Heat transfer of a row of three butane/air flame jets impinging on a flat plate

Experiments were performed to investigate the heat transfer characteristics of a row of three premixed, laminar, butane/air flame jets impinging on a water-cooled flat plate. The between-jet interference was found to reduce the heat transfer rate in the jet-to-jet interacting zone due to the depressed combustion. The interference became stronger when the jet-to-jet spacing and/or the nozzle-to-plate distance were/was small. The positive pressure existed in the between-jet interacting zone caused the asymmetric flame and heat transfer distribution of the side jet. The meeting point of the spreading wall jets of the central and the side jets did not occur at the midpoint of the neighboring jets, but at a location shifted slightly outwards. The maximum local heat flux and the maximum area-averaged heat flux occurred at a moderate nozzle-to-plate distance of 5d with a moderate jet-to-jet spacing of 5d. The lowest area-averaged heat flux was produced when both the jet-to-jet spacing and the nozzle-to-plate distance were small. Comparing with a single jet under the same experimental conditions, the heat transfer rates in both the stagnation point and the maximum heat transfer point were shown to be enhanced in a row of three-jet-impingement system. The present study provided detailed information on the heat transfer characteristics of a row of three in-line impinging flame jets, which had rarely been reported in previous study.     

穿孔管消声器有流声学性能的数值预测

应用穿孔声阻抗新模型和有流三维有限元方法,预测穿孔管消声器的传递损失,并在消声器试验台上采用双负载法测量消声器的传递损失,预测结果和试验结果吻合良好,表明穿孔声阻抗新模型适用于穿孔管消声器有流声学性能预测。穿孔管消声器传递损失结果显示,随着气流马赫数增加,消声频带有向高频段延伸的趋势,同时通过频率处和高频范围的传递损失也有明显提高。     

Thermal performance optimization of a flat plate solar air heater using genetic algorithm

Thermal performance of solar air heater is low and different techniques are adopted to increase the performance of solar air heaters, such as: fins, artificial roughness etc. In this paper an attempt has been done to optimize the thermal performance of flat plate solar air heater by considering the different system and operating parameters to obtain maximum thermal performance. Thermal performance is obtained for different Reynolds number, emissivity of the plate, tilt angle and number of glass plates by using genetic algorithm.     

Thermal performance of an air solar collector with an absorber plate made of recyclable aluminum cans

The present paper describes the development and testing of an efficient single-glass air solar collector with an absorber plate made of recyclable aluminum cans (RAC). This collector was designed as a proposal to use recycle recyclable materials to build absorber plates of air solar collectors at an acceptable cost. The absorber plate of the collector consisted of eight circular cross section air flow channels of 128 recyclable aluminium cans. Each channel was built with 16 recyclable cans blackened with common opaque black paint of 0.903 absorptance and 0.097 reflectance. The design parameters to determine the size of the collector were obtained by implementing a simulation model for double flow air solar collectors. Also, to determine the appropriate configuration for a uniform air flow distribution inside the eight RAC air channels, a hydrodynamic numerical study was carried out. The RAC air solar collector designed and built was tested outdoors following the ASHRAE 93-86 standard to determine the time constant, the thermal efficiency and the incidence angle modifier. Comparison between the predicted theoretical temperatures and the measured ones were in good agreement. Comparison between the thermal efficiency of the RAC air solar collector with the ones reported in the literature is presented.     

Correlations for solar air heater duct with V-shaped perforated baffles as roughness elements on absorber plate

An experimental investigation has been carried out to study the effect of heat transfer and friction characteristics of air passing through a rectangular duct which is roughened by V-down perforated baffles. The experiment encompassed Reynolds number (Re) from 3800 to 19,000, relative roughness height (e/H) values of 0.285–0.6, relative roughness pitch (P/e) range of 1–4 and open area ratio values from 12% to 44%. The effect of roughness parameters on Nusselt number (Nu) and friction factor (f) has been determined and increase in heat transfer and friction loss has been observed for ducts having a roughened test plate. Maximum Nusselt number is observed for the relative roughness pitch ranging from 1.5 to 3 for flow and geometrical parameters under consideration. The experimental data have been used to develop Nusselt number and friction factor correlations as a function of roughness and flow parameters.     

Heat transfer and wall pressure characteristics of a twin premixed butane/air flame jets

Experimental studies were carried out to investigate the flame shape and the heat transfer and wall pressure characteristics of a pair of laminar premixed butane/air flame jets impinging vertically upon a horizontal water-cooled flat plate at jet Reynolds numbers of 800, 1000 and 1200, respectively. Equivalence ratio of the butane/air mixture was maintained constantly at unity. The flame shape, the pressure distribution on the impingement plate and the heat transfer from the flame to the plate were greatly influenced by the interference occurred between the two flame jets. This interference caused a sharp pressure peak at the between-jet midpoint and the positive pressures at the between-jet area, which led to the separation of the wall jet from the impingement plate after collision. Such interference became more significant when the non-dimensional jet-to-jet spacing (S/d) and the nozzle-to-plate distance (H/d) were reduced. Heat transfer in the interaction zone between the jets was at the lowest rate due to this interference at the smallest S/d ratio of 2.6, resulting from the separation of the high-temperature inner reaction zone of the flame from the impingement plate. On the other hand, the interference enhanced the heat transfer in the interaction zone between the jets when the S/d ratio was greater than 5, by enhancing the heat transfer coefficient. The average heat flux of the impingement plate was found to increase significantly with the increasing H/d ratio until H/d=6. The present study provided detailed information on flame shape and the heat transfer and wall pressure characteristics of a twin laminar pre-mixed impinging circular flame jets, which has rarely been reported in previous studies.     

Effect of dual micro fuel jets on mixing performance of hydrogen in cavity flameholder at supersonic flow

In this article, numerical simulations were done to study the influence of the various hydrogen injections on the mixing rate in the cavity flameholder of the scramjet. This study tried to present the main effective parameters on the flow feature and distribution of the hydrogen jet within a cavity in supersonic free stream domain. In order to simulate the cavity flameholder with micro air/fuel jets, a three-dimensional model is chosen and computational fluid dynamic approach is used for the simulations. The effect of significant parameters is studied by using the Reynolds-averaged Navier–Stokes equations with Menter's Shear Stress Transport (SST) turbulence model. The effect of horizontal and vertical fuel injection is comprehensively studied. Moreover, the characteristics of the mixing in various free stream velocities (M = 1.2, 2.2 and 3.2) are examined and the effects of micro air jet on the size of ignition domain for preserving flame holder are investigated. Results show that the increase of free stream Mach number significantly enhances the mixing of horizontal fuel injection in the cavity. The obtained results reveal that the injection of micro air jets enhances the mixing rate in low Mach number (M = 1.2). Our findings also show that vertical hydrogen injection considerably increases the mixing zone within the cavity and the mixing rate significantly improves by rising free stream velocity.     

Performance of suspended flat plate air heater

In this communication, a heat transfer model to predict the transient behaviour of a suspended flat plate solar collector with constant flow of fluid (air) above the absorber has been presented. A reflecting sheet with an air gap between the absorber plate and bottom insulation to reduce heat loss has been used. The effect, on performance of the air heater, of the parameters viz, spacing between cover and plate, heat capacity of air and absorber plate, flow rate of fluid and collector length have been studied. The effect of changing the averaging inlet temperature with varying collector length has also been studied.     

Analysis of parameters affecting the performance of gas turbines and combined cycle plants with vapor absorption inlet air cooling

The integration of an aqua‐ammonia inlet air‐cooling scheme to a cooled gas turbine‐based combined cycle has been analyzed. The heat energy of the exhaust gas prior to the exit of the heat recovery steam generator has been chosen to power the inlet air‐cooling system. Dual pressure reheat heat recovery steam generator is chosen as the combined cycle configuration. Air film cooling has been adopted as the cooling technique for gas turbine blades. A parametric study of the effect of compressor–pressure ratio, compressor inlet temperature, turbine inlet temperature, ambient relative humidity, and ambient temperature on performance parameters of plants has been carried out. It has been observed that vapor absorption inlet air cooling improves the efficiency of gas turbine by upto 7.48% and specific work by more than 18%, respectively. However, on the adoption of this scheme for combined cycles, the plant efficiency has been observed to be adversely affected, although the addition of absorption inlet air cooling results in an increase in plant output by more than 7%. The optimum value of compressor inlet temperature for maximum specific work output has been observed to be 25 °C for the chosen set of conditions. Further reduction of compressor inlet temperature below this optimum value has been observed to adversely affect plant efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

太阳能吸收式制冷机性能分析

在太阳辐射动态变化的情况下,对制冷量为5kW的水冷式太阳能吸收式制冷机的性能进行了模拟,得出了集热器出口水温随时间变化的规律曲线以及在此规律的影响下吸收式制冷机的性能曲线。模拟结果表明水冷式太阳能吸收式制冷机在理论上是切实可行的,但是集热器出口水温度的变化以及冷却水温度对系统性能有较大的影响。冷却水温度越低、系统的性能系数越高。     

Performance of a two channel suspended flat plate solar air heater

In the present communication, an analytical model to study the performance of a two channel suspended flat plate air heater is presented. The effect of different parameters, e.g. spacing between the plates, plate length, same and different flow rates of air in the two channels of the air heater, on the air temperature has been studied. A comparison of single channel and two channel air heaters has also been made. Numerical calculations have been made for a typical cold day in Delhi, viz. Jan. 26, 1980.     

Evaporation performance of a new plate‐type heat exchanger with winding tubes on plate surfaces (estimation of performance of the heat exchanger)

A method for evaluating and predicting the performance of a newly developed plate‐type heat exchanger as an evaporator for water‐refrigerant systems such as chillers has been developed. The main component of the developed heat exchanger consists of plates packed together in a casing with winding tubes connected to both sides of the plates. Refrigerant flows inside the tubes, and water flows in the space between the plates. A herringbone‐like pattern is formed in this space by the cross sections of the winding tubes. The newly developed method estimates evaporation performance of the developed heat exchanger using new empirical correlations. There are correlations for heat transfer and pressure drop in winding‐tube banks on the water side, and correlation for the pressure drop on the refrigerant side. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(4): 245–257, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20009     

Enhancement of steam absorption into a film of LiBr aqueous solution falling over a downward‐facing plate

An experimental study was performed on the enhancement of steam absorption into a LiBr aqueous solution. The enhancement method proposed here is to set an absorption heat transfer plate facing downward to generate free convection within a liquid film falling over the plate. The experiment was conducted varying the tilt angle of the heat transfer plate in a range of 40 to 90°. The heat transfer coefficients were compared for both cases of the heat transfer plate facing upward and downward. It was found from the experimental results that the downward‐facing plate has a higher heat transfer coefficient than the upward‐facing plate, which confirmed that free convection and mixing occur in the liquid film and enhance the absorption heat transfer in the case of the downward‐facing plate. The enhancement effect becomes remarkable as the tilt angle approaches horizontal, though the liquid film becomes thick and its thermal resistance increases. © 2002 Wiley Periodicals, Inc. Heat Trans Asian Res, 31(8): 606–616, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.10062     

大型轴类工件喷气冷却流动和传热特性的数值模拟

以某喷气冷却装置为参考,对缝隙喷气冷却大型轴类工件展开研究.通过数值模拟研究了具有两相对缝隙的大型轴类工件(直径D=1 000～3 000 mm)喷气冷却装置内的漉动传热特性,对比数值计算结果与实验数据验证了模型预测的准确性,探讨了大型喷气冷却装置内部气体的流动特点,分析了双缝隙喷气冷却轴类工件的传热规律,获得了轴类工...     

基于SYSNOISE软件的穿孔管消声器声学性能分析

为减小穿孔管消声器模型的复杂性,通过在SYSNOISE软件中定义阻尼传递矩阵对穿孔管进行模拟,仿真结果与Sullivan和Crocker预测和试验测量结果吻合良好,验证了方法的可行性与正确性。通过对不同穿孔率和不同尺寸的穿孔管消声器的消声特性的比较,得出结论:穿孔管消声器的消声特性在k₀l值较小时与共振腔消声器的消声特性类似,在k₀l值较大时与扩张室消声器的消声特性类似。     

Experimental study of flame propagation across a perforated plate

Flame propagation across a single perforated plate was experimentally studied in a square cross-section channel. Experiments were performed in premixed hydrogen-air mixture with different equivalence ratios and initial pressures, aiming at identifying the parametric influence. High-speed schlieren photography and pressure records were used to capture the flame front and obtain the pressure build-up. Four stages for the flame front crossing the perforated plate were obtained, namely, laminar flame, jet flame, turbulent flame and secondary flame front. Following ignition, a laminar flame was obtained, which was nearly not affected by the confinement. This laminar flame was squeezed to pass through the perforated plate, producing the jet flame with a step change on velocity. Turbulent flame was generated by merging the jets, which facilitated the acceleration of the flame front. Secondary flame front induced by Rayleigh-Taylor instability was clearly observed in the process of the turbulent front moving forward. Both velocity and pressure are enhanced in this stage. Parametric studies suggested that the secondary flame front is more obvious in the stoichiometric mixture with higher initial pressure, and characterized by a faster propagation velocity and a bigger pressure rise.     

Evaluation of a new,perforated heat flux plate design

Accurate measurement of heat flux is essential to optimize structural and process design and to improve understanding of energy transfer in natural systems. Laboratory and field experiments evaluated the performance of a new, perforated heat flux plate designed to reduce flow distortion for environmental applications. Laboratory tests involving dry and saturated sand showed that performance of the new CAPTEC plate is comparable to a solid, standard REBS plate. Very low thermal gradients may have however led to poor performance of the CAPTEC plate in saturated sand. Water infiltration and redistribution experiments using clayey and sandy soils showed an apparent reduced disruption of liquid water and vapour in the soil surrounding the CAPTEC plate as compared to solid Hukseflux and standard REBS plates. Surface area of REBS plate, though smaller than that of CAPTEC, did not lead to any significantly improved evaporation, due to perforations on CAPTEC plate. Field tests in a loam soil indicated that the CAPTEC plates were durable and produced daily total flux values within ~ 0.15 MJ m^− 2 of independent estimates.     

Thermal performance investigation of double pass-finned plate solar air heater

In this paper, the double pass-finned plate solar air heater was investigated theoretically and experimentally. An analytical model for the air heater was presented. Numerical calculations had been performed under Tanta (latitude, 30° 47′N and longitude, 31°E) prevailing weather conditions. The theoretical predictions indicated that the agreement with the measured performance is fairly good. Comparisons between the measured outlet temperatures of flowing air, temperature of the absorber plate and output power of the double pass-finned and v-corrugated plate solar air heaters were also presented. The effect of mass flow rates of air on pressure drop, thermal and thermohydraulic efficiencies of the double pass-finned and v-corrugated plate solar air heaters were also investigated. The results showed that the double pass v-corrugated plate solar air heater is 9.3–11.9% more efficient compared to the double pass-finned plate solar air heater. It was also indicated that the peak values of the thermohydraulic efficiencies of the double pass-finned and v-corrugated plate solar air heaters were obtained when the mass flow rates of the flowing air equal 0.0125 and 0.0225 kg/s, respectively.     

Thermal performance improvement of premixed hydrogen/air fueled cylindrical micro-combustor using a preheater-conductor plate

A micro-combustor is the key component of the micro thermo photovoltaic power generation system. The energy conversion efficiency of the system strongly depends on the outer wall temperature and the exergy efficiency of the micro-combustor. A novel preheater-conductor plate was designed to be inserted into a cylindrical micro-combustor to improve the outer wall temperature and the exergy efficiency by preheating premixed hydrogen/air mixture via the preheater plate and conducting out the heat in the combustion chamber via the conductor plate. The impact of the width of preheater plate, the gradually increased and decreased thickness with divergent angle and convergent angle of conductor plate, and the inserted number of conductor plate on the thermal performance of the micro-combustor were investigated. It is found that the gradually varying thickness of the conductor plate has a slight influence on micro-combustor performance compared to other factors. Inserting a preheater-conductor plate with the 0.5 mm-wide preheater plate and the three 0.5 mm-thick conductor plates improve the mean outer wall temperature and the exergy efficiency of the micro-combustor by 173 K and 22.9% respectively. It is indicated that the proposed preheater-conductor plate is capable of considerably improving the thermal performance of premixed hydrogen/air fueled cylindrical micro-combustor.     

余热回收吸收式制冷集中空调方案研究

为回收大型炼油装置丰富的低温余热用于生活区的夏季集中空调,本文对余热资源状况和生活区集中空调建筑物供冷负荷分别进行了综合标定和统计计算,在分析比较的基础上确定采用余热热水型溴化锂吸收式制冷冷水机组和半集中式风机盘管全水型空调系统,并利用现有双管制热水集中供暖管网和泵站输送空调冷水,可以显著地节约投资。技术经济分析表明,该方案在技术上可行,节能效果和经济效益十分显著,而且可以大大改善厂区的热污染和居民的生活条件。