158 PHILlPS TECHNICAL REVIEW VOLUME 29

A compact heat 'exchanger of high thermal efficiency

G. Vonk

One of the products of the experience gained with regenerators for gas refrigeratingmachines at Philips Research Laboratories has been the development of an extremelycompact heat exchanger of high thermal efficiency. This new heat exchanger is usedin thePhilips helium liquefier.

Construction, characteristics and application

The production of cold at the temperature of liquidhelium (4.2 OK) is usually accomplished by means ofthe Jou le-Thomson effect. Compressed helium gas iscooled with the aid of a number of precooler stages andheat exchangers to below what is called the inversiontemperature, and the gas is then allowed to expandthrough a throttle or expansion valve. In this process itis cooled still further and some of the gas is liquefied.The gas- contained in the reservoir above the liquid issucked in again by the compressor and gives up itscold in the heat exchangers to the helium flowing fromthe compressor to the expansion valve (fig. 1). Ifliquid helium is drawn off from the reservoir, thenfresh helium gas must of course be continuously sup-plied (at S in fig. I).The efficiency of such a system for reaching an ex-

tremely low temperature depends to a considerableextent on the thermal efficiency of the heat exchangers.The cold loss in the heat exchangers, which has to becompensated by the cold production in the precoolerstages and the expansion valve, must be kept as lowaspossible. The lower the temperature of refrigeration,the greater the power required per watt of refrigeration(the Carnot efficiency decreases with decreasing tem-perature).In the research at Philips Research Laboratories into

high-efficiency refrigeration at 4 "K using a gas re-frigerating machine combined with a Joule-Thomsonstage, it was therefore necessary to devise a heat ex-changer with a very high thermal efficiency. To keepdown the size ofthe equipment, the heat exchanger hadto be very compact, which also keeps to a minimum thecold losses to the surroundings. This investigation ledto the type of heat exchanger discussed below, knownas the gauze-type heat exchanger.

, Ir. G. Vonk, formerly with Philips Research Laboratories, isnow with the Philips Product Division Glass, Eindhoven.

The principle used in the design of the new heatexchanger is shown in fig. 2. The channels for the twoflows are almost completely filled with pieces of thincopper gauze mounted at right angles to the directionof flow, the wires of the mesh passing through thewall dividing one channel from the other. With thisconstruction a large heat-transfer area in a small vol-ume is achieved, and the wall between the channelshas a very low thermal resistance, since copper is a

Fig. 1. Illustrating the principle of a helium liquefier or refriger-ator at a temperature of4 "K, making use of the Joule-Thornsoneffect. Camp compressor. Ri and R2 precooling stages (e.g. 80and 15 OK). JK expansion valve; as it passes through this valve'the helium gas is cooled sufficiently for part of it to become liquid.C helium vessel. Hl, H2 and Hr. heat exchangers; the gas flow-ing from C to the compressor gives up its cold here to the gasflowing from the compressor to the expansion valve.

1968, No. 5 COMPACT HEAT EXCHANGER 159

Q r-A

--.A'

1 1 1

Fig. 2. Principle of the design of a gauze-type heat exchanger.a) Transverse cross-section of the channels. b) Longitudinalcross-section AA' of the channel. G copper gauze. W walls.

very good conductor of heat. Tn addition the heat trans-fer per unit area of the copper is also relatively high: itis known that the heat transfer to the packing materialin a channel, in this case the copper gauze, is greaterfor a more finely divided material.The actual construction is somewhat more cornpli-

cated than fig. 2 suggests. There are in fact manychannels, not just two. The two flows are distributedamong the channels in such a way that each channel issurrounded by four others carrying the opposite flow(fig. 3). This arrangement gives a very intensive ther-mal contact between the two flows. A further advan-tage of using a large number of narrow channels in-stead of two wide ones is that the heat in the wires onlyhas to be transported over a small distance. This alsofavours a high efficiency.The new heat exchangers are constructed in the

following way. A large number of squares of coppergauze are made, whose wire diameter is say200microns.A similar nurn ber of sq uares of paper of the same size

Fig. 3. In the actual heat exchangers there are in fact many chan-nels, not just two as in fig. 2a. The two opposing flows (denotedby crosses and dots) are distributed in such a way that eachchannel is surrounded by lour others carrying the opposite flow.

are also made: these are impregnated with a cresol res-in and an array of holes is punched in them (fig. 4).The squares of gauze and paper are then stacked alter-nately in a jig which is then clamped up and heated toa temperature of about 150 De. During the heating, anaxial pressure is applied. The high temperature softensthe resin in the paper, and as a result of the axial pres-sure, the pieces of paper are pressed into the gauze andstick firmly together. The stack is kept at the hightemperature until the thermosetting process of thecresol resin is completed. The result is a coherent struc-ture of paper and gauze containing a large number ofparallel channels, as shown in fig. 3.

The compactness achieved by this method is appar-ent from the heat-transferring area per unit volume,which is as great as 3000 m2/m3.

As can be seen in the photograph, the channels at theedges are only half as wide as the inner ones, and thecross-section of those in the corners is only a quarter ofthat of the inner channels. The reason for this is thatthese channels are not in contact with four others butonly with three (at the edges) or two (at the corners).Since the cross-sections of these channels are madesmaller, the copper wires in them do not have totransport more heat than those in the other channels.

A useful feature of the construction is that the suc-cessive pieces of gauze are thermally insulated from oneanother by the impregnated paper, making the longi-tudinal thermal cond uction of the heat exchanger partic-ularly low. The heat flow from the "hot" to the "cold"end of the heat exchanger is therefore small, and thusthe cold loss due to this heat flow is also small.

The thickness of the walls between the channels ofthe heat exchanger shown in fig. 4 is 2.5 mm. At thisthickness the thermal resistance of the wall is stillsufficiently low and there is absolutely no risk of gasleakage. If the heat exchanger has been properly made,dividing walls of this thickness do not give any leakageof gas even after the heat exchanger has been cycleda thousand times between the temperature of liquidnitrogen and room temperature. In addition, walls2.5 mm thick can withstand a pressure difference of200 atmospheres.

The flows are distributed correctly among the chan-nels by means of distribution blocks fitted to the twoends of the heat exchangers: a pattern of holes drilledthrough the blocks connects the appropriate channels.Fig. 4 shows a transparent model of one of these ter-minal blocks. The real blocks are made of brass, andare fixed to the heat exchanger by means of an adhe-sive bond which can withstand extremely low temper-atures.

Because of its large number of parallel channels thedevice is not limited to heat exchange between just two

160 PHILIPS TECHNICAL REVIEW VOLUME 29

flows. The heat exchanger discussed and illustratedhere can in principle be used for simultaneous heat ex-change between 49 different flows. The Philips heliumliquefier makes use of gauze-type heat exchangers forheat exchange between three flows.

Since the heat exchanger was developed for use in asystem like that of fig. 1, it was designed with parti-

the insulation losses and the longitudinal thermal con-duction, and assume that the heat transfer coefficientand the thermal conductivity of copper are not tem-perature-dependent, then the temperature in such a heatexchanger varies as shown in fig. 5. The quantity 'Yjiseq ual to the ratio of the difference between inflow andoutflow temperatures - identical for both flows in this

Fig. 4. Complete heat exchanger (at the back on the left) together with a number of compo-nents. The heat exchanger consists of a block as shown in figs. 2 and 3 (on the right; height12 cm, cross-section 8 x 8 cm), terminated at both ends by a brass block for dividing the twoflows between the channels. At the front on the left is a plastic model of a terminal block, andone of the pieces of copper gauze and two of the sheets of impregnated perforated paper fromwhich the stack is built up are shown in the centre of the picture.

cular attention to heat exchange between gases. Thiskind of exchanger can however be used equally wellfor heat exchange between gas and liquid or betweenliquids.

Some performance figures

Efficiency

The thermal efficiency 'Yjof a heat exchanger is de-fined as the ratio of the actual quantity of heat trans-ferred to the maximum quantity of heat that can betransferred. We shall now consider the special, simplecase of a balanced gauze-type heat exchanger, i.e. aheat exchanger in which the product of mass flow andspecific heat is identical for both flows. If we neglect

case - to the maximum value which this differencecould have:

(1)'Yj=---THi- TLi

I n the above case the relation between 'Yjand the designparameters also assumes a simple form:

A*n= A'!'~'

(2)

Here A* is a dimensionless quantity for which:

1 1 1 WoA * = 8HAH + 8LAL + Àcu S· (3)

The three terms on the right-hand side may be re-

1968, No. 5 COMPACT HEAT EXCHANGER 161

garded as three reciprocal, dimensionless thermal re- /00,---,------,----_,-- ,-__ -,_--,sistances. The first term relates to the heat transfer fromthe relatively hot flow to the copper wires (subscriptsH), the second to the loss of heat by the wires to the rel-atively cold flow (subscripts L). The third term relates ell

to the passage of heat through the wall. For each of tthe channels the quantity A is equal to aA/W, where Ia is the coefficient of heat transfer between flow andgauze, A is the area of the heat-transfer surface and Wthe heat capacity flow, i.e. the product of mass flowand specific heat. In addition, e is the "fin efficiency"(see below), a is the thickness of the dividing wall, Àcu

lH,I-----\...Ti.uf-----!...

liH -liH7)=-'-._uTH,-ft.,T

I'i-~-+-THu

'i---.l- TLi

o _X

Fig. 5. Variation of temperature T with distance x along thechannels (length I) for a balanced heat exchanger with no insu-lation losses or longitudinal thermal conduction. The tempera-tures with a subscript H relate to the "hot" flow which is fallingin ternperature, and those with the subscript L to the "cold" flowwhich is rising in température. The efficiency 1) is the ratio ofthe temperature differences indicated by the two arrows.

the thermal conductivity of copper, and S the totalcross-sectional area of all the copper wires passingthrough a dividing wall. For any given heat exchangerthe third term on the right-hand side of eq uation (3) canbe directly calculated. The A-values have been takenfrom measurements which have been made on regen-erators for gas refrigerating machines at PhilipsResearch Laboratories. It was found that, for a stackof n gauzes not in contact with each other, A can berepresented by A = CA X 211, and for gauzes that are incontact with each other by A = CA xl/d, where I is theheight of the stack and d the diameter of the copperwires. Fig. 6 shows how CA depends on the Reynoldsnumber Re, for four values of the packing factor f,when the flowing medium is a gas. An unexpectedaspect of the above results is that CA does not dependon any geometric quantities other than f and d.

Now let us look at e. Since the thermal resistance ofthe wires differs from zero, heat transport takes placefrom one channel to another only if there is a tempera-

40%

~--+----r----~---~~~~35%30%

5~1-L~1~0·1---2~-L--L~-J5-J-LR~e-L,~02n---~2---

Fig. 6. The dimensionless quantity CA, which is one of the factorsthat deterrnine the efficiency of the heat exchanger, as a functionof the Reynolds number Re, for four values ofthe packing factor,j; i.e. the part of the volume of the channels taken up by thecopper wire. For small Re, CA ex t l Re ; with increasing Re theslope ofthe curve decreases. (Re = evdlft, where e is the density,and v the velocity which the gas would have, for the sarnc massflow, if the channel were completely empty; ft is the dynamicviscosity of the gas.)

ture gradient in the copper wires. This applies not onlyto the part of the wires contained in the wall, but equal-ly to the parts inside the channels. The temperaturegradient in the parts of the wires in the channels canbe allowed for in the same way as with cooling fins, byusing in the calculations an apparent coefficient of heattransfer a', which is smaller than the true one: a' =e«. The value of the quantity e, the "fin efficiency",can be calculated when the form of the fin is known;in our case it is a wire.

In jig. 7 the calculated and measured values of A*are plotted as a function of the mass flow m of themedium for the heat exchanger in fig. 4. The difference

lOO o\_-\o \

o,',0,"0,

"

0.04

T40 0.02

20

Fig.7. Variation of the dimensionless quantity A*, which de-termines the efficiency 1), as a function of the mass flow m for aheat exchanger like that of fig. 4. The solid line relates to thecalculated values; the values derived from measurements differonly very slightly from them (dashed line). The cortespondingcurve of 1 - 1) is also shown. The true values of 1 - 1) are about10 % higher because of the cold loss due to longitudinal conduc-tion of heat.

162 PHILIPS TECHNICAL REVIEW' VOLUME 29

between the calculated and the measured values is15-20 %. One of the reasons for this discrepancy couldbe that the wall of the channels is not flat and the flowis not in actual fact distributed completely uniformlyover the channels. From the values found for A* itfollows at once that 1]varies between about 99% and96% in the region of m values investigated. Fig. ialso shows a curve representing the variation of1 -1] with n1. A curve of this kind shows more clearlyhow the cold loss increases with increasing m than acurve of 1]plotted against m.The measured values of A* given in fig. 7 were found

by deducting from the measured total losses the coldloss due to longitudinal thermal conduction in theheat exchanger - this loss has in fact been disregardedhere. As already 'mentioned, this heat conduction isrelatively small: at room temperature the longitudinalthermal conductivity is only 0.5 W/moC, and it iseven less at lower temperatures. In practice - i.e.in the case of fig. 7 at '11 values of 1 to 2 gis - thecold loss due to longitudinal heat conduction is about10% of the total cold loss of the heat exchanger. Thetrue values of 1-1] in fig. 7 are therefore of the orderof about 10% greater than those shown.

Flow resistance

An important quantity in assessing the usefulnessof a heat exchanger is the flow resistance. The expres-sion for the pressure difference LIp across this resist-ance may be written in the form:

LIp = Cw X tev21ld.

Here I and d have the same meaning as above; e isthe density of the gas, v the velocity which the gaswould have for the mass flow if the channel werecompletelyempty, and Cw is a dimensionless quantitydepending solely on the Reynolds number and thepacking factor (fig. 8).

Comparing fig. 8 with fig. 6 we see that with in-creasing packing factor the quantity Cw increases(and with it the pressure difference LIp), which is adisadvantage. However, CA (and hence A* or the effi-ciency 1]) increase with the packing factor, which isan advantage. It is therefore necessary to strike a com-promise. The proper choice depends on the nature ofthe application. '

2r---~~~~~~~~~------r---~--~Cw

il071---_~_------"'Io.-~+--""'O;:--I-~:---I----I---I

Fig. 8. The resistance factor Cw - see equation (4) - as a func-tion of Re for the same four values of the packing factor f as infig. 6. For small Re, Cw ex: I/Re.

(4)

In an arrangement like that of fig. 1 the total flowresistance is determined mainly by the resistance en-countered by the expanded gas: owing to the lowpressure the density of this gas is low and the velocity,for the same mass flow, is therefore high. Generallyspeaking, the total pressure difference can be keptsufficiently low in a heat exchanger with the channelpattern shown, where the flow cross-sections for high-pressure and low-pressure :flow are equal. If the pres-sure of the expanded gas is extremely low - thispressure is related to the temperature at which thecold is required - it is better to increase the flowcross-section for the expanded gas at the expense ofthat for the compressed gas. This can easily be done inmanufacture by punching a different pattern of holesin the impregnated sheets of paper.

Summary. An extremely compact counter-flow heat exchangerhas been developed that has a high thermal efficiency and a notunduly high flow resistance for gases. It is made from a stack ofalternate rectangular sheets of copper gauze and sheets of paperofthe same size, impregnated with cresol resin, in which a patternof holes has been punched. The stack is heated under pressure,which softens the resin so that the sheets of paper stick to eachother through the gauze. The resin then hardens, and a largenumber of channels are thus obtained, separated by walls pene-trated by the wires of the gauze, which gives the walls a lowthermal resistance. The flows are divided among the channels bymeans of terminal blocks in such a way that each channel issurrounded by a number of channels through which the counter-flow passes. The thermal conductivity in the direction of flowis extremely low.

1968, No. 5 163

Recent scientific publicationsThese publications are contributed by staff of laboratories and plants which formpart of or co-operate with enterprises of the Philips group of companies, particularlyby staff of the following res.earchlaboratories:

Philips Research Laboratories, Eindhoven, Netherlands EMullard Research Laboratories, Redhill (Surrey), England MLaboratoires d'Electronique et de Physique Appliquée, Limeil-Brévannes

(S.O.), France LPhilipsZentrallaboratorium GmbH, Aachenlaboratory, Weisshausstrasse,

51 Aachen, Germany , APhilips Zentrallaboratorium GmbH, Hamburg laboratory, Vogt-Kölln-

Strasse 30, 2 Hamburg-Stellingen, Germany HMBLE Laboratoire de Recherche, 2 avenue Van Becelaere, Brussels 17

(Boitsfort), Belgium. B

Reprints of most of these publications will be available in the near future. Requestsfor reprints should be addressed to the respective laboratories (see the code letter) orto Philips Research Laboratories, Eindhoven, Netherlands.

G. A. Acket & J. de Groot: Measurements of the cur-rent/field strength characteristic of n-type galliumarsenide using various high-power microwave tech-niques.IEEE Trans. ED-14, 505-511, 1967 (No. 9). E

G. Arlt & P. Quadftieg: Piezoelectricity in UI-V com-pounds with a phenomenological analysis of the piezo-electric effect.Phys. Stat. sol. 25, 323-330, 1968 (No. I). A

F. Th. Backers: Einige Betrachtungen über die PAL-Verzögerungsleitung.Nachrichtentechn. Z. 20, 473-477, 1967 (No. 8). E

V. Belevitch: On the theory of non-linear resonance innarrow-band circuits.Philips Res. Repts. 23, 87-102, 1968 (No. I). B

V. Belevitch & J. Neirynck: Eddy currents in thin sur-faces of revolution at low frequencies.Philips Res. Repts. 23, 77-86, 1968 (No. I). B

H. J. Bensieck: Second-order approximations for thedetermination of the resonance frequencies of partiallyfilled resonators.Philips Res. Repts. 23, 103-107, 1968 (No. 1). H

G. Blasse & A. Bril: Study of energy transfer fromSb3+, Bi3+,Ce3+ to Sm3+, Eu3+, Tb3+, Dy3+.J. chem. Phys. 47, 1920-1926, 1967 (No. 6). E

G. Blasse & A. Bril: Fluorescence of rhodium-activatedaluminum oxide.J. Electrochem. Soc. 114, 1306-1307, 1967 (No. 12). E

H. van den Boom: Simple method of rotating samplesin microwave cavities at low temperatures.Rev. sci. Instr. 38; 1529-1530, 1967 (No. 10). E

K. Bulthuis: Effect of uniaxial stress on silicon andgermanium.Physics Letters 25A, 512-514, 1967 (No. 7). E

K. Bulthuis: Effect of high uniaxial pressure along themain crystallographic axes for silicon and germanium.Philips Res. Repts. 23, 25-47, 1968 (No. I). E

K. H. J. Buschow, J. F. Fast, A. M. van Diepen (Na-tuurkundig Laboratorium der Universiteit van Amster-dam) & H. W. de Wijn (idem): Magnetic dilution ofrare-earth aluminum cubic Laves phases RAh.Phys. Stat. sol. 24, 715-720, 1967 (No. 2). E

A. Charles-Georges & A. Salmon: Usinage de cavitésde pompage pour lasers "solides".Acta electronica 10, 315-330, 1966 (No. 3). L

A. Cohen & J. 't Hart (Institute for Perception Re-search, Eindhoven): On the anatomy of intonation.Lingua 19, 177-192, 1967 (No. 2).

E. H. P. Cordfunke (Reactor Centrum Nederland) &A. A. van der Giessen: Particle properties and sinteringbehaviour of uranium dioxide.J. nuel. Mat. 24, 141-149, 1967 (No. 2). E

M. B. Das (Associated Semiconductor ManufacturersLtd.): Charge-control analysis of m.o.s. and junction-gate field-effect transistors.Proc. IEE 113, 1565-1570, 1966 (No. 10) ..

M. B. Das (Associated Semiconductor ManufacturersLtd.): Generalised high-frequency network theory offield-effect transistors.Proc. IEE 114, 50-59, 1967 (No. I).

R. Dessert: Lasers "solides" àfonctionnement continu.Acta electronica 10, 295-314, 1966 (No. 3). L.

A. van der Drüt, Tine E. Horsman & C. Langereis :Investigations on the preferred orientations in vapour-deposited lead-monoxide layers.Philips Res. Repts. 23, 48-61, 1968 (No. I). E

164 PHILIPS TECHNICAL REVIEW VOLUME 29

P. P. J. van Engelen & J. C. M. Henning: Electronicstructure of a Ti3+ centre in SrTi03.Physics Letters 25A, 733-735, 1967 (No. 10). E

J. L. Goldstein (Institute for Perception Research,Eindhoven): Auditory spectral filtering and monauralphase perception.J. Acoust. Soc. Amer. 41, 458-479, 1967 (No. 2).

N. Hansen: Evaluation of the sticking probability ofgases chemisorbed on metal films without measure-ments of gas pressure. .Suppl. Nuovo Cim. 5, 389-398, 1967 (No. 2). A

G. Klein & H. Hagenbeuk: Accurate triangle-sine con-verter.Electronic Engng. 39, 700-704, 1967 (No. 477). E

A. Klopfer: Interactions of electrons with adsorbedwater. .Suppl. Nuovo Cim. 5, 606-611, 1967 (No. 2). A

D. J. Kroon & J. M. van Nieuwland: Techniques ofpropagation at millimetre and submillimetre wave-lengths.Spectroscopie techniques for far infra-red, submilli-metre and millimetre waves, ed. D. H. Martin, North-Holland Publ. Co., Amsterdam 1967, p. 309-380. E

H. de Lang: In memoriam Dr. P. M. van Alphen.Ned. T. Natuurk. 33, 268-270, 1967 (No. 9). E

W. Lems: Magnetic properties of electrodeposited FeNifilms, H.Philips Res. Repts. 23, 62-76, 1968 (No. I). E

F. A. Lootsma: Extrapolation in logarithmic program-ming.Philips Res. Repts. 23, 108-116, 1968 (No. I). E

M. H. vanMaaren: Note on the diffusion and solubilityof lithium in gallium antimonide.Phys. Stat. sol. 24, K 125-128, 1967 (No. 2). E

G. Marie, P. Wurtz & R. Le Pape: Etude d'un laserau néodyme déclenché par un obturateur à effetPockeIs.Acta electronica 10, 249-293, 1966 (No. 3). L

Ä. G. van Nie: Measuring currents down to 10-17 Awith a low noise level by means of a dynamic capacitorelectrometer.IEEE Int. Conv. Rec. IS, Part 8, 59-65, 1967. E

J. M. van Nieuwland& M. T. Vlaardingerbroek: Cyclo-tron waves in InSb.IEEE Trans. ED-14,' 596-599, 1967 (No. 9). E

A. van Oostrom: Modulation of Bayard-Alpert ioniza-tion gauges with grid end-caps.J. sci. Instr. 44, 927-930, 1967 (No. 11). E

c. van Opdorp: The concentration gradient of Zn neara p-n junction in III-V compounds.J. appl. Phys. 38, 5411-5412, 1967 (No. 13). E

P. Penning & D. Polder: Dynamical theory for simul-taneous X-ray diffraction, Part I. Theorems concerningthe n-beam case;P. Penning: idem, Part H. Application to the three-beam case.Philips Res. Repts. 23, 1-11, 12-24, 1968 (No. I). E

J. Polman: Sensitive 4 mm Lecher wire interferometerfor electron concentration measurements in low-densityplasmas.Rev. sci. Instr. 38, 1631-1633, 1967 (No. 11). E

M. J. Prescott & J. Basterfield: The observation of dis-locations in yttrium gallium garnet by a photoelasticmethod.J. Mat. Sci. 2, 583-588, 1967 (No. 6); , M

O. Reifenschweiler: Bohrlochuntersuchungen mit Neu-tronen.Haus der Technik - Vortragsveröffentlichungen No.133, 30-42, 1967. E

G. Renelt & H. W. Neuhaus: Übertragungseigenschaf-ten des Lesedrahtes einer Ferritkernspeichermatrix.Nachrichtentechn. Z. 20, 722-728, 1967 (No. 12). H

G. Simon: Calculation of the elastic properties of ger-manium.J. Phys. Chem. Solids 28,2349-2358, 1967(No. 12). A

G. Simon: Calculations of the elastic moduli and theirpressure derivatives for the alkali metals.J. Phys. Chem. Solids 29, 63-68, 1968 (No. I). A

J. M. Stevels: Centres de couleur induits par irradiationdans les systèmes vitreux.Verres et Réfr. 21, 279-288, 1967 (No. 4). E

T. L. Tansley: Forward current injection modulationof photocurrent in p-n heterojunctions.Phys. Stat. sol. 24, 615-622, 1967 (No. 2). M

B. Tuck: Photoluminescence of compensated p-typeGaAs.J. Phys. Chem. Solids 28, 2161-2168, 1967(No. 11). M

K. J. de Vos (Philips Radio, Gramophone and Tele-vision Division, Eindhoven): The relationship betweenmicrostructure and magnetic properties of alnico alloys.Thesis, Eindhoven 1966.

J. C. Walling: Characteristic admittance of an arrayof rectangular conductors.Electronics Letters 3, 481-483, 1967 (No. 11). M

H. W. de Wijn (Natuurkundig Laboratorium der Uni-versiteit van Amsterdam), A. M. van Diepen (idem) &K. H. J. Buschow: Nuclear magnetic resonance andmagnetic susceptibility of SmA13.Phys. Rev. 161,253-257, 1967 (No. 2). E

G. Zanmarchi: Optical measurements on the antiferro-magnetic semiconductor MnTe.J. Phys. Chem. Solids 28, 2123-2130, 1967 (No. 11). E

Volume 29, 1968, No. 5 Published 12th June 1968pages 129-164