Investigation of Wickless Heat Pipe Performance Filled With R134a

The wickless heat pipe (theroosyphon) is ordinate of three divisions the condenser, evaporator and insulated region (adiabatic region). In this work, the condenser and evaporator regions are made of copper tube with a length of 300 mm, for each an exterior diameter of 28.2 mm and an interior diameter of 26.4 mm. While the insulated region has a length of 400 mm and an exterior diameter of 28.2 mm. The evaporator region of the heat pipe bounded by a coiled heat source that represented the heat source. The condenser is encapsulated in a plastic cylinder to accommodate the flow of the cooling water. Thermosyphon has been filled by R- 134a working fluid. The effect of heat input, filling ratio and sink temperature were all tested and measurement. The results showed that the heat transfer performance increases when the applied energy to the evaporator increases while the total heat transfer efficiency of the heat pipe increases the gradient temperature between the medium of the evaporator and the condenser increases. The optimum fill rate is 119 % (250g), the sink temperature is 20°C, and it has been found to be suitable for optimum heat pipe performance.

Advanced Modeling of Enclosed Airspaces to Determine Thermal Resistance for Building Applications

Enclosed airspaces to reduce heat flow have been recognized for well over 100 years. Airspaces with one or more reflective surfaces define reflective insulation (RI) assemblies, a product type used in walls, roofs, windows with multiple panes, curtain walls and skylights. The thermal resistance (R value) of airspaces depends on the emittance of all surfaces, airspace dimensions and orientation, heat flow direction and surfaces temperatures. The modeling of RI now includes CFD coupled with radiation to quantify the total heat transfer. This study compares a validated model for airspace R values with existing methods such as ISO 6946 and hot-box results that provide the R values in the ASHRAE Handbook of Fundamentals. The existing methods do not include an airspace aspect ratio. This study showed that the aspect ratio can impact the R value by a factor of two. The impact of aspect ratio was calculated for double airspaces variation such as that for single airspaces. The present calculations are two-dimensional and also consider all the bounding airspace surfaces, while previous methods are one-dimensional and do not include surface temperature variations or detailed radiative transport.

An experimental study of the temperature evolution of a single fin submerged in a phase changing material during melting at different heat fluxes

An experimental setup has been designed to study a single cylindrical fin placed in a cylindrical enclosure filled with phase changing material (PCM). The heat flux to the fin is measured at the top of the fin. The temperature evolution at different fin heights is measured by thermocouples placed internally in the fin. The evolution of these temperatures has been studied for different heat fluxes. This provides insight in the contribution of the different fin heights to the total heat transfer to the PCM during the different stages of the melting process. As such they can be used to assess the effectiveness of the fin over its length. After approximately 6h, the fin temperature stabilizes during melting. Due to the temperature drop over the fin, the bottom temperature reached is significantly lower than the temperature at the top and the contribution of this lower part to the total heat transfer is lower as well. For heat fluxes higher than 3805±75 W/m2, the steady-state temperatures at fin locations in contact with the melting PCM are similar. For low heat fluxes, this steady-state temperature is not reached during a 12h experiment. Longer experiments are thus needed to study the steady-state behaviour at these lower heat fluxes.

Definition and analysis of overall heat-transfer coefficient at the sections of “hot” export petroleum pipeline operating in northern winter conditions

Background. Receiving information on overall heat-transfer coefficient of pipeline pumping down the heat oil is required for resolving a number of process challenges: definition of specific cooling-off intensity of delivered petroleum, optimization of delivery processes, insulation efficiency assessment of pipeline sections etc. Aim. The actual values of the heat transfer coefficients are the most reliable basis for the implementation of optimization and technological calculations during thermohydraulic modeling and development of measures (a) to save energy during hot pumping and (b) to increase the reliability of the “hot” pipeline in order to exclude the possibility of its self-stopping and “freezing”. In the context of assessing the technological reliability of pumping, the determination and analysis of the total heat transfer coefficient for the sections of the oil pipeline were carried out and the capabilities of this methodological approach were demonstrated. Materials and methods. In the article, by the example of 266-kilometer long export pipeline (Ø 300 mm), functioning in «hot» delivery mode is presented the calculation process of defining the actual values of overall heat-transfer coefficient in route sections, and is done the analysis of this coefficient values, operation heating mode of the pipeline and their related factors of technological reliability of oil delivery process. Results. The difference in the values of the overall heat transfer coefficient at the sections of the pipeline is shown, which allows us to come to a practical conclusion about the different intensities of the thermal processes occurring in its different linear sections (aboveground, underground with intersection of marshy soils and rivers, with and without thermal insulation, operating in non-isothermal and isothermal modes). Conclusions. The proposed approach to determining the actual values of the total heat transfer coefficient for sections of the “hot” oil pipeline in combination with the analysis of the data obtained provides opportunities that are largely in demand from a methodological point of view and extremely important from a practical standpoint.

Improving the Heat Transfer Rate of Air Conditioning Condenser by Material Optimization

Air conditioning systems have condensers that remove unwanted heat from the refrigerant and transfer the heat outdoors. The optimization of the global exploit of heat exchanging devices is still a burdensome task due to different design parameters involved. There is need for more and substantial research into bettering cooling channel materials so as to ensure elevated performance, better efficiency, greater accuracy, long lasting and low cost heat exchanging. The aim of this research work is to improve the heat transfer rate of air conditioning condenser by optimizing materials for different tube diameters. Simulations using thermal analysis and Computational Fluid Dynamic (CFD) analysis were carried out to determine the better material and fluid respectively. The analysis was done using Analysis System software. Different parameters were calculated from the results obtained and graphs are plotted between various parameters such as heat flux, static pressure, velocity, mass flow rate and total heat transfer. The materials used for CFD analysis are R12 and R22, and for thermal analysis are copper and aluminium. From the CFD analysis, the result shows that R22 has more static pressure, velocity, mass flow rate and total heat transfer than R12 at condenser tube diameter 6 mm. In thermal investigation, the heat flux is more for copper material at condenser tube diameter 6 mm. Copper offers maximum heat flux. Also, refrigerant R22 scores maximum for the heat transfer criteria, but cannot be recommended due to toxicity

An Experimental Investigation of Water Vapor Condensation from Biofuel Flue Gas in a Model of Condenser, (2) Local Heat Transfer in a Calorimetric Tube with Water Injection

In order for the operation of the condensing heat exchanger to be efficient, the flue gas temperature at the inlet to the heat exchanger should be reduced so that condensation can start from the very beginning of the exchanger. A possible way to reduce the flue gas temperature is the injection of water into the flue gas flow. Injected water additionally moistens the flue gas and increases its level of humidity. Therefore, more favorable conditions are created for condensation and heat transfer. The results presented in the second paper of the series on condensation heat transfer indicate that water injection into the flue gas flow drastically changes the distribution of temperatures along the heat exchanger and enhances local total heat transfer. The injected water causes an increase in the local total heat transfer by at least two times in comparison with the case when no water is injected. Different temperatures of injected water mainly have a major impact on the local total heat transfer until almost the middle of the model of the condensing heat exchanger. From the middle part until the end, the heat transfer is almost the same at different injected water temperatures.

A numerical study on heat transfer performances of horizontal ground heat exchangers in ground-source heat pumps

Horizontal ground heat exchangers (HGHEs) have advantages such as convenient construction and low cost; however, their application and popularization are restricted owing to traditional linear HGHEs occupying large space and presenting low total heat transfer capacity. Spiral-coil and slinky-coil HGHEs have been proposed, but currently a comprehensive comparison and evaluation for these types of HGHEs are still needed. In this study, a three-dimensional heat transfer model of the three types of HGHEs for ground source heat pumps (GSHPs) was established. Based on the simulation results, the long-term heat transfer performances were investigated, including the temperature field of surrounding energy-storage soils, outlet working fluid temperature, coefficient of performance (COP) of units, and surplus temperature of the energy-storage soils. A new concept named heat transfer capacity per heat-affected area was proposed in this paper. It is found that the spiral-coil HGHEs have the best performances in terms of working-fluid outlet temperature, unit COP, total heat transfer capacity, heat transfer rate heat-affected area. The linear HGHEs shows the best performances in terms of mitigating heat imbalance risk and heat transfer rate per length. The results provide a reliable basis for selection of HGHE types in engineering practice and improvement guide in the future.

Review on Heat Transfer Enhancement by Rectangular Fin

Heat generation of engineering appliances has bad effect in handling the system can cause the trouble, short life cycle of machines, frequent maintenance requirements and low reliability of systems. The passive cooling technique has been widely used to solve such problems. This review work summarizes the heat transfer enhancement technique in a rectangular fin with economic way. So many research about the enhancement of heat transfer by rectangular fins experimentally and numerically and found very significant result. In this review, various types of rectangular fin structures are studied simultaneously. It is revealed through reviewing the related literature that the highest value of equivalent heat transfer enhancement is found the increase in average heat transfer performance of inverted triangular notched fin 50.51% as compared with plane rectangular fin and the perforated fin total heat transfer rate increased by 38.9% compared to regular fin. Furthermore, by reduction of the optimal fin spacing, heat flux can be changed by 20% in standard rectangular fin when compared with regular fin spacing. Also cooling performance of the inclined rectangular fin with 60° of tilt angle is seen to be as 6% higher than solid rectangular fin. This article can be considered as a benchmark in the practical application for enhances the heat transfer rates.