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THE MINISTRY OF SUPPLY
Author(s) -
Tyerman Donald
Publication year - 1941
Publication title -
the political quarterly
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.373
H-Index - 37
eISSN - 1467-923X
pISSN - 0032-3179
DOI - 10.1111/j.1467-923x.1941.tb01780.x
Subject(s) - christian ministry , citation , politics , library science , computer science , political science , operations research , law , mathematics
Thu note describes a frost point hygrometer sultable for measurrng the water vapow content of the au in supersoruc wind tunnels at any stagnatux press-vlthln their present range of operation. It uses co2 as a coolant and 1s economxal m construction and operation. LIST C!Y CONTENTS 1 Introduction 2 2 Descrlptlon of hygrometer 2 I)etennatlon of the water vapour content of a sample of au : Further development References LIST OF ILLUSTRATIONS Frost pomt hygrometer I Molller diagram for air saturated with water vapour at vapour-solzd equrllbrlum for sub-freezmg temperatures Vapour pressure of co2 : Hygrometer uwtallatu3n 4-l-1 Introduction-In order to avoid spurious readings in supersonic wind tunnel tests lt 1s essential to control the humidity of the air in the tunnel to some small value. Thm note describes a frost point hygrometer suitable for measuring humidities down to at least 0.0005 lb of water/lb of air over the range of pressures at whxh variable density wind tunnels operate. This requires a coolant capable of giving a minimum temperatti of-40°C if the tunnel is to be operated at pressures down to 2.5 lb/sq in ,aa;. with control to any intermediate temperature up to O°C or above. coolant used is carbon dioxide throttled from a high pressure cylinder. The main advantages of this hygrometer are:-1. Simplicity and cheapness of construction and operation. 2. Speed with which a frost point oanbe obtained (especially desirable for intermittent tunnels). 3. Freedom from leaks (essential at pressures less than atmospheric). Fine degree of control of temperature. The hygrometer described here is in operasion in the 9" x 9" sver-sonic wand tunnel at the R.A.E. and has been used for a short time without any serious troubles. A-more elaborate form employing CO2 coolant is in use in AIReriC. and 1s described in Ref. 1. 2 Description of hygrometer Flg.1 1s a detailed drawing of the hygrometer. It consists essen-txd3.y of an arrangement for cooling a metal disk over which 1s passed the air whose humidity is required. The formation of frost is noted v~ually; ' the temperature of the disc at which frost is deposited on it is measured by a thermocouple, and the pressure of the air in the hygrometer is measured directly from a gauge. From this information the water content of the 8x-can be derived using the chart in Fig. 2 reproduced from Ref. 2. iviore specifically the construction and operation of the …