WO1992010710A1

WO1992010710A1 - A method and arrangement for producing minimum refrigerant flows

Info

Publication number: WO1992010710A1
Application number: PCT/SE1991/000823
Authority: WO
Inventors: Bo Frejd
Original assignee: Stal Refrigeration Ab
Priority date: 1990-12-07
Filing date: 1991-12-03
Publication date: 1992-06-25
Also published as: AU8935191A; SE9003920D0; SE9003920L; SE467592B

Abstract

In refrigerating systems and heat pump systems, thermostatic expansion valves are used to deliver a precisely correct quantity of refrigerant to an evaporator under changing operational conditions. The valve shall maintain equilibrium between delivery of the refrigerant and the removal by suction of said refrigerant under all operating conditions. In order to prevent the expansion valve of a refrigerating or heat pump system from remaining closed due to low bulb temperature, where several refrigerating batteries/evaporators with expansion valves are arranged in parallel and where a substantially constant suction pressure prevails and closing of the valve will not therefore influence the system suction pressure, there has been arranged over the expansion valve, between the high pressure side and the low pressure side, a connection (5, 6, 8) which has an adjustable or fixed through-flow area and which will guarantee that a minimum amount of refrigerant is vapourized in the evaporator such as to produce superheated gas for heating a bulb connected to the expansion valve.

Description

A METHOD AND ARRANGEMENT FOR PRODUCING MINIMUM REFRIGERANT FLOWS

DESCRIPTION

Technical Field

The present invention relates to a method and to an arrangement for delivering a minimum flow of refrigerant to an evaporator of a refrigerating system or heat pump system, in order to prevent an expansion valve included in the system from remaining in a closed position due to low bulb temperature.

Background Art

In refrigerating systems and heat pump systems, thermo- static expansion valves are used to deliver precisely the correct amount of refrigerant to an evaporator under changing operating conditions. The valve shall maintain equilibrium between the time that refrigerant enters the valve to the time that refrigerant is drawn therefrom by suction, under all operating conditions. The refrige- rant shall leave the evaporator in a gaseous state and have a temperature which is some degrees higher than the vapourization temperature of the refrigerant used. Thus, the gaseous refrigerant shall leave the evaporator in a superheated state, i.e. shall be heated above the saturation temperature. Thermostatic expansion valves can thus be considered to be superheating regulators and are intended to control the course of the refrigerant in a refrigerating system which includes one or more evapo¬ rators. The manner in which the thermostatic expansion valve operates is determined by the mutual coaction between a bulb pressure, which is dependent on the temperature of the vapourized refrigerant, and the bulb filling and functions to exert an opening force on the valve, a vapourizing pressure, which functions to close the valve, and an adjustable spring pressure which also functions to close the valve. When the valve closing forces are in equilibrium with the valve opening force, the state of the valve opening remains unchanged. If the bulb becomes heated due to the evaporator receiving too little liquid refrigerant, the bulb pressure will increase and therewith further lift a valve needle in the expansion valve, resulting in an increase in the through-flow cross-section. A fall in vapourizing pres¬ sure has a similar effect. In this case, however, a drop in bulb temperature or a rise in vapourization pressure moves the valve needle in the valve closing direction. The bulb pressure and the vapourization pressure are thus directly related to one another and directly dependent on one another. Both of these forces together determine the extent to which the valve is opened, depending on the extent to which the evaporator is filled at that time, and provides the best possible use under all operating conditions.

Disclosure of the Invention

In order to prevent an expansion valve of a refrigera¬ ting system or heat pump system from remaining closed as a result of low bulb temperature, where several refrig¬ erating batteries/evaporators equipped with expansion valves are connected in parallel and where a substan¬ tially constant suction pressure prevails and thus where closing of the valve will not affect the system suction pressure, there has been arranged across the expansion valve, between the high pressure side and the low pres- sure side, a connection which has an adjustable or a fixed through-flow area and which will guarantee that a minimum quantity of refrigerant is vapourized in the evaporator to produce a superheated gas for heating a bulb connected to the expansion valve. Thus, subsequent to closing the valve, the bulb will be heated to a given extent through the vapourization of a smallest amount of refrigerant in the evaporator such as to generate super¬ heated gas, therewith causing the expansion valve to reopen.

Brief Description of the Drawings

Figures 1-3 illustrate different embodiments of the inventive connection across the expansion valve; and

Figure 4 illustrates an embodiment of a system which includes several evaporators arranged in parallel and provided with inventive expansion valves.

Best Mode of Carrying Out the Invention

Figure 1 illustrates a conventional thermostatic expan¬ sion valve 1 of a refrigerating system having an evapo¬ rator 2 , a bulb 3 and a closure valve 4. The high pressure side of the system is connected to the low pressure side thereof by means of a connecting pipe 5. The connecting pipe may have an adjustable through-flow cross-section or may be provided with an exchangeable flow throttling function. The connection 5 guarantees that a minimum quantity of refrigerant is always able to pass beyond the expansion valve when the valve 4 is open and the system compressor is in operation. Should the expansion valve 1 close, a given amount of refrigerant will thus by-pass the valve and be vapourized in the evaporator, therewith producing superheated gas for heating the bulb 3, and thereby causing the expansion valve to re-open. Figures 2 and 3 illustrate alternative embodiments of by-pass connections by means of which a minimum quantity of refrigerant by-passes the valve in accordance with the invention. In the Figure 2 embodiment, a hole 6 is formed in the valve seat 7 of the expansion valve 1.

The diameter of the hole 6 may be chosen with respect to the construction performance of the expansion valve. The hole may also be provided with an adjustable con¬ striction or provided with exchangeable constriction- producing plates. In the Figure 3 embodiment, a pas¬ sageway 8 or like channel is provided in the valve plug 9. As with the Figure 2 embodiment, the dimensions of the passageway 8 are chosen with respect to the con¬ struction performance of the expansion valve, or the passageway may be given an adjustable cross-sectional area.

Figure 4 is a simplified illustration of several evapo¬ rators connected in parallel and provided with expansion valves-. When the bulb 3 detects a drop in temperature, the system expansion valve will close. When the suction pressure throughout the whole of the system is substan¬ tially constant, the valve will remain closed. However, by causing a minimum amount of refrigerant to by- ass the expansion valve, this minimum amount of refrigerant will be vapourized and heat the bulb 3 such as to open the expansion valve 1.

Claims

1. A method for delivering a minimum flow of refriger¬ ant to an evaporator in order to prevent a thermostatic expansion valve remaining closed due to low bulb tem¬ perature in a refrigerating system or heat pump system, c h a r a c t e r i z e d by causing said minimum flow to the evaporator to by-pass the expansion valve, where¬ in a bulb connected to the expansion valve in the system is heated and therewith result in opening of the expan¬ sion valve.

2. An arrangement for delivering a minimum flow of refrigerant to an evaporator so as to prevent a thermo- static expansion valve remaining closed due to a low bulb temperature in a refrigerating system or heat pump system, c h a r a c t e r i z e d in that a connection (5, 6, 8) is arranged between the high pressure side and the low pressure side over the expansion valve.

3. An arrangement according to Claim 2, c h a r a c ¬ t e r i z e d in that said connection (5) is arranged parallel with the expansion valve (1) and may be provi¬ ded with an adjustable cross-sectional area or with exchangeable flow throttling functions.

4. An arrangement according to Claim 2, c h a r a c ¬ t e r i z e d in that said connection (6) has the form of a hole provided in a valve seat (7) of the expansion valve (l) and may be provided with an adjustable con¬ striction or with exchangeable constriction forming plates.

5. An arrangement according to Claim 2, c a r a c ¬ t e r i z e d in that the connection (8) has the form of a passageway (8) or the like provided in a valve plug (9) of the expansion valve, and may be provided with an adjustable cross-sectional area.

AMENDED CLAIMS

[received by the International Bureau on 4 May 1992 (04.05.92) ; original claims 1-5 replaced by amended claims 1-4 ( 1 page) ]

1. An arrangement for delivering a minimum flow of refrigerant to an evaporator in a refrigerating system or heat pump system to bypass a thermostatic expansion valve for heating a bulb connected to the expansion valve to prevent the expansion valve from remaining closed due to low bulb temperature, characterized in that an adjustable connection (5, 6, 8) is arranged over and parallel with the expansion valve between the high pressure side and the low pressure side.

2. An arrangement according to claim 1, characterized in that said connection (5) is arranged as a connection with exchangeable flow throttling functions.

3. An arrangement according to claim 1, characterized in that said connection is arranged as an adjustable hole (6) in a valve seat (7) to the expansion valve (1) and may be as such provided with an adjustable constriction or may be provided with exchangeable constric¬ tion forming plates. 4. An arrangement according to claim 1, characterized in that said connection is arranged as a passageway (8) or the like in a valve body (9) of the expansion valve and may be as such provided with an adjustable cross-sectional area.