United States Air and Radiation EPA/430/R-92/009

Environmental Protection (ANR-445) October 1992

Agency

EPA Finite Element Analysis of Heat

Transfer Through the Gasket

Region of Refrigerator/Freezers

Printed on Recycled Paper

 EE-RM-93-801 COMMENT OR6

&EPA 

United States 

Environmental Protection 

Agency 

Air and Radiation 

(ANR-445) 

EPAl430/R-921009 

October 1992 

Finite Element Analysis of Heat 

Transfer Through the Gasket 

Region of 'Refrigerator/Freezers 

@ Printed on Recycled Paper 
Finite Element Analysis of Heat Transfer

through the Gasket Region of Refrigerator/Freezers

BY

Shirley Flynn and Keith Rouch

Department of Mechanical Engineering

University of Kentucky, Lexington, KY 40506

and

H. Alan Fine

Global Change Division

U.S.-E.P.A., Washington, DC 20460

October 1992

 EE-RM-93-801 COMMENT OR6

Finite Element Analysis of Heat Transfer 

through the Gasket Region of Refrigerator/Freezers 

BY 

Shirley Flynn and Keith Rouch 

Department of Mechanical Engineering 

University of Kentucky, Lexington, KY 40506 

and 

H. Alan Fine 

Global change Division 

U.S.-E.P.A., Washington, DC 20460 

october 1992 
Finite Element Analysis of Heat Transfer

through the Gasket Region of Refrigerator / Freezers

ABSTRACT

Heat flow through the gasket region of a refrigerator/freezer (R/F) cabinet is a significant fraction of the total R/F

thermal load. Reductions in this mode of heat transfer will thus

result in lower R/F energy consumption.

Finite element analyses (FEA) of two gasket used in U. S.

R/Fs are developed. These models show that the thermal properties of the gasket have little influence on heat transfer in the

gasket region, while heat flow down the metal door and cabinet

flanges greatly impacted the overall rate of heat transfer into

the cabinet.

Gasket designs incorporating the modifications suggested by

the FEA were developed and tested in prototype R/Fs. Total R/F

energy consumption reductions of 5 to 8 percent were achieved.

These reductions were slightly less than the 5 to 11 percent

reductions predicted by the models.

ii

 EE-RM-93-801 COMMENT OR6

Finite Element Analysis of Heat Transfer 

through the Gasket Region of Refrigerator/Freezers 

ABSTRACT 

Heat flow through the gasket region of a refrigerator/freezer (R/F) cabinet is a significant fraction of the total R/F 

thermal load. Reductions in this mode of heat transfer will thus 

result in lower R/F energy consumption. 

Finite element analyses (FEA) of two gasket used in U. S. 

R/Fs are developed. These models show that the thermal properties of the gasket have little influence on heat transfer in the 

gasket region, while heat flow down the metal door and cabinet 

flanges greatly impacted the overall rate of heat transfer into 

the cabinet. 

Gasket designs incorporating the modifications suggested by 

the FEA were developed and tested in prototype R/Fs. Total R/F 

energy consumption reductions of 5 to 8 percent were achieved. 

These reductions were slightly less than the 5 to 11 percent 

reductions predicted by the models. 

ii 
Contents

Abstract ..................................................... ii

Figures ...................................................... iv

Tables ..................... v ..................................

Introduction , ......... o ... o .............. o ................. 1

Finite Element Models ... ........... o ............. oo .......... 2

FEA Results - Current Designs ................................ 6

FEA Results - New Designs...: 14

Measurements - New Designs ................................... 26

Conclusions .................................................. 28

Acknowledgements ............................................. 29

References ................................................... 29

iii

 EE-RM-93-801 COMMENT OR6

contents 

Abstract. 

Figures. 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

. . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Tables ........................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Introduction. 

Finite Element Models ..•. 

FEA Results Current Designs. • • • • • • • • • • • • • • • • • • • • 0 • • • • • • • • • • 

FEA Results 

Measurements 

New Designs .. • • 0 • • • • 0 • • • • • • • • • • • • • • • • • • 0 • • • • 

New Designs ..•...•.•......•......•....•.•...•. 

ii 

iv 

v 

1 

2 

6 

14 

26 

Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 

Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

References ................................................ . 

iii 

29 

29 
Figures

Number

1 Finite element model of SubZero gasket region ............. 3

2 Finite element model of GE gasket region .................. 4

3 Temperature profiles in SubZero gasket . ................... 8

4 Temperature profiles in SubZero gasket

without decorative cover .................................. 10

5 Finite element model for the GE gasket

including the foam in the door and cabinet ................ 11

6 Temperature profiles in GE gasket ......................... 12

7 Finite element model and temperature profiles

for modified SubZero gasket containing a low

conductivity gas .......................................... 15

8 Finite element model and temperature profiles for

modified GE gasket containing a low conductivity gas ...... 16

9 Finite element model and temperature profiles for

uncoupled heat flow in modified SubZero gasket ............ 18

10 Finite element model and temperature profiles for

modified SubZero gasket region which includes a

plastic clip and approximately half plastic door

and cabinet flanges ...................................... 20

11 Finite element model and temperature profiles for

modified GE gasket region which includes a plastic

clip and approximately half plastic door and cabinet

flanges .................................................. 21

12 SubZero gasket region load reductions for various

flange modifications ...................................... 22

13 GE gasket region load reductions for various flange

modifications ............................................ 25

iv

 EE-RM-93-801 COMMENT OR6

Figures 

Number 

1 Finite element model of SubZero gasket region .........•.•. 3 

2 Finite element model of GE gasket reg10n .................. 4 

3 Temperature profiles in SubZero gasket .... 0 •••••••• 0 •••••• 8 

4 Temperature profiles in SubZero gasket 

without decorative cover .................................. 10 

5 Finite element model for the GE gasket 

including the foam in the door and cabinet .•.•....•...•... 11 

6 Temperature profiles in GE gasket •..•..••....••........... 12 

7 Finite element model and temperature profiles 

for modified SubZero gasket containing a low 

conducti vi ty gas .......................... 0 • • • • • • • • • • • • • • • 15 

8 Finite element model and temperature profiles for 

modified GE gasket containing a low conductivity gas ..•... 16 

9 Finite element model and temperature profiles for 

uncoupled heat flow in modified SubZero gasket •••........• 18 

10 Finite element model and temperature profiles for 

modified SubZero gasket region which includes a 

plastic clip and approximately half plastic door 

and cabinet flanges...................................... 20 

11 Finite element model and temperature profiles for 

modified GE gasket region which includes a plastic 

clip and approximately half plastic door and cabinet 

flanges ........ 0 •••••••••••••••••••••••••••••••••••• CI • • • • 21 

12 SubZero gasket region load reductions for various 

flange modifications...................................... 22 

13 GE gasket region load reductions for various flange 

modifications ......................... 0 • • • • • • • • • • • • • • • • • • 25 

iv 
Tables

Number

1 Properties of Materials ................................... 5

2 Variation of SubZero Gasket-Region U-value

with R/ F Temperatures .................................... 6

3 Variation of SubZero Gasket-Region U-Values

with Heat Transfer Coefficients ........................... 7

4 Effect of Flange/Foam Boundary Condition on

Overall Gasket Heat Transfer Coefficient .................. 13

5 Comparison of U-values for'Gaskets containing

Air and Krypton ........................................... 14

6 Comparison of U-values for the SubZero Gasket

with Coupled and Uncoupled Flanges . ....................... 17

7 U-Values for SubZero Gasket Region with a Portion

of the Flanges changed to Plastic ......................... 23

8 U-Values for GE Gasket Region with a Portion of

the Flanges changed to Plastic ............................ 24

9 Effect of Flange/ Foam Boundary Condition on

U-Value of Modified GE Gasket Region ...................... 26

v

 EE-RM-93-801 COMMENT OR6

Tables 

Number 

1 Properties of Materials...................... . . . . . . . . • . . • . 5 

2 Variation of SubZero Gasket-Region U-value 

wi th R/ F Temperatures ...•.................. 0 • • • • • • • • • • • • • 6 

3 Variation of SubZero Gasket-Region U-Values 

with Heat Transfer Coefficients ....••••.•..•.•.•...... ~... 7 

4 Effect of Flange/Foam Boundary Condition on 

Overall Gasket Heat Transfer Coefficient .....•............ 13 

5 comparison of U-values for'Gaskets containing 

Air and Krypton .. III ••••••••••••••••••••••••• 0 •••• III •• 0 • • • • • • 14 

6 Comparison of U-values for the SubZero Gasket 

with Coupled and Uncoupled Flanges .•.•.......•.........•.. 17 

7 U-Values for SubZero Gasket Region with a Portion 

of the Flanges changed to Plastic ...........•...........•. 23 

8 U-Values for GE Gasket Region with a Portion of 

the Flanges changed to Plastic .........................•.. 24 

9 Effect of Flange/Foam Boundary Condition on 

U-Value of Modified GE Gasket Region .•................•... 26 

v 
INTRODUCTION

Heat transfer through the gasket region significantly

contributes to the thermal load through the refrigerator/freezer

(R/F) cabinet . Recent finite element analyses of

refrigerator/freezers to assess the impact of the addition of

super insulation on the energy consumption of R/Fs showed approximately 25 percent of the total thermal load entered the cabinet

through the gasket region , i.e. the gasket and flanges. (1) This

load increased to over 35 percent of the total for a cabinet

that was nearly completely covered with super insulation. Clearly, heat transfer through the gasket region is an important

portion of the overall heat transfer flux, and becomes even more

important as the rest of the cabinet becomes more insulated.

Analyses and tests performed in the design of a super efficient R/F in 1980 ( 2) demonstrated that the heat flow through the

gasket region could be halved with the addition of a second

gasket. Difficulties in implementing the double-gasket concept,

however, have prevented its use in production units.

This report presents the results of finite element analysis

(FEA) of heat flow through two gasket/flange designs employed in

1991 in U.S. refrigerator/freezers . Modifications to the designs

that could yield significant R/F thermal load reductions are also

presented and evaluated.

1

 EE-RM-93-801 COMMENT OR6

INTRODUCTION 

Heat transfer through the gasket region significantly 

contributes to the thermal load through the refrigerator/freezer 

(R/F) cabinet. Recent finite element analyses of 

refrigerator/freezers to assess the impact of the addition of 

super insulation on the energy consumption of R/Fs showed approximately 25 percent of the total thermal load entered the cabinet 

through the gasket region, i~e. the gasket and flanges. (1) This 

load increased to over 35 percent of the total for a cabinet 

that was nearly completely covered with super insulation. Clearly, heat transfer through the gasket region is an important 

portion of the overall heat transfer flux, and becomes even more 

important as the rest of the cabinet becomes more insulated. 

Analyses and tests performed in the design of a super efficient R/F in 1980 (2) demonstrated that the heat flow through the 

gasket region could be halved with the addition of a second 

gasket. Difficulties in implementing the double-gasket concept, 

however, have prevented its use in production units. 

This report presents the results of finite element analysis 

(FEA) of heat flow through two gasket/flange designs employed in 

1991 in U.s. refrigerator/freezers. Modifications to the designs 

that could yield significant R/F thermal load reductions are also 

presented and evaluated. 

1 
FINITE ELEMENT MODELS

Two gasket designs were selected for analysis in this study,

a gasket employed in SubZero side by side models and a gasket

used in General Electric top-mount freezer units. These gaskets

represent the extremes of complexity of cross section designs for

gaskets found in U.S. R/Fs.

Gasket dimensions were obtained for the finite element

analyses by cutting the gaskets perpendicular to their length.

Photographic transparencies of the cross sections were then made

and projected onto a sheet of paper . The approximately seven

times enlarged images were then traced and measured . Correct

dimensions were achieved by including a scale in the photographs

of the gaskets . Gasket thicknesses of 0.48 and 0.56 inches were

found for the SubZero and GE gaskets, respectively.

Analyses were performed for the gasket region which included the gasket, mounting clip, flanges and a small portion of

the outer steel case . A small portion of the liner and foam

insulation was also included in several analyses of the GE gasket

region. Flanges, mounting clip, case and liner were assumed to

have a thickness of 0.024 inches. The finite element models of

the Subzero and GE gasket regions are shown in Figures 1 and 2.

The thermal conductivity for the plastic gasket material and

liner, flexible gasket magnet, air contained within the gasket,

and metal flanges, clip and case used in this analysis are shown

in Table 1. Engineering units and the values used by the finite

element code ANSYS are given.

2

 EE-RM-93-801 COMMENT OR6

FINITE ELEMENT MODELS 

Two gasket designs were selected for analysis in this study, 

a gasket employed in SubZero side by side models and a gasket 

used in General Electric top-mount freezer units. These gaskets 

represent the extremes of complexity of cross section designs for 

gaskets found in U.S. R/Fs. 

Gasket dimensions were obtained for the finite element 

analyses by cutting the gaskets perpendicular to their length. 

Photographic transparencies of the cross sections were then made 

and projected onto a sheet of paper. The approximately seven 

times enlarged images were then traced and measured. Correct 

dimensions were achieved by including a scale in the photographs 

of the gaskets. Gasket thicknesses of 0.48 and 0.56 inches were 

found for the SubZero and GE gaskets, respectively. 

Analyses were performed for the gasket region which included the gasket, mounting clip, flanges and a small portion of 

the outer steel case. A small portion of the liner and foam 

insulation was also included in several analyses of the GE gasket 

region. Flanges, mounting clip, case and liner were assumed to 

have a thickness of 0.024 inches. The finite element models of 

the SubZero and GE gasket regions are shown in Figures 1 and 2. 

The thermal conductivity for the plastic gasket material and 

liner, flexible gasket magnet, air contained within the gasket, 

and metal flanges, clip and case used in this analysis are shown 

in Table 1. Engineering units and the values used by the finite 

element code ANSYS are given. 

2 
Figure 1. Finite element model of SubZero gasket region. Black

areas within model represent metal components, dark

gray are plastic and light gray are air.

3

 EE-RM-93-801 COMMENT OR6

Figure 1. Finite element model of SubZero gasket region. Black 

areas within model represent metal components, dark 

gray are plastic and light gray are air. 

3 
Figure 2. Finite element model of GE gasket region. Black areas

within model represent metal components , dark gray are

plastic and light gray are air.

4

 EE-RM-93-801 COMMENT OR6

Figure 2. Finite element model of GE gasket region. Black areas 

within model represent metal components, dark gray are 

plastic and light gray are air. 

4 
Table 1. Properties of Materials

M t i l

Thermal Conductivity

a er a

Engineering Units ANSYS Units

(BTU*in)/(hr*ft2*°F) (BTU* in)/(hr*in2*OF)

Plastic 1.016 0.007055

Magnet 1.016 0.007055

Air 0.18 0.00125

Metal 315 . 0 2.1875

Convection heat transfer boundary conditions were employed

for the inner and outer surfaces. In most calculations, heat

transfer from the flanges or case to the foam insulation which

fills the R/F doors and walls was assumed to be negligible compared to that along the metal piece. The foam / metal surfaces

were, thus , assumed adiabatic . Convection within the gasket

pockets was also assumed to be negligible.

Total heat flow rates through the gasket and flanges were

calculated in the postprocessing module of ANSYS by summing the

fluxes out of the elements which would constitute the surfaces of

the gasket and flanges on the inside of the R/F. The overall

heat transfer coefficient, U or U-value , was calculated from the

following equation:

U=Q / dT

where Q was the total heat transfer rate out of the gasket region , and dT was the overall temperature difference.

5

 EE-RM-93-801 COMMENT OR6

Table 1. Properties of Materials 

Thermal Conductivity 

Material 

Engineering units ANSYS units 

(BTU*in)/(hr*ft 2 *oF) (BTU*in)/(hr*in2 *oF) 

Plastic 1.016 0.007055 

Magnet 1.016 0.007055 

Air 0.18 0.00125 

Metal 315.0 2.1875 

Convection heat transfer boundary conditions were employed 

for the inner and outer surfaces. In most calculations, heat 

transfer from the flanges or case to the foam insulation which 

fills the R/F doors and walls was assumed to be negligible compared to that along the metal piece. The foam/metal surfaces 

were, thus, assumed adiabatic. Convection within the gasket 

pockets was also assumed to be negligible. 

Total heat flow rates through the gasket and flanges were 

calculated in the postprocessing module of ANSYS by summing the 

fluxes out of the elements which would constitute the surfaces of 

the gasket and flanges on the inside of the R/F. The overall 

heat transfer coefficient, U or U-value, was calculated from the 

following equation: 

U = Q / dT 

where Q was the total heat transfer rate out of the gasket region, and dT was the overall temperature difference. 

5 
FEA RESULTS - CURRENT DESIGNS

The SubZero gasket region was analyzed with the steel case

extended to form the decorative gasket cover found on production

units, as shown in Figure 1, and with this piece removed. The

results of these analyses and those performed on the GE gasket

follow.

SubZero Gasket - Four combinations of R/F interior temperature, Tin , and ambient temperature,Tout, were analyzed. Since

the thermal conductivities were assumed to be independent of

temperature , the heat transfer rate should be proportional to

Tout-Tin ;

and U should be independent of the temperature difference. Table 2 shows the results for heat transfer coefficients

of 2 Btu/(hr*ft2*°F) at the inner and outer surfaces . The effect

of heat transfer coefficient on the overall heat transfer coefficient is shown in Table 3.

Table 2 . Variation of SubZero Gasket-Region

U-Values with R/F Temperatures

Temperature Total Heat Overall Heat

Tin 1FTout Transfer Rate

Btu/(hr*in)

Trans . Coef f . , U

Btu/(hr*in*°F)

0 & 70 0.2825 4.036E-3

0 & 90 0 .3632 4 . 036E-3

40 & 70 0 .1211 4 .036E-3

40 & 90 0 . 2018 4.036E-3

6

 EE-RM-93-801 COMMENT OR6

FEA RESULTS - CURRENT DESIGNS 

The SubZero gasket region was analyzed with the steel case 

extended to form the decorative gasket cover found on production 

units, as shown in Figure 1, and with this piece removed. The 

results of these analyses and those performed on the GE gasket 

follow. 

SubZero Gasket - Four combinations of R/F interior temperature, Tin' and ambient temperature,Tout ' were analyzed. Since 

the thermal conductivities were assumed to be independent of 

temperature, the heat transfer rate should be proportional to 

Tout-Tin; and U should be independent of the temperature difference. Table 2 shows the results for heat transfer coefficients 

of 2 Btu/(hr*ft 2 *oF) at the inner and outer surfaces. The effect 

of heat transfer coefficient on the overall heat transfer coefficient is shown in Table 3. 

Table 2. Variation of SubZero Gasket-Region 

U-Values with R/F Temperatures 

Temperature Total Heat Overall Heat 

Tin & Tout Transfer Rate Trans. Coeff. , of Btu/(hr*in) Btu/(hr*in*oF) 

0 & 70 0.2825 4.036E-3 

0 & 90 0.3632 4.036E-3 

40 & 70 0.1211 4.036E-3 

40 & 90 0.2018 4.036E-3 

6 

U 
Table 3. Variation of SubZero Gasket-Region U-Values with

Heat Transfer Coefficients

Surface Heat

Trans. Coefficient

Btu/ (hr*ft2 * °F)

Overall Heat

Trans. Coeff., U

Btu/(hr*in*°F)

Percent Heat

Flow through

Clip & Flanges

1

2

5

10

2.407E-3

4. 036E-3

7. 347E-3

11.22E-3

17.5

21.0

28.8

37.0

The percentage of heat flow through the two metal flanges

plus the metal clip shown in Table 3 is the percentage of the

total energy entering the R/F cabinet from the gasket region as a

result of convection from the ends of the two flanges and the

clip. The heat flow rates from each of these three surfaces were

nearly identical, and thus contributed equally to the total. As

shown in Figure 3 for the 90 °F to 0°F temperature combination and

heat transfer coefficients equal 2 Btu/(hr*ft2*°F), all three

surfaces attain the same temperature . As all three were assumed

to have the same thickness, equal heat transfer rates should

result.

The nonlinear nature of the isotherms shown in Figure 3

indicates that the percentage of heat flow through the flanges

and clip is not indicative of the importance of their influence

on the overall heat transfer process . In fact, nearly all of the

heat entering the outer surface of the gasket region flows down

the metal pieces avoiding the gasket . The heat flow then disperses across the gasket near the inner surface of the R/F, and

then is transferred into the R/F by convection.

Removing the decorative metal cover,- i.e. the extension of

7

 EE-RM-93-801 COMMENT OR6

Table 3. Variation of SubZero Gasket-Region U-Values with 

Heat Transfer Coefficients 

Surface Heat Overall Heat Percent Heat 

Trans. Coefficient Trans. Coeff., U Flow through 

Btu/(hr*ft2*oF) Btu/(hr*in*oF) Clip & Flanges 

1 2.407E-3 17.5 

2 4.036E-3 21.0 

5 7.347E-3 28.8 

10 11.22E-3 37.0 

The percentage of heat flow through the two metal flanges 

plus the metal clip shown in Table 3 is the percentage of the 

total energy entering the R/F cabinet from the gasket region as a 

result of convection from the ends of the two flanges and the 

clip. The heat flow rates from each of these three surfaces were 

nearly identical, and thus contributed equally to the total. As 

shown in Figure 3 for the gooF to OaF temperature combination and 

heat transfer coefficients equal 2 Btu/(hr*ft2 *OF) , all three 

surfaces attain the same temperature. As all three were assumed 

to have the same thickness, equal heat transfer rates should 

result. 

The nonlinear nature of the isotherms shown in Figure 3 

indicates that the percentage of heat flow through the flanges 

and clip is not indicative of the importance of their influence 

on the overall heat transfer process. In fact, nearly all of the 

heat entering the outer surface of the gasket region flows down 

the metal pieces avoiding the gasket. The heat flow then disperses across the gasket near the inner surface of the R/F, and 

then is transferred into the R/F by convection. 

Removing the decorative metal cover, ·i.e. the extension of 

7 
Figure 3. Temperature profiles in SubZero gasket with 00 and

90°F temperature extremes and heat transfer coefficients at the inner and outer surfaces of

2 Btu / ( hr*ft2*OF).

8

 EE-RM-93-801 COMMENT OR6

Figure 3. Temperature profiles in SubZero gasket with 0° and 

gooF temperature extremes and heat transfer coefficients at the inner and outer surfaces of 

2 Btu / (hr*ft 2 *oF). 

8 
the metal case over the gasket shown in Figure 1, had an insignificant effect on the temperature profile, as shown in Figure 4.

The minor changes which occurred were primarily in the higher

temperature isotherms and the overall heat transfer coefficient

increased by less than one percent to 4.069E-3 Btu /( hr*in*OF) at

surface heat transfer coefficients of 2 Btu/( hr*ft2*OF). The

overall heat transfer coefficient increased by about 0.03

Btu/(hr * in*OF ) and the percentage of heat flow through the

flanges and clip increased by about 0.1 percent regardless of the

surface heat transfer coefficients.

GE Gasket - The GE gasket , shown in Figure 2, consists of

the same materials as the SubZero gasket. Calculations were made

with boundary conditions similar to those for the Subzero gasket,

i.e. convection on the inner and outer surfaces and adiabatic

surfaces at the flange / foam and case/foam surfaces. A second set

of calculations in which foam was assumed to conduct heat through

the cabinet and door adjacent to the gasket region was also

performed . The model for this analysis is shown in Figure 5.

The results of the calculations for the 00 to 90°F temperature

extremes and heat transfer coefficients of 2 Btu/(hr*ft2*OF)

differ by approximately two percent , see Table 4. The temperature profiles for the gasket region with adiabatic flange/foam

surfaces are shown in Figures 6.

9

 EE-RM-93-801 COMMENT OR6

the metal case over the gasket shown in Figure 1, had an insignificant effect on the temperature profile, as shown in Figure 4. 

The minor changes which occurred were primarily in the higher 

temperature isotherms and the overall heat transfer coefficient 

increased by less than one percent to 4.069E-3 Btu/(hr*in*oF) at 

surface heat transfer coefficients of 2 Btu/(hr*ft2*oF). The 

overall heat transfer coefficient increased by about 0.03 

Btu/(hr*in*oF) and the percentage of heat flow through the 

flanges and clip increased by about 0.1 percent regardless of the 

surface heat transfer coefficients. 

GE Gasket - The GE gasket, shown in Figure 2, consists of 

the same materials as the SubZero gasket. Calculations were made 

with boundary conditions similar to those for the SubZero gasket, 

i.e. convection on the inner and outer surfaces and adiabatic 

surfaces at the flange/foam and case/foam surfaces. A second set 

of calculations in which foam was assumed to conduct heat through 

the cabinet and door adjacent to the gasket region was also 

performed. The model for this analysis is shown in Figure 5. 

The results of the calculations for the 0° to 90°F temperature 

extremes and heat transfer coefficients of 2 Btu/(hr*ft2*oF) 

differ by approximately two percent, see Table 4. The temperature profiles for the gasket region with adiabatic flange/foam 

surfaces are shown in Figures 6. 

9 
Figure 4. Temperature profiles in SubZero gasket without its

decorative cover at 00 and 90°F temperature extremes

and heat transfer coefficients at the inner and

outer surfaces of 2 Btu / (hr*ft2*°F).

10

 EE-RM-93-801 COMMENT OR6

Figure 4. Temperature profiles in SubZero gasket without its 

decorative cover at 0° and gooF temperature extremes 

and heat transfer coefficients at the inner and 

outer surfaces of 2 Btu / (hr*ft2*oF). 

10 
Figure 5. Finite element model for the GE gasket including the

foam in the door and cabinet adjacent to the flanges.

11

 EE-RM-93-801 COMMENT OR6

Figure 5. Finite element model for the GE gasket including the 

foam in the door and cabinet adjacent to the flanges. 

11 
Figure 6. Temperature profiles in GE gasket with 00 and 90°F

temperature extremes and heat transfer coefficients

at the inner and outer surfaces of

2 Btu / ( hr*ft2*OF).

12

 EE-RM-93-801 COMMENT OR6

Figure 6. Temperature profiles in GE gasket with 0° and gooF 

temperature extremes and heat transfer coefficients 

at the inner and outer surfaces of 

2 Btu / (hr*ft2*oF). 

12 
Table 4. Effect of Flange/Foam Boundary Condition on

Overall Gasket Heat Transfer Coefficient

Flange/Foam Overall Heat Overall Heat

Heat Transfer Transfer Rate Trans. Coef f . , U

Assumption Btu/(hr*in) Btu/(hr*in*°F)

GE

adiabatic 0.5940 6.600E-3

conduction 0.5810 6.456E-3

SubZero

adiabatic 0.3632 4.036E-3

Heat flow through the metal flanges was again approximately

20 percent of the total. The rate from the cabinet flange was

nearly identical to that for the Subzero gasket. The rate for

the door flange was nearly four times higher. This was as ex-.

pected, however, as the door flange extended beyond the gasket

into the R/F and increased its surface area for convection by

about a factor of four.

Convection from the appendage on the inside of the R/F near

the cabinet side on the GE gasket accounted for about 25 percent

of the total heat flow through the gasket/flange region. Excluding heat flow from the flanges and the appendage yields a

total heat flux of 0.3217 Btu/(hr*in). This rate is twelve

percent higher than that for the SubZero gasket, excluding heat

flow through the metal clip and flanges. The GE gasket was 16

percent thicker than the SubZero gasket. Thus comparable heat

flow rates per unit thickness'would occur, if the gaskets had

similar cross sections.

13

 EE-RM-93-801 COMMENT OR6

Table 4. Effect of Flange/Foam Boundary Condition on 

Overall Gasket Heat Transfer Coefficient 

Flange/Foam Overall Heat Overall Heat 

Heat Transfer Transfer Rate Trans. Coeff. , 

Assumption Btu/(hr*in) Btu/(hr*in*oF) 

GE 

adiabatic 0.5940 6.600E-3 

conduction 0.5810 6.456E-3 

SubZero 

adiabatic 0.3632 4.036E-3 

U 

Heat flow through the metal flanges was again approximately 

20 percent of the total. The rate from the cabinet flange was 

nearly identical to that for the SubZero gasket. The rate for 

the door flange was nearly four times higher. This was as expected, however, as the door flange extended beyond the gasket 

into the R/F and increased its surface area for convection by 

about a factor of four. 

Convection from the appendage on the inside of the R/P near 

the cabinet side on the GE gasket accounted for about 25 percent 

of the total heat flow through the gasket/flange region. Excluding heat flow from the flanges and the appendage yields a 

total heat flux of 0.3217 Btu/(hr*in). This rate is twelve 

percent higher than that for the SubZero gasket, excluding heat 

flow through the metal clip and flanges. The GE gasket was 16 

percent thicker than the SubZero gasket. Thus comparable heat 

flow rates per unit thickness' would occur, if the gaskets had 

similar cross sections. 

13 
FEA RESULTS - NEW DESIGNS

Modifications to the current gasket designs including changing the gas inside the gasket and changing the flange design

were evaluated. The results of these calculations are presented

below.

Low Conductivity Gas - Low conductivity gases, such as

krypton, have been proposed as alternatives to polyurethane foams

insulation materials. (3) If the air pockets within the gasket

contribute significantly to reduce the U-value of the gasket,

switching the gas within these pockets to a low conductivity gas

could significantly reduce the U-value of the gasket.

The modified SubZero and GE gasket designs showing the

pockets which contain low conductivity gas are presented in

Figures 7 and 8 . A comparison of the U-values with air and with

krypton in these pockets is shown in Table 5. The conductivity

of krypton was assumed to equal 0.067 (Btu*in)/(hr*ft2*°F), or

about 37 percent that of air, and heat transfer coefficients of 2

Btu/(hr*ft2*° F) were used for these calculations.

Table 5. Comparison of U-values for Gaskets containing

Air and Krypton

G k t

U-Value [Btu/(hr*in*OF)] containing

as e

Air Krypton

SubZero 4.036E-3 3.859E-3

GE 6.600E-3 6.180E-3

14

 EE-RM-93-801 COMMENT OR6

FEA RESULTS - NEW DESIGNS 

Modifications to the current gasket designs including changing the gas inside the gasket and changing the flange design 

were evaluated. The results of ·these calculations are presented 

below. 

Low Conductivity ~ - Low conductivity gases, such as 

krypton, have been proposed as alternatives to polyurethane foams 

insulation materials. (3) If the air pockets within the gasket 

contribute significantly to reduce the U-value of the gasket, 

switching the gas within these pockets to a low conductivity gas 

could significantly reduce the U-value of the gasket. 

The modified SubZero and GE gasket designs showing the 

pockets which contain low conductivity gas are presented in 

Figures 7 and 8. A comparison of the U-values with air and with 

krypton in these pockets is shown in Table 5. The conductivity 

of krypton was assumed to equal 0.067 (Btu*in)/(hr*ft 2 *OF) , or 

about 37 percent that of air, and heat transfer coefficients of 2 

Btu/(hr*ft 2 *OF) were used for these calculations. 

Table 5. Comparison of U-values for Gaskets containing 

Air and Krypton 

U-Value [Btu/(hr*in*oF)] containing 

Gasket 

Air Krypton 

SubZero 4.036E-3 3.859E-3 

GE 6.600E-3 6.180E-3 

14 
Figure 7. Finite element model and temperature profiles for

modified SubZero gasket containing a low conductivity

gas (white areas within gasket).

15

 EE-RM-93-801 COMMENT OR6

Figure 7. Finite element model and temperature profiles for 

modified SubZero gasket containing a low conductivity 

gas (white areas within gasket). 

15 
Figure 8. Finite element model and temperature profiles for

modified GE gasket containing a low conductivity gas

(white areas within gasket).

16

 EE-RM-93-801 COMMENT OR6

Figure 8. Finite element model and temperature profiles for 

modified GE gasket containing a low conductivity gas 

(white areas within gasket) . 

16 
The overall SubZero and GE gasket heat transfer coefficients

were reduced by 4.4 and 6.4 percent, respectively. While-the

reductions are significant , it is relatively small compared to

the 63 percent reduction in the thermal conductivity of the gas

in the pockets . As pointed out earlier, the temperature profiles

within the gasket indicate that heat flows down the metal flanges

and then across the inner portion of the gasket . Thus, changing

the rate of heat flow through the flanges and not the thermal

resistance of the gasket by changing the gas within it, should

have a larger impact on the gasket -region U-value.

Flange Modifications - The hypotheses that heat flow down

the flanges was of primary importance to the overall heat flow

problem was tested by uncoupling the flanges from the SubZero

gasket . This was accomplished in the model by "inserting" an

adiabatic surface between the flanges and the gasket . The result

was a nearly 50 percent reduction in the U-value of the gasket

region, see Table 6.

Table 6. Comparison of U-values for the SubZero Gasket

with Coupled and Uncoupled Flanges

Ga k t

U-Value [ Btu/(hr * in*°F)] containing

s e

Air Krypton

coupled 4.036E-3 3.859E-3

uncoupled 2.139E- 3 1.949E-3

The temperature profiles for the uncoupled model presented

in Figure 9 show that heat must now flow through the gasket when

the flanges are uncoupled from the gasket. Furthermore, while

17

 EE-RM-93-801 COMMENT OR6

The overall SubZero and GE gasket heat transfer coefficients 

were reduced by 4.4 and 6.4 percent, respectively. While'the 

reductions are significant, it is relatively small compared to 

the 63 percent reduction in the thermal conductivity of the gas 

in the pockets. As pointed out earlier, the temperature profiles 

within the gasket indicate that heat flows down the metal flanges 

and then across the inner portion of the gasket. Thus, changing 

the rate of heat flow through the flanges and not the thermal 

resistance of the gasket by changing the gas within it, should 

have a larger impact on the gasket-region U-value. 

Flange Modifications - The hypotheses that heat flow down 

the flanges was of primary importance to the overall heat flow 

problem was tested by uncoupling the flanges from the SubZero 

gasket. This was accomplished in the model by "inserting" an 

adiabatic surface between the flanges and the gasket. The result 

was a nearly 50 percent reduction in the U-value of the gasket 

region, see Table 6. 

Table 6. Comparison of U-values for the SubZero Gasket 

with Coupled and Uncoupled Flanges 

U-Value [Btu/(hr*in*oF)] containing 

Gasket 

Air Krypton 

coupled 4.036E-3 3.859E-3 

uncoupled 2.139E-3 1.949E-3 

The temperature profiles for the uncoupled model presented 

in Figure 9 show that heat must now flow through the gasket when 

the flanges are uncoupled from the gasket.- Furthermore, while 

17 
Figure 9. Finite element model and temperature profiles for

uncoupled heat flow,in modified SubZero gasket. (Adiabatic surfaces between flanges and gasket not shown.)

18

 EE-RM-93-801 COMMENT OR6

Figure 9. Finite element model and temperature profiles for 

uncoupled heat flow "in modified SubZero gasket. (Adiabatic surfaces between flanges and gasket not shown.) 

18 
uncoupling reduced the U-value by about a factor of two, replacing the air within the gasket with krypton reduces the U-value by.

only an additional ten percent.

Uncoupling heat flow between the flanges and gasket can not,

in practice , be accomplished by placing adiabatic surfaces between the flanges and gasket. Replacing the metal clip which

holds the gasket in place and part of the metal flanges with

plastic as shown in Figures 10 and 11 could be implemented in

production and could produce the same result.

Modifications to the SubZero gasket region shown in Figure

10 include changing the metal retaining clip to plastic, changing

the portion of the door flange between the mounting socket and

interior of the R / F to plastic and changing the portion of the

cabinet flange between the end of the gasket magnet and interior

of the R/F to plastic. The U-value resulting for the modified

gasket region was 1.775E - 3 Btu / (hr*in* ° F), a nearly 60 percent

reduction.

As it may not be possible to make such drastic changes in

practice on all models, calculations were performed for flange

designs which embodied a fraction of the above described modifications. U-values which resulted from changing the clip and/or a

fraction of the above metal portions of the flanges to plastic

are summarized in Table 7 and plotted in Figure 12.

19

 EE-RM-93-801 COMMENT OR6

uncoupling reduced the U-value by about a factor of two, replacing the air within the gasket with krypton reduces the U-value by . 

only an additional ten percent. 

Uncoupling heat flow between the flanges and gasket can not, 

in practice, be accomplished by placing adiabatic surfaces between the flanges and gasket. Replacing the metal clip which 

holds the gasket in place and part of the metal flanges with 

plastic as shown in Figures 10 and 11 could be implemented in 

production and could produce the same result. 

Modifications to the SubZero gasket region shown in Figure 

10 include changing the metal retaining clip to plastic, changing 

the portion of the door flange between the mounting socket and 

interior of the R/F to plastic and changing the portion of the 

cabinet flange between the end of the gasket magnet and interior 

of the R/F to plastic. The U-value resulting for the modified 

gasket region was 1.77SE-3 Btu / (hr*in*oF), a nearly 60 percent 

reduction. 

As it may not be possible to make such drastic changes in 

practice on all models, calculations were performed for flange 

designs which embodied a fraction of the above described modifications. U-values which resulted from changing the clip and/or a 

fraction of the above metal portions of the flanges to plastic 

are summarized in Table 7 and plotted in Figure 12. 

19 
Figure 10. Finite element model and temperature profiles for

modified SubZero gasket region which includes a

plastic clip and approximately half plastic door and

cabinet flanges.

20

 EE-RM-93-801 COMMENT OR6

Figure 10. Finite element model and temperature profiles for 

modified SubZero gasket region which includes a 

plastic clip and approximately half plastic door and 

cabinet flanges. 

20 
Figure 11. Finite element model and temperature profiles for

modified GE gasket region which includes a plastic

clip and approximately half plastic door and cabinet

flanges.

21

 EE-RM-93-801 COMMENT OR6

Figure 11. Finite element model and temperature profiles for 

modified GE gasket region which includes a plastic 

clip and approximately half plastic door and cabinet 

flanges. 

21 
60 7

W

50

O

30-I

0

0.25 0. 50 0.75 1.00

. Fraction Plastic

1.25

Figure 12. SubZero gasket region load reductions for various

flange modifications.

Door & Cabinet

22

 EE-RM-93-801 COMMENT OR6

Figure 12. SubZero gasket region load reductions for various 

flange modif ication"s. 

22 
Table 7. U-Values for SubZero Gasket Region with a Portion of

the Flanges changed to Plastic

% Proposed Modification

U-value % Reduction

clip I door I cabinet

0 0 0 4.036E-3 0

100 0 0 3.977E-3 1.5

100 25 0 3.677E-3 8.9

100 50 0 3.409E-3 15.5

100 75 0 3.240E-3 19.7

100 100 0 3.138E-3 22.2

100 0 25 3.459E-3 14.3

100 0 50 3.114E-3 22.8

100 0 75 2.905E-3 28.0

100 0 100 2.780E-3 31.1

100 25 25 3.151E-3 21.9

100 50 50 2.504E-3 38.0

100 75 75 2. 068E-3 48.8

100 100 100 1.775E-3 56.0

Changing the metal clip to plastic has a relatively small

effect of 1.5 percent. Changing either the door or cabinet

flange can reduce the heat flow by approximately 25 percent.

Similarly making half of the proposed changes to the door and

cabinet flanges will produce almost a 40 percent reduction. The

effects are also additive as shown by the open circles in Figure

12, which correspond to the sum of the individual reductions.

(Note: When adding values in Table 7, 1.5% must be subtracted

from the sum so that the effect of the clip is not double counted.)

Modifications to the GE gasket region consisted of changing

the clip from metal to plastic, changing the portion of the door

flange from the center of the clip to the interior of the R/F

from metal to plastic and changing the portion of the cabinet

flange from the center of the clip to the interior of the R/F

from metal to plastic. Similar reductions to those for the

23

 EE-RM-93-801 COMMENT OR6

Table 7. U-Values for SubZero Gasket Region with a Portion of 

the Flanges changed to Plastic 

% Proposed Modification 

U-value % Reduction 

clip door cabinet 

0 0 0 4.036E-3 0 

100 0 0 "3.977E-3 1.5 

100 25 0 3.677E-3 8.9 

100 50 0 3.409E-3 15.5 

100 75 0 3.240E-3 19.7 

100 100 0 3.138E-3 22.2 

100 0 25 3.459E-3 14.3 

100 0 50 3.114E-3 22.8 

100 0 75 2.905E-3 28.0 

100 0 100 2.780E-3 31.1 

100 25 25 ." 3.151E-3 21.9 

100 50 50 2.504E-3 38.0 

100 75 75 2.068E-3 48.8 

100 100 100 1.775E-3 56.0 

Changing the metal clip to plastic has a relatively small 

effect of 1.5 percent. Changing either the door or cabinet 

flange can reduce the heat flow by approximately 25 percent. 

Similarly making half of the proposed changes to the door and 

cabinet flanges will produce almost a 40 percent reduction. The 

effects are also additive as shown by the open circles in Figure 

12, which correspond to the sum of the individual reductions. 

(Note: When adding values in Table 7, 1.5% must be subtracted 

from the sum so that the effect of the clip is not double counted. ) 

Modifications to the GE gasket region consisted of changing 

the clip from metal to plastic, changing the portion of the door 

flange from the center of the clip to the interior of the R/F 

from metal to plastic and changing the portion of the cabinet 

flange from the center of the clip to the interior of the R/F 

from metal to plastic. Similar reductions to those for the 

23 
Subzero gasket are shown in Table 8 and Figures 13.

Table 8. U-Values for GE Gasket Region with a Portion of

the Flanges changed to Plastic

% Proposed Modification

U-va lue % Reduc on ti

clip I door I cabinet

0 0 0 6.600E-3 0

100 0 0 6.382E-3 3.3

100 25 0 6. 015E-3 8.9

100 50 0 5.304E-3 19.6

100 75 0 5.040E-3 23.6

100 100 0 4.865E-3 26.3

100 0 25 5.479E-3 17.0

100 0 50 5.022E-3 23.9

100 0 75 4.790E-3 27.4

100 0 100 4.695E-3 28.9

100 25 25 5.110E-3 22.6

100 50 50 3. 923E-3 40.6

100 75 75 3.376E-3 48.8

100 100 100 3. 070E-3 53.5

As with the SubZero gasket, the clip has a minor effect on

the U-value, a 3.3 percent reduction. Modifications to the door

flanges produced up to a 26 percent reduction , and up to 29 percent reductions were calculated for modifications to the cabinet

only. Reductions of over fifty percent were, also, possible and

the reductions were cumulative , as shown by the open circles in

Figure 13.

A final calculation was made to determine if heat flow

through the foam adjacent to the flanges would significantly

affect the reductions described above. A model similar to that

shown in Figure. 5 but with the clip and portions of the flanges

described above changed to plastic, was employed in this calculation. As shown in Table 9, including the heat flow through the

24

 EE-RM-93-801 COMMENT OR6

SubZero gasket are shown in Table 8 and Figures 13. 

Table 8. U-Values for GE Gasket Region with a Portion of 

the Flanges changed to Plastic 

% Proposed Modification 

U-value 9,-

0 Reduction 

clip door cabinet 

0 0 0 6.600E-3 0 

100 0 0 6.382E-3 3.3 

100 25 0 6.015E-3 8.9 

100 50 0 5.304E-3 19.6 

100 75 0 5.040E-3 23.6 

100 100 0 4.865E-3 26.3 

100 0 25 5.479E-3 17.0 

100 0 50 5.022E-3 23.9 

100 0 75 4.790E-3 27.4 

100 0 100 4.695E-3 28.9 

100 25 25 5.110E-3 22.6 

100 50 50 3.923E-3 40.6 

100 75 75 3.376E-3 48.8 

100 100 100 3.070E-3 53.5 

As with the SubZero gasket, the clip has a minor effect on 

the U-value, a 3.3 percent reduction. Modifications to the door 

flanges produced up to a 26 percent reduction, and up to 29 percent reductions were calculated for modifications to the cabinet 

only. Reductions of over fifty percent were, also, possible and 

the reductions were cumulative, as shown by the open circles in 

Figure 13. 

A final calculation was made to determine if heat flow 

through the foam adjacent to the flanges would significantly 

affect the reductions described above. A model similar to that 

shown in Figure 5 but with the clip and portions of the flanges 

described above changed to plastic, was employed in this calculationa As shown in Table 9, including the heat flow through the 

24 
60 --1

Door & Cabinet

30-I

0 -i ,f

0.00

Cabinet Only

0.25 0. 50 0.75 1.00

Fraction Plastic

1.25

Figure 13. GE gasket region load reductions for various flange

modifications.

25

 EE-RM-93-801 COMMENT OR6

60 

tR Door & Cabinet 

~ 0 

~ 50 

0 0 .1""'"1 

~. 

() 

;::J 40 'D 

Q) 

0::: 

'D 

cd 

30 Cabinet Only 

0 

~ Door Only 

~ 20 

0 

.1""'"1 

OJ) 

Q) 

~ 10 

~ 

Q) 

~ 

lfl 0 

cd 0.00 0.25 0.50 0.75 1.00 1.25 C,) Fraction Plastic 

Figure 13. GE gasket region load reductions for various flange 

modifications. 

25 
foam adjacent to the door and cabinet flanges increased the Uvalue of the gasket region by less than 2 percent.

Table 9. Effect of Flange / Foam Boundary Condition on

U-Value of Modified GE Gasket Region

Flange/Foam Overall Heat Overall Heat

Heat Transfer Transfer Rate Trans. Coeff., U

Assumption Btu/(hr*in) Btu/(hr*in*OF)

adiabatic 0.2763 3. 070E-3

conduction 0.2801 3.119E-3

MEASUREMENTS - NEW DESIGNS

A method to measure the total heat flux through the gasket

region of a R/F cabinet does not exist . Measurements of the

total energy consumption of two prototype R/Fs were thus used in

conjunction with the EPA Refrigerator Analysis (ERA) model (4) to

determine if the predicted energy reductions could be achieved in

practice.

Both prototypes had gasket cross sections similar to the

Subzero gasket , but neither had the decorative metal gasket cover

shown in Figure 1. Other notable differences to the model shown

in Figure 1 were that the cabinet flange was not as wide as the

gasket for both prototypes and that the plastic liner and not a

metal clip was used to hold the gasket in place in prototype B.

Prototype A - The cabinet flange for this unit ended at the

inside edge of the gasket magnet as is shown in Figure 10. The

remainder of the flange was , however, not plastic but rather a

small air gap. Still air would produce the same effect as having

26

 EE-RM-93-801 COMMENT OR6

foam adjacent to the door and cabinet flanges increased the Uvalue of the gasket region by less than 2 percent. 

Table 9. Effect of Flange/Foam Boundary Condition on 

U-Value of Modified GE Gasket Region 

Flange/Foam Overall Heat Overall Heat 

Heat Transfer Transfer Rate Trans. Coeff., 

Assumption Btu/(hr*in) Btu/(hr*in*oF) 

adiabatic 0.2763 3.070E-3 

conduction 0.2801 3.119E-3 

MEASUREMENTS - NEW DESIGNS 

U 

A method to measure the total heat flux through the gasket 

region of a R/F cabinet does not exist. Measurements of the 

total energy consumption of two prototype R/Fs were thus used in 

conjunction with the ~PA Refrigerator Analysis (ERA) model (4) to 

determine if the predicted energy reductions could be achieved in 

practice. 

Both prototypes had gasket cross sections similar to the 

SubZero gasket, but neither had the decorative metal gasket cover 

shown in Figure 1. Other notable differences to the model shown 

in Figure 1 were that the cabinet flange was not as wide as the 

gasket for both prototypes and that the plastic liner and not a 

metal clip was used to hold the gasket in place in prototype B. 

Prototype A - The cabinet'flange for this unit ended at the 

inside edge of the gasket magnet as is shown in Figure 10. The 

remainder of the flange was, however, not plastic but rather a 

small air gap. still air would produce the same effect as having 

26 
plastic in this region . If, however, convection to the R/F

interior occurred in this gap, the flange would behave exactly as

that shown in Figure 1. The exact configuration shown in Figure

10 was then easily obtained by placing plastic insulating tape

between the end of the metallic flange and the inside of the R/F.

No modifications were made to the door flange in prototype A.

The calculations presented in Table 7 suggest that a 30

percent decrease in the total heat flux for the gasket region

would results from this modification , if convection was present

in the air gap. Reducing the gasket heat load by this amount in

the ERA model predicted a 9 percent energy reduction . Measurements yielded 7 to 8 percent.

The agreement between the measurement and models is very

good . It is possible even better agreement would be obtained by

employing a lower heat transfer coefficient in the air gap. This

would be warranted , as some restriction to air flow is likely.

Prototype B - The door flange was changed in this unit by

removing the portion of the flange located under the gasket and

between the liner mounting screws . This portion of the flange

accounts for about 80 percent of the heat transfer path and

should produce about that fraction of the 22 percent reduction

for this modification shown in Table 7. Reducing the gasket heat

flow by this amount in the ERA model predicted a 5 percent reduction in total energy consumption for this unit . This result is

in excellent agreement with the 4 to 5 percent that was measured.

The cabinet flange in this model was similar to that in

prototype A, i. e. it did not extend the entire length of the

gasket. It did, however , extend beyond the magnet approximately

27

 EE-RM-93-801 COMMENT OR6

plastic in this region. If, however, convection to the RIF 

interior occurred in this gap, the flange would behave exactly as 

that shown in Figure 1. The exact configuration shown in Figure 

10 was then easily obtained by placing plastic insulating tape 

between the end of the metallic flange and the inside of the R/F. 

No modifications were made to the door flange in prototype A. 

The calculations presented in Table 7 suggest that a 30 

percent decrease in the total heat flux for the gasket region 

would results from this modification, if convection was present 

in the air gap. Reducing the gasket heat load by this amount in 

the ERA model predicted a 9 percent energy reduction. Measurements yielded 7 to 8 percent. 

The agreement between the measurement and models is very 

good. It is possible even better agreement would be obtained by 

employing a lower heat transfer coefficient in the air gap. This 

would be warranted, as some restriction to air flow is likely. 

Prototype ~ - The door flange was changed in this unit by 

removing the portion of the flange located under the gasket and 

between the liner mounting screws. This portion of the flange 

accounts for about 80 percent of the heat transfer path and 

should produce about that fraction of the 22 percent reduction 

for this modification shown in Table 7. Reducing the gasket heat 

flow by this amount in the ERA model predicted a 5 percent reduction in total energy consumption for this unit. This result is 

in excellent agreement with the 4 to 5 percent that was measured. 

The cabinet flange in this model was similar to that in 

prototype A, i. e. it did not extend the entire length of the 

gasket. It did, however, extend beyond the magnet approximately 

27 
one sixth of the way in the freezer and one third of the way in

the fresh food section. As with prototype A, plastic tape was

employed to fill in the air gap in both the freezer and fresh

food sections. Table 7 would suggest an 18 percent reduction for

the fresh food section and a 30 percent reduction for the freezer

section . As this modification was done after the door flange was

changed the total reductions should be 36 and 48 percent.

The ERA model was again used to simulate the R/F with the

reduced gasket heat input and predicted an.11 percent energy

reduction . Measurements showed a 7 to 8 percent reduction. As

noted above , better agreement would have been attained with a

lower convective heat transfer coefficient in the air gap.

Agreement was, however, quite good.

CONCLUSIONS

• Heat flow through the gasket region of refrigerator/ freezers

is modeled using finite element analysis.

• Heat flow through the gasket and flanges is highly coupled.

• Decreasing the thermal resistance of the gasket by incorporating a low conductivity gas in the pockets of the gasket

has a modest effect on the gaskets thermal performance.

• Replacing about half of,either the metal door flange or

cabinet flange with plastic can reduce the heat flow through

the region by 25 percent.

Replacing about half of the door and cabinet flanges with

28

 EE-RM-93-801 COMMENT OR6

one sixth of the way in the freezer and one third of the way in 

the fresh food section. As with prototype A, plastic tape was 

employed to fill in the air gap in both the freezer and fresh 

food sections. Table 7 would suggest an 18 percent reduction for 

the fresh food section and a 30 percent reduction for the freezer 

section. As this modification was done after the door flange was 

chan~ed the total reductions should be 36 and 48 percent. 

The ERA model was again used to simulate the R/F with the 

reduced gasket heat input ahd predicted an.11 percent energy 

reduction. Measurements showed a 7 to 8 percent reduction. As 

noted above, better agreement would have been attained with a 

lower convective heat transfer coefficient in the air gap. 

Agreement was, however, quite good. 

CONCLUSIONS 

Heat flow through the gasket region of refrigerator/freezers 

is modeled using finite element analysis. 

Heat flow through the gasket and flanges is highly coupled. 

Decreasing the thermal resistance of the gasket by incorporating a low conductivity gas in the pockets of the gasket 

has a modest effect on the gaskets thermal performance. 

Replacing about half of·either the metal door flange or 

cabinet flange with plastic can reduce the heat flow through 

the region by 25 percent. 

Replacing about half of the door and cabinet flanges with 

28 
plastic can reduce the U-value of the gasket region by half.

• Measured and predicted reductions in total R/F energy consumption resulting from modified gasket designs are in good

agreement.

ACKNOWLEDGEMENTS

The authors wish to thank Mr. Qin Zhou, Mr . Kwangil Kim, Dr.

Sungpil Won and Prof . Reinhardt Radermacher of the Department of

Mechanical Engineering at the University of Maryland for performing the energy testing on the prototype refrigerator/freezers.

REFERENCES

1. H. A. Fine, G . J. Haworth and R . Srikanth, "Performance Test

Results for Refrigerator / Freezers containing Vacuum Insulation

Panels", Proceedings of the International Conference on CFCs and

Halons , Berlin, Germany, February 24 - 26 , 1992 , FGU Berlin, pp.

305 - 15.

2. W. D. Lee, Development of a High Efficiency , Automatic

Defrost Refrigerator/Freezer: Phase I - Design and Development,

ORNL/ Sub-7255 / 2, Oak Ridge National Laboratory , Oak Ridge , Tenn.,

1980.

3. B. T. Griffith , D. Arastah and S. Selkowitz, HighPerformance Non-CFC-Based Thermal Insulation : Gas Filled Panels,

California Institute for Energy Efficiency , Berkeley , Calif.,

1992.

4. R. L. Merriam , EPA Refrigerator Analysis Program, U.S.

Environmental Protection Agency , Washington, DC, 1992.

29

 EE-RM-93-801 COMMENT OR6

plastic can reduce the U-value of the gasket region by half. 

Measured and predicted reductions in total R/F energy consumption resulting from modified gasket designs are in good 

agreement. 

ACKNOWLEDGEMENTS 

The authors wish to thank Mr. Qin Zhou, Mr. Kwangil Kim, Dr. 

Sungpil Won and Prof. Reinhardt Radermacher of the Department of 

Mechanical Engineering at the University of Maryland for performing the energy testing on the prototype refrigerator/freezers. 

REFERENCES 

1. H. A. Fine, G. J. Haworth and R. Srikanth, "Performance Test 

Results for Refrigerator/Freezers containing Vacuum Insulation 

Panels", Proceedings of the International Conference on CFCs and 

Halons, Berlin, Germany, February 24 - 26, 1992, FGU Berlin, pp. 

305 - 15. 

2. W. D. Lee, Development of £ High Efficiency, Automatic 

Defrost Refrigerator/Freezer: Phase I = Design and Development, 

ORNL/Sub-7255/2, Oak Ridge National Laboratory, Oak Ridge, Tenn., 

1980. 

3. B. T. Griffith, D. Arastah and S. Selkowitz, HighPerformance Non-CFC-Based Thermal Insulation: Gas Filled Panels, 

California Institute for Energy Efficiency, Berkeley, Calif., 

1992. 

4. R. L. Merriam, EPA Refrigerator Analysis Program, U.S. 

Environmental Protection Agency, Washington, DC, 1992. 

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