1

CHAPTER – 5

INVESTIGATIONS OF VARIOUS METHODS FOR DESIGN OF

BTS

Optimised thermal design of BTS is carried out with many design options. Lot

of feasible thermal design decisions are made before arriving to the preliminary

thermal design .The most critical design is edge guide support where PWBs are

supported at the edges and bosses/stand offs are touched at the middle of the

PWBs.Edge guide option supports the PWBs more robustly so as to withstand severe

vibrations and shocks during transportation and also utilised for carrying large amount

of heat. In this work analysis is initiated without the conduction path at the critical

components. Later design is proceeded with conduction path and fan failure criteria

for different fan tray options.

5.1. BTS DESIGN WITHOUT CONDUCTION PATH

Design is carried out with three of 60 mm external fans and without any

conduction path to the critical components. This analysis case is performed for design

feasibility and also to identify what all the components require conduction path.

2

5.1.1. Temperature contours of System Board

Fig.5.1 Temperature profile of SB

Temperatures shown in the figure 5.1 refers to component junction temperatures.

Maximum temperature 133.7ºC is experienced on processor component in system

board.

Top side components Bottom sde components

3

5.1.2. Temperature contours of BB

Fig.5.2 Temperature profile of BB Top side

Fig.5.3 Temperature profile of BB Bottom side

Temperatures shown near the component are component junction temperatures.

Case temperature is considered for SFP cage. Maximum temperature of around 209°C

is reached in DSP component placed in baseband board.

4

5.1.3. Temperature contours of PB

Fig.5.4 Temperature profile of PB

Temperatures shown in the figure 5.4 explains the temperature contour on the

PB. The junction temperature of the components is mentioned near the components.

Maximum temperature of 166.6 ºC reached in Free wheel Mosfet component.

5

5.1.4. Temperature contours of Chassis

Fig.5.5 Surface temperature of chassis

Chassis surface temperature distribution is shown in the figure5.5. Maximum chassis

surface temperature of 81.2 °C is experienced near the base band board region.

6

5.1.5. External ambient temperature distribution

Fig.5.6 Outlet air temperature distribution

Maximum exit air temperature reached 76 °C.

5.1.6. Velocity profile

Fig.5.7 Velocity profile over the top heat sink of the chassis

7

Fig.5.8 Velocity profile through vent

5.1.7. Fan Operating Point

Table 5.1 Fan Operating pressure & flow

Fan Position Volume Flow(CFM) Volume Flow(m3/Sec) Static Pressure(Pa)

Middle Fan 17.17350 0.00810 27.56

Left Fan 17.38580 0.00820 26.696

Right Fan 17.30550 0.00816 27.021

Fig.5.9 Fan Operating curve details

Left Fan Middle Fan Right Fan

8

Individual fan operating flow and static pressure values are shown in the Tables

5.1 and 5.2. Effective flow through the system is around 0.02446 m3/sec (51.86 cfm)

and system pressure is maximum of 27.556 Pa

5.1.8. Summary of the results

Table 5.2 Component temperature details in System Board & PIU

9

Table 5.3 Component temperature details in BB

Derated component temperature values listed in the tables 5.3 and 5.4 are taken in

BTS thermal design to improve product reliability.This is as per MIL Standards.

Table 5.4 Component temperature details in PB

The summary of computed junction, case and ambient temperature values are listed in

the Tables 5.2, 5.3 and 5.4. Values that are marked in the red colur are above the

10

component specification and failed in the product design.Hence these components

require cooling for the robust design.

5.1.9. Observations and recommendations for the preliminary design

Majority of the critical components on all boards are failed while exceeding

vendor operating thermal margin in the preliminary design phase.As a deisgn

methodlogy,some middle mechanics which is so called heat towers will be introduced

to establish good conduction path between chassis body and components.This inturn

increases the conduction heat transfer to the outer ambient.

5.1.10. Coupling details SB, BB, PB

After the thermal feasibility design, it is decided to keep the towers on the

following devices to cool below the vendor specified temperature limit.Here towers as

metal protrusion are considred for coupling the components with chassis.

Table 5.5 Coupling details of SB & PIU

11

Table 5.6 Coupling details of BB

Table 5.7 Coupling details of PB

Components coupled to the chassis are tabulated in the Tables 5.5, 5.6 and 5.7.

During feasible study thermal simulation is carried out without heat towers. Based on

the study, power dissipation and surface area in consultation with H/W team, coupling

the components with mechanics are considered.

12

5.2. BTS DESIGN WITH CONDCUTION PATH

Assumptions and inputs are same as the previous section but the critical

components which are identified during initial feasibility have been coupled with the

chassis to enhance the conduction heat transfer path.This coupling method is termed

as heat towers.

5.2.1. Temperature contours of SB

Fig.5.10 Temperature profile of SB

Temperatures shown in the figure 5.10 refers to component junction

temperatures.Maximum temperature 127ºC is experienced on regulator (D193)

component in system board.

Top side components Bottom side components

13

5.2.2. Temperature contours of BB

Fig.5.11 Temperature profile of BB Top side

Fig.5.12 Temperature profile of BB Bottom side

Temperatures shown near the component are component junction temperatures.

Case temperature is considered for SFP cage. Maximum temperature of around

115.5°C is reached in dual bidirectional I2C bus component placed in base

band board.

14

5.2.3. Temperature contours of PB

Fig.5.13 Temperature profile of PB

Temperatures shown in the figure 5.13 explains the temperature contour on the

PB. The junction temperature of the components is mentioned near the components.

Maximum temperature of 99.1ºC reached in power board component.

15

5.2.4. Temperature contours of Chassis

Fig.5.14 Surface temperatures of chassis

Chassis surface temperature distribution is shown in the figure 5.14. Maximum

chassis surface temperature of 81.2 °C is experienced near the base band board

region.

5.2.5. Internal ambient temperature distribution

Fig.5.15 Internal ambient temperature of chassis

16

Maximum internal ambient temperature reached above SB and BB is 79.3 and 84.2°C

Maximum internal ambient temperature above PB is 84.8°C and PIU is 84.9°C.

5.2.6. External ambient temperature distribution

Fig.5.16 Outlet air temperature distribution

Maximum exit air temperature reached 76 °C.

5.2.7. Velocity profile

Fig.5.17 Velocity profile over the top heat sink of the chassis

17

Fig.5.18 Velocity profile through vent

Velocity profile profile above and below are as same as the as the preliminary

design as outer ressitance is not changed.

5.2.8. Fan Operating Point

Table 5.8 Fan Operating pressure & flow

Fan Position Volume Flow(CFM) Volume Flow(m3/Sec) Static Pressure(Pa)

Middle Fan 17.17350 0.00810 27.56

Left Fan 17.38580 0.00820 26.696

Right Fan 17.30550 0.00816 27.021

Fig.5.19 Fan Operating curve details Left Fan Middle Fan Right Fan

18

Individual Fan operating flow and static pressure values are shown in the Tables

5.8 and Figure 5.19. Effective flow through the system is around 0.02446 m3/sec

(51.86cfm). System pressure experiencing maximum of 27.556 Pa.The static pressure

and flow have not varied with respect to the preliminary design case as external

resistance is un altered.

5.2.9. Summary of the results

Table 5.9 Component temperature details in SB & PIU

19

Table 5.10 Component temperature details in BB

Derated value of component in sl.number1 is same as vendor datasheet because

the junction temperature of that component is less than 110°C. Hence same value as

vendor specified value is considered as derated value.

Table 5.11 Component temperature details in PB

20

The Summary of computed junction, case and ambient temperature values are

listed in the Tables 5.9, 5.10 and 5.11 for System/plug-in, base band and power board

respectively. The sign in the Table 5.9 denotes the storage temperature considered as

junction temperature for the corresponding components.

5.2.10. Observations and recommendation with heat towers

The observations and recommendations with conduction path are listed in the Table

5.12, given below.

Table 5.12 Observations for further activities

Description Observations Further Activities

System

Board(SB)

In SB, except Regulator

component (Sl.No.16,MCOMPO

No.4344594), all components are

within the allowable junction

temperature as per vendor data

sheet

In system board (SB),

components having Sl.Nos

3,6,7,9,10,11,13,16,17 and 18 are

above the derated temperature

values

Simulation will be carried

out with further design

improvement on mechanics

to meet regulator

component (Sl.No.16,

MCOMPO NO. 4344594)

cooling requirement to

achieve vendor data

temperature.

Discussion is required on

derating values.

Base band

Board(BB)

In Base band board (BB),

components having

Sl.Nos.4,12,13,15,20,22 and 23

are above the derated temperature

Values.

Power

Board(PB)

All components in power board

(PB) are below Derating guideline

temperature Values and vendor

21

Recommednations of the thermal analysis are tabulated in the above Table 5.12.

This table also gives the further activities to be carried out in order to achieve the

derated temperature values of the components in the respective boards.

5.3. BTS DEIGN WITH FAN FAILURE CONDITION FOR

3*60MM

The results of temperature distribution in SB, BB and PB for fan failed conditions are

explained below.

data sheet value

Plug-in

Unit(PIU)

In Plug in unit (PIU) board

LIUcomponent is above the

derated temperature limit but

within vendor specified

temperature.

Simulation will be carried

out with further design

improvement on mechanics

to meet the Derating

values

System level Effective flow through the system

is around 0.02446 m3/sec

(51.86cfm).

System pressure experiencing

maximum of 27.556 pa

Maximum surface temperature of

chassis reached 81.2 °C, which

qualifies as ‘hot’. Due to higher

temperature experienced on the

surface of the chassis it is

advisable to have a warning

sticker for safety consideration.

22

Table 5.13 Fan failure condition for SB & PIU

5.3.1. Observations of Fan fail condition in SB and PIU

Majority of critical components are above the vendor datasheet temperature

and derating temperature limit.

In fan failed condition components temperature is relatively more in middle

fan failure condition. (i.e. Middle fan failure is worst than left and right fan

failure condition).

Critical component in PIU board is below the vendor data sheet and above the

derated temperature value in all fan fail condition.

23

Table 5.14 Fan failure condition for BB

5.3.2. Observations of Fan fail condition in BB

Components temperature in BB board is higher in fan failed condition.

In BB components temperature is relatively less with right fan failure

condition compared to left and middle fan failure condition.

In fan fail condition left fan failure is worst effect compared to middle and

right fan fail condition

24

Table 5.15 Fan failure condition for PB

5.3.3. Observations of Fan fail condition in PB

All components in PB are within vendor specified temperature value and

derated temperature value with fan fail condition (left, middle and right).

In PB components temperature is relatively less with right fan failure

condition compared to left and middle fan failure condition.

In fan fail condition left fan failure is worst effect compared to middle and

right fan fail condition.

25

5.4. BTS THERMAL DESIGN WITH 2*92MM FAN

Two of 92mm fan tray is used to study the thermal performance of the BTS

mechanics.

5.4.1. Thermal model

Thermal Model of BTS with 2*92mm fan tray is shown in below Figure 5.20.

Fig.5.20 Thermal model with 2*92mm Fan assembly

Fig.5.21 Block diagram of fan position considered for Thermal simulation

Figure 5.21 represents the block representation of fan position from left and right

corner.

26

5.4.2. Thermal Model Considerations

All thermal model assumptions are same as previous sections.

Figure 5.21 shows the horizontal as well as axial distance of fans and obstruction.

5.4.3. Mechanical Model Considerations

Fan details considered for dimensions having 2*92mm fan assembly.Fan curve

is scaled down to 85% of maximum speed. Fan curve based on vendor

datasheet.Vents near fan are approximated with rectangular geometry of equal area.

5.4.4. Fan details (92mm) considered for thermal simulation

Fig.5.22 Vendor data fan curve 92mm fan

27

Table 5.16 Flow Vs Static pressure for 92mm fan

Fig.5.22 shows the flow Vs static pressure curve of 92mm fan specified by vendor.

This fan curve points are used for thermal simulation. The Table 5.16 shows the

values provided in the data sheet and calculated value for 85% of the maximum speed

which is calculated. The value considered for the simulation is the calculated value

for 85% of the fan speed.

5.4.5. Temperature contour details of SB

Top Side Bottom Side

Fig.5.23 Temperature contour for SB

28

Fig.5.24 Temperature contour for BB

Fig.5.25 Temperature contour for PB

Bottom side Top side

29

Fig.5.26 Temperature contour for Exit air

Fig.5.27 Temperature contour for Chassis

Figures 5.26 and 5.27 describe the temperature contours of all three PCB’s, exit

air temperature and temperature distribution on chassis surface. The summary of the

each component temperature on the board is discussed in the section 5.4.9

5.4.6. Observations on Exit Air Temperature and Chassis Temperature

The air temperature reaches maximum value of 73.1°C at exit of the chassis.

The temperature rise from inlet to exit is around 8.1°C. Maximum surface

temperature of chassis is reaching up to 79°C. The maximum value of surface

temperature is reaching near the base band board region (BB region)

30

Fig.5.28 Flow distribution through upper chassis

5.4.7. Flow Distribution Pattern

Fig.5.29 Flow distribution through Vents & near obstructions

The air flow distribution from the fan throw the chassis is in figures 5.28 and 5.29.

Figure 5.28 shows the velocity vector throw the heat sink of the upper chassis (i.e

below top cover) in isometric view and top view.

Flow distribution through upper

Chassis (Top View)

Flow distribution through upper

Chassis (Isometric View)

Flow distribution through Vents Flow distribution near Obstructions

31

Figure5.29 explains the flow distribution through the vents and near the

obstruction.The maximum velocity through the heat sink of the upper chassis is

reaching 10.6 m/sec. Flow distribution through the vents shows the maximum

velocity of 10.9 m/sec.

The space below the vents will be obstruction for the flow. The air flow coming

from the fan will be obstructed and the flow path gets deviated. The maximum flow

velocity reached when the flow get obstructed is 7.64 m/sec.

5.4.8. Fan Operating curve

Fig.5.30 Fan operating curve for Left & Right Fan

Fan operating curve for left and right fan is shown inFigure 5.30. The operating

pressure of left fan is 71.6 Pa and flow rate for that pressure is 0.016 m3/sec. The right

fan has the flow rate of 0.026 m3/sec for the operating pressure of 44.2 Pa.

Mechanical obstruction is same for both the fans. The flow from two fans is

getting obstructed at different places. The system resistance, obstructing geometry and

location of fans are also affecting the operating pressure. Hence there is difference in

operating pressure.

Left Fan Right Fan

32

5.4.9. Comparision of Simulation Results with 3*60 & 2*92mm fan

Table 5.17 Temperature results of SB & PIU

In SB all components are well below the vendor specified maximum

temperature when working with 92 mm fan

Components marked with red colour are above the derating temperature

values.

Components like processor (Mcompo No.4332632) is within the limit when

derating temperature values are reconsidered.

In PIU component temperature is within vendor specified temp, but

marginally is above by 0.5°C than derating temp.

33

Table 5.18 Temperature results of BB

All components in BB are within vendor specified temperature values.

Components marked with red color are not meeting the derating guidelines.

34

Table 5.19 Temperature results of PB

All Components in PB are within vendor specified maximum junction

temperature and derating guideline values.

5.4.10. Observations with 92mm Fan

Based on the summary of temperature results, the components temperature in all

boards can be compared in two cases (i.e. for 3*60mm fan and 2*92 mm fan).

In SB there is a reduction in temperature by using 2*92 than 3*60mm. The

temperature reduction in SB is more than 2.2°C for all components junction

temperature.

Junction temperature of component located in PIU is reduced around 4.9°C.

In BB, the least temperature reduction is around 2.0°C for components

junction temperature.

In PB, temperature reduction in component junction temperature is between

1.7 to 3.6°C.

35

From the above simulation results, reduction in temperature for all

components in all boards (SB/PIU, BB and PB) with 2*92mm fan assembly is

noticeed. Hence it can be concluded that the performance of 2*92mm fan is

better than the 3*60mm fan.

5.4.11. Fan comparison details

Single fan comparison

60 mm Fan 92 mm fan

Dimensions 60x60x25.5 mm Dimensions 92x92x38.5mm

Max flow 29.3 CFM Max flow 77.7 CFM

Max static pressure 150 Pa Max static pressure 270 Pa

Acoustic level 49 dB Acoustic level 55 dB

System fan comparison

3 *60 mm Fans 2 *92 mm fan 3 * 92 mm fan

Dimensions 60x60x25.5

mm

Dimensions

92x92x38.5mm

Dimensions

92x92x38.5mm

Max flow 87.9 CFM

(Parallel flow)

Max flow 155.4

CFM(Parallel flow)

Max flow 233.1

CFM(Parallel flow)

Max static pressure 150

Pa

Max static pressure 270

Pa

Max static pressure 270

Pa

Acoustic level 58.6 dB

based on 3 similar

sources

Acoustic level 61 dB

based on two similar

sources

Acoustic level 64.6 dB

based on three similar

sources

2*92 mm fan is able to deliver more volumetric flow with marginally increased

acoustic level (approx 2 dB) compared with the 3*60 mm fans.

36

5.5. BTS DESIGN FOR FAN FAILURE CONDITION WITH

2*92MM FAN ASSEMBLY

Fan failure condition is simulated to ensure when one of the fan fails in its

function.During fan failure, the failed fan will act as a vent where air flow can happen

from functioning fan. This is modeled and simulated.

Fan Failure condition is required to determine the temperature raise of the

component when one of the fans stops functioning.

Fig.5.31 Block diagram of Left fan failure

Fig.5.32 Block diagram of Right fan failure

Figures 5.31 and 5.32 shows the block diagram of left fan and right fan failure

in 2*92 mm fan tray respectively.

37

Fig.5.33 Flow distribution through the fan (Left fan failure)

Fig.5.34 Flow distribution through the fan (Right fan failure)

Figures 5.33 and 5.34 show the flow distribution during left and right fan failed

condition. The failed fans are acting as vent where it allows air to flow.

The results of components temperature in SB, BB and PB for fan failure conditions

are explained in this section

Left fan Right fan

Left fan Right fan

38

Table 5.20 Fan failure condition for SB & PIU

5.5.1. Analysis on fan fail condition in SB and PIU

During left fan failure condition the rise in SB components are relatively less

compared to right fan failure condition.

The minimum temperature rise due to left fan failure is 2.2°C where as for

right fan failure condition the minimum temperature rise is 3.5°C.

In PIU board the component temperature is relatively high during left fan

failure condition than right fan failure condition.

The temperature rise in PIU component is around 4.5°C during left fan failure

condition and temperature rise due to right fan failure condition is 3.3°C.

39

Table 5.21 Fan failure condition for BB

5.6. OBSERVATIONS OF FAN FAIL CONDITION IN BB

The minimum temperature rise due to left fan fail condition is 4.8°C and for

that of right fan failure condition minimum temperature rise is 2.1°C

Few components are within derating temperature values during right fan

failure condition. But they are above the limit during left fan failure condition

(Please refer Sl.No.16 and17).

Thermal impact is more due to left fan failure condition than right fan failure

condition for components in BB.

40

Table 5.22 Fan failure condition for PB

5.6.1. Observations of Fan fail condition in PB

During left fan failure condition the minimum temperature rise is around 4.9°C.

During the right fan failure condition the minimum temperature rise is 1.8°C.

PB components have more impact due to left fan failure condition than right

fan failure condition.

5.7. BTS THERMAL DESIGN WITH 3*92MM FAN ASSEMBLY

The thermal performance of BTS mechanics with 3*92mm fan assembly is

provided data sheet.

41

5.7.1. Thermal model

Front Isometric View Rear Isometric View

Fig.5.35 Thermal model with 3*92mm Fan assembly

Fig.5.36 Block diagram of fan position in 3*92mm Fan Assembly

Figure 5.36 shows the block diagram of fan position considered in 3*92 mm fan tray.

5.7.2. Thermal Model Considerations:

All thermal Model assumptions are as per the section 4.2.1. Figure 5.36 shows

the horizontal as well as axial distance of fans and obstruction.

42

5.8. TEMPERATURE CONTOUR DETAILS

Top Side Bottom Side

Fig.5.37 Temperature contour for SB

Top Side Bottom Side

Fig.5.38 Temperature contour for BB

43

Fig.5.39 Temperature contour for PB

Fig.5.40 Temperature contour for Exit air

Fig.5.41 Temperature contour for Chassis

Temperature contours of all three PCB’s, exit air temperature of the chassis and

temperature distribution on chassis surface are shown in above Figures. The summary

of the each component temperature on the board is discussed in the section 5.8.4.

44

5.8.1. Observations on Exit Air Temperature and Chassis Temperature

The air temperature reaches maximum value of 72.1°C at exit of the chassis.

The temperature raise from inlet to exit is around 7.1°C.Maximum surface

temperature of chassis is reaching up to 79.5°C. The maximum value of surface

temperature is reaching near the base band board region (BB region).

5.8.2. Air flow Distribution

Fig.5.42 Flow distributions through upper chassis

Flow distribution through upper Chassis (Isometric View)

45

Fig.5.43 Flow distributions through Vents & near obstructions

The air flow distribution from the fan through the chassis is shown in Figures

5.42 and 5.43. The velocity vector through the heat sink of the upper chassis

(i.e.below top cover) is shown in Figure 5.42. The figure represents both the isometric

view and top view. The flow distribution through the vents and near the obstruction is

shown in Figure 5.43. The maximum velocity through the heat sink of the upper

chassis is reaching around 11.7 m/sec. Flow distribution through the vents shows the

maximum velocity of 12.1 m/sec. The air flow coming from the fan will get

Flow distribution through Vents Flow distribution near Obstructions

Flow distribution through upper Chassis (Top View)

46

obstructed by the space below the vents. The maximum flow velocity reached when

the flow get obstructed is around 9.41 m/sec.

5.8.3. Fan Operating curve

Fig.5.44 Operating Condition for Left, Middle and Right fan

Fan operating curve for left, middle and right fan is shown in Figure 5.44. The

operating pressure of left fan is 73.8 Pa and flow rate for that pressure is

0.0152m3/sec. The middle fan has the flow rate of 0.0146 m3/sec for the operating

pressure of 75.0 Pa. Right Fan operating pressure is 74.2 m3/sec with flow rate of

0.0147 m3/sec.

Right Fan Middle Fan Left Fan

47

5.8.4. Summary – Simulation results of 3*92mm fan Assembly

Table 5.23 Temperature results of SB & PIU

In SB all components are well below the vendor specified maximum

temperature

Components marked with red colour are above the derating temperature

values.

Components like processor (Mcompo No.4332632) will be within the limit

when derating temperature values are reconsidered.

48

In PIU board the LIU component is marginally higher by 0.9°C than derating

temperature value.

Effective flow of 2*92mm and 3*92mm fan assembly is more or less same.

Components temperature of Sl.no.16, 17 and 18 are little higher with 3*92mm

fan compared to 2*92 mm fan. These components are cooled by means of

natural convection inside the chassis, and temperature is governed by flow

pattern over the chassis. This determines local internal ambient for cooling of

the components which resulted in a little rise in temperature.

Table 5.24 Temperature results of BB

All components in BB are within vendor specified temperature values.

Components marked with red color are not meeting the derating guidelines.

49

Table 5.25 Temperature results of PB

All components in PB are within vendor specified maximum junction

temperature and derating guideline values.

5.8.5. Comparison between 3*92mm and 2*92mm fan

Effective flow through the chassis is almost same for both 3*92 and 2*92 mm

fan assembly

Most of the component temperatures are same for both fan assembly.

3*92mm fans are not operating in the optimum range in the system due to

flow condition between fans.

Few components with 3*92 mm assembly are slightly higher than 2*92mm

fan due to flow pattern above the upper chassis.

50

5.8.6. Observations with 3*92mm Fan

Based on the summary of temperature results and above observations

All components in SB, BB, PB and PIU are well below vendor specified

maximum values.

The operating flow is not upto the mark due to the system resistance,

obstruction to the flow and placement location of the fans.

However, there is a marginal improvement on cooling of all components in all

boards as compared with 2*92mm fan assembly and considerable

improvement compared with 3*60mm fan assembly

Note: Even the temperature results of components with 3*92mm assembly are

better. The temperature results of the components in 3*92mm fan assembly will be

simulated with fan failed conditions. The fan failed condition simulation results will

give the information of rise in components temperature when either of the fan stops its

function.

5.9. FAN FAILURE CONDITION FOR 3*92MM FAN ASSEMBLY

Fan failure condition is carried out to ensure when one of the fan fails in its

function. During fan failure, the failed fan will act as a vent where air flow can

happen from functioning fan. The model of the failed fan will remain the same but

flow will not happen from the failed fan. Fan failure condition simulation is required

to determine the temperature rise of the component when one of the fans stop

functioning.

51

Fig.5.45 Block diagram of Left fan failure in 3*92mm fan assembly

Fig.5.46 Block diagram of Middle fan failure in 3*92mm fan assembly

Figures 5.45 and 5.46 are the block diagrams representing the left and middle

fan failed condition in 3*92 fan assembly

Fig.5.47 Block diagram of Right fan failure in 3*92mm fan assembly

52

Figure 5.47 represents the block diagram of right fan failed condition in

3*92mm fan assembly

Fig.5.48 Flow distribution through Left failed fan

Fig.5.49 Flow distribution through Middle failed fan

Fig.5.50 Flow distribution through Right failed fan

53

Figures 5.48, 5.49 and 5.50 shows the flow distribution when left, middle and

right fans are failed. The failed fan acts as vent and allows air to flow through the

failed fan.

Table 5.26 Fan failure condition for SB & PIU in 3*92mm fan assembly

Table 5.26 is tabulated with the components temperature results of SB due to

fan failed conditions (left, middle and right fan failed conditions). Components

marked with red colour in tables 5.26 and 5.27 are more than the derated value.

Below tables are provided with components temperature in BB and PB

54

Table 5.27 Fan failure condition for BB in 3*92mm fan assembly

Table 5.28 Fan failure condition for PB in 3*92mm fan assembly

55

5.9.1. Observations of fan failed conditions in 3*92 mm Fan assembly

All the components in SB are below the vendor specified value with fan failed

conditions (left, middle and right fan failure)

Middle fan failure has more impact in SB components temperature than left

and right fan failure. In SB components of Sl.no.16 have temperature rise of

5.4 °C due to middle fan failure compared to all fans running condition.

In SB, components of Sl.no.16, 17 and 18 are having more temperature rise

due to middle fan failure.

LIU component in PIU is below vendor specified value.

In PIU board LIU component is having more impact by left fan failure than

middle fan and right fan failure. Right fan failure is having least impact on

component in PIU board.

All the components in BB are well below the vendor specified value with fan

failed conditions (left, middle and right fan failure).

For BB components left fan failure is having more impact than middle and

right fan failure.

Components of Sl.no.12 and 13 in BB have temperature rise of around 5°C

due to left fan failure compared to all fans running condition.

Middle fan failure is having relatively more impact than right fan failure for

all components in BB.

All the components in PB are well below the vendor specified and derated

values with fan failed conditions (left, middle and right fan failure).

56

Even though all components are well within safe limit, due to fan failure there

is relative rise in all component temperatures in PB compared with all fans

running condition.

Heat towers are provided for components of Sl.no.16, 17 and 18 in SB inorder

to reduce the temperature. This will be finalized after thermal Validation test

in proto2.

Thermal simulation can be performed by increasing the vents in the bottom to

enhance the flow of air through bottom vents which will increase convective

heat transfer.

Due to the increase in bottom vent the fan operating point is shifted to

optimum range. This is finalized based on the thermal validation testing

sample.

5.10. BTS THERMAL DESIGN WITH SPEED REDUCTION OF

92MM FAN

To obtain the equivalent thermal results of 3*60mm fan by reducing the speed

of 3*92mm fan

5.10.1. Details of 60mm and 92mm fan

Vendor curve details (60mm fan) Vendor curve details (92mmfan)

Fig.5.51 Vendor specified curve details for 60mm and 92mm fan

57

Figure 5.51 explains the curve details specified from vendor for 60mm and

92mm fan. The curve is given for 100% of maximum speed. The maximum

rotational speed of 60mm fan is 6800 rpm and that of 92mm fan is 5400rpm. The

flow discharge Vs static pressure points for 60mm and 92mm fan at 85% of maximum

speed is considered based on above curves for previous analysis. In present analysis

the above curve points for 92mm fan is used for calculating the flow discharge and

static pressure for lower rotational rpm.

5.10.2. Assumptions for present analysis

System resistance for both cases with 3*60mm fan assembly and 3*92mm fan

assembly are assumed same.

Fan laws are applicable to both 60mm and 92mm diameter fans.

5.10.3. Procedure

As initial step airflow and static pressure points for 60mm fan at 85% of

maximum speed is obtained using fan law. For same condition (85% of max.Speed),

points are obtained for 92mm fan. Based on the air flow rate, as first cut trial, points

are obtained for 70% of maximum speed using fan law. Next, flow points are obtained

for reduced speeds in steps of 10% from previous rotational rpm. (i.e Flow points

obtained for 60%, 50% , 40% and 30% of maximum speed). For 92mm fan the flow

rate at 30% of maximum speed is less than 85% of maximum speed of 60mm fan.

Hence for analysis rotational speed with 40 to 70 % of maximum speed of 92mm fan

is considered. Thermal simulation is carried out for 40, 50, 60 and 70% of maximum

speed for 92mm fan and temperature results are compared with 60mm fan thermal

results which runs at 85% maximum speed . The flow discharge Vs static pressure

58

points for 60mm fan and for 92mm fan with different speeds are tabulated in below

tables. The points are used for obtaining fan curve for different rotational speed.

Table 5.29 Flow discharge Vs Static pressure points for 60mm fan

Table 5.30 Flow discharge Vs Static pressure points for 92mm fan

Tables 5.29 and 5.30 are tabulated with flow discharge and static pressure

points at 85% of maximum speed for 60mm and 92mm fan.

59

Table 5.31 Discharge Vs Static pressure points for 92mm fan at different speeds

Table 5.31 gives the information of discharge Vs static pressure points of 92mm

fan at different speed (i.e 30, 40, 50, 60 and 70% of maximum speed). For obtaining

the curve the units for discharge and static pressure are used as cfm and inches of

water respectively. However, the results are given in SI units in the later section

5.10.5. The above embedded excel sheet gives the information of Tables 5.29, 5.30

and 5.31.

Fig.5.52 Fan curve at different speed

Figure 5.52 shows the Flow Vs static pressure curve for 85% of maximum

speed of 60mm fan and 40 to 70 % maximum speed of 92mm fan. From the graph it

60

can be seen that all fan speeds from 40 to 70% maximum speed of 92mm fan has flow

rate more than 85% maximum speed of 60mm fan.

5.10.4. Temperature Results

Table 5.32 Components temperature comparison in SB for 60 and 92mm fan

Table 5.32 shows the temperature values of components in SB for various speed

of 92mm fan assembly and 85% maximum speed of 60mm fan assembly. In SB 40

and 50% speed of 92mm fan results in more or less same temperature as 85% of

60mm fan.

61

Table 5.33 Components temperature comparison in BB for 60 and 92mm fan

Table 5.33 shows the temperature values of components in BB for various speed

of 92mm fan assembly and 85% maximum speed of 60mm fan assembly. In BB 50%

speed of 92mm fan results in more or less same temperature as 85% of 60mm fan.

62

Table 5.34 Components temperature comparison in PB for 60 and 92mm fan

Table 5.34 shows the temperature values of components in BB for various speed

of 92mm fan assembly and 85% maximum speed of 60mm fan assembly. In BB 50%

speed of 92mm fan results in more or less same temperature as 85% of 60mm fan.

5.10.5. Fan operating point

Left fan Right fan Middle fan

Fig.5.53 Operating curve for 60mm fan at 85% of maximum speed

63

Left fan Right fan Middle fan

Fig.5.54 Operating curve for 92mm fan at 40% of maximum speed

Left fan Right fan Middle fan

Fig.5.55 Operating curve for 92mm fan at 50% of maximum speed

The Figure 5.53 shows the operating point of left, middle and right fan of 60mm

fan assembly. The Figures 5.54 and 5.55 shows the operating point of left, middle

and right fan of 92mm fan assembly with 40 and 50% of maximum speed.

64

Left fan Right fan Middle fan

Fig.5.56 Operating curve for 92mm fan at 60% of maximum speed

Left fan Right fan Middle fan

Fig.5.57 Operating curve for 92mm fan at 70% of maximum speed

The Figures 5.56 and 5.57 shows the operating point of left, middle and right fan of

92mm fan assembly with 60 and 70% of maximum speed.

Table 5.35 Operating point for 60mm fan

Fan Possition Volume Flow (m3/sec)

Static Pressure(Pa)

Left Fan 0.00820 26.70

Middle Fan 0.00810 27.56

Right Fan 0.00810 27.02

65

Table 5.36 Operating point for 92mm fan

The Table 5.35 gives the operating point of 60mm fan operating at 85% of

maximum speed. The operating point is tabulated for left, middle and right fan. Table

5.36 shows the operating point for left, middle and right fan of 92mm fan assembly

with various speeds from 40 to 70% of maximum speed.

5.10.6. Observations

By comparing the temperature of the components in all the boards it is observed that

50% of maximum speed for 92mm fan experiences the thermal distribution in

the BTS unit as same as the 60mm fan with 85% of maximum speed.

However, all speeds more than 50% of maximum speed (i.e 60 and 70% of

maximum speed) are having better thermal margin as compared with 60mm

fan running at 85% of maximum speed.

Fan speed should not be set less than 50% of maximum speed for 92mm fan as

the operating flow will not be adequate for further reduction in fan speed.

Please refer Table 5.35 and Table 5.36. (In 92mm fan 40% of maximum speed

operating flow is less than the 60mm fan running at 85% of maximum speed)

The operating point of 92mm fan for all considered percentage of maximum

speed is not in the optimum operating range.

66

The operating point has to be shifted to optimum range by reducing the system

resistance

5.11. THERMAL VALIDATION OF BTS

Objective of thermal validation is as follows

To measure the case/ambient temperature of selected components located in

PIU board for below mentioned cases

CASE 1: BTS unit with 65°C ambient all fan running condition (60% fan

speed) with 65 mm fan assy.

CASE 2: BTS unit with 65°C ambient all fan running condition (60% fan

speed) with 92 mm fan assy.

To compare the results with computed temperature.

5.11.1. Test Configuration

BTS unit is run at 65°C thermal chamber ambient condition.

Testware (Traffic) for stressing the components for max power dissipation

Measurements carried out at 65°C ambient condition and components

temperature measured during all three fans running.

5.11.2. System Configuration for 92 mm Fan Assy

The system configuration is as following for BTS mechanics

SB (System board) and BB (Base band board) will be placed in upper chassis

of BTS mechanics.

Power board will be placed in lower chassis in BTS mechanics

67

Components which possess heat tower in SB and BB will be attached to upper

chassis heat sink of BTS mechanics.

Components which possess heat tower in PB will be attached to lower chassis

heat sink.

Stressing software (Traffic) will be used to exercise all the components to the

maximum power for measurement.

External air flow in BTS will be with 3*92mm fan assembly (all fans

running).

For easy change of the actual interface according to customer’s need it has

Plug-in unit

On top of the main frame power distribution Unit (PB) is located.

5.11.3. Temperature measurement with 92 mm fan assy

Fig.5.58 TC placements on System board (SB) Components

Figure 5.58 explains the placement of thermocouple on the components considered

for measuring the temperature in System board (SB).

T-Type (36 AWG) thermocouples are used to measure case temperature of the

components.

68

Table 5.37 TC locations in SB/PIU

Table 5.37 shows the temperature measuring place of the components located in

SB/PIU.

Picture below explains the placement of thermocouple on the components

considered for measuring the temperature in Base band board (BB).

Fig.5.59 TC placement on Base band board (BB) components

69

Table 5.38 TC locations in BB

Table 5.38 shows the temperature measuring place of the components located in BB

Figure 5.60 explains the placement of thermocouple on the components considered

for measuring the temperature in Power board (PB).

Fig.5.60 TC placement on Power board (PB) components

70

Table 5.39 TC locations in PB

Table 5.39 shows the temperature measuring place of the components located in PB

TC location 317, 318, and 319 are measured for chassis surface temperature of BB,

air inlet and air exit of unit.

Fig 5.61 TC placement on General PIU

5.11.4. Thermal Validation Test Procedure

Components considered for measurements are cleaned with isoproponal

solution which removes dust and other particles. Thermocouples are attached to the

surface of the components using thermal paste(Loctite 384) and thermal tape.Thermal

71

gel (Putty 304) is used to couple the component surface and heat tower. Checked for

proper fitting and IP protected condition.The data path during the thermal test is

network Processor LLP LIU External loopback. All devices in system,

baseband and power board are powered on and stressed as per the requirement.

Working condition of thermocouple is checked by measuring the ambient temperature

before the system is powered on.

The below given instructions are followed for conducting the test

• The system is stressed using the software tools so that all components are at

required loading condition. In this test the components are stressed partially.

• “Engineering investigation" testing - the system is kept power on for a

minimum of two hour to reach steady state.

• Once the system is stabilized, the temperature measurement is logged for

analysis.

• Measurements are carried out as per the test configuration.

In baseband board traffic path are stressed and all interfaces are initialized. The

power drawn by the unit without applying external load to PB is around 98Watts.

(Voltage of 48V and Current of 2.04 amp).To get the exact temperature inside,

external loads are driven by PB. PB power ports are connected with passive loads.

The power consumption of passive loads are 4 numbers of 48V, 20A and 1 number of

48V, 5 A.The extra power in PB added due to drop by connected passive loads is 17

Watts.The total power supplied to the unit including external loading is around

115Watts.

After the measurements the working condition of the system is ensured through

hardware input

72

5.11.5. Thermal Validation Test Results with 92 mm Fan Assy

The system is tested for the required test cases and data is recorded as per the

requirement.

The component temperatures are checked against the allowable limit to verify

pass/fail criteria. Summary of test results will be represented in table form to ensure

the pass file criteria.

Table 5.40 Validated results for the components in the SB/PIU

The system board components validated temperature and simulated

temperatures are tabulated in Table 5.40.

73

Table 5.41Validated results for the components in the BB

The table 5.41 gives the validated temperature values of the components located

in base band board (BB) and simulated value.

Table 5.42 Validated results for the components in the PB

The table 5.42 is provided with the validated temperature results of the

components located in the power board (PB) and the simulated temperature.

Table 5.43 Chassis Case, Inlet and Exit Air Temperature

74

Sl.No. TC location Temperature (°C)

1 Chassis case (BB side) 70.7

2 Air temperature at the chassis outlet 68.2

3 Inlet air/thermal chamber 65.0

Chassis case temperatures and inlet/outlet air temperature are mentioned in the

Table 5.43. The inlet air temperature/thermal chamber air temperature at steady state

condition and chassis case temperature at BB side are mentioned in the Table 5.43.

The junction temperatures for validated component are obtained from measured

case temperature.

The junction temperature is calculated from measured case temperature using

below relation.

Junction temperature (Tj) = Case Temperature (Tc) + Junction to case resistance

(Rjc) times the power (P)

i. e. Tj = Tc + Rjc *P

Where Tj, Tc are in °C,

Rjc in °C/W and

P in watts.

Components whose Rjc values are not given in data sheet are calculated using

below equation.

Rjc = t / (K*A)

75

Where t is the half thickness of the component (m),

K is thermal conductivity (W/m°K),

A is cross section area (m2)

5.11.6. Thermal Validation Results and Discussions of 92 mm fan assy

All the critical components measured during testing are well below the

allowable vendor data sheet.

In SB, all components are within the limit of NSN derated values except

processor component (MCOMPO NO: 4332632).

In baseband board except L2 switch component (MCOMPO NO: 4331812) all

other components are within derated values.

All components in power board are within limit of derated values.

Difference in temperatures in the components with respect to the simulation

values are due to power dissipation.

The temperature difference between the inlet and exit air temperature is

around 3.2°C and case temperature is around 70.7°C near BB side.