Heat pulse

In the calculations proposed by Camia (44), a heat pulse is produced within the calorimeter cell, which is initially in thermal equilibrium. The heat pulse diffuses through the heat-conducting body toward the heat sink which is maintained at a constant temperature 03. 

The third method is a variation of the second a heat pulse dg is supplied, keeping both the pressure and temperature constant by means of a feedback system. In this process, some moles of liquid 3He are solidified the latent heat of solidification is the measured dg. Since from Clapeyron equation ... 

In the heat pulse method, the sample of heat capacity C is thermally linked to the thermal bath (at temperature rB) by a conductance G. 

Only in the latter case, the measurement is practically adiabatic. Otherwise, it is necessary to extrapolate data to get the effective ST at t = 0 (start of the heat pulse) [2,3], The heat capacity of the addendum (Caddendum = CXh + CSp + CH) can be obtained by a separate measurement without the sample. The heat pulse technique is typically used in the 0.05 1 K temperature range. 

Extrapolation of the picosecond simulations would imply that isothermal and laser-induced desorption results should be in qualitative agreement for nonspecific heating pulses of 1 to 10 ns duration. Of course this may not hold if all desorption occurs during the leading edge of the laser pulse or if the desorption process is driven by a nonthermal maihanism. Nevertheless, incomplete equilibration is not expected to play a major role for translational or rotational accommodations if the residence times are longer than 10 ns. 

Representative TOF spectra following 532 nm heating pulses for three different rotational states of NO are presented in Fig. 8. These spectra appeared to consist of contributions from two distinct desorption channels a slow thermal channel and a fast non-Boltzmann channel. The distinctly different rotational distributions observed for these two components (see below) provided additional support for such an interpretation. 

The instruments for polymer HPLC except for the columns (Section 16.8.1) and for some detectors are in principle the same as for the HPLC of small molecules. Due to sensitivity of particular detectors to the pressure variations (Section 16.9.1) the pumping systems should be equipped with the efficient dampeners to suppress the rest pulsation of pressure and flow rate of mobile phase. In most methods of polymer HPLC, and especially in SEC, the retention volume of sample (fraction) is the parameter of the same importance as the sample concentration. The conventional volumeters— siphons, drop counters, heat pulse counters—do not exhibit necessary robustness and precision [270]. Therefore the timescale is utilized and the eluent flow rate has to be very constant even when rather viscous samples are introduced into column. The problems with the constant eluent flow rate may be caused by the poor resettability of some pumping systems. Therefore, it is advisable to carefully check the actual flow rate after each restarting of instrument and in the course of the long-time experiments. A continuous operation— 24h a day and 7 days a week—is advisable for the high-precision SEC measurements. THE or other eluent is continuously distilled and recycled. 

Detonotion, Flash-Across, Heat Pulse and Hypervelocity Phenomena. According to Cook (Ref 3), the phenomenon of heat pulse was first recognized by Dr W.S. McKewan of NOTS, China Lake, Calif while viewing microsecond, color, framing photographs of Nitromethane (NM) detonated thru SPHF (shock-pass-heat-filter) glass plates in experiments conducted by D.H. Pack,... 

In order to accurately determine the speed of the flash-across phenomenon, the experiment was repeated and recorded by streak camera with color film. Also thinner SPHF plates were used. In the streak camera trace, 8.5 (isec after each initial wave entered the NM, a hot spot appeared at the surface of each plate and flashed to the center of the chge each at the phenomenal speed of 35 mm/fisec. Cook (Ref 3) considers the flash-across phenomenon to be the heat pulse predicted by M.A. Cook, R. Keyes A.S. Filler (Ref 1)... 

Detonation, Heat Pulse Phenomenon in-See under Detonation, Flash-Actoss, Heat Pulse and Hypervelocity Phenomena... 

From similar space-time high-speed camera studies of the shock initiation to detonation of NMe, Cook et al (Ref 9) observed a flasb-across phenomenon in which, an apparent wave of luminescence originated in the explosive behind the initial compression front and propagated at a reported velocity of 35 mm/ftsec to overtake the initial compression front. This "flash, across phenomenon was interpreted as a heat transfer wave caused by a sudden increase in the thermal conductivity of the shock-compressed NMe. The phenomenon was taken as a direct observation of the "heat pulse , which Cook et al had predicted in 1955 (Ref 2)... 

Gases (pp 75-7) Reaction Zone in Condensed Explosives (pp 77-9) Observations Pertaining to Spike Theory (pp 79-87) and Heat Pulse (pp 87-9)... 

Heat pulse) 91-122 (Deton wave shape and density properties) 123-4 (Reaction rates in deton) 123 (Nozzle theory) 124 (Curved-front theory) 125-28 (Geometrical model) ... 

Under the heading "General Case , Ma ek states (p 47) that in order to solve eq (1) with out approximations subject to specific boundary conditions, one has to resort to numerical procedures. G. B. Cook (Refs 6a 7a) treated two problems by means of calcns with. digital computers. First is the case of a slab of solid expl,one face of which was in contact with. a constant-temp bath. In the 2nd case the expl was subjected to a time-dependent heat pulse. In both. cases the time to ignition and the critical condition for ignition are given as... 

The conditions responsible for the jumping detonation are evidently those for propagation of deton thru inert media such as glass and steel in which the shock wave first outruns the reaction and is then suddenly overtaken after the chemical reaction has finally built to a critical stage in which.a heat pulse is able to propagate (Ref 52, p 59)... 

Heat Pulse. (Also see Detonation, Flash-Across, Heat Pulse and Hypervelocity Phenomena in Vol 4, p D348-49). A concept advanced by M.A. Cook (Refs 1 2) to provide a theoretical mechanism for the shock initiation of explosives. Cook also used the heat pulse concept in his explanation of certain unusual luminosity effects observed primarily in the detonation of liquid explosives. Briefly stated, Cook believes that detonation is initiated when as a result of rising temperature, produced by reaction in the already shocked region of an explosive, a portion of the explosive becomes thermally super-conductive and a heat-pulse flashes thru it and catches up with the shock front. Studies conducted by Kendrew Whitbread (Ref 3) tend to discount the necessity for postulating a heat-pulse in a theoretical explanation of shock initiation or the above unusual luminosity effects. More recent studies of shock initiation have also failed to produce any conclusive evidence of a heat-pulse ... 

In essence, this model states that initiation occurs when a shocked region of LE becomes thermally superconductive (as a result of rising temp due to partial decompn of the shocked LE) and a heat pulse flashes across the shocked LE and catches up with the original shock front. As described in the article on Heatpulse (p H59-L), alternate explanations are possible for some of the observations that Cook considers to be the main experimental support for his heat pulse . Similarly, Dremin et al (Ref 17) have suggested an alternate ex-... 

Detonation, flash-across, heat pulse and hypervelocity phenomena 4 D348... 

Thermal volumetric Liquids only 1 Measures time taken for liquid to flow between two detectors by means of a heat pulse High pressure liquid phase chromatography (Section 6.8.3 and Volume 2, Chapter 19) No moving parts. Suitable for high pressures and temperatures... 

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