The present invention relates to absorption heat transfer machines for transferring heat against a temperature gradient, and to working fluids for use therein.

Machines which transfer heat against a temperature ^" gradient i.e. from a relatively cold heat source to a heat sink at higher temperatures are well known. These machines may be described as refrigerating machines. Refrigerating machines working on the absorption principle are well known. In such absorption heat transfer machines a pair of working substances is used which may be described as a refrigerant and an absorbent. The heat transfer process takes place in a closed system. Heat is taken into the system from outside by evaporation of the refrigerant in an evaporator. The evaporated refrigerant then passes to an absorber in which the refrigerant is absorbed in an absorbent which is poor in refrigerant. Heat is produced by the absorption and is given up to an external coolant.

The liquid absorbent, now rich in refrigerant, is passed to a second evaporator (the generator) where heat is supplied to drive out the refrigerant from the absorbent. The resulting solution poor in refrigerant is returned to the absorber. The refrigerant vapour is cooled and liquefied by heat exchange with an external coolant and then returned to the first evaporator.

Refrigerating machines may be used either to withdraw heat from material which it is desired to cool in which case they may be termed as refrigerators. Alternatively they may be used to introduce heat into material which it is desired to heat eg the air inside a house.

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Machines intended for heating may be the conventional heat pumps in which heat at a relatively high temperature provides the energy to transfer heat from a relatively low temperature heat source to a heat sink at an Intermediate temperature. Alternatively heat may be supplied from a heat source at an intermediate temperature and transferred to a heat sink at a relatively high temperature by making use of the energy obtained by the transfer of some of the heat down a temperature gradient from the heat source at intermediate temperature to a second heat sink at a lower temperature. Such machines may be described as heat transformers.

Working fluid pairs (refrigerant and absorbent) for use in absorption refrigerating machines should in particular satisfy the following requirements:

(a) the difference in boiling temperature between the refrigerant and the mixture of refrigerant and adsorbent should be as great as possible,

(b) the mixture of refrigerant and absorbent should not be solid In the range of compositions and working temperatures used,

(c) the mixture of refrigerant and absorbent should be thermally stable,

(d) the expenditure of energy required for rectifying the mixture evaporated from the generator in order to separate the absorbent from the refrigerant should be low,

(e) the viscosity of the mixture of refrigerant and absorbent in the range of working temperatures and compositions should be low.

The present invention relates to a mixture of substances suitable for _tse in an absorption heat transfer machine, characterised in that the mixture comprises tetrahydrofuran and at least one of benzyl alcohol, diethyl sebacate, or quinoline. According to a further aspect of the present invention there is provided a process for transferring heat against a temperature gradient by an absorption process using a refrigerant which is tetrahydrofuran and an absorbent which is at least one of benzyl alcohol, diethyl sebacate, or quinoline.

The composition of the working fluid will of course vary in different parts of the heat transfer machine. However the absorbent preferably is 50-952 by weight of the total weight of working fluid (refrigerant plus absorbent) in the heat transfer machine as a whole.

. The mixture of refrigerant and absorbent introduced into the machine may contain various additives such as corrosion inhibitors, stabilisers and/or surface active agents. These will generally remain in the absorbent unless they are volatile.

The present invention will now be illustrated by reference to the following examples.

Measurements were carried out on various absorbents and on mixtures of the absorbents containing 10% wt tetrahydrofuran and 90% wt absorbent. The stability of the mixtures was also determined by sealing samples into a glass ampoule and heating for 100 hours at 200°C. The samples were then examined by gas chromatography to test for the presence of decomposition products. None were found.

TABLE

BP of tetrahydrofuran 65.5°C.

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