Thermal-hydraulic Performance Of Heat Exchanger Research Articles

Numerical and experimental investigations on the thermal-hydraulic performance of heat exchangers with Schwarz-P and gyroid structures

The fluid flow and heat transfer are investigated in high-performance heat exchangers with Schwarz-P and Gyroid structures using numerical and experimental approaches. This study was carried out first for laminar flow (Re = 10–100, Pr = 3–6) numerically and second for turbulent flow (Re = 1850–5500, Pr = 3.5) numerically and experimentally. All simulations were performed with COMSOL software to investigate the flow patterns, thermal performance, and pressure drop in heat exchangers based on the Schwarz-P and Gyroid with various unit cell numbers between 1 and 64. For low Re simulations, it is observed that the heat transfer coefficient and performance evaluation coefficient (PEC) increase with increasing the number of cells (or decreasing the cell size) in a constant volume. By redefining the Reynolds number based on the hydraulic inlet diameter and the velocity at the inlet of the structure, the Colburn and friction coefficients become independent of the structure's density. Correlations are provided to predict these coefficients. The results show that the Gyroid with 64-unit cells provides an average of 24 % (maximum 33 %) enhancement in the PEC and 40 % (maximum 46 %) Nusselt number improvement over the tube banks. On the contrary, the Schwarz-P does not have an improvement in PEC or Nusselt number compared to the tube bank. For the high Re study, several prototype heat exchanger samples based on the Schwarz-P and Gyroid structures were fabricated utilizing the FDM 3D-printing technique with no support structures to show that these heat exchangers could be manufactured. The SLM method was also used to fabricate a Gyroid heat exchanger for use in the experimental studies. The performance of a Gyroid heat exchanger made of AlSi10Mg has been tested for input flow rates ranging from 1 to 3 L per minute. For numerical simulation, the k-epsilon and K–W-SST turbulence models are employed and their results are compared with the present experimental data. It is found that the results of the K–W-SST model provide better agreement with experimental ones.

Numerical study on the effects of circuits on thermal-hydraulic performance in an indoor unit with small diameter in air conditioner

The distributed parameter method is adopted to establish a simulation model of the indoor unit of a split-type household air conditioner with a diameter of 5 mm. The circuits of forward and reverse cross are proposed, and the effects of different circuits on the thermal-hydraulic performance of heat exchanger are revealed. Compared with the prototype, the heat load of the forward and reverse cross is increased more obviously. The forward and reverse cross can realize the strengthening of the heat load by changing the spatial distribution of heat load and temperature difference. The forward and reverse cross under the cooling condition can improve the temperature difference of the second row. The heat loads of the two-phase zone and the vapor phase zone increase to a certain extent. Under the cooling condition for circuit-3, the heat load is increased by 6.65%, and the pressure drop in refrigerant side is slightly increased. Under the heating condition for circuit-3, the heat load and pressure drop in refrigerant side are similar to that of the prototype. Meanwhile, the circuit-3 has the most obvious improvement effect on the non-uniformity of pressure drop under different conditions.

Air-side flow and heat transfer characteristics research and empirical correlations of wavy fins in negative gauge pressure environment

ABSTRACT When the vehicle cooling system works in negative gauge pressure environment of plateau, it will face the problem of reduced heat transfer performance, which will lead to an increase in vehicle energy consumption. So, there’s important meaning in studying the thermal-hydraulic performance of heat exchangers and optimizing the design of which for negative gauge pressure environments. In this article, experimental study of wavy fin heat exchanger is carried out in negative gauge pressure environment, and then the numerical simulation model is established. The effects of fin size parameters (fin pitch, fin height and fin amplitude) on the temperature field and flow field distribution of wavy fins are studied. Empirical correlations of Colburn j factor and Friction factor f are obtained according to 336 groups of numerical simulation results. The heat transfer coefficient of air side at −44kPa negative pressure is decreased by 34% on average compared with atmospheric pressure, and the friction factor f is increased by 61.5%. The average deviations of correlations for j and f are 2.3% and 2.7%, respectively. The results could be used in engineering practice of design and optimization of wavy fin heat exchangers for vehicle cooling systems operate in plateau environment.

COP optimization of propane pre-cooling cycle by optimal Fin design of heat exchangers: Efficiency and sustainability improvement

The demand for LNG (liquefied natural gas) increases each year, and relevant studies have been developed in order to reduce both power consumption and greenhouse gas emissions of LNG plants. Multistream plate-fin heat exchangers (MPFHE) are widely used in these plants due to their large heat transfer surface area per unit volume for multi-phase flows. The thermal-hydraulic performance of heat exchangers also impacts on compressor shaft work of liquefaction plants. In this study, an automated optimization procedure is performed for commonly used MPFHE in a three-stage propane pre-cooling cycle to maximize the coefficient of performance (COP) of liquefaction plants. Four geometric input parameters (fin type, fin height, fin thickness, and fin frequency) have been selected for the optimization. The optimal heat exchangers and operating conditions of the entire refrigeration cycle and their feasibility are taken into account. The optimal fin designs of the heat exchangers affect the cycle operating conditions, which results in COP improvements of 18.9%, 2.5%, and 9.4%, and ranging from 7% to 32% of mitigation in CO2 emission when compared to the literature cases. Compared with the baseline case, the COP is improved by 9.4%, compressor shaft power is reduced by 7.1% (about 11.2 MW), heat transfer is augmented by 1.5% (3.8 MW), and CO2 emission is reduced by 6.3 t/h, which result in more efficient and sustainable LNG production.

On the Role of Nanofluids in Thermal-hydraulic Performance of Heat Exchangers-A Review.

Heat exchangers are key components in many of the devices seen in our everyday life. They are employed in many applications such as land vehicles, power plants, marine gas turbines, oil refineries, air-conditioning, and domestic water heating. Their operating mechanism depends on providing a flow of thermal energy between two or more mediums of different temperatures. The thermo-economics considerations of such devices have set the need for developing this equipment further, which is very challenging when taking into account the complexity of the operational conditions and expansion limitation of the technology. For such reasons, this work provides a systematic review of the state-of-the-art heat exchanger technology and the progress towards using nanofluids for enhancing their thermal-hydraulic performance. Firstly, the general operational theory of heat exchangers is presented. Then, an in-depth focus on different types of heat exchangers, plate-frame and plate-fin heat exchangers, is presented. Moreover, an introduction to nanofluids developments, thermophysical properties, and their influence on the thermal-hydraulic performance of heat exchangers are also discussed. Thus, the primary purpose of this work is not only to describe the previously published literature, but also to emphasize the important role of nanofluids and how this category of advanced fluids can significantly increase the thermal efficiency of heat exchangers for possible future applications.

A comparative experimental study on the performance of staggered tube-bundle heat exchanger with unequally-pitch and equally-pitch arrangement in oscillating flow

A novel staggered tube-bundle seawater heat exchanger with unequally-pitch arrangement, which the transversal and longitudinal tube pitches are inhomogeneous, is firstly proposed and applied in the closed-loop seawater source heat pump system. An experimental system that can induce the regular wave to simulate the seawater flow is established to investigate the thermal resistance ratio, overall heat transfer coefficient, thermal efficiency of heat exchanger under various wave parameters. The thermal performance, hydraulic performance, and comprehensive thermal-hydraulic performance of heat exchangers with unequally-pitch arrangement and equally-pitch arrangement are compared. The results indicate that the unequally-pitch arrangement of tube-bundle heat exchanger can significantly enhance the overall heat transfer coefficient and thermal efficiency, meanwhile decrease the pressure drop, and consequently improve the comprehensive performance. The present study is conducive to improve the performance potential of staggered tube-bundle seawater heat exchanger and promote the exploitation of ocean thermal energy.

Optimization of inlet part of a microchannel ceramic heat exchanger using surrogate model coupled with genetic algorithm

High temperature resistance and corrosion resistance make ceramic materials available for heat exchangers operating under high temperature or harsh chemical conditions. And the importance of the effect of flow maldistribution on thermal-hydraulic performance of heat exchangers has been demonstrated by a lot of researches. In this work, the nonuniformity of fluid flow is focused on to improve the performance of a microchannel ceramic heat exchanger. The inlet part of a microchannel ceramic heat exchanger is optimized using surrogate model coupled with genetic algorithm. Specifically, 30 sample points are designed by Latin hypercube sampling method and calculated by computational fluid dynamics. Radial basis neural network is established with the sample data and employed to predict the specific fluid flow distribution within design space as a surrogate model. Specifically, the surrogate model predicts the specific flow distribution instead of a single target value of nonuniformity in previous surrogate model. The results indicate that such a method has a significant advantage over the previous surrogate model. The genetic algorithm is implemented to search for the optimal point. The nonuniformity of fluid flow is reduced by 68.2% and pressure drop is increased by 6.6% by the optimization, which means the uniformity of fluid flow in the heat exchanger is improved significantly with just a little cost of pressure drop.

Continuum equations for the prediction of shell-side flow and temperature patterns in heat exchangers

The so-called fluid-tube continuum approach to describe the thermal-hydraulic performance of heat exchangers is critically reviewed. Special attention is given to the correct formulation of the boundary conditions, and a derivation of the equations starting from basic principles is presented. The resulting linear system of partial differential equations, a Laplace equation and two linear convection equations, is solved numerically by a finite element approximation method based on the least squares minimum principle. Finally, the numerical results are compared with experimental data. The agreement is good.