Minichannel Heat Exchanger Research Articles

Entropy generation of boehmite alumina nanofluid flow through a minichannel heat exchanger considering nanoparticle shape effect

This paper aims to study the effect of nanoparticle shape on the entropy generation characteristics of boehmite alumina nanofluid flowing through a horizontal double-pipe minichannel heat exchanger. Boehmite alumina (γ-AlOOH) nanoparticles of different shapes (cylindrical, brick, blade, platelet, and spherical) are dispersed in a mixture of water/ethylene glycol as the nanofluid. The nanofluid and water flow in the tube side and annulus side of the heat exchanger, respectively. The effects of the Reynolds number and nanoparticle concentration on the frictional entropy generation rate, thermal entropy generation rate, total entropy generation rate and Bejan number are numerically analyzed for different nanoparticle shapes. The obtained results demonstrated that the nanofluids containing platelet shape and spherical shape nanoparticles have the highest and lowest rates of thermal, frictional, and total entropy generation, respectively. Additionally, it was found that the rates of thermal, frictional, and total entropy generation increase with an increase in the Reynolds number, while the opposite is true for the Bejan number. Furthermore, it was inferred from the obtained results that the increase of nanoparticle concentration results in higher frictional and total entropy generation rates and lower Bejan number.

Hydrothermal analysis of turbulent boehmite alumina nanofluid flow with different nanoparticle shapes in a minichannel heat exchanger using two-phase mixture model

Exploring the effect of nanoparticle shape on the fluid flow characteristics of boehmite alumina nanofluid in a horizontal double-pipe minichannel heat exchanger is the goal of this study. The proposed boehmite alumina nanofluid could consist of dispersed cylindrical, brick, blade, platelet, and spherical shape nanoparticles in a mixture of water/ethylene glycol. In this study, the water and nanofluid pass through the annulus and tube side of the heat exchanger, respectively. To accurately simulate the behavior of nanofluid, the two phase mixture model is utilized in the simulation. In this investigation, the effect of different Reynolds numbers, nanoparticle concentrations and shapes versus important hydrothermal properties are investigated. The results show that, the spherical and platelet shape lead to the highest and lowest performance index of heat exchanger, respectively. Moreover, it is found that the rates of heat transfer, overall heat transfer coefficient, pressure drop, and pumping power increases with increase in Reynolds number and nanoparticle concentration, while the opposite trend is observed for performance index of the heat exchanger. For instance, at the Reynolds number of 20000, by boosting the nanoparticle concentration from 0.5 to 2%, the performance index for nanofluid containing platelet shape and spherical shape nanoparticles reduces by 130.63 and 3.88%, respectively.

Impact of variable fluid properties on forced convection of Fe3O4/CNT/water hybrid nanofluid in a double-pipe mini-channel heat exchanger

The objective of this study is to assess the hydrothermal performance of a non-Newtonian hybrid nanofluid with temperature-dependent thermal conductivity and viscosity compared with a Newtonian hybrid nanofluid with constant thermophysical properties. A counter-current double-pipe mini-channel heat exchanger is studied to analyze the effects of the hybrid nanofluid. The nanofluid is employed as the coolant in the tube side, while the hot water flows in the annulus side. Two different nanoparticles including tetramethylammonium hydroxide-coated Fe3O4 (magnetite) nanoparticles and gum arabic-coated carbon nanotubes are used to prepare the water-based hybrid nanofluid. The results demonstrated that the non-Newtonian hybrid nanofluid always has a higher heat transfer rate, overall heat transfer coefficient, and effectiveness than those of the Newtonian hybrid nanofluid, while the opposite is true for the pressure drop, pumping power, and performance evaluation criterion. Supposing that the Fe3O4-carbon nanotube/water hybrid nanofluid is a Newtonian fluid with constant thermal conductivity and viscosity, there leads to large error in the computation of pressure drop (1.5–9.71%), pumping power (1.5–9.71%), and performance evaluation criterion (18.24–19.60%), whereas the errors in the computation of heat transfer rate, overall heat transfer coefficient, and effectiveness are not considerable (less than 2.91%).

Nanoparticle shape effects on thermal-hydraulic performance of boehmite alumina nanofluid in a horizontal double-pipe minichannel heat exchanger

The aim of the present study is an investigation of the impact of nanoparticle shape on the hydrothermal characteristics of boehmite alumina nanofluid flowing through a horizontal double-pipe minichannel heat exchanger. Boehmite alumina (γ-AlOOH) nanoparticles of different shapes (i.e. cylindrical, brick, blade, platelet, and spherical) are dispersed in a mixture of water/ethylene glycol as the nanofluid. The effects of the Reynolds number and nanoparticle concentration on the heat transfer rate, overall heat transfer coefficient, effectiveness, pressure drop, pumping power, and performance index are numerically analyzed for different nanoparticle shapes. The results reveal that the nanofluids containing cylindrical and platelet shaped nanoparticles have the highest and lowest thermal conductivity, respectively. Additionally, it is found that the highest and lowest viscosity belong to the nanofluids with platelet shaped and spherical nanoparticles, respectively. Furthermore, it is depicted that, among the considered nanoparticle shapes, platelet shaped demonstrates better heat transfer characteristics, while performance index of the heat exchanger for nanofluid containing spherical nanoparticles is higher. Finally, it is inferred from the obtained results that the increase of Reynolds number and nanoparticle concentration result in a higher heat transfer rate, overall heat transfer coefficient, pressure drop, and pumping power and a lower performance index.

Performance enhancement of unitary and packaged air conditioners with phase change material

A novel method of lowering condensing temperature of unitary and packaged air conditioners from 55 0C to around 45 0C is proposed with Phase Change Material (PCM) around the channels of Mini Channel Heat Exchanger (MCHE). Primary components of an air-conditioning system along with MCHE with PCM around its mini channels are modeled in MATLAB. A case study is performed considering the temperature-time profile of three Indian cities, viz. Bhopal, Jaipur, and Hyderabad to estimate the hourly energy consumption and saving in electrical energy input at various timings throughout the day, particularly in peak summer. Simulation results show that on an average there will be 15 to 25% reduction in power consumption with enhanced performance of an air conditioner throughout the year. Melting of PCM in MCHE begins at around 10.00 hours and continue up to around 22.00 hours during peak summer months depending on the geographical region and then onwards solidification begins and the entire PCM solidifies by around 10.00 hours depending on the temperature of air during the night. The maximum quantity of PCM required is estimated to be 375 kg per TR with latent heat of fusion of 201 kJ/kg.

Simulation on convective heat transfer of MPCMS in minichannel heat exchanger based on DPM model

Simulation on convective heat transfer of MPCMS in minichannel heat exchanger based on DPM model

Experimental comparison of an air-to-water refrigeration system working with R134a and R1234yf

In this work, the use of R1234yf as a drop-in replacement for R134a in an air to water refrigeration system used to produce cool water at 7 °C is studied. This equipment was constructed in our laboratory with a minichannel heat exchanger working as condenser and a plate heat exchanger working as evaporator resulting in a 2.5 kW water chiller, which initially was working with R134a as refrigerant. A brief description of the refrigeration system and the installation used to test its behaviour as well as the uncertainty analysis is presented.Then, the test matrix defined in order to evaluate the effect of the different variables of interest on the performance of the refrigeration cycle is also presented. Air inlet temperature in the condenser was varied in order to analyse the influence of a variation in the ambient temperature. Other variables were varied in order to analyse the influence of different operating conditions as a variation in the compressor frequency or in the condenser fan velocity (by varying air inlet velocity). Finally, the subcooling degree was varied in order to compare a system with refrigerant receiver (no subcooling) and a system without refrigerant receiver and different refrigerant charge (different subcooling).According to the results obtained, R1234yf performs worse than R134a, presenting lower cooling capacity and higher compressor consumption in all tests, with a global efficiency around 25% lower. This can be explained by its lower isentropic and volumetric efficiency, which could be related to the type of lubricant used.

Design and experimental testing of a Mini Channel Heat Exchanger made in Additive Manufacturing

In order to achieve a polytropic expansion through a reciprocating machine, an extremely compact heat exchanger is designed. It is a Mini Channel Heat Exchanger (MCHE), cross-flow configuration, aluminium made. The exchanger was expected to work with air on one side and water or diathermic oil on the other. The exchanger was also expected to bear high pressure on the air side (up to 12 bar). These pressures are too high for exchangers made up by glue collected plates. So, the additive manufacturing DMLS technique was used to make the exchanger. This technique gave also the chance to produce the needed collectors together with the exchanger, so there is no need of welding process. Then, the exchanger was tested in stationary conditions to characterize it. First, the geometrical constrains and the exchanger requirements are presented. Then a simplified design calculation is used to roughly predict its performance. Finally, the experimental test rig and the experimental data are shown.

Experimental Investigation of the Effect of Gravity on Heat Transfer and Instability in Parallel Mini-channel Heat Exchanger

Mini-channel heat exchangers draw significant attention due to their capability of dissipating high flux heat in a relatively controllable way. The properties of heat transfer and instability of the parallel minichannel heat exchangers were investigated on orbit. The heat exchangers were installed as the evaporators of a two-phaseflow loop in the first Chinese cargo ship (TZ1). R134a was selected as working fluid of the loop. The heat exchangers were designed to be gravitydominated, with the channels’ cross section of 1 × 3 mm2, or larger. Small temperature fluctuation was found on the surface of one heat exchanger. It may be caused by the flow-rate fluctuation among the channels; and it could be more likely occur in microgravity. The necking at each entrance of the channels could suppress the fluid fluctuation inside the heat exchanger. For gravity-dominated channels, gravity plays a decisive role in the vapor-liquid distribution in the channels, which in turn affects the heat transfer coefficient of the heat exchanger.

Statistical method for the determination of the minichannel heat exchanger’s thermal characteristics

The paper presents a new statistical method for the determination of the experimental thermal characteristics of mini- and microchannel heat exchangers. These exchangers are suitable for small scale ORC (Organic Rankine Cycle) installations, CHP (Combined Heat and Power) generation or other applications like electronic equipment. It is not possible in practice to measure the temperature inside mini- and microchannels and only statistical methods may be used to determine the exchanger’s characteristics. There are many such methods which are the modifications of the Wilson plot method. However, the presented method has some advantages. Both fluid flows are treated symmetrically and flow rates and temperature values may be changed simultaneously. In many other methods it is necessary to stabilize one fluid flow while changing the second one. The correlations for Nusselt number may easily be chosen without changing the method itself. The linear coefficients are calculated analytically, but in the case of additional nonlinear coefficients, the numerical method may easily be used. The presented statistical method was verified based on the experimental data of the prototype minichannel heat exchanger.

Experimental investigation and development of new correlation for flow boiling heat transfer in mini-channel

The flow boiling heat transfer of refrigerant R134a in horizontal multiport mini-channel was experimentally investigated in this paper. Two kinds of mini-channels made of aluminum alloy with the hydraulic diameter of 0.63 mm for 23 rectangular channels and 0.72 mm for 14 rectangular channels were studied. Electric heating film was adopted to provide direct uniform heat flux. The experimental results were obtained with the vapor quality between 0 and 1, the heat flux ranging from 10 to 60 kW/m2, the mass flux ranging from 128 to 560 kg/(m2.s) and the saturation pressure from 0.22 to 0.58 MPa. It was found that nucleate boiling dominates in the low vapor quality region and the heat transfer coefficients of mini-channel are higher than those in conventional channel. The heat transfer coefficients increase with the increasing of both heat flux and saturation pressure but have little dependence with the mass flux. In the high vapor quality region, connective boiling is the main contributor. Heat flux and saturation pressure have little influence on the heat transfer coefficients, but the influence of mass flux is obvious. There is a small increase in heat transfer coefficient with an increase of mass flux. Accordingly, a new correlation for flow boiling heat transfer in mini-channel of R134a was proposed based on Gungor and Winterton correlation. The mean relation deviation is −1.76% and the mean absolute relation deviation is 19.0% respectively. This new correlation is proved to have an obvious accuracy improvement in predicting the flow boiling heat transfer coefficient of R134a in mini-channel. The present work can provide a guidance to the design of mini-channel heat exchanger.

Heat flux variation between neighboring channels in compact minichannel heat exchangers

The channel-to-channel heat flux variation was studied by solving numerically the conjugate, three-dimensional, transient heat transfer problem of louvered fins bounded by multiport aluminum plates. Two different multiport plate configurations (A and B) were analyzed while the geometry of fins was kept constant. Configuration A had 11 round channels of 1.2 mm in diameter and Configuration B had 22 square channels of 0.54 × 0.54 mm2 each. Free stream air velocities analyzed were 1–5 m/s (ReLp = 82–410), and incoming air temperature was 20 °C and 30 °C at constant wall temperature of 10 °C.Numerical results show that heat flux flow downstream from the leading edge was dependent on geometrical parameters (size and number of channels, dimensions of fins) and the properties of air flow (incoming flow velocity, temperature and air flow morphology within the louvered fins domain). The overall heat flux difference between the leading channel and the trailing one was 73% at air velocity of 5 m/s, while this difference was almost 96% at 1 m/s for plate B. Multiport plate A had a heat flux difference between the first and the last channel of 68.7% and 93.8% at 5 m/s and 1 m/s respectively. The magnitude of heat flux at ΔT = 10 K (T = 20 °C) was two times smaller compared to the case of ΔT = 20 K (T = 30 °C).

Thermal and hydraulic characteristics of a minichannel heat exchanger operated with a non-Newtonian hybrid nanofluid

Abstract In this study, thermal and hydraulic characteristics of a non-Newtonian hybrid nanofluid are investigated in a double-tube minichannel heat exchanger. The nanofluid contains two different nanoparticles, namely Tetra Methyl Ammonium Hydroxide (TMAH) coated Fe3O4 nanoparticles and Gum Arabic (GA) coated Carbon Nanotubes (CNTs). The nanofluid and water flow in the tube side and annulus side of the heat exchanger, respectively. Variable thermal conductivity and viscosity are applied in the simulations. Numerical solutions are performed based on both Reynolds number and mass flow rate, and the heat transfer rate in the heat exchanger, overall heat transfer coefficient, effectiveness, pressure drop, pumping power, and performance index are evaluated under different conditions. The results show that adding the nanoparticles causes a further increment in heat transfer rate at lower Reynolds numbers, such that the increase in heat transfer rate of the nanofluid compared with water at Reynolds numbers 500 and 2000 is 53.8% and 28.6%, respectively. The findings obtained show a promising view for use of this hybrid ferrofluid in mini heat exchangers.

Selected studies of flow maldistribution in a minichannel plate heat exchanger

Abstract Analysis of the state of-the-art in research of minichannel heat exchangers, especially on the topic of flow maldistribution in multiple channels, has been accomplished. Studies on minichannel plate heat exchanger with 51 parallel minichannels with four hydraulic diameters, i.e., 461 μm, 574 μm, 667 μm, and 750 μm have been presented. Flow at the instance of filling the microchannel with water at low flow rates has been visualized. The pressure drop characteristics for single minichannel plate have been presented along with the channels blockage, which occurred in several cases. The impact of the mass flow rate and channels’ cross-section dimensions on the flow maldistribution were illustrated.

Experimental transient response of a minichannel heat exchanger with step flow variation

Heat exchangers are essential components of many systems and their use is extended to include various industrial, chemical, and automotive applications. Heat exchanger behavior affects the total performance of a thermal system. Enhancing this critical component leads to improving the system overall performance and thus its energy efficiency. Since a heat exchanger operates in conjunction with other process equipment, its evaluation under a transient condition is crucial. A transient response of heat exchangers is necessary to evaluate the exchanger performance when subjected to a change in its conditions. The scarcity of experimental data on a transient response of heat exchangers in general and minichannel exchangers in particular is the main motivation for this research. This work is an investigation of an experimental characterization of the transient response of a cross flow liquid-air heat exchanger subjected to step changes in liquid mass flow rate. Hot fluid mass flow rate step changes of 0.5, 0.8, 1.5, and 2.0 are considered and the liquid outlet temperature response time is presented. The results are compared with the limited experimental work from the literature. While the outlet temperatures of both fluids do not respond instantaneously to the step change in the primary fluid mass flow rate, the cold fluid exhibits a faster response time than that of the hot fluid. The step variation increases the Reynolds number which results in a longer hot fluid response time to reach the steady state. The outcome of this work is valuable in the design, selection, and analysis of heat exchangers. The experimental data provided in this work can be used to establish a database for future advances in research. It also provides an overview of the characteristic behavior of certain parameters such as fluid temperatures, response time, and residence time when the heat exchanger is subjected to a change in the hot fluid mass flow rate.

Study on the performance of TEG with heat transfer enhancement using graphene-water nanofluid for a TEG cooling system

Improvement of the heat transfer effect of cold side of a thermoelectric generator (TEG) is one of the approaches to enhance the performance of the TEG systems. As a new type of heat transfer media, nanofluids can enhance the heat transfer performance of working liquid significantly. In this study, the performance of a commercial TEG with graphene-water (GW) nanofluid as coolants in a minichannel heat exchanger is investigated experimentally at low temperatures. The results show that the output power of TEG increases with the flow rate under 950 mL/min. However, the fluid flow rate has no influence on the output power of TEG with higher flow rate (larger than 950 mL/min) when the heat transfer dynamic balance state of the system is reached. The optimal concentration and flow rate of nanofluid are 0.1 wt% and 950 mL/min, respectively. At the optimal conditions, the improved voltage, output power and conversion efficiency with GW nanofluid applied in the cooling system are increased by 11.29%, 21.55% and 3.5% in comparison with those with only water applied, respectively.

Irreversibility analysis for flow of a non-Newtonian hybrid nanofluid containing coated CNT/Fe3O4 nanoparticles in a minichannel heat exchanger

Irreversibilities caused by heat transfer and friction are evaluated for a non-Newtonian hybrid nanofluid flow in a double-tube minichannel heat exchanger by calculating entropy generation rates. The nanofluids are prepared by dispersing two different nanoparticles, namely Tetra Methyl Ammonium Hydroxide (TMAH) coated Fe3O4 nanoparticles and Gum Arabic (GA) coated Carbon Nanotubes (CNTs). Variable thermophysical properties are employed such that thermal conductivity is considered dependent on temperature and concentration, while viscosity is dependent on temperature, concentration and shear rate. The results show that heat transfer is the main cause in entropy generation at low concentrations while friction is the main factor at high concentrations. By increasing water temperature at the annulus side, the nanofluid thermal entropy generation increases while the nanofluid frictional entropy generation decreases. For low magnetite concentration, maximum thermal entropy generation occurs at the lowest CNT concentration while for high magnetite concentration, it happens at the highest CNT concentration. By increasing the Reynolds number, minimum point of thermal entropy generation moves toward smaller magnetite concentrations. In addition, at low magnetite concentration, total entropy generation rate possesses a minimum (optimal) point with respect to CNT concentration while an ascending trend is observed at high magnetite concentrations.

Evaluation of a condenser based on mini-channels technology working with R410A and R32. Experimental data and performance estimate

In this paper, R32 is investigated as a replacement refrigerant for R410A. The Global Warming Potential (GWP) of R32 is only 675, 32% of that of R410Awhich has a GWP of 2088. Theoretical and experimental investigations are carried out on the performance of the condensation process within a mini-channel tube. Mini-channel heat exchangers technology allows reducing refrigerant charge and lets use flammable refrigerants. Due to the aspect ratio, high heat transfer coefficients are also registered.The experimental data recorded show that, for any given saturation temperature or refrigerant mass velocity, both the heat transfer coefficient and the frictional pressure gradient are always higher for R32. So, a numerical analysis based on the experimental data was developed to determinate which refrigerant performs better. The results of this numerical analysis show that, although at high refrigerant mass velocities R410A performs better, a given heat power can be always achieved with lower mass velocities and thus with a lower compressor power input when using R32. Therefore, it can be concluded that using R32 in a mini-channel condenser reduces the environmental impact and improves the energy efficiency of the system.

Experimental Study of Alternative Minichannel Heat Exchanger for Scooter Radiator

Experimental Study of Alternative Minichannel Heat Exchanger for Scooter Radiator

Experimental assessment of the replacement of a conventional fin-and-tube condenser by a minichannel heat exchanger in an air/water chiller for residential air conditioning

This paper analyses the performance of an air/water chiller typically used for residential air conditioning when a minichannel condenser is used in replacement of a conventional fin-and-tube condenser. The experimental facility, the data reduction process and the uncertainty analysis are briefly described and then the experimental results are presented and discussed, comparing the results obtained with both, the minichannel and the fin-and-tube condenser. Additionally, the chiller is numerically modelled using a commercial refrigeration system modelling software (IMST-ART). The good agreement between experimental and numerical results allows validating the model that is then used to calculate the mass of refrigerant contained in all the components of the system, as well as other operational parameters of interest not measured experimentally. The analysis of the results shows that replacing a conventional fin-and-tube condenser by a minichannel condenser allows, under almost any operating condition, reducing the mass of refrigerant increasing efficiency and cooling capacity.