Comparison of Convective Heat Transfer Coefficient and Friction Factor of TiO2 Nanofluid flow in a tube with Twisted Tape Inserts

Nanofluids have gained extensive attention due to their role in improving the efficiency of thermal systems. The present study reports a further enhancement in heat transfer coefficients in combination with structural modifications of flow systems namely, the addition of tape inserts. Experiments are undertaken to determine heat transfer coefficients and friction factor of TiO2/water nanofluid up to 3.0% volume concentration at an average temperature of 30 C. The investigations are undertaken in the Reynolds number range of 8000-30,000 for flow in tubes and with tapes of different twist ratios. A significant enhancement of 23.2% in the heat transfer coefficients is observed at 1.0% concentration for flow in a tube. With the use of twisted tapes, the heat transfer coefficient increased with decrease in twist ratio for water and nanofluid. The heat transfer coefficient and friction factor are respectively 81.1% and 1.5 times greater at Re ¼ 23,558 with 1.0% concentration and twist ratio of 5, compared to values with flow of water in a tube. An increase in the nanofluid concentration to 3.0% decreased heat transfer coefficients to values lower than water for flow in a tube and with tape inserts. A thermal system with tape insert of twist ratio 15 and 1.0% TiO2 concentration gives maximum advantage ratio, if pressure drop is considered along with enhancement in heat transfer coefficient

Numerical Investigation of Ground Cooling Potential for Malaysian Climate

Geographically, Malaysia located between 1° and 7° in North latitude and 100° and 120° in East longitude with the average daytime temperature about 31°C. However, temperature at 24°C is commonly applied for human comfort in commercial and residential building which is increasing the demand of electricity for cooling. This leads to the utilization of renewable energy and source of thermal storage such as ground [Shekerchian et al., 2012]. Ground has high thermal inertia in which about 46% energy from the sun is absorbed by the earth which makes temperature fluctuations at the ground surface attenuated deeper in the ground. At a sufficient depth, the ground temperature is lower than the outside temperature. When ambient air is drawn through buried pipe called ground heat exchanger (GHE), the air is cooled [Pfafferott, 2003]. This air can be used for human comfort by means of ventilation and can be used for other application. Towards of GHE implementation, this paper discusses underground temperature variation with considering different depth and thermal diffusivity based on mathematical model

Study of Effect of Thermal Diffusivity on Ground Temperature for Malaysian Climate

Ground has been proven that it is able to supply cooling and heating resulting in significant reduction of electricity consumption. This paper discusses potential of ground towards implementation of ground thermal storage by using ground heat exchanger (GHE) to supply passive cooling for any application. Analysis has been conducted based on empirical equation from conduction heat transfer for depth up to 6 m and thermal diffusivity from 0.04 to 0.1 m2/day. The main input parameters were obtained from local weather station for three consecutive years. The results showed that significant reduction of temperature occur at depth below than 2.0 m in which cooling can be supplied constantly throughout the year. Temperature amplitude also gets attenuated relatively with depth in which amplitude less than 1°C occur at depth more than 4 m for thermal diffusivity 0.04 m2/day. In addition, thermal diffusivity plays important role in determining ground temperature variation. It has been obtained that the temperature amplitude significantly increase when the thermal diffusivity increase. Therefore, this paper had suggested that the application of GHE should be placed in condition of thermal diffusivity 0.06 m2/day and below

A Review of Ground Heat Exchangers for Cooling Application in the Malaysian Climate

The ground heat exchanger (GHE) is one of the energy sources that has been identified since the 1970s which is able to produce sustainable energy for cooling which is in passive side. GHEs are widely implemented around the world, especially in European countries and a few Asian countries. In Malaysia, application of GHE is still considered as a new passive cooling approach in building energy reduction. Therefore, this paper reviews several important ways of implementing GHE in order to supply passive cooling for any application. The review covers general implementation of the GHE for thermal comfort and agricultural greenhouse cooling. The ground temperature variation used in different researches is also reviewed in this paper as an important part of identifying potential GHE implementations. Design and performance aspects of the GHE are also reviewed. Finally, this paper summarizes the potential and benefit of GHE implementation in the Malaysian climate for cooling applications to reduce the energy used in buildings and greenhouse gas emission

Heat Transfer of Alumina Sands in Fluidized Bed Combustor with Novel Circular Edge Segments Air Distributor

Fluidized bed combustor, which consists of a reaction chamber, an air distribution plate, uses inert particles, as its bed material. In order to ensure stable operation, it is apparent that the operating velocity of the air should be sufficiently large so that the flow rate through it is relatively undisturbed by the bed pressure fluctuation above it. However, high distributor pressure drop in fluidized bed system is undesirable because it will lead to high energy input in the blower to supply the fluidization air to fluidize the inert sand particles. Thus, the new novel designs of air distributor that consists of circular edge segments that contributed to low pressure drop and improvement of heat and mass transfer in fluidized bed combustor is introduced and will become primary interest of this research. The effects of temperature variations between an electrically heated tube immersed vertically in fluidized bed and alumina particles of various sizes were experimentally studied. In this paper, the data for heat transfer coefficient for an electrically heated vertical tube immersed vertically in fluidized bed combustor consists of alumina particles diameter ranging from (Full-size image (10 K)= 100, 177 and 250 μm) is reported at temperature from 50 oC to 250 oC

The Effect of Flowrate and Effectiveness on Theoretical Design and Thermal Characteristic of a GHE

Ground heat exchanger is an exciting technique to reduce energy consumption in building especially in hot climate countries. Implementation of GHE for commercial unit in Malaysia is almost none in record. Thus, performance study of the GHE in Malaysia is crucial to be conducted either experimentally or numerically. Therefore, this paper presents the performance of GHE in term of effectiveness, outlet temperature and rate of heat transfer based on mathematical model. The model is developed based on cross flow heat exchanger with one fluid unmixed. There are two variable parameter used in the analysis which is effectiveness and flowrate of the air for 25 meter length of a PVC pipe. Three effectiveness values which is 0.8, 0.9 and 0.99 have been analysed in this study. Meanwhile, flowrate of air is ranging from 0.02 to 0.2 kg/s. Results show that flowrate at 0.02 kg/s gives great temperature reduction in the pipe compared with higher flowrate. However, flowrate of 0.2 kg/s produces higher cooling potential. Characteristic of the GHE for the rate of heat transfer with 80, 90 and 99 percent effectiveness also have been developed and it has been found that effectiveness of 0.9 provide good combination between flowrate and the rate of heat transfer for 25 meter length of the pipe

Air Distributor Designs for Fluidized Bed Combustors: A Review

Fluidized bed combustion (FBC) has been recognized as one of the suitable technologies for converting a wide variety of biomass fuels into energy. One of the key factors affecting the successful operation of fluidized bed combustion is its distributor plate design. Therefore, the main purpose of this article is to provide a critical overview of the published studies that are relevant to the characteristics of different fluidized bed air distributor designs. The review of available works display that the type of distributor design significantly affects the operation of the fluidized bed i.e., performance characteristics, fluidization quality, air flow dynamics, solid pattern and mixing caused by the direction of air flow through the distributors. Overall it is observed that high pressure drop across the distributor is one of the major draw backs of the current distributor designs. However, fluidization was stable in a fluidized bed operated at a low perforation ratio distributor due to the pressure drop across the distributor, adequate to provide uniform gas distribution. The swirling motion produced by the inclined injection of gas promotes lateral dispersion and significantly improves fluidization quality. Lastly, the research gaps are highlighted for future improvement consideration on the development of efficient distributor designs

Improvement On Particulate Mixing Through Inclined Slotted Swirling Distributor In A Fluidized Bed: An Experimental Study

Previous studies show that excellent particulate mixing in a fluidized bed can reduce the operating cost during fluidization. Therefore, this paper investigates enhancement of particulate mixing in a fluidized bed by using novel inclined slotted swirling distributor. To reduce the cost of pumping power, small size, low pressure blower is used in the study. Moreover, Geldart group B bed materials with different bed aspect ratios and distributor designs viz., perforated plate, circular edged slots (90°) and novel swirling (45°) distributors are used. The novel distributor with 45° inclined slots was found to be effective at enhancing the circulation rate. Swirling flow pattern of the bed materials in a clock-wise direction is obvious in shallow bed, and two-layer transversal-lateral circulation motions are observed in deep bed. It can be concluded from the study that excellent particulate mixing as per rotated distributors is made possible by novel swirling-type distributor without the implementation of electric motor and mechanical rotation

Performance Evaluation of Evacuated Tube Solar Collector Using Water-Based Titanium Oxide (TiO2) Nanofluid

Experiments are undertaken to determine the efficiency of evacuated tube solar collector using water-based Titanium Oxide (TiO2) nanofluid at Pekan campus (3˚32’ N, 103˚25’ E) Faculty of Mechanical Engineering, University Malaysia Pahang for conversion of solar thermal energy. Malaysia lies in the equatorial zone with an average daily solar insolation of more than 900 W/m² and can reach a maximum of 1200 W/m² for most of the year. Traditionally, water is pumped through the collector at an optimum flow rate, for extraction of solar thermal energy. If the outlet temperature of water is high, further circulation of water through the collector is useless. This is due to low thermal conductivity of water of 0.6 W/m.K compared to metals which is many orders higher. Hence, it is necessary to reduce the surface temperature either by pumping water at higher flow rate or by enhancing the fluid properties by dispersing with nanoparticles. Pumping water at higher flow rates is not advantageous as the overall efficiency of the system is lowered. Liquids in which nanosize particles of metal or their oxides are dispersed in a base liquid such as water are known as 'Nanofluid'. It results in higher values of thermal conductivity compared to the base liquid. The thermal conductivity increases with concentration and temperature of the nanofluid. The increase in thermal conductivity with temperature is advantageous for applications in collectors, as the solar insolation varies throughout the day, with a minimum in the morning reaching a maximum at 2.00p.m and reducing thereafter. The efficiency of the collector estimated using TiO2 nanofluid of 0.3% concentration is about 0.73, compared to water which is about 0.58. The efficiency is enhanced by 16.7% maximum with 30-50nm size TiO2 nanoparticles dispersed in water, compared to the system working with water. The flow rate is fixed at 2.7 litres per minute for both liquids