Abstract: This paper explores the criterion on the similarity of heat transfer of supercritical fluid flow in vertical pipes at different diameters by performing comparative experiments. The diameter of the pipe is chosen at 4.4 or 9.0 mm with a heated length of 2 m. The mass flux and wall heat flux are at (400 kg/m 2 s, 30 kW/m 2 ), (400 kg/m 2 s, 50 kW/m 2 ) (1200 kg/m 2 s, 50 kW/m 2 ) with a pressure at 8.12 MPa. By measuring the inlet fluid temperature and wall temperatures, heat transfer coefficients are obtained at various inlet fluid conditions. Analytical criterion for the similarity of the heat transfer behavior is proposed and the validity of the analytical criterion is examined by comparing it with the experimental observations. It is shown that by having same length to diameter ratio and wall heat flux to mass flux ratio a similarity of heat transfer behavior was maintained both in the normal heat transfer mode and deteriorated heat transfer mode. It is also noted that the flow at bigger diameter is more susceptible to the reduction in the heat transfer due to buoyancy.

Abstract: A new model for simulating air-to-refrigerant heat exchangers, which accounts for conduction along the fins (tube-to-tube), is introduced. This model is based on a segment-by-segment approach and is developed to be general purpose and flexible simulation tool. To account for fin conduction, the heat exchanger is spatially modeled on a Cartesian grid. A set of equations that conserve energy over a segment of a heat exchanger is introduced. A sub-dividable segment model is introduced that accounts for changing flow regimes, and associated wall temperatures, within a tube segment. The model prediction is validated against experimental data obtained from experiments and the literature. The predicted results agree within ±3% of overall heat load and all tube-bend temperatures agree within ±3.9 °C of measured temperatures for the first set of experiments. For the second set of experiments, all predicted tube-bend temperatures agree within ±8.5 °C and overall heat load agrees within ±5%.

Abstract: Monitoring method and system are provided for dynamically determining flow rate of a first fluid and a second fluid through a heat exchanger. The method includes: pre-characterizing the heat exchanger to generate pre-characterized correlation data correlating effectiveness of the heat exchanger to various flow rates of the first and second fluids through the heat exchanger; sensing inlet and outlet temperatures of the first and second fluids through the heat exchanger, when operational; automatically determining flow rates of the first and second fluids through the heat exchanger using the sensed inlet and outlet temperatures of the first and second fluids and the pre-characterized correlation data; and outputting the determined flow rates of the first and second fluids. The automatically determining employs the determined effectiveness of the heat exchanger in interpolating from the pre-characterized correlation data the flow rates of the first and second fluids.

Abstract: Single-effect absorption cycles with and without refrigerant circulation are analytically modelled. Using heat exchanger effectiveness and the Duhring equation, the governing equations of the absorption cycles are reduced to cubic and quadratic equations, whose solution allows quick analytic simulation of absorption systems with minimal information on working fluids. The models are valid for chillers, heat pumps and heat transformers and are useful for evaluation of working fluids and quick simulation of absorption cycles.

Abstract: A prototype liquid-to-refrigerant heat exchanger was developed with the aim of minimizing the refrigerant charge in small systems. To allow correct calculation of the refrigerant side heat transfer ...

Abstract: This study involved the determination of convective heat transfer coefficient in both helical and straight tubular heat exchangers under turbulent flow conditions. The experiments were conducted in helical heat exchangers, with coils of two different curvature ratios (d/D = 0.114 and 0.078), and in straight tubular heat exchangers at various flow rates (1.89 x 10−4 6.31 x 10−4 m/s) and for different end-point temperatures (92 149 ◦C). The results show that the overall heat transfer coefficient (U) in the helical heat exchanger is much higher than that in straight tubular heat exchangers. In addition, U was found to be larger in the coil of larger curvature ratio (d/D = 0.114) than in the coil of smaller curvature ratio (d/D = 0.078). The inside (hi) and outside (ho) convective heat transfer coefficients were determined based on the overall heat transfer coefficient and a correlation to compute the inside convective heat transfer coefficient (hi) as a function of NRe, NPr, and d/D was developed.

Abstract: A parametric study of a solid oxide fuel cell-gas turbine (SOFC-GT) hybrid system design is conducted with the intention of determining the thermodynamically based design space constrained by modern material and operating limits. The analysis is performed using a thermodynamic model of a generalized SOFC-GT system where the sizing of all components, except the fuel cell, is allowed to vary. Effects of parameters such as pressure ratio, fuel utilization, oxygen utilization, and current density are examined. Operational limits are discussed in terms of maximum combustor exit temperature, maximum heat exchanger effectiveness, limiting current density, maximum hydrogen utilization, and fuel cell temperature rise. It was found that the maximum hydrogen utilization and combustor exit temperature were the most significant constraints on the system design space. The design space includes the use of cathode flow recycling and air preheating via a recuperator (heat exchanger). The effect on system efficiency of exhaust gas recirculation using an ejector versus using a blower is discussed, while both are compared with the base case of using a heat exchanger only. It was found that use of an ejector for exhaust gas recirculation caused the highest efficiency loss, and the base case was found to exhibit the highest overall system efficiency. The use of a cathode recycle blower allowed the largest downsizing of the heat exchanger, although avoiding cathode recycling altogether achieved the highest efficiency. Efficiencies in the range of 50-75% were found for variations in pressure ratio, fuel utilization, oxygen utilization, and current density. The best performing systems that fell within all design constraints were those that used a heat exchanger only to preheat air, moderate pressure ratios, low oxygen utilizations, and high fuel utilizations. Copyright © 2010 by ASME.

Abstract: Computation of overall heat transfer coefficients in a triple tube heat exchanger (TTHE) is more complicated than in the case of a double tube heat exchanger (DTHE) as the two overall heat transfer coefficients are not independent of one other. A new procedure was developed to calculate these overall heat transfer coefficients and an effective overall heat transfer coefficient value for known inlet and outlet temperatures, and heat capacities of the fluids (product and heating/cooling medium). In this study, this newly developed procedure was utilized and the overall heat transfer coefficients and axial temperature distribution of fluids were computed for a cooling process for different flow rates and inlet temperatures of the fluid streams. The effectiveness of the TTHE was compared to that of a DTHE of identical length. It was observed that when the fluids were flowing in a cocurrent manner, the temperature of the cooling medium with lower heat capacity exceeded the temperature of the product before the fluids exit the TTHE, which caused a decrease in the effectiveness of the TTHE.

Abstract: The exact analytical correlations to calculate radiation heat transfer rate from a diffuse and gray plate-fin heat sink are presented. These correlations involve a view factor that can be exactly calculated using a rather complex set of equations. A very simple approximate correlation for this view factor is proposed that results in radiation heat transfer rates that are accurate with a maximum error of about 11%.

Abstract: This paper focuses on the heat transfer analysis of compact heat exchangers through artificial neural network (ANN). The ANN analysis includes heat transfer coefficient, pressure drop and Nusselt number in the compact heat exchangers by using available experimental results in a case study. In this study, data sets are established in 15 different test channel configurations. A feed-forward back-propagation algorithm is used in the learning process and testing the network. The learning process is applied to correlate the heat transfer analysis for different ratios of rib spacing and height, various Reynolds numbers, different inlet–outlet temperatures, heat transfer areas and hydraulic diameters. Various hidden numbers of the network are trained for the best prediction of the heat transfer analysis. Heat transfer coefficient, pressure drop and Nusselt number values are predicted by the network algorithm. The results are then compared with the experimental results of the case. The trained ANN results perform well in predicting the heat transfer coefficient, pressure drop and Nusselt number with an average absolute mean relative error of less than 6% compared with the experimental results for staggered cylindrical ribbed and staggered triangular ribbed of test channels in the case study. The ANN approach is found to be a suitable method for heat transfer analysis in compact heat exchangers. Copyright © 2007 John Wiley & Sons, Ltd.

Abstract: The membrane-based total heat exchanger is a device to recover both sensible heat and moisture from the exhaust air stream from a building. Heat and mass transfer intensification has been undertaken simultaneously in two directions: air-side augmentation with cross-corrugated triangular ducts and material-side augmentation with a novel composite-supported liquid membrane (CSLM). Performance of heat and mass transfer intensification has been investigated numerically. As a first step, the convective heat and mass transfer coefficients in the flow passages are calculated. Then, the heat and moisture diffusion resistance through the CSLM itself is estimated. Finally, the sensible and moisture-recovery effectiveness are obtained with effectiveness-NTU (number of transfer units) methodology. It is found that the new concept of cross-corrugated triangular ducts with CSLM has a 14% higher sensible effectiveness and a 46% higher latent effectiveness in comparison with a traditional total heat exchanger of parallel...

Abstract: Experimental research was conducted to understand heat transfer characteristic of pulsating heat pipe in this paper, and the PHP is made of high quality glass capillary tube. Under different fill ratio, heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage. The effects of heating position on heat transfer were discussed. The experimental results indicate that no annular flow appears in top heating condition. Under different fill ratios and heat transfer rate, the flow pattern in PHP is transferred from bulk flow to semi-annular flow and annular flow, and the performance of heat transfer is improved for down heating case. The experimental results indicate that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%. But for pulsating heat pipe with changing diameters the thermal resistance is higher than that with uniform diameters.

Abstract: Detection of one or more abnormal situations is performed using various statistical measures, such as a mean, a median, a standard deviation, etc. of one or more process parameters or variable measurements made by statistical process monitoring blocks within a plant. This detection may include determination of the health and performance of one or more heat exchangers in the plant, and in particular, detection of a fouling condition of the one or more heat exchangers. Among the statistical measures, the detection may include calculation of an overall thermal resistance of the heat exchanger, which may be indicative under certain circumstances of heat exchanger performance and in particularly degradation of heat exchanger performance as a result of heat exchanger fouling.

Abstract: The results of heat transfer to supercritical water flowing upward in a vertical tight 7-rod bundle consisting of tubes of 5.2-mm outside diameter and 485-mm heated length are presented. The heat-transfer data were obtained at pressures of 22.5, 24.5, and 27.5 MPa, mass flux within the range from 700 to 1500 kg/m2 s, inlet temperature from 125 to 325°C, outlet temperature up to 379°C and heat flux up to 1.6 MW/m2 (heat flux rate up to 1.5 kJ/kg). Temperature regimes of the bundle cooled by supercritical water were stable and easily reproducible within the whole range of the mass and heat fluxes, even when a deteriorated heat transfer took place. The data resulted from the study could be applicable for a reference estimation of heat transfer in future designs of the fuel bundles.Copyright © 2008 by ASME

Abstract: In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent heat transfer rate at the electronic-packaging/heat-sink-assembly interface from the knowledge of temperature measurements taken within the packaging. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors in these measurements upon the precision of the estimated results is also considered. Results show that an excellent estimation on the time-dependent heat transfer rate can be obtained for the test case considered here.