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Background: High blood pressure is common in acute stroke and is a predictor of poor outcome; however, large trials of lowering blood pressure have given variable results, and the management of high blood pressure in ultra-acute stroke remains unclear. We investigated whether transdermal glyceryl trinitrate (GTN; also known as nitroglycerin), a nitric oxide donor, might improve outcome when administered very early after stroke onset.Methods: We did a multicentre, paramedic-delivered, ambulance-based, prospective, randomised, sham-controlled, blinded-endpoint, phase 3 trial in adults with presumed stroke within 4 h of onset, face-arm-speech-time score of 2 or 3, and systolic blood pressure 120 mm Hg or higher. Participants were randomly assigned (1:1) to receive transdermal GTN (5 mg once daily for 4 days; the GTN group) or a similar sham dressing (the sham group) in UK-based ambulances by paramedics, with treatment continued in hospital. Paramedics were unmasked to treatment, whereas participants were masked. The primary outcome was the 7-level modified Rankin Scale (mRS; a measure of functional outcome) at 90 days, assessed by central telephone follow-up with masking to treatment. Analysis was hierarchical, first in participants with a confirmed stroke or transient ischaemic attack (cohort 1), and then in all participants who were randomly assigned (intention to treat, cohort 2) according to the statistical analysis plan. This trial is registered with ISRCTN, number ISRCTN26986053.Findings: Between Oct 22, 2015, and May 23, 2018, 516 paramedics from eight UK ambulance services recruited 1149 participants (n=568 in the GTN group, n=581 in the sham group). The median time to randomisation was 71 min (IQR 45–116). 597 (52%) patients had ischaemic stroke, 145 (13%) had intracerebral haemorrhage, 109 (9%) had transient ischaemic attack, and 297 (26%) had a non-stroke mimic at the final diagnosis of the index event. In the GTN group, participants' systolic blood pressure was lowered by 5·8 mm Hg compared with the sham group (pvs 3 [2–5]; n=558, in the sham group; 1·04 [0·84–1·29]; p=0·69). We found no difference in secondary outcomes, death (treatment-related deaths: 36 in the GTN group vs 23 in the sham group [p=0·091]), or serious adverse events (188 in the GTN group vs 170 in the sham group [p=0·16]) between treatment groups.Interpretation: Prehospital treatment with transdermal GTN does not seem to improve functional outcome in patients with presumed stroke. It is feasible for UK paramedics to obtain consent and treat patients with stroke in the ultra-acute prehospital setting.Funding: British Heart Foundation.

An investigation has been undertaken to examine the stability of a gas-liquid interface in a vertical cylindrical vessel subjected to a sinusoidal vertical motion. Experimental results indicate that there is a certain limiting critical frequency at which the gas-liquid interface becomes unstable, significant amounts of liquid are thrown vertically from the interface and the interface thus loses its coherent structure. Experimental data are compared with analytical solution based on the reduction of governing non-viscous equations to Mathieu equation, and good agreement between theory and experiment is found.

This paper considers the outflow of a liquid from a single outlet vessel, i.e. a vessel in which the outflowing liquid is displaced by another fluid which enters the vessel through the same opening. The simplest possible arrangement is investigated: a sealed axisymmetric cylindrical vessel with an outlet in its base, in which water is displaced by air. It is shown experimentally that the average liquid discharge velocity is independent of the liquid level in the vessel and the shape of the outlet for the range of outlets employed; it increases weakly with both the diameter of the vessel and the diameter of the outlet.

A model is developed for predicting the influence of the containing walls on heat transfer processes in stagnant beds of solid particles. The model describes the effect of the walls on the mean voidage of the bed and on the mean effective thermal conductivity of the bed. The theoretical predictions are compared with available experimental data.

An investigation has been made of air-water flow in Y-junctions, which are frequently used in industrial applications. The air-water flow is stratified in the sloping limbs approaching the junction and this paper examines the phenomena occurring at the junction and in the following freely discharging vertical pipe. It is shown that three flow regimes can exist in the vertical limb following the junction: freely-falling water, homogeneous flow of water and air, and flow of water with a small amount of residual air accompanied by the flooding of the junction. The flow regimes are described and predictions for transitions between them are developed.

One of the flow regimes occurring in horizontal two-phase flows is characterized by periodic large waves “surging” along the tube. This flow, called “slug” flow, has been frequently observed in low and high pressure gas liquid systems, but it has been noticed that slugging is absent in certain liquid-liquid two-phase systems. A method is developed giving the necessary conditions for the presence of slug flow. This method quantitatively explains the observed absence of slugging in certain liquid-liquid flows.

It has been shown previously (Gardner & Kubie 1976) that a two-liquid system provides a better analogue for investigating certain aspects of high pressure boiler tube hydrodynamics than air and water at atmospheric pressure. A study is presented here of the flow of n- butyl acetate and water, and iso-amyl alcohol and water in helical coils and the general conclusion is that strongly stratified conditions of either completely separated phases or of drops of one phase in the other exist until velocities are high enough to produce drops sufficiently fine to be dispersed by the turbulence. The critical condition for the breakdown of the separated phases to produce drops is quantitatively correlated with the mass flowrates needed to avoid low quality dryout in both high pressure water and high pressure freon helical boilers. Some evidence is available to support two criteria indicating that low quality dryout will not be observed for sufficiently low pressures in steam-water systems and, perhaps, for small enough bore tubes.

Measurements were made of the size distribution and maximum size of drops in liquid-liquid systems. The data on the maximum drop size, together with other data available in the literature, are assessed in the light of Hinze's [1] theory. It is shown that the dispersion of drops in a gravitational field transverse to the flow can be predicted using correlations for the terminal velocity and for the drop diffusivity.

Two parameters of particle or droplet dynamics which are of importance in describing their behaviour in turbulent pipe flows are their settling velocity and eddy diffusivity. It is usually assumed that the settling velocity in turbulent flow is equal to that in still fluid and on the basis of this assumption the eddy diffusivity is usually determined experimentally from the distribution of droplets or particles in horizontal turbulent flow. Since the settling velocity has a strong influence on the resultant value of the eddy diffusivity, the influence of turbulence on settling velocity is investigated in this work. A simple stochastic model of settling in turbulent flow is developed and it is shown that a considerable retardation of still fluid settling velocity is possible for a wide range of conditions.

The influence of gas bubbles on heat transfer in gas fluidized beds has been investigated. A platinum wire has been used as a heat-transfer probe and the aggregative gas fluidized bed has been simplified by generating a single continuous stream of gas bubbles into an incipiently fluidized bed. It has been found that in the case of aggregative gas fluidized beds of small particles operating below the radiative temperature level, transient conduction into the emulsion phase is responsible for at least 90% of heat transfer and that the remainder is contributed by the superimposed gas convection. A theoretical model of the bubble induced heat transfer has been developed. Finally, experimental justification for the concept of the property boundary layer introduced in [2] is presented.

The mechanism of heat transfer at surfaces in fluidized beds is discussed and a variant of the penetration theory is developed in which the packet theory of heat transfer is modified to allow for, and describe quantitatively, property variations in the packet in the region of the surface. Property variations are described in terms of the voidage variations in the vicinity of a constraining surface which are modelled from simple geometrical considerations. The model of the heat-transfer process derived here shows good agreement with experimental data without recourse to any of the semi-empirical approximations that are features of the previous models.

The influence of gas bubbles on heat transfer in two phase gas-liquid systems has been investigated. Platinum wires have been used as heat-transfer probes and the two phase flow has been simulated by generating a single continuous stream of discrete gas bubbles into a stationary liquid. The contribution of various modes of heat transfer has been determined. It has been found that transient conduction into the liquid is the predominant mode of the bubble induced heat transfer and is responsible for about 75 per cent of heat transfer. Convection contributes the remainder. A theoretical model of the bubble induced heat transfer based on the surface renewal and penetration theory has been developed.

A two-liquid system provides a better analogue for visualization purposes of high pressure boiler systems, where the density ratio is typically 4:1, than air and water at atmospheric pressure. A study is presented of the flow of isoamyl alcohol and water in sloping tubes and a stratified ribbon of alcohol is found, which is not seen with air and water, and this accounts for some corrosion failures in boilers. A critical condition is also encountered when the ribbon starts to be broken into drops and this quantitatively explains the occurrence of a minimum in the curve of burnout heat flux vs water velocity in steam-water systems from 11 to 18 MN/m 2 .

The distribution of voidage in the wall regions of randomly packed beds of uniform spheres is investigated. A general equation relating the local voidage to the distribution of the spheres is derived and is combined with some simple observations about the bed to develop a model of particle packing near containing walls. The results of the analysis are in good agreement with available experimental data.