Three-fluid Heat Exchanger Research Articles

Influence of flow non-uniformity on the dynamic behaviour of three-fluid cross-flow compact heat exchanger

The flow uniformity at any cross-section along the flow is highly influenced due to different practical limitations such as improper header/distributor design, manufacturing defect etc. Hence, the compact three-fluid heat exchanger with cross-flow arrangement is numerically investigated with non-uniform flow at the entrance of central fluid for four feasible flow arrangements (C1,2,3,4) for turbulent flow regime. The experiments are conducted to validate the numerical solutions obtained from Implicit Finite Difference scheme. The dynamic response of the cross-flow three-fluid heat exchanger is analysed with step and sinusoidal perturbation at the entry and both the cooling and heating efficacy of the heat exchanger is discussed. The model is made more realistic by incorporating the dispersive axial heat conduction effect within the fluids as well as at the inlet section of heat exchanger (Dankwert's boundary condition) and wall longitudinal heat conduction in the conducting walls. Four cases of flow non-uniformity (P, Q, R and S), which resemble the most realistic and possible case of non-uniform flow in the heat exchangers are selected for present study. It is learnt that case P and case Q offers the maximum and the minimum augmentation or deterioration in the efficacy of heat exchanger when non-uniform flow exists only in central fluid. The impact of flow non-uniformity on the performance of heat exchanger is more significant in turbulent flow regime than laminar. The analysis is further extended for the flow non-uniformity in all the three fluid streams simultaneously and for certain combinational case of U (uniform flow), P and Q. It is found that flow non-uniformity drastically affects the heat exchanger's efficacy and the upshot of axial dispersion causes more deterioration in the thermal performance than that by longitudinal heat conduction.

Steady and Transient Behavior of Cross-Flow Three-Fluid Heat Exchanger With Temperature Nonuniformity in All the Fluids—A Detailed Investigation

Abstract Cross-flow three-fluid plate-fin heat exchanger is analyzed under both steady-state and transient conditions with a nonuniform inlet temperature of all the three fluids. The influence of the longitudinal heat conduction and axial dispersion in the separating sheets and three fluids, respectively, is also considered. Five different combinations (modes) of temperature nonuniformity in the three fluids have been considered and compared for the performance. An important phenomenon of temperature cross between/among the fluids has been observed and presented for certain modes of temperature nonuniformity and operating conditions. The effect in the performance has been presented on the basis of mean exit temperature and deterioration factor. Implicit finite difference technique has been used for the numerical solution. The heat exchanger's performance is found to be dependent on the mode of temperature nonuniformity, number of transfer units, and the operating parameters.

A Novel Equivalence Approximate Model for Second Law Based Optimization of Three-Fluid Cross-Flow Plate-Fin Heat Exchanger Using Genetic Algorithm

Abstract Number of entropy generation is a significant performance evaluation factor for heat exchanger as it results in trade-off between heat transfer and pressure drop. Optimization of the three-fluid heat exchanger (3−FHX) for minimum number of entropy generation unit requires ε−NTU relation which is unavailable for three-fluid cross-flow heat exchanger due to various complexities involved. A new approximate methodology for the optimization is presented by proving the equivalence of 3−FHX with a coupled two-fluid heat exchanger (2−FHX) followed by using ε−NTU relationship for 2−FHX. The experimental and numerical validation of the equivalence model is presented. Three-fluid cross-flow compact heat exchanger with offset strip fins is optimized for minimum number of entropy generation units using genetic algorithm (GA). Optimum design variables including heat distribution factor are determined for different cross-flow arrangements of 3−FHX with heat duty and pressure drop as constraint for both even and uneven fin dimensions case in all the passages. The present complex model including large number of continuous design variables can be handled well by GA. Validation of the results is carried out by using graphical techniques and very good agreement is observed. Additionally, sensitivity of the heat exchanger dimension has also been checked on the number of entropy generation along with the pressure drop in all the three fluids.

Development and composition of a data center heat recovery system and evaluation of annual operation performance

The huge energy consumption of data centers has reached 416.2 billion kWh of electricity, which is responsible for 2% of the world’s total electricity consumption in 2017. Data center heat recovery for district heating is one of the most promising methods to reuse data center low grade waste heat. This paper proposes a heat recovery system with a heat pump/heat pipe integrated unit based on three-fluid heat exchanger. The system operates in three modes: heat recovery mode, heat pipe mode and mechanical cooling mode. Experimental results show that the comprehensive energy efficiency ratio of heat recovery mode reaches 4.47 when the heating supply water temperature is 50 °C. Annual performance of the heat recovery system in a 5 kW data center is analyzed in Tianjin. Results show that the comprehensive energy efficiency ratio of the whole system throughout the year is 4.75, which indicates great potential in heat recovery for district heating at cold regions.

Design and performance simulation of a novel hybrid PV/T-air dual source heat pump system based on a three-fluid heat exchanger

To pursue an environmentally friendly and efficient heating solution, a novel hybrid PV/T-air dual source heat pump based on a three-fluid heat exchanger was proposed. In the heating season, the system can absorb energy from solar and air simultaneously; in the non-heating season, the PV modules can be cooled actively or passively by heat pipe. The system was designed to provide heating and electricity for a rural single-family house in Beijing, and a mathematical model was developed. The results indicated that: (1) compared to a conventional air-source heat pump, the energy consumption of this system throughout the heating season was reduced by 13.1%; (2) for electricity generation, compared to a conventional PV panel, the electrical energy output increased by 14.7%. Additionally, the proposed integrated system has the advantages of a compact structure, standardized production, easy maintenance, and no risk of freezing.

Thermodynamic Optimization of Three-Fluid Cross-Flow Heat Exchanger Using GA and PSO Heuristics

Optimization technique for a three-fluid cross-flow plate-fin heat exchanger with offset strip fins is developed, considering significant variables subjected to given constraints. The objective of optimization is focused on maximizing the hot fluid effectiveness and minimizing the number of entropy generation units in the three-fluid cross-flow plate-fin heat exchanger. Governing equations for a cross-cocurrent flow arrangement of a three-fluid heat exchanger are solved using finite element method for given boundary conditions. The obtained mean exit fluid temperatures from FEM are used to determine the rate of entropy generation and hot fluid effectiveness of the heat exchanger. Results obtained from the optimization of a reduced model of two-fluid cross-flow heat exchanger is compared with previously published results, thus serving as a validation of the optimization technique. Geometric parameters of the heat exchanger are varied to get the optimum results. The present investigation uses two different heuristics, namely Genetic algorithm (GA) and Particle Swarm Optimization (PSO) to find the optimum design values based on the objectives. Minimization of number of entropy generation units is treated to be a single objective function and optimum solutions are determined using both GA and PSO, both giving a function value of 0.0534786. Similarly, considering maximization of the hot fluid effectiveness, the optimum function value from both techniques is found to be 0.99997095. The results obtained from both the methods are compared and provides almost identical design values, with PSO taking lesser time for execution. Also, considering minimization of number of entropy generation units and maximization of hot fluid effectiveness of the heat exchanger as objective functions, multi-objective optimization is performed using GA alone and the multiple results obtained has been illustrated as a pareto-front.

Analysis, prediction and multi-response optimization of heat transfer characteristics of a three fluid heat exchanger using response surface methodology and desirability function approach

In the present study, an effort is made to evaluate the effect of four non-dimensional input parameters i.e. curvature ratio (δ), non-dimensional coil pitch (λ), tube side Reynolds number (Rei) and outer annulus side Reynolds number (Reo) on thermal performance of the Three Fluid Heat Exchanger (TFHE). Interaction between these input parameters and their influences on heat transfer characteristics of the TFHE i.e. entropy generation number, Ns and tube side Nusselt number, Nu are assessed by a statistical RSM model developed by Box–Behnken design approach. Adequacy of the model is checked by ANOVA analysis and capability of the developed model is tested towards effective prediction of the output responses. Sensitivity analysis is performed to identify and rank various critical parameters with respect to their order of importance. To assess the optimal levels of input variables, a multi-response optimization analysis is performed using desirability function approach for maximum heat transfer i.e. Nu and minimum irreversibility loss i.e. Ns in the TFHE. It is found that the minimum value of entropy generation number and maximum value tube side Nusselt number for the optimum performance of the TFHE are predicted as 0.0719 and 115.244, respectively with a composite desirability, D of 0.903077. Performance of TFHE is found to be enhanced by 33.73% of reduction in entropy generation number and 21.46% increment in tube side Nusselt number.

Performance analysis of an internally-cooled plate membrane liquid desiccant dehumidifier (IMLDD): An analytical solution approach

An internally-cooled parallel-plate membrane-based liquid desiccant dehumidifier (IMLDD) with cooling tubes inside the solution channels has been used for air dehumidification. The concept is similar to a three-fluid heat and mass exchanger containing processing air, liquid desiccant, and refrigerant streams. The processing air and the liquid desiccant streams flow in the neighboring channels, which are formed by the plate membranes. A row of the cooling tubes are installed in each solution channel to take away the absorption heat generated in the solution by absorbing the water vapor transferred from the processing air across the membranes into the solution. A lumped parameter model is established in a unit cell containing an air channel, a plate membrane, a solution channel, and a row of the cooling tubes, to study the heat and mass transports in the IMLDD. An analytical solution of the normalized governing equations is obtained based on the dimensionless parameters, which have their specific physical meanings. Sensible cooling effectiveness, dehumidification effectiveness, dehumidification rate, energy transfer rate of the air stream, and the ratio of the sensible heat transfer rate of the water stream to the energy transfer rate of the air stream are then calculated. Only a few operating conditions of inlet water temperatures and sensible heat capacity ratios from previous studies have been employed to validate the model. However more validations would be conducted in future under more operating conditions. It can be found that the performances of the IMLDD are largely improved when the water inlet temperature is decreased to keep the solution temperature always in a relatively small level. The water inlet temperature is recommended to be set as about 20 °C, which is somewhat smaller than the solution inlet temperature.

Numerical Investigation on Three-fluid Heat Exchanger for Hybrid Energy Source Heat Pumps

Abstract Hybrid energy source heat pump system is one of the best solutions to achieve efficient and stable utilization of renewable energies such as solar energy, geothermal energy, etc. The Three-fluid heat exchanger can realize heat transfer from the refrigerant to the outside air and the inside water simultaneously or independently, which will keep the refrigerant well distributed under difference working modes. The simulation model is built and validated for performance analysis of the three fluid heat exchanger based on Matlab and REFPROP. Three heat exchangers with different flow path designs are investigated for the heat transfer and pressure loss. The results show that the heat exchanger can give better performance by optimization of heat transfer coefficient and the pressure loss. Moreover, the influence on the heat exchanger from the variation of the air flow speed, air temperature, water flow speed and water temperature are also been analyzed.

Performance Analysis of Three Fluid Heat Exchanger Used in Solar Flat Plate Collector System

Abstract In the present study, the thermal performance of a three fluid heat exchanger (TFHE) used in solar flat plate collector system is studied. The TFHE is an improved version of double pipe heat exchanger, where a helical tube is inserted between two concentric straight tubes for better performance. This paper presents a new technique of simultaneous air and water heating in TFHE using solar energy. The heating cost can be minimised considerably by supplying the hot water or thermal fluid from a solar flat plate collector through the helical tube of TFHE to heat incoming cold air and water in the inner most pipe and outer annulus. The TFHE is investigated experimentally and validated by comparing the result of experimental approach with literature. Decent agreements between the experimental and literature values are observed. The purpose of this study is to determine the effect of Reynolds number and Dean number on performance of the TFHE in steady-state for both flow configurations. The overall heat transfer coefficients, U o,h-n varies directly and effectiveness, ɛ h-n varies inversely with hot water volume flow rate, however hot water flow rate have least or no effect on coil side Nusselt number, Nu h . The effect of inner Dean Numbers on overall heat transfer coefficients, U o,h-n and effectiveness, ɛ h-n is negligible in parallel flow configuration, however is appreciable in counter flow configuration.ommittee of RAAR 2016.

Experimental investigation of convective heat transfer in an inserted coiled tube type three fluid heat exchanger

In the present study, an experimental investigation of a three fluid heat exchanger (TFHE) has been performed. The TFHE presented here is an improved version of double pipe heat exchanger, where a helical tube is inserted between two concentric straight tubes. The curvature ratio, δ = 0.1315, pitch to inside diameter, p/dci = 2.88 of the helical tube are taken constant during the test while range of coil side Reynolds number are varied between 9000 and 54,000 during this investigation. Coil side Nusselt numbers are calculated using traditional Wilson plot technique and compared with the Nusselt numbers reported from literature for both parallel and counterflow configurations. Temperature distribution data has been obtained using analytical approach and experimental approach for three fluids. The effect of variation in volume flow rate on performance of the TFHE is assessed as well. Overall heat transfer co-efficient found to be increased in each case when flow rate of different fluids in TFHE increased. The effectiveness decreases or increases, which are the combined effect of residence time, capacity ratio, R and NTU. TFHE provides optimized performance, when flow rate of normal water increases in counter flow configuration. Simultaneous space heating and water heating is the novelty of the proposed TFHE.

Effect of ambient heat-in-leak on transient behaviour of three-fluid heat exchanger with two thermal communications using finite element method

In the current paper the effect of ambient heat in leak on transient behaviour of three-fluid heat exchangers is described using the finite element method. The solution is obtained for parallel flow three-fluid heat exchanger with two thermal communications; it is obtained for step change in the inlet temperature of hot fluid. Comparison with the previously published steady results shows excellent agreement. The effect of heat in leak is studied on the time to reach steady state, temperature profiles and outlet temperatures. As the cold fluid is exposed to ambient the effects are more significant on it than intermediate and hot fluids. This method is so versatile that it could be applied to calculate the step, exponential, sinusoidal, ramp disturbances in inlet temperatures of any of the fluids.

Performance Definitions for Three-Fluid Heat and Moisture Exchangers

This paper presents performance definitions for calculating the overall effectiveness of three-fluid heat and moisture exchangers. The three-fluid heat and moisture exchanger considered in this paper is a combination of a liquid-to-liquid heat exchanger for heat transfer between a desiccant solution and a refrigerant and an energy exchanger for heat and moisture transfer between desiccant solution and air streams. The performance definitions presented in this paper are used to calculate the overall sensible and latent effectivenesses of a three-fluid heat and moisture exchanger, which has been tested under air cooling and dehumidifying operating conditions in a previous work (Abdel-Salam et al., 2016, “Design and Testing of a Novel 3-Fluid Liquid-to-Air Membrane Energy Exchanger (3-Fluid LAMEE),” Int. J. Heat Mass Transfer, 92, pp. 312–329). The effectiveness of this three-fluid heat and moisture exchanger is compared when calculated using the traditional energy exchanger effectiveness equations and the overall performance definitions. Results show that the overall performance definitions provide effectiveness values that are less sensitive to changes in the inlet refrigerant temperature and therefore are more generally applicable for energy exchanger design than the traditional effectiveness equations used in the literature.

Transient behavior of three-fluid heat exchanger with three thermal communications under step change in inlet temperature of fluids using finite element method

In the present paper the transient temperature response of a counter-flow three-fluid heat exchanger with three thermal communications is investigated numerically using finite element method. Comparison with the previously published steady state results shows excellent agreement. The effects of step change in inlet temperature of fluids on time to reach steady state, outlet temperature of fluids, effectiveness are studied. Variation of design parameters like H1, H2 R1, R2 and NTU is also studied. The time to reach the steady state is independent of the amplitude of step change in the inlet temperature of fluids. For a step-change in the inlet temperature of the any fluid, the outlet temperature of other two fluids reach steady state faster than the fluid whose inlet temperature is changed. This method is so versatile that it could be applied to calculate the exponential, sinusoidal, ramp disturbances in inlet temperatures of any of the fluids.

Performance of co-current and counter-current parallel flow three-fluid heat exchanger due to perturbations in flow

Transient behaviour of co-current and countercurrent parallel flow three-fluid heat exchanger with all the three fluids unmixed, has been numerically investigated for perturbations provided in flow. Results are presented for step change in flow rate of all the three fluids. It has been found that the mean exit temperature is greatly affected due to variation in the flow rate and thereby affecting the rate of heat transfer among the three fluids.

Numerical investigation on fin-tube three-fluid heat exchanger for hybrid source HVAC&R systems

The energy consumption of HVAC&R systems is increasing rapidly, and application of hybrid source systems is an alternative solution. Utilizing three-fluid heat exchanger in hybrid source HVAC&R system can make the system more compact in construction, higher in thermal efficiency and lower in reliability risk. In this paper, a simulation model of a fin-tube three-fluid heat exchanger is built with distributed-parameter method and validated by experimental data. Based on the demand of a new type of hybrid source system, the optimal circuit arrangement type and tube diameter are achieved. The heat transfer rates of the three fluids under different working conditions are investigated. The results also show that to ensure that cold fluid 1 is superheated in the outlet for the stable running of the system, flow rate and inlet pressure of the hot fluid and air inlet temperature should be higher than certain values, while flow rate and inlet pressure of cold fluid 1 should be lower than certain values. Air flow rate can be adjusted freely without range limit. This paper will help the design of fin-tube three-fluid heat exchanger and promote its application in HVAC&R systems.

Dynamic behaviour of a three fluid heat exchanger subjected to step change in inlet temperature of hot and cold fluids

Purpose – The purpose of this paper is to analyse the dynamic behaviour of a three-fluid heat exchanger subjected to a step change in the temperature and velocity of the fluids at the inlet. Design/methodology/approach – The analysis is carried out using the finite element methodology, adopting the Galerkin’s approach, using implicit method for transient behaviour. Findings – The effect of step changes in the inlet temperature of hot and cold fluids show that an increase in the fluid inlet temperatures leads to increased outlet temperatures of all fluids and decreased hot fluid effectiveness. The exit temperatures of the fluids do not show any response initially for a certain period of time with the step changes. The time to reach steady state is independent of the step change in inlet temperature of the hot and the cold fluids. Research limitations/implications – The findings of this paper is limited to constant property situations. Practical implications – The findings will be useful in designing contro...

Integrated system of mechanical refrigeration and thermosyphon for free cooling of data centers

The number of data centers is increasing rapidly in recent years. Huge amount of energy is consumed by the cooling equipment of data centers for its year round working. Cutting down the energy consumption of cooling equipment becomes an urgent need and free cooling is an ideal way. It is proposed an integrated system of mechanical refrigeration and thermosyphon (ISMT) by combining two independent loops, mechanical refrigeration loop and thermosyphon loop, with a three-fluid heat exchanger. The new ISMT has three modes: mechanical refrigeration, thermosyphon free cooling and dual mode. The experimental results show that it has sufficient cooling capacity of all these three working modes. The EER of the thermosyphon mode reaches 10.7 and 20.8 when the indoor and outdoor temperature difference is 10 °C and 20 °C, respectively, and the AEER of the ISMT is 12.6, which is much higher than traditional air conditioners (TAC). The annual energy consumption in four cities located in different climate zones of China is calculated and compared to TAC in a small data center. The annual energy-saving rate is 5.4%–47.3% when the indoor temperature is set on 27 °C, and it is higher in colder zones for longer working time of thermosyphon free cooling.

Finite Element Analysis of Three-Fluid Heat Exchanger for Diesel Engine Exhaust Heat Recovery System

In internal combustion engines, only a part of the fuel energy flow is transformed into power available at the crankshaft, while the most part of the fuel energy flow is lost as coolant, exhaust gases and other waste heat flows.The focus of this study is to evaluate the performance of three-fluid re-circulating type heat exchanger to recover energy from exhaust gas The cold fluid is re-circulated to enhance the recovery of heat from the exhaust gases. Finite element model of the heat exchanger is developed based on the detailed geometry and the specific working conditions and the effectiveness of the heat exchanger is computed. Non-Dimensional parameters are introduced which makes the analysis more versatile. The effectiveness is computed for different values of NTU, Heat capacity ratios, Overall heat transfer coefficient ratio between fluid channels and the inlet temperature.

Transient behavior of co-current parallel flow three-fluid heat exchanger

Transient behavior of co-current parallel flow three-fluid compact heat exchangers with the effect of two-dimensional longitudinal heat conduction through the separating sheet and axial dispersion in fluids has been investigated numerically by using the Gauss–Seidel iterative technique for step excitation provided to hot fluid inlet temperature. The results reveal that the performance of the heat exchanger is affected when two-dimensional longitudinal conduction in separating sheets and axial dispersion in fluids are considered.