US20150060019A1

US20150060019A1 - Pulsating multi-pipe heat pipe

Info

Publication number: US20150060019A1
Application number: US14/083,766
Authority: US
Inventors: Chih-Yung Tseng
Original assignee: Industrial Technology Research Institute ITRI
Current assignee: Industrial Technology Research Institute ITRI
Priority date: 2013-09-02
Filing date: 2013-11-19
Publication date: 2015-03-05
Also published as: CN104422319A; CN104422319B; TWI579519B; TW201510457A

Abstract

A pulsating multi-pipe heat pipe having its metal pipes arranged in-parallel and bent in snake-shaped loop, is capable of making the working fluid flow through the pulsating multi-pipe heat pipe, enhance the pressure difference therein so as to improve its heat-dissipating effect and successfully overcome the problems of horizontal action when the heat pipe is laid in horizontal position. This is done by attaching at least a chambered connector in the metal pipes having their cross-sectional areas greater than the total cross-sectional areas of the metal pipes or furnishing at least a pair of communicative penetrating holes at the side-by-side adjacent pipe walls making the working fluid create cross-flow within the pulsating multi-pipe heat pipe.

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application is based on, and claims priority from, Taiwan (International) Application Serial Number 102131568, filed on Sep. 2, 2013, the disclosure of which is hereby incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates to a heat pipe for heat dissipating purpose, and more particularly, to a pulsating multi-pipe heat pipe furnished at least a chambered connector having a cross-sectional area that is greater that the total cross-sectional area of the multi-pipe or furnished at least a pair of penetrating hole.

BACKGROUND

The heat pipe having good heat transfer performance is widely applied in electronic devices for heat-dissipating, especially personal computers, and notebook computers,. In general, facing the heat-dissipating demands for the plane heat-generating mode, it is necessary to have the design of heat pipe by employing a number of heat pipes simultaneously to be able to satisfy the requirements of heat-dissipating. However, employing a number of heat pipes will result in the difficulties on heat-dissipating design as well as the assembly and manufacturing of heat-dissipating module. Two half frames the vapor chamber is a more suitable heat-dissipating device than the conventional heat pipe.
The difficulties for using vapor chamber having capillary action lies in the sintering fabrication of the capillary structure. The reasons are as follows:

1. The larger the vapor chamber, the harder it is to control the uniformity of the capillary structure, thereby it is apt to result in instability in performance;
2. The larger the vapor chamber, the larger the sintering furnace is needed which results in increasing the fabrication cost and lowering the mass production speed;
3. The strength of the pipe wall of the vapor chamber will be substantially lower after annealing process is performed which results in its inability to keep its required strength to respond to the internal and external pressure variation.

Since the sintering process of the capillary structure can derive so many fabrication problems, a pulsating or oscillating heat pipe becomes another alternative for the vapor chamber.
The overall structure of the pulsating heat pipe nowadays is rather simple. The driving force of the pulsating heat pipe is an action generated by the heat pipe having relatively smaller pipe diameter, and by making use of the capillary action, gravitational force subjected to the working fluid, as well as the vapor pressure subjected to the absorbing heat However, since the capillary action of the conventional pulsating single-pipe heat pipe is very limited, the actuating force of the pulsating single-pipe heat pipe depends mainly on the gravitational force. For this reason, when it comes to the situation that the heat pipe is laid in horizontal position or is laid in negative-angle position, or in any skew positions where the heat-absorbing end is higher the heat-dissipating end, the conventional pulsating single-pipe heat pipe will not be able to be actuated. Disregarding the fact that several methods, such as employing magnetic fluid and controlled by an external magnetic field depicted in the dissertation published by Shafii et al., employing a check-valve device illustrated in Patent No. I33187718, Taiwan, R.O.C. or other papers etc., actuation problems for the negative (upside-down) position and skew position are still unresolved since the gravitational force in these position are relatively small and the working fluid from the heat-absorbing end is difficult to flow back to the heat-dissipating end. As a result, the horizontal actuation problem is unable to be resolved and the thermal resistance is incapable to be approved. This kind of application limitation forms the main challenge to the pulsating heat pipe applied in vapor chamber.

SUMMARY

In light of the disadvantages of the prior arts, the present disclosure provides a pulsating multi-pipe heat pipe that aims to ameliorate at least some of the disadvantages of the prior art or to provide a useful alternative.
In view of the fact that the pulsating single-pipe heat pipe of the prior art is incapable of being actuated when it is laid in horizontal position or in the position when its heat-absorbing end is higher than the heat-dissipating end, the present disclosure provides a pulsating multi-pipe heat pipe to resolve the incapability problem of the prior art. The pulsating multi-pipe heat pipe of the present disclosure having two in-parallel metal pipes with equal diameter placed side-by-side and bent into a snake-shaped closed loop has a chambered connector furnished to make the two metal pipes become communicative with a heat-absorbing area at the first end and a heat-dissipating area at the second end or has two adjacent face-to-face penetration holes drilled respectively at the metal pipes and soldered between them to form a passage to make the two metal pipes communicate each other. Through the communicating mode of the plurality of metal pipes, the pulsating multi-pipe heat pipe of the present disclosure is capable of creating unbalanced volumetric filling quantity of working fluid, and when it comes to actuating, the filling quantity is capable of generating dynamic and alternate variation making it capable of being actuated when it is in negative 90° position or in the position when its heat-absorbing end is higher than the heat-dissipating end
and staying in unbalanced force for a long time for the working fluid contained in the metal pipes. Therefore, the pulsating multi-pipe heat pipe of the present disclosure is capable of being actuated when it is laid in either horizontal or negative angular positions, thereby achieving the heat-dissipating effect..
The embodiments of the present disclosure includes a plurality of snake-shaped loops having the same diameter and each having a plurality of chambered connectors to make the pulsating multi-pipe heat pipe of the present disclosure become communicative.
The embodiments of the present disclosure also includes a plurality of snake-shaped loops having different diameter and each having a plurality of chambered connectors to make the pulsating multi-pipe heat pipe of the present disclosure become communicative.

BRIEF DESCRIPTION OF THE DRAWINGS

The accomplishment of this and other objects of the present disclosure will become apparent from the following description and its accompanying drawings of which:

FIG. 1 is a plan view of a schematic drawing of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure

FIG. 2 is a plan view of a schematic drawing of the second embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 3 is a plan view of a schematic drawing of the third embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 4 is a plan view of a schematic drawing of the fourth embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 5 is a plan view of a schematic drawing of the fifth embodiment of the combined type heat pipe of the pulsating multi-pipe heat pipe of the present disclosure; and

FIG. 6 is a plan view of a schematic drawing showing the connection and the way of communication between the chambered connector and the pipes of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 6A˜6C is a plan view of a schematic drawing showing the flowing status of the working fluid between the chambered connector and the pipes of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 7 is a plan view of a schematic drawing showing the penetrating holes and the way of communication between the pipes of the sixth embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 7A is a plan view of a schematic drawing showing the penetrating holes and the way of communication between the pipes of an alternate sixth embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 8 is a thermal resistance chart showing the variation curve of the thermal resistance against time when the heat pipe is laid in horizontal position of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 9 is a thermal resistance chart showing the variation curve of the thermal resistance against time when the heat pipe is placed in negative 90 degree position of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure;

FIG. 10 is a thermal resistance chart showing the variation curve of the thermal resistance against time when the heat pipe is placed in negative 90 degree, negative 90 degree, and negative 45 degree positions of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure.

DETAILED DESCRIPTION

FIG. 1 is a plan view of a schematic drawing of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure. As shown in FIG. 1, the pulsating multi-pipe heat pipe (1) of the first embodiment of the present disclosure is formed by having two in-parallel metal pipes (11), (12) with equal diameter placed side-by-side and bent into a snake-shaped closed loop (13). What is more, the pulsating multi-pipe heat pipe of the first embodiment (1) of the present disclosure having a chambered connector (14) furnished to make the two metal pipes (11), (12) become communicative has a heat-absorbing area (15) at a first end and a heat-dissipating area (16)at a second end.
FIG. 2 is a plan view of a schematic drawing of the second embodiment of the pulsating multi-pipe heat pipe of the present disclosure. As shown in FIG. 2, the pulsating multi-pipe heat pipe (2) of the second embodiment of the present disclosure has the same structural disposition as the pulsating multi-pipe heat pipe (1) of the first embodiment of the present disclosure except that the two metal pipes (21), (22) are in different diameter.
FIG. 3 is a plan view of a schematic drawing of the third embodiment of the pulsating multi-pipe heat pipe of the present disclosure. As shown in FIG. 3, the pulsating multi-pipe heat pipe (3) of the third embodiment of the invention has the same structural disposition as the pulsating multi-pipe heat pipe (1) of the first embodiment of the invention except that the two metal pipes (31), (32) are furnished with two chambered connector (33), (34) instead of one chambered connector (14). However, that the structural disposition can be varied by having the metal pipes (31), (32) in different diameter or by having three chambered connectors instead of two is also within the scope of the present disclosure.
FIG. 4 is a plan view of a schematic drawing of the fourth embodiment of the pulsating multi-pipe heat pipe of the present disclosure. As shown in FIG. 4, the pulsating multi-pipe heat pipe (4) of the fourth embodiment of the present disclosure has the same structural disposition as the pulsating multi-pipe heat pipe (1) of the first embodiment of the present disclosure except that there are there are three in-parallel metal pipes (41), (42), (43) furnished instead of two metal pipes (11), (12). However, that the structural disposition can be varied by having the metal pipes (41), (42), (43) in different diameter or by having at least two chambered connectors instead of one is also within the scope of the present disclosure.
FIG. 5 is present disclosure a plan view of a schematic drawing of the fifth embodiment of the combined type heat pipe of the pulsating multi-pipe heat pipe of the present disclosure. As shown in FIG. 5, the pulsating multi-pipe heat pipe (5) of the fifth embodiment of the present disclosure is a combined type heat pipe (5) having two unequal-diameter heat pipes (51) and (52) each having a single metal pipe uses a common chambered connector (55) connected between thereof with a heat-absorbing area in a center part (56) thereof and a heat-dissipating area, at a third end (58) and a fourth end (57) respectively thereof. However, that the structural disposition can be varied by having two equal-diameter heat pipes or by having two or two more chambered connectors instead of one is also within the scope of the present disclosure.
It is worthwhile to emphasize here that in all the Figures, the hatch lines in all the metal pipes are intended to differentiate different pipe diameter rather than showing cross-sectional mark.
FIG. 6 is a plan view of a schematic drawing showing the connection and the way of communication between the chambered connector and the pipes of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure. As shown in FIG. 6, first of all, a hole is drilled at each end of the chambered connector (14), then each of the metal pipes (11), (12) are attached to the holes and is welded thereof. If, for example, the diameter of the metal pipes (11), (12) is D which is 0.1˜8.0 mm, the width W and height H of the chambered connector (14) is 2 D˜10 D and its Length L is 2 D˜20 D. Referring also to FIG. 1, when the heat absorbing area (15) is heated, the working fluid in the metal pipes will evaporate and increase its vapor pressure to push the working fluid to flow through the metal pipes the heated working fluid will then flow to the heat-dissipating area (16) to achieve the heat transferring effect.
FIG. 6A˜6C are plan views of schematic drawings showing the flowing status of the working fluid between the chambered connector and the pipes of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure. As shown in FIGS. 6A, 6B, and 6C, the dotted shade area indicates the working fluid while the arrow head indicates the direction of the flow of the working fluid. As shown in FIG. 6A, when the pressure of the working fluid on the right-hand side of the metal pipes (11), (12) is greater than the pressure of the working fluid on the left-hand side of the pipe (11), (12), the working fluid will flow from the right-hand side of the metal pipes (11), (12) through the chambered connector (14) toward the left-hand side of the metal pipes (11), (12). On the contrary, As shown in FIG. 6B, when the pressure of the working fluid on the left-hand side of the metal pipes (11), (12) is greater than the pressure of the working fluid on the right-hand side of the pipe (11), (12), the working fluid will flow from the left-hand side of the metal pipes (11), (12) through the chambered connector (14) toward the right-hand side of the metal pipes (11), (12). As shown in FIG. 6C, when the pressure of the working fluid of both the right-hand side and left-hand side of the metal pipe (12) as well as the pressure of working fluid of the left-hand side of the metal pipe (11), is greater than the pressure of the working fluid on the right-hand side of the metal pipe (11), then the working fluid in both sides of the metal pipe (12) and the working fluid of the left-hand side of the metal pipe (12) will all flow through the chambered connector (14) toward the right-hand side of the metal pipe (11). In this way, by employing the pressure difference in the metal pipes (11), (12), the working fluid in the metal pipes (11), (12) will result in a cross-flow through the chambered connector (14) making random distribution, non-uniform flow filling, and creating unbalance force, thereby the overall piping flow system is capable of successfully overcoming the starting problem when the metal pipes (11), (12) are disposed in horizontal position, in skew position, or even in up-side-down position with the heat-absorbing end up for working fluid vaporization and the heat-dissipating end down for vapor condensing (negative 90 degree position) where the gravitational force of the working fluid is not working well or without working in the metal pipes (11), (12) because the metal pipes (11), (12) are disposed in upside down position.
FIG. 7 is a plan view of a schematic drawing showing the penetrating holes and the way of communication between the pipes of the sixth embodiment of the pulsating multi-pipe heat pipe of the present disclosure. As shown in FIG. 7, instead of furnishing the above-mentioned chambered connector (14), two adjacent face-to-face penetration holes (63), (64) are drilled respectively at the metal pipes (61), (62) after the metal pipes (61), (22) are pulling apart a small distance to facilitate the drilling work, and the two metal pipes (61), (62) are then pulled back to be contacted side-by-side and soldered between them to form a passage to make the two metal pipes (61), (62) communicate each other.
FIG. 7A is a plan view of a schematic drawing showing the penetrating holes and the way of communication between the pipes of an alternate sixth embodiment of the pulsating multi-pipe heat pipe of the present disclosure. In view of the inconveniency of drilling two adjacent face-to-face penetration holes (63), (64) respectively at the metal pipes (61), (62) that need to be pulled apart a small distance to leave a space to facilitate the drilling work, an alternate way is to drill a hole (65) on the opposite side of the metal pipes (61) all the way through the above-mentioned two adjacent face-to-face penetration holes (63), (64) respectively at the metal pipes (61), (62) and then have them solder to form a passage to make the two penetration holes (63), (64) communicate each other without have the metal pipes (61), (62) pull apart. Afterward, the hole (65) is sealed by soldering. In addition, if D is the diameter of the metal pipes (61), (62), the lengths L2 of the penetration holes (63), (64) in pipe's axial direction are preferably in the range of 2 D˜20 D where the dimension of D is in the range of 0.1˜8.0 mm.
Among the above-mentioned embodiments, the second embodiment shown in FIG. 2 is chosen to be the preferred embodiment, and similar metal pipe disposition like the way of having the metal pipes formed by engraving on a plat is still in the range of the present disclosure.

Experimental Embodiment

Experimental work is performed and charts showing the variation of thermal resistance against heating time are drawn to make comparisons between the conventional pulsating single-pipe heat pipe and the pulsating multi-pipe heat pipe of the present disclosure. First of all, both the conventional heat pipe and the heat pipe of the present disclosure are vacuumized and filled with working fluid by 60% of the total volume of the piping system. Thereafter, heat Q_inis added to both of the conventional pulsating single-pipe heat pipe and the pulsating multi-pipe heat pipe of the invention, and in the same time, the disposition is varied with different orientation angle of the piping systems from horizontal, Vertical, +90 degree, −90 degree to −45 degree, and thereafter, charts and measured equivalent coefficient of heat transfer K_effin W/mK as well as thermal resistance in Celsius degree per Watt (° C./W) against heating time in second are drawn as shown in FIG. 8, FIG. 9, and FIG. 10 respectively by the use of the following formula:
R _th=(T _h −T _L)/Q _in
FIG. 8, 9, 10 are thermal resistance charts showing the variation curve of the thermal resistance against time when the heat pipe is laid in horizontal position, positive 90 degree position, negative 90 degree position, and negative 45 degree positions of the first embodiment of the pulsating multi-pipe heat pipe of the present disclosure with abscissa being the heat subjecting time in second and ordinate being the equivalent thermal resistance in ° C./W.
As shown in FIG. 8, when the conventional pulsating single-pipe heat pipe is laid in horizontal position, i.e. in zero-degree operation angle, the thermal resistance keeps constant at 7° C./W, in other word, almost no significant variation in thermal resistance is found, thereby, no significant heat-dissipating effect is performed.
As shown also in FIG. 8, when the conventional pulsating single-pipe heat pipe of non-uniform runner is laid in horizontal position, the average thermal resistance is around 0.5˜0.7° C./W, and the average heat-transfer coefficient K_avgis around 4,240 W/mK where W being the thermal power in Watt and m being length in meter while K being the absolute temperature in Kelvins temperature scale.
Referring again to FIG. 8, when the pulsating multi-pipe heat pipe of the present disclosure is laid in horizontal position, the average thermal resistance is around 0.07˜0.4° C./W, and the average heat-transfer coefficient K_avgis around 5,524 W/mK. As shown in FIG. 9, it is found that when the conventional pulsating single-pipe heat pipe of non-uniform runner is laid in negative 90° position, the average thermal resistance is 6.4° C./W and the temperature is unchanged. That is to say that when the conventional pulsating single-pipe heat pipe of non-uniform runner is laid in negative 90° position, no heat dissipating effect can be achieved. On the other hand, when the pulsating multi-pipe heat pipe of the present disclosure is laid in negative 90° position, the average thermal resistance is only 0.16° C./W and the temperature is a fluctuant. That is to say that even the pulsating multi-pipe heat pipe of the present disclosure is laid in negative 90° position (upside down position), the heat dissipating function still works. As shown in FIG. 10, when the pulsating multi-pipe heat pipe of the present disclosure is laid in positive 90°, negative 90°, and negative 45° positions respectively, the variation of thermal resistance are all smaller than 20% which indicates that the gravitational force affect on the heat-dissipating effect is small. In addition, the filling rate of working fluid of the pulsating multi-pipe heat pipe of the present disclosure is 60%.
To summarize the above-mentioned description, when it comes to action, the pulsating multi-pipe heat pipe of the present disclosure is capable of creating unbalanced volumetric filling quantity of working fluid, generating dynamic and alternate variation, and staying in unbalanced force for a long time for the working fluid contained in the metal pipes. Therefore, the pulsating multi-pipe heat pipe of the present disclosure is capable of being actuated when it is laid in either horizontal or negative angular positions.
In conclusion, by employing a pulsating multi-pipe heat pipe together with using one or a number of chambered connectors, the present disclosure is capable of making the pulsating multi-pipe heat pipes communicate one another. Moreover, when it comes to action, the heat pipe is capable of making the working fluid persistently actuate to perform evaporation and condensation. Therefore, the pulsating multi-pipe heat pipe of the present disclosure is capable of not only successfully overcoming the horizontal actuation problem but also actuating even when it is laid in negative 90° position (an upside-down position with the heat-dissipating end down and the heat-absorbing end up), thereby achieving the heat-dissipating effect.
It will become apparent to those people skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the present disclosure. In view of the foregoing description, it is intended that all the modifications and variation fall within the scope of the following appended claims and their equivalents.

Claims

What is claimed is:

1. A pulsating multi-pipe heat pipe, comprising:

at least two metal pipes having a plurality of snake-shaped bent loops at a first end thereof, while the other end is a second end, and the two metal pipes are in-parallel, and having a working fluid that is filled thereof; and

at least a chambered connector to be connected to both ends of each of the at least two metal pipes.

2. The pulsating multi-pipe heat pipe in claim 1, wherein the diameters of the at least two metal pipes are equal.

3. The pulsating multi-pipe heat pipe in claim 1, wherein the diameters of the at least two metal pipes are unequal.

4. The pulsating multi-pipe heat pipe in claim 1, wherein the dimension of the diameter of the metal pipes is in the range of 0.1˜8.0 mm.

5. The pulsating multi-pipe heat pipe in claim 1, wherein both the dimensions of the width and height of the chambered connector are in the range of 2 D˜10 D while the length of which is in the range of 2 D˜20 D where D being the diameter of the heat pipe.

6. The pulsating multi-pipe heat pipe in claim 1, wherein the pulsating multi-pipe heat pipe is capable of being operated either in horizontal and or in negative 90° positions when the heat pipe is filled with working fluid and is subjected to heat.

7. The pulsating multi-pipe heat pipe in claim 1, wherein the filling rate of the working fluid is in a range of 30˜80% (volumetric ratio).

8. The pulsating multi-pipe heat pipe in claim 1, wherein a heat-absorbing end is at the first end and a heat-dissipating end is at the second end.

9. A pulsating multi-pipe heat pipe, comprising:

a combined pulsating multi-pipe heat pipe having their second ends connected each other at the center part and their other two ends at the third and fourth ends, each of the combined pulsating multi-pipe heat pipes being a single pipe has a plurality of snake-shaped bent loops at the third and the four end respectively and having a working fluid that is filled thereof; and

at least a chambered connector to be connected at both ends of the metal pipes and at the center part of the combined pulsating multi-pipe heat pipe, to be a common chambered connector.

10. The pulsating multi-pipe heat pipe in claim 9, wherein the diameters of the at least two metal pipes are equal.

11. The pulsating multi-pipe heat pipe in claim 9, wherein the diameters of the at least two metal pipes are unequal.

12. The pulsating multi-pipe heat pipe in claim 9, wherein the dimension of the diameter of the metal pipes is in the range of 0.1˜8.0 mm.

13. The pulsating multi-pipe heat pipe in claim 9, wherein both the dimensions of the width and height of the chambered connector are in the range of 2 D˜10 D while the length of which is in the range of 2 D˜20 D where D being the diameter of the heat pipe.

14. The pulsating multi-pipe heat pipe in claim 9, wherein the pulsating multi-pipe heat pipe is capable of being operated either in horizontal and or in negative 90° positions when the heat pipe is filled with working fluid and is subjected to heat.

15. The pulsating multi-pipe heat pipe in claim 9, wherein the filling rate of the working fluid is in a range of 30˜80% (volumetric ratio).

16. The pulsating multi-pipe heat pipe in claim 9, wherein the center part is a heat-absorbing end while the third end and the fourth end thereof is a heat-dissipating end.

17. A pulsating multi-pipe heat pipe, comprising:

at least two metal pipes having a plurality of snake-shaped bent loops at a first end thereof and having a working fluid that is filled thereof; and

two penetration holes being adjacent and face-to-face are drilled respectively at the metal pipes at a second end and soldered between them to form a passage to make the two metal pipes communicate each other.

18. The pulsating multi-pipe heat pipe in claim 17, wherein the diameters of the at least two metal pipes are equal.

19. The pulsating multi-pipe heat pipe in claim 17, wherein the diameters of the at least two metal pipes are unequal.

20. The pulsating multi-pipe heat pipe in claim 17, wherein the dimension of the diameter of the metal pipes is in the range of 0.1˜8.0 mm.

21. The pulsating multi-pipe heat pipe in claim 17, wherein the length of the penetration holes is in the range of 2 D˜20 D where D being the diameter of the heat pipe.

22. The pulsating multi-pipe heat pipe in claim 17, wherein the pulsating multi-pipe heat pipe is capable of being operated either in horizontal and or in negative 90° positions when the heat pipe is filled with working fluid and is subjected to heat.

23. The pulsating multi-pipe heat pipe in claim 17, wherein the filling rate of the working fluid is in a range of 30˜80%.

24. The pulsating multi-pipe heat pipe in claim 17, wherein the first end of the at least two metal pipes having a plurality of snake-shaped heat pipes is a heat-absorbing end while the second end thereof is a heat-dissipating end.