This paper is a sequel to two earlier studies of friction (I)† and eddy diffusion (2) carried out for the same flow conditions as in the present study of heat transfer. Heat was transferred to an upward flowing suspension of 0-40 μ zinc particles in pipes of 1, 2 and 3 in bore. The solids/gas flow rate was in the range 0 < Ws/ W g< 17 and the pipe Reynolds number in the range 3·5 × 104< Re < 105. It was found that the fractional increase in heat transfer coefficient due to the presence of solids was always less than the increase in the friction factor. Minimum values of both these parameters are often observed in the range 1 < W s/ W q< 2·5. This paper gives further evidence that turbulence is suppressed by the particles, particularly when the duct is small and Re is large; in this case the wall Nusselt number, Nu s, is markedly reduced below the value when gas flows alone. However, when the pipe is large and Re is low, Nu s can be substantially higher than the value for gas alone. In this case the suspension is a superior coolant to the flow of gas alone.

Molten-salt reactors (MSRs) can provide inexpensive industrial process heating in addition to generating electricity. In most cases, this can be best accomplished by design simplification, which results in improvements to MSR's already existing and inherently strong safety characteristics. This is just one of a number of possible future scenarios that will influence the way in which MSR technology can develop and become marketable. The emphasis in this paper is to develop a reactor with application to the widest possible range of industries. This paper concentrates on the need to develop the inherent safety characteristics of the single fluid thermal reactor with the expectation that sufficient reliability and safety will be achieved in design so that these power generators will eventually be accepted for close integration into the fabric of modern society. It seems inevitable that the required licensing procedures needed for MSRs will vary considerably depending on their type because different designs vary so much. Those used for low-temperature process heat in addition to power generation require much less demanding regulatory procedures than those operating at higher temperatures. This is largely because long-term corrosion is more problematic at higher temperatures and present-day construction materials limit the development of MSRs from reaching their full potential. With appropriate experience with operating early designs of MSRs it is reasonable to expect that lower temperature versions will become certifiable for use in close proximity to a large range of human activities. Ultimately these reactors will be controllable remotely without the local attendance of technical staff.

By using non-dimensional Navier-Stokes equations in systems where partial modelling complications can be avoided, it is shown that geometrically similar systems can exhibit identical behaviour but according to different time scales where the latter are also within our own control. These models indicate that the physical nature of time is not related to a fundamental constant, but the passage of time can have a different but still constant value in a particular system of our own choosing. This observation also adds to our knowledge relating to the dichotomy of interpreting time either as a flowing parameter or, alternatively, just accepting it as a part of space-time. The observation adds evidence in favour of both viewpoints. The conclusions also seem relevant to biological species, chemical processes in general and other branches of physics. Using earlier work of Prigogine and others, it also appears that instantaneous time has important properties dividing past and future time into two segments which differ fundamentally in physical characteristics. This seems to explain the 'raison d'tre' of the second law of thermodynamics and the necessarily asymmetrical nature of time in our own world where mathematical symmetry of physical laws is the norm. This entropic time barrier also seems to explain the physically intangible nature of past events and their possible natural importance as former lower entropy forms of existence. It is concluded that these physical features of time are necessary for the existence of any form of life and Darwinian evolution, in particular. The conclusions may also help to throw further light on other suggested theories and observations in physics and the role of quantum decoherence in life and its adaptive ability.

In the near future, we will need an internationally based system for worldwide planning of future energy resources and their effect on the world environment. Logically, this should be a responsibility of the United Nations, which already possesses much of the infrastructure needed and is already active in this area. Because different nations have different resources, different problems and different needs, it is reasoned that a flexible and diplomatic approach is also called for. We will need to try to secure support from all nations, and the economies and cultures of many nations differ considerably. This calls for special skills in negotiation. This is complicated by the varied, uncertain and changing technological facilities, which we have at our disposal. After a brief and comparative review of these facilities, an outline of the structure of the internationally coordinating organisation is suggested, followed by examples of the different types of issues which are likely to be encountered. These are: reintroducing improved technology to a nation, which has suffered grievous environmental harm from inadequate similar technology such as the Fukushima incident; nations with especially difficult transport problems; nations with perceived overpopulation problems; using UN and other expertise for nations still undergoing development; applying persuasive pressure by peaceful means. Finally, by outlining a large-scale cooperative venture by several nations, the mode of operation of the suggested U.N coordinating body is outlined. The example used is the choice of thorium-based molten-salt reactor technology using both fast and thermal neutron spectra. This appears to be the only choice we have, as other sustainable systems cannot accommodate the size of our problems. The only exception is using the Desertec solar project, which appears to be disadvantaged by being significantly more expensive. Molten-salt reactors would give a 1000-year energy security for industrialised energy-hungry nations on the Far East/Pacific Rim, which is the example considered. This system would use modern actinide burn-up technology to make nuclear-waste disposal a more acceptable proposition. Thus, nuclear waste can become a lowlevel and disposable hazard after only about 300 years of storage. After this storage, the waste becomes a valuable resource due to production of rare transmuted elements.

Urban designs often cannot be adapted to changing life-styles. Alternatively, some examples may incur prohibitive costs of retrofitting. In today's fast-moving society the urban designer faces an increasing variety of problems. Some of these are considerations which have merely changed. These include urban and interurban transport; waste disposal and recycling; unemployment and workforce mobility; education and recreational facilities. Other considerations are more novel such as developments in manufacturing technology; likely changes in taxation methods; reducing domestic incomes; promotion of racial and religious harmony; retailing, or hiring of products as an alternative; product reliability; alternative ways of dwelling purchase; adapting planning to accommodating changes in climate particularly in high temperature zones. The paper concludes with an outlined large-scale planning proposal using solar power for large-scale electricity supplies integrating the economic and social interests of Europe and Africa This example requires some of the above and some additional considerations.