Requirements for comfortable living and working con- ditions have resulted in an increased demand for air con- ditioning. The latter is normally carried out using a vapour compression system powered by electricity and incorpo- rating a chlorofluorocarbon (CFC) refrigerant. Generation of electricity by conventional means results in vast quan- tities of CO 2 being released to the atmosphere. Concerns over global warming and the environmental damage caused by CFC refrigerants have stimulated research to develop alternate systems for air conditioning. One such system is based on evaporative cooling. This technique eliminates environmental damage and offers energy sav- ings in running costs. Among the various methods of evap- orative cooling, indirectevaporative cooling has been used widely in industrial and commercial air conditioning (Joudi and Mehdi, 2000; Suri, 2001), not only because it operates at very low energy cost, but also because it cools the air without adding moisture to it. Indirectevaporative cooling may be applied to buildings in the form of a chilled ceiling. This technique is becoming increasingly popular in many European countries as an alternative means of air conditioning (Costelloe and Finn, 2003; Gasparella and Longo, 2003).
The paper presents laboratory test results of an integrated heatpipe and ceramic tube based evaporative cooling prototype for air conditioning in buildings. The cooler integrates durable porousceramic tubes as water saturated media materials and heat pipes as efficient heat transfer devices. The ceramic tubes and the heat pipes straddle across two separate air ducts to form a wet and dry channel respectively. The thermal performance of the cooler was measured at various air inlet conditions of temperature, humidity and mass flow rates. The experimental measurements show that the cooling system can provide sufficient cooling as high as 1220 W/m 2 of the wet media exposed surface area and depressing ambient temperature to 12 ℃. Equally, it was measured that the wet bulb effectiveness of the cooler can reach 86%.
B. Small Scale Experimental Set-up and Procedure The primary aim of this experiment is to evaluate the thermal performance of the heatpipe based IEC system. To achieve that a prototype unit, presented in Fig 7b, was built and tested under various climates and ambient air conditions. The basic specifications used for the fabricated heat and mass exchanger are summarized in Table II. The Heatpipe based IEC experimental rig was equipped with a variable speed fan to draw the air at controlled temperature and humidity from an environmental chamber and blow throughout the test-rig, while water is drawn from an overhead tank. Ten thermocouples were installed at several points of the device to measure temperature. Data logger was used to record readings during the experiment and save the data on a computer.
The paper presents laboratory test results of an integrated heatpipe and ceramic tube based evaporative cooling prototype for air conditioning in buildings. The cooler integrates durable porousceramic tubes as water saturated media materials and heat pipes as efficient heat transfer devices. The ceramic tubes and the heat pipes straddle across two separate air ducts to form a wet and dry channel respectively. The thermal performance of the cooler was measured at various air inlet conditions of temperature, humidity and mass flow rates. The experimental measurements show that the cooling system can provide sufficient cooling as high as 1220 W/m 2 of the wet media exposed surface area and depressing ambient temperature to 12℃. Equally, it was measured that the wet bulb effectiveness of the cooler can reach 86%.
Figure-2 represent experimental setup of WHP solar system. Where an integrated multi - branch evaporator consist of (12) cylindrical copper tubes connected together from the bottom by (elbow and T section joints) to form the evaporator structure. In this method the liquid is distributed evenly into each tube. that leads to made the WHP evaporator operate as a single system with regular distribution of heat transfer process and reduce the problems caused by dry out limitation as there is always liquid in the bottom to compensate if any tube test drying. The system, which contains an adiabatic section, is connected from the top by a horizontal tube as a condenser, with a diameter larger than the evaporator tubes to increase the surface area of the condenser. The horizontal shape enables to around it by other tube to concentrate a double pipeheat exchanger.
A comparison study of the use of two different heat removal units was conducted to examine the performance of thermoelectric cooler box. The heat removal units employed were a heat sink fin-fan and a double fan heatpipe. Parameters measured as performance indicators are cooling capacity, temperature differences, and COP. In addition, the effect of electrical power on temperature difference and COP was also investigated. The cooler box size is 285 mm x 245 mm x 200 mm and constructed from styrofoam. The results show that there is no difference of the use of a double fan heatpipe or a heat sink fin-fan on the cooler box performances. The Carnot COP decreases with the time, while the experimental COP increases with the time then it is constant after the steady condition has been achieved. Increasing the power decreases the COP but increases the temperature difference. Keywords: Cooler box, Thermoelectric, Heat removal unit, COP
ABSTRACT: An evacuated tube solar collector is theoretically modelled and fabricated with evacuated tube and heatpipe. Optimized parameter for (ETSC) evacuated tube solar collector is evaluated numerically by doing outdoor testing at Coimbatore district Tamilnadu. The time required by this collector to gain the heat is less compared to other collectors. The outlet temperature varies from 50°C to 79°C while the ambient temperature ranges from 24°C to 33°C. The regression analysis is performed to find the best model. Five different models were used to fit the experimental data. The best curve fitting with highest correlation coefficient and lowest value of RMSE(Root Mean Square Error) is obtained using models available in MATLAB. The ETSC is designed and fabricated with the length and diameter of 1.8 and 0.058 m respectively.
conventional size as well as micro channel systems. Thus, many studies do exist in literature that deals with such systems which helped to understand the thermo- hydrodynamics of single phase as well as two-phase systems. Additionally, two more types of fluid flow that find application in many engineering systems (a) oscillating flow (or oscillatory flow), and (b) pulsating flow (or pulsatile flow). When there is no net mean velocity of the fluid in any direction and it is only oscillating back and forth about a fixed point with a superimposed frequency only then the flow is called oscillating flow. Where in case of pulsating flow, an oscillating velocity is superimposed with the one directional translational velocity. Therefore in pulsating flow time-average velocity is non-zero whereas in oscillating flow time-average velocity is zero over any particular period of cycle at any instant. This type of flow mainly characterized by two parameters namely (i) frequency of oscillation, f (or Womersley number, Wo), and (ii) amplitude of oscillation (A). Because of rapid motion, convective heat transfer may increase in such cases. The effect of pulsations on heat transfer is an interesting problem for researchers due to its wide occurrences in many real time situations at macro as well as mini/micro level.
The most common direct evaporative coolers are essentially metal cubes or plastic boxes with large flat vertical air filters, called ‘‘pads”, in their walls. Consisting of very wet table porous material, they are kept moist by water dripped continuously onto their upper edges. Motorized centrifugal fans within the boxes draw in air through the pads, which both cools and humidifies the air. The discharged air from coolers, often referred to as ‘‘washed air”, is used for cooling. Many coolers have two or three fan speeds, so the user can modulate the output as needed. The inner configuration of a drip-type direct evaporativecooler consists of three pads in the side walls and the last side used as the washed air outlet. Water is sprinkled to wet the pad material and is recycled from the basin by a pump. The water sprinkled onto the top edges of the pads is distributed further by gravity and capillarity. The drip cooler effectiveness depends largely on the pads combining a maximum clean wet surface area with minimum air flow resistance. This requires materials having either good wicking characteristics or surfaces that spread water rapidly by capillary action in addition to allowing air to easily pass. If there is no heat transfer from the surroundings, the air is cooled and humidified with constant enthalpy; that is, the air loses a certain amount of sensible heat but gains an equal amount of latent heat of water vapor. The water temperature in the basin will be slightly higher than the wet-bulb temperature of the inlet air during a stable operation period of the cooler. Thus its operation state is different to that of the cooling tower to some extent. The following numerical simulation focuses on the heat and mass transfer of a direct evaporativecooler in which air flow channels are formed by the alternate layers of two kinds of wet table papers with different wave angles, as shown in Fig 2. The x-axis denotes the air flow direction, the y-axis denotes the width direction of the pad, and the z-axis denotes the water sprinkling direction .
Evaporative cooling of water and atmospheric air is one of the first ways to implement artificial cold in the history of human development. Modern problems in low- energy energy and environment require the search for alternative solutions in the field of climate technology. Evaporative cooling is a non-mechanical way, but its efficiency is significantly limited by climatic conditions. At the same time, interest in the possibilities of evapora- tive coolers has increased in recent years, due to their low energy consumption and environmental cleanliness [1–3]. Among the technical systems for which evaporative cooling can significantly improve the thermoeconomic efficiency are compressor and gas turbine units. As it is known, when working compressor plants with compres- sion of atmospheric air there is a deviation of the regime parameters from the nominal due to changes in the ther- mal parameters of the air at the input: pressure, tempera- ture and relative humidity.
Malli and et al.  studied experimentally the thermal performance of two types of cellulosic pads, which were made from corrugated papers. The pads areas are 50 X 50 cm 2 with 7.5, 10, and 15 cm thicknesses. Dai and Sumathy  investigated a cross-flow direct evaporativecooler, in which the wet durable honeycomb paper constitutes as the packing material. They have developed a mathematical model,
University, Hong Kong
b Faculty of Science and Technology, Technological and Higher Education of Hong Kong, Hong Kong
The indirectevaporativecooler (IEC), regarded as a low-carbon cooling device, was proposed as fresh air pre-cooling and heat recovery device in the air-conditioning system to break the region limitation of application in hot and humid areas. In this hybrid system, the exhausted air with low temperature and humidity from air-conditioned space is used as secondary air to cool the inlet fresh air. As the dew point temperature of the fresh air is high, condensation may occur in the dry channels. However, the modeling of IEC with condensation has been seldom studied and corresponding parameter sensitivity analysis is also lacking. So the paper established a new numerical model taking the condensation from primary air into consideration. Two evaluation indexes (wet-bulb efficiency and enlargement coefficient) were proposed to investigate the thermal performance of IEC with condensation. Sensitivity analysis was conducted among seven parameters by orthogonal test and variance analysis.
analysed the performance of heatpipe experimentally by using the titanium nanoparticles of 21nmdiameter.They have c oncluded that heatpipe with 0.10% nanoparticles volume concentration, the thermal efficiency is 10.60% higher than that with the based working fluid. Mozumder et al., (2010) conducted an experiment for different thermal loads and fill ratio to assess the performance of heatpipe in wet run and dry run conditions. Concluded that the fill ratios of working fluid greater than 85% of volume of evaporator show better result.For a 2W heat input capacity, the thermal resistance observed in the dry run was 10.5 °C/W and that in wet run was 7.25 °C/W. Apart from that, Senthilkumar et al., (2011) employed four cylindrical heat pipes, which were filled with de-ionized water, copper nanofluid, an aqueous solution of n- hexanol and copper nanoparticle in an aqueous solution of n-hexanol separately and tested for its performance. The thermal efficiency decreased as inclination angle > 30° and > 45° for water and copper nanofluid respectively. Gabriela (2011) investigated thermal performance of thermosyphon heatpipe using iron oxide nanoparticles. The thermal resistance was low at 90° and 5.3%. An increase of heat transfer rate of 39% is obtained for a 2% iron oxide nanoparticles and an increase with 42% for 5.3% iron oxide nanoparticles concentration level at 90° Nandy (2013) conducted thermal performance of screen mesh wick heat pipes with different nanofluids such as Al 2 O 3 -water, Al 2 O 3 -ethylene Glycol,TiO 2 -water,TiO 2 -ethylene glycol and ZnO ethylene
The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations.
The collector has been placed facing due south with a tilt angle of 11° to the horizontal. The elliptical heat pipes have been brazed to the absorber sheet in such a way that the evaporator section of the heatpipe is in the collector and condenser section is protruding outside the collector. The water circulated through the condenser section at inlet and outlet temperatures were measured by K-type thermocouple. Solar intensity at the test site was measured using EPPLY pyranometer. The heatpipe surface temperature, absorber plate temperatures and glass plate temperatures were
improved the thermal performance of the heatpipe with a volume concentration of 2% for maximal heat transfer enhancement. Compared with distilled water, it is observed that there is a overall decrease of 32 % in thermal resistanceat different heat inputs, inclination angle and concentration than that with the based working fluid at 40% filling ratio.
Fig .1. The consumption of communication base station.
Since 1970, heatpipe exchangers have been extensively applied in many industries including HVAC systems. Hayama and Hong-Koo et al. studied the effects of the parameters and the way of supply air on the communication base station. They reported that the change of velocity has more obvious effect than that of temperature on energy saving, and under air supply system could improve the temperature distribution to obtain a good energy saving effect. Al-Rabghi  and Wang  et al. used outdoor air for cooling, which can decrease 30% energy consumption of air conditioning system. El-Baky and Mohamed  stated that the incoming fresh air could be cooled down by the application of heatpipe exchanger between two streams of fresh and return air in an air conditioning system,. Firouzfar  et al. established that the application of methanol-silver nanofluid as the working fluid in a two-phase thermosyphon heat exchangers saves energy by 9-31% for cooling and 18-100% for reheating the air supply stream in an air conditioning system.
 Changhong Zhan, Zhiyin Duan, Xudong Zhao Energy Volume 36, Issue 12, December 2011, Pages 6790–6805.  Kumaresan, S. Mohaideen Abdul Khader, S. Karthikeyan, R. Velraj, Convective heat transfer characteristics of CNT nanofluids in a tubular heat exchanger of various lengths for energy efficient cooling/heating system, International Journal of Heat and Mass Transfer, 60 (2013) 413-42.
Available online 27 April 2018
Interest in the use of heat pipes in solar applications is increasing due to their role in improving the heat transfer performance of solar collectors. In order to effectively utilise heat pipes, their performance under various operating conditions and inclination angles need to be investigated. In this work, numerical and experimental studies were carried out to investigate the effects of heat input and inclination angle on the wall temperature distributions and thermal resistance of thermosyphon heatpipe. A Computational Fluid Dynamics (CFD) model was developed using ANSYS Fluent to simulate the flow and mass transfer using volume of fluid (VOF) approach together with user - defined function (UDF) to simulate the phase change processes at various inclination angles. Experiments were carried out to validate the CFD model at heat inputs of 81.69W and 101.55W with temperature distribution results showing good agreement of ±4.2% average deviation. Also the predicted thermal resistance at different inclination angles showed good agreement with the experimental ones with maximum deviation of ±5.7%. Results showed that as the heat input increases, the heatpipe wall temperature increases and the thermal resistance decreases. Experimental and numerical results showed that increasing the inclination angle will improve the thermosyphon heatpipe performance to reach its maximum value at 90o, but this effect decreases as the heat input increases.
Due to the human need for energy, a more efficient way of using it is a major challenge in the scientific community. The thermal performance of heatpipe is one the most important part of these types of investigation in the field of heat transfer. Heat pipes are enclosed, passive two phase heat transfer devices. They make use of the highly efficient heat transport process of evaporation and condensation to maximize the thermal conductance between a heat source and a heat sink. They are often referred to as thermal superconductors because they can transfer large amounts of heat over relatively large distances with small temperature differences between the heat source and heat sink. The amount of heat that can be transported by these devices is normally several orders of magnitude greater than pure conduction through a solid metal. They are proven to be very effective, low cost and reliable heat transfer devices for applications in many thermal management and heat recovery systems. They are used in many applications including but not limited to passive ground/road anti-freezing, baking ovens, heat exchangers in waste heat recovery applications, water heaters and solar energy systems and are showing some promise in high-performance electronics thermal management for situations which are orientation specific.