Comparison of Numerical Simulation and Experimental Results for Crossflow and Counterflow Microchannel Heat Exchangers

Thermal performances of gas-to-gas counter-flow and parallel-flow microchannel heat exchanger have been investigated. Working fluid used is air. Heat transfer rates of both heat exchangers are compared with those calculated by a conventional log-mean temperature difference method. The results show that the log-mean temperature difference method can be employed to a parallel-flow configuration whereas that cannot be employed to a counter-flow configuration. This study focuses on the partition wall which separates hot and cold passages of the microchannel heat exchanger. The partition wall is negligibly thin for a conventional-sized heat exchanger. In contrast, the partition wall is thick compared with channel dimensions for a microchannel heat exchanger. A model which includes the effect of the thick partition wall is proposed to predict thermal performances of the microchannel heat exchangers. The heat transfer rates obtained by the model agree well with those obtained by the experiments. Thermal performances of the counter-flow and parallel-flow microchannel heat exchangers are compared with respect to one another based on temperature of the partition wall. The comparison results show that thermal performances of the counter-flow and parallel-flow microchannel heat exchangers are identical. This is due to performance degradation induced by the thick partition wall of the counter-flow microchannel heat exchanger. This study reveals that the thick partition wall dominates thermal performance of a gas-to-gas microchannel heat exchanger.

With the continuous worldwide energy use increase, energy efficiency is gaining high importance. Consequently, many methods have been investigated for potential energy savings. One of these methods is the use of heat recovery systems. These systems basically re-use waste heat and reduce energy consumption. Also, they are increasingly used to reduce heating and cooling demands of buildings. Their main feature is to provide fresh air to the place which is heated by the exhaust air with the help of a heat exchanger (HEX) working between two different temperature sources. The most commonly used types of heat exchangers in ventilation systems are cross-flow and counter-flow heat exchangers. Cross-flow heat exchangers have a thermal efficiency in the range of 50-75% while counter-flow heat exchangers have 75-95%. Many studies have been carried out to increase the efficiency of this type of heat exchangers. In this study, different designs of cross-flow and counter-flow exchangers are compared using ANSYS Fluent software. The aim is to determine how the plate surface geometry affects heat transfer and pressure drop. It is aimed to find the optimum design with maximum efficiency, high heat transfer and low pressure drop for heat exchangers. As a result, it has been observed that thermal efficiency increased from 18% to 60% when changing from cross flow to counter flow in flat plate design, while it increased from 25% to 77% in enhanced plate designs. For enhanced designs, counter flow heat exchanger is 52% more efficient than cross flow heat exchanger. Also, improvements to increase the surface area and turbulence in both flow types have increased heat transfer and thermal efficiency.

Comparative study of the performance of the M-cycle counter-flow and cross-flow heat exchangers for indirect evaporative cooling – Paving the path toward sustainable cooling of buildings

Heat transfer characteristics of a gas-to-gas counterflow microchannel heat exchanger have been experimentally investigated. Temperatures and pressures at inlets and outlets of the heat exchanger have been measured to obtain heat transfer rates and pressure drops. The heat transfer and the pressure drop characteristics are discussed. Since the partition wall of the heat exchanger is thick compared with the microchannel dimensions, a simple heat exchange model with constant wall temperature is proposed to predict the heat transfer rate. The predicted heat transfer rate using the constant wall temperature model agrees well with the experimental results.

Crossflow heat exchangers are essential for cooling and ventilation systems, transferring heat between two airstreams without mixing. This research explores the optimisation of microchannel heat exchangers by examining different channel geometries such as square-smooth, square-baffle, and square-wavy utilising hybrid nanofluids of multi-walled carbon nanotubes and nanodiamonds in water to assess their effects on heat transfer and pressure drop. The heat exchanger features eight channels on the bottom and eight on the top, facilitating separate flows of cold and hot fluids through insulated pathways. The model uses partial differential equations for momentum, energy, continuity, and boundary conditions, solved by the Gaussian weighted residual finite element method. Response surface methodology identifies the optimal configuration, while data analysis, including sensitivity analysis and optimisation testing, focuses on enhancing the performance of cross-flow microchannel heat exchangers. This study aims to identify the best thermal efficiency arrangement among three channel geometries. Specifically, the square-wavy channel improves heat transfer by 3.28 percent at a Reynolds number of 20 and boosts thermal efficiency by 2.11 percent when its value is 2. These results offer key insights for optimising the geometry of heat exchangers, providing insight and enhancing thermal efficiency while managing pressure drop levels.

The effect of a partition wall on heat transfer characteristics of a two-stream gas-to-gas counterflow microchannel heat exchanger has been numerically investigated. The flow passages of the microchannel heat exchanger are plane channels of 100 μm in height and 20 mm in length. The material of the partition wall is assumed to be stainless steel. The computations were performed for a wide range of flow rate to investigate heat transfer characteristics of the microchannel heat exchanger. Moreover, computations for various partition wall thicknesses were conducted to investigate the effect of the wall thickness. The thickness ranged from 200 μm to 6 μm while the channel height was fixed at 100 μm. Numerical results show that heat transfer characteristics of a gas-to-gas counterflow microchannel heat exchanger are affected by partition wall thickness. Computations for various partition wall thicknesses and thermal conductivities of the partition wall were performed. The results were compared with those of a single microchannel with constant wall temperature. Applicability of the assumption of constant wall temperature was revealed.

The effect of the hybrid suspension on the intrinsic characteristics of microencapsulated phase change material (MEPCM) slurry used as a coolant in counterflow microchannel heat exchanger (CFMCHE) with different velocities is investigated numerically. The working fluid used in this paper is a hybrid suspension consisting of nanoparticles and MEPCM particles, in which the particles are suspended in pure water as a base fluid. Two types of hybrid suspension are used (Al2O3 + MEPCM and Cu + MEPCM), and the hydrodynamic and thermal characteristics of these suspensions flowing in a CFMCHE are numerically investigated. The results indicated that using hybrid suspension with high flow velocities improves the performance of the microchannel heat exchanger while resulting in a noticeable increase in pressure drop. Thereupon, it causes a decrease in the performance index. Moreover, it was found that the increment of the nanoparticles’ concentration can rise the low thermal conductivity of the MEPCM slurry, but it also leads to a noticeable increase in pressure drop. Furthermore, it was found that as the thermal conductivity of Cu is higher than that for Al2O3, the enhancement in heat transfer is higher in case of adding Cu particles compared with Al2O3 particles. Therefore, the effectiveness of these materials depends strongly on the application at which CFMCHE is employed.

A heat exchanger model for mixtures and pure refrigerant cycle simulations

A systematic experimental investigation was conducted to evaluate the heat Transfer characteristics of a copper-nickel multi tube with corrugated copper fins in a cross flow heat exchanger. The heat transfer rate from a tube can be augmented either by increasing the surface area, by number of fins or by creating turbulence in the flow. Experiment was carried out under the copper fin tube type heat exchanger in which no. of fins is mounted along the full length of heat exchanger. The effect of no. of fins on a full length heat exchanger on the heat transfer coefficient was experimentally investigated in case of different mass flow rate of water and air. The performance evaluation of cross flow heat exchanger with copper fins was carried out for water temperature varying from 38°C to 64°C and water velocity 0.07735m/s to 0.271m/s and air velocity 3.194m/s to 14.52m/s. It was found that on the basis of different flow rate of water and air heat transfer coefficient increases constantly on the water and air side respectively.

A systematic experimental investigation was conducted to evaluate the heat Transfer characteristics of a copper-nickel multi tube with corrugated copper fins in a cross flow heat exchanger. The heat transfer rate from a tube can be augmented either by increasing the surface area, by number of fins or by creating turbulence in the flow. Experiment was carried out under the copper fin tube type heat exchanger in which no. of fins is mounted along the full length of heat exchanger. The effect of no. of fins on a full length heat exchanger on the heat transfer coefficient was experimentally investigated in case of different mass flow rate of water and air. The performance evaluation of cross flow heat exchanger with copper fins was carried out for water temperature varying from 38°C to 64°C and water velocity 0.07735m/s to 0.271m/s and air velocity 3.194m/s to 14.52m/s. It was found that on the basis of different flow rate of water and air heat transfer coefficient increases constantly on the water and air side respectively.

Thermal and hydrodynamic analysis of a cross-flow compact heat exchanger

The present study investigated the comparisons of the heat transfer and pressure drop of the microchannel and minichannel heat exchangers, both numerically and experimentally. The results obtained from this study indicated that the heat transfer rate obtained from microchannel heat exchanger was higher than those obtained from the minichannel heat exchangers; however, the pressure drops obtained from the microchannel heat exchanger were also higher than those obtained from the minichannel heat exchangers. As a result, the microchannel heat exchanger should be selected for the systems where high heat transfer rates are needed. In addition, at the same average velocity of water in the channels used in this study, the effectiveness obtained from the microchannel heat exchanger was 1.2–1.53 times of that obtained from the minichannel heat exchanger. Furthermore, the results obtained from the experiments were in good agreement with those obtained from the design theory and the numerical analyses.

A steady-state performance model of multirow multipass cross-flow tubular heat exchangers is developed. The proposed matrix approach uses the concepts of local effectiveness, energy balance, and number of transfer units (NTU) applied to every pass/row in the cross-flow heat exchanger to predict thermal performance. The method can predict the total effectiveness of assemblies of heat exchangers. Several circuiting configurations, such as overall counter-cross-flow, overall parallel cross-flow, and fluids in parallel in one of the streams, were considered. Predictions of the steady heat transfer performance of selected multirow multipass cross-flow heat exchangers are obtained by applying the general matrix approach. The heat exchanger geometries selected for the comparative study represent common cross-flow heat exchanger configurations used in industry. For these heat exchangers the overall heat exchanger effectiveness values were computed for various capacity rate ratios and NTU values. The validity of the matrix approach was then verified by comparing the resulting predictions with those obtained using the P-NTU approach and the Domingos method for the selected complex cross-flow heat exchanger configurations.

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

Second law analysis and heat transfer in a cross-flow heat exchanger with a new winglet-type vortex generator