Study on shell side heat transport enhancement of double tube heat exchangers by twisted oval tubes

The tubular heat exchangers described exhibited a sensitivity to flow-induced tube vibration at about 50% of their design shell-side flow. Following a detailed theoretical analysis, the heat exchangers were modified by the helical spacer method providing additional tube supports in-between the existing support plates and in the U-bend. This modification aimed at allowing the heat exchangers to operate safely and reliably at full load, including a 25% overload. Post modification sound and vibration testing was performed which confirmed the adequacy of the modification. The test results showed however, that at the overload condition, an unusual acoustic wave inside the shell was developing. It was determined that this wave would not be harmful to the safe operation of the heat exchangers. The paper will discuss the findings in more detail.

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

Journal of Pressure Vessel Technology ◽

10.1115/1.4035827 ◽

2017 ◽

Vol 139 (2) ◽

Cited By ~ 1

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.

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Shell-Side Pressure Drop in the Multi-Baffled Shell-and-Tube Heat Exchangers

Bulletin of JSME ◽

10.1299/jsme1958.8.644 ◽

1965 ◽

Vol 8 (32) ◽

pp. 644-651 ◽

Cited By ~ 4

Author(s):

Seikan ISHIGAI ◽

Eiichi NISHIKAWA ◽

Yoshiaki NAKAYAMA ◽

Shigeo TANAKA ◽

Ikuo SAIDA ◽

...

Keyword(s):

Pressure Drop ◽

Heat Exchangers ◽

Shell Side ◽

Side Pressure ◽

Shell And Tube

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Performance Analysis and Design Optimization of Shell and Tube Heat Exchangers

10.21203/rs.3.rs-407371/v1 ◽

2021 ◽

Author(s):

praveen math

Keyword(s):

Heat Transfer ◽

Heat Exchanger ◽

Heat Exchangers ◽

Pressure Loss ◽

Fluid Flows ◽

Hot Water ◽

Flow Conditions ◽

Shell Side ◽

Shell And Tube ◽

Side Flow

Abstract Shell and Tube heat exchangers are having special importance in boilers, oil coolers, condensers, pre-heaters. They are also widely used in process applications as well as the refrigeration and air conditioning industry. The robustness and medium weighted shape of Shell and Tube heat exchangers make them well suited for high pressure operations. The aim of this study is to experiment, validate and to provide design suggestion to optimize the shell and tube heat exchanger (STHE). The heat exchanger is made of acrylic material with 2 baffles and 7 tubes made of stainless steel. Hot fluid flows inside the tube and cold fluid flows over the tube in the shell. 4 K-type thermocouples were used to read the hot and cold fluids inlet and outlet temperatures. Experiments were carried out for various combinations of hot and cold water flow rates with different hot water inlet temperatures. The flow conditions are limited to the lab size model of the experimental setup. A commercial CFD code was used to study the thermal and hydraulic flow field inside the shell and tubes. CFD methodology is developed to appropriately represent the flow physics and the procedure is validated with the experimental results. Turbulent flow in tube side is observed for all flow conditions, while the shell side has laminar flow except for extreme hot water temperatures. Hence transition k-kl-omega model was used to predict the flow better for transition cases. Realizable k- epsilon model with non-equilibrium wall function was used for turbulent cases. Temperature and velocity profiles are examined in detail and observed that the flow remains almost uniform to the tubes thus limiting heat transfer. Approximately 2/3 rd of the shell side flow does not surround the tubes due to biased flow contributing to reduced overall heat transfer and increased pressure loss. On the basis of these findings an attempt has been made to enhance the heat transfer by inducing turbulence in the shel l side flow. The two baffles were rotated in opposite direction to each other to achieve more circulation in the shell side flow and provide more contact with tube surface. Various positions of the baffles were simulated and studied using CFD analysis and th e results are summarized with respect to heat transfer and pressure loss.

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Performance Study of Heat Exchangers with Continuous Helical Baffles on Different Inclination Angles

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.655-657.461 ◽

2013 ◽

Vol 655-657 ◽

pp. 461-464 ◽

Cited By ~ 1

Author(s):

Su Fang Song

Keyword(s):

Heat Transfer ◽

Heat Transfer Coefficient ◽

Heat Exchanger ◽

Pressure Drop ◽

Transfer Coefficient ◽

Heat Exchangers ◽

Performance Study ◽

Three Dimensional Model ◽

Shell Side ◽

Inclination Angles

The three-dimensional model of heat exchangers with continuous helical baffles was built. The fluid flow dynamics and heat transfer of shell side in the helical baffled heat exchanger were simulated and calculated. The velocity, pressure and temperature distributions were achieved. The simulation shows that with the same baffle pitch, shell-side heat transfer coefficient increased by 25% and the pressure drop decreases by 18% in helical baffled heat exchanger compared with segmental helical baffles. With the analyzing of the flow and heat transfer in heat exchanger in 5 different inclination angles from 11°to 21°, it can be found that both shell side heat transfer coefficient and pressure drop will reduce respectively by 86% and 52% with the increases 11°to 21°of the inclination angles. Numerical simulation provided reliable theoretical reference for further engineering research of heat exchanger with helical baffles.

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Pressure Testing Feedwater Heaters and Power Plant Auxiliary Heat Exchangers

ASME 2010 Power Conference ◽

10.1115/power2010-27106 ◽

2010 ◽

Author(s):

Stanley Yokell

Keyword(s):

Heat Transfer ◽

Power Plant ◽

Heat Exchangers ◽

Wire Drawing ◽

Pressure Vessels ◽

Shell Side ◽

Auxiliary Equipment ◽

National Board ◽

Pressure Testing ◽

Test Pressure

This paper discusses factory and field pressure testing of tubular heat transfer equipment such as closed feedwater heaters, steam surface condensers and power plant auxiliary heat exchangers built to Section VIII Division 1 of the ASME Boiler and Pressure Vessel Code (the ASME Code) and repaired or altered in accordance with the National Board Inspection Code (NBIC). It discusses the ASME Code’s and the NBIC’s requirements for hydrostatically testing unfired pressure vessels which includes tubular heat transfer equipment. It points out that using pressure gage indications of pressure loss to determine if there is a leak from the tube side to the shell side when the back face of the tubesheet is not visible does not reveal very small leaks or weeping. For the purposes of this paper, we define weeping, VRRLeak, as a leak of 20 drops per hour or approximately 1 cm3 [0.061 in3]. During typical half-hour hydrostatic test pressure holding periods, such weeping would amount to 10 drops of water on the tubesheet face or 0.5 cm3 [0.0305 in3]. Weeping through tube-to-tubesheet joints of high-pressure feedwater heaters can lead to wire drawing (wormholing), which can materially reduce the heater life. Leaks from the channel to the shell side of steam surface condensers and auxiliary condensers can introduce brackish water into the condensate. Depending upon the fluid flowing in the tubes, contaminants can enter the shell side of other auxiliary equipment when the channel pressure is higher than that of the shell. The paper concludes that Users must advise Designers and Manufacturers of the hazards of small leaks through the tube-to-tubesheet joints. It recommends that these three entities must agree on suitable leak tests.

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