Increasing Water Flow Rate Research Articles

NUMERICAL INVESTIGATION OF HEAT TRANSFER FROM A POROUS PLATE WITH TRANSPIRATION COOLING

The present study is focused on investigation of heat transfer from a porous plate by cooling of air and surface with transpiration cooling. Effects of Reynolds number of hot air (Re= 3035, 3200, 3300, 3580), effects of flow rate of water as a coolant (ṁ water = 0.000083, 0.000116, 0.000166, 0.000249 kg/s) on local wall temperature and cooling efficiency of porous flat and the system inside a rectangular channel with air as a hot gas stream and water as a coolant were investigated numerically. In this study; different from the literature, transpiration cooling was used as a cooling mechanism of air. It was observed from the results that increasing Reynolds number causes an increase on surface temperature and a decrease on cooling efficiency of porous plate and system. Increase of Reynolds number from Re=3035 to 9430 causes a decrease of efficiency of the system of 13.7%. Increasing water flow rate nine times causes not only a decrease on average surface temperature of 1.1% but also an increase of 6.5% on efficiency of porous plate and an increase of 19.1% on cooling efficiency of the system. Numerical results prepared by RNG k-e turbulence model generally have a good approximation with experimental results.

Anti-freezing operation strategies of natural draft dry cooling system

In frozen days, natural draft dry cooling system (NDDCS) faces a serious freezing risk, so it is of great concern to propose anti-freezing measures. In this work, the coupled thermo-flow models of NDDCS with steam condenser in a typical 600 MW power plant are developed, and the anti-freezing circulating water flow rate and opening degree of louvers are simultaneously calculated for air-cooled sectors under cold ambient conditions. At not very low ambient temperatures, the anti-freezing of NDDCS can be reached by increasing water flow rate alone. Besides, at −10 °C in the absence of winds, the minimum water flow rate of 16.84 kg/s can prevent NDDCS from freezing. But as the ambient temperature drops further, the louvers should be closed down synchronously. At the low ambient temperature of −30 °C, the louvers are switched down with the opening degree of 55% in the absence of winds, 16% and 15% at the wind speeds of 4 m/s and 16 m/s respectively for the frontal sector, besides the anti-freezing water flow rate is kept highest as 50.505 kg/s. If the operating turbine back pressure is higher than the anti-freezing back pressure, NDDCS can be free from freezing in cold winter.

Experimental examination of large capacity liFePO4 battery pack at high temperature and rapid discharge using novel liquid cooling strategy

To overcome the significant amounts of heat generated by large-capacity battery modules under high-temperature and rapid-discharge conditions, a new liquid cooling strategy based on thermal silica plates was designed and developed. The superior thermal conductivity of the thermal silica plate combined with the excellent cooling effect of water led to a feasible and effective composite liquid cooling system during long cycle testing. The experimental results showed that the addition of thermal silica plates can greatly improve the cooling capacity that can allow the maximum temperature difference to be controlled at 6.1°C and reduce the maximum temperature of the battery module by 11.3°C, but still outside the optimum operating temperature range. The water flow significantly enhanced the cooling performance/stability, and slight temperature fluctuations were observed during cycling. The cooling performance obviously improved as the flow rate rose. When the velocity reached a critical value, further increase in water flow rate induced a slight influence on the cooling capacity due to the limitation of the materials. The maximum temperature (Tmax) could be reduced to 48.7°C, and temperature difference (∆T) could be maintained within 5°C when the water flow velocity increased to 4 mL/s, which was determined as the best value. The energy consumed by the water pump is only 1.37% of the total energy of the battery module. Overall, these findings should provide novel strategies for the design and optimization of battery thermal management system.

Experimental Investigation of Heat and Mass Transfer in Evaporative Heat Exchangers at Variable Operating Conditions

The evaporative heat exchanger has numerous applications in transferring heat. In this research an experimental study of the heat and mass transfer has been conducted on an experimental evaporative heat exchanger. The study involves the effect of cold water mass flow rate, hot water inlet temperature, air flow rate, injection holes diameter and horizontal distance between injection holes on the heat transfer, overall heat transfer coefficient, effectiveness and mass transfer. The results obtained indicate an increase of heat and mass transfer with the increase of hot water flow rate, hot water inlet temperature, air flow rate and injection holes diameter.

Visualisation study on Pseudomonas migulae AN-1 transport in saturated porous media

Influence of granular size and groundwater flow rate on transport of Pseudomonas migulae AN-1 in saturated porous media was non-invasively and visually investigated with a novel imaging technique based on our previously established green fluorescent protein-tagging approach. AN-1 was transported faster than water was. The finer the media were, the greater the enhancement of bacterial velocity was. Mass recovery (MR) increased, while deposition rate coefficient (Kc) decreased, with increasing granular size. Similar and linear trends of MR and Kc, respectively, were quantitatively observed with increasing water flow rate. The images revealed that the initial shape of bacterial plume after injection was a narrow strip along the injection well and an ellipsoid in the lower part of the injection well in medium and coarse sand, respectively. Bacterial plume migrated horizontally in medium sand, but shifted slightly downward in coarse sand. Under similar conditions, the fluorescent area carrying AN-1 in medium sand was larger than that carrying AN-1 in coarse sand during the same period. The visualisation method of this study captured both the movement of free-state and retained bacteria that adhered to sediments. A continuous biological zone composed of planktonic and retained AN-1 was observed. These findings are significant for actual bioremediation.

Thermal Performances of Two Stage Molten Salt Steam Generator

Abstract Thermal performances of two stage molten salt steam generator were experimentally investigated in this article. The two stage system consisted of primary U shape heat exchanger and secondary shell and tube heat exchanger, and its overall heat transfer coefficient, steam generation rate and thermal efficiency were further analyzed under different molten salt flow rates and water flow rates. According to the experimental results, the overall heat transfer coefficients of the primary and secondary heat exchanger both increase as the molten salt flow rising. As the water flow rate increases, the overall heat transfer coefficient of the primary heat exchanger first increases and then decreases, while that of the secondary heat exchanger gradually increases. As the molten salt flow rate and water flow rate increase, the steam generation rate and the thermal efficiency of the secondary heat exchanger both increase, while the thermal efficiencies of the primary heat exchanger and the whole system first increase, approaching their maximums with optimal molten salt flow rate and water flow rate respectively, and then begin to drop.

Design and experimental study of a small-sized organic Rankine cycle system under various cooling conditions

This paper experimentally studies the performance and feature of a kW-scale organic Rankine cycle system which was operated under various cooling conditions using R123 as working fluid. A self-designed radial inflow turbine was applied to this system in order to testing its performance. A test of the power generation system under various cooling conditions was conducted. The system performance and turbine operational state are distinctly influenced by the cooling water mass flow rate. The experiment results show the turbine performances for various rotational speeds, isentropic efficiencies, and thermal efficiencies. The maximum thermal efficiency 5.30% and a turbine isentropic efficiency 75.2% can be obtained with a water flow rate of 0.591 kg/s. The system net power increased from 889.47 W to 1242.67, with the flow rate of water increasing. With the increase of water flow rate, the exergy loss of evaporator increased, and those of condenser and turbine decreased.

A developed solar-powered desalination system for enhancing fresh water productivity

A solar-powered desalination system using condenser integrated with flat-plate solar collector and vacuum pump was developed for producing fresh water and compared its performance with the ordinary solar desalination system without vacuum pump under different operational conditions. Systems temperatures added to ambient temperature were measured with hour intervals, under all experimental conditions for both solar desalination systems. Heat and mass transfer regimes were conducted for the used parallel condenser. Performance of the two systems was studied as a function of change in water salinity level and water tank flow rate and evaluated in terms of recorded temperatures, condenser efficiency, water productivity and cost. The experimental results reveal that the developed system increases water productivity for all water salinities compared with the ordinary system due to the presence of vacuum pump. The same results also reveal that water productivity increased and cost decreased by increasing water flow rate using the developed system while the vice versa was noticed using the ordinary system. Maximum fresh water productivity values of 10.94 and 7.27 L/d corresponding to cost values of 0.031 and 0.030US $/L were recorded at ground water tank flow rates of 0.80 and 0.40 L/h using developed and ordinary systems, respectively.

Numerical Analysis of Liquid Water Removal Characteristics in a PEMFC Gas Channel with Trapezoidal Cross-section

The water removal characteristics in a PEMFC trapezoidal gas channel are investigated with the volume of fluid (VOF) method. For the case of wall contact angle of 60 degree, liquid water attaches on the top wall and moves toward the exit. In contrast, liquid water moves along the channel side corner or GDL surface irregularly for the higher wall contact angles. The hydrophillic wall contact angle of 60 degrees provides more favorable diffusion of reactants to cathode reaction sites as the GDL surface water coverage ratio approaches zero even if the water flow rate increases.

Experimental evaluation of the performance and energy efficiency of a Vacuum Multi-Effect Membrane Distillation system

The main goal of the current manuscript is the experimental outdoor testing of a Vacuum Multi-Effect Membrane Distillation (V-MEMD) System, the evaluation of the performance and energy efficiency under real operating conditions and the overall design of system components under local economic conditions. This system has a nominal capacity of 30–50L/h and operating temperature range of 50–85°C. The MD system utilizes the memsys V-MEMD modules with four effects. Supporting equipment and systems such as heating, cooling, feed, brine, distillate, recirculation and vacuum loops (cycles) were designed, purchased, installed and tested as an integrated system under outdoor environmental conditions. Experiments were conducted with tap and artificial saline water 30mS/cm as feed streams. The system performance testing showed that the distillate production can reach 50L/h at 80°C of inlet heating water. The system distillate production was found to increase mainly with the increase of heating water temperature and flow rate. The energy efficiency indicators of the system was calculated based on the obtained experimental data, namely Specific Thermal Energy Consumption (STEC) ranged between 300–700kWh/m3, Gained Output Ratio (GOR) was recorded to vary between 1–2.2 and Performance Ratio (PR) was calculated to be 0.4–0.9kg/Mj.

Fabrication and Analysis of Solar Powered and Peltier Model Based Device for Desalination of Marine Water

A solar-powered desalination system using condenser integrated with concave solar collector and centrifugal pump was developed for producing fresh water under different operational conditions. Systems temperatures added to ambient temperature were measured with hour intervals, under all experimental conditions for both solar desalination systems. Heat and mass transfer regimes were conducted for the condenser and heat exchanging tubes. Performance of the two systems was studied as a function of change in water salinity level and water tank flow rate and evaluated in terms of recorded temperatures, water productivity and cost. The experimental results may reveal that the developed system increases water productivity for all water salinities compared with the ordinary system due to the presence of centrifugal pump. The same results may also reveal that water productivity increased and cost decreased by increasing water flow rate using the developed system while the vice versa. Results obtained from two systems are analyzed for suitability of drinking by measuring the minerals.

Parametric study of a tandem desalination system based on humidification-dehumidification process with 3-stage heat recovery

A heat recovery with tandem desalination system based on humidification and dehumidification process was investigated experimentally in this paper. The sketch and principle of a 3-stage multi-effect solar HDH desalination process are given out. These are the one-dimensional heat and mass transfer control models of humidifier and condenser. The mathematical model of the system is developed and governing conservation equations are numerically solved by using the Engineering Equation Solver (EES). In this experiment, different effects of heating ways on the high and middle stages of the desalination unit were studied, including spraying temperature, air flow rate, condenser drainage and the supplement water mass flow rates. The maximum yield of the unit can reach 0.182m3/h, the maximum GOR of the system can reach about 2.65. The results indicate that the yield of the system decreases with the increase of the supplement water flow rate and condenser drainage. In order to ensure the stability and reliability of the system, the optimal yield can be realized only when isothermal heating is adopted in higher and middle stages. The system obtains fresh water by multi-stage isothermal heating mode and the cost is about $2.5 per ton.

Numerical and experimental investigation of UV disinfection for water treatment

Disinfection by ultraviolet (UV) for water treatment in a UV reactor is numerically and experimentally investigated in this paper. The flow of water, UV radiation transportation as well as microorganism particle trajectories in the UV reactor is simulated. The effects of different parameters including UV transmittance (UVT), lamp power and water flow rate on the UV dose distribution and average UV dose are studied. The UV reactor performance in terms of average UV dose under these parameters is analysed. Comparisons are made between experiments and simulations on the average UV dose and reasonable agreement is achieved. The results show that the fluence rate increases exponentially with the increase of UVT. The UV dose distribution profiles moves to a high range of UV dose with the increase of UVT and lamp power. The increase of water flow rate reduces the average exposure time of microorganism particles to the UV light, resulting in the shifting of UV dose distribution to a low range of UV dose. A linear relationship is observed between fluence rate and the average UV dose. The average UV dose increases with the increase of lamp power while it decreases with the increase of UVT and water flow rate.

다중관형 CO2급탕열교환기의 열적성능에 대한 해석연구

본 연구에서는 길이 4.5 m와 7.5 m의 다중관 <TEX>$CO_2$</TEX> 급탕 열교환기의 열전달 및 압력강하 특성을 <TEX>${\epsilon}-NTU$</TEX> 방법을 사용하여 해석하고 결과를 기존의 실험 데이터와 비교하였다. 급탕 열교환기는 쉘측에 물이 흐르고 8개로 구성된 내부 튜브에 <TEX>$CO_2$</TEX>를 흐르게 하였으며 열전달 효율을 최대화하기 위하여 대향류로 설계하였다. 각 노드에 대한 물과 <TEX>$CO_2$</TEX> 냉매의 유동에 대한 에너지 평형 방정식은 단면분할법을 이용하여 해석하였다. 열전달율 계산값은 실험값과 <TEX>${\pm}5%$</TEX> 범위 내에서 잘 일치하였다. 반면에 물의 출구온도는 물 유량이 증가함에 따라 거의 선형적으로 감소하며 계산값과 실험값은 <TEX>${\pm}3%$</TEX> 내에서 일치하였다. 결과에서 열전달율은 4.5 m와 7.5 m 급탕 열교환기 모두 물 유량 또는 <TEX>$CO_2$</TEX> 입구온도가 증가함에 따라 거의 선형적으로 증가하였으며, 반면에 물 유량이 증가함에 따라 물의 출구온도는 선형적으로 감소하였다. <TEX>$CO_2$</TEX> 압력강하 계산값과 실험값은 <TEX>$CO_2$</TEX>가 고유량일 때 5 % 내에서 잘 일치한 반면에 <TEX>$CO_2$</TEX>가 저유량일 때 실험값이 약 20 % 높게 나타났다. In this study, the heat transfer and pressure drop characteristics were evaluated for multi-tube <TEX>$CO_2$</TEX> water heaters with lengths of 4.5 m and 7.5 m. The evaluation was done using the -NTU method, and the results were compared with experimental data. Water flows through the shell side of the water heater, while <TEX>$CO_2$</TEX> flows through 8 inner tubes. The heater uses a counter-current design to maximize the heat transfer efficiency. The energy balance equation describing the flows of <TEX>$CO_2$</TEX> and water for each node is set up using the section-by-section method. The calculated heat transfer rates agree well with the experimental data within <TEX>${\pm}5%$</TEX> error. The outlet water temperature decreased linearly with the increase of the water flow rate. The calculated heat transfer rates agreed well with the experimental data within <TEX>${\pm}3%$</TEX> error. The results show that the heat transfer rate increases almost linearly with the increase of water flow rate or <TEX>$CO_2$</TEX> inlet temperature in both the 4.5-m and 7.5-m water heaters, whereas the water outlet temperature linearly decreases with the increase of the water flow rate. The comparison of the <TEX>$CO_2$</TEX> pressure drop between the calculation and experiment results shows good agreement at the high <TEX>$CO_2$</TEX> flow rate within 5 % error, but the value is about 20 % higher in the experimental pressure drop at the low <TEX>$CO_2$</TEX> flow rate.

Two phase flow of liquids in a narrow gap: Phase interference and hysteresis

Co-current flow of two immiscible liquids, such as oil and water in a planar fracture, exhibits nonlinear structures which become important in many natural and engineering systems such as subsurface flows, multiphase flows in lubrication joints, and coating flows. In this context, co-current flow of oil and water with variable rates is experimentally studied in a Hele-Shaw cell, various flow regimes are classified, and relative permeabilities for the phases are analysed thoroughly. Similar to multiphase pipe flows, multiphase flow in planar gaps shows various flow regimes, each having different flow rate/pressure gradient behaviour. As well as recovering the known results in the immiscible displacements in Hele-Shaw cell where the fluid-fluid interface remains stable/unstable for favorable/adverse viscosity ratios, it is found that the co-current flow of two fluids with different viscosities results in three distinct flow regimes. Before breakthrough of non-wetting phase, i.e, water, a “linear displacement” flow regime initially establishes at very low water injection rates. This stable movement turns into a “fingering advancement” flow regime at high water flow rates and Saffman-Taylor instability develops normal to the direction of the flow. After the breakthrough, a “droplet formation” flow regime is identified where the droplets of wetting phase, oil, are trapped in the water phase. For subsurface flow applications, we quantify these regimes through relative permeability curves. It is reported that as the water flow rate increases, the relative permeabilities and flow channels become smooth and regular. This behaviour of relative permeability and saturations shows dominance of capillary forces at low flow rates and viscous forces at higher flow rates. Variable injection rates provide the interface structures for both drainage and imbibition process, where the wetting phase saturation decreases and increases respectively. It is shown that relative permeability curves exhibit hysteresis, thus the process is irreversible.

On the laws of combustion wave suppression by free water in a homogeneous porous layer of organic combustible materials

The conditions of suppression of a combustion wave propagating along a homogeneous porous layer of organic combustible materials are investigated basing upon a physico-mathematical model. The dependence of free water effervescence intensity on the water volume fraction and the medium temperature is presented. A water supply source in motion is employed to suppress the combustion wave. It is shown that an increase in the mass water flow rate results in a considerable increase in the maximum velocity of the source motion, at which the combustion wave can be suppressed. This is due to a reduction in the loss of the water evaporating above the burning zone. The effect of the water supply point displacement on the efficiency of combustion wave suppression is analyzed.

Temperature optimization of high concentrated active cooled solar cells

Active cooling is essential for solar cells operating under high optical concentration ratios. A system comprises four solar cells that are in thermal contact on top of a copper tube is proposed. Water is flowing inside the tube in order to reduce solar cells temperature for increasing their performance. Computational Fluid Dynamics (CFD) simulation of such system has been performed in order to investigate the effect of water flow rate, tube internal diameter, and convective heat transfer coefficient on the temperature of the solar cells. It is found that increasing convective heat transfer coefficient has a significant effect on reducing solar cells temperatures operating at low flow rates and high optical concentration ratios. Also, a further increase of water flow rate has no effect on reducing cells temperatures.

Increased resistance to detachment of adherent microspheres and Bacillus spores subjected to a drying step

In various environments, including that of food processing, adherent bacteria are often subjected to drying conditions. These conditions have been shown to result in changes in the ability of biofilms to cross-contaminate food in contact with them. In this study, we investigated the consequences of a drying step on the further ability of adherent bacterial spores to resist detachment. An initial series of experiment was set up with latex microspheres as a model. A microsphere suspension was deposited on a glass slide and incubated at 25, 35 and 50°C for times ranging from 1h to 48h. By subjecting the dried slides to increasing water flow rates, we showed that both time and temperature affected the ease of microsphere detachment. Similar observations were made for three Bacillus spores despite differences in their surface properties, especially regarding their surface physicochemistry. The differences in ease of adherent spore detachment could not be clearly linked to the minor changes in spore morphology, observed after drying in various environmental conditions. In order to explain the increased interaction between spheres or spores and glass slides, the authors made several assumptions regarding the possible underlying mechanisms: the shape of the liquid bridge between the sphere and the substratum, which is greatly influenced by the hydrophilic/hydrophobic characters of both surfaces; the accumulation of soil at the liquid/air interface; the presence of trapped nano-bubbles around and/or under the sphere.

Performance testing of a novel 3-fluid liquid-to-air membrane energy exchanger (3-fluid LAMEE) under desiccant solution regeneration operating conditions

Liquid-to-air membrane energy exchangers (LAMEEs) use semi-permeable membranes to transfer heat and moisture between air and desiccant solution, and prevent the transfer of desiccant droplets to the airside. A 2-fluid flat-plate LAMEE is composed of several adjacent air and desiccant solution channels each separated by a semi-permeable membrane. A 3-fluid LAMEE is the new generation of LAMEEs which has a structure similar to a 2-fluid flat-plate LAMEE. The novelty of the 3-fluid LAMEE is that it includes titanium tubes inside the desiccant solution channels to control the temperature of the desiccant solution along the exchanger. In this paper, the performances of a 2-fluid LAMEE and 3-fluid LAMEE are tested and compared under diluted desiccant solution regeneration operating conditions. Also studied are the effects of operating conditions (inlet heating water temperature, heating water mass flow rate, desiccant solution mass flow rate, and inlet desiccant solution temperature) on the performances of the 2-fluid and 3-fluid LAMEEs. For the chosen test conditions, results show that effectiveness and moisture removal rate of the 3-fluid LAMEE are higher than the 2-fluid LAMEE under the entire range of inlet heating water temperature, heating water flow rate, and desiccant solution flow rate studied. The effectiveness and moisture removal rate of the 3-fluid LAMEE increase as the inlet heating water temperature and/or flow rate increases. The sensible, latent, and total effectivenesses, and moisture removal rate of the LAMEE increase by 38%, 40%, 39%, and 6 times when the temperature of desiccant solution is maintained constant along the exchanger. Compared with the 2-fluid LAMEE, the sensible, latent, and total effectivenesses, and moisture removal rate of the 3-fluid LAMEE are improved by up to 104%, 141%, 128%, and 17 times, respectively.

저온 폐열 활용을 위한 2중 효용 2단 흡수식 히트펌프 시뮬레이션

막대한 산업용 에너지가 폐열로 버려지는 상황에서 폐열, 특히 저온 폐열의 효과적인 이용은 매우 중요하다. 본 연구에서는 $160^{\circ}C$ 의 고온 열원과 $17^{\circ}C$ 저온 하수열을 사용하여 $50^{\circ}C$ 의 온수를 $70^{\circ}C$ 로 승온시키며 성적계수는 1.6을 만족하는 2중 효용 2단 흡수식 히트펌프 사...