Aluminum Plate-fin Heat Exchanger Research Articles

Experimental insights into thermoelectric freezer systems: Feasibility and efficiency

This study presents an experimental investigation into the operational performance of a thermoelectric (TE) freezer system. A freezer unit is composed of two-stage thermoelectric modules, an aluminum plate fin heat exchanger sink with fans positioned either on top or directing airflow through the center, and a cooling block incorporating circulating icy water for heat dissipation. Three distinct configurations, featuring varying numbers of freezer units and fan arrangements, underwent testing using a 300-liter freezer prototype under typical room conditions, specifically at 21 °C. The findings illustrate that the minimum temperature inside the freezer cabinet can achieve −16.0 °C across all configurations. Moreover, the cooling capacity can reach up to 74.7 W, with the thermoelectric coefficient of performance (COP) achieving a maximum of 0.45, while the system COP ranges from 0.23 to 0.28. The minimum TE power consumption and TE system power consumption are recorded at 138.8 W and 174.4 W, respectively, suggesting feasibility for practical residential freezer applications. This investigation sets the stage for the development of TE freezers integrated with ice thermal storage applications.

Investigation on strength and fracture mechanism of aluminum plate-fin structures at cryogenic temperature

In order to improve the service life of aluminum plate-fin heat exchangers and prevent them from thermal stress damage at cryogenic temperature, the strength and fracture mechanism of their plate-fin structures is studied at cryogenic temperature based on axial tensile test and scanning electron microscope (SEM) observation. Through axial tensile test, the mechanical properties and stress-strain curve can be obtained for plate-fin structures. Compared to the performance of plate-fin structures at room temperature, the yield limit, tensile strength and strain interval length (from yield limit to tensile strength) increased by 42.9 %, 49.5 % and 23.6 % for plate-fin structures at cryogenic temperature, respectively. This shows that plate-fin structures at cryogenic temperature have greater toughness and plasticity. Through SEM observation, the differences and commonality of fracture mechanism are compared and analyzed for the typical zones of plate-fin specimens. The results can be concluded that the fracture mode of plate-fin specimens belongs to quasi-cleavage fracture, and mainly shows the morphological characteristics of small cleavage sections, tearing ridges and dimples. Meanwhile, the fracture process and specific morphological characteristics of plate-fin specimens at cryogenic temperature are different from those at room temperature. Under the influence of thermal stress at cryogenic temperature and stress concentration, the fracture area of plate-fin specimens at cryogenic temperature is only located in the brazing zone. There is a significant displacement in the horizontal direction for specimens at cryogenic temperature when their temperature returns to room temperature after fracture. Therefore, the fracture in the brazing zone can be prevented for plate-fin structures at cryogenic temperature by adding brazing filler metal and improving the brazing process under process permission. The slow heating/cooling mode can be adopted for aluminum plate-fin heat exchangers to prevent them from thermal stress damage in the start-stop and operation stages.

Commissioning of a replacement subatmospheric cold box for Jefferson Lab’s Central Helium Liquefier

Jefferson Lab’s Cryogenics Department has designed, fabricated, installed, and commissioned a new subatmospheric cold box to replace one of the two existing units within our Central Helium Liquefier (CHL). The replacement cold box, dubbed SC1R, pumps saturated helium vapor at 0.0385 atm from Jefferson Lab’s continuous electron beam accelerator facility (CEBAF) cryomodules to maintain an operating temperature of nominally 2.1 K. This is accomplished using a five-stage cryogenic centrifugal compressor (cold compressor) system and a brazed aluminum plate-fin heat exchanger operating between 2.1 K and 4.5 K. In this paper we will describe our experience commissioning the SC1R cold box. We will discuss pump-down of the system to 2.1 K and steady-state operation at the cold compressor design flow rates of 170, 200, and 250 g/s. Performance of the heat exchanger and cold compressors has been mapped across a range of flow rates and optimized for CEBAF operations. This commissioning data will be used to monitor future performance and adapt to changing load requirements.

Improved heat transfer and friction correlations of aluminum offset-strip fin heat exchangers for helium cryogenic applications

• Improved performance correlations of cryogenic helium through OSFs were proposed. • Comparative thermal–hydraulic performance at different temperatures were studied. • Accuracy and robustness of the correlations’ prediction ability were validated. • Sensitivity of Re , Pr and η f on j values in laminar and turbulent regions was analyzed. • Correlations were qualified for OSF performance prediction in helium refrigerators. Aluminum plate-fin heat exchangers (PFHEs) with offset-strip fins (OSFs) are widely used in modern helium liquefaction/refrigeration systems characterized by enhanced heat transfer abilities and high compactness. This study numerically and experimentally investigated the thermal–hydraulic characteristics of cryogenic helium gas flowing through various OSF channels. Through the comparative tests conducted by well-validated numerical model as well as the contrast experiments respectively at room and nitrogen liquefaction temperatures, the results indicated that the OSF performance was not only affected by fin geometrical structures, but also deeply influenced by additional effect factors under actual cryogenic operating conditions. Based on the orthogonal table with 0.077 ⩽ α ⩽ 1.103 , 0.008 ⩽ δ ⩽ 0.15 and 0.029 ⩽ γ ⩽ 0.333 , the heat transfer and pressure drop performance of OSFs was systematically studied at a wide range of Re number ( 200 ⩽ Re ⩽ 12000 ) in three common refrigeration stages (300 K @ 12 bar, 77 K @ 6 bar and 20 K @ 2 bar). To improve the prediction accuracy of the correlations at low temperatures, the non-dimensional Pr Number and iteratively-solved fin efficiency η f that considering the thermophysical property variations of fluid and metal were introduced in the correlations of Colburn j and Fanning friction f factors. Compared with the experimental data, the proposed model had strong robustness of prediction ability, with the predicted errors of 11.33% and 22.49% respectively for j and f factors. Additionally, the effect of Pr number and η f occupied different weights in the j factors from laminar to turbulent flow. The sensitivity of the heat transfer performance with respect to each condition parameter was also discussed. Different from the most of the existing correlations derived from the fitted data based on common steam-to-air tests, the proposed correlations were more qualified for predicting the thermal–hydraulic performance of OSF channels in PFHEs through the cool-down process in helium refrigerators.

The influence of residual stress for the strength of plate-fin structures in the typical operation process of Liquefied Natural Gas (LNG) heat exchanger

In order to ensure the safe operation of heat exchangers in the Liquefied Natural Gas (LNG), the stress analysis model of aluminum Plate-Fin Structure (PFS) is established based on the thermal-elastic-plasticity theory. The residual stress distribution of PFS and its influence on the structural strength is analyzed by the thermal-structural coupling method. The results indicate that the residual stress distribution of PFS is very complex, and the residual stress reaches the peak at the Brazed Joint (BJ). Due to the equivalent stress at BJ near the fin is higher than that at BJ near the plate, cracks are more easily produced at BJ near the fin. Therefore, the existence of residual stress has a negative impact on PFS, which may increase the possibility of strength failure at BJ under the typical operating conditions (normal operation, cut-down and heat-up) of the heat exchanger. In addition, the residual stress gradually decreases with the brazing cooling rate decrease. The residual stress within the PFS will be effectively reduced by properly reducing the brazing cooling rate, which can slow down the strength failure of the PFS. The above research results will provide an important basis for the design and safe operation of the aluminum plate-fin heat exchanger.

A correlation for heat transfer and flow friction characteristics of the offset strip fin heat exchanger

The correlation for heat transfer and flow friction characteristics of fins is the basis for the optimization of heat exchangers, and it is of great importance to develop generally accurate formulas. To study the hydrodynamics and heat transfer characteristics of offset strip fins, Fluent is adopted to conduct the numerical simulation. Based on the calculation results of empirical correlations, the fluid constitutive model under different Reynolds numbers is determined in order to ensure the prediction efficiency and accuracy of offset strip fins. Good agreements are obtained between the numerical simulation and the Manglik & Bergles correlation, which verifies the validity and reliability of the numerical simulation method. Due to the fact that the traditional empirical formula is not able to cover the general specifications of Chinese domestic offset strip fins, the correlation of flow and heat transfer characteristics is improved based on the numerical simulation results and the industrial standard (Aluminum plate-fin heat exchanger NB/T 47006-2009). By coupling the Manglik & Bergles equation with the ALEX equation, a new relational expression of offset strip fins is proposed.

Capacity enhancement of indigenous expansion engine based helium liquefier

Development of technology and understanding for large capacity helium refrigeration and liquefaction at helium temperature is indispensable for coming-up projects. A new version of helium liquefier designed and built to provide approximately 35 liters of liquid helium per hour. The refrigeration capacity of this reciprocating type expansion engine machine has been increased from its predecessor version with continuous improvement and deficiency debugging. The helium liquefier has been built using components by local industries including cryogenic Aluminum plate fin heat exchangers. Two compressors with nearly identical capacity have been deployed for the operation of system. Together they consume about 110 kW of electric power. The system employs liquid Nitrogen precooling to enhance liquid Helium yield. This paper describes details of the cryogenic expander design improvements, reconfiguration of heat exchangers, performance simulation and their experimental validation.

Design and Construction of Nitrogen Liquefier

The design and construction of nitrogen liquefier begins with the process design of the cycle. The simulation of the cycles has been done using the software Aspen HYSYS. The compressor unit is available in the laboratory. Two number of high effectiveness, vacuum brazed aluminum plate fin heat exchangers are designed and fabricated. Turboexpander is designed and all of its components are fabricated. A suitable modification has been done with a precession needle valve to operate as a long stem JT valve. For separating the liquid, a phase separator is designed and fabricated. All the components are assembled inside a double walled cold box with pipes as per the process need. The necessary pressure, temperatureand other measuring instruments, valves and safety devices are mounted on the liquefier. After successful running of the liquefier, for the mass flow rate of 296 kg/hr for gaseous nitrogen, it is expected to deliver 17.44 lit/hr of liquid nitrogen.

Development and performance test of a small trailer-mounted moveable natural gas liquefier

A portable small liquefier for natural gas or coal-bed methane liquefaction has been designed and tested. The liquefier is very compact, and the compressor is directly mounted on a trailer. The liquefier is based on a mixed-refrigerant liquefaction cycle with R22 precooling. Most of the components in the liquefier are easily available off-the-shelf refrigeration products. An oil-lubricated single-stage R22 screw compressor is used for the mixed-refrigerant compression. An aluminum plate-fin heat exchanger with four flow passages was designed as the core of the cold box. The liquefier was tested for about 4months by circulating pure methane as the natural gas resource. A maximum liquefaction capacity of 15,000Nm3 was achieved with a minimum specific power consumption of about 0.54kWh/Nm3. This liquefier can be used in various applications such as small natural gas or coalbed methane exploitations, distributed peak-shaving, and boil-off gas reliquefaction. These can also be used as a flexible distributed liquefaction center with a set of small liquefiers.

알루미늄 플레이트-핀 열교환기의 분배기 형상비에 따른 분배특성에 관한 해석적 연구

Aluminum plate-fin heat exchangers (ALPHEs) are widely used in petroleum and gas-treated processes. The performance of the ALPHE is strongly dependent on the distribution characteristics of the header and the distributors of each fluid. In this paper, we define the aspect ratio in the side-entry type distributor and analyze the distribution characteristics using CFD-based numerical methods. The phenomena of velocity deviation and distribution with the aspect ratio and the inlet Reynolds number were analyzed by applying relative and absolute maldistribution parameters, and an optimum aspect ratio with the inlet Reynolds number was presented.

The Limit Load Interactions of the Brazed Aluminum Plate-Fin Heat Exchanger Header Under Combined Piping Loads

In order to investigate the strength design problem of the brazed aluminum plate-fin heat exchanger header under complex external piping loads, the limit load interactions of the header under combined piping loads are studied in this paper. To establish the limit piping load interaction curves, nonlinear finite element analysis assuming the elastic perfectly plastic material model is performed by using the commercial finite element analysis software ANSYS and multiple piping load combinations, which are the combination of orthogonal bending moment components, torque component-shear force component, bending moment component-axial force component, compound bending moment-axial force component, and torque component-compound shear force, of the header with six opening ratios ranging from 0.5 to 1 are explored. The results of the interaction diagrams show that the feasible combined piping load zone of the header derived from the interaction curves can be simplified as a triangular zone determined by the individual limit piping load components safely and the simplified feasible zone is suggested to be used for establishing a simplified safety assessment method for the header under combined piping loads.

Mathematical modeling of a multi-stream brazed aluminum plate fin heat exchanger

The need for small size and lightweight heat exchangers in many applications has resulted in the development of many heat transfer surfaces. This type of heat exchanger is much more compact than can be practically realized with circular tubes. In this work a steady-state mathematical model that representing one of the plate fin heat exchangers enclosed in cold box of an ethylene plant has been developed. This model could evaluate the performance of the heat exchanger by predicting the outlet temperatures of the hot and cold streams when the inlet conditions are known. The model has been validated by comparing the results with actual operating values and the results showed good agreement with the actual data. Sensitivity analysis was applied on the model to illustrate the main parameters that have the greatest influence on the model calculated results. The sensitivity analysis showed that the hot stream outlet temperature is more sensitive to cold streams inlet temperatures and less sensitive to hot stream inlet temperature and thermal resistance (fouling), while the cold stream outlet temperature is more sensitive to cold streams inlet flow rate and less sensitive to fouling.