Correlations In Open Literature Research Articles

An experimental study of falling film evaporation in vertical channels with perforated fins of a plate-fin heat exchanger

In this paper, the heat transfer characteristics of falling film evaporation of pure refrigerant HCFC123 were experimentally investigated in a pilot scale plate-fin heat exchanger with perforated fins. The experiments have been carried out under the conditions that the mass flux is in the range of 23 to 49 kg/m2s, the corresponding inlet Reynolds number from 200 to 500, the heat flux from 3.2 to 9.5 kW/m2, and the evaporation pressure about 0.3 MPa. The variation laws of the local heat transfer coefficient versus the main parameters, including the inlet Reynolds number, heat flux and vapor quality were discussed. By introducing the two-phase convective multiplier F as a function of Lockhart-Martinelli parameter, a correlation for the two-phase forced convective component of the local boiling heat transfer coefficient was developed, and compared with correlations in open literature. By using a superposition method, the local boiling heat transfer coefficient that includes the contributions of forced convective boiling and nucleate boiling was analyzed. The predictions of local heat transfer coefficients were found to be in good agreement with experimental data.

Effect of Temperature Ratio on Jet Impingement Heat Transfer in Active Clearance Control Systems

Impinging jet arrays are typically used to cool several gas turbine parts. Some examples of such applications can be found in the internal cooling of high-pressure turbine airfoils or in the turbine blade tip clearances control of aero-engines. The effect of the wall-to-jets temperature ratio (TR) on heat transfer is generally neglected by the correlations available in the open literature. In the present contribution, the impact of the temperature ratio on the heat transfer for a real engine active clearance control system is analyzed by means of validated computational fluid dynamics (CFD) computations. At different jets Reynolds number and considering several impingement array arrangements, a wide range of target wall-to-jets temperature ratio is accounted for. Computational results prove that both local and averaged Nusselt numbers reduce with increasing. An in-depth analysis of the numerical data shows that the last mentioned evidence is motivated by both the heat transfer incurring between the spent coolant flow and the fresh jets and the variation of gas properties with temperature through the boundary layer. A scaling procedure, based on the TR power law, was proposed to estimate the Nusselt number at different wall temperature levels necessary to correct available open-literature correlations, typically developed with small temperature differences, for real engine applications.

Experimental Study on Heat and Mass Transfer in Ammonia Evaporative Condensers

This paper reports theoretical and experimental results on ammonia heat and mass transfer coefficient in evaporative condensers. The theoretical study, based on the review performed by the authors, uses currently available correlations in open literature and presents modeling results.The experimental study was carried out on specially designed set-ups that allowed both measuring and acquisition of data and aimed to determine: mass transfer coefficient at water/air interface; heat transfer coefficient at tube wall/water interface; heat transfer coefficient at condensing refrigerant/tube wall interface. Experimental and theoretical values were further compared, in order to validate the correlations used, under specific geometrical configuration of the evaporative condenser under study and specific operating conditions. The paper concluded that all correlations used describe, more or less accurately, the heat and mass transfer process in ammonia evaporative condensers and performs a comparative analysis of the results, based on deviation shown with respect to experimental values.The paper also addresses the current ecological aspect implied by refrigerants, by choosing ammonia, a natural, environmentally friendly refrigerant, known for its zero ozone depleting potential and zero global warming effect.

Effect of Target Wall Curvature on Heat Transfer and Pressure Loss From Jet Array Impingement

Experiments to investigate the effect of target wall curvature on heat transfer and pressure loss from jet array impingement are performed. A jet plate configuration is studied with constant hole diameters and spacings. The geometry of the jet plate has streamwise jet spacings of 5.79 jet diameters, spanwise jet spacings of 4.49 jet diameters, and a jet-to-target plate distance of 3 jet diameters. For the curved case, the radius of the target plate is r/D = 31.57. A flat target wall setup with identical geometric spacing is also tested for direct comparison. Jet spacings were chosen such that validation and comparison can be made with open literature. For all configurations, spent air is drawn out in a single direction, which is tangential to the target plate curvature. Average jet Reynolds numbers ranging from 55,000 to 125,000 are tested. A steady-state measurement technique utilizing temperature-sensitive paint (TSP) is used on the target surface to obtain Nusselt number distributions. Pressure taps placed on the sidewall of the channel are used to evaluate the flow distribution in the impingement channel. Alongside the experimental work, CFD was performed utilizing the v2 − f turbulence model to better understand the relationship between the flow field and the heat transfer on the target surface. The main target of the current study is to quantify the impact of target wall radius and the decay of heat transfer after the impingement section, and to check the open literature correlations. It was found that the target wall curvature did not cause any significant changes in either the flow distribution or the heat transfer level. Comparisons with established correlations show similar level but different trends in heat transfer, potentially caused by differences in L/D. CFD results were able to show agreement in streamwise pitch-averaged Nusselt number levels with experimental results for the curved target plate at higher Re numbers.

Heat transfer coefficient for condensation of steam on freely formed falling liquid jets

This article presents the research results of direct contact condensation of steam on freely formed falling liquid jets. After the comparison of experimental data and open literature correlations it was concluded that published correlations does not provide accurate coverage of experimental data. A new correlation was established in the following form urn:x-wiley:00011541:media:aic15233:aic15233-math-0001 © 2016 American Institute of Chemical Engineers AIChE J, 62: 2579–2584, 2016

Thermally Developing Single-Phase Flows in Microtubes

The pressure drop and heat transfer due to the flow of de-ionized water at high mass fluxes in microtubes of ∼ 254 μm and ∼ 685 μm inner diameters is investigated in the laminar, transition and the turbulent flow regimes. The flow is hydrodynamically fully developed and thermally developing. The experimental friction factors and heat transfer coefficients are respectively predicted to within ±20% and ±30% by existing open literature correlations. Higher single phase heat transfer coefficients were obtained with increasing mass fluxes, which is motivating to operate at high mass fluxes and under thermally developing flow conditions. The transition to turbulent flow and friction factors for both laminar and turbulent conditions were found to be in agreement with existing theory. A reasonable agreement was present between experimental results and theoretical predictions recommended for convective heat transfer in thermally developing flows.

Experimental and Numerical Investigation of the Gas Side Heat Transfer and Pressure Drop of Finned Tubes—Part I: Experimental Analysis

In this study, a heat transfer and pressure drop correlation are determined for helically I- and U-shaped finned tubes as well as for solid I-finned tubes at constant transverse and longitudinal spacing. In the heat transfer correlation, the influence of the number of tube rows arranged in flow direction is taken into consideration. A detailed description of the test rig and the data reduction procedure is presented. A thorough uncertainty analysis was performed to validate the results. The investigation has shown that the influence of the fin geometry on the heat transfer of the helically segmented I- and U-shaped tubes can be disregarded. The heat transfer correlation, which is valid for the helically segmented I- and U-shaped tubes in a staggered arrangement, can describe 90% of all measurement data within ±15%. All measurements are performed for constant transverse and longitudinal spacing. For the pressure drop coefficient, two new correlations, which are only valid for helically segmented U shaped finned tubes in a staggered arrangement, show an average deviation of approximately ±13% for 90% of all measurement results. All new correlations are compared with correlations from open and established literature for industrial boiler applications. The new heat transfer and pressure drop correlations show a relative deviation of ±20% in comparison with correlations in open literature. The new pressure drop correlations show the same characteristic as most correlations in the open literature.

Thermal Stability and Safe Venting of the Tri-N-Butyl Phosphate-Nitric Acid-Water (“Red Oil”) System - I: Two-Layer System Mass Transfer Theory

Accurate prediction of the bubble-enhanced mass transport rate of dissolved water from a layer of aqueous nitric acid (“aqueous phase”) to an overlying, reactive layer of tri-n-butyl phosphate and nitric acid (“organic phase”) is crucial to assessing the conditions for a runaway reaction in the organic phase. This paper presents a rational, predictive model of the concentration profile history of a dissolved species in a vertical column comprising an organic phase overlying an aqueous phase. The model incorporates both interfacial and axial dispersion limitations to species transport. Open-literature correlations on enhanced heat transfer in bubbling pools, after conversion to mass transfer correlations, provide the model’s needed interfacial resistance coefficients. The model shows that in laboratory-scale systems interfacial limitations to dissolved species mass transport are controlling while in full-scale columns mass transport is axial dispersion controlled. The model is capable of rationalizing available measurements of dissolved species mass transfer between the organic and aqueous phases. A previous interpretation of the measurements is shown to be incorrect.