Flow Heat Exchanger Research Articles

Importance of Three-Dimensional Vehicle Heat Exchanger Modeling

Abstract This article demonstrates, via a comprehensive study, the necessity of using a 3D computational fluid dynamics (CFD) approach for heat exchanger (HTX) modeling within underhood vehicle simulation. The results are presented as the difference between 1D and 3D CFD approaches with a focus on auxiliary fluid (e.g., coolant) temperature prediction as a function of primary fluid (e.g., air) inlet conditions. It has been shown that the 1D approach could significantly underpredict auxiliary fluid inlet temperature due to neglecting the spatial distribution of primary fluid velocity magnitude. The resultant difference in the auxiliary fluid flow HTX inlet temperature is presented and discussed as a function of the uniformity index (UI) of the primary fluid flow velocity magnitude. In addition, the 3D HTX model’s importance is demonstrated in an industrial example of full 3D underhood simulation.

Analytical and experimental investigation on heat transfer and flow parameters of Multichannel louvered fin cross flow heat exchanger using iterative LMTD and ∊-NTU method

Automotive Heat exchangers plays vital role by ensuring human comfort in cabin by maintaining optimum temperature and maintains operating temperature of Internal Combustion(IC) engine within permissible limits. In this work, iteration based mathematical model to solve for analytical thermo-hydraulic performance estimation of a typical heat exchanger is adopted with Log Mean Temperature Difference (LMTD) method by incorporating the variation in properties of fluids during each iteration, since the overall thermal resistance ratio between targeted & calculated Heat Rejection Rate (HRR) has to be converged to unity to solve for the actual thermal performance of the heat exchanger. This condition ensures convergence and there is no deviation between the two adjacent iterations in terms of HRR value. Additionally, the above condition ensures that deviation between analytical value calculated by Effectiveness-NTU (∊-NTU) method and experimental data will be reduced significantly due to the proposed iterative LMTD approach adopted in this work. Along with iterative LMTD methodology, ∊-NTU method is adopted for last iteration to cross-verify the obtained value of the HRR for same operating conditions. In order to evaluate heat transfer coefficients for air and coolant side, standard correlations are used from well-established and validated literature data. For coolant side pressure drop calculations, network solution methodology is adopted where fluid flow behavior in each segment of heat exchanger is studied in detail and analytical relationships are used to predict net pressure drop in entire heat exchanger. In our mathematical model, louvered fin effects on heat transfer is taken into account by adopting colburn approach and the geometrical effects of internal fins on flow channels is also included. Experimental validations tests are carried out to compare with the analytical results of HRR, Coolant Side Pressure Drop (CSPD) and Air Side Pressure Drop (ASPD) across heat exchanger. A good agreement is found between experimental and analytical results which validates the accuracy of present mathematical model and methodology, the maximum deviation for HRC is 4% on higher side, for CSPD and ASPD it is 15.4%,8.7% on higher side respectively.

Estimation of local heat flux with CFD and enhanced conjugate gradient method for laminar and turbulent flow in a helical coil tube heat exchanger

Estimation of local heat flux with CFD and enhanced conjugate gradient method for laminar and turbulent flow in a helical coil tube heat exchanger

Comparison of thermal performances between copper and stainless steels on application of graphene coatings

Computational Fluid Dynamics (CFD) and heat transfer simulations are conducted for a cross flow heat exchanger. The heat exchanger consists of a linear pipe carrying a heated fluid. The thermal interactions between the heated fluid having a laminar flow and the walls of the pipe have been studied under the influence of an external environment of water having a turbulent flow, in a direction normal to the pipe. A RANS model with a k-ε variant was used to model the behavior of different material pipes which were observed under the varying conditions of turbulence, velocity, pressure and vorticity. When subjected to the same conditions, plots of the temperature gradient, isothermal contours, heat transfer coefficient against Reynolds number and thermal conductivity modelled against the various graphene coating thicknesses studied have shown that out of Copper and Stainless Steel the former has shown the most significant increase in thermal conductivity on the addition of a Graphene coating. Furthermore, to check for optimum efficiency, the same study was conducted with an internal coating of a Graphene layer for the aforementioned materials. It has been observed that an outer coating was not only more economically feasible, but also showed better thermal performance compared to an inner coating of graphene for copper, however it did improve the thermal performance of Stainless Steel significantly.

Experimental study of heat transfer and pressure drop analysis of the air/water two-phase flow in a double tube heat exchanger equipped with dual twisted tape turbulator: Simultaneous usage of active and passive methods

In this paper, simultaneous use of active and passive methods for enhancing the thermal performance of a double-tube heat exchanger was investigated. This was done by injecting air bubbles into the working fluid and utilizing a dual twisted tape turbulator. Effects of these two procedures on the Nusselt number and pressure drop were evaluated when applied simultaneously. We further studied the effect of cold water flow rate on thermal parameter. The results indicated that the Nusslte number increases with the decrease of turbulator ratio and increases with the increase of bubble injection flow rate, cold water flow rate and the Reynolds number. The findings further showed that the simultaneous use of the two methods could increase the Nusselt number by 98–114%, 3–14%, and 20–39% compared to the cases with a simple tube heat exchanger, a turbulator-equipped heat exchanger (without bubble injection), and a heat exchanger with bubble injection (without turbulator), respectively.

Study on turbulent flow in wave wall tube heat exchanger

The traditional straight wall tube heat exchanger has low heat exchange efficiency, in order to solve this problem, the turbulent flow in wave wall tube heat exchanger was studied by numerical simulation. It is found that the unique corrugated structure of the heat exchange tube in the wave wall tube heat exchanger can improve the flow state of the fluid in the heat exchanger. The average pressure drop of heat exchanger gradually increases with the increase of Reynolds number Re. Under the same conditions, the average pressure drop of wave wall tube heat exchanger is lower than that of straight wall tube heat exchanger. The improvement of heat exchange performance of heat exchanger can not be realized only by increasing the inlet flow of heat exchanger. The wave wall tube heat exchanger can strengthen the heat exchange of the fluid in the heat exchanger.

Analysis of parallel flow heat exchanger using SiO2 nanofluids in the laminar flow region

Convective and overall heat transfer coefficients of SiO2 nanofluid flowing in a concentric DTHE are determined experimentally. The tests are carried out in the 800<Re<1900 range using SiO2/22nm nanofluids prepared in 0.2, 0.6 and 1.0% volume concentrations in 30:70 ratio glycerol-water mixture base liquid. The thermal and physical properties of silica nanofluids are determined in the range of 20-80°C. Viscosity, thermal conductivity, and density of nanofluids increased with particle concentration whereas specific heat decreased. Thermal conductivity and specific heat of nanofluids increased with temperature while viscosity and density decreased. Heat transfer experiments are conducted using nanofluids at a bulk temperature of 35°C in a laminar developing flow region. Overall heat transfer coefficient and convective HTC of 1.0% silica nanofluids are increased by 21.2 and 36.3% compared to base liquid.

Experimental study and comparative performance analysis on thermal-hydraulic characteristic of a novel longitudinal flow oil cooler

The longitudinal flow heat exchanger possesses lots of merits but it exhibits poor heat transfer coefficient at low Re condition, which makes it difficult to be applied in the high viscosity fluid area. In this paper, a heat transfer augment solution for lubricating oil flowing on shell side of a novel longitudinal flow twisted trifoliate tube oil cooler was proposed. Experiments were conducted to comparatively investigate the thermal–hydraulic performance of a twisted trifoliate tube oil cooler and a conventional segmental baffle oil cooler. The tube side study demonstrates that the Nu and f of the twisted trifoliate tube are 17.5–75.8% and 16.9–62.9% larger than that of the smooth circular tube. The shell side study shows that at the same oil mass flow rate, the shell side heat transfer coefficient of the twisted trifoliate tube oil cooler is 66.3–148.9% higher than that of the conventional segmental baffle oil cooler with pressure drop increased by 31.6–65.2%. Furthermore, the shell side performance evaluation criterion h/ΔP of the twisted trifoliate tube oil cooler is 1.46 times larger than that of the conventional segmental baffle oil cooler on average. The possible mechanisms responsible for the heat transfer enhancement are analyzed. In addition, the predictive correlations of tube side and shell side of the twisted trifoliate tube bundles for Nu and f are deduced based on the experimental data. Results from current research could provide useful correlations and beneficial guidance for design and application of the longitudinal flow heat exchanger in low Re ranging of 40–250.

Transient experimental investigation of airside heat transfer in a crossflow heat exchanger

• Experimental analysis is performed to study the dynamic response of a heat exchanger. • Residence time is found to have a significant effect on the response time. • Transient air heat transfer coefficient is obtained by energy balance on the wall. • An empirical correlation of airside Nusselt number is developed. • The response time of both fluids was not instantaneous to the step imposed. The increase in energy consumption and the demand for effective thermal management systems necessitate the search for enhanced heat exchangers with high thermal performance, lower weight, and compact size. Crossflow heat exchangers are a key component in the thermal management system of many industries such as HVAC, automotive, etc. Transient analysis helps predict the behavior of heat exchangers when they experience variations in their operational conditions in terms of flow rate or temperature. This work experimentally studies the dynamic response of a cross flow heat exchanger to overcome the data scarcity in transient airside and presents the results for various cases of step changes in air mass flow rate. The effect of the step change on heat transfer is investigated and presented by airside Nu, fluids dimensionless temperature, airside Re, heat transfer rates, and Colburn j factor. Results show that the two fluids do not respond instantaneously to the step imposed. The magnitude of the step change has a dissimilar effect on the response time of each fluid. The response time increases with the increase in the step change. A generalized empirical correlation is obtained to predict the airside Nu. This study advances the control of heat exchangers by exploring their transient response due to step changes in one of the fluids inlet condition.

An experimentally validated evaporative phase change heat transfer model for low mass flux applications using R134a in plate heat exchangers

Plate frame heat exchangers are common in liquid-coupled vapor compression systems due to their compactness and ease of maintenance. In some of these systems, the refrigerant within the evaporator can enter the heat exchanger as a subcooled liquid. As a result, the refrigerant passes through three different phases: single-phase liquid, two-phase fluid, and a superheated vapor. Unfortunately, there have been limited prior studies that have identified the best method to predict performance under these circumstances. Furthermore, previous investigations have not evaluated refrigerant evaporation in large industrial sized plate frame heat exchangers under conditions experienced in the present study experimental test facility, especially at mass fluxes below 7 kg m −2 s −1 . In the present investigation, a model was developed to predict the performance of plate and frame heat exchangers when the fluid enters as a subcooled liquid and exits as a superheated vapor. The model used full-sized plate heat exchanger geometry that was discretized into 20 sections to accurately capture local heat transfer and pressure drop effects. The model was validated using an R134a counter flow heat exchanger used in a turbo-compression cooling system test facility that had subcooled liquid entering the evaporator at low mass fluxes. A variety of empirical correlations were evaluated to determine what combination yielded the best predictive capability over the following range of conditions: 5.8 < G < 6.8 kg m −2 s −1 , 2 < q ″ < 2.8 kW m −2 , and 10 °C < T sat < 15 °C. When the correlations used a fixed control volume length in the heat flux calculation, the most accurate combination resulted in a mean absolute error of 5.5%. Future studies can use the approach described here to optimize heat exchanger size and performance.

Investigations on the effect of graphene coating on thermophysical properties of aluminium and mild steel for cross flow heat exchanger

In a cross-flow heat exchanger, heat transfer and fluid dynamics studies were conducted to observe the performance of graphene coated pipes. The heat exchanger consists of a linear pipe made of Aluminum 6061-T6 and Mild Steel in separate studies carrying a heated fluid. The thermal interactions between the heated fluid having a laminar flow and the walls of the pipe have been studied under the influence of an external environment of water having a turbulent flow, in a direction normal to the pipe. A RANS model with a k-ε variant was used to model the behavior of different material pipes which were observed under the varying conditions of turbulence, velocity, pressure, and vorticity. When subjected to the same conditions, plots of the temperature gradient, isothermal contours, heat transfer coefficient against Reynolds number and thermal conductivity modelled against the various graphene coating thicknesses studied have shown that out of Aluminum 6061-T6 and Mild Steel, the former has shown a significant increase in thermal conductivity on the addition of a Graphene coating. Simulation results showed an increase in Aluminium 6061 T6′s conductivity by 6.8975% with a continuous decrease in the heat transfer coefficient, whereas Mild Steel showed an anomaly in the heat transfer coefficient value which peaked at 1.2 mm thickness of graphene coating with a value of 3858.862 W/m2K.

Optimization procedure of a new type counter–flow heat exchanger

Plenty of studies exist in books and archival journals dealing with different types of heat exchangers. In the paper an analytical approach to evaluate the overall heat transfer coefficient of a new type heat exchanger is presented. Derived equations are applied to multi-objective optimization of a very large economizer of a recovery boiler, when the exchanger mass and size should be small but simultaneously heat transfer rate high.

Enhancing the concentric tube properties by optimizing operational parameters

Concentric tube warmth interchanger are used for multitude employment ranging from heat transfer for low cease packages to coolants in space cars. Typical heat alternate equations are sufficient to resolve problems related to finite temperature difference. However, scientific solutions require complicated calculations that considers losses and minute hast dissipations to offer accurate outcomes. Mathematical and analytical methods of counter go with the flow heat exchanger is carried out in this look at. Enumeration of heat change throughout counter float is facilitated by way of incorporating Runge-Kutta Method. Comparison among the two evaluation techniques is executed for 2 situations making use of NTU approach. During one of the conditions the input values had been maintained as same, all through the second one conditions, the input values were various. The Runge-Kutta Method gave correct results for both the situations.

Design of a compact mesh-based high-effectiveness counter-flow heat exchanger and its integration in remote cooling systems

Compact high-effectiveness Counter Flow Heat EXchangers (CFHEX) are crucial components of recuperative coolers, such as Joule-Thomson and Turbo-Brayton coolers and of remote cooling systems realised by a convective loop. This paper presents a design and analysis of a cryocooler-based remote cooling system that extends the cooling capabilities of a two-stage cryocooler. Increased heat exchange between high- and low-pressure channels is established by adding copper mesh material. A compact effective mesh-based CFHEX design covering the 4.5-290 K temperature and 1–10 bar pressure operation ranges is presented. The discretised numerical model of the CFHEX is also presented and covers a wide field of parameters, including axial conduction, variable material and fluid properties based on experimental and theoretical data and wall-mesh thermal contact conductance. In our design the latter has shown to have a significant influence on the effectiveness of the CFHEX based on the analysis of a range of inner tube materials. The sizing of a high-performance CFHEX with a predicted effectiveness of 96.5 % (number of transfer units (NTU)=27.6) and an accumulated pressure drop of 15 mbar using the model is demonstrated. The outlook for future work and experimental measurements of the parameters to complete the numerical model is presented.

Fluid flow and heat transfer characteristics in plate-fin heat exchanger with irregular-shaped hole leading flow structure

Fluid flow and heat transfer characteristics in plate-fin heat exchanger with irregular-shaped hole leading flow structure

New system of heat recovery from parked vehicles: Experiments and analysis

The present study suggests a new concept of heat recovery applied to underhoods of vehicles parked in underground parkings. The advantages of this concept is twofold: (1) enabling cool the environment around the parked vehicle and under its hood (2) considering to use the excess of heat under the hood to heat/preheat water in use in public buildings. This system shows potential performance especially in car parking where a large number of vehicles is present such as supermarkets, universities, schools, etc. The feasibility of recovering energy from underhoods of parked vehicles is performed in the study. An experimental setup equipped with thermocouples, a heat exchanger and a fan is implemented. The engine is stopped after a certain period of operation then measurements are performed on two types of engines: V4 and V6. The temperature of the hot air aspirated by the V4 and V6 engine reached 40 °C and 54 °C respectively. The hot air is used for heating water using a finned-tube cross flow heat exchanger where the recovered heat rate reached around 500 W. In addition, a case study for the parking of the Lebanese International University along with an economic study are considered. From the study, 300 cars are assumed to be present daily in the parking, equipped by different engines (V4, V6 and V8). Consequently, the recovered energy obtained during the 80 min is estimated at 97 kWh, which permits to heat 4000 L of water from 20 °C to 40 °C.

Mixed Mesh Finite Volume Method for 1D Hyperbolic Systems with Application to Plug-Flow Heat Exchangers

We present a finite volume method formulated on a mixed Eulerian-Lagrangian mesh for highly advective 1D hyperbolic systems altogether with its application to plug-flow heat exchanger modeling/simulation. Advection of sharp moving fronts is an important problem in fluid dynamics, and even a simple transport equation cannot be solved precisely by having a finite number of nodes/elements/volumes. Finite volume methods are known to introduce numerical diffusion, and there exist a wide variety of schemes to minimize its occurrence; the most recent being adaptive grid methods such as moving mesh methods or adaptive mesh refinement methods. We present a solution method for a class of hyperbolic systems with one nonzero time-dependent characteristic velocity. This property allows us to rigorously define a finite volume method on a grid that is continuously moving by the characteristic velocity (Lagrangian grid) along a static Eulerian grid. The advective flux of the flowing field is, by this approach, removed from cell-to-cell interactions, and the ability to advect sharp fronts is therefore enhanced. The price to pay is a fixed velocity-dependent time sampling and a time delay in the solution. For these reasons, the method is best suited for systems with a dominating advection component. We illustrate the method’s properties on an illustrative advection-decay equation example and a 1D plug flow heat exchanger. Such heat exchanger model can then serve as a convection-accurate dynamic model in estimation and control algorithms for which it was developed.

Thermal entropy and exergy efficiency analyses of nanodiamond/water nanofluid flow in a plate heat exchanger

The study is aimed to understand the heat transfer coefficient and thermal entropy generation analyses of plate heat exchanger by using water-based nanodiamond nanofluids. The experiments were conducted in the volume concentration range: 0 ≤ ϕ ≤ 1.0%, the Reynolds number range: 140 ≤ Re ≤ 610, the mass flow rate range: 0.05≤ṁ≤0.183kg/s, and the Peclet number range from 895.78 ≤ Pe ≤ 3882.72, respectively. The effect of Reynolds number, Peclet number and particle volume loadings of nanodiamond nanofluids on heat transfer characteristics and entropy generation has been investigated. Water and nanodiamond nanofluids were considered as hot and cold medium in the plate heat exchanger, respectively, for the experimental study. The study reveals considerable augmentation in heat transfer coefficient and Nusselt number with an increase of nanofluid particle loadings. The study showed 32.50%, 55.47%, 35.11%, 22.80%, and 18.93% enhancements in overall heat transfer coefficient, heat transfer coefficient, Nusselt number, pressure drop and pumping power compared to base fluid at a Reynolds number of 526.37 at ϕ = 1.0%. Improved effectiveness, number of transfer units and exergy efficiency of 14.41%, 32.81% and 19.72% was observed at ϕ = 1.0% and at a Reynolds number of 526.37 against base fluid data. The thermal entropy and friction entropy generation was showed decreasing and increasing trends respectively, in the measured particle volume loadings. The Bejan number and entropy generation number demonstrated the roles of heat transfer and friction factor in the entropy generation. From the experimental results a new Nusselt number and friction factor correlations were proposed.

Improving the performance of the air-cooling unit in the cooling system of a radar

The article discusses the issues of reducing the size of the cooling unit of the antenna of a radar station by improving the gas-dynamic processes occurring in the air-cooling unit. The results of the experimental studies of the gas flow in a plate-fin heat exchanger, being blown by one axial fan are presented. The feasibility of changing the number of axial fans for organizing a more uniform flow around the heat-exchange surfaces has been determined by calculation and theoretical methods. The calculation results are confirmed by experimental studies of the air flow in the segment of the heat exchanger, which is provided by a smaller fan.

Probabilistic modeling and reliability-based design optimization of a ground source heat pump system

The optimization design of a ground source heat pump (GSHP) system can be crucial in improving its performance and economic competitiveness. The effect of probabilistic uncertainties of design variables in a GSHP system was analyzed using reliability-based design optimization (RBDO) method. An analytical borehole heat transfer model was selected as the frame of energy simulation in this work. With the goal to minimize the cumulative costs over a 20-year lifespan of the GSHP system, a non-linear optimization was carried out under three constraint factors imposed on the internal flow in ground heat exchanger: The inlet water temperature, water pressure losses and Reynolds number to ensure turbulent flow. Three design variables including depth of boreholes, ground pipe radius and mass flow rate, and two random variables at the installation site, including the groundwater velocity and ground thermal conductivity were considered in this investigation. Different uncertainty levels were assigned into the probability indexes of all five variables, which were studied under multiple reliability levels of all three constraints. Results showed that uncertainties of variables can strongly affect the system reliability and total cost determination. The compromised increment of system cost to ensure the reliability was discussed, and the optimal combinations of design variables (borehole depth, pipe radius and mass flow rate) were also given under different designing scenarios.