scholarly journals Stirling Refrigerating Machine Modeling Using Schmidt and Finite Physical Dimensions Thermodynamic Models: A Comparison with Experiments

Entropy ◽  
2021 ◽  
Vol 23 (3) ◽  
pp. 368
Author(s):  
Cătălina Dobre ◽  
Lavinia Grosu ◽  
Alexandru Dobrovicescu ◽  
Georgiana Chişiu ◽  
Mihaela Constantin
Keyword(s):  
Temperature Difference ◽  
Finite Temperature ◽  
Heat Exchangers ◽  
Experimental Results ◽  
Thermodynamic Models ◽  
Machine Modeling ◽  
Stirling Refrigerator ◽  
Exergy Balance ◽  
Comparison With Experiments ◽  
Physical Dimensions

The purpose of the study is to show that two simple models that take into account only the irreversibility due to temperature difference in the heat exchangers and imperfect regeneration are able to indicate refrigerating machine behavior. In the present paper, the finite physical dimensions thermodynamics (FPDT) method and 0-D modeling using the Schmidt model with imperfect regeneration were applied in the study of a β type Stirling refrigeration machine.The 0-D modeling is improved by including the irreversibility caused by imperfect regeneration and the finite temperature difference between the gas and the heat exchangers wall. A flowchart of the Stirling refrigerator exergy balance is presented to show the internal and external irreversibilities. It is found that the irreversibility at the regenerator level is more important than that at the heat exchangers level. The energies exchanged by the working gas are expressed according to the practical parameters, necessary for the engineer during the entire project. The results of the two thermodynamic models are presented in comparison with the experimental results, which leads to validation of the proposed FPDT model for the functional and constructive parameters of the studied refrigerating machine.

scholarly journals Artificial Neural Network Simulation of Energetic Performance for Sorption Thermal Energy Storage Reactors

Energies ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 3294
Author(s):  
Carla Delmarre ◽  
Marie-Anne Resmond ◽  
Frédéric Kuznik ◽  
Christian Obrecht ◽  
Bao Chen ◽  
...  
Keyword(s):  
Neural Network ◽  
Artificial Neural Network ◽  
Energy Storage ◽  
Thermal Energy ◽  
Temperature Difference ◽  
Thermal Energy Storage ◽  
Heat Storage ◽  
Experimental Results ◽  
Physical Models ◽  
Artificial Neural

Sorption thermal heat storage is a promising solution to improve the development of renewable energies and to promote a rational use of energy both for industry and households. These systems store thermal energy through physico-chemical sorption/desorption reactions that are also termed hydration/dehydration. Their introduction to the market requires to assess their energy performances, usually analysed by numerical simulation of the overall system. To address this, physical models are commonly developed and used. However, simulation based on such models are time-consuming which does not allow their use for yearly simulations. Artificial neural network (ANN)-based models, which are known for their computational efficiency, may overcome this issue. Therefore, the main objective of this study is to investigate the use of an ANN model to simulate a sorption heat storage system, instead of using a physical model. The neural network is trained using experimental results in order to evaluate this approach on actual systems. By using a recurrent neural network (RNN) and the Deep Learning Toolbox in MATLAB, a good accuracy is reached, and the predicted results are close to the experimental results. The root mean squared error for the prediction of the temperature difference during the thermal energy storage process is less than 3K for both hydration and dehydration, the maximal temperature difference being, respectively, about 90K and 40K.

Analysis of the Thermal Stress at the Tubesheet in Floating-Head or U-Tube Heat Exchangers

2017 ◽  
Vol 139 (2) ◽  
Author(s):  
Jiuyi Liu ◽  
Caifu Qian ◽  
Huifang Li
Keyword(s):  
Thermal Stress ◽  
Heat Exchanger ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Influence Factors ◽  
Area Ratio ◽  
Shell Side ◽  
Tube Heat Exchanger ◽  
Numerical Tests ◽  
Hole Area

Thermal stress is an important factor influencing the strength of a heat exchanger tubesheet. Some studies have indicated that, even in floating-head or U-tube heat exchangers, the thermal stress at the tubesheet is significant in magnitude. For exploring the value, distribution, and the influence factors of the thermal stress at the tubesheet of these kind heat exchangers, a tubesheet and triangle arranged tubes with the tube diameter of 25 mm were numerically analyzed. Specifically, the thermal stress at the tubesheet center is concentrated and analyzed with changing different parameters of the tubesheet, such as the temperature difference between tube-side and shell-side fluids, tubesheet diameter, thickness, and the tube-hole area ratio. It is found that the thermal stress of the tubesheet of floating-head or U-tube heat exchanger was comparable in magnitude with that produced by pressures, and the distribution of the thermal stress depends on the tube-hole area and the temperature inside the tubes. The thermal stress at the center of the tubesheet surface is high when tube-hole area ratio is very low. And with increasing the tube-hole area ratio, the stress first decreases rapidly and then increases linearly. A formula was numerically fitted for calculating the thermal stress at the tubesheet surface center which may be useful for the strength design of the tubesheet of floating-head or U-tube heat exchangers when considering the thermal stress. Numerical tests show that the fitted formula can meet the accuracy requirements for engineering applications.

scholarly journals Thermal Steady States of Gases in a Gravitational Field

2011 ◽  
Vol 66 (1-2) ◽  
pp. 123-133
Author(s):  
Kunihiko Kigoshi
Keyword(s):  
Heat Transfer ◽  
Gravitational Field ◽  
Temperature Difference ◽  
Thermal Gradient ◽  
Vertical Direction ◽  
Steady States ◽  
Gas Pressure ◽  
Experimental Results ◽  
Gravity Effect ◽  
Gas Molecules

This paper presents results on observations of a temperature difference between the top and bottom of a vessel filled with gas in a gravitational field. The observed temperature at the top of the vessel was always lower than the temperature at the bottom of the vessel, and this temperature difference was persistent and steady over more than 20 h. The magnitude of the temperature difference depends on the types of gas molecules present but is independent of the gas pressure in the vessel within the range from 2.7×104 Pa to 27 Pa. A temperature difference between the top and the bottom is only observed along the vertical direction and is only observed when the vessel contains a gas. These experimental results indicate a gravity effect on molecular heat transfer which enables the transport of energy in the gas without a thermal gradient.

Evaporation of Single Drops of n-Pentane/n-Hexane Mixtures in Water

1992 ◽  
Vol 114 (4) ◽  
pp. 965-971 ◽  
Author(s):  
H. Shimaoka ◽  
Y. H. Mori
Keyword(s):  
Heat Transfer ◽  
Temperature Difference ◽  
Vapor Bubble ◽  
Experimental Results ◽  
Rise Velocity ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Transfer Characteristics ◽  
Preceding Work ◽  
Liquid Vapor

The evaporation of isolated drops (2.1−3.0 mm diameter) of nonazeotropic n-pentane/n-hexane mixtures in the medium of water was observed under pressures of 0.11−0.46 MPa and temperature differences up to 27 K. The mole fractions of n-pentane, x, in the mixtures were set at 0.9, 0.5, 0.1, and 0, to be completed by the condition x = 1 set in a preceding work (Shimaoka and Mori, 1990). Experimental results are presented in terms of the instantaneous rise velocity of, and an expression of instantaneous heat transfer to, each drop evaporating and thereby transforming into a liquid/vapor two-phase bubble and finally into a vapor bubble. The dependencies of the heat transfer characteristics on the pressure, the temperature difference, and x are discussed.

scholarly journals Study of the Performance of a Novel Radiator with Three Inlets and One Outlet Based on Topology Optimization

Micromachines ◽  
2021 ◽  
Vol 12 (6) ◽  
pp. 594
Author(s):  
Tao Zhou ◽  
Bingchao Chen ◽  
Huanling Liu
Keyword(s):  
Topology Optimization ◽  
Heat Exchanger ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Exchange Capacity ◽  
Numerical Results ◽  
Fluid Temperature ◽  
Channel Depth ◽  
Goal Model ◽  
Flow And Heat Transfer

In recent years, in order to obtain a radiator with strong heat exchange capacity, researchers have proposed a lot of heat exchangers to improve heat exchange capacity significantly. However, the cooling abilities of heat exchangers designed by traditional design methods is limited even if the geometric parameters are optimized at the same time. However, using topology optimization to design heat exchangers can overcome this design limitation. Furthermore, researchers have used topology optimization theory to designed one-to-one and many-to-many inlet and outlet heat exchangers because it can effectively increase the heat dissipation rate. In particular, it can further decrease the hot-spot temperature for many-to-many inlet and outlet heat exchangers. Therefore, this article proposes novel heat exchangers with three inlets and one outlet designed by topology optimization to decrease the fluid temperature at the outlet. Subsequently, the effect of the channel depth on the heat exchanger design is also studied. The results show that the type of exchanger varies with the channel depth, and there exists a critical depth value for obtaining the minimum substrate temperature difference. Then, the flow and heat transfer performance of the heat exchangers are numerically investigated. The numerical results show that the heat exchanger derived by topology optimization with the minimum temperature difference as the goal (Model-2) is the best design for flow and heat transfer performance compared to other heat sink designs, including the heat exchanger derived by topology optimization having the average temperature as the goal (Model-1) and conventional straight channels (Model-3). The temperature difference of Model-1 can be reduced by 37.5%, and that of Model-2 can be decreased by 62.5% compared to Model-3. Compared with Model-3, the thermal resistance of Model-1 can be reduced by 21.86%, while that of Model-2 can be decreased by 47.99%. At room temperature, we carried out the forced convention experimental test for Model-2 to measure its physical parameters (temperature, pressure drop) to verify the numerical results. The error of the average wall temperature between experimental results and simulation results is within 2.6 K, while that of the fluid temperature between the experimental and simulation results is within 1.4 K, and the maximum deviation of the measured Nu and simulated Nu was less than 5%. This indicated that the numerical results agreed well with the experimental results.

An Experimental Method for Fast Evaluating Thermoelectric Generators Using one pair of P- and N-type Legs

2021 ◽  
pp. 1-12
Author(s):  
Ting Zhao ◽  
Kewen Li ◽  
Yuhao Zhu ◽  
Lin Jia ◽  
Xiaoyong Hou ◽  
...  
Keyword(s):  
Experimental Method ◽  
Output Power ◽  
Temperature Difference ◽  
Open Circuit Voltage ◽  
Open Circuit ◽  
Experimental Results ◽  
Single Pair ◽  
Thermoelectric Generators ◽  
Cross Sectional ◽  
Specific Temperature

Abstract Thermoelectric generators (TEG) are widely used in many industries. The voltage and output power of TEG chips are critical indicators to evaluate the performance of TEGs. The conventional method is to directly test the output voltage and power of the whole TEG chip that contains 127 pairs of PN (P- and N-type) legs (127-PN-TEG). However, the assembling of these PN legs is very time-consuming. In order to reduce experimental time and the consumption of TEG materials, we proposed an experimental method. We developed the test apparatus for the rapid evaluation of TEG performance using a TEG chip with a single pair of PN legs (1-PN-TEG). We made several 1-PN-TEGs and 127-PN-TEGs using the same thermoelectric material (bismuth telluride). We then measured the voltage and the power of these 1-PN-TEGs and 127-PN-TEGs, respectively. The experimental results were compared and analyzed. The comparison showed that the voltage of 127-PN-TEG is equal to the voltage of 1-PN-TEG times 127, which implies that we could use the test data of 1-PN-TEG to evaluate the performance of 127-PN-TEG. Using the experimental device developed in this paper, we also studied the effects of the PN leg area (cross-sectional area of PN legs) and the pressure applied over the TEGs on the output power of 1-PN-TEG. The experimental results showed that the power per unit area decreases with an increase in the 1-PN-TEG's PN leg area when the temperature difference between the hot and cold sides was constant. Under a specific temperature difference conditions, the open-circuit voltage and the output power will increase with the pressure applied on the TEG chips.

THE EFFECT OF LIQUID SUCTION HEAT EXCHANGER SUB-COOLER ON PERFORMANCE OF A FREEZER USING R404A AS WORKING FLUID

2015 ◽  
Vol 76 (11) ◽  
Author(s):  
Muhammad Nuriyadi ◽  
Sumeru Sumeru ◽  
Henry Nasution
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cooling Capacity ◽  
Experimental Results ◽  
Working Fluid ◽  
Liquid Line ◽  
Cabin Temperature

This study presents the effect of liquid-suction heat exchangers (LSHX) sub-cooler in a freezer. The LSHX sub-cooler is a method to increase the cooling capacity of the evaporator by lowering temperature at the condenser outlet. The decrease in temperature of the condenser outlet will cause a decrease in the quality refrigerant entering the evaporator. The lower the quality of the refrigerant entering the evaporator, the higher the cooling capacity produced by the evaporator. The LSHX sub-cooler utilizes a heat exchanger to transfer heat from the outlet of the condenser (liquid line) to the suction of the compressor. In the present study, three different LSHX sub-coolers in the freezer with cabin temperature settings of 0, -10 and -20oC were investigated. The results showed that the lowest and the highest of effectiveness of the heat exchanger were 0.28 and 0.58, respectively. The experimental results also showed that EER reduction is occurred at the cabin temperature setting of 0oC and -10oC, whereas the EER improvements were always occurred at the cabin temperature settings of -20oC.

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