Dynamic Behavior of Three-Fluid Crossflow Heat Exchangers

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Manish Mishra ◽  
P. K. Das ◽  
Sunil Sarangi
Keyword(s):  
Dynamic Behavior ◽  
Transient Response ◽  
Heat Exchangers ◽  
Temperature Response ◽  
Axial Dispersion ◽  
Transient Temperature ◽  
Inlet Temperature ◽  
Two Dimensional ◽  
Large Capacitance ◽  
Transient Temperature Response

A transient temperature response of three-fluid heat exchangers with finite and large capacitance of the separating sheets is investigated numerically for step, ramp, exponential, and sinusoidal perturbations provided in the central (hot) fluid inlet temperature. The effect of two-dimensional longitudinal conduction in the separating sheet and of axial dispersion in the fluids on the transient response has been investigated. A comparison of the dynamic behavior of four possible arrangements of three-fluid crossflow heat exchangers has also been presented.

Transient Behavior of Crossflow Heat Exchangers With Longitudinal Conduction and Axial Dispersion

2004 ◽  
Vol 126 (3) ◽  
pp. 425-433 ◽  
Author(s):  
Manish Mishra ◽  
P. K. Das ◽  
Sunil Sarangi
Keyword(s):  
Heat Transport ◽  
Heat Exchangers ◽  
Temperature Response ◽  
Transient Behavior ◽  
Axial Dispersion ◽  
Transient Temperature ◽  
Inlet Temperature ◽  
Conductive Heat ◽  
Two Dimensional ◽  
Transient Temperature Response

Transient temperature response of the crossflow heat exchangers with finite wall capacitance and both fluids unmixed is investigated numerically for step, ramp and exponential perturbations provided in hot fluid inlet temperature. Effect of two-dimensional longitudinal conduction in separating sheet and axial dispersion in fluids on the transient response has been investigated. Conductive heat transport due to presence of axial dispersion in fluids have been analyzed in detail and shown that presence of axial dispersion in both of the fluid streams neutralizes the total conductive heat transport during the energy balance. It has also been shown that the presence of axial dispersion of high order reduces the effect of longitudinal conduction.

Transient Behavior of Crossflow Heat Exchangers Due To Sinusoidal Excitation

2010 ◽  
Vol 132 (9) ◽  
Author(s):  
Manish Mishra ◽  
P. K. Das ◽  
Sunil Sarangi
Keyword(s):  
Heat Exchangers ◽  
Present Method ◽  
Good Accuracy ◽  
Temperature Response ◽  
Transient Behavior ◽  
Graphical Form ◽  
Transient Temperature ◽  
Inlet Temperature ◽  
Transient Temperature Response ◽  
Sinusoidal Excitation

Transient temperature response of crossflow heat exchangers with both fluids unmixed and finite wall capacitance is investigated numerically for sinusoidal excitation provided in hot fluid inlet temperature. The effect of two-dimensional longitudinal conduction in separating sheet and the axial dispersion in fluids has also been considered on the thermal performance of the heat exchanger. The present method has good accuracy and simplicity. An attempt has also been made to study the performance of the sinusoidal excitation in the graphical form.

scholarly journals A New Analytical Model for Calculating Transient Temperature Response of Vertical Ground Heat Exchangers with a Single U-Shaped Tube

Energies ◽  
2020 ◽  
Vol 13 (8) ◽  
pp. 2120
Author(s):  
Shichen Gao ◽  
Changfu Tang ◽  
Wanjing Luo ◽  
Jiaqiang Han ◽  
Bailu Teng
Keyword(s):  
Analytical Model ◽  
Transient Response ◽  
Heat Exchangers ◽  
Temperature Response ◽  
Thermal Response ◽  
Thermal Storage ◽  
Transient Temperature ◽  
Ground Heat Exchangers ◽  
Proposed Model ◽  
Transient Temperature Response

The transient temperature response is of great importance for evaluating the thermal capacity of ground heat exchangers (GHE). Based on the composition line source theory and superposition principle, we have developed a novel analytical model in Laplace space for calculating the temperature transient response. In comparison to the existing models, this proposed model can account for the fluid thermal storage effect and heat rate difference between the two legs of the single U-tube. With the aid of this proposed model, we conduct a thorough sensitivity analysis to investigate the effects of different influencing factors on the thermal transient response. The calculated results show that fluid thermal storage and the rate difference can significantly influence the thermal response during the early studied period. Therefore, the effect of fluid thermal storage should not be neglected when the early-time thermal response is investigated. The thermal interference between the two legs will reduce the heat capacity of GHEs. A large distance between these two legs can be favorable for practical use.

Experimental and Theoretical Analysis of Transient Response of Plate Heat Exchangers in Presence of Nonuniform Flow Distribution

2008 ◽  
Vol 130 (5) ◽  
Author(s):  
N. Srihari ◽  
Sarit K. Das
Keyword(s):  
Steady State ◽  
Heat Exchangers ◽  
Sudden Change ◽  
Temperature Response ◽  
Flow Distribution ◽  
Transient Temperature ◽  
Nonuniform Flow ◽  
Flow Rates ◽  
Plate Heat ◽  
Flow Maldistribution

Transient analysis helps us to predict the behavior of heat exchangers subjected to various operational disturbances due to sudden change in temperature or flow rates of the working fluids. The present experimental analysis deals with the effect of flow distribution on the transient temperature response for U-type and Z-type plate heat exchangers. The experiments have been carried out with uniform and nonuniform flow distributions for various flow rates. The temperature responses are analyzed for various transient characteristics, such as initial delay and time constant. It is also possible to observe the steady state characteristics after the responses reach asymptotic values. The experimental observations indicate that the Z-type flow configuration is more strongly affected by flow maldistribution compared to the U-type in both transient and steady state regimes. The comparison of the experimental results with numerical solution indicates that it is necessary to treat the flow maldistribution separately from axial thermal dispersion during modeling of plate heat exchanger dynamics.

A Comparative Analysis of Thermal Blood Perfusion Measurement Techniques

1987 ◽  
Vol 109 (3) ◽  
pp. 218-225 ◽  
Author(s):  
R. Kress ◽  
R. Roemer
Keyword(s):  
Blood Flow ◽  
Steady State ◽  
Time Window ◽  
Measurement Techniques ◽  
Temperature Response ◽  
Blood Perfusion ◽  
Analytical Models ◽  
Transient Temperature ◽  
Two Dimensional ◽  
Transient Heating

The object of this study was to devise a unified method for comparing different thermal techniques for the estimation of blood perfusion rates and to perform a comparison for several common techniques. The approach used was to develop analytical models for the temperature response for all combinations of five power deposition geometries (spherical, one- and two-dimensional cylindrical, and one- and two-dimensional Gaussian) and three transient heating techniques (temperature pulse-decay, temperature step function, and constant-power heat-up) plus one steady-state heating technique. The transient models were used to determine the range of times (the time window) when a significant portion of the transient temperature response was due to blood perfusion. This time window was defined to begin when the difference between the conduction-only and the conduction-plus-blood flow transient temperature (or power) responses exceeded a specified value, and to end when the conduction-plus-blood flow transient temperature (or power) reached a specified fraction of its steady-state value. The results are summarized in dimensionless plots showing the size of the time windows for each of the transient perfusion estimation techniques. Several conclusions were drawn, in particular: (a) low perfusions are difficult to estimate because of the dominance of conduction, (b) large heated regions are better suited for estimation of low perfusions, (c) noninvasive heating techniques are superior because they have the potential to minimize conduction effects, and (d) none of the transient techniques appears to be clearly superior to the others.

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