12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics 2016

Permanent URI for this collectionhttp://hdl.handle.net/2263/61359

Browse

Now showing 1 - 20 of 293

Experimental investigation of effusion and film cooling for gas turbine combustor
(HEFAT, 2016) Inanli, S.; Yasa, T.; Ulas, A.
Experimental study was conducted to understand the heat transfer characteristics of film or effusion cooled test plates that represent the gas turbine combustor liner. Two effusion cooling test plates having different hole angles (30 and 75° with horizontal) were used. Film cooling tests were conducted by six different slot geometries. Test geometries were the scaled-up model of real combustor liner. Three different blowing ratios were applied for each test plate geometry. Surface cooling effectiveness was determined for each test condition by measuring the surface temperature distribution by infrared thermography technique. Effects of geometrical and flow parameters on cooling effectiveness were investigated.
Experimental investigation of domestic gas boiler fitted with organic rankine cycle module
(HEFAT, 2016) Wajs, J.; Mikielewicz, D.; Bajor, M.
The results of investigations conducted on the prototype of vapour driven micro-CHP unit integrated with a gas boiler are presented. The system enables cogeneration of heat and electric energy to cover the energy demand of household. The idea of such system is to produce electricity for own demand or for selling it to the electric grid – in such situation the system user will became the prosumer. A typical commercial gas boiler, additionally equipped with an organic Rankine cycle (ORC) module based on environmentally acceptable working fluid can be regarded as future generation unit. In the paper the prototype of innovative domestic cogenerative ORC system, consisting of a conventional gas boiler and a small size axial vapour microturbines (in-house designed for ORC and the commercially available for Rankine cycle (RC)), evaporator and condenser were scrutinised. In the course of study the fluid working temperatures, rates of heat, electricity generation and efficiency of the whole system were obtained. The tested system could produce electricity in the amount of 1 kWe. Some preliminary tests were started with water as working fluid and the results for that case are also presented. The investigations showed that domestic gas boiler was able to provide the saturated/superheated ethanol vapour (in the ORC system) and steam (in the RC system) as working fluids.
Experimental investigation of a helical coil heat exchanger operating at sub- and supercritical state in a small-scale solar orc installations
(HEFAT, 2016) Lazova, M.; Kaya, A.; Huisseune, H.; De Paepe, M.
In this study, an experimental investigation of the performance a helical coil heat exchanger operating at sub- and supercritical conditions was carried out. The heat exchanger was coupled and tested in a small-scale Organic Rankine Cycle installation with a net cycle capacity of 3 kW and with a heat source inlet temperature of 100 °C. The first measurements were conducted under controlled conditions in a laboratory. Towards determining the effects of different parameters on the heat transfer rate in the heat exchanger several set of measurements were conducted. Particularly, the performance analysis are elaborated considering the changes of various parameters such as the mass flow rate, inlet temperature and operating pressure of the organic (working) fluid (R-404A) at the cold side. While all the parameters at the inlet of the hot side were kept stable for all set of measurements. From the experimental results and the performance evaluation of the heat exchanger it was found that a better performance is achieved when operating at supercritical state.
Experimental investigation on heat transfer characteristics of high blockage ribs channel
(HEFAT, 2016) Yang, Weihua; Xue, Shulin
The heat transfer and pressure loss characteristics on a square channel with two opposite surfaces roughened by high blockage ratio ribs are measured by systematic experiments. Reynolds number studied in the channel range from 1400 to 4500. The rib height(e) to hydraulic diameter(D) ratios are 0.2 and 0.33, respectively. The rib spacing(p) to height ratio(p/e) ranges from 5 to 15. The rib orientations in the opposite surfaces are symmetric and staggered arrangement. The experimental results show that (1) the heat transfer coefficients are increased with the increase of rib height and Reynolds number, though at the cost of higher pressure losses; (2)when the rib spacing to height ratio is 10, it keeps a highest heat transfer coefficient in three kinds of rib spacing to height ratio 5, 10 and 15; (3)the heat transfer coefficient of symmetric arrangement ribs is higher than the staggered arrangement ribs, but the pressure losses of symmetric arrangement ribs is larger than the staggered arrangement ribs.
Experimental investigation into the effect of circumferential non-uniform heat flux on a circular tube in the laminar flow regime
(HEFAT, 2016) Reid, W.J.; Dirker, Jaco; Meyer, Josua P.
In this experimental investigation the influence of buoyancy driven secondary flow on the effective length-wise heat transfer coefficient in a circular horizontal tube is considered for liquid water at different applied external circumferential heat flux distributions. The test section consisted of a 2 m long stainless steel tube with an inner diameter of 27.8 mm and a wall thickness of 2.77 mm. Hydrodynamic fully developed inlet flow at a uniform temperature of approximately 20°C was considered for a Reynolds number range from 650 to 2600. Three externally imposed heat flux distributions were examined: a fully uniform heat flux condition along the length and the circumference of the tube and another two, where only the lower or upper halves of the tube experienced uniform heat flux, while the non-heated halves were externally adiabatic. Results showed that the heat flux distribution had a significant influence on the effective Nusselt number. The fully uniform heat flux distribution cases produced the highest Nusselt numbers. The cases where only the lower half of the tube was heated had higher Nusselt numbers than the cases where only the upper half was heated.
Experimental characterization of the entrained droplet velocities into a submerged gaseous jet
(HEFAT, 2016) Berna, C.; Julia, J.E.; Escriva, A.; Munoz-Cobo, J.L.; Pastor, J.V.
The study of submerged gaseous jets injected into stagnant water pools began in the 70s caused by the fact that they are commonly found in many industrial processes and engineering applications, such as underwater propulsion, metallurgical and chemical processes or nuclear reactors. Consequently it is important to be able to characterize these processes. The low air-water density ratio and the aggressiveness of the pool discharge process result in very complicated flow structures, which are inherently unsteady and turbulent. This poses a major challenge for the measurement of the various parameters involved in the discharge of gaseous submerged jets. Experimental studies of round turbulent air jets submerged in stagnant water are described in this paper. In particular, the entrained droplet velocity, which is crucial for the characterization of the jet, was determined. The experiments were performed using a water tank equipped with an air injector. A high speed camera in conjunction with Particle Image Velocimetry (PIV) techniques was used to measure the velocity of the entrained droplets during jet spreading. Results indicate that the droplet velocity distribution follows a decreasing exponential function. Moreover, the Reynolds number at the injector nozzle was used to develop a correlation linking the initial jet properties and the mean velocity of the entrained droplets. This work represents a new step towards a better understanding of the behavior of submerged gas jets injected into aqueous mediums. The velocity of the entrained droplets was determined, both its mean and distribution function. The extension of the present work to different nozzle diameters and aqueous mediums properties will be addressed in an upcoming paper.
Exergo-economic analysis of waste heat Organic Rankine Cycle
(HEFAT, 2016) Radulovic, Jovana
Organic Rankine Cycle is one of the most promising solutions for utilisation of waste heat. Even though several devices have been operating successfully over the last decade, the technology is far from being widely implemented, with the cost being the primary hindrance. ORC typically yields low efficiency, and there is a number of safety concerns regarding working fluids and device operation. In the current study we have thermodynamically simulated the performance of several working fluids in an ORC system powered by waste heat. Energetic and exergetic analyses, according to the first and the second principles, show expected system outputs depending on the thermo-physical fluid parameters. Power output, thermal and exergetic cycle efficiencies and exergy destruction in individual cycle components were evaluated for a range of operational parameters. Sensitivity analysis included variation of high cycle pressure, expander inlet temperature, isentropic efficiency of the expander and the pump, and the pinch point temperature differences in the evaporator and the condenser. Economic analysis was conducted for the considered cycle designs, linking energetic and exergetic results with the component cost rates.
Experimental and numerical investigation of thermal performance of a crossed compound parabolic concentrator with PV cell
(HEFAT, 2016) Li, W.; Paul, M. C.; Sellami, N.; Mallick, T. K.; Knox, A. R.
Crossed compound parabolic concentrator (CCPC) is a solar energy device used to increase the photovoltaic (PV) cell electrical power output. CCPC’s thermal and optical performance issues are equally important for a PV cell or module to work under a favourable operating condition. However, most work to-date is emphasised on its optical performance paying a little attention to the thermal characteristics. In this contribution, we investigate the thermal performance of a CCPC with PV cell at four different beam incidences (0o, 10o, 20o, 30o and 40o). Initially, experiment is performed in the indoor PV laboratory at the University of Exeter with 1kW/m2 radiation intensity. 3D simulations are carried out to first validate the predicted data and then to characterise the overall performance. Results show that the temperature in the PV silicon layer is the highest at 0o and 30o, with the top glass cover of CCPC having the lowest temperature at all the incidences. The temperature and optical efficiency profiles at the various incidences predicted by simulation show very good agreement with the measurements, especially at 0o incidence. This study provides useful information for understanding the coupled optical-thermal performance of the CCPC with PV cell working at various conditions.
Ewod-controlled dual liquid prism for adaptive beam steering
(HEFAT, 2016) Cheng, Jiangtao; Wu, Felix H.
Solar energy accounts for the greatest source of renewable energy on the earth. The use of photovoltaic (PV) and concentrating photovoltaic (CPV) technology has been the most promising method of harvesting solar energy. These CPV systems often require bulky motor-driven tracking devicesto steer the sun's beams onto solar cells. The cost of providing and maintaining these tracking systems is the primary inhibitor for widespread application. The purpose of this work is to overcome the need for mechanical solar trackers through the use of an electrowetting-driven solar tracking (EWST) system. The electrowetting-driven solar tracking system consists of an array of novel electrowetting-assisted dual liquid prisms, which are filled with immiscible fluids that have large differences in refractive indices. The naturally formed meniscus between the fluids can function as a dynamic optical prism. Via the full range modulation of the liquid prisms, incident sunlight can be adaptively tracked, steered and focused onto concentrated photovoltaic cells through a fixed optical condenser (Fresnel lens). Furthermore, unlike the conventional, cumbersome motor-driven tracking systems used today, the liquid prism system introduced in this work would be suitable for rooftop application. The results of this work reveal that the EWST system has the potential to generate 70% more green energy at 50% of the vonventional PV capital cost.
Experimental and numerical study of freezing water around a cylindrical tube : application to desalination
(HEFAT, 2016) Jaouahdou, Aroussia; Safi, Mohamed
To face the shortage in fresh water, many techniques are used nowadays for brackish and seawater desalination. One of them which consume the less energy is freezing. This process allows the separation of the different salt water’s components and gives rise to a saltier liquid phase called brine and a solid phase of ice becoming fresh water after melting. The quantity and the quality of the products depend, among other, on the geometry of the surface of the exchanger on which will occur the freezing. In this paper, we present experimental and numerical results of fresh and seawater freezing around a circular Cu cylindrical tube immersed into a cavity filled with water to freeze. The tube is fed by a refrigerant coming from a cryostat. A data logger was used to register temperature at different times. Shadowgraphs allowed to visualize the birth and growth of ice. Numerical simulations were based on Navier- stokes, energy and species equations in transient flow. FLUENT software was used to solve theses partial differential equations using a bi-dimensional formulation and an appropriate mesh. Thus temperature, velocity, concentration and flow visualization were investigated and compared to experimental ones. It was found that: 1) Vertical tube produced more ice than the horizontal one. 2) Less the water is salty, more is the production of ice. 3) Dendrites may appear and delay heat and mass transfer.
Enhancing heat transfer rate by interaction of water - liquid metal interface surface
(HEFAT, 2016) Elnajjar, E.; Al Omari, S.-A.B.; Matter, Y.S.
Motivated with the continuous demand of having efficient cooling techniques to keep up with the incessant development of electronics and consequently the increased rate of their heat generation. The enhancement of the heat transfer rate of water as a prime coolant which is used in many thermal management applications became an area of study of many researchers. The present work experimentally studied the enhancement of heat transfer of a low thermal conductivity coolant (water) interfacing with another high thermal conductivity material, such as liquid metal (Gallium). For a variable volume ratio defined as the ratio of the Gallium volume to the water volume, the rate of cooling heat transfer is observed. Taking place by monitoring the temperature cooling for both coolants to room temperature. The study covers a range of volume ratios from 0 to 4 in steps of 1.0. The results suggested an enhancement of the heat transfer rate directly proportional to the increase of the volume ratio for both, constant water volume and constant Gallium volume.
Evaluation of heat transfer correlations for helical coils based on measurements of a solar organic rankine cycle operating at subcritical conditions
(HEFAT, 2016) Kaya, A.; Lazova, M.; Kosmadakis, G.; De Paepe, M.
Organic Rankine cycle (ORC) is an acknowledged method for utilizing low temperature heat sources for generating electricity. Among many applications at heat sources such as internal combustion engines and industrial facilities, solar power is a significant energy source. For solar boilers, helical coil heat exchangers are widely used. The design of these heat exchangers are made with conventional methods, which are mostly not validated for ORC conditions, namely larger tube diameters and working fluids. In order to analyse the accuracy of conventional helical coil heat transfer correlations in design, the geometry and performed measurements at subcritical conditions of a helical coil heat exchanger is taken as reference for the off-design. The helical coil is electrically heated for simulating the photovoltaic/thermal (PV/T) collectors, for testing the solar ORC concept. Then the ORC is coupled with the PV/T collectors on the field for the complete solar ORC system. The inlet conditions of the existing installation are used for sizing and rating via 9 two-phase heat transfer correlations existing in the literature for the tube-side of helical coil. The helical coil outer diameter is 33,7 mm, whereas the shell inner and outer diameter are 0,526 m and 0,674 m, respectively. The coil diameter is 0,6 m. Three measurements are made at changing ORC medium (R404a) mass flow rates, namely 0,1 kg/s, 0,17 kg/s and 0,24 kg/s. R404a’s inlet temperature changes between 21,9 °C and 33,6 °C at a pressure range of 17,5 – 31,6 bars (representing the saturation temperature). In all three cases, the heating water inlet conditions are fixed at an inlet temperature of 95,3 °C and a mass flow rate of 2,67 kg/s.
Evaluation of single heated channel and subchannel modelling on a nuclear once through steam generator (OTSG)
(HEFAT, 2016) Hamedani, A.; Noori-Kalkhoran, O.; Shirani, A.S.
Steam generator is one of the most important components of pressurized-water reactor. This component plays the role of heat transfer and pressure boundary between primary and secondary side fluids. The Once Through Steam Generator (OTSG) is an essential component of the integrated nuclear power system. In this paper steady state analysis of primary and secondary fluids in the Integral Economizer Once Through Steam Generator (IEOTSG) have been presented by Single Heated Channel (SHC) and subchannel modelling. Models have been programmed by MATLAB and FORTRAN. First, SHC model has been used for this purpose (changes are considered only in the axial direction in this model). Second, subchannel approach that considers changes in the axial and also radial directions has been applied. Results have been compared with Babcock and Wilcox (B&W) 19-tube once through steam generator experimental data. Thermal-hydraulic profiles have been presented for steam generator using both of models. Accuracy and simplicity of SHC model and importance of localization of thermal-hydraulic profiles in subchannel approach has been proved.
Enhancement of solidification of phase change materials around finned tubes
(HEFAT, 2016) Ismail, K.A.R.; Silva, P.D.; Lino, F.A.M.; Lago, T.G.S.
Phase change materials (PCMs) are the most attractive thermal energy storage media due to their reduced storage volume and isothermal behavior during charging and discharging processes. Their main drawback is the slow thermal response due to the low thermal conductivity. Various methods for PCM thermal conductivity enhancement have been investigated by many researchers. The present study has the objective of investigating fins for enhancing thermal conductivity of PCM and meliorate their thermal performance. The formulated model for the horizontal radial finned tube is based on pure conduction in the PCM and numerically treated by finite difference and Alternating Direction Implicit (ADI) formulation. The numerical code is optimized and the numerical predictions were validated against experimental results. Additional numerical and experimental measurements were realized to investigate the effects of the cooling fluid temperature, its mass flow rate, diameter, thickness and material of the fin on the interface velocity, solidified mass and the time for complete solidification.
A lock-in CCD camera based method for thermal diffusivity measurement by an improved photothermal beam deflection slope method
(HEFAT, 2016) Cifuentes, A.; Vargas, E.; Marín, E.; Alvarado, S.; Cabrera, H.; Delgado, O.; Calderon, A.
Photothermal beam deflection is a well-established technique for measuring thermal diffusivity. A linear relationship that arises in this technique is that given by the phase lag of the thermal wave as a function of the distance to a punctual heat source when unidimensional heat diffusion can be guaranteed. This relationship is useful in the calculation of the sample’s thermal diffusivity, which can be obtained straightforwardly by the so-called slope method, if the pump beam modulation frequency is well-known. The measurement procedure requires the experimenter to displace the probe beam a given distance from the heat source, measure the phase lag at that offset and repeat this for as many points as desired. This process can be quite lengthy in dependence of the number points. Here we present a detection scheme that overcomes this limitation and simplifies the experimental setup using a Web-cam that substitutes all detection hardware utilizing motion detection techniques and software digital signal post-processing. The used Logitec C920 camera does not have on board lock-in capabilities, so specialized self-referenced lock-in software was developed for this application. Basically, a video is recorded for several pump beam excitation cycles and is post-processed so that a phase image is obtained. The usefulness of the method is demonstrated by measurements of test samples.
Evaporation cooling using a bionic micro porous evaporation system
(HEFAT, 2016) Drabiniok, E.; Hartmann, S.; Neyer, A.
The temperature increase due to incident solar radiation has an adverse impact on the electrical output of photovoltaic (PV) modules. A theoretical model of the fabricated and tested bionic evaporation backside cooling was established and verified by experimental investigation. A micro fluidic structure featuring micro pores consists of two polymer layers attached on the backside of a PV cell model. The thermal performance of roof mounted PV modules with rear panel air ventilation was mathematically described and extended by the cooling capabilities of the developed bionic evaporation foil. The experimental investigations performed in a roof equivalent test environment consisting of a wind tunnel within a climate chamber were in good accordance to the established model. Experimentally temperature reductions at low incident solar power of less than 575W causing an efficiency gain for up to 4:8% have been demonstrated while the model implicates an efficiency increase of 10% for real roof systems at an incident solar radiation of 1000W.
A dynamic control model to improve the response speed for an air-condition system
(HEFAT, 2016) Wang, J.; Geng, S.B.; Yuan, L.
A procedure for deriving a dynamic model of an HVAC system was described in this paper. The system consists of a zone, cooling coils and fan. Room thermal balance model and dynamic model of HVAC control system components including sensor, cooling coils and ducts, were established. These models accurately predicted the effect of inlet air temperature, airflow rate, and inlet chilled water temperature on the room temperature. During closed loop control of output air temperature, chilled water flow rate was used as a control input. Vriable water volume (VWV) was control by Fuzzy adaptive control (FA) combined with proportional integral derivative (PID) control algorithms (FA-PID). Computational simulations of two different control algorithms PID and FA-PID control were carried out in toolbox Simulink of Matlab. The fuzzy parameters were carefully tuned to produce less oscillatory responses. The results showed that the system based on FA-PID control is capable of controlling the disturbance efficiently with less time lag and small error than PID control.
Enhanced heat transfer in oscillatory flows within multiple-hole baffled tubes
(HEFAT, 2016) Gonzalez-Juarez, Daniel; Martínez, David S.; Herrero-Martín, Ruth; Solano, Juan P.
Compound enhancement techniques are considered to be the forefront of heat transfer enhancement. In this work, the combination of active and passive techniques in low-Reynolds number tube flows is explored by means of the superposition of a fully-reversing oscillatory flow into a baffled tube. This arrangement has been employed during the last twenty-years in the so called ‘oscillatory baffled reactors’, focusing on the achievement of plug flow. Little work has been done, however, on the experimental and numerical analysis of the enhanced convective heat transfer that follows the resulting chaotic flow. A standard single-hole baffle geometry has been previously characterized experimentally by some authors, whereas the potential of multiple-hole baffles has not been studied from the point of view of enhanced heat transfer. A numerical investigation has been undertaken to examine the heat transfer augmentation in multiple-hole baffled tubes with fully-reversing oscillatory flow. Different circular baffles with 1, 3, 7, 19 and 43 holes are analyzed, all of them releasing the same total cross sectional area. The flow across these baffles generates a beam of jets which extend downstream and upstream –according to the reversing flow - showing different swirl structures that promote intensive radial mixing and early onset of turbulence. As a consequence, heat transfer between the fluid and the tube wall is significantly enhanced. A circular tube of 25 mm inner diameter has been modeled with 10 baffles uniformly spaced. The simultaneously hydrodynamic and thermal developing flow has been simulated with uniform heat flux as boundary condition in the tube wall, using water as working fluid. The achievement of spatial and time periodicity is thoroughly analyzed prior to the data reduction for the computation of Nusselt number. The time-resolved and time-averaged heat transfer characteristics are presented for an oscillating frequency ranging from f=0.1 Hz to f=1Hz and oscillating amplitudes of x0=𝑑� , 2𝑑�/3 and 𝑑�/3 (where 𝑑� is the inner hole diameter for each baffle). The strong dependency of Nusselt number on the operating parameters of the oscillations is reported. Besides, the positive influence of an increasing number of baffle holes is demonstrated, and a description of the flow structures that induce this heat transfer augmentation is discussed.
Effects of the resin's thermal conductivity on temperature of the qfn64 electronic device subjected to free convection
(HEFAT, 2016) Bairi, A.; Ortega, Hermoso C.; San, Martín Ortega D.
The reliability, durability, performance and correct operating of the quad flat non lead 64 (QFN64) packages are directly linked to their thermal state. In some works published recently, the thermal conductivities of the materials constituting the package are assumed as isotropic and temperature independent, corresponding to the average values considered in similar studies These important characteristics can however vary depending on the manufacturing process of the device and the used materials. The molding compound's thermal conductivity (resin) used for encapsulating the QFN64 package significantly affects the thermal behaviour of this electronic package during operation when it is subjected to natural convection. These effects are quantified in this work by varying this conductivity between -80% and + 80% of its average value. The 3D numerical solution done by means of the control volume method clearly shows that the maximal temperature reached into the source of this device is affected by this parameter for a wide range of the generated power and various inclinations of the device relative to the horizontal. The correlation proposed in this work allow optimizing the thermal design and increase the reliability of this electronic device widely used in various engineering fields.
Effects of a moving membrane on the wake behavior of a circular cylinder
(HEFAT, 2016) Maktouf, N.; Ben Moussa, A.; Turki, S.
The aim of this paper is to investigate a novel technique to control the flow around a circular cylinder. This technique consists of putting a moving membrane stuck to the cylinder. The commercial software Ansys fluent 16.0 is used. The motion of the moving membrane is governed by a user-defined function. The numerical simulation is performed for the Reynolds number equal to Re=150. By changing the frequency of the oscillating membrane from f=0.1Hz to f=6.0Hz, we found that the drag coefficient is significantly affected and its curve shows a beat phenomenon for f around 4.5 Hz.

Browse

Recent Submissions