Search

The thermal performance of a Z shape enthalpy heat exchanger utilising 70 gsm Kraft paper as the heat and moisture transfer surface has been investigated. Effects of different inlet air humidity ratio conditions on the heat exchanger effectiveness and on the energy recovered by the heat exchanger have been the main focus of this investigation. A typical air conditioning cooling coil which incorporates an enthalpy heat exchanger has been modelled for tropical climate. Under test conditions, results have shown that latent effectiveness and the moisture resistance coefficient have strong dependency on the inlet air humidity ratio. Moreover, the latent effectiveness has been found to be strongly dependent on the moisture resistance coefficient rather than the convective mass transfer coefficient. Finally, annual energy analysis for Singapore weather conditions have also shown that energy recovered under variable inlet air conditions is 15% less than that recovered under constant inlet air conditions for the same heat exchanger. [ABSTRACT FROM AUTHOR]

Paper membranes have long been used in an enthalpy exchanger. However, there has been a continuous concern on the durability or the anti-bacterial performance. In this study, heat and moisture transfer characteristics of a recently-developed PE/PA (polyethylene/polyacetate) composite membrane was investigated as a possible substitute to the paper membrane. Results showed that the diffusion coefficients of the PE/PA membrane (7.7 × 10−10 m2/s to 1.8 × 10−9 m2/s) were higher than those of the paper membrane (1.8 × 10−11 m2/s to 6.0 × 10−11 m2/s). Furthermore, the diffusion coefficient increased as relative humidity increased, reached a maximum at 50 % to 60 % and then decreased. For PE/PA membrane, the sorption constant increased as temperature increased, which was the reversed trend to the paper membrane. Successful prediction of the moisture transfer effectivenesses of the separate pseudo-counter flow enthalpy exchangers further strengthened the validity of the obtained diffusion coefficients. [ABSTRACT FROM AUTHOR]

In this paper, the heat transfer characteristics of multiple pairs of vortex generators (VG) mounted on vertical plate fins of plate fin heat sink (PFHS) are evaluated using computational fluid dynamic simulations. The delta winglet pairs are used as longitudinal VGs, and they are mounted one after the other in the axial direction. Critical design parameters for the double pair of VGs (DPVGs) are identified, and a design of experiment-based simulations is carried out to develop a response surface model for Nusselt number and thermal hydraulic performance parameter. Results show winglet length is a critical design parameter compared with winglet height, and the axial inter VG distance between VG pairs plays a crucial role in improving the heat transfer characteristics. The optimum inter VG distance for a double pair of VG is evaluated, and it is 2.2 to 3 times the length of the delta-winglet. Thermal hydraulic performance of PFHS with double pair of VG is 1.49 times higher than that of plain PFHS. Finally, the variation of heat transfer characteristics against velocity is also evaluated for the PFHS with a DPVG. [ABSTRACT FROM AUTHOR]

The performance of the heat exchanger has a huge impact on the cycle efficiency and levelised cost of electricity in solar thermal power generation. This paper proposes a novel scaled structure for the cold-side channel of the printed circuit heat exchanger (PCHE) that combines good heat transfer performance with lower pressure drop. A numerical simulation is employed to investigate and compare the performance of PCHEs with scaled, zigzag, and straight channels. When using the comprehensive performance evaluation criteria (PEC) as evaluation indicator, the scaled channel demonstrate the best overall performance, with an increase in comprehensive performance by 6 % and 12 % compared to zigzag and straight channels, respectively. The above conclusions indicate that the adoption of scaled channel structures could enhance the heat transfer performance of PCHE, providing valuable insights for the development and improvement of novel PCHE and other heat exchanger's heat transfer efficiency. [ABSTRACT FROM AUTHOR]

The performance of the heat exchanger has a huge impact on the cycle efficiency and levelised cost of electricity in solar thermal power generation. This paper proposes a novel scaled structure for the cold-side channel of the printed circuit heat exchanger (PCHE) that combines good heat transfer performance with lower pressure drop. A numerical simulation is employed to investigate and compare the performance of PCHEs with scaled, zigzag, and straight channels. When using the comprehensive performance evaluation criteria (PEC) as evaluation indicator, the scaled channel demonstrate the best overall performance, with an increase in comprehensive performance by 6 % and 12 % compared to zigzag and straight channels, respectively. The above conclusions indicate that the adoption of scaled channel structures could enhance the heat transfer performance of PCHE, providing valuable insights for the development and improvement of novel PCHE and other heat exchanger's heat transfer efficiency. [ABSTRACT FROM AUTHOR]

The performance of the refrigeration system is largely influenced by the heat exchanger, and there are various methods for increasing heat exchange efficiency. In this paper, the effect of changes in the internal shape of an evaporator with different heat transfer areas on the performance under actual refrigerator operating conditions was analyzed. The type of evaporator includes a grooved evaporator and a composite grooved evaporator with a relatively large heat transfer area. The performance evaluation was evaluated by refrigerant optimization, on-off operational test, and steady state energy test. The optimum refrigerant amount for both systems is 76 g. When a composite grooved evaporator was used, monthly energy consumption was relatively saved by 2.7 kWh/month. In addition, the composite grooved evaporator has consumption and 2.2 % higher cooling capacity than the grooved evaporator. In conclusion, COP improved by 1.33 %. [ABSTRACT FROM AUTHOR]

The strength of the joint between the heat exchange tube and the tube plate affects the performance and operation cycle of the heat exchanger. Different expansion processes were adopted for same material Q345R+10# and dissimilar materials Q345R+S30403 joints, respectively, in order to verify the performance of the joint under frequent heating and cooling during actual operation. Through theoretical calculation of expansion pressure, the same expansion pressure and similar expansion degree were applied to each group of joint specimens, and the pull-off stress of Q345R+10# joints of the same material at room temperature, 100 °C, 200 °C and 300 °C was compared, as well as the sealing and pull-off stress of Q345R+10# and Q345R+S30403 joints before and after thermal vibration. This paper mainly introduces the expansion process of the joints between heat exchanger tubes and tube plate. Mechanical and hydraulic tube expansion machines were used for tube expansion experiments, and the joint specimens were treated with heat treatment and thermal vibration to simulate the operating temperature of the equipment. The expansion quality and expansion performance of the joint were analyzed to determine the optimal expansion pressure, and the sealing performance and tensile resistance of the joint were tested, so as to provide a reference for the processing and manufacturing of the joint between the heat exchanger tube and tube plate similar to the heat exchanger. [ABSTRACT FROM AUTHOR]

This paper presents the test approach to investigate the effects of gas flow rate on particulate deposition inside the exhaust gas recirculation (EGR) coolers. The tests were carried out on a diesel engine equipped with the EGR cooler that a given total gas flow rate passed through and that contained pluggable exchanger tubes to adjust the flow rate in the tubes. Test results show that under the given coolant temperature and EGR gas temperature, the lower flow rate in the exchanger tube is and the longer tubes are, the more particulate with Dp > 50 nm deposit in the cooler. With the given total gas flow rate passing through the cooler, the lower flow rate in the exchanger tube is and the longer tubes are, the larger deposit mass is inside the cooler. In the cases of longer tubes, the effects of gas flow rate on the deposit mass are depends on the effects of gas velocity on the particulate deposition, rather than the effects of flow rate on the particulate number passing through the heat exchanger tube per minute. [ABSTRACT FROM AUTHOR]

With developments of turbo-compounding and two-stage turbocharging technologies, two-stage turbine is increasingly applied in automotive engines. This paper numerically investigates the characteristic of a two-stage turbine on a turbo-compound engine under pulsating flow conditions. The behaviors of turbine stages with the swallowing capacity ratio (SR) equals to 2.0, under low, mid and high load conditions were studied. Results show that the Low pressure turbine (LPT) is more sensitive to the pulsating flow, especially at low load conditions, compared with High pressure turbine (HPT). It is caused by the dramatic change of velocity ratio in LPT. Results also show that the load split between HPT and LPT under pulsating flow conditions deviates from that at quasi-steady conditions, indicating the different behaviors of the two-stage turbine under pulsating conditions. [ABSTRACT FROM AUTHOR]

This paper presents a life prediction method based on several accelerated life test data for brazed plate heat exchanger. For this purpose, accelerated life tests were performed with pressure cycle and fluid temperature as accelerating stresses. Statistical analyses of the two test data sets and their combination were conducted. As a result, the shape parameter of Weibull distribution, the accelerating index of pressure cycle, the activation energy, and the life cycles under normal use conditions for the brazed plate heat exchanger were obtained. [ABSTRACT FROM AUTHOR]

The Earth air heat exchanger is a better passive technology to the use of geothermal energy. The findings from the study brings us that technology of varying temperature with the soil temperature found many benefits like energy saving and environment preservation. These benefits may help us lot in future in the field of renewable energy resources which is peak demand of the society. The loss of energy can be minimized with the help such type of systems. In this research paper efforts are made to analyze the accomplishment of a low cost cooling system of outdoor air for hot-dry climate. The effect of velocity, length and drop in temperature of the air is studied at the inlet and outlet of the pipe. The results show that maximum temperature drop available at low velocities because air gets larger time to get heat transfer in the underground pipe in soil and also the greater length of the pipe of earth air heat exchanger has more effect on performance of earth air heat exchanger. [ABSTRACT FROM AUTHOR]

The compact tube heat exchanger located behind the air-intake can achieve quick cooling of high-temperature air to ensure the normal operation of the pre-cooled aeroengine. It has great impact on the engine's performance. The total pressure distribution at the heat exchanger inlet is inevitably uneven due to the influence of the air-intake. This paper studies the effect of three typical inlet distortions with different amplitudes using porous model and dual cell model. The results indicated that the outlet total pressure distortion is not sensitive to the inlet total pressure distortion. However, it affects the total pressure recovery and the total temperature distortion at the outlet by altering the pressure loss in the heat exchanger upstream and the flux distribution at the heat-transfer-zone entrance, respectively. This leads to a reduction of heat transfer. The effect of inlet distortions varies with distortion type. And it becomes more severe with increasing distortion. [ABSTRACT FROM AUTHOR]

This paper describes the numerical results of the heat transfer enhancement mechanism of tubes containing rectangular-cut twisted tapes with alternate axes (ARC-TTs). Influence of the length of cut ratio ( LR = L/ w = 2.0, 2.4 and 2.8) and width of cut ratio ( WR = W/ w = 0.7, 0.8 and 0.9) on the heat transfer rate, friction factor and thermal performance characteristics are presented. The contour plots of predicted streamlines, velocity field, temperature field, and local Nusselt number distribution are also given for a better understanding of heat transfer mechanism. The results of the tube containing a classical twisted tape are also reported, for comparison. It can be observed that the use of ARC-TTs results in more disordered streamlines and higher turbulent intensity than that of the classical twisted tape. The numerical results also show that heat transfer and friction loss decrease as Length of cut ratio ( LR) and Width of cut ratio ( WR) increase while thermal performance factor shows reverse trend. In the studied range, utilizing ARC-TTs offers thermal performance factor up to 1.5. [ABSTRACT FROM AUTHOR]

To predict the flow resistance of a compact heat exchanger with an offset strip fin, a large number of correlations have been developed and these correlations have been well used in the engineering field. Recently, three-dimensional computational analysis has been frequently used for the design and verification of heat exchangers. To improve the accuracy of three-dimensional numerical analysis and reduce the resources used for the analysis, the fins of compact heat exchangers are assumed to be a porous medium generally. To predict the flow resistance of an offset strip fin assumed to be a porous medium, the resistance must be separated into viscous and inertial resistances. However, the correlations developed so far for the offset strip fin have not been able to distinguish between these resistance types. In this paper, we propose a new friction model that can represent the flow resistance of an offset strip fin as the sum of the viscous and inertial resistances. The new friction correlation model has a maximum error of 10 % compared to existing correlation models. In addition, using the new friction model, the permeability and the Ergun constant for offset strip fins are defined as functions of offset strip fin parameters. Therefore, when predicting the flow resistance of a compact heat exchanger with an offset strip fin using three-dimensional numerical analysis, viscous and inertial resistances can be defined without additional calculations or tests for a porous medium approach. [ABSTRACT FROM AUTHOR]

In view of Kyoto protocol, there is a pressing need to reduce the energy consumption and environmental impacts of domestic appliances. In the total energy consumption of household appliances, domestic refrigerator plays a vital role. Alternate refrigerants and improvement in the performance of the components can contribute to tackle the above issue in a domestic refrigeration system. In this paper, the performance of a domestic refrigeration system with brazed plate heat exchanger as condenser, and working with refrigerants such as R290/R600a and R134a was studied using experimental method. The result showed that the system with water-cooled brazed plate heat exchanger reduces the per day energy consumption of a system from 21% to 27% and increases the COP from 52% to 68%, when compared to conventional system. The compressor discharge temperature and dome temperature are also dampened. For R134a and R290/R600a, the TEWI of the system with water-cooled brazed plate heat exchanger is lower than that of the system with air-cooled condenser by 26.8% and 21%, respectively. Among the refrigerants, R290/R600a showed higher performance than R134a. [ABSTRACT FROM AUTHOR]

The increasing application on high laser power in industries required studies in the portion of pump radiation absorbed by laser media that exchanges to heat. Heat may cause thermal stress, stress birefringence and thermal lens effects. These effects can destroy the optical properties of the laser medium, decrease the beam quality and may lead to medium break. In this paper, the thermal and stress analyses of continuous and pulsed end-pumped Nd:YAG slab laser are studied using finite element method. Heat deposited in the slab is removed by cooling water, flowing on the largest faces of the slab, which surrounds the active media. The temperature and stress distributions of the end-pumped Nd:YAG slab are defined by coupled field methods in the ANSYS commercial finite element software. The value of maximum temperature and stress in the slab which is affected by an end-pumping are calculated. Finally the maximum pump-power range which can be applied to the slab is determined using the limit of maximum stress in the slab. The analyses are done in from transient to steady-state regimes for continuous pumping. Results show that deposited heat due to the pulsed pumping acts like a mechanical impact. [ABSTRACT FROM AUTHOR]

Radiation recuperator is a class of indirect contact heat exchanger widely used for waste heat recovery in high temperature industrial applications. At higher temperatures heat loss is higher and as the cost of energy continues to rise, it becomes imperative to save energy and improve overall energy efficiency. In this light, a radiation recuperator becomes a key component in an energy recovery system with great potential for energy saving. Improving recuperator performance, durability, and its design and material considerations has been an ongoing concern. Recent progress in furnace design and micro turbine applications together with use of recuperators has resulted in reduced fuel consumption, increased cost effectiveness and short pay-back time periods. Due to its high commercial value and confidential nature of the industry, little information is available in the open literature as compared to convection recuperators where results are well documented. This review paper intends to bridge the gap in literature and provides valuable information on experimental and theoretical investigations in radiation recuperator development along with identification of some unresolved issues. [ABSTRACT FROM AUTHOR]

Among tubular heat exchangers, fin-tube types are the most widely used in refrigeration and air-conditioning equipment. Efforts to enhance the performance of these heat exchangers included variations in the fin shape from a plain fin to a slit and louver type. In the context of heat transfer augmentation, the performance of vortex generators has also been investigated. Delta winglet vortex generators have recently attracted research interest, partly due to experimental data showing that their addition to fin-tube heat exchangers considerably reduces pressure loss at heat transfer capacity of nearly the same level. The efficiency of the delta winglet vortex generators widely varies depending on their size and shape, as well as the locations where they are implemented. In this paper, the flow field around delta winglet vortex generators in a common flow up arrangement was analyzed in terms of flow characteristics and heat transfer using computational fluid dynamics methods. Flow mixing due to vortices and delayed separation due to acceleration influence the overall fin performance. The fin with delta winglet vortex generators exhibited a pressure loss lower than that of a plain fin, and the heat transfer performance was enhanced at high air velocity or Reynolds number. [ABSTRACT FROM AUTHOR]

An organic Rankine cycle (ORC) can be applied to recover the low-grade waste heat. In this paper, the performances of five different types of ORC are evaluated. These configurations include a simple ORC, an ORC with an internal heat exchanger (IHE), an ORC with an open feed organic fluid heater (OFOH), an ORC with a closed feed organic fluid heater (CFOH), and an ORC with a reheater. First, the feasible working region is defined for an ORC operating together with an internal combustion engine. Subsequently, the thermal efficiency of each ORC is maximized using a genetic algorithm. Finally, the characteristics of each ORC are analyzed and compared using a combination of the first law and second law method. Our analysis indicates that the ORC with an IHE showed the best thermodynamic performance. The ORC with an OFOH and the ORC with a CFOH are sub-optimal while the simple ORC and the ORC with a reheater are the last choice. The effects of the expander inlet pressure, the condenser outlet temperature and the expander isentropic efficiency on system performance of each ORC were also analyzed. [ABSTRACT FROM AUTHOR]

Plumbing is necessary for boilers and heat exchangers and in buildings and power plants, including those that produce green energy. Further, among all the components used in plumbing, piping systems are subjected to high temperatures and pressures. A twisted or cracked pipe adversely affects the efficiency of a power plant and production rate of a factory or causes secondary accidents. This study investigates the safety evaluation of the SUS material, which is mainly used in boiler and heat exchanger piping. SUS is an inelastic material; therefore, the leak-before-break concept of fracture mechanics, for which various safety evaluation methods and specifications have been presented, can be applied during the design stage. However, the test is performed as a substitute for the actual pipe testing because of the high cost and difficulty level. Thus, a method to test compact pipes based on various loading ratios is developed. This study determines the test jig shape to obtain fragility similar to the theoretical value. The proposed test method is only available under certain load conditions and requires a new J-integral when the jig geometry or load ratio is changed. Therefore, the J-integral equation for each load condition is integrated to propose a J-integral equation independent of the load ratio. [ABSTRACT FROM AUTHOR]

In this study, an artificial neural network (ANN) model was applied to predict the thermo-hydraulic performance of the offset-strip fin heat exchanger. The ANN model was used for predicting the thermo-hydraulic performance to improve the prediction accuracy and extend the applicable range compared to the results of using the empirical equations reported in previous studies. The main parameters of these empirical equations were fin height (0.134 < α < 0.997), fin length (0.012 < δ < 0.048), fin width (0.041 < γ < 0.121), and Reynolds number (120 < Re <104). In addition, the Fanning friction factor f and the Colburn factor j were considered as the outputs of the ANN model. The impact of the parameters on the thermo-hydraulic performance of the heat exchanger was quantitatively evaluated, and the prediction accuracy was improved over a wide range for the thermo-hydraulic performance generated by the ANN model. Thus, the results obtained using the ANN model agreed well with the experimental data over a wider range than possible for the previous empirical correlations, showing extremely high accuracy and validity of the ANN model in comparison to the empirical equations. [ABSTRACT FROM AUTHOR]

The refrigerant charge is one of the important parameters that determines the performance and power consumption of an air conditioner. Refrigerant charge fault occurs because of refrigerant leakage as well as initial charge fault. Since refrigerant charge loss resulting from a leakage is a gradual process, it is difficult to detect it in an early stage of leakage. In this study, the refrigerant charge of an air conditioner was estimated using predictions of its start-up characteristics obtained from a gray box model. The dynamic characteristics of heat exchangers were assumed to vary with the refrigerant charge as well as operating conditions. Furthermore, the moving boundary method was used to determine the transient behavior of the refrigerant in the condenser and evaporator. Additionally, correction factors were employed in the heat exchanger model. The correction factors were correlated under training conditions of the air conditioner, and the accuracy of the model was verified by comparing its predictions with experimental results under test conditions. The condensation temperature was selected for estimating the refrigerant charge amount. The refrigerant charge could be estimated within a prediction error of 5 % by minimizing the differences between simulation and experimental data. The proposed method can be used for predicting the refrigerant charge and detecting faults in air conditioners during refrigerant leakage on the basis of the start-up characteristics of the air-conditioners. [ABSTRACT FROM AUTHOR]

Ammonia-fed solid oxide fuel cell (SOFC) power generation systems are very promising owing to their high efficiency and ease of fuel storage. However, understanding the complexity of fuel cell stacks and systems supplied by ammonia remains challenging. Therefore, it is proposed to investigate the standalone SOFC system to clearly elucidate the behavior of the stack and realize facile implementation. In this study, the stack was modeled and validated using experimental data to confirm its output characteristics. The system efficiency was then calculated under various operating conditions, such as current density, fuel utilization, and stack in/out temperature. The results show that the system efficiency is approximately 54 % and is highly dependent on fuel utilization and current density but not on temperature differences. However, the system can only operate at a temperature difference of 65 °C or higher owing to the effectiveness of the heat exchanger on the fuel side. [ABSTRACT FROM AUTHOR]

Based on the theory of fluid-structure interaction (FSI), the flow characteristics and mechanical properties of torsional flow heat exchanger (TFHX) and cross torsional flow heat exchanger (CTFHX) were numerically studied. The simulation results were compared with the experimental results to verify the reliability of the numerical simulation. The results show that the pressure drop of CTFHX decrease is 30.31-32.56 % lower than that of TFHX, and the heat transfer coefficient is found to lower by 16.8-18.5 %, but the comprehensive performance h/ΔP is increased by 14.8-17.9 %. There is also a higher stress around the baffle holes, and the influence of temperature load on stress is much greater than that of pressure load. Moreover, the linearization results of hazardous locations show that CTFHX has greater stress. This study provides theoretical guidance for the structural optimization and equipment maintenance of heat exchanger. [ABSTRACT FROM AUTHOR]

This study extends the investigations of Kim [11] to a wet condition, who tested heat exchangers having fins of the smooth wave or herringbone wave geometry on 12.7 mm tubes under dry condition. Results showed that the j and f factors were independent of the fin pitch. Furthermore, the smooth wave fin geometry yielded 22 % to 28 % higher j factors, and 24 % to 28 % higher f factors compared with the herringbone wave geometry. The ratios of the j/f1/3 between the smooth wave and the herringbone wave configuration were 1.07, 1.14 and 1.19 for 1 row, 2 row and 4 row, respectively. These ratios were approximately the same as those obtained under dry condition [11]. Both for the smooth and the herringbone wave fin samples, the wet surface yielded higher j and f factors than the dry surface. For example, at a fin pitch of 3.0 mm of the smooth wave fin geometry, the j factors under wet condition were 2 % to 40 % higher than those under dry condition. Similarly, the f factors under wet condition were 56 % to 64 % higher than those under dry condition. [ABSTRACT FROM AUTHOR]

In the steam generator of a sodium-cooled fast reactor, heat transfer occurs from the primary sodium flow side at high temperature to the secondary water flow side at low temperature. Preventing the interaction between sodium and water in the heat exchanger is important to avoid a reactive explosion. To do so, the concept of the copper bonded steam generator, which consists of heat-exchanger modules with cross-flow-type arrangement, was recently proposed. In this cross-type arrangement, the sodium flow should be as uniform as possible throughout the horizontal channels in terms of the heat transfer efficiency between the sodium and water sides. This study aims to design a perforated plate leading to uniform sodium flow distribution throughout the 66×33 channels. The geometrical design and location of the perforated plate are optimized using numerical simulation. The designed plate improves the flow distribution uniformity at a slight cost of pressure loss. [ABSTRACT FROM AUTHOR]

The cooling performance improvement of a heat exchanger was investigated for a totally enclose air-to-air cooled high-voltage induction motor. Using dual cell heat exchanger model, 3D full mesh of the motor was created and the cooling improvement effect of the motor was numerically evaluated according to use of various design factors, such as tubes with 8 internal fins, the number of baffles, and heat exchanger housing that recycles exhaust air. The numerical models were verified through experimental testing. The results show that applying the tubes with internal fins and heat exchanger housing to recycle exhaust air to the motor reduces the average temperature rise in the stator winding by about 2.7 °C and 1.2 °C, respectively. But increasing the number of baffles in the heat exchanger from one to three increases the average temperature of the stator winding by 3.1 °C due to the increased pressure drop across tube banks. We can conclude that air flow resistance analysis of the entire system should be considered and also important on cooling performance in a TEAAC motor with external heat exchanger. [ABSTRACT FROM AUTHOR]

Nanofluids are suspensions of nanosized nanoparticles in the base fluid which shows superior performance in heat transfer applications. As different nanoparticles have different characteristics, thus the selection of a proper nanoparticle for a given application becomes a very crucial task. Thus, the selection of nanoparticle has to be performed in such a manner that it will give a maximum thermal performance that to at least cost. This study involves the multiple attribute decision-making (MADM) method to select optimal metal oxide nanoparticles. In the present method, to determine the weights of different attributes considered, the analytical hierarchy method (AHP) is used and then to obtain the final ranking, a technique for order preference by similarity to ideal solution (TOPSIS) is used. In the present study, the problem regarding the selection of suitable nanoparticle for heat exchanger applications is discussed. The most studies nanomaterials i.e., CuO, Al2O3, TiO2, SiO2, ZnO, Fe2O3 are considered with different attributes. It is found that copper oxide (CuO) and aluminum oxide (Al2O3) is the first-best and second-best alternatives, respectively. Empirical results obtained prove that this is a feasible approach to solving the nanoparticle selection problem. [ABSTRACT FROM AUTHOR]

In the present study, an improved heat exchanger model is proposed to efficiently analyze the cold oil removal process inside a fuel-cooled oil cooler. When exposed to low temperature condition, oil within a heat exchanger begins to congeal, preventing oil flow and causing loss of cooling. The conventional heat exchanger models, however, shows limits in reflecting the highly varying viscosity effects due to large temperature difference. To overcome this, the conventional porous media model was rewritten with the friction and Colburn j-factors that include the temperature dependent property variation. The property correction method by Shah and Sekulic [31] was added to enhance the prediction accuracy. Also, a relief valve model based on the porous media approximation is developed. The developed models were validated against the experimental data. Transient three-dimensional numerical simulations are carried out to analyze the effects of operating conditions on de-congealing phenomenon inside the FCOC. [ABSTRACT FROM AUTHOR]

Heat exchangers are frequently installed at an inclined angle to reduce the height of the air-conditioning unit. The inclination may deteriorate the thermal performance of the heat exchanger, and the effect will be more severe for an aluminum heat exchanger compared with a conventional fin-and-tube heat exchanger. However, the literature shows very limited investigations on this subject. In this study, a series of tests were conducted for a newly-developed aluminum heat exchanger, which has an additional drainage channel at downstream of the fin. Results showed that the pressure drop increased as inclination angle increased. However, the heat transfer coefficient showed a minimum behavior at approximately 45° inclination angle. This was true both for dry and wet conditions. The effect of inclination angle on the ratio between wet and dry j and f factor was not significant, which suggested that the inclination did not alter the condensate pattern on the louver fin (louver-bridging, fin-bridging, etc.) significantly. Comparison of the thermal efficiency indices (j/f1/3) of the present sample with those of the conventional sample (having no drainage channel) showed that the thermal performance improvement is significant under wet condition, which confirms the excellent condensate drainage of the present sample. [ABSTRACT FROM AUTHOR]

In this study, a thermal storage type heat exchanger that combines heat storage and heat exchange functions has proposed and the heat transfer characteristics of the new type of heat exchanger were analyzed through experiments. The proposed thermal storage type heat exchanger has a shell and tube structure and allows mutual heat transfer between three or more mediums, including a phase change material (PCM). This thermal storage type heat exchanger contains 52.2 kg of a PCM with a phase change temperature of 68.8 °C to provide heat storage function. The heat transfer experiment of the heat exchanger confirmed the effect of the temperature change of the heating medium under the same flow conditions. Furthermore, due to the structural characteristics of the thermal storage type double shell and tube heat exchanger (TSDHE), the phenomenon of three-medium heat exchange (hot water-cold water, hot water-PCM, additional water-PCM) was verified during the experimental process. In particular, due to the PCM filled inside the heat exchanger, the cold water received a heat transfer of 3 kW or higher from the PCM for at least 5 min (maximum 33 min), even when the hot water supply (heat source) was stopped. The results of this study will be used as basic data for applying a thermal storage type evaporator to a high temperature heat pump that generates steam using industrial waste heat. [ABSTRACT FROM AUTHOR]

The effect of adsorber heat exchanger (adHEX) material on the system performance of a silica gel-water, fin-tube type adsorption chiller was investigated for three typical materials, aluminum (Al), copper (Cu) and stainless steel (SS), following both the first and second laws of thermodynamics. High thermal conductivity was expected to shorten switching time and prolong adsorption/desorption period, and consequently result in a larger amount of water vapor, and lower thermal mass. In other words, since the product of density and heat capacity increases the heat supplied to the system, higher thermal performance was expected for Cu. However, preliminary calculations failed to confirm the expectation. This study examined the causes by artificially changing the Al thermo-physical properties to those of the Cu and SS. Above a threshold thermal conductivity, the main cause was found to be the material's density, and below the threshold, thermal conductivity was most important. The Al adHEX showed 0.518 of COP, 221 W/kg of SCP and 0.115 of ηe, which were 6.85 % and 6.53 % higher in COP and exergy efficiency than the Cu adHEX. [ABSTRACT FROM AUTHOR]

Presently, countries are trying to increase their energy efficiency. Therefore, the operating temperatures of very high temperature reactor (VHTR) and high temperature gas-cooled reactor (HTGR) are increasing in order to increase overall efficiency. A metallic material's intrinsic creep property is a limitation in this scenario. Inconel 617 alloy is a candidate material used in the intermediate heat exchangers of the VHTR and HTGR. Therefore, in this work, graphene, which is a promising ultra-thin material, is utilized as an efficient coating to augment the creep property of the Inconel 617 alloy substrate. The Inconel 617 alloy substrate is coated with graphene via a transfer methodology. The small punch creep test methodology is applied in order to measure the creep lifetime of the specimens. From the experimental results it can clearly be seen that the creep lifetime of the Inconel 617 alloy substrate specimen increases by a significant 5~20 % with the transferred graphene coating compared to the as-received Inconel 617 alloy specimen. [ABSTRACT FROM AUTHOR]

Air conditioners consist of heat exchangers, fans, motors and compressors as major components. From the viewpoint of noise, the compressor occupies a very large portion. In this study, rotary compressor which is mainly used in domestic air conditioner was discussed. The noise generated from the rotary compressor can be classified into pressure pulsation of the refrigerant and structural vibration. During the operation of the compressor, the behavior of the refrigerant and the internal structure of the compressor strongly interact with each other. Therefore, an integrated interpretation is required when analyzing from the viewpoint of refrigerant. In this study, the rotary compressor behavior is implemented using the FSI technique and the noise and valve behavior with and without discharge muffler are analyzed. [ABSTRACT FROM AUTHOR]

The effect of winglet height on the thermal-hydraulic performance of finned tube heat exchanger (FTHE) is investigated numerically. The rectangular winglet pairs (RWPs) having 5° attack angle are placed in common flow up (CFU) manner adjacent to the tubes for analysis. The air-side performance evaluation has been done based on the area goodness factor (j/f). The working fluid (air) is considered as incompressible fluid. Additionally, MOORA (multi objective optimization on the basis of ratio analysis) method is employed to get the best performance order of various configurations by taking Nusselt number (Nu) and area goodness factor (j/f) as beneficial attributes and friction factor (f) as a non-beneficial attribute having equal significances. The present study reveals that the rectangular vortex generators having 60 % of the channel height provides the better thermal hydraulic performance compared to the other considered cases. [ABSTRACT FROM AUTHOR]

The combined use of generation and propulsion gas turbines and steam turbines is efficient and can meet the environmental regulations. In this study, the thermodynamic performance of waste heat recovery systems of a marine gas turbine was analyzed. These systems combine the steam Rankine cycle and the organic Rankine cycle to form a dual-loop cycle. Working fluids R32, R134a, R152a and R1234yf, that are low-global warming potential, were selected for the organic Rankine cycle. All of the working fluids exhibited better performance than for the single-loop cycle, and R134a exhibited the greatest efficiency with energy and exergy efficiencies of 29.50 % and 45.58 %, respectively. The most important components contributing to the exergy destruction of the cycle were the heat exchangers. Therefore, it is essential to select the optimum heat exchanger as well as the working fluid in the waste heat recovery system for marine gas turbines. [ABSTRACT FROM AUTHOR]

Surface enhancement in heat exchangers has been actively researched, but enhancements have been mainly on the tube side, involving optimization of the geometry. The effect of surface enhancement has been studied in great detail experimentally, but numerical studies are scarce and involve performance comparisons based on the friction factor and Nusselt number. However, true performance can be assessed based on entropy generation minimization. We performed a numerical study on tubes with helical groove formation to assess entropy generation minimization. The tube data were initially validated experimentally and tube performance was then examined via thermal enhancement factors and entropy generation minimization. The Reynolds number was taken as 5000 to 10000 in accordance with an experimental study. All the tubes had an enhancement factor greater than unity, meaning that they were thermally efficient. However, with regard to irreversibility, the tube with the minimum pitch-0.051 m-(GT02) produced the lowest value and hence the minimum entropy generation rate, and thus represented the optimal choice for heat exchangers. [ABSTRACT FROM AUTHOR]

Organic Rankine cycle (ORC) power systems are widely used for low-temperature heat recovery. The radial turbine is the most important component in the ORC system and its performance is significantly dependent on the working fluid. Therefore, the effect of different working fluid on the performance of radial turbine in ORC system for the low-temperature heat source (120~180 °C) was investigated. First, the feasibilities of different working fluids for 150 kW radial turbine using R600a as designed working fluid were investigated. The thermal aerodynamic calculation of R600a at design condition was conducted with evaporation temperature 95 °C and condensation temperature 38 °C. The operation parameters of 5 non-designed working fluids (R600, R245fa, R245ca, R123 and R601a) were selected in the same temperature variation range as R600a. Then, the performance of a radial turbine for six working fluids at design condition was analyzed, and their three-dimensional flow field performances were also obtained by CFD numerical simulation. Finally, to broaden the operation range of the radial turbine and investigate the matching relationship between operation parameters and different working fluids, the off-design performances of radial turbine using six working fluids were analyzed and the effect of rotation speed, inlet pressure and inlet temperature on the performance of radial turbine was obtained. Results show that the performance of the radial turbine using the designed working fluid R600a is the best with efficiency of 82.7 % and output power of 150.5 kW. For the non-designed working fluids, the comprehensive performance of R600 was also judged to be good owing to the highest efficiency (85.1 %) and a relatively high power output (115.8 kW) among the fluids tested. For other working fluids, the output power of the radial turbine decreased obviously. There exists an optimum rotation speed for different working fluids to ensure that the radial turbine has the highest efficiency. The inlet pressure has a larger effect on the performance of the radial turbine than that of the inlet temperature. The results can provide basic data for the optimization design and operation of radial turbines in the ORC system. [ABSTRACT FROM AUTHOR]

The present work aims to investigate the thermo-hydraulic performance of a counter-current corrugated plate heat exchanger working with MgO/ethylene glycol nanofluid. MgO nanoparticles were dispersed in ethylene glycol at different weight (mass) concentrations of 0.1 %, 0.2 % and 0.3 % and nanofluids were introduced to a heat exchanger in form of a counter-current flow to exchange heat with water. The test rig provided conditions to measure the influence of different operating parameters such as fluid flow, mass concentration and inlet temperature of the nanofluid on heat transfer coefficient, pressure drop, and thermal performance index of the heat exchanger. Results showed that flow rate and mass concentration can intensify the convective heat transfer coefficient. However, they both increase the pressure drop of the system. The heat transfer coefficient, pressure drop was found to be enhanced by 35 % and 85 %, respectively at wt.% = 0.3. Interestingly, inlet temperature was found to only increase the heat transfer coefficient slightly (up to 9.8 % at wt.% = 0.3) and had no influence on the values of pressure drop. The presence of MgO nanoparticles was found to increase the thermo-hydraulic performance index of the heat exchanger by 34 %. [ABSTRACT FROM AUTHOR]

For the last few decades there has been very remarkable growth in electronics and computing technologies and it is still continuing unceasingly. The performance of various engineering devices is limited by thermal management problems. The present investigation deals with heat transfer augmentation through pin fins in gamma of an air-filled rectangular cavity as function of corresponding pertinent factors- fin height, fin spacing as well as Rayleigh number and suggests a direction of future advancements. The experiments are carried out for wide domains of numerous persuading parameters- fin height (12.5 mm ≤ L ≤ 37.5 mm), fin spacing (25 mm ≤ S ≤ 100 mm) and Rayleigh number (360000 ≤ Ra ≤ 680000). Fin spacing is determined as most critical parameter affecting system performance. [ABSTRACT FROM AUTHOR]

In the authors’ previous work, an embossed plate heat exchanger was proposed to the adsorption bed and results showed that the plate heat exchanger adsorption chiller had a lower Coefficient of performance (COP) but higher Specific cooling power (SCP) than those of a fin-tube type adsorption chiller, which shows high potential to resolve one of the most serious disadvantages of the adsorption cooling system, i.e., system size. However, only one section of the repeating embossed pitch plate was used and a uniform inlet flow condition was applied, which might have caused a distortion in estimated performance. We have reassessed the embossed plate heat exchanger adsorption bed by including the end effect to examine the real benefit of the proposed heat exchanger. The result showed that SCP was not significantly changed, while a 66.4 % increase in COP was observed. The proposed embossed plate heat exchanger adsorption bed is expected to provide advantages in both COP and SCP compared to a fin-tube type adsorption bed. [ABSTRACT FROM AUTHOR]

A numerical study on the heat exchanger design process has been conducted in order to propose a more effective method for the preliminary design of highly efficient and compact heat exchanger. The ε-NTU based performance prediction program and the heat exchanger database having performance correlations of various fin-type heat exchanger were developed. Numerical characteristics of the genetic, pattern search, and simulated annealing algorithms for the heat exchanger sizing were compared in terms of the accuracy and the computational speed. The effect of margins in design requirements were examined through the size ranking and the response surface analysis. The usefulness of the entropy generation minimization was appraised by comparing to the case when the objective function was the volume of the heat exchanger. [ABSTRACT FROM AUTHOR]

This research presents a drift flux model to simulate steady state refrigerant flow through horizontal lateral straight capillary tube-suction line heat exchangers with refrigerant R134a as a working fluid. The geometry of capillary tube is divided into two regions: An entrance length and lateral heat exchanger length. Metastable flow phenomenon is neglected in this work. To better study of fluid behavior in non-adiabatic capillary tube, according to the refrigerant state at the entrance of heat exchanger region, three modes were studied and the fundamental equations were solved for all three modes, then the results were analyzed. The present data using a drift flux model were validated with previous numerical work with a homogeneous model with obtaining reasonable agreement. By considering the slip ratio effects in drift flux model, therefore, this model could able to predict refrigerant flow behavior more accurately than other two-phase flow models in non-adiabatic flow condition through capillary tube. [ABSTRACT FROM AUTHOR]

This study is purposed to estimate the pressure drop and thermal performance of three-dimensional heat exchanger units by the porous approximation, considering inertia effects. The full three-dimensional (3D) estimation of the thermal performance of the heat exchanger is very difficult because of the great complexity of the louvered-fin shape and lack of numerical resources. The volume grid used for this study was less than 10 million computational units. In order to verify the interpretation results, a compact heat exchanger having 9500 louver fins and 3D header tanks was tested experimentally and numerically. The simulation results for the air-side pressure drop agree well with the experimental result within 10 %, while the thermal effectiveness of the air was within 9.5 % of the experimental results. The present numerical method can be an effective tool to estimate the performance of multi-louver finned heat exchangers by using limited numerical resources. [ABSTRACT FROM AUTHOR]

An experimental study on heat transfer and pressure drop characteristics was performed at single phase flow in two Brazed plate heat exchangers (BPHEs) with different geometries. The corrugation density of one of the BPHE (Type II) was two times as high as that of the other BPHE (Type I). The hydraulic diameter of the type II BPHE was 2.13 mm, which was 38 % smaller than that of the type I BPHE. Also, the cross section shape of the flow channels for the type II BPHE was different from that for conventional BPHEs due to the unusual corrugation patterns and brazing points. The experimental conditions for temperatures were varied from 4.6 °C to 49.1 °C, and for mass flow rates were changed from 0.07 kg/s to 1.24 kg/s. The measured results showed that pressure drop in the type II BPHE was about 110 % higher than that in the type I BPHE. Nu of the type II was higher than that of the type I BPHE and the enhancement became larger with the increase of Re at the ranges above 800. New correlations for f and Nu were proposed by this study and their prediction accuracy could be improved by considering the surface enlargement factor in the correlations. The performance evaluation of the two BPHEs was performed by ( j/ f ) which represented the ratio of heat transfer and pressure drop performance. Also, a new parameter, the capacity compactness of PHE, was proposed and it presented the PHE capacity per unit volume and unit log mean temperature difference. The comparison showed that the two BPHEs had similar values of the ( j/ f ), whereas they had significantly different values of the capacity compactness. The capacity compactness of the type II BPHE was 1.5 times higher than that for the type I BPHE. [ABSTRACT FROM AUTHOR]

Dynamic performance simulation of a CFB boiler in a commercial-scale power plant is reported. The boiler system was modeled by a finite number of heat exchanger units, which are sub-grouped into the gas-solid circulation loop, the water-steam circulation loop, and the inter-connected heat exchangers blocks of the boiler. This dynamic model is an extension from the previously reported performance simulation model, which was designed to simulate static performance of the same power plant, where heat and mass for each of the heat exchanger units were balanced for the inter-connected heat exchanger network among the fuel combustion system and the water-steam system. Dynamic performance simulation was achieved by calculating the incremental difference from the previous time step, and progressing for the next time step. Additional discretization of the heat exchanger blocks was necessary to accommodate the dynamic response of the water evaporation and natural circulation as well as the transient response of the metal temperature of the heat exchanger elements. Presentation of the simulation modeling is organized into two parts; system configuration of the model plant and the general approach of the simulation are presented along with the transient behavior of the sub-models in Part I. Dynamic sub-models were integrated in terms of the mass flow and the heat transfer for simulating the CFB boiler system. Dynamic simulation for the open loop response was performed to check the integrated system of the water-steam loop and the solid-gas loop of the total boiler system. Simulation of the total boiler system which includes the closed-loop control system blocks is presented in the following Part II. [ABSTRACT FROM AUTHOR]

Hybrid friction diffusion bonding (HFDB) is a solid-state bonding process first introduced by Helmholtz-Zentrum Geesthacht to join aluminum tube-to-tube sheet joints of Coil-wound heat exchangers (CWHE). This study describes how HFDB was successfully used to manufacture 316L test samples simulating tube-to-tube sheet joints of stainless steel CWHE for molten salt coolants as foreseen in several advanced nuclear- and thermal solar power plants. Engineering parameters of the test sample fabrication are presented and results from subsequent non-destructive vacuum decay leak testing and destructive tensile pull-out testing are discussed. The bonded areas of successfully fabricated samples as characterized by tube rupture during pull-out tensile testing, were further investigated using optical microscopy and scanning electron microscopy including electron backscatter diffraction. [ABSTRACT FROM AUTHOR]

This research represents an experimental investigation of the metastable flow and re-condensation phenomenon through non-adiabatic lateral helical capillary tubes and suction tube heat exchanger. The results show that mass flux ratio has a vital role: It affects metastable flow and also reverse heat transfer phenomenon through non-adiabatic helical capillary tube. Therefore, by increasing of the mass flux ratio, the rate of heat transfer between them decreases. In contrast to the strong rate condition of heat transfer between them, reverse heat transfer or re-condensation maybe happen. Moreover, experimental results show that for R134 flow with mass flux ratio more than 57.84, metastable flow exists in non-adiabatic capillary tube with 0.9144 mm inner diameter, 30 mm coil diameter, 6.18 m length, 4 mm inner diameter of compressor suction tube. [ABSTRACT FROM AUTHOR]

Today the helical coil heat exchanger is being employed widely due to its dominant advantages. In this study, a mathematical model was established to predict off-design works of the helical heat exchanger. The model was based on the LMTD and e-NTU methods, where a LMTD correction factor was taken into account to increase accuracy. An experimental apparatus was set-up to validate the model. Results showed that errors of thermal duty, outlet hot fluid temperature, outlet cold fluid temperature, shell-side pressure drop, and tube-side pressure drop were respectively ±5%, ±1%, ±1%, ±5% and ±2%. Diagrams of dimensionless operating parameters and a regression function were also presented as design-maps, a fast calculator for usage in design and operation of the exchanger. The study is expected to be a good tool to estimate off-design conditions of the single-phase helical heat exchangers. [ABSTRACT FROM AUTHOR]

Brazed plate heat exchangers (BPHEX) are broadly used in water source heat pump systems for their large heat transfer capacity. Despite their high heat transfer rate, their high-performance rate tends to decrease sharply, due to fouling and they cannot be cleaned. So the thermal and fouling resistances of washable Shell and helically coiled tube heat exchangers (SCHEX) are designed and experimentally investigated in this study. Heat exchangers with two different tube types are studied and compared with a brazed plate heat exchanger. The overall thermal resistance coefficient of the heat exchangers as determined by using Wilson plots is 38% lower than that of the brazed plate heat exchanger at a Reynolds number of 2460. Fouling test results revealed that regular maintenance and physical cleaning can be used to maintain the thermal resistance of fouling of the washable heat exchanger at a level equal to or less than that of the brazed plate heat exchanger. [ABSTRACT FROM AUTHOR]