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Numerical modeling of incline plate LiBr absorber

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Abstract

Among major components of LiBr–H2O absorption chillers is the absorber, which has a direct effect on the chillier size and whose characteristics have significant effects on the overall efficiency of absorption machines. In this article, heat and mass transfer process in absorption of refrigerant vapor into a lithium bromide solution of water-cooled incline plate absorber in the Reynolds number range of 5 < Re < 150 is performed numerically. The boundary layer assumptions are used for the mass, momentum and energy transport equations and the fully implicit finite difference method is employed to solve the governing equations. Dependence of lithium bromide aqueous properties to the temperature and concentration is employed as well as dependence of film thickness to vapor absorption. An analysis for linear distribution of wall temperature condition carries out to investigate the reliability of the present numerical method through comparing with previous investigation. The effect of plate angle on heat and mass transfer parameters is investigated and the results show that absorption mass flux and heat and mass transfer coefficient increase as the angle of the plate increase. The main parameters of absorber design, namely Nusselt and Sherwood numbers, are correlated as a function of Reynolds Number and the plate angle.

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Abbreviations

D :

Mass diffusivity (m2/s)

g :

Gravitational acceleration (m/s2)

h fg :

Heat of absorption (J/kg)

h m :

Local mass transfer coefficient (m/s)

\( \bar{h}_{\text{m}} \) :

Average mass transfer coefficient (m/s)

h t :

Local heat transfer coefficient (W/m2 K)

\( \bar{h}_{\text{t}} \) :

Average heat transfer coefficient (W/m2 K)

k :

Thermal conductivity (W/m K)

L :

Plate length (m)

M abs :

Average mass flux (kg/m2 s)

m abs :

Absorption mass flux (kg/m2 s)

M :

Number of nodes in ε direction

N :

Number of nodes in η direction

Nu :

Nusselt number

P :

Absorber pressure (Pa)

Pr :

Prandtl number = υ/α

q :

Heat flux (W/m2)

Re :

Reynolds number

Sc :

Schmidt number = υ/D

Sh :

Sherwood number

T :

Temperature (°C)

x :

Axis to flow direction (m)

y :

Axis perpendicular to flow direction (m)

u :

Velocity in x direction (m/s)

v :

Velocity in y direction (m/s)

θ :

Plate angle (degree)

α:

Thermal diffusivity (m2/s)

δ:

Film thickness (m)

ε:

Non-dimensional x axis

Г:

Film flow rate (kg/m s)

η:

Non-dimensional y axis

μ:

Solution viscosity (kg/m s)

υ:

Kinematic viscosity (m2/s)

ρ:

Solution density (kg/m3)

ω:

Salt (LiBr) mass concentration in the solution

abs:

Absorption

b:

Bulk

c:

Cooling water

e:

Equilibrium

f:

Film

in:

Inlet

out:

Outlet

surf:

Surface

s:

Solution

w:

Wall

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Authors and Affiliations

  1. School of Mechanical Engineering, Sharif University of Technology, 11155-9567, Tehran, Iran

    Shahram Karami & Bijan Farhanieh

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  1. Shahram Karami
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  2. Bijan Farhanieh
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Correspondence to Shahram Karami.

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Karami, S., Farhanieh, B. Numerical modeling of incline plate LiBr absorber. Heat Mass Transfer 47, 259–267 (2011). https://doi.org/10.1007/s00231-010-0715-2

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  • DOI: https://doi.org/10.1007/s00231-010-0715-2

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