Zigzag-channel Printed Circuit Heat Exchangers Research Articles

Dynamic behavior of a high-temperature printed circuit heat exchanger: Numerical modeling and experimental investigation

Printed circuit heat exchanger (PCHE) is one of the leading intermediate heat exchanger (IHX) candidates for the Very High Temperature Reactors due to its capability for high-temperature and high-pressure applications. An IHX serves to isolate the reactor primary system from electricity generation and process heat application plants, and therefore must be robust to maintain the entire system integrity during normal and off-normal conditions. Understanding the PCHE dynamic behavior is of importance in the design of a PCHE-type IHX since the dynamics of the PCHE will influence accident progression in most accident scenarios. In addition, any transient in the power conversion unit or process heat plant will propagate back to the reactor primary system via the PCHE. In this study, the dynamic behavior of a zigzag-channel PCHE, subject to helium inlet temperature variations and helium mass flow rate step changes on both the hot and cold sides, was simulated and analyzed. Three sets of transient tests were experimentally conducted in a high-temperature helium test facility to examine the dynamic performance of the PCHE and to assess the PCHE dynamic model. Comparisons of the numerical results and experimental data indicate that the numerical solutions are sufficiently accurate and that the feasibility of the dynamic model developed for predicting the steady-state and transient performance of the PCHE is confirmed.

Pressure drop and heat transfer characteristics of a high-temperature printed circuit heat exchanger

Printed circuit heat exchanger (PCHE) is one of the leading intermediate heat exchanger (IHX) candidates to be employed in the very-high-temperature gas-cooled reactors (VHTRs) due to its capability for high-temperature, high-pressure applications. In the current study, a reduced-scale zigzag-channel PCHE was fabricated using Alloy 617 plates for the heat exchanger core and Alloy 800H pipes for the headers. The pressure drop and heat transfer characteristics of the PCHE were investigated experimentally in a high-temperature helium test facility (HTHF) at The Ohio State University. The PCHE helium inlet temperatures and pressures were varied up to 464°C/2.7MPa for the cold side and 802°C/2.7MPa for the hot side, respectively, while the maximum helium mass flow rates on both sides of the PCHE reached 39kg/h. The corresponding maximum channel Reynolds number was approximately 3558, covering the laminar flow and laminar-to-turbulent flow transition regimes. New pressure drop and heat transfer correlations for the current zigzag channels with rounded bends were developed based on the experimental data. Comparisons between the experimental data and the results obtained from the available PCHE and straight circular pipe correlations were conducted. Compared to the heat transfer performance in straight circular pipes, the zigzag channels provided little advantage in the laminar flow regime but significant advantage near the transition flow regime.

Modeling and analysis of a printed circuit heat exchanger for supercritical CO2 power cycle applications

The supercritical carbon dioxide (S-CO2) based Brayton cycle is a good alternative to conventional power cycles because of high cycle efficiency, compact turbo machinery and compact heat exchangers. In this cycle, the majority of heat transfer (approximately 60–70% of total cycle heat transfer) occurs in the regenerator. For the regenerator, micro-channel heat exchanger is an attractive option because of its high surface-area-to-volume ratio. In this study, the performance of a printed circuit heat exchanger (PCHE) with straight and zigzag channels is evaluated. The study is performed for fully turbulent conditions. The channel diameter and the operating Reynolds number play significant roles in the overall heat transfer and pressure drop of hot and cold channels of S-CO2. For zigzag channels, it is found that a larger bend angle and smaller linear pitch perform better than a smaller bend angle and large linear pitch combination. Correlations for Nusselt number and friction factor are developed using ANSYS Fluent and are subsequently utilized in one dimensional (1D) thermal modeling of the heat exchanger. For the same thermal capacity, the model indicates that the zigzag channel PCHE volume is significantly smaller than that of a straight channel PCHE because of higher heat transfer coefficient. However, the pressure drop incurred in the former design is larger.

Optimization of airfoil-type PCHE for the recuperator of small scale brayton cycle by cost-based objective function

Supercritical carbon dioxide (SCO2) Brayton cycle gives high efficiency of power cycle with small size. Printed circuit heat exchangers (PCHE) are proper selection for the Brayton cycle because their operability at high temperature and high pressure with small size. Airfoil fin PCHE was suggested by Kim et al. (2008b), it can provide high heat transfer-like zigzag channel PCHE with low pressure drop-like straight channel PCHE. Optimization of the airfoil fin PCHE was not performed like the zigzag channel PCHE. For optimization of the airfoil fin PCHE, the operating condition of the recuperator of SCO2 Integral Experiment Loop (SCIEL) Brayton cycle test loop at Korea Atomic Energy Research Institute (KAERI) was used. We performed CFD analysis for various airfoil fin configurations using ANSYS CFX 15.0, and made correlations for predicting the Nusselt number and the Fanning friction factor. The recuperator was designed by the simple energy balance code with our correlations. Using the cost-based objective function with production cost and operation cost from size and pressure drop of the recuperator, we evaluated airfoil fin configuration by using total cost and suggested the optimization configuration of the airfoil fin PCHE.

Numerical investigation on thermal–hydraulic performance of new printed circuit heat exchanger model

Three-dimensional numerical analysis was performed to investigate heat transfer and pressure drop characteristics of supercritical CO 2 flow in new Printed Circuit Heat Exchanger (PCHE) model using commercial CFD code, Fluent 6.3. First, numerical analysis for conventional zigzag channel PCHE model was performed and compared with previous experimental data. Maximum deviation of in-outlet temperature difference and pressure drop from experimental data is about 10%. A new PCHE model has been designed to optimize thermal–hydraulic performance of PCHE. The new PCHE model has several airfoil shape fins (NACA 0020 model), which are designed to streamlined shape. Simulation results showed that in the airfoil shape fin PCHE, total heat transfer rate per unit volume was almost same with zigzag channel PCHE and the pressure drop was reduced to one-twentieth of that in zigzag channel PCHE. In airfoil shape fin PCHE model, the enhancement of heat transfer area and the uniform flow configuration contributed to obtain the same heat transfer performance with zigzag channel PCHE model. And the reduction of pressure drop in airfoil shape fin PCHE model was caused by suppressing generation of separated flow owing to streamlined shape of airfoil fins.