Additive manufacturing (AM) enables improved heat exchanger (HX) designs where performance is based on the achievable geometry. However, consequences of the AM process that affect HX performance such as increased surface roughness, dimensional tolerance issues, and defects like cracks may vary among identically designed AM parts due to AM machine settings. This paper experimentally compares the thermal and hydraulic performance of three AM HXs built using a traditionally manufactured, stamped aluminum oil cooler design. The AM HXs exhibited significantly higher air-side pressure drop and higher heat transfer rate than the traditional HX in large part due to increased AM surface roughness. Among AM HXs, one AM HX had notably higher heat transfer rate and air-side pressure drop due to poor print quality on the thin air-side fin features. The fin thickness among AM HXs also varied by about 15%, and there were only slight differences in surface roughness. This study indicates that functional HXs built using AM vary in performance even when the same digital model is used to print them and that AM HXs as a group can perform considerably differently than their traditional counterparts.

The heat transfer and fluid flow performance of a hybrid jet plus multipass microchannel heat sink in two-phase operation is evaluated for the cooling of a single large area, 3.61 cm 2 , heat source. The two-layer branching microchannel heat sink is evaluated using HFE-7100 as the coolant at three inlet volumetric flow rates of 150, 300, and 450 ml/min. The boiling performance is highest for the flow rate of 450 ml/min with the maximum heat flux value of 174 W/cm 2 . Critical heat flux (CHF) was observed at two of the tested flow rates, 150 and 300 ml/min, before reaching the maximum operating temperature for the serpentine heater. At 450 ml/min, the heater reached the maximum allowable temperature prior to observing CHF. The maximum pressure drop for the heat sink is 34.1 kPa at a heat flux of 164 W/cm 2 . Further, the peak heat transfer coefficient value of the heat sink is 28,700 W/m 2 K at a heat flux value of 174 W/cm 2 and a flow rate of 450 ml/min. Finally, a validated correlation of the single device cooler is presented that predicts heat transfer performance and can be utilized in the design of multidevice coolers.

Presented in this paper is an experimental investigation of the steady-state air-side pressure drop through a delugable bare tube bundle. The tube bundle forms a part of a systematic investigation of the subcomponents of a hybrid dry/wet dephlegmator (HDWD), also known as a secondary steam condenser, used in direct dry-cooling. A modular bare tube bundle is designed and built to experimentally investigate the pressure drop in a counter-flow test facility with 19 mm and 25 mm tubes at various tube depths. The tests are conducted under both dry and wet (deluged) operating modes. The test results are used to develop empirical correlations for both dry and wet operating modes. The absolute average error is found to be 3.2% between the measured and predicted values for the dry correlation and for the wet correlation the absolute average error is found to be 4.5%. The newly developed correlation is used in a thermal case study to illustrate the effect of the under- and overprediction that the air-side pressure drop will have on a relatively small evaporative cooler where two cases corresponding to fan power consumptions of 1.1 kW and 5.5 kW were considered.

The pilot diesel quantity (m pilot ) has an impact on the liqueified nitrogen gas (LNG)-diesel dual-fuel engine, but it is very difficult for a dual-fuel engine with the traditional injection system to adjust m pilot to meet various operating conditions in practice. In recent years, with great progress in common rail diesel injection technology, m pilot can be adjusted accurately by the electronic control system, which is an advantage for operation with the diesel–LNG dual-fuel. In order to optimize m pilot of the diesel–LNG dual-fuel engine, the combustion and performance of a dual-fuel engine with the m pilot of 5.05 mg/cyc, 5.20 mg/cyc, 5.69 mg/cyc, 6.31 mg/cyc and 6.91 mg/cyc under 50% load at speed of 1600 r/min were analyzed. Experimental results show that, with an increase in m pilot , the maximum in-cylinder pressure, rate of pressure rise, and heat release rate of dual-fuel obviously increase, the crank angles of the maximum value move forward, and the combustion duration becomes shorter. The mean value of peak in-cylinder pressure (p max ) increases obviously while the standard deviation of it decreases, and the distribution of that focuses. The mean value of the crank angle corresponding to p max pressure decreases except for the m pilot of 5.05 mg/cyc, while the standard deviation of that gradually decreases, the distribution of it focuses and moves forward. The brake power increases while the brake-specific fuel consumption (BSFC) decreases, the CO and HC decrease, while the CO 2 , NO x, and smoke density emissions increase.

The present paper reports numerical results of the melting driven natural convection in an inclined rectangular enclosure filled with nano-enhanced phase change material (NePCM). The enclosure is heated from the bottom side by a flush-mounted heat source (microprocessor) that generates heat at a constant and uniform volumetric rate and mounted on a substrate (motherboard). All the walls are considered adiabatic. The purpose of the investigation is analyzing the effect of nanoparticles insertion by quantifying their contribution to the overall heat transfer. Combined effects of the PCM type, the inclination angle and the nanoparticles fraction on the structure of the fluid flow and heat transfer are investigated. A 2D mathematical model based on the conservation equations of mass, momentum, and energy was developed. The governing equations were integrated and discretized using the finite volume method. The SIMPLE algorithm was adopted for velocity–pressure coupling. The obtained results show that the nanoparticles insertion has an important quantitative effect on the overall heat transfer. The insertion of metallic nanoparticles with different concentrations affects the thermal behavior of the heat sink. They contribute to an efficient cooling of the heat source. The effect of nanoparticles insertion is also shown at the temperature distribution along the substrate.

In this paper, the radiating effect of working gas on thermal performance of plane solar heaters is investigated. In the numerical simulation of gas flow, the continuity and momentum equations are solved using the finite volume method (FVM) in which the pressure-velocity coupling is handled by the SIMPLE algorithm. To obtain the temperature distribution, the conservation of energy in the fluid and solid media is solved by the finite difference technique. The distribution of radiating intensity which is needed to calculate the raditive term in the gas energy equation is computed by numerical solution of the radiative transfer equation (RTE) using the discrete ordinate method (DOM). The effect of the variation of different parameters on the predicted thermal efficiency of plane solar heater is investigated by presenting the performance plot. The obtained results show that when the gas medium participates in radiation, the gas temperature at the outlet section increases considerably, especially at high optical thicknesses. Also, the temperature difference between the absorber plate and flowing gas decreases, and more uniform temperature distribution takes place inside the solar heater, which leads to a considerable increase of thermal efficiency. Comparison between the present numerical results and the experimental data published in literature shows good agreement.

The ultra compact combustor (UCC) aims to increase the thrust-to-weight ratio of an aircraft gas turbine engine by decreasing the size, and thus weight, of the engine’s combustor. The configuration of the UCC as a primary combustor enables a unique cooling scheme to be employed for the hybrid guide vane (HGV). A previous effort conducted a computational fluid dynamics (CFD) analysis that evaluated whether it would be possible to cool this vane by drawing in freestream flow at the stagnation region of the airfoil. Based on this study, a cooling scheme was designed and modified with internal supports to make additive manufacturing of the vanes possible. This vane was computationally evaluated comparing the results with those of a solid vane and hollow vane without cooling holes as a demonstration of the improvements offered by this design. Furthermore, the effects of the internal support structure were deemed beneficial to surface cooling when evaluated through comparisons of internal pressure distribution and overall effectiveness. Following the computational study, the vane was manufactured and experimentally evaluated with the results compared to those of an uncooled solid vane. The experimental results validated the computational analysis and demonstrated through pressure and temperature measurements that the cooled vane had a reduced surface temperature compared to the uncooled vane and that pressure distributions supported coolant flow through film-cooling holes.

Two-phase closed thermosyphon (TPCT) is a cost-effective heat transfer device with high thermal efficiency owing to extensive interphase heat and mass transfer. Thus, TPCT has found many industrial applications. Proper selection of the working fluid could further improve efficiency of TPCT, and nanofluids with superior thermal properties are suitable choices. Numerical simulation of boiling and condensation, natural circulation, and hybrid nanofluid modeling in a closed space is a notable challenge and current study is devoted to this subject. In this study, a novel methodology for incorporating the effects of compressibility and thermal expansion into all thermophysical properties of both phases is developed and programmed into a validated computational fluid dynamics (CFD) code. Distilled water, a regular nanofluid, Al 2 O 3 /water, and a hybrid nanofluid, TiSiO 4 /water are selected as the working fluids. Experimental data for wall thermal profile are employed to validate the numerical simulation. Then, overall thermal resistance is evaluated in terms of nanoparticles concentration and input power variations. Results indicate that the numerical methodology developed in this study could evaluate the optimum state of TPCT in an efficient and accurate manner and the optimum state for regular and hybrid nanofluid demonstrates 48% and 54% improvement over distilled water, respectively. Furthermore, a subtle relation between the thermal resistance and the height to which fluid column rises in TPCT has been discerned and quantified, which is used as a supplement to the conventional qualitative method of reasoning to justify the somewhat controversial behaviors of nanofluid application in TPCT.

To improve air pollution, we must reduce soot particulates in vehicle exhaust gas, which are inevitably harmful to the environment as well as to human health. Many countries are setting new regulations of nanoscale particle emission. Then, a ceramic porous filter such as diesel particulate filters (DPFs) has been developed. However, as more particles are trapped within their wall pores, the pressure difference (drop) across the filter increases. Resultantly, this situation could worsen the fuel efficiency, simultaneously with less torque. Usually, the filter regeneration process for particle oxidation inside the filter should be periodically needed. Thus, a filter with lower pressure drop would be preferable. In the current stage, the responses of the pressure drop during both particle filtration and oxidation are not fully understood. This is because these are the small-scale processes, and we cannot observe the internal physical phenomenon experimentally. In this paper, focusing on the exhaust flow with soot particles, the filtration was numerically simulated by a so-called lattice Boltzmann method (LBM). Here, the time-variation of the filter-back pressure was evaluated, which is important for the transport phenomena in the porous filter. For comparison, the pressure drop during the filter regeneration was also simulated to show the different pressure response affected by the soot oxidation zone.

Varying aspect ratio (AR) channels are found in modern gas turbine airfoils for internal cooling purposes. Corresponding experimental data are needed in understanding and assisting the design of advanced cooling systems. The present study features a two-pass rectangular channel with an AR = 4:1 in the first pass with the radial outward flow and an AR = 2:1 in the second pass with the radial inward flow after a 180 deg tip turn. Effects of rib coverage near the tip region are investigated using profiled 45 deg ribs (P/e = 10, e/D h ≈ 0.11, parallel and in-line) with three different configurations: less coverage, medium coverage, and full coverage. The Reynolds number (Re) ranges from 10,000 to 70,000 in the first passage. The highest rotation number achieved was Ro = 0.39 in the first passage and 0.16 in the second passage. Heat transfer coefficients on the internal surfaces were obtained by the regionally averaged copper plate method. The results showed that the rotation effects on both heat transfer and pressure loss coefficient are reduced with an increased rib coverage in the tip turn region. Different rib coverage upstream of the tip turn significantly changes the heat transfer in the turn portion. Heat transfer reduction (up to −27%) on the tip wall was seen at lower Ro. Dependence on the Reynolds number can be seen for this particular design. The combined geometric, rib coverage, and rotation effects should be taken into consideration in the internal cooling design.

Large eddy simulation (LES) of nonreacting turbulent flow in a multiswirler model combustor is carried out at elevated pressure and high temperature. Flow interaction between the main stage and the pilot stage is discussed based on the time-averaged and instantaneous flowfield. Flow dynamics in the multiswirling flow are analyzed using a phase-averaged method. Proper orthogonal decomposition (POD) is used to extract dominant flow features in the multiswirling flow. Numerical results show that the main stage and the pilot stage flows interact with each other generating a complex flowfield. Flow interaction can be divided into three regions: converging region, merging region, and combined region. A precessing vortex core (PVC) is successfully captured in the pilot stage. PVC rotates with a first dominant frequency of 2756 Hz inducing asymmetric azimuthal flow instabilities in the pilot stage. POD analyses for the velocity fields also show dominant high-frequency modes (mode 1 and mode 2) in the pilot stage. However, the dominant energetic flow is damped rapidly downstream of the pilot stage such that it has a little effect on the main stage flow.

Both analytical and computational methods for solidification problems are introduced. First, the inward solidification process in a spherical vessel is studied. Expressions of the stress, displacement in the solid phase, and the liquid pressure are deduced based on the solidification interface position. A phase-change expansion orientation factor is introduced to characterize the nonisotropic expansion behavior at the freezing interface. Then, an efficient coupled thermomechanical finite-element method is proposed to evaluate the thermal stress, strain, displacement, and pressure in solidification problems with highly nonlinear constitutive relations. Two particular methods for treating the liquid phase with fixed-grid approaches are introduced. The thermal stress is computed at each integration point by integrating the elastoviscoplastic constitutive equations. Then, the boundary value problem described by the global finite-element equations is solved using the full Newton–Raphson method. This procedure is implemented into the finite-element package abaqus via a FORTRAN subroutine UMAT. Detailed implementation steps and the solution procedures are presented. The numerical model is validated first by the analytical solutions and then by a series of benchmark tests. Finally, an example of solidification in an open reservoir with a free liquid surface is introduced. Potential industrial applications of the numerical model are presented.

A simultaneously developing microchannel gas flow is analyzed numerically, using the vorticity–stream function form of the Navier–Stokes equation, together with the fluid energy equation and the solid wall heat conduction equation. Rarefaction, shear work, viscous dissipation, pressure work, axial conduction, and conjugate effects on heat transfer characteristics are investigated. The shear work contribution to the wall heat flux is evaluated in both the developing and the fully developed flow regions and compared with the conductive wall heat flux. The assumption of hydrodynamically fully developed, thermally developing flow—normally used in the analysis of channel heat transfer—is assessed and compared with the simultaneously developing flow case. Analytical expressions for the fluid flow and heat transfer parameters under fully developed conditions are also derived and compared with the numerical results for verification. The analysis presented shows that the shear work and the combined viscous dissipation and pressure work result in extending the thermal entrance length by far. Heat conduction in the wall also contributes to increase the thermal entry length. The results presented also demonstrate the shear work contribution to heat transfer in the slip flow regime, although minor in the very first portion of the thermal entrance length, and it becomes progressively more significant as the flow thermal development conditions are approached and turns out to be exactly equal in magnitude to the conductive wall heat flux in the thermally fully developed region, resulting in a zero Nusselt number, as verified by both the exact and numerical solutions.

This study compares two numerical strategies for modeling flow and heat transfer through mini- and microchannel heatsinks, the unit cell approximation, and the full 3D model, with the objective of validating the former approach. Conjugate heat transfer and laminar flow through a 2 × 2 cm 2 copper–water heatsink are modeled using the finite element package COMSOL Multiphysics 5.0. Parametric studies showed that as the heatsink channels’ widths were reduced, and the total number of channels increased, temperature and pressure predictions from both models converged to similar values. Relative differences as low as 5.4% and 1.6% were attained at a channel width of 0.25 mm for maximum wall temperature and channel pressure drop, respectively. Due to its computational efficiency and tendency to conservatively overpredict temperatures relative to the full 3D method, the unit cell approximation is recommended for parametric design of heatsinks with channels’ widths smaller than 0.5 mm, although this condition only holds for the given heatsink design. The unit cell method is then used to design an optimal heatsink for server liquid cooling applications. The heatsink has been fabricated and tested experimentally, and its thermal performance is compared with numerical predictions. The unit cell method underestimated the maximum wall temperature relative to experimental results by 3.0–14.5% as the flowrate rose from 0.3 to 1.5 gal/min (1.1–5.7 l/min).

The heat transfer in a pin finned duct is augmented by the protrusion in this study. The realizable k–ε turbulence model coupled with the enhanced wall function is used to obtain the flow structure and heat transfer characteristics. Six different rotational numbers (Ro = 0, 0.2, 0.4, 0.6, 0.8, and 1.0) and three different protrusion locations have been introduced. The pin fins and protrusions are placed on a simplified three-dimensional rectangular duct. Numerical results reveal that the Nusselt number in the pin finned channel has remarkable increase after adoption of the protrusions. In addition, the protrusion location and the rotational number have significant influence on the heat transfer distribution. The high rotational number is in favor of heat transfer enhancement on the endwall surface. Furthermore, the highest Nusselt number is occurred where protrusion is near the pin fin windward side.

The lean combustion chamber of low NO x emission engines has a short distance between combustion outlet and nozzle guide vanes (NGVs), with strong swirlers located upstream of the turbine inlet to from steady circulation in the combustion region. Although the lean combustion design benefits emission control, it complicates the turbine’s aerodynamics and heat transfer. The strong swirling flow will influence the near-wall flow field where film cooling acts. This research investigates the influence of inlet swirl on the film cooling of cascades. The test cascades are a 1.95 scale model based on the GE-E 3 profile, with an inlet Mach number of 0.1 and Reynolds number of 1.48 × 10 5 . Film cooling effectiveness is measured with pressure-sensitive paint (PSP) technology, with nitrogen simulating coolant at a density ratio of near to 1.0. Two neighboring passages are investigated simultaneously, so that pressure and suction side the film cooling effectiveness can be compared. The inlet swirl is produced by a swirler placed upstream, near the inlet, with five positions along the pitchwise direction. These are as follows: blade 1 aligned, passage 1–2 aligned, blade 2 aligned, passage 2–3 aligned and blade 3 aligned. According to the experimental results, the near-hub region is strongly influenced by inlet swirl, where the averaged film cooling effectiveness can differ by up to 12% between the neighboring blades. At the spanwise location Z/Span = 0.7, when the inlet swirl is moved from blade 1 aligned (position 5) to blade 2 aligned (position 3), the film cooling effectiveness in a small area near the endwall can change by up to 100%.

The present research work is undertaken to develop ASHRAE like standard rating charts for currently used refrigerants R-134a and R-410A and their potential low global warming potential (GWP) substitutes R-1234yf and R-32, respectively. A self-adjustable mass prediction algorithm has been developed using an averaging technique. Based on this, a matlab code dynamically linked to refprop v. 9.0 software has been developed that solves governing equations of mass, momentum, and energy. Two-phase flow inside the capillary tube is assumed homogeneous and metastability is ignored in the proposed model. The proposed numerical models are in good agreement with the available experimental data with overall percentage mean deviation is less than 6%. Coil diameter plays an important role in adjusting the mass flow rate in the helical capillary tube. Coiling of capillary tube causes an increase in friction pressure drop and a reduction in refrigerant mass flow rate. It has been found that the mass flow rate reduces by about 5% as coil diameter is reduced from 120 to 20 mm.

The shell condenser is one of the key components of underwater vehicles. To study its thermal performance and to design a more efficient structure, a computational model is generated to simulate condensation inside straight and helical channels. The model combines empirical correlations and a MATLAB-based iterative algorithm. The vapor quality is used as a sign of the degree of condensation. Three calculation models are compared, and the optimal model is verified by a comparison of simulated results and available experimental data. Several cases are designed to reveal the effects of various inlet conditions and the diameter-over-radius (D h / R) ratio. The results show that the inlet temperature and mass rate significantly affect the flow and heat transfer in the condensation process, the heat transfer capabilities of the helical channels are much better than that of the straight channel, and both the heat transfer coefficient and total pressure drop increase with the decrease of D h / R . This study may provide a useful reference for performance prediction and structural design of shell condensers used for underwater vehicles and may provide a relatively universal prediction model for condensation in channels.

Three-dimensional numerical study of R134a flow boiling under overload was conducted based on the VOF model. A series of simulations were implemented with a 1.002 mm circular tube under six gravity levels ranging from 1 to 15 g and three directions ( θ ) ranging from 0° to 180° with mass fluxes of 200, 350, and 500 kg/m 2 s, outlet vapor qualities of 0.041, 0.082, and 0.164, and saturation pressure of 0.71MPa. The gravity conditions were introduced into the momentum equation during the simulations. Comparisons among flow boiling characteristics under different gravity levels and directions are made, and significant effects of overload are found. With the increasing overload, the vapor phase distributions of flow boiling gradually turn into forms similar to ellipsoids/spheres, stratified flow, and elongated slugs, at θ = 0°, 90°, and 180°, respectively. Accordingly, the heat transfer coefficient keeps almost stable at θ = 0° and 180°, but decreases obviously at θ = 90°; the frictional pressure drop decreases at θ = 0°, decreases slightly at θ = 90°, but increases at θ = 180°. Making θ away from 90° is a potential method to avoid the flow boiling heat transfer deterioration under overload.

This technical paper presents results of an air-cooled supercritical CO 2 (sCO 2 ) finned-tube sink heat exchanger (HX) performance test comprising wide range of variable parameters (26–166 °C, 7–10 MPa, 0.1–0.32 kg/s). The measurement covered both supercritical and subcritical pressures including transition of pseudocritical region in the last stages of the sink HX. The test was performed in a newly built sCO 2 experimental loop which was constructed within Sustainable Energy (SUSEN) project at Research Centre Rez (CVR). The experimental setup along with the boundary conditions are described in detail; hence, the gained data set can be used for benchmarking of system thermal hydraulic codes. Such benchmarking was performed on the open source Modelica-based code ClaRa. Both steady-state and transient thermal hydraulic analyses were performed using the simulation environment DYMOLA 2018 on a state of the art PC. The results of calculated averaged overall heat transfer coefficients (using Gnielinski correlation for sCO 2 and IPPE or VDI for the air) and experimentally determined values shows reasonably low error of + 25% and – 10%. Hence, using the correlations for the estimation of the heat transfer in the sink HX with a similar design and similar conditions gives a fair error and thus is recommended.