Flat Heat Research Articles

CFD based Approach to Channel Depth Optimization of Forced Convection Flat Plate Solar Air Heater

This work attempts to present numerical simulation of solar collector to optimize channel depth which was directly affect the heat transfer rate and efficiency of the solar air heater by FLUENT. Simulation is an important tool for design and operation control. For the designer, simulation makes it possible to find the optimum design and operating parameters. In the present work the computational fluid dynamics (CFD) tool has been used to simulate the solar flat plate air heater for better understanding the heat transfer capability. 3D model of the collector involving air inlet, absorber plate, glass, plate and thermal storage is modeled and the structured grid was created by HYPERMESH. The results were obtained by using FLUENT software. The objective of this work is to compare the outlet temperature, heat gain, first law efficiency of the different channel depth and find out the optimum value of channel depth.

Heating residential water using parabolic trough concentrators: theoretical calculations and analysis

The present work concerns theoretical and case studies related to a new design of residential water heating using parabolic trough. To proceed, the thermal modelling of parabolic trough concentration and flat plate heat collection is drawn. Then, the case of Beirut city is considered to compare the performance of three different configurations of heating water: flat plate, parabolic trough and parabolic trough with tracking. It was shown that the enhancement of water heating using parabolic trough with respect to flat plate collector depends on the criterion of comparison. Particularly for the same volume occupied on the roof, the use of parabolic trough has shown to decrease the time of heating water to 70°C by 22.4% (a decrease from 52.2 h to 40.5 h) without tracking and 33% (a decrease from 52.2 h to 35 h) with tracking.

Study of Pressure Drop, Friction Factor & Heat Transfer Characteristics of Compact Heat Exchangers using CFD

This paper mainly focuses on the different views and flows of flat rectangular tube heat exchangers using computational fluid dynamics (CFD). This literature review consists of flattened tubes with triangular cross-sections. The importance of heat exchangers has been increasing in automobile industry, aerospace industries and other industries. For over fifty years due to several reasons specified below. A CFD Progression is used to get different curvature ratio of the amount of heat that is transferred, those characteristics can be found using ANSYS FLUENT 13.0. Normally, Rectangular heat exchangers of area density is greater than 700 m3 for gases and it is greater than 300m3, when it is operating in liquid or two phase streams. It is known that by using the CFD the characteristics of fluid flows, the amount of pressure drops and friction factors can be easily found during the thermal analysis in ANSYS FLUENT 13.0. These characteristics can be analyzed both in the design process as well as optimization process. Some extra CFD coding can be reduced by using these CFD softwares. CFD has become the internal part of design process eliminating the entire process of prototyping. The present work, the liquid flow in and out arrangement was analyzed by using flow characteristics and the amount of heat transferred using computational fluid dynamics. Flow mixing is due to different temperatures of fluid flow characteristics which influence the overall efficiency.

THE STUDY OF AN INNOVATIVE HEAT REMOVAL MODEL OF THE ALUMINUM-ACETONE FLAT PLATE HEAT PIPE ON HIGH POWER LEDS

It is well known that heat generation will be harmful to high power LEDs. It is hardly effectively dissipated and results in a serious problem in the luminous efficiency. The most important issue in LED research is to find a potential design of heat removal. The purpose of this study is to design the LEDs combined with the cooling module of the aluminum-acetone flat plate heat pipe by the experimental and numerical simulation for obtaining high efficiency in heat removal. The high power LEDs with and without heat pipe cooling module are compared. The numerical simulation is built and agrees with the experiment. The heat removal efficiency of the cooling module reaches 92.09% and drops the junction temperature of LED about 36°C. This cooling module has proven to be effective in solving the heat concentration problems associated with the LED chips. In short, the phase change cooling module will apply on the electronic component of high heat concentration for more effective cooling method.

Design, fabrication and performance evaluation of solar dryer for banana

An indirect, active-type, environmentally friendly, low-cost solar dryer was designed to dry various agricultural products. The dryer was built by locally available, biologically degradable, low-cost materials. The dryer consists of solar flat plate air heater with three layers of insulation, drying chamber and a fan with a regulator to induce required air flow in the system. Banana is the chosen crop for the experimentation since it is high in production and also has substantial loss in India. Also, dried bananas are having good nutritive value which makes it as essential diet. The experiments were conducted to dry banana slices and to study its drying characteristics like rate of drying and quality of dried banana in terms of taste, colour and shape. The dryer has the following features: two different air flow configurations (air flow between glass cover and absorber plate called as the top flow and air flow between absorber plate and the bottom insulation of solar collector called as the bottom flow), forced flow with variable flow rates from 0–3 m/s and two different mounting schemes (conventional trays and wooden skewers). In the top and bottom flow experiments, the bottom flow provided about 2.5 °C higher chamber temperatures than the top flow for the same solar energy input. The efficiency of top flow configuration was found to be 27.5 %, whereas the efficiency of bottom flow configuration was found to be higher at 38.21 %. The results also agree well with the theoretical calculations performed as 60 W of energy can be saved for the same energy input. The drying rate was found to increase when wooden skewers were used instead of conventional trays. At the end of the day, the total difference in moisture content is found to be 3.1 % which is considerable knowing that the rate of drying drastically decreases with time. Banana dried at 1 m/s air flow rate was of the best quality in terms of colour, taste and shape when compared to drying at 0.5 and 2 m/s air flow rate while the weather condition and ambient conditions were almost the same for all the cases with negligible difference.

Design of the Cooling Module of LEDs Based on the Aluminum-Acetone Flat Plate Heat Pipe

The waste heat generated by high power LEDs is hardly effectively dissipated, therefore, it results in a serious problem in the luminous efficiency. The most important issue of the LED research is to find a potential design of heat removal and solve the problem of LED over-heating. The purpose of this study is to design the LEDs combined with the cooling module of the aluminum-acetone flat plate heat pipe by the experiment for the high efficiency of heat removal. The aluminum-acetone flat plate heat pipe is innovative proposed by our team. The high power LEDs with and without heat pipe cooling module is compared. The heat removal efficiency of the cooling module of the aluminum-acetone flat plate heat pipe reaches 77% and drops the junction temperature of LED about 36 °C. The cooling module of the aluminum-acetone flat plate heat pipe has proven to be effective in solving the heat concentration problems associated with the LED chips. In short, the phase change cooling module will apply on the electronic component of high heat concentration for more effective cooling method.

Влияние нагрева (охлаждения) плоской пластины на структуру пограничного слоя при обтекании ее высокотемпературным потоком

Влияние нагрева (охлаждения) плоской пластины на структуру пограничного слоя при обтекании ее высокотемпературным потоком

Nano-scale carbon onions produced by laser photolysis of toluene for detection of optical, humidity, acetone, methanol and ethanol stimuli

Laser liquid medium pyrolysis (LLMP) process has been used to deposit an onion like carbon (OLC) hierarchical structure using toluene as carbon source at various laser power density settings of 2.54, 6.62 and 9.17W/cm2 on Si (100). The coin tower structure of carbon deposits was observed for 2.54W/cm2 and the wheat flower structure consists of OLC for 6.62 and 9.17W/cm2 of laser power. The formation of OLC hierarchical structure deposition has been confirmed using Scanning Electron Microscopy, X-ray Diffraction, Transmission Electron Microscopy, Electron Energy Loss Spectroscopy and Raman Spectroscopic studies. The mechanism of OLC hierarchical structure formation has been discussed. The gas sensing station incorporated with flat heater has been established to sense the Volatile Organic Compounds (VOC) e.g. methanol, ethanol and acetone at room temperature (25°C) and 32% of relative humidity (RH). A good linear relationship between sensitivity and VOCs concentration has been observed in the range of 34–148ppm. The selectivity of OLC device to alcohol (20.5) is found to be double as compared to acetone (10). The p- to n-type semiconductor transition of the OLC has been observed with the increasing Relative Humidity (RH). The OLCs response to the light reveals photoelectric effect and the conduction is found to be incident photon wavelength dependence.

Research on Heat and Mass Transfer of Flat Grooved Heat Pipes

Flat grooved heat pipes, which are especially useful in obtaining a high degree of temperature uniformity on flat surfaces, have been successfully used in the temperature control of electronic systems, however, the mechanisms governing the flow and heat transfer of this kind of heat pipes are still under scrutiny as some reported results cannot be reproduced by others or some assumptions have been proven to be unreasonable or ideal. The theoretical and experimental studies on flat grooved heat pipes and introduce work performed on modeling flat grooved heat pipes are reviewed in this paper.

Energy Efficiency and Cost Effectiveness of Solar Water Heaters

There are different opinions on the question of energy and economic efficiency of solar water heaters. Some researchers believe in high effectiveness of solar water heater application while others questions their cost effectiveness. In this arti¬cle detailed investigations have been accomplished to discover energy and economic real efficien¬cy of different types of solar water heaters on the base of suggested procedure for their real payback periods determination. It’s proved that flat type solar water heater has much longer payback than newly suggested cylindrical shell and tube type solar water heater.

Effect of Sintering Temperature and Time in Nickel Wick for Loop Heat Pipe with Flat Evaporator

This paper specifically addresses the effect of changing the constant temperature region of the sintering temperature curve in manufacturing nickel powder capillary structure (wick) on the performance of a flat loop heat pipe (FLHP). The sintering temperature curve is composed of three regions: a region of increasing temperature, a region of constant temperature, and a region of decreasing temperature, with the sintering time and temperature in the region of constant temperature having significant effect on the permeability of the wick. In this study, for wick manufacturing the temperatures in this region tested range from 550°C to 650°C and the time from 30 minutes to 60 minutes. The properties and internal parameters of the wick are measured, and the wick is placed into FLHP for performance testing. Experimental results show that at sintering temperature of 550°C and lasting about 45 minutes, maximum heat load is 200W, minimum thermal resistance is 0.32°C/W, permeability is , porosity is 66%, effective porosity is 3.8and heat flux is around 21W/cm2; related literatures have only reported maximum heat load increase of 25%.

A combined hydro-thermal characterization of high-porosity metal foam test sections with discrete pore-size gradients

In this study, aluminum foam test sections with discrete pore-size gradients were experimentally investigated. The test sections, which were created by combining foams with up to three different values of pores per inch (PPI), were uniformly heated from below by a flat heater and cooled by a controlled air stream flowing through the foam. The overall dimensions of the foams tested were 25.4mm wide and 6.4mm thick, and the individual length of a foam section varied between 101.6mm, 50.8mm, and 25.4mm, depending on the number of segments with different PPIs being tested. The pressure drops were measured, and the heat transfer coefficients were calculated for all foam combinations considered. The hydrodynamic results showed that the number of sections did not affect the overall pressure drop across the test section if all segments had the same PPI. Also, a higher heat transfer coefficient was observed when air flowed first through the foam with the larger pores (smaller PPI) compared with that of the test section in the reversed orientation. However, the heat transfer coefficients of the mixed-foam test sections were not greater than their better performing whole-foam counterpart, at least for the samples tested. This suggests that, perhaps, metal foams with more refined geometric features could be exploited to allow the tradeoffs between heat transfer, required pumping power, weight, etc., to become identifiable.

A parametric study on a humidification–dehumidification (HDH) desalination unit powered by solar air and water heaters

The performance of a solar powered humidification–dehumidification desalination system is theoretically investigated for various operating and design parameters of the system under climatological conditions of Antalya, Turkey. The primary components of the system are a flat plate solar water heater, a flat plate double pass solar air heater, a humidifier, a dehumidifier and a storage tank. The mathematical model of the system is developed and governing conservation equations are numerically solved by using the Fourth order Runge–Kutta method. Daily and annual yields are calculated for different configurations of the system such as only water heating, only air heating and water–air heating.

Investigation of Mathematical Modelling to Assess the Performance of Solar Flat Plate Collector

A study was under taken to assess the performance of solar flat plate water heater. A customized standard test rig was used for the performance study. Heat transfer phenomena in the collector system were calculated by using theoretical model. From the study it was found that various parameters have effects on the performance of the solar collector system are as follows. In order to improve the thermal efficiency of the solar collector system, inlet water temperature should be as low as possible. The efficiency is increases more or less linearly with ambient temperature. Increasing the thickness of insulation beyond 5 cm is worthless. Efficiency of the solar collector system will decreases with increase of wind speed. Transmission ratio of glass cover should be more than 0.95 in order to obtain higher thermal efficiency of the collector. If ambient temperature increases there will be higher efficiency of solar collector system because of less heat loss to thesurroundings.

Experimental investigation on heat pipe cooling for Hybrid Electric Vehicle and Electric Vehicle lithium-ion battery

In this work, we explored the use of heat pipe as cooling device for a specific HEV lithium-ion battery module. The evaporator blocks of heat pipe modules were fixed to a copper plate which played the role of the battery cooling wall. A flat heater was glued to the other surface of the copper plate and reproduced heat generated by the battery. The temperature at the cooper plate/heater interface corresponds to that of the battery module wall. An AMESim model of the battery was developed to estimate the cells' temperature within the battery. In inclined positions, a very slender evolution of the cooper plate/heater interface temperature was noticed, which means heat pipe works efficiently under different grade road conditions. Even though natural convection and chimney effect are not enough, coupling heat pipes with a confined ventilation structure is an efficient way to keep cells' temperature within its optimal range with an even temperature distribution. Furthermore, only low rate ventilation is necessary, which helps avoid parasitic power consumption and noise level in the vehicle.

Effect of heat storage and fuel price on energy management and economics of micro CCHP cogeneration systems

In the present work, a typical combined cooling, heating and power (CCHP) system comprised of boiler, flat solar collectors, absorption chiller and heat storage tank was investigated. The described system was considered to supply the given electricity, cooling and heating demand of a residential building; with heating and cooling needs of 100 and 50 kW, respectively. To find the optimum hybrid configurations with high reliability, low costs, low fuel consumption and emissions, a computer program was provided by authors in FORTRAN language. Different fuel prices were considered in the present work. The results indicated that the optimal operation strategy changes with Boiler and NGG fuel prices while it also changes with increasing the number of solar collectors, heat storage capacity and consequently decreasing total annual emission.

Heat Transfer Characteristic of Flat Trapezoid Grooved Micro Heat Pipes

To study the heat transfer performance of micro heat pipe, theoretical analysis of flat plate micro heat pipe with trapezoid cross section are presented in this paper. A one-dimensional stationary mathematical model for micro heat pipe grooved capillary flow using finite volume method (FVM) was established. The micro heat pipe had vapor space connect with each other and the influences of shear stress between vapor and fluid in the working process were described in the model which made the model more precisely. The axial variation of working fluid distribution in the heat pipe, pressure difference between vapor and liquid, and velocity of vapor and liquid were analyzed. In addition, the maximum heat transport capacity of micro heat pipe was calculated. The simulation results showed good agreement with the experiment results, and it could predict the heat transfer performance accurately, which was useful to micro heat pipe structural design.

Measuring significant inhomogeneity and anisotropy in indoor convective air turbulence in the presence of 2D temperature gradient

Using a novel set up, experimental study of the statistical properties of a light beam propagating horizontally through indoor convective air turbulence in the presence of a 2D temperature gradient (TG) is presented. A laser beam enters a telescope from its back focal point by virtue of an optical fiber and is expanded and recollimated by it and then passes through the turbulent area. Then the beam enters another telescope’s aperture. A mask consisting of four similar widely separated small subapertures was installed in front of the second telescope’s aperture. The subapertures were equidistant from the optical axis of the telescope and located at the corners of a square. A flat plane heater is used to produce a vertical TG in the medium. Due to the limited width of the heater, a horizontal component for the TG appeared. Near the focal plane of the second telescope, four distinct images of the source are formed and recorded by a CCD camera. Due to the turbulence all the images (spots) in the successive frames fluctuate. Using the four spot displacements we have calculated the fluctuations of the angle of arrival (AA) over the subapertures. The statistical properties of the optical turbulence are investigated using variance analysis of the AA component fluctuations at horizontal and vertical directions over the subapertures for different temperatures of the heater at different heights of the beam path from the heater. Experimental results show that when the heater is turned off, the variances of horizontal and vertical components of the AA fluctuations are approximately equal to zero over all the subapertures. When it is turned on, the variance of the horizontal component of the AA fluctuations over all of the subapertures are larger than those from the vertical one. In addition, in this case, we find a significant dependence of the variance of the AA components on the height from the heater.

Design Optimization of a Chip-Size Microchannel Heat Sink for High Power Devices

A novel design of flat chip-size microchannel heat sink for high power devices cooling is proposed and optimized. The inlet of cooling media is placed in the highest heat flux region, leading the coolest media into the region with the highest temperature directly, and as a result, the overall cooling efficiency is improved. Simultaneously, the collect channel is set and the inlet position is slightly off-center, which achieves a uniform temperature distribution. With the aid of a computational fluid dynamics (CFD) method, the temperature distribution of microchannel heat sink under steady-state conditions is examined and the microchannel distribution is optimized, forming an optimal design for the chip-size microchannel heat sink.

Performance simulation of a natural circulation solar air heater with phase change material energy storage

The one-dimensional radial heat conduction in a phase change material (PCM) heat storage system that is encapsulated in cylindrical pipes in a single glazed flat plate natural circulation solar air heater is presented. The PCM is prepared in modules, with the modules equispaced across the absorber plate. Enthalpy method is applied to convert the relevant energy balance equations into dimensionless forms for easy tracking of the moving phase boundaries. Crank-Nicolson implicit finite difference scheme which has the features of being stable, accurate and fast in its solution is used in the solution of the governing equations subject to suitable initial and boundary conditions. The scheme is applied at each node and the resulting simultaneous equations are solved using the Gauss-Seidel iterative method. An existing computer programme in BASIC known as the EGGINC which was developed for the rectangular channel containing the PCM is modified to cylindrical coordinate for the pipes containing the PCM to predict the temperature distributions in the solar air heater. The predicted temperatures of the system are compared with the experimental data under daytime no-load condition over the ambient temperature range of 18.5-36.0OC and daily global irradiation of 4.9-20.1MJ/m 2 -day. The predicted temperatures were found to agree closely with experimental data. Keywords : Phase change material, Natural circulation; Solar air heater; implicit finite difference, Predicted temperatures