Browse Prior Art Database

HEAT VALVE

IP.com Disclosure Number: IPCOM000026363D
Original Publication Date: 1991-Aug-31
Included in the Prior Art Database: 2004-Apr-05
Document File: 4 page(s) / 148K

Publishing Venue

Xerox Disclosure Journal

Abstract

There are many situations in which it is desired to be able to rapidly heat at least part of a system to an operating temperature while retaining the ability to dissipate relative large quantities of heat if the control temperature is exceeded. A prime example is an automotive engine where we want to quick warm-up in the winter but the capability of sustained operation in the summer. This is enabled in an automobile via a thermostat which prevents the internally-circulated coolant from passing through the primary heat dissipator (the radiator) if the coolant temperature is below the desired value.

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Page 1 of 4

XEROX DISCLOSURE JOURNAL

HEAT VALVE

Dale R. Ims

19

Proposed Classification
U.S. C1.346/140R Int. C1. GOlD 15/18

20

13

- 10 ACTUATING FORCE

XEROX DISCLOSURE JOURNAL - Vol. 16, No. 4 July/August 1991 229

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Page 2 of 4

HEAT VALVE(Cont'd)

There are many situations in which it is desired to be able to rapidly heat at least part of a system to an operating temperature while retaining the ability to dissipate relative large quantities of heat if the control temperature is exceeded. A prime example is an automotive engine where we want to quick warm-up in the winter but the capability of sustained operation in the summer. This is enabled in an automobile via a thermostat which prevents the internally-circulated coolant from passing through the primary heat dissipator (the radiator) if the coolant temperature is below the desired value.

Similarly, in a thermal ink jet (TIJ) printer, it is desired to rapidly heat the printhead to the desired operating temperature (with a small amount of power), but sustained high density printing requires a substantial heat sink mass. This requires the equivalent of the automobile's thermostat in the coolant circuit. However, liquid cooling presents an undesirable complication in an ink jet printer.

An essentially completely mechanical mechanism is desired which acts as a heat valve - isolating the TIJ printhead from the primary heat sink during warm-up but coupling the two together during periods of sustained high- density printing.

The difficulty with building a mechanical heat valve is that relatively large masses of metal are required to conduct reasonable amounts of heat with small temperature drop. For example, a lmm thick x lcm wide x 2cm long strip of copper has a thermal resistance (end-to-end) of 5"Uwatt. Thus, conducting 5 watts of power through the above strip would result in a 25°C temperature difference from end to end. Thus, relatively large cross sections of metal are required to conduct reasonable quantities of heat. Likewise, conduction of heat across an interface between two members requires a relatively large contact area and a substantial contact force. The thermal resistance of the connection between the two members is, of course, dependent on surface finish, contact force, and proper alignment of the two surfaces. A small amount of grease applied to the two contact surfaces may sub...