Mass and Heat Transfer Characteristics of a Single-High Aspect Ratio Microchannel Absorber

Micro Channels ◽

Mass And Heat Transfer

Recently, study on a microscale-based absorption refrigeration system has sprung up motivated by the need of efficient energy utilization. Heat-driven absorption systems offer a possibility of generating both power and cooling with environment friendly refrigerants, such as ammonia/water and LiBr/water. However, these systems are often large in size and low in COP especially in single stage absorption systems. These characteristics of absorptions systems make them unattractive in most cases. This work introduces the utilization of micro-channel enhanced surfaces as heat exchangers to enhance the component and system performance, to reduce the system size and to reduce the cost of the system as well. In this work, a new concept of enhancing heat and mass transfer processes is applied in the absorber part of the absorption cycle by using a single micro-channel. Due to its merit of high area to volume ratio, microchannel technology has been well theoretically validated to be a very effective and potential choice for enhancing heat transfer performance. But there is a lack of research work on the mass transfer performance in micro-channels. This work investigated simultaneous mass and heat transfer characteristics of a novel microchannel absorber that uses LiBr/water as the working fluid. A microchannel with hydraulic diameter of 0.7mm is employed in this characterization study. Velocity distribution, pressure drop, concentration and temperature profile inside the microchannel as well as effects of the inlet absorbent concentration, flow rate and temperature together with the refrigerant flow rate on the heat/mass transfer are predicted. Investigations on the optimum inlet angle design of a single channel absorber are also presented in the end of this work. Feasibility of this novel absorber design was proved via this numerical simulation as the mass transfer taking place inside the mixing channel was observed to achieve the identical performance but with a size reduction by 1/27 compared to a conventional falling film absorber. A 7 times enhancement of the heat transfer coefficient was also achieved with the comparison of a macro-scale based absorber configuration.

ASME 2013 11th International Conference on Nanochannels, Microchannels, and Minichannels ◽

An Experimental Study of Two Phase Flow in Impinging Micro Channels

10.1115/icnmm2013-73073 ◽

2013 ◽

Author(s):

Liang-Han Chien ◽

Han-Yang Liu ◽

Wun-Rong Liao

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Flow Rate ◽

Heat Sink ◽

Heat Transfer Performance ◽

Experimental Result ◽

Working Fluid ◽

Transfer Performance ◽

Two Phase ◽

Micro Channels

A heat sink integrating micro-channels with multiple jets was designed to achieve better heat transfer performance for chip cooling. Dielectric fluid FC-72 was the working fluid. The heat sink contained 11 micro-channels, and each channel was 0.8 mm high, 0.6 mm wide, and 12 mm in length. There were 3 or 5 pores on each micro-channel. The pore diameters were either 0.24 or 0.4 mm, and the pore spacing ranged from 1.5 to 3 mm. In the tests, the saturation temperature of cooling device was set at 30 and 50°C, and the volume flow rate ranged from 9.1 to 73.6 ml/min per channel (total flow rate = 100∼810 ml/min). The experimental result showed that heat transfer performance increased with increasing flow rate for single phase heat transfer. For heat flux between 20 and 100 kW/m2, the wall superheat decreases with increasing flow rate at a fixed heat flux. However, the influence of the flow rate diminished when the channels are in two phase heat transfer regime. Except for the lowest flow rate (9.1 ml/min), the heat transfer performance increased with increasing jet diameter/spacing ratios. The best surface had three nozzles of 0.4 mm diameter in 3.0 mm jet spacing. It had the lowest thermal resistance of 0.0611 K / W in the range of 200 ∼ 240 W heat input.

Heat Transfer Characteristics of Oscillating Heat Pipe With Water and Ethanol as Working Fluids

Journal of Heat Transfer ◽

10.1115/1.4002366 ◽

2010 ◽

Vol 132 (12) ◽

Cited By ~ 17

Author(s):

Haizhen Xian ◽

Yongping Yang ◽

Dengying Liu ◽

Xiaoze Du

Keyword(s):

Heat Transfer ◽

Heat Pipe ◽

Inclination Angle ◽

Heat Transfer Performance ◽

Filling Ratio ◽

Working Fluid ◽

Transfer Performance ◽

Oscillating Heat Pipe ◽

Transfer Characteristics

In this paper, experiments were conducted to achieve a better understanding of the oscillating heat pipe (OHP) operating behavior with water and ethanol as working fluid. The experimental results showed that there existed a necessary temperature difference between the evaporator and the condenser section to keep the heat pipe working. The maximum effective conductivity of the water OHP reached up to 259 kW/m K, while that of the ethanol OHP is of 111 kW/m K. Not all the OHPs are operated in the horizontal operation mode. The heat transfer performance of the ethanol OHP was obviously affected by the filling ratio and the inclination angle but the influence law is irregular. The effect of the filling ratio and the inclination angle of the water OHP were smaller than that of the ethanol one. The heat transfer performance of the OHP was improved with increase of operating temperature. The startup characteristics of the OHP depended on the establishment of the integral oscillating process, which was determined by the operating factors. The startup temperature of the ethanol OHP varied from 40°C to 50°C and that of the water, OHP varied from 40°C to 60°C without considering the horizontal operating mode. The water OHP showed a better performance and more stable heat transfer characteristics than the ethanol OHP, which had no obvious advantages of the startup capability as well.

ASME 2009 7th International Conference on Nanochannels, Microchannels and Minichannels ◽

Experimental Study on a Honeycomb Micro Channel Cooling System

10.1115/icnmm2009-82059 ◽

2009 ◽

Author(s):

Yonglu Liu ◽

Xiaobing Luo ◽

Wei Liu

Keyword(s):

Heat Transfer ◽

Flow Rate ◽

Cooling System ◽

Test System ◽

Working Fluid ◽

Micro Channel ◽

Pumping Power ◽

Cooling Performance ◽

Working Media

A honeycomb porous micro channel cooling system for cooling of electronic chips was proposed. Experimental investigation was conducted to determine the heat transfer characteristics and cooling performance of this micro channel cooling system. The heat transfer capabilities of the cooling system with different pipe diameters, different working media and various pumping power were evaluated. The influences of working flow rate and test system on the cooling performance were also analyzed experimentally. The results showed that the better cooling capability of the system not only relied on the increasing pump power, but also the agreement between pumps diameters and system pipes diameters. The thermo-physical characters and mass flow rate of the working fluid were also important to the system performance.

Flow Boiling Heat Transfer of R123/R134a Mixture in a Micro-Channel

2010 14th International Heat Transfer Conference, Volume 1 ◽

10.1115/ihtc14-22365 ◽

2010 ◽

Cited By ~ 1

Author(s):

Sehwan In ◽

Sangkwon Jeong

Keyword(s):

Heat Transfer ◽

Boiling Heat Transfer ◽

Flow Boiling ◽

Micro Channel ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Flow Boiling Heat Transfer ◽

Micro Channels

This paper describes the flow boiling heat transfer of R123/R134a mixture in a single round micro-channel with 0.19 mm ID. The flow boiling heat transfer coefficients were measured with the variation of mixture composition (R123 mole fraction: 0.502, 0.746) at various experimental conditions: mass velocities (314, 392, 470 kg/m2-s), heat fluxes (10, 15, 20 kW/m2) and vapor qualities (0.2–0.85). The heat transfer characteristics of R123/R134a mixture are similar to those of pure R123 observed in the previous flow boiling experiment. The similarity of heat transfer characteristics denotes that the heat transfer is governed by evaporation of thin liquid film around the elongated bubbles like the case of pure R123. The heat transfer coefficients of R123/R134a mixture are compared with those of equivalent pure refrigerant by the correlation developed from pure R123 experimental results. The large reduction of heat transfer coefficients compared with pure refrigerant is found in micro-channels flow boiling by the mass transfer effect of mixed refrigerant. In addition, macro-channel correlations for mixed refrigerant do not make accurate prediction about the reduction of heat transfer coefficients.

Influence of Different Rib Height on Heat Transfer Augmentation in Rectangular Convergent / Divergent Channels With Continuous Ribs on Bottom Surface

ASME 2013 Gas Turbine India Conference ◽

10.1115/gtindia2013-3570 ◽

2013 ◽

Author(s):

K. Sivakumar ◽

E. Natarajan ◽

N. Kulasekharan

Keyword(s):

Heat Transfer ◽

Flow Rate ◽

Heat Transfer Performance ◽

Rectangular Channel ◽

Bottom Surface ◽

Transfer Performance ◽

Smooth Channel ◽

Mean Diameter

The work reported in this paper is a systematic experimental study of friction and heat transfer characteristics of divergent /convergent rectangular ducts with an inclination angle of 1° in the y-direction. Measurements were taken for a convergent / divergent rectangular channel of aspect ratio, AR = 1.25 to 1.35 with three uniform rib heights, e = 3, 6 and 9 mm the ratio between rib height (e) to hydraulic mean diameter (Dm) are 0.0348, 0.0697 and 0.1046, a constant rib pitch distance, P = 60 mm. The flow rate in terms of average Reynolds numbers based on the hydraulic mean diameter (Dm) of the channel was in a range of 20000 to 50,000 is 0.085 m. A ceramic strip of 10 mm thickness is used as a heating coil has been attached on top and bottom surfaces for the test sections. The heat transfer characteristics degraded with increase in the rib height in 90° attached ribs over smooth channel. The heat transfer performance of the divergent/convergent ducts for 3, 6 and 9 mm ribs was conducted under identical mass flow rate based on the Reynolds number. In convergent duct having three test sections each having three different size ribs 3, 6, and 9mm. Similarly, divergent section is also three different rib heights duct. So, in our experiments has totally 6 different ducts were used. In addition, the acceleration / deceleration caused by the cross section area, the divergent duct generally shows enhanced heat transfer behavior for three different rib sizes, while the convergent duct has an appreciable reduction in heat transfer performance.

ASME 2015 13th International Conference on Nanochannels, Microchannels, and Minichannels ◽

Multiphase Approach on Heat Transfer Performance of Micro-Channel Using Hybrid Carbon Nanofluid

10.1115/icnmm2015-48117 ◽

2015 ◽

Cited By ~ 1

Author(s):

Rajesh Nimmagadda ◽

K. Venkatasubbaiah

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Volume Concentration ◽

Convective Heat Transfer Coefficient ◽

Working Fluid ◽

Micro Channel ◽

Flow And Heat Transfer ◽

Multiphase Mixture

Laminar forced convection flow of nanofluids in a rectangular micro-channel has been numerically studied. The study is carried out to investigate the flow and heat transfer characteristics of hybrid single walled carbon nanotube (SWCNT) and Copper (Cu) nanofluid in a micro-channel. Hybridization of SWCNT and Cu nanoparticles are varied with different proportions such as 50% - 50%, 70% - 30% and 30% - 70% using sphericity based effective thermal conductivity evaluation. A two-dimensional multiphase mixture model has been developed and the effects of Reynolds number, nanoparticles mixture volume concentration on the flow and heat transfer characteristics of hybrid (SWCNT + Cu) nanofluids are reported. The accuracy of present numerical model has been validated with the experimental and numerical results available in the literature. The results show that the average convective heat transfer coefficient increases with increase in Reynolds number. It is also observed that 1 vol.% hybrid nanofluid (0.7 vol.% SWCNT + 0.3 vol.% Cu) significantly enhances the average convective heat transfer coefficient than that of pure water. Moreover, the multiphase mixture approach showed better enhancement in terms of heat transfer when compared with single phase homogenous model. The study concludes that hybrid nanofluids with suitable volume concentration of carbon (SWCNT) nanoparticles can be used as modern working fluid based on cooling requirement. Further, hybridizing nanoparticles at higher volume concentrations will minimize the working fluid cost and also enhances the heat transfer characteristics in comparison with pure metal based nanofluids.

Numerical Investigation on the Influence of Surface Flow Direction on the Heat Transfer Characteristics in a Granite Single Fracture

Applied Sciences ◽

10.3390/app11020751 ◽

2021 ◽

Vol 11 (2) ◽

pp. 751

Author(s):

Xuefeng Gao ◽

Yanjun Zhang ◽

Zhongjun Hu ◽

Yibin Huang

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Flow Rate ◽

Flow Direction ◽

Heat Extraction ◽

Geothermal System ◽

Heat Transfer Capacity

As fluid passes through the fracture of an enhanced geothermal system, the flow direction exhibits distinct angular relationships with the geometric profile of the rough fracture. This will inevitably affect the heat transfer characteristics in the fracture. Therefore, we established a hydro-thermal coupling model to study the influence of the fluid flow direction on the heat transfer characteristics of granite single fractures and the accuracy of the numerical model was verified by experiments. Results demonstrate a strong correlation between the distribution of the local heat transfer coefficient and the fracture morphology. A change in the flow direction is likely to alter the transfer coefficient value and does not affect the distribution characteristics along the flow path. Increasing injection flow rate has an enhanced effect. Although the heat transfer capacity in the fractured increases with the flow rate, a sharp decline in the heat extraction rate and the total heat transfer coefficient is also observed. Furthermore, the model with the smooth fracture surface in the flow direction exhibits a higher heat transfer capacity compared to that of the fracture model with varying roughness. This is attributed to the presence of fluid deflection and dominant channels.

A Fundamental View of the Flow Boiling Heat Transfer Characteristics of Nano-Refrigerants

Volume 7: Fluids and Heat Transfer, Parts A, B, C, and D ◽

10.1115/imece2012-87788 ◽

2012 ◽

Cited By ~ 2

Author(s):

Lorenzo Cremaschi

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Liquid Phase ◽

Transfer Coefficient ◽

Boiling Heat Transfer ◽

Flow Boiling ◽

Working Fluid ◽

Flow Boiling Heat Transfer

Driven by higher energy efficiency targets and industrial needs of process intensification and miniaturization, nanofluids have been proposed in energy conversion, power generation, chemical, electronic cooling, biological, and environmental systems. In space conditioning and in cooling systems for high power density electronics, vapor compression cycles provide cooling. The working fluid is a refrigerant and oil mixture. A small amount of lubricating oil is needed to lubricate and to seal the sliding parts of the compressors. In heat exchangers the oil in excess penalizes the heat transfer and increases the flow losses: both effects are highly undesired but yet unavoidable. This paper studies the heat transfer characteristics of nanorefrigerants, a new class of nanofluids defined as refrigerant and lubricant mixtures in which nano-size particles are dispersed in the high-viscosity liquid phase. The heat transfer coefficient is strongly governed by the viscous film excess layer that resides at the wall surface. In the state-of-the-art knowledge, while nanoparticles in the refrigerant and lubricant mixtures were recently experimentally studied and yielded convective in-tube flow boiling heat transfer enhancements by as much as 101%, the interactions of nanoparticles with the mixture still pose several open questions. The model developed in this work suggested that the nanoparticles in this excess layer generate a micro-convective mass flux transverse to the flow direction that augments the thermal energy transport within the oil film in addition to the macroscopic heat conduction and fluid convection effects. The nanoparticles motion in the shearing-induced and non-uniform shear rate field is added to the motion of the nanoparticles due to their own Brownian diffusion. The augmentation of the liquid phase thermal conductivity was predicted by the developed model but alone it did not fully explain the intensification on the two-phase flow boiling heat transfer coefficient reported in previous work in the literature. Thus, additional nano- and micro-scale heat transfer intensification mechanisms were proposed.