Optimization of the Thermodynamic Efficiency of a Recuperative Heat Exchanger

2000 ◽  
Author(s):  
George A. Adebiyi
Keyword(s):  
Heat Exchanger ◽  
Thermal Capacity ◽  
Thermodynamic Efficiency ◽  
Second Law ◽  
Inlet Temperature ◽  
Counter Flow ◽  
Cold Stream ◽  
Prandtl Numbers ◽  
Recuperative Heat Exchanger

Abstract A heat exchanger is strictly speaking a thermal exergy transfer device, and the proper measure of its efficiency is the second law efficiency. This article considers the efficiency of a single-pass, recuperative heat exchanger in which a given stream of hot fluid is available for heating a cold stream of fluid in a specified manner. The analysis takes cognizance of the required exergy input to overcome fluid friction in the flow passages, as well as the thermal exergy flow rates for the fluid streams, in the determination of the second-law efficiency. Maximization of the second-law efficiency is found to provide a basis for sizing the heat exchanger for optimum thermodynamic efficiency of operation. The key parameters that determine this optimum include the number of transfer units (NTU), the ratio of thermal capacity rates (Cr), a dissipation parameter which involves the Eckert and Prandtl numbers, and the flow configuration (whether parallel-flow, or counter-flow). Other parameters relevant to the performance of the heat exchanger are the tare capacity (εtare), and the ratio of the inlet temperature of the hot fluid to the ambient temperature.

scholarly journals Thermal Analysis of the Effects of Multifaceted Conditions on Performance of Shell-and-Tube Heat Exchanger

2021 ◽  
Vol 6 (1) ◽  
pp. 69-75
Author(s):  
Taiwo O. Oni ◽  
Ayotunde A. Ojo ◽  
Daniel C. Uguru-Okorie ◽  
David O. Akindele
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Parallel Flow ◽  
Hot Water ◽  
Inlet Temperature ◽  
Fiber Glass ◽  
Counter Flow ◽  
Tube Heat Exchanger ◽  
Shell And Tube ◽  
Flow Configurations

A shell-and-tube heat exchanger which was subjected to different flow configurations, viz. counter flow, and parallel flow, was investigated. Each of the flow configurations was operated under two different conditions of the shell, that is, an uninsulated shell and a shell insulated with fiber glass. The hot water inlet temperature of the tube was reduced gradually from 60 oC to 40 oC, and performance evaluation of the heat exchanger was carried out. It was found that for the uninsulated shell, the heat transfer effectiveness for hot water inlet temperature of 60, 55, 50, 45, and 40 oC are 0.243, 0.244, 0.240, 0.240, and 0.247, respectively, for the parallel flow arrangement. For the counter flow arrangement, the heat transfer effectiveness for the uninsulated shell are 2.40, 2.74, 5.00, 4.17, and 2.70%, respectively, higher than those for the parallel flow. The heat exchanger’s heat transfer effectiveness with fiber-glass-insulated shell for the parallel flow condition with tube hot water inlet temperatures of 60, 55, 50, 45, and 40 oC are 0.223, 0.226, 0.220, 0.225, and 0.227, respectively, whereas the counter flow condition has its heat transfer effectiveness increased by 1.28, 1.47, 1.82, 1.11, and 1.18%, respectively, over those of the parallel flow.

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

2010 ◽  
Vol 14 (1) ◽  
pp. 103-114 ◽  
Author(s):  
Ahmed Kohil ◽  
Hassan Farag ◽  
Mona Ossman
Keyword(s):  
Sensitivity Analysis ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Ethylene Plant ◽  
Inlet Flow Rate ◽  
Cold Stream ◽  
Inlet Conditions ◽  
Good Agreement

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.

A Thermodynamic Efficiency Concept for Heat Exchange Devices

1983 ◽  
Vol 105 (1) ◽  
pp. 199-203 ◽  
Author(s):  
L. C. Witte ◽  
N. Shamsundar
Keyword(s):  
Heat Exchanger ◽  
Heat Exchange ◽  
Energy Use ◽  
Second Law Of Thermodynamics ◽  
Thermodynamic Efficiency ◽  
Second Law ◽  
Two Fluids ◽  
Environment Temperature ◽  
Efficiency And Effectiveness ◽  
The Mean

A thermodynamic efficiency based on the second law of thermodynamics is defined for heat exchange devices. The efficiency can be simply written in terms of the mean absolute temperatures of the two fluids exchanging heat, and the appropriate environment temperature. It is also shown that for a given ratio of hot to cold inlet temperatures, the efficiency and effectiveness for particular heat exchange configurations are related. This efficiency is compared to second-law efficiencies proposed by other authors, and is shown to be superior in its ability to predict the effect of heat exchanger parameter changes upon the efficiency of energy use. The concept is applied to typical heat exchange cases to demonstrate its usefulness and sensitivity.

scholarly journals Evaluation of a counter-flow microchannel heat exchanger performance with air-water vapor mixture to liquid water

2020 ◽  
Vol 194 ◽  
pp. 01025
Author(s):  
C. Ren ◽  
J.H. Weng ◽  
J.N. Yan ◽  
L. Wang ◽  
H.L. She ◽  
...  
Keyword(s):  
Water Vapor ◽  
Heat Exchanger ◽  
Liquid Water ◽  
Inlet Temperature ◽  
Outlet Temperature ◽  
Vapor Mixture ◽  
Counter Flow ◽  
Microchannel Heat Exchanger ◽  
Operation Conditions ◽  
Continuum Flow

Given its configuration and operation conditions, the performance of a counter-flow microchannel heat exchanger (MCHX) is evaluated through detailed calculations. The fluids, both liquid water and air, are considered as continuum flow flowing in microchannels. The MCHX has 59 sheets, and each sheet has 48 microchannels. The microchannels for both fluids have the same cross section of 0.8mm×1mm and same length of 200mm. Log mean temperature difference method is adopted for this evaluation. Using appropriate equations, the properties of air-water vapor mixture are calculated based on that of the two components. Given the inlet temperature for liquid water(35℃) and air (170℃),the calculated outlet temperature for both fluids are 55.5℃ and 43.3℃, respectively. The results also show that the air at the outlet is saturated. The overall heat transfer coefficient reaches 100W/m2ꞏK, which is much higher than that of conventional heat exchanger with similar fluid combinations.

Second-Law-Based Thermoeconomic Optimization of Two-Phase Heat Exchangers

1987 ◽  
Vol 109 (2) ◽  
pp. 287-294 ◽  
Author(s):  
S. M. Zubair ◽  
P. V. Kadaba ◽  
R. B. Evans
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Heat Exchanger ◽  
Transfer Coefficient ◽  
Heat Exchangers ◽  
Unit Cost ◽  
Second Law ◽  
Inlet Temperature ◽  
Two Phase ◽  
Transfer Resistance

This paper presents a closed-form analytical method for the second-law-based thermoeconomic optimization of two-phase heat exchangers used as condensers or evaporators. The concept of “internal economy” as a means of estimating the economic value of entropy generated (due to finite temperature difference heat transfer and pressure drops) has been proposed, thus permitting the engineer to trade the cost of entropy generation in the heat exchanger against its capital expenditure. Results are presented in terms of the optimum heat exchanger area as a function of the exit/inlet temperature ratio of the coolant, unit cost of energy dissipated, and the optimum overall heat transfer coefficient. The total heat transfer resistance represented by (1/U = C1 + C2 Re−n) in the present analysis is patterned after Wilson (1915) which accommodates the complexities associated with the determination of the two-phase heat transfer coefficient and the buildup of surface scaling resistances. The analysis of a water-cooled condenser and an air-cooled evaporator is presented with supporting numerical examples which are based on the thermoeconomic optimization procedure of this paper.

Modeling of Recuperative Heat Exchanger in a Joule-Thomson Cooler

2001 ◽  
Author(s):  
Kim Choon Ng ◽  
Jinbao Wang ◽  
Hong Xue
Keyword(s):  
Heat Conduction ◽  
Heat Exchanger ◽  
Heat Exchangers ◽  
Cooling System ◽  
Experimental Measurements ◽  
Temperature Dependent ◽  
Counter Flow ◽  
Flow Heat ◽  
Temperature Dependent Properties ◽  
Recuperative Heat Exchanger

Abstract To develop effective heat exchangers for miniature and micro Joule-Thomson (J-T) cooling system, the performance of a recuperative heat exchanger is analyzed and evaluated. The evaluation is based on a theoretical model of the Hampson-type counter-flow heat exchanger. The effect of the pressure and temperature-dependent properties and longitudinal heat conduction are considered. The results of the numerical simulation are validated with the corresponding experimental measurements. The performance of the heat exchanger on effectiveness, flow and various heat conduction losses as well as liquefied yield fraction are analyzed and discussed. The simulation model provides a useful tool for miniature J-T cooler design.

scholarly journals Some Facts Resulting from the Key Variables Used in the Description of the Recuperative Heat Exchangers

2018 ◽  
Vol 68 (3) ◽  
pp. 249-260
Author(s):  
Štefan Gužela ◽  
František Dzianik
Keyword(s):  
Heat Exchanger ◽  
Heat Exchangers ◽  
Basic Assumption ◽  
Optimal Operation ◽  
Point Of View ◽  
Limit Values ◽  
Key Variables ◽  
Recuperative Heat Exchanger ◽  
Selection Of

AbstractThere are the various types of heat exchangers. The selection of the heat exchanger right type is the first basic assumption for its optimal operation. The heat exchanger calculation itself is another prerequisite for its optimal operation. This article deals with the variables which are usually used to describe the stationary operation of any recuperative heat exchanger with two incoming and two outgoing streams. The knowledge of these variables, including the facts resulting from them, is necessary not only from the point of view of the calculation but also from the point of view of the evaluation of the experimental data of any heat exchanger. The variables values needed for the calculation of heat exchangers, so-called key variables, must always fall within the values range determined on the basis of generally valid knowledge about heat exchangers. The article also deals with the determination of the limit values defining the values range of these key variables.

Critical Heat Balance Error for a General Imbalanced Heat Exchanger

2016 ◽  
Author(s):  
Zhifeng Zhang ◽  
Bofeng Bai
Keyword(s):  
Experimental Data ◽  
Heat Exchanger ◽  
Entropy Generation ◽  
Heat Balance ◽  
Thermal Capacity ◽  
Inlet Temperature ◽  
Positive Entropy ◽  
Temperature Ratio ◽  
Heat Exchanger Design ◽  
Balance Error

The reliability of experimental data are important for heat exchanger design and evaluation. In the present paper, we extended the concept of Critical Heat Balance Error (CHBE) to a general imbalanced heat exchanger with thermal capacity ratio great than 1. Based on the principle of positive entropy generation in experiment, were analytically expressed the CHBE under the influence of different thermal capacity ratios. Interestingly, we found the same analytical expression as previous research which is, CHBE = −(1 − τ)(1 − ε), where ε and τ are heat exchanger efficiency and inlet temperature ratio, respectively. Therefore, we claim this analytical filter can be used for a general heat exchanger with any thermal capacity configuration.

Isentropic recuperative heat exchanger with regenerative work transfer

2000 ◽  
Vol 214 (4) ◽  
pp. 609-618 ◽  
Author(s):  
H V Rao
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Counter Flow ◽  
Specific Heats ◽  
Flow Heat ◽  
Recuperative Heat Exchanger ◽  
The Relationship ◽  
Ideal Method ◽  
Two Fluid ◽  
The Ideal

A counter-flow heat exchanger is considered to be the ideal method for recuperative heat transfer between hot and cold fluid streams. In this paper the concept of an isentropic heat exchanger with regenerative work transfer is developed. The overall effect is a mutual heat transfer between the two fluid streams without any net external heat or work transfers. The effectiveness for an isentropic heat exchanger with regenerative work transfer is derived for the case of fluid streams with constant specific heats and it is shown that it is greater than unity. The ‘isentropic effectiveness’ of a heat exchanger is defined. The relationship between the entropy generation and effectiveness for the traditional heat exchanger is also examined and compared with that of the isentropic heat exchanger. The practical realization of isentropic operation of a heat exchanger and its possible application are briefly considered.

Second law thermodynamic analysis of imbalanced counter flow heat exchanger for energy conservation

2020 ◽  
pp. 250-262
Author(s):  
K. Manjunath
Keyword(s):  
Heat Exchanger ◽  
Energy Conservation ◽  
Entropy Generation ◽  
Diameter Ratio ◽  
Second Law ◽  
Exergetic Efficiency ◽  
Minimum Entropy ◽  
Counter Flow ◽  
Flow Heat ◽  
Length To Diameter Ratio

Entropy generation of imbalanced counter flow heat exchanger is analyzed to know the thermal behavior effects such as entropy generation minimization and exergetic efficiency. The analysis of first law which does not considers different irreversibilities such as transfer of heat, drop in fluid pressure and mass flow streams unbalance is possible from second law of thermodynamics studies. In this analysis the parameters which are considered are length to diameter dimensions of heat transfer equipment tube, fluid streams capacity ratio, Reynolds number of fluid and type of fully developed fluid flow. To understand the behavior of heat exchanger the heat capacity rate of heat exchanger’s maximum value is changed for both cases of hot stream and cold stream. Optimum heat exchanger geometrical dimension namely length-to-diameter ratio can be obtained from the second law analysis corresponding to lower total entropy generation and higher second law efficiency which leads to energy conservation. Accordingly, for the minimum entropy generation and maximum exergetic efficiency resulted, the optimum length-to-diameter ratio are obtained for different cases considered.

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