scholarly journals Numerical Investigation of Latent Thermal Storage in a Compact Heat Exchanger Using Mini-Channels

2021 ◽  
Vol 11 (13) ◽  
pp. 5985
Author(s):  
Amir Abdi ◽  
Justin Ningwei Chiu ◽  
Viktoria Martin
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Flow Rate ◽  
Air Flow ◽  
Volume Ratio ◽  
Air Flow Rate ◽  
Packing Factor ◽  
Mini Channels ◽  
The Mean ◽  
Channel Type

This paper aims to numerically investigate the thermal enhancement of a latent thermal energy storage component with mini-channels as air passages. The investigated channels in two sizes of internal air passages (channel-1 with dh = 1.6 mm and channel-2 with dh = 2.3 mm) are oriented vertically in a cuboid of 0.15 × 0.15 × 0.1 m3 with RT22 as the PCM located in the shell. The phase change is simulated with a fixed inlet temperature of air, using ANSYS Fluent 19.5, with a varying number of channels and a ranging air flow rate entering the component. The results show that the phase change power of the LTES improves with by increasing the number of channels at the cost of a decrease in the storage capacity. Given a constant air flow rate, the increase in the heat transfer surface area of the increased number of channels dominates the heat transfer coefficient, thus increasing the mean heat transfer rate (UA). A comparison of the channels shows that the thermal performance depends largely on the area to volume ratio of the channels. The channel type two (channel-2) with a slightly higher area to volume ratio has a slightly higher charging/discharging power, as compared to channel type one (channel-1), at a similar PCM packing factor. Adding fins to channel-2, doubling the surface area, improves the mean UA values by 15–31% for the studied cases. The variation in the total air flow rate from 7 to 24 L/s is found to have a considerable influence, reducing the melting time by 41–53% and increasing the mean UA values within melting by 19–52% for a packing factor range of 77.4–86.8%. With the increase in the air flow rate, channel type two is found to have considerably lower pressure drops than channel type one, which can be attributed to its higher internal hydraulic diameter, making it superior in terms of achieving a relatively similar charging/discharging power in exchange for significantly lower fan power. Such designs can further be optimized in terms of pressure drop in future work, which should also include an experimental evaluation.

Oxidation and Heat Transfer Studies in Graphite Channels: I. The Effect of Air Flow Rate on the C-O2and CO-O2Reactions

1962 ◽  
Vol 12 (1) ◽  
pp. 39-45 ◽  
Author(s):  
Donald G. Schweitzer ◽  
George C. Hrabak ◽  
Robert M. Singer
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Air Flow ◽  
Air Flow Rate

scholarly journals Numerical Simulation and Optimization of Waste Heat Recovery in a Sinter Vertical Tank

Energies ◽  
2019 ◽  
Vol 12 (3) ◽  
pp. 385 ◽  
Author(s):  
Chenyi Xu ◽  
Zhichun Liu ◽  
Shicheng Wang ◽  
Wei Liu
Keyword(s):  
Heat Transfer ◽  
Power Consumption ◽  
Flow Rate ◽  
Heat Dissipation ◽  
Waste Heat ◽  
Air Flow ◽  
Particle Diameter ◽  
Exergy Destruction ◽  
Air Flow Rate ◽  
Simulation And Optimization

In this paper, a two-dimensional steady model is established to investigate the gas-solid heat transfer in a sinter vertical tank based on the porous media theory and the local thermal non-equilibrium model. The influences of the air flow rate, sinter flow rate, and sinter particle diameter on the gas-solid heat transfer process are investigated numerically. In addition, exergy destruction minimization is used as a new principle for heat transfer enhancement. Furthermore, a multi-objective genetic algorithm based on a Back Propagation (BP) neural network is applied to obtain a combination of each parameter for a more comprehensive performance, with the exergy destruction caused by heat transfer and the one caused by fluid flow as the two objectives. The results show that the heat dissipation and power consumption both gradually increase with an increase of the air mass flow rate. Additionally, the increase of the sinter flow rate results in a decrease of the heat dissipation and an increase of the power consumption. In addition, both heat dissipation and power consumption gradually decrease with an increase of the sinter particle diameter. For the given structure of the vertical tank, the optimal operating parameters are 2.99 kg/s, 0.61 kg/s, and 32.8 mm for the air flow rate, sinter flow rate, and sinter diameter, respectively.

scholarly journals Heat transfer in the vortex zone of a cyclone-bed chamber of furnace unit with fluidized bed

2019 ◽  
Vol 64 (1) ◽  
pp. 87-97
Author(s):  
E. A. Pitsuha ◽  
E. K. Buchilko ◽  
Yu. S. Teplitskii ◽  
D. S. Slizhuk
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Fluidized Bed ◽  
Flow Rate ◽  
Radial Direction ◽  
Air Flow ◽  
Air Flow Rate ◽  
Outlet Hole ◽  
The Heat Transfer Coefficient

An experimental investigation of the heat-transfer coefficient to a spherical probe in a cyclone-bed chamber with fluidized bed in the “cold” and “hot” regimes has been carried out. The heat-transfer coefficient was determined by the regular thermal regime. The dependences of the heat-transfer coefficient in the vortex-bed furnace on the various parameters: the diameter of the outlet hole, the air flow rate, the share of the bottom blast and the location of the probe were determined. It is revealed that in the “cold” regime the heat-transfer coefficient has practically constant value in the radial direction, it almost does not depend on the diameter of the outlet hole and the share of the bottom blast and depends significantly on the position of the probe along the height of the furnace and the air flow rate. The effect of flow swirling on the heat-transfer coefficient in a cyclone-bed chamber with fluidized bed is determined. When the fuel burns (“hot” regime), the heat-transfer coefficient is not constant in the radial direction and accept the maximum values in the central area of the chamber. At the same time, the part of conductive-convective component in the total heat-transfer coefficient to the spherical probe, depending on its radial position, is estimated at 40–70 %. The results can be used in the design and creation of modern high-efficiency furnaces for burning local solid biofuels.

scholarly journals Thermal Performance and Energy Saving Analysis of Indoor Air–Water Heat Exchanger Based on Micro Heat Pipe Array for Data Center

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 393 ◽  
Author(s):  
Heran Jing ◽  
Zhenhua Quan ◽  
Yaohua Zhao ◽  
Lincheng Wang ◽  
Ruyang Ren ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Energy Saving ◽  
Heat Pipe ◽  
Flow Rate ◽  
Data Center ◽  
Data Centers ◽  
Air Flow ◽  
Air Flow Rate ◽  
Cold Energy

According to the temperature regulations and high energy consumption of air conditioning (AC) system in data centers (DCs), natural cold energy becomes the focus of energy saving in data center in winter and transition season. A new type of air–water heat exchanger (AWHE) for the indoor side of DCs was designed to use natural cold energy in order to reduce the power consumption of AC. The AWHE applied micro-heat pipe arrays (MHPAs) with serrated fins on its surface to enhance heat transfer. The performance of MHPA-AWHE for different inlet water temperatures, water and air flow rates was investigated, respectively. The results showed that the maximum efficiency of the heat exchanger was 81.4% by using the effectiveness number of transfer units (ε-NTU) method. When the max air flow rate was 3000 m3/h and the water inlet temperature was 5 °C, the maximum heat transfer rate was 9.29 kW. The maximum pressure drop of the air side and water side were 339.8 Pa and 8.86 kPa, respectively. The comprehensive evaluation index j/f1/2 of the MHPA-AWHE increased by 10.8% compared to the plate–fin heat exchanger with louvered fins. The energy saving characteristics of an example DCs in Beijing was analyzed, and when the air flow rate was 2500 m3/h and the number of MHPA-AWHE modules was five, the minimum payback period of the MHPA-AWHE system was 2.3 years, which was the shortest and the most economical recorded. The maximum comprehensive energy efficiency ratio (EER) of the system after the transformation was 21.8, the electric power reduced by 28.3% compared to the system before the transformation, and the control strategy was carried out. The comprehensive performance provides a reference for MHPA-AWHE application in data centers.

Heat Transfer Characteristic and Critical Heat Flux in Mist Dispersed Flow

2004 ◽  
Author(s):  
Tomoyasu Tanaki ◽  
Ken Nemoto ◽  
Hiroyasu Ohtake ◽  
Yasuo Koizumi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Rate ◽  
Air Flow ◽  
Water Flow Rate ◽  
Heating Surface ◽  
Air Flow Rate ◽  
Mist Flow ◽  
Mist Cooling

The heat transfer in mist cooling for low droplet density, focusing on the heat transfer characteristics, behaviors of liquid on a heating surface and measurements of liquid droplets by LDA was investigated experimentally. Steady heat transfer experiments of a copper block were conducted for mist flow of air and water in a range of air flow rate from 40 to 120 1N/min. Water flow rate was 0.3, 0.9, 1.8, 4.0 and 8.0 1/hr, respectively. Mist flow of water and air forming in a fully conical nozzle with a mixture camber was supplied on the heating surface arranged for horizontal-upward position. The critical heat flux increased with an increasing liquid flow rate. The critical heat flux decreased as the air flow rate increased. Three correlations of the mist cooling rate for non-boiling, evaporation of droplets and evaporation of the liquid film were developed with microscopic parameters of two-phase flow, respectively.

Thermal analysis on charging and discharging behaviour of a phase change material-based evacuated tube solar air collector

2016 ◽  
Vol 27 (2) ◽  
pp. 156-172 ◽  
Author(s):  
Neeraj Mehla ◽  
Avadhesh Yadav
Keyword(s):  
Phase Change ◽  
Total Energy ◽  
Phase Change Material ◽  
Flow Rate ◽  
Air Flow ◽  
Air Flow Rate ◽  
Flow Rates ◽  
Solar Air Collector ◽  
Evacuated Tube ◽  
Change Material

The performance analysis on the phase change material-based evacuated tube solar air collector was examined under consecutive and simultaneous charging and discharging modes. Acetamide was used as phase change material. The system performance was evaluated on the basis of the phase change material storage system energy efficiency, exergy efficiency, collector efficiency, the instantaneous energy stored in the phase change material and total energy stored by the system at low and high air flow rates of 0.018 kg/s and 0.035 kg/s, respectively. The maximum average efficiency (17.9%) of the collector was obtained at a high air flow rate during simultaneously charging and discharging of the phase change material. The results obtained demonstrate that the system is more effective when it is operated with high air flow rate during simultaneously charging and discharging of the phase change material. The average total energy at high air flow rates is 1.01 to 1.02 times more in comparison to that at low air flow rates. The findings show the feasibility of the phase change material-based evacuated tube solar air collector for producing hot air for space heating during consecutive and simultaneous charging and discharging of the phase change material in northen Indian climatic conditions. This system would be relevant in areas with good sunlight.

Research on Combustion Characteristics of a Jet Flame With Penetration of Side Micro-Jets

2011 ◽  
Author(s):  
Yu-chun Cao ◽  
Zheng-wei Wang
Keyword(s):  
Flow Rate ◽  
Air Flow ◽  
Flame Structure ◽  
Volume Ratio ◽  
Clean Energy ◽  
Flame Length ◽  
Air Flow Rate ◽  
Jet Flame ◽  
Air Volume ◽  
The Common

Nowadays as clean energy gas is being got more widely utilization in the industrial fields, such as the industrial boilers and kilns. How to improve the combustion performance, including the high efficiency and low pollution emission of the gas flame, is becoming the hot topic for the combustion researchers. In this paper, an innovative jet flame with side micro-jets has been proposed and its effects on the flame structure and its performance have also been investigated. Due to the changes of the initial combustion conditions, mixing and aerodynamics which results from the perturbation of the side micro-jets, such a lifted jet flame have different flame structure compared with the common premixed flame. Results show that use of the micro-jets can control, to a certain extent, the flame structure, including the flame length, lift-off distance and blow-off limit. With the same fuel and air flow rate, the flame length with the side micro-jets will decrease about 5%–40% as the air volume ratio a increases from 58%–76%. Compared with the common diffusion flame, such a jet flame demonstrates to be easier to be momentum-dominated flame. The flame length with 2 micro-jets is about 5% less than with 6 micro-jets under the same fuel and air flow rate. With the same α, the fewer number of the controlled jets lead to the flame with relatively shorter length, not easier to be blown off and higher NOx emission. With certain fuel flow rate, the critical air volume ratio is largest for the flame with 3 micro-jets, which is more difficult to be blown off than the cases with 2, 4 or 6 micro-jets.

Experimental Study of a Solar Air Heater With a New Arrangement of Transverse Longitudinal Baffles

2017 ◽  
Vol 139 (3) ◽  
Author(s):  
Afaq Jasim Mahmood
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Thermal Efficiency ◽  
Air Flow ◽  
Maximum Temperature ◽  
Maximum Efficiency ◽  
Solar Air Heater ◽  
Air Flow Rate ◽  
Double Pass ◽  
Air Heater

This study presents a new design for improving the convection heat transfer coefficients of double-pass solar air heater. Three cases were described by using a different number of transverse baffles (three, five, and seven) in the lower channel of the collectors; steel mesh sheets were also used to enlarge the heat transfer area. All collectors have a space of 25 mm between its glass covers and a 50 mm depth of air channel. Furthermore, this work examined the effect of air flow rate and baffles number on device's thermal efficiency and outlet temperature. The experimental results indicate raises in the thermal efficiency as the air flow rate goes from 0.011 kg/s to 0.038 kg/s. A maximum efficiency of 68% was obtained from the case of seven baffles at the air flow rate of 0.038 kg/s. Moreover, the difference between collector's inlet and outlet temperatures, ΔT, indicated an inverse relationship with air flow rate. Thus, the results show ΔT increases as the air flow rate reduced. The maximum temperature difference recorded was 54 °C, which achieved using seven baffled solar air heater at 0.011 kg/s air flow rate in the middle of the day. It has also been found that thermal efficiency of double-pass solar air heater is greater than single-pass solar air heater, using same air flow rate and number of baffles. Finally, the pressure drop associated with increasing the number of baffles and air flow rate was deliberated.

Flow and Thermal Characteristics Analysis of Plate–Finned Tube and Annular–Finned Tube Heat Exchangers fo In–Line and Staggered Configurations

2020 ◽  
Vol 22 (4) ◽  
pp. 1407-1418
Author(s):  
Shadman Sakib ◽  
Abdullah Al-Faruk
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Air Flow ◽  
Thermal Characteristics ◽  
Finned Tube ◽  
Air Flow Rate ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Exit Temperature

AbstractAs the effective selection of fin can greatly enhance the performance of heat exchanger, heat transfer and pressure drop performance on the air-side of annular and rectangular finned tube heat exchangers were numerically investigated. Two types of tube arrangement (in-line and staggered alignment) were examined for 6 different air flow rate for both the heat exchangers using computational fluid dynamics software package ANSYS FLUENT. Renormalization group theory (RNG) based k-ε turbulence model was employed to handle the unsteady three-dimensional flow and the conjugate heat transfer characteristics. The exit temperature were determined from the simulated results and then the LMTD, heat transfer rate and air-side heat transfer coefficient were calculated. The numerical flow visualization results revealed few important aspects, such as, the development boundary layers between the fins, the formation of the horseshoe vortex system, and the local variations of the velocity and temperature on the fin geometries. The result shows that as the air flow rate increased the exit temperature decreased but the overall heat transfer increased. Staggered configuration shows higher heat transfer characteristics over the in-line configuration. The rectangular finned tube shows 17 to 24% improvement in heat transfer over the annular finned tube.

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