and

1

^eoSeo

1

h

co co

(14)

(15)

Zi

Z

9

Zi and Z9 The thermal resistance between the heat source and the external surface of the evaporator and between the external surface of the condenser and the heat sink respectively are given by

evaporative and

Z2 and Z8 are the thermal resistances across the thickness of the tube wall in the the condenser respectively, which is determined as

Цр./р,)

2nlek

and

(17)

7 = ln(D,/D)

8 2nlck

2.2.1 Internal resistant.

Z3p =

______ 1______ Ф3д°’20°’4 (iDLe)0-6

(18)

Z3 and Z7 are the internal resistances due to pool and film boiling of the working fluid which is divided into Z3p is resistant from pool boiling:

Z3f is resistant from film boiling at the evaporator section :

Z = CQ13

3f " Бі4/У/3ЬєФ 24/3 (19)

when g is gravity (m/s2)

C is constant of cylinder tube C = (1/4)(3/n)43 = 0.235

Ф2 is Figure of Merit:

(20)

( 3 2 у ‘ "

Lkl Pl

,l

L is Latent heat of working fluid (kJ/kg)

kl is thermal conductivity of working fluid as liquid phase (W/moC) pl is density of working fluid as liquid phase (kg/m3)

, is viscosity of working fluid as liquid phase (N/m)

: Ф

3

= 0.325 x

0.5^0.3~ 0.7 pl kl Cpl p 0.25, 0.4,, 0.1 pv L Ul

(21)

0.23

Ф3 Figure of Merit (3)

Cpl is the specific heat at constant pressure of working fluid as liquid phase (kJ/kgoC)

pv is the density of working fluid as vapor phase (kg/m3)

Pv is the vapor pressure of working fluid (Pa)

Pa is the atmospheric pressure 101.3 kPa and the condition for using Z3p and Z3f as Z3 is if Z3p > Z3f so

Z3 = Z3p

if Z3p < Z3f so

Z3 = Z3PF+Z3f(1-F) (22)

when F is the filling ratio that is defined by

Vi

F =

(23)

ALe

Vl is the volume of working fluid (m3)

A is the area cross section of the pipe (m2)

Z7

(24)

CQ1/3 g1/3LcФ

4/3 2

Z7 is the resistance from film boiling of working fluid at the condenser section

Z4 and Z6 are the thermal resistances that occur at the vapor liquid interface in the evaporator and the condenser respectively. These are always neglected, being exceedingly small.

Z5 is the effective thermal resistance due to the pressure drop of the vapor as it flows from the evaporative to the condenser. It is small compared to Z3 and Z7.

Z10 is the axial thermal resistance of the wall of the container. This is always neglected, being exceedingly small. Due to Z4,Z6,Z5 and Z10 always being neglected because of being exceedingly small, thus the overall thermal resistance is approximated by

(25)

Ztotal = Z1 + Z2 + Z3 + Z7 + Z8 + Z9