Transient Temperature Fields in Crossflow Heat Exchangers With Finite Wall Capacitance

1988 ◽  
Vol 110 (1) ◽  
pp. 49-53 ◽  
Author(s):  
M. Spiga ◽  
G. Spiga
Keyword(s):  
Heat Capacity ◽  
Heat Exchangers ◽  
Green's Functions ◽  
Green’S Functions ◽  
Temperature Fields ◽  
Transient Temperature ◽  
Inlet Temperature ◽  
Transform Method ◽  
Transfer Resistance ◽  
Primary Fluid

Solutions are provided in nondimensional form for the transient analysis of direct-transfer crossflow heat exchangers, with both fluids unmixed and finite wall heat capacity. The two-dimensional transient temperature distributions of core wall and both fluids are determined by analytical methods for any externally applied variation of the primary fluid inlet temperature. The general solutions are derived by the local energy balance equations, and are presented as simple integrals of the Green’s functions, which represent the pulse response following a deltalike perturbation in the inlet temperature of the primary fluid, and are deduced using the Laplace transform method. The Green’s functions are expressed as integrals of modified Bessel functions, in terms of the heat capacity ratios, number of transfer units, heat transfer resistance and flow capacitance ratios.

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.

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.

scholarly journals A Series Solution for Heat Conduction Problem with Phase Change in a Finite Slab

2014 ◽  
Vol 2014 ◽  
pp. 1-9 ◽  
Author(s):  
Ryoichi Chiba
Keyword(s):  
Heat Capacity ◽  
Phase Change ◽  
Temperature Profile ◽  
Series Solution ◽  
Thermal Loading ◽  
Heat Conduction Problem ◽  
Finite Thickness ◽  
Transient Temperature ◽  
Temperature Dependent ◽  
Transform Method

A two-dimensional differential transform method is applied to solve one-dimensional phase change problems in a slab of finite thickness, which is subjected to convective thermal loading at one surface and a constant prescribed temperature at the other. In the problems, the initial temperature of the slab does not necessarily have to be the same as the fusion temperature. A series solution is derived for the temperature profile in the melting or solidifying slab with temperature-dependent thermal conductivity and volumetric heat capacity. The latent heat effect of the phase change is incorporated into the temperature-dependent heat capacity. Numerical results demonstrate the effects of the temperature-dependent parameters on the transient temperature profile of the slab.

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.

Heat Exchanger Efficiency

2006 ◽  
Vol 129 (9) ◽  
pp. 1268-1276 ◽  
Author(s):  
Ahmad Fakheri
Keyword(s):  
Heat Capacity ◽  
Heat Exchanger ◽  
Temperature Difference ◽  
Heat Exchangers ◽  
Second Law Of Thermodynamics ◽  
Arithmetic Mean ◽  
Inlet Temperature ◽  
Mean Temperature ◽  
Flow Heat ◽  
The Ideal

This paper provides the solution to the problem of defining thermal efficiency for heat exchangers based on the second law of thermodynamics. It is shown that corresponding to each actual heat exchanger, there is an ideal heat exchanger that is a balanced counter-flow heat exchanger. The ideal heat exchanger has the same UA, the same arithmetic mean temperature difference, and the same cold to hot fluid inlet temperature ratio. The ideal heat exchanger’s heat capacity rates are equal to the minimum heat capacity rate of the actual heat exchanger. The ideal heat exchanger transfers the maximum amount of heat, equal to the product of UA and arithmetic mean temperature difference, and generates the minimum amount of entropy, making it the most efficient and least irreversible heat exchanger. The heat exchanger efficiency is defined as the ratio of the heat transferred in the actual heat exchanger to the heat that would be transferred in the ideal heat exchanger. The concept of heat exchanger efficiency provides a new way for the design and analysis of heat exchangers and heat exchanger networks.

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.

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