary conditions on two ends of the SPs, the effectiveness of constant wall temperature boundary conditions increases by 31.7 ∼ 35.8 %, and the effectiveness of constant heat flux boundary conditions increases by 22.8 %. The model of cross flow PFHE is used to investigate the effect of configuration and operation parameters on the heat transfer amount and the pump power. The cross flow PFHE is optimized to arrive at the maximization of heat transfer amount per unit pump power (HTPUP). In the three-stream cross flow PFHE studied, the heat transfer amount almost doesn’t change when the xz projected area is maintained and one projected length (z side length) is changing. The pump power is the lowest and the HTPUP is the largest when z side length of PFHE (z side is the flow direction of the fluid with large mass flowrate) is 0.15 ∼ 0.2 m.

Experimental investigation of a hybrid configuration of solar thermal collectors and desiccant indirect evaporative cooling system

This paper presents the integrated performance of a solar-assisted desiccant dehumidifier along with Maisotsenko cycle (M-cycle) counter flow heat and mass exchanger. This system handles latent load and sensible load separately. The hybrid configuration of solar thermal collectors was analyzed for efficiency of solar collectors and solar fraction. High consumption of fossil fuels, which are already present in a limited amount, is also associated with environmental problems and climate change issues, as these increase the chances of global warming. These issues demand of us to shift towards renewable energy resources. Increase in world energy use results in a number of environmental problems, such as climate change, in addition to global warming and ozone depletion. In building services, HVAC systems are major concerns. To overcome the requirement, conventional air conditioning and vapor compression systems are mainly used for air conditioning, although these also have some environmental problems. Solar thermal applications in combination with other renewable-energy-dependent cooling practices have generated a huge interest towards sustainable solutions, keeping in view several techno-economical, environmental, and climatic advantages. The experimental investigation reveals that the maximum outlet temperature and efficiency of solar thermal collectors was 87°C and 56% respectively. The maximum cooling capacity of the system is evaluated at 4.6 kW.

A 6-kW thermally self-sustained two-stage CO2 methanation reactor: design and experimental evaluation of steady-state performance under full-load conditions

This study designed and evaluated a 6-kW, two-stage CO2 methanation reactor, with the aim of effectively recovering the heat generated by the reaction and condensation of the by-product H2O, securing a high CO2 conversion (≥99%) under low pressure without any external thermal input for catalyst temperature control, i.e., thermally self-sustained. The H2 feed was split, with the majority being fed into the first reactor and the remainder into a second reactor. The heat-carrier flow was also split between the stages and, thereby, the second reactor was cooled by supplying only a fraction of the heat-carrier that had been heated in the first reactor. Reactor inner diameters of 16 and 25 mm, as well as parallel and counter flow heat exchange configurations were compared in the second reactor, using a 1-kW test rig. The results showed that the use of a 16-mm reactor diameter and a parallel flow configuration in the second reactor realize a higher total heat recovery with the 99% CO2 conversion. The steady-state performance of the designed 6-kW two-stage reactor was evaluated at 200 kPa (G) under full load. The reactor consequently recovered more than 70% of the total generated heat at 99% CO2 conversion, increasing the heat-carrier temperature from room temperature (inlet heat-carrier temperature) to 137 °C (outlet heat-carrier temperature).

Operator-Based Fractional-Order Nonlinear Robust Control for the Spiral Heat Exchanger Identified by Particle Swarm Optimization

Fractional-order calculus and derivative is extended from integral-order calculus and derivative. This paper investigates a nonlinear robust control problem using fractional order and operator theory. In order to improve the tracking performance and antidisturbance ability, operator- and fractional-order-based nonlinear robust control for the spiral counter-flow heat exchanger described by the parallel fractional-order model (PFOM) is proposed. The parallel fractional-order model for the spiral counter-flow heat exchanger was identified by particle swarm optimization (PSO) and the parameters of a fractional-order PID (FOPID) controller were optimized by the PSO. First, the parallel fractional-order mathematical model for a spiral counter-flow heat exchanger plant was identified by PSO. Second, a fractional-order PID controller and operator controller for the spiral heat exchanger were designed under the identified parallel fractional-order mathematical model. Third, the parameters of the operator and fractional-order PID were optimized by PSO. Then, tracking and antidisturbance performance of the control system were analyzed. Finally, comparisons of two control schemes were performed, and the effectiveness illustrated.